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Nov 1997

Volume 15, Issue 6, pp. 1853-2949


Electrostatic tip-surface interaction in scanning force microscopy: A convenient expression useful for arbitrary tip and sample geometries

Fredy R. Zypman and Steven J. Eppell

J. Vac. Sci. Technol. B 15, 1853 (1997); http://dx.doi.org/10.1116/1.589567 (8 pages) | Cited 9 times

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The electrostatic energy between a dielectric scanning force microscope (SFM) tip and a point charge is obtained in closed form as a function of the separation of the two objects. Applications of this result to both spherical and arbitrary tip shapes are discussed. Also, utilizing kinematic data, a method is given to experimentally extract the force due to the tip-sample interaction from a typical SFM instrument. This is done by analyzing the time dependent motion of the tip. The result is based on the use of a time dependent analysis of the force distance curve which is unavoidable in motion regimes in which the tip accelerates, as in the snap-to-contact process. © 1997 American Vacuum Society.  
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
07.79.Lh Atomic force microscopes
68.35.B- Structure of clean surfaces (and surface reconstruction)
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Local work function for Cu(111)–Au surface studied by scanning tunneling microscopy

J. F. Jia, K. Inoue, Y. Hasegawa, W. S. Yang, and T. Sakurai

J. Vac. Sci. Technol. B 15, 1861 (1997); http://dx.doi.org/10.1116/1.589568 (4 pages) | Cited 11 times

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We report results of the measurement of local work function, or apparent barrier height, on the Au/Cu(111) surface using scanning tunneling microscopy (STM). By measuring a response of tunneling current to a change of the tunneling gap distance during scanning, we can obtain a work function image simultaneously with a topographic STM image. In this way, we could successfully observe the difference in local work function due to different elements and atomic structures. Our results show that the mean work function value of the Au overlayer is 7±3% larger than that of the Cu(111) substrate and the value of the work function of the second Au layer is the same as that of the first Au layers within the measurement uncertainty. At the step edges, the work function values are lower than that on the terrace. The width and depth of the low work function trough at Au–Au, and Cu–Au single height steps were also obtained. The measured values are consistent with those measured on vicinal surfaces. This work also suggests that the local work function measurement can be used to identify the element on a surface and that the STM is quite useful to get information on how the work function is related with surface structures and how the work function spatially changes on nanometer scales. © 1997 American Vacuum Society.
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

In situ scanning force microscopy study of TiN layers in sulphuric acid

M. Herranen, M. Nordin, and J.-O. Carlsson

J. Vac. Sci. Technol. B 15, 1865 (1997); http://dx.doi.org/10.1116/1.589569 (6 pages) | Cited 2 times

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Morphological changes of sputter-deposited TiN films in 0.1 M sulphuric acid have been followed in situ with scanning force microscopy at different potentials. Disappearance of small structures was observed with increasing potential up to 1.2 V. A further increase of potential above 1.5 V resulted in growth of larger grains. Two passivation peaks at about 0.6 and 1.2 V, respectively, were recorded for the TiN films. The passivating layers formed at these two passivation peaks were characterized by x-ray photoelectron spectroscopy. At the lower passivation peak, titanium suboxides or oxynitrides were detected, while TiO2 was formed at potentials above 1.2 V. © 1997 American Vacuum Society.
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81.65.Rv Passivation
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Scanning thermal microscope tip-induced chemical reaction on solid organometallic compound thin films

L. Zhou, G. Q. Xu, H. T. Ng, and S. F. Y. Li

J. Vac. Sci. Technol. B 15, 1871 (1997); http://dx.doi.org/10.1116/1.589570 (5 pages) | Cited 2 times

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This article has successfully demonstrated for the first time a chemical reaction induced by a resistive thermal tip. The resulting structures were subsequently imaged by scanning thermal microscopy (SThM) and atomic force microscopy. The thermal conductivity contrast in SThM images suggested that palladium acetate thin film could be decomposed to palladium metal. The resulting palladium metallic features can form down to the substrate and adhere well on the substrate by using thinner precursor palladium acetate film. The effect of control resistance and tip scan rate on resulting features has also been studied. The results obtained indicate the potential application of SThM tip induced chemical reaction in device fabrication. © 1997 American Vacuum Society.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
07.79.-v Scanning probe microscopes and components
07.20.-n Thermal instruments and apparatus
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Tunneling spectroscopy on semiconductors with a low surface state density

Ch. Sommerhalter, Th. W. Matthes, J. Boneberg, P. Leiderer, and M. Ch. Lux-Steiner

J. Vac. Sci. Technol. B 15, 1876 (1997); http://dx.doi.org/10.1116/1.589571 (8 pages) | Cited 14 times

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A detailed study of tunneling spectroscopy concerning semiconductors with a low surface state density is presented. For this purpose, I–V curves under dark conditions and under illumination were measured on the (0001) van der Waals surface of a p-type WS2 single crystal, which is known to be free of intrinsic surface states. The measurements are interpreted by an analytical one-dimensional metal-insulator-semiconductor model, which shows that the presence of the finite tunneling current has to be considered in the calculation of the tip-induced bandbending. Rectification of the dark I–V curves is explained by the absence of an inversion layer at the semiconductor surface. In contrast, the I–V curves measured for different light intensities and tip-sample separations indicate the existence of an optically induced inversion layer. Since no surface recombination needs to be considered to model these spectra, we conclude that bulk recombination, diffusion and direct tunneling of photogenerated minority charge carriers are the dominant processes for semiconductors with a low density of surface states. In contrast to the standard interpretation of tunneling spectroscopy, which can be applied to semiconductors with a high surface state density, our results clearly show that in this case the normalized differential conductivity (dI/dU)/(I/U) cannot be used to determine the energetic distribution of the local surface state density. © 1997 American Vacuum Society.
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73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling

Dielectric breakdown of silicon oxide studied by scanning probe microscopy

Takao Yasue, Yoshiko Yoshida, Hiroshi Koyama, Tadao Kato, and Tadashi Nishioka

J. Vac. Sci. Technol. B 15, 1884 (1997); http://dx.doi.org/10.1116/1.589572 (5 pages) | Cited 17 times

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The applicability of scanning probe microscopy in the dielectric breakdown characteristics of silicon oxide has been demonstrated. Our study demonstrates that the measurement on the oxide is free from the effect of trapped charge created by Fowler–Nordheim tunneling when a sufficient distance is maintained between the measuring points. In this condition, for a 13-nm-thick oxide, the dielectric breakdown voltages were found to be so uniform as to fluctuate only 1%. We applied this method to oxides on the wafers from two different vendors, and found that the dielectric breakdown strength of the oxide depends on the difference on the Si substrates. We also applied this method to a square oxide pattern surrounded by a field oxide, and the result was that the dielectric breakdown strength of the oxide on the edge is lower than the one in the center. © 1997 American Vacuum Society.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Jp Dielectric breakdown and space-charge effects
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.61.Ng Insulators
77.55.-g Dielectric thin films

Synthesis, structure, and optical properties of nanometer-sized In2O3 capped by anionic surfactant

Wu Xiaochun, Wang Rongyao, Zou Bingsuo, Wu Pengfei, Xu jiren, and Huang Wei

J. Vac. Sci. Technol. B 15, 1889 (1997); http://dx.doi.org/10.1116/1.589573 (4 pages) | Cited 2 times

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In this article, nanometer-sized In2O3 organosol capped with a layer of anionic surfactants was prepared using microemulsion method. Its structure and optical properties were investigated through transmission electron microscopy, ultraviolet-visible absorption spectra, photoluminescence spectra and Z-scan technique. It was found that the prepared In2O3 organosol showed a series of new optical properties, which can be explained by its special oxygen vacancy structure. These new optical properties enhance its applications in information optics. © 1997 American Vacuum Society.
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61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
42.65.An Optical susceptibility, hyperpolarizability
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.66.Jg Amorphous semiconductors; glasses
73.22.-f Electronic structure of nanoscale materials and related systems
82.70.Gg Gels and sols
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
78.55.Hx Other solid inorganic materials
78.40.Ha Other nonmetallic inorganics
81.05.Hd Other semiconductors

Evolution of surface morphology in the initial stage of nitridation of the Si(111)-7×7 surface by nitrogen ions

Jeong Sook Ha, Kang-Ho Park, Wan Soo Yun, El-Hang Lee, and Seong-Ju Park

J. Vac. Sci. Technol. B 15, 1893 (1997); http://dx.doi.org/10.1116/1.589574 (6 pages) | Cited 8 times

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The evolution of surface morphology in the initial stage of nitridation of Si(111)-7×7 has been investigated by using a scanning tunneling microscope (STM) and low energy electron diffraction (LEED). The STM and LEED measurements were done on the Si(111) surface nitrided under different experimental conditions including the variations in the nitrogen ion energy, nitrogen ion dose, nitridation temperature, and the postannealing temperature. A growth mechanism of the silicon nitride layer in the initial stage was proposed based upon a comparison of the surface morphology obtained under different nitridation conditions. For the growth of uniform and large silicon nitride islands, it was necessary to have proper heat treatment of the surface. In particular, the surface postannealed at 980 °C after nitridation at 950 °C produced dramatically enlarged flat silicon nitride islands compared to that postannealed at the same temperature after nitridation at room temperature, and is probably due to improved mobilities of the reacting species with elevation of the nitridation temperature. © 1997 American Vacuum Society.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Cy Elemental semiconductors

Fourier transform infrared study of porous silicon dipped into Cr3+ solution

Y. M. Huang and B. G. Zhai

J. Vac. Sci. Technol. B 15, 1899 (1997); http://dx.doi.org/10.1116/1.589575 (3 pages) | Cited 4 times

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We have measured Fourier transform infrared (FTIR) spectra of Cr3+ immersed porous silicon after annealing at different temperatures. After dipping porous silicon into Cr3+ solution, three additional peaks appear at 807, 886, and 940 cm−1 in the FTIR spectrum. When annealed in nitrogen at different temperatures for various durations, the peak at 807 cm−1 remains almost unchanged, the height of peak 886 cm−1 decreases gradually, while the peak at 940 cm−1 disappears quickly. This decay process occurs much faster at higher annealing temperature. These FTIR features reflect the surface chemistry change after immersed into Cr3+ solution. © 1997 American Vacuum Society.
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78.30.Am Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
81.05.Rm Porous materials; granular materials
61.72.Cc Kinetics of defect formation and annealing

Expression for the growth rate of selective epitaxial growth of silicon using dichlorosilane, hydrogen chloride, and hydrogen in a low pressure chemical vapor deposition pancake reactor

Poonacha Kongetira, Gerold W. Neudeck, and Christos G. Takoudis

J. Vac. Sci. Technol. B 15, 1902 (1997); http://dx.doi.org/10.1116/1.589576 (6 pages) | Cited 3 times

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A semiempirical expression was developed for the growth rate of selective epitaxial growth (SEG) and epitaxial lateral overgrowth of silicon in a rf heated cold-wall low pressure chemical vapor deposition pancake reactor for the dichlorosilane-HCl–H2 system. The model was obtained for temperatures ranging from 920 to 1020 °C, system pressures from 40 to 150 Torr, and over a range of HCl and dichlorosilane gas flows. The growth rate expression is the sum of a growth term which is a function of the partial pressures of dichlorosilane (SiCl2H2) and hydrogen, and an etch term that varies with the partial pressure of HCl. The growth and etch terms have a temperature Arrhenius relation with activation energies of Egr=2.266 and Eet=1.349 eV, respectively. Included is a term to account for the SEG growth rate dependence on the ratio of SiO2 area coverage to silicon wafer area. A methodology was developed for obtaining the coefficients for the semiempirical growth rate expression from several sets of experiments. © 1997 American Vacuum Society.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
85.40.Sz Deposition technology
81.05.Cy Elemental semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Determination of trace metallic impurities on 200-mm silicon wafers by time-of-flight secondary-ion-mass spectroscopy

Paul K. Chu, Bruno W. Schueler, Fraser Reich, and Patricia M. Lindley

J. Vac. Sci. Technol. B 15, 1908 (1997); http://dx.doi.org/10.1116/1.589577 (5 pages) | Cited 6 times

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Surface contamination on silicon wafers is an important issue in integrated circuit fabrication. The concentration of many surface metallic impurities is below the detection limit of total reflection x-ray fluorescence (TXRF). Vapor phase decomposition—atomic absorption spectroscopy (VPD-AAS) cannot reveal the lateral distribution of these impurities even though the detection limits can be as low as 107 atoms/cm2. The time-of-flight secondary-ion-mass spectroscopy (TOF-SIMS) technique can deliver sensitivity close to that by VPD-AAS for many metallic impurities. For example, the detection limits of Fe, Al, Na, and K are 6×108, 3×108, 7×107, and 3×107 atoms/cm2, respectively. In addition, this technique can disclose the lateral distribution of the impurities as well as information on organic contaminants. This article addresses some of the latest development of TOF-SIMS in the determination of surface impurities of 200-mm silicon wafers. When choosing conditions such that the analysis is integrated throughout the native oxide layer, good quantitative correlation with TXRF and VPD-AAS data can be achieved. © 1997 American Vacuum Society.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.35.Dv Composition, segregation; defects and impurities
81.05.Cy Elemental semiconductors
61.72.S- Impurities in crystals

Degradation measurements using fully processed test transistors in high density plasma reactors for failure analysis

Ravisangar Muniandy, Ron Boylan, Roland Chin, Nick Bell, and Robert Sankman

J. Vac. Sci. Technol. B 15, 1913 (1997); http://dx.doi.org/10.1116/1.589578 (6 pages) | Cited 2 times

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The objective of this study was for it to serve as a guide for understanding high density plasma induced damage during wafer fabrication and etchback for device debug, electron-beam, and failure analysis. A study of electrical degradation of packaged and fully processed transistors that were functionally etched back was carried out. Two high density plasma technologies, electron cyclotron resonance (ECR) and inductively coupled plasma (ICP), from various vendors, were evaluated. Transconductance (gm), threshold voltage (Vt), subthreshold slope, and gate leakage (Ig) were measured before and after the functional etch. Degradation took place even without polysilicon being directly exposed to the plasma. It was found that there is a strong correlation between the threshold voltage shift, and gate current shift, and they exhibit a bimodal relationship. The gate edge intensive transistor was most susceptible to degradation. The design of the etchers seemed to be the key factor rather than the choice of technology (ECR or ICP) with regard to transistor degradation. Gate oxide breakdown due to the charging of metal lines, caused by nonuniform electrical charging of the surface, adequately explains the observed transistor parameter shifts. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Low temperature deposition of SiNx:H using SiH4–N2 or SiH4–NH3 distributed electron cyclotron resonance microwave plasma

F. Delmotte, M. C. Hugon, B. Agius, and J. L. Courant

J. Vac. Sci. Technol. B 15, 1919 (1997); http://dx.doi.org/10.1116/1.589579 (8 pages) | Cited 10 times

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Silicon nitride films were deposited at floating temperature using distributed electron cyclotron resonance plasma enhanced chemical vapor deposition (DECR-PECVD) on Si and InP substrates. The deposition parameters studied included the nature of gases (SiH4–N2 or SiH4–NH3) and the gas phase composition (SiH4/N2 or SiH4/NH3). The experimental results establish that to obtain device quality Si3N4, it is desirable to use N2 instead of NH3 and a high diluted SiH4 gas phase. These process parameters yield to a high resistivity (1016 Ω cm) and a high critical field (4.5 MV/cm). These properties confirm that the DECR technique is well suited for processing III–V compound semiconductors. NH3 does not induce such promising characteristics in terms of electrical properties but silicon nitride deposited with this gas is particularly interesting for applications where no stress is required. © 1997 American Vacuum Society.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
85.40.Sz Deposition technology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Gc Amorphous semiconductors

Effects of cleaning and postoxidation annealing on thin oxides

G. Franco, C. M. Camalleri, V. Raineri, G. Ghidini, C. Clementi, and F. Pellizzer

J. Vac. Sci. Technol. B 15, 1927 (1997); http://dx.doi.org/10.1116/1.589580 (9 pages)

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The aim of this work is to study the influence on the oxide quality of various cleaning procedures performed before growing a thin dielectric in a steam ambient. Different measurement methods were applied showing the improved effectiveness of constant electric field stress versus constant current density stress method to detect a cleaning, which causes particle problems on the wafer. The effect evaluation of a postoxidation treatment on different oxide thickness was also carried out. © 1997 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
81.05.Cy Elemental semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Integration of unit processes in a shallow trench isolation module for a 0.25 μm complementary metal–oxide semiconductor technology

A. Chatterjee, I. Ali, K. Joyner, D. Mercer, J. Kuehne, M. Mason, A. Esquivel, D. Rogers, S. O’Brien, P. Mei, S. Murtaza, S. P. Kwok, K. Taylor, S. Nag, G. Hames, et al.

J. Vac. Sci. Technol. B 15, 1936 (1997); http://dx.doi.org/10.1116/1.589581 (7 pages) | Cited 7 times

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This article presents a study of the issues in integrating the pattern, fill, planarization, and surface cleanup processes to design a shallow trench isolation (STI) flow suitable for 0.25 μm complementary metal–oxide semiconductor technologies. Technological choices and their effects on the characteristics of the STI technology are discussed. Experimental data are presented to illustrate how process choices at various stages of the STI flow are made to optimize the STI structure. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices
85.40.Ls Metallization, contacts, interconnects; device isolation

Correlated electrical and optical measurements of firing semiconductor bridges

Jongdae Kim, Sang Gi Kim, and K. C. Jungling

J. Vac. Sci. Technol. B 15, 1943 (1997); http://dx.doi.org/10.1116/1.589582 (6 pages) | Cited 2 times

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Description is given of a high-resolved optical multichannel analyzer (OMA) system and of a firing set whereby OMA records and electrical measurements from a single discharge of a semiconductor bridge (SCB) may be accurately correlated in time. Such a correlation obtained by the novel experimental system is used in order to explain the dynamic discharge behaviors, especially the plasma formation, of the bridges. From the results of the experiments, the minimum electric field to generate a plasma from the W-land SCB is about 0.77×103 V/cm and the time required to evolve the plasma from the bridge is about 1.5 μs, for the SCB 47 μm long and 140 μm wide. © 1997 American Vacuum Society.
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52.80.Qj Explosions; exploding wires
85.30.-z Semiconductor devices
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.Ds Electric and magnetic measurements
84.30.Sk Pulse and digital circuits

Generation of subquarter-micron resist structures using optical interference lithography and image reversal

J. Y. Decker, A. Fernandez, and D. W. Sweeney

J. Vac. Sci. Technol. B 15, 1949 (1997); http://dx.doi.org/10.1116/1.589583 (5 pages) | Cited 7 times

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We show that by using interference lithography coupled with image reversal techniques we can generate resist structures ranging from one-dimensional gratings to two-dimensional arrays of posts and holes. These resist structures have high aspect ratios and nearly vertical sidewalls. The structure dimensions are accurately controlled by varying the exposure dose. These structures play critical roles in the generation of subwavelength structured surfaces for optical applications. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.25.Hz Interference

Investigation of the proximity effect in amorphous AlF3 electron-beam resists

G. S. Chen and C. J. Humphreys

J. Vac. Sci. Technol. B 15, 1954 (1997); http://dx.doi.org/10.1116/1.589584 (7 pages) | Cited 6 times

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A proximity effect occurs when two features having a close proximity are exposed using conventional organic electron-beam resists, subsequently causing overexposure of the region between the two features and ultimate broadening of the features. In this study, we employ probes of a through-focal series to irradiate amorphous AlF3 (a-AlF3) inorganic films. A proximity effect of a very different nature is also observed while employing the a-AlF3 films as self-developing electron-beam resists. Such an effect distorts the closely spaced features and sets a limit on the proximity of those nanometer-scaled features. According to the results of electron microscopy obtained while examining the peculiar behavior of the proximity effect, mass-transport phenomena are critical in the damaging behavior of the a-AlF3 films. Besides, our results presented herein demonstrated the ability of the through-focal probes to produce aluminum nanostructures of varying sizes in thin films containing a-AlF3 self-developing resists. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Air-bridges, air-ramps, planarization, and encapsulation using pyrolytic photoresist in the fabrication of three-dimensional microstructures

G. A. Porkolab, Y. J. Chen, Seyed Ahmad Tabatabaei, Sambhu Agarwala, F. G. Johnson, Oliver King, M. Dagenais, Russell E. Frizzell, W. T. Beard, and D. R. Stone

J. Vac. Sci. Technol. B 15, 1961 (1997); http://dx.doi.org/10.1116/1.589585 (5 pages) | Cited 4 times

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Pyrolyzation of photolithographically patterned photoresist on semiconductor substrates such as silicon, gallium arsenide, and indium phosphide, results in a convex-shaped, chemically inert, temporary form that functions as a mold upon which to lift-off evaporated thin films such as metals. The pyrolyzation process is simply a bake on a standard laboratory hot-plate that is ramped from room temperature to 300 °C air. The pyrolytic-photoresist form is subsequently removed in an oxygen plasma stripper leaving behind the three-dimensional lifted off thin films of free-standing, convex-shaped, full-arch air-bridges or half-arch air-bridges that we call air-ramps. Some applications are interconnects for high-speed devices; inter-level interconnects; out-of-plane coils for out-of-plane inductors; microdomes for eletromagnetic shielding; electrodes for field-emitter tips; and microelectromechanical structures. Pyrolyzing photoresist does not alter the good planarization capabilities of photoresist. Because pyrolytic photoresist is a version of the earliest form of synthetic thermoset resin called Bakelite, it can also be used as a reasonably good encapsulation material. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.10.Cm Micromechanical devices and systems
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Polarization-dependent contrast in near-field optical microscopy

Kiyoshi Kobayashi and Osaaki Watanuki

J. Vac. Sci. Technol. B 15, 1966 (1997); http://dx.doi.org/10.1116/1.589586 (5 pages) | Cited 3 times

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This article presents a simple modeling and simulation of experiments with a near-field optical microscope or a photon scanning tunneling microscope (PSTM) in the sub-100-nm range. The simulation employs a semimicroscopic and perturbative approach based on field propagator and linear response theory. A probe tip and sample are approximated as nanometric spheres in order to clarify the behavior of the near-field and far-field signal intensities, I, and the contrast, i.e., visibility, (Imax−Imin)/(Imax+Imin), for s and p polarization of incident light and three scanning methods: constant height, constant intensity, and constant distance. The signal intensity then becomes a function of the taper angle of the fiber probe tip θ or the numerical aperture of the collecting lens, in addition to the variables mentioned above. Note that the signal intensity I(θ=90°) corresponds to that for the near-field. The simulated polarization-dependent intensity and contrast are in good qualitative agreement with the experimental results. At the same time, for each polarization and scanning method, there is an optimal angle θ for maximizing the contrast and maintaining a high signal intensity. This result indicates that the taper angle and scanning method are very important factors in the polarization-dependent contrast and resolution of near-field optical microscopy. © 1997 American Vacuum Society.
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07.79.Fc Near-field scanning optical microscopes

Synthesis of electrostatic focusing and deflection systems

M. Szilagyi and H. Cho

J. Vac. Sci. Technol. B 15, 1971 (1997); http://dx.doi.org/10.1116/1.589587 (12 pages) | Cited 1 time

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In this article, we present synthesis of an ion beam column as a single entity, based on combined focusing and deflection (CFD). We present seven cases as examples of designing CFD systems by synthesis. Four of those are examples resulting from the a priori given multielectrode approach using a multipurpose multipole system with nine or five units. In these cases, the units have short cylindrical rings or disks cut into segments with geometrically octupole symmetry. In one example we are using the cubic spline method. The other two cases are examples obtained by using both methods in the case of a separate group of axially symmetric electrostatic lenses and electrostatic postlens deflectors. By using a sequential optimization technique combined with the gradient method and the Hooke–Jeeve’s method for a multipurpose multipole system with nine units, our calculations show that one can produce a beam spot radius less than 7 nm and current density of 614 A/cm2, scanned over a 2-mm-square field for a field ionization source. We also present comparison of our CFD system with other published data. The results display substantial improvements, especially for a field ionization source with smaller energy spread ΔU=1 eV and higher acceptance half-angle γ0=2.3 mrad. A sensitivity analysis is given, and the optimum working distances of a given CFD system are presented for the minimum beam spot radius. © 1997 American Vacuum Society.
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41.85.Ne Electrostatic lenses, septa

Effect of rapid thermal annealing on the microstructure and electrical characteristics of Au/Ni/Au/Ge/Ni multilayers deposited on n-type InGaAs

J. Morais, T. A. Fazan, R. Landers, R. G. Pereira, E. A. S. Sato, and W. Carvalho

J. Vac. Sci. Technol. B 15, 1983 (1997); http://dx.doi.org/10.1116/1.589588 (4 pages)

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The effect of rapid thermal annealing on the microstructure and contact resistance of Au/Ni/Au/Ge/Ni multilayers deposited on InGaAs:Si layers was studied by Auger electron spectroscopy (AES) and the transmission line method. The reaction process at the interfaces after thermal annealing was monitored by Auger depth profiles (AES in conjunction with ion sputtering). We have observed that the formation of a NiGeAs layer at the interface plays an important role in obtaining contacts with low specific resistance, similar to GaAs. Based on these results, we have obtained extremely low specific contact resistance [(4±1)×10−8 Ω cm2] for annealing temperatures higher than 400 °C. © 1997 American Vacuum Society.
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73.40.Ns Metal-nonmetal contacts
68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing

Bias-temperature stability of the Cu(Mg)/SiO2/p-Si metal-oxide-semiconductor capacitors

T. Suwwan de Felipe, S. P. Murarka, S. Bedell, and W. A. Lanford

J. Vac. Sci. Technol. B 15, 1987 (1997); http://dx.doi.org/10.1116/1.589589 (3 pages) | Cited 7 times

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This work studies the consequences of alloying copper with 2 at % magnesium on the transport of copper through the SiO2 dielectric when subjected to bias temperature aging (BTA). Metal-oxide semiconductor structures, that were thermally annealed at different temperature, were BTA under an electric field of 2.35 MV/cm at varying temperatures and for varying periods of time. The resulting capacitance–voltage (C–V) and I–V curves indicate that the samples thermally annealed above 300 °C form a passivating film between the oxide-metal interface and the metal surface. This oxide film is assumed to cause an inhibition of the diffusion or drifting of copper into the SiO2 and is responsible for the observed stability in the C–V and I–V curves. © 1997 American Vacuum Society.
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84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices

Characterization of AL–Y alloy thin films deposited by direct current magnetron sputtering

Y. Liu, R. Singh, K. Poole, R. J. Diefendorf, J. Harriss, and K. Cannon

J. Vac. Sci. Technol. B 15, 1990 (1997); http://dx.doi.org/10.1116/1.589590 (5 pages) | Cited 2 times

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Thin films of Al-1.27 wt %Y were deposited by dc magnetron sputtering. Adding yttrium to the aluminum drastically reduced the metal’s grain size and also improve the uniformity of grain size distribution. Upon annealing at a temperature of 450 °C for 30 min, grain growth was insignificant, while the electrical resistance dropped from 6.05 to 2.95 μΩ cm. The as deposited films consisted of Al4Y and α-Al supersaturated with yttrium. After annealing, β-Al3Y precipitated instead of α-Al3Y. The Al–Y films had much higher resistance to hillock formation than did Al-1 wt %Si films. © 1997 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys
66.30.Qa Electromigration

Growth and fractal scaling nature of copper thin films on TiN surface by metal organic chemical vapor deposition from hexafluoroacethylacetonate Cu(I) vinyltrimethylsilane

Young-Bae Park, Shi-Woo Rhee, and Jae-Hwa Hong

J. Vac. Sci. Technol. B 15, 1995 (1997); http://dx.doi.org/10.1116/1.589591 (6 pages) | Cited 4 times

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The initial stage of growth and fractal scaling nature of copper (Cu) films, deposited by metal organic chemical vapor deposition on TiN substrate using hexafluoroacethylacetonate Cu(I) vinyltrimethylsilane precursor, was investigated by means of Auger electron spectroscopy, atomic force microscopy (AFM), x-ray diffraction, transmission electron microscopy, and scanning electron microscopy (SEM). Cu films were deposited in the surface reaction controlled regime (<200 °C) onto a columnar structure TiN substrate and discontinuous island growth was observed due to oxygen contamination of the TiN surface. Preferred orientation of the deposited Cu film changed as a function of the deposition time and coverage. The roughness exponent (α) and lateral correlation length (ξ) of Cu films grown under different growth stages were studied. From AFM measurement, it was found that the roughness exponent increased with increasing deposition time and the lateral correlation length also increased as the grains coalesced, which was also compared with SEM images. For island growth mode at the early stage of growth, α was below 0.65 and it saturated at 0.75 for the continuous growth mode. © 1997 American Vacuum Society.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
61.43.Hv Fractals; macroscopic aggregates (including diffusion-limited aggregates)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Bx Metals, semimetals, and alloys

Effect of the in situ thermal treatments on Ir/n-type Si (111) Schottky contacts

F. J. Jiménez-Leube, M. Clement, J. Sanz-Maudes, J. M. Blanco, and J. J. Serrano

J. Vac. Sci. Technol. B 15, 2001 (1997); http://dx.doi.org/10.1116/1.589592 (10 pages) | Cited 1 time

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In this article we analyze the effect of the in situ thermal treatments on the properties of the Ir/ n-type Si (111) Schottky contacts. The samples were annealed in the evaporation system at 400 °C for 15 min and at 450 °C for 15 min or 2 h. Rutherford backscattering spectroscopy spectra and secondary ion mass spectroscopy compositional profiles indicate that as result of the different thermal treatments performed in the samples there is a clear diffusion of silicon into the iridium layer but the composition of the metal–semiconductor interface cannot be determined. It has been shown previously that a small quantity of IrSi can be formed at an Ir–Si interface when Ir layers are deposited on Si. The current-voltage-temperature (I-V-T) behavior of these diodes indicates that it is dominated by the effect of spatial fluctuations of the surface barrier. After the thermal treatment at 400 °C for 15 min the diodes show I-V characteristics that can be perfectly justified by the unidimensional model of the thermionic emission theory. The Schottky barrier value at 0 K (0.92 eV) and the temperature coefficient of the barrier (3⋅10−4 V/K) corresponds with that previously reported for the IrSi. When the annealing temperature is raised to 450 °C, the resulting devices show a nonhomogeneous barrier with similar values to those found at room temperature. Increasing the annealing time to 2 h leads to devices showing an increase in the ideality factor value (1.12), along with a barrier height value at room temperature (0.86 eV) which coincides with that previously reported for the IrSi1.75. The 0 K barrier height (0.72 eV) indicates that a phase transformation at the interface has taken place. © 1997 American Vacuum Society.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing
85.30.Hi Surface barrier, boundary, and point contact devices
66.30.Ny Chemical interdiffusion; diffusion barriers

Influence of AlSiTi grain boundaries on the plasma etch rate

Edgar Schönbächler, Baudouin Lecohier, and Wolfgang Fichtner

J. Vac. Sci. Technol. B 15, 2011 (1997); http://dx.doi.org/10.1116/1.589593 (5 pages) | Cited 1 time

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The influence of the microstructure of an AlSiTi alloy on plasma etch rate is presented in this work. Metal films were individually sputtered onto silicon wafer substrates using different deposition conditions based on a design-of-experiments approach. The grain structure was analyzed for each metal film extracting the average grain size and the grain-size standard deviation. It was found that the etch rate increases with increasing average grain size and grain size standard deviation. Although grain size and standard deviation are dependent on each other in this experiment, we could show that the etch rate varies independently for each grain structure parameter. The physical mechanism at the base of this phenomenon deals with the different composition of grains and grain boundaries. Impurities and minority alloying materials segregate in grain boundaries, which are etched more slowly. A general approach to model the etch rate was performed calculating a factor which includes the total grain boundary length per surface unit. This factor can be expressed using average grain size and grain size standard deviation. We found that the etch rate decreases for increasing values of this factor, thus confirming the grain boundary model. © 1997 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
85.40.Ls Metallization, contacts, interconnects; device isolation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
81.05.Bx Metals, semimetals, and alloys

Schottky contacts on reactive-ion etched InGaP

Ján Kuzmík, Juraj Darmo, Robert Kúdela, Štefan Haščík, and Želmíra Mozolová

J. Vac. Sci. Technol. B 15, 2016 (1997); http://dx.doi.org/10.1116/1.589594 (5 pages)

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We report on the technology and properties of Schottky contacts on reactive-ion etched n-In0.49Ga0.51P (n=7.5×1017 cm−3). A mixture of CH4/H2 was used for a controllable smooth dry etching of InGaP while a CCl2F2-based plasma was shown to enable a highly selective etching of GaAs over InGaP. Current–voltage (I–V), capacitance–voltage (C–V) methods and deep-level transient spectroscopy (DLTS) were used for diode characterization. CCl2F2-based reactive-ion etching (RIE) led to diodes with barrier heights of 0.67 eV (from I–V measurements) and ideality factors of 1.24, which are parameters that are very close to those of the reference (not dry etched) sample. Additional C–V and DLTS characterization has confirmed no detectable damage for CCl2F2-based RIE. On the other hand, hydrogenation after CH4/H2 plasma led to substantial passivation of donors which were successfully reactivated after 430–470 °C rapid thermal annealing (RTA). For this type of processing we measured barrier heights of 0.70–0.75 eV and ideality factors of 1.25–1.27, depending on the temperature of the RTA. DLTS on CH4/H2-RIE based diodes has shown that, in contrast to the reference sample, no bulk deep traps are generated with RTA. We point out that thermal treatment also led to changes in the interface states density which may be responsible for the diode barrier height increase. © 1997 American Vacuum Society.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing

Molecular beam epitaxy growth of Iny2Al1−y2As/In0.73Ga0.27As/Iny1Al1−y1As/ InP P-HEMTs with enhancement conductivity using an intentional nonlattice-matched buffer layer

C. Jiang, B. Xu, H. X. Li, F. Q. Liu, Q. Gong, W. Zhou, D. H. Zhu, J. B. Liang, and Z. G. Wang

J. Vac. Sci. Technol. B 15, 2021 (1997); http://dx.doi.org/10.1116/1.589218 (5 pages) | Cited 2 times

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Pseudomorphic Iny2Al1−y2As/In0.73Ga0.27As/Iny1Al1−y1As (y1⩾0.52) modulation-doped heterostructures with an intentional nonlattice-matched buffer layer were successfully grown by molecular beam epitaxy on (100)InP substrates. Fourier transform photoluminescence and double crystal x-ray diffraction measurements show a superior crystalline quality in the high In content channel, when In mole fraction increases from y1=0.52 to 0.55 in the Iny1Al1−y1As buffer layer. In this case, an increasing of 16.3% and 23.5% for conductivity (μ×ns) and mobility, related to the strain compensation in the In0.73Ga0.27As channel, was achieved, respectively, comparing to the structure containing a well-lattice matched buffer layer. With increasing the mismatch further (y1=0.58), a morphology with cross-hatched pattern was observed due to the onset of a large amount of misfit dislocations, and the electronic characterization is not able to be improved continuously. Because we can realize high quality strained P-HEMTs in a relative wide range of equivalent beam flux (EBF) ratios, the stringent control over the constant EBF is not indispensable on this In-based material system. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Structure and interfacial stability of (111)-oriented InAsSb/InAs strained-layer multiquantum well structures

Scott C. Theiring, Manoj R. Pillai, Scott A. Barnett, and Bruce W. Wessels

J. Vac. Sci. Technol. B 15, 2026 (1997); http://dx.doi.org/10.1116/1.589217 (5 pages) | Cited 2 times

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Biaxially strained InAsxSb1−x/InAs (111)-oriented multiquantum well structures with x≈0.8 have been grown by metalorganic vapor phase epitaxy. The quality of the multiquantum well structures was assessed by double-crystal x-ray diffraction (θ–2θ scans) and kinematical computer simulations. The x-ray diffraction pattern of an InAs0.79Sb0.21/InAs multiquantum well film showed eight orders of satellite peaks, with a low diffuse background, indicating that excellent (111)-oriented structures can be achieved. The simulations modeled the compositional broadening of the interfaces, layer thickness fluctuations, and lattice spacing fluctuations of the compositionally modulated structures. The simulations indicated that the InAs/InAsSb interfaces were compositionally broadened over at least 0.5 nm, and that the layer thickness fluctuations of the highest quality structure were below the detection limit of 0.1 nm. Segregation of the antimony during deposition appears to be the primary cause of the compositional broadening. Simulations indicated that the layer thickness fluctuations increased with deposition rate, from less than 0.1 nm at a deposition rate of 8.4 nm/min to 1.2 nm at a deposition rate of 24 nm/min. The increase in the interface roughness was attributed to changes in surface reaction kinetics due to a shift in the III/V ratio at higher growth rates. © 1997 American Vacuum Society.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Fx Diffusion; interface formation
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.Ct Interface structure and roughness

Fabrication of high-aspect-ratio InP-based vertical-cavity laser mirrors using CH4/H2/O2/Ar reactive ion etching

Jeff E. Schramm, Dubravko I. Babić, Evelyn L. Hu, John E. Bowers, and James L. Merz

J. Vac. Sci. Technol. B 15, 2031 (1997); http://dx.doi.org/10.1116/1.589219 (6 pages) | Cited 10 times

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The addition of oxygen to methane/hydrogen/argon reactive ion etching (RIE) processes can mitigate polymer deposition, and produce vertical etched sidewalls. This work contrasts the various ways in which the oxygen may be incorporated into methane/hydrogen/argon reactive ion etching of deep (>5 μm) InGaAsP/InP multilayers. Three methods are investigated: a “continuous” process in which a fixed amount of oxygen is added to methane/hydrogen/argon for the duration of the etch, a “cyclical” process in which the methane/hydrogen/argon RIE processes alternates with oxygen RIE, and a hybrid process which incorporates the advantages of both former methods. These processes are applied to the fabrication of tall (>10 μm) InGaAsP/InP quarter-wave mirrors for long-wavelength vertical-cavity lasers; the various benefits and limitations of the various approaches are discussed. It is found that the hybrid process allows formation of deeply etched structures (15 μm) with vertical profiles. © 1997 American Vacuum Society.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
42.55.Px Semiconductor lasers; laser diodes
42.79.Bh Lenses, prisms and mirrors
42.86.+b Optical workshop techniques
81.65.Cf Surface cleaning, etching, patterning

High-resolution depth profiling of InxGa1−xAs/GaAs multiple quantum well structures by combination of secondary ion mass spectrometry and x-ray diffraction techniques

C. Gerardi, C. Giannini, A. Passaseo, and L. Tapfer

J. Vac. Sci. Technol. B 15, 2037 (1997); http://dx.doi.org/10.1116/1.589220 (9 pages) | Cited 2 times

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In this work we investigate multiple quantum well semiconductor structures by secondary ion mass spectrometry (SIMS) and high-resolution x-ray diffraction measurements. The combined use of these techniques turns out to be a very powerful tool for an accurate investigation of both structural and chemical characteristics of complex structures consisting of thin alternating layers. We show that the x-ray data allow us to increase the accuracy of the SIMS analyses providing internal standards, for both depth scale and concentration calibration. This procedure allows us: (i) to determine accurate quantitative SIMS concentration profiles which lead to the determination of the elemental concentration in the quantum wells, (ii) the mole fraction and layer thickness of embedded layers, and (iii) also to investigate eventual segregation and diffusion phenomena occurring at the interfaces. Our procedure is demonstrated on a set of InxGa1−xAs/GaAs multiple quantum well structures grown by metalorganic chemical vapor phase epitaxy. The experiments, performed by secondary ion mass spectrometry and high-resolution x-ray diffraction measurements, as well as the methodology of the data analyses are discussed in detail. As the main result of our investigation we obtained the precise indium distribution in each of the investigated samples with an accuracy below 5% and the individual barrier and well layer thickness. © 1997 American Vacuum Society.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.05.cp X-ray diffraction

Surface modification of InP by diffraction-patterning utilizing laser dry etching

Manoj Prasad, Harry E. Ruda, and Jan J. Dubowski

J. Vac. Sci. Technol. B 15, 2046 (1997); http://dx.doi.org/10.1116/1.589221 (6 pages)

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Laser based dry etching of semiconductors offers a useful way of integrating patterning with growth for optoelectronic device development. In this article we demonstrate XeCl excimer laser based dry etching of InP. Experiments were carried out using a 10% gas mixture of chlorine diluted in helium. Studies were made of the effect of laser fluence on the etching process and how this influences pattern development. Based on these studies, surface electromagnetic waves were used to form ripple patterns and the optimum conditions for interference pattern development are reported. These studies show that a relatively low fluence is not conducive to pattern development. We also utilize diffraction from slits of different shapes in tandem with laser dry etching for the patterning of structures in semiconductors. This technique offers the potential to develop relatively damage-free structures. These structures may be suitable for devices used in a number of applications such as telecommunications. © 1997 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
42.79.Dj Gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer
79.20.Ds Laser-beam impact phenomena
42.86.+b Optical workshop techniques

Compression in transconductance at low gate voltages in submicron GaAs metal semiconductor field-effect transistors

M. M. Ahmed

J. Vac. Sci. Technol. B 15, 2052 (1997); http://dx.doi.org/10.1116/1.589222 (5 pages)

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In submicron GaAs metal semiconductor field-effect transistors, the shift in the transconductance (gm) peak towards the high negative gate voltage end is often observed. Factors causing this abnormality were investigated. It is believed that if the surface potential and the Schottky barrier potential are of the same order of magnitude then there will be a strong probability that the peak gm value will appear at high negative gate voltages rather than near zero gate bias. It was shown that under these circumstances the drain current at low gate biases is not under the direct influence of gate depletion but rather is controlled by surface depletion in the gate-drain gap. At high negative gate voltages, depletion under the gate has the dominant effect on channel current, and the device exhibits an improved performance. Recessed gate technology is thought to be a solution to eliminate the surface state effects of a free drain-source surface. It was shown that a simple gate recess will not eliminate the possibility of gm compression and shift unless the Schottky barrier potential is greater than the free-surface potential. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices

Role of rate window, transient time, and reverse bias field on the deep levels of LT-GaAs by field effect transient spectroscopy

N. C. Halder and T. Goodman

J. Vac. Sci. Technol. B 15, 2057 (1997); http://dx.doi.org/10.1116/1.589223 (10 pages) | Cited 4 times

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We have investigated the effect of rate window, transient time, and reverse bias field on the deep levels in molecular beam epitaxy (MBE) grown, Si-doped, low temperature (LT) GaAs by field effect deep level transient spectroscopy (FEDLTS). As far as we know, this is the first successful paper on LT-GaAs investigated by FEDLTS. The applied rate window (R=t2/t1) ranged from 5 to 8 with interval 1, transient time from 5 to 50 s, and reverse bias field from −0.5 to −4×105 V/cm. The capacitance transients (CT) were recorded from 70 to 380 K at temperature intervals of 0.5, 1, or 2 K and analyzed by modulating function waveform analysis. The CT were relatively strong marked by very short growth time (∼5 s). At the measurement transient time greater than 5 s, the CT began to deteriorate showing no further resolution. On the other hand, the FEDLTS spectra were quite dense due to a large number of overlapping deep levels which were found to be very sensitive to the selection of rate window, measurement transient time, and reverse bias electric field. LT-GaAs was found to posses as many as nine electron trap levels in contrast to five deep trap levels observed in MBE-grown, Si-doped, high temperature GaAs studied earlier. © 1997 American Vacuum Society.
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71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Ey III-V semiconductors

Electrical characterization of diamond and graphite coated Mo field emitters

M. T. McClure, R. Schlesser, B. L. McCarson, and Z. Sitar

J. Vac. Sci. Technol. B 15, 2067 (1997); http://dx.doi.org/10.1116/1.589224 (5 pages) | Cited 8 times

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Current–voltage characteristics of tip-shaped molybdenum field emitters were investigated before and after coating with diamond or graphite powders. Stable emission was observed only after annealing and formation of a conductive Mo carbide layer at the metal-coating interface. Both coated emitters displayed enhanced emission and “turn-on” voltages reduced by a factor of 2 as compared to the uncoated emitters. For the graphite coated emitter, the enhancement was attributed to an increase in the field enhancement factor due to the coating morphology. Roughening of the Mo-diamond interface via carbide formation during the annealing step was presumed to have been the cause for the enhanced emission for the diamond coated emitter. The transmission probabilities for the Mo-diamond and diamond-vacuum interfaces were calculated, using the WKB method, based on an emission mechanism from the intrinsic diamond’s conduction band minimum. With a field locally enhanced to 108 V/cm, the transmission probability for the diamond-vacuum interface was 108 times larger than that of the Mo-diamond interface. This evaluation confirmed that the electron affinity of the diamond surface is not a governing factor in the emission from intrinsic diamond. © 1997 American Vacuum Society.
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85.45.Db Field emitters and arrays, cold electron emitters
79.70.+q Field emission, ionization, evaporation, and desorption
73.30.+y Surface double layers, Schottky barriers, and work functions

Field emission characteristics of diamondlike carbon films synthesized by pulsed laser deposition process using a Au-intermediate layer

F. Y. Chuang, W. C. Wang, H. F. Cheng, C. Y. Sun, and I. N. Lin

J. Vac. Sci. Technol. B 15, 2072 (1997); http://dx.doi.org/10.1116/1.589225 (5 pages) | Cited 7 times

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The characteristics of the diamondlike carbon (DLC) films deposited on Au-coated silicon substrate are observed to vary markedly with the substrate temperature. Large relative proportion of sp3-bonds had pronouncedly improved the electron emission properties of the DLC films. A low turn on field as 7 V/μm and a large emission current density as 2000 μA/cm2, at 20 V/μm, were achieved for DLC/Au/Si films deposited at 200 °C. Too high a substrate temperature (i.e., 600 °C) induced graphitization that degraded the field emission behavior. The DLC/Au/Si films grow in a similar behavior as DLC/Mo/Si films, but possess substantially better field emission characteristics. The scanning electron microscopic and secondary ion mass spectroscopics analyses implied that the main factor is the improvement on the interfacial structure through the interdiffusion between DLC, Au, and Si layers. © 1997 American Vacuum Society.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.15.Fg Pulsed laser ablation deposition

Silicon nanocolloids prepared by a newly designed dc sputtering apparatus

Y. Zhu, K. Kimura, and L. D. Zhang

J. Vac. Sci. Technol. B 15, 2077 (1997); http://dx.doi.org/10.1116/1.589226 (2 pages) | Cited 1 time

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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
82.70.Dd Colloids
81.05.Cy Elemental semiconductors
81.15.Cd Deposition by sputtering

Nanofabrication using neutral atomic beams

J. H. Thywissen, K. S. Johnson, R. Younkin, N. H. Dekker, K. K. Berggren, A. P. Chu, M. Prentiss, and S. A. Lee

J. Vac. Sci. Technol. B 15, 2093 (1997); http://dx.doi.org/10.1116/1.589227 (8 pages) | Cited 19 times

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We present a survey of neutral atom lithography. The combination of nm-scale features, large-area parallel deposition, and effective resists demonstrates the promise of atoms as a lithographic element. We demonstrate the transfer of 70-nm-wide features from a neutral atomic beam into a substrate using several resists, including self-assembled monolayers of alkanethiolates on Au and of alkylsiloxanes on SiO2, and “contamination” resists deposited from vapor. Unlike photons and electrons, noble gas atoms in energetic metastable states have an internal state structure that is easily manipulable, introducing the possibility of novel lithographic schemes based on the optical quenching of internal energy. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
03.75.Be Atom and neutron optics
01.30.Rr Surveys and tutorial papers; resource letters
41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
07.77.Gx Atomic and molecular beam sources and detectors
68.18.-g Langmuir-Blodgett films on liquids

Single electron electronics: Challenge for nanofabrication

Haroon Ahmed

J. Vac. Sci. Technol. B 15, 2101 (1997); http://dx.doi.org/10.1116/1.589228 (8 pages) | Cited 21 times

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Single electronics has the potential to overcome the limitations of complementary metal oxide semiconductor (CMOS) technology as device dimensions shrink towards the 10 nm scale. The basis of single electronics is the Coulomb blockade of electron transport which occurs when an electron can be localized on an isolated island. Many structures have been devised to demonstrate the Coulomb blockade and single electron transistors (SETs), based on this effect have been constructed. Metallic structures can be fabricated with vertical and lateral island and tunnel barrier structures in which the Coulomb blockade has been demonstrated at temperatures up to 77 K. Semiconductor single electronics has also been demonstrated with GaAs and silicon based structures. Silicon on insulator has the attractive feature that it may be used for conventional CMOS circuits as well as single electronics in the same chip. Several applications of SETs have been demonstrated such as memories and logic circuits. Memories based on charge storage on nanoislands and operating at room temperature will almost certainly have applications in the future. Nanofabrication for SETs requires advances in lithographic techniques well beyond the current state of the art to the sub 10 nm size scale. Electron beam lithography and scanning probe techniques offer the best prospects for the future although some more esoteric techniques based on atomic particle deposition and colloid chemistry may also offer some benefits. © 1997 American Vacuum Society.
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85.35.Gv Single electron devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Potentials and challenges for lithography beyond 193 nm optics

John Canning

J. Vac. Sci. Technol. B 15, 2109 (1997); http://dx.doi.org/10.1116/1.589229 (3 pages) | Cited 9 times

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The growth of the semiconductor industry continues to be driven to a large extent by steady advances in microlithography. Renewal of the Semiconductor Industry Association Roadmap is underway and accelerating requirements are predicted. The 130 nm generation is anticipated to be available in the year 2003, but the path to get there is not obvious. To meet the needs of its members, SEMATECH is embarking on a program to explore and narrow the technology options on the roadmap. The goal is to make a data-driven decision by late 1997. As an introduction to this Special Session on 0.13 Micron Lithography for Manufacturing, this article reviews the Lithography Technology Working Group requirements and potential solutions for roadmaps. The SEMATECH program to narrow the options beyond 193 nm optics is presented in detail, including the critical issues for each technology. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Lithography with 157 nm lasers

T. M. Bloomstein, M. W. Horn, M. Rothschild, R. R. Kunz, S. T. Palmacci, and R. B. Goodman

J. Vac. Sci. Technol. B 15, 2112 (1997); http://dx.doi.org/10.1116/1.589230 (5 pages) | Cited 28 times

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Projection photolithography at 157 nm was studied as a possible extension of current 248-nm and planned 193-nm technologies. At 157 nm, lasers are available with ∼8 W average power. Their line width is narrow enough as to enable the use of catadioptric, and maybe all-refractive optics similar to those used at 248 and 193 nm. The practicality of such designs is further enhanced by measurements of calcium fluoride, which show that its absorption is sufficiently small (∼0.004 cm−1) at 157 nm. Binary masks with chromium and chromeless phase shifting masks were fabricated on calcium fluoride as the transparent substrate. Robust photoresists at 157 nm still need to be developed, and they probably will be of the top surface imaging or bilayer type. Indeed, a silylation resist process was shown to have characteristics at 157 nm similar to those at 193 nm. The calcium fluoride based masks were integrated with the silylation process and a home-built, small-field, 0.5-numerical aperture stepper to provide projection printing with features as small as 80 nm. These initial results indicate that 157-nm lithography has the potential to become a manufacturing technology at dimensions well below 100 nm. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.62.Cf Industrial applications

X-ray lithography: Status, challenges, and outlook for 0.13 μm

Jerome P. Silverman

J. Vac. Sci. Technol. B 15, 2117 (1997); http://dx.doi.org/10.1116/1.589231 (8 pages) | Cited 41 times

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X-ray lithography (XRL) has been under development since the early 1980s, and has reached a state of relative maturity. Numerous devices, including dense and complex integrated circuits, have been fabricated using XRL for one or more critical levels. While development of XRL technology itself continues, XRL is in use in several locations around the world for process development of advanced DRAM (1 Gb and beyond) and logic (0.18 μm and below) integrated circuits. Most of the tool set in use today comes from commercial vendors. Resolution using XRL has been demonstrated at dimensions down to 70 nm or below. Excellent critical dimension (CD) control results have been achieved in simple, single-layer, commercially available resists; for example, a total CD variation of 22 nm (3σ) has been achieved using a mask with a CD variation of 18 nm (3σ). Because of these capabilities, along with the experience and relative maturity of the technology, we believe that XRL is the technology best positioned to succeed optical lithography and be available for timely insertion into manufacturing for 0.13 μm ground rules, as well as to be extendible to 0.10 μm and below. In order to be accepted for manufacturing, however, significant work remains to be done. In particular, new e-beam mask writers and wafer aligners are needed, along with improved mask inspection and repair tools. Mask fabrication processes must also be advanced. The ability to satisfy these needs is not expected to be limited by fundamental physics, but rather is expected to depend on skilled engineering design and implementation. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
01.30.Rr Surveys and tutorial papers; resource letters

Electron beam lithography for 0.13 μm manufacturing

Mark A. McCord

J. Vac. Sci. Technol. B 15, 2125 (1997); http://dx.doi.org/10.1116/1.589232 (5 pages) | Cited 34 times

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General requirements for the use of electron beam lithography in direct write manufacturing of silicon integrated circuits are discussed. 50 keV is suggested as an optimum beam energy, since this is the minimum beam energy that can achieve high aspect ratio structures (4:1) in single layer resists in a manufacturing environment. Higher beam energies result in an inefficient exposure process requiring larger currents; this combination will lead to excessive resist and wafer heating. Lower voltages will require the use of top surface imaging or multilayer resists, which have concerns of processing complexity, resist charging, and defects. At 50 keV, some form of proximity correction is required to achieve reasonable control of critical dimensions. While one of the principle arguments for low voltage lithography is that it avoids the need for proximity correction, proximity correction is a solvable problem for large chips and is therefore a less risky approach than developing a reliable surface imaging resist technology. From a quick review of available resists and recent resist progress, it appears that a sensitivity of 5 μC/cm2 at 50 kV is the best that will be achieved in the next several years. Neglecting overheads, for a design point of 40 8 in. wafers/h, a peak beam current of 13 μA for a raster scan or projection tool is required. One of the major challenges of designing a tool with such high beam currents is controlling space charge effects so that there is minimal impact on lithographic quality. After discussing the characteristics of various high speed electron beam writers that have been made to date, it will be concluded that there are two types of systems that have the best chance of meeting all of the requirements—a projection system such as SCALPEL, and a multibeam system with hundreds of independently blanked beamlets. These systems minimize space charge effects by spreading out the electrons through a larger volume of space, allowing a larger total beam current. However, in order to make these systems a commercial reality, a great deal of innovation, research, and development are still required. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Scattering with angular limitation projection electron beam lithography for suboptical lithography

Lloyd R. Harriott

J. Vac. Sci. Technol. B 15, 2130 (1997); http://dx.doi.org/10.1116/1.589339 (6 pages) | Cited 37 times

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There are several candidate lithography technologies for the postoptical era early in the next century. The scattering with angular limitation projection electron-beam lithography (SCALPEL) approach combines the high resolution and wide process latitude inherent in electron beam lithography with the throughput of a parallel projection system. In the SCALPEL system, a mask consisting of a low atomic number membrane and a high atomic number pattern layer is uniformly illuminated with high energy (100 keV) electrons. The entire mask structure is essentially transparent to the electron beam so very little of the beam energy is deposited in it. The portions of the beam which pass through the high atomic number pattern layer are scattered through angles of a few milliradians. An aperture in the back focal plane of the electron projection imaging lenses stops the scattered electrons and produces a high contrast image at the plane of the semiconductor wafer. This article describes how a lithography system based on the SCALPEL principle can be used for semiconductor manufacturing lithography for feature sizes beyond the capabilities of optical lithography. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Ion projection lithography: Next generation technology?

G. Gross

J. Vac. Sci. Technol. B 15, 2136 (1997); http://dx.doi.org/10.1116/1.589340 (3 pages) | Cited 4 times

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It is generally agreed that optical lithography is the method of choice for production of integrated circuits having minimum dimensions of down to 200 nm. By applying special enhancement techniques and complex resist processes the limit of optical lithography can be shifted down to about 150 nm in production using an exposure wavelength of 193 nm. However, this 193 nm equipment will be a one generation tool, so that new concepts are necessary for exposing structures smaller than 150 nm. The situation for this time (after about 2003) is still unclear. As lithography tools for after the year 2003 are not yet defined, there is an urgent need for preparative work for closing this technology gap. One of the most promising candidates for reaching 100 nm and below in production is ion projection lithography. In this article, the advantages and risks of this technique are compared to other possible candidates like x-ray, e-beam, and extreme ultraviolet. Insoluble production problems are identified. The feasibility of the relevant mask technologies, the availability of resist techniques are throughput and cost competitiveness are discussed. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Two-dimensional stage self-calibration: Role of symmetry and invariant sets of points

Michael R. Raugh

J. Vac. Sci. Technol. B 15, 2139 (1997); http://dx.doi.org/10.1116/1.589341 (7 pages) | Cited 4 times

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The National Technology Roadmap for Semiconductors has set a goal of 0.1–0.07 μm features for the end of the decade. Improved calibration methods will be required to achieve this goal. A rigorous method for using an electron (e)-beam stage to calibrate itself, known as stage self-calibration, was published in 1985 and has since been refined in various ways and shown to be capable of accuracy throughout the workspace in the range of the machine’s repeatability. This article presents symmetry and invariant sets as the governing features of self-calibration, using classical reversal methods as illustrations. The term symmetry is used in a dual sense; it refers both to the symmetry of a pattern of points and to the rigid motions that characterize the symmetry of the pattern. The geometric perspective gained in this way can be exploited to derive techniques and explicit error bounds for high-accuracy self-calibration. The article will be of interest to process engineers and metrologists seeking insights and methods for improving the accuracy of high-precision stages. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
06.20.F- Units and standards
02.10.Ab Logic and set theory

Neural network model for global alignment incorporating wafer and stage distortion

Amir A. Ghazanfarian, R. F. W. Pease, Xun Chen, and Mark A. McCord

J. Vac. Sci. Technol. B 15, 2146 (1997); http://dx.doi.org/10.1116/1.589342 (5 pages) | Cited 1 time

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One of the most crucial emerging challenges in lithography is achieving rapid and accurate alignment under a wide variety of conditions brought about by the different overlying films occluding the marks. The problem is exacerbated by planarizing processes such as chemical mechanical polishing that reduce the topographical contrast used to view the marks and by distortion of the wafer and of the stage. Thus, an effective learning process is needed to rapidly acquire the best possible positional information from an array of the marks across the wafer. In this article, a neural network model for global alignment is described. The wafer and stage distortions can be incorporated into the model. The algorithm finds the best fit for the wafer distortion and at the same time compensates for both stage and wafer distortion. The algorithm can also learn to identify and ignore any alignment marks that yield significantly erratic signals. A few common distortion functions will also be used to test the model. Preliminary simulation results show alignment errors <5 nm in the presence of Gaussian noise with σ=30 and 500 nm sinusoidal stage distortion. Also the simulations show that increasing the magnitude of stage distortion has no impact on the results. It will be shown that considering wafer distortion can reduce the alignment error more than 10 times in the case of bowed and distorted wafers. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.05.Mh Neural networks, fuzzy logic, artificial intelligence

Monitoring of subquartermicron line and space pattern by ellipsometry

Hiroshi Arimoto

J. Vac. Sci. Technol. B 15, 2151 (1997); http://dx.doi.org/10.1116/1.589343 (4 pages) | Cited 1 time

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This article reports on the ellipsometric monitoring of 0.3- and 5-μm pitch line/space patterns fabricated by electron-beam (EB) lithography (HL700F). The effects of exposure dosage on pattern formations and the subsequent ellipsometric measurements were investigated. The results suggest that ellipsometry can be practical for monitoring pattern widths and cross-sectional shapes. Regression analysis was applied to predict the linewidths by using ellipsometric parameters. A good agreement between the predicted and actual values was achieved. Remaining errors of 3.7 and 2.8 nm are considered to be due to actual fluctuations in pattern widths or errors in CD-SEM measurements. Exposure doses which would provide a good index to ensure that patterns are well formed, and that the remaining resist is thick enough were also predicted. Regression analysis results were used to evaluate the widths of monitoring patterns fabricated regularly by a variable shaped EB machine (HL600) over the course of six months. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.60.Fs Polarimeters and ellipsometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
02.50.Sk Multivariate analysis

Scanning electron microscope matching and calibration for critical dimensional metrology

Herschel Marchman

J. Vac. Sci. Technol. B 15, 2155 (1997); http://dx.doi.org/10.1116/1.589344 (7 pages) | Cited 4 times

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The mean value of a measurement set with precision σ has an offset relative to an accepted standard. Calibration of an instrument involves subtracting the offset between the mean value and the reference. Unfortunately, imaging characteristics for most types of microscopes are not constant. Slight changes in feature wall angle, edge and surface roughness, or material properties can dramatically affect the precision and accuracy offset of the metrology instrument. Of course it would be impossible to fabricate a reference standard for every type of sample, as this would require an a priori knowledge of the feature characteristics as well as an infinite number of reference artifacts. Typically the process engineer will use in-house or “golden standards” to track the repeatability of a measurement tool. Unfortunately, variations in the features to be measured will cause the accuracy offset to change in ways that are unknown to the engineer. Furthermore, the offsets of multiple tools in a set will not only change with respect to the reference but also relatively to each other. It is the minimization of this relative offset between the various measurement tools that is referred to as matching. It should be noted that one could use a member in the nonreference set of tools, but then the question naturally arises of which one is most correct. It is desirable for a reference tool to provide the complete topography of a structure, as well as the ability to reduce the effects of sample variation (i.e., edge roughness) through spatial averaging. In this article, a method for using atomic force microscopes to provide reference values for matching of on-line scanning electron microscopes will be described. © 1997 American Vacuum Society.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.20.F- Units and standards
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Photon tunneling microscopy of latent resist images

J. A. Liddle, A. T. Fernandez, R. Cirelli, M. M. Mkrtchyan, A. E. Novembre, M. L. Peabody, and G. P. Watson

J. Vac. Sci. Technol. B 15, 2162 (1997); http://dx.doi.org/10.1116/1.589345 (5 pages) | Cited 2 times

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The ability to examine latent resist images can provide a means of separating out the influences of the exposure itself from the subsequent postexposure bake and from the development process in determining the form of the final developed image. We describe the technique of photon tunneling microscopy (PTM) and its application to examining latent resist features. The PTM is based upon the concept of frustrated total internal reflection, and can give information on latent images that is highly sensitive to both changes in topography as small as 1 nm and refractive index changes on the order of 10−2–10−3. Preliminary modeling shows how this technique can give quantitative information about the progress of the radiation induced chemistry in resist. Experimental data for two positive-tone, chemically amplified materials, ARCH2 and CAMP1 illustrate the potential of the technique. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.79.Cz Scanning tunneling microscopes
07.68.+m Photography, photographic instruments; xerography
82.50.-m Photochemistry
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Application of transmission electron detection to SCALPEL mask metrology

R. C. Farrow, M. T. Postek, W. J. Keery, S. N. Jones, J. R. Lowney, M. Blakey, L. A. Fetter, J. E. Griffith, J. A. Liddle, L. C. Hopkins, H. A. Huggins, M. Peabody, and A. Novembre

J. Vac. Sci. Technol. B 15, 2167 (1997); http://dx.doi.org/10.1116/1.589346 (6 pages) | Cited 5 times

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Linewidth measurements were performed on a 4X scattering with angular limitation in projection electron lithography (SCALPEL) e-beam lithography mask using the transmitted electron signal in a modified scanning electron microscope. Features as small as 0.24 μm were measured on the mask. The thin membrane mask structure that was used is found to provide sufficient transmitted signal contrast at energies ranging from 10 to 30 keV. The linewidth measurement accuracy is mostly limited by the variations in the material and not the measurement system. It is concluded that the linewidth measurement technique using transmitted electrons is suitable for the potential certification of SCALPEL mask standards. © 1997 American Vacuum Society.  
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85.40.Hp Lithography, masks and pattern transfer

Obtaining a physical two-dimensional Cartesian reference

Michael T. Takac, Jun Ye, Michael R. Raugh, R. Fabian Pease, C. Neil Berglund, and Geraint Owen

J. Vac. Sci. Technol. B 15, 2173 (1997); http://dx.doi.org/10.1116/1.589347 (4 pages) | Cited 2 times

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A two-dimensional self-calibration method obtains Cartesian traceability for high-precision tools. The calibration method incorporates group theory principles yielding mathematical solutions to a physical Cartesian reference. The calibration method was developed by Stanford University, Hewlett Packard, IBM and funded by the Semiconductor Research Corporation. The method was applied to Leica’s LMS2000 and LMS2020 systems. © 1997 American Vacuum Society.
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06.20.F- Units and standards
85.40.Hp Lithography, masks and pattern transfer
02.20.-a Group theory

Evaluation of the long-term stability of critical-dimension measurement scanning electron microscopes using a calibration standard

Fumio Mizuno, Minoru Shimizu, Katsuhiro Sasada, and Takeshi Mizuno

J. Vac. Sci. Technol. B 15, 2177 (1997); http://dx.doi.org/10.1116/1.589348 (4 pages) | Cited 2 times

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In critical-dimension measurement using critical-dimension measurement scanning electron microscopes (CD-SEMs), measurement variation due to a long-term instability of CD-SEM cannot be disregarded to achieve a measurement reproducibility of 3 nm, which is required for next-generation subquarter-micron large scale integrations. We have evaluated the long-term stability of the Hitachi S-8820 CD-SEM by using a calibration standard, which has 0.24 μm pitch structures. The results of our evaluation have demonstrated that the use of the calibration standard for CD-SEMs was effective for checking the instability of instruments, which might produce inaccuracy and imprecision of CD measurements, and measurement error due to instrumentation of 1 nm can be achieved by precise control of instrumental parameters using the calibration standard. © 1997 American Vacuum Society.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.20.F- Units and standards
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Contamination reduction in low voltage electron-beam microscopy for dimensional metrology

W. H. Bruenger, H. Kleinschmidt, W. Hässler-Grohne, and H. Bosse

J. Vac. Sci. Technol. B 15, 2181 (1997); http://dx.doi.org/10.1116/1.589349 (4 pages) | Cited 2 times

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Contamination of structures to be analyzed in an electron microscope is a severe problem for dimensional metrology applications, especially for low voltage electron microscopy. Two methods for contamination reduction which do not use a temperature variation of the sample or its environment have been investigated in this article. First, injection of inert and reactive gases into the area of electron-beam impact to create a locally confined area of increased pressure which reduces the contamination growth by a factor of 2. Second, prescanning the surroundings of the area is intended for metrology measurements. This method effectively immobilizes contaminants on the specimen surface if the delay time between immobilization and measurement is short enough (approximately 40 ms), to avoid the replenishment of contaminants. A combination of the two techniques is recommended for a damage free low voltage electron-beam metrology. © 1997 American Vacuum Society.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Accurate alignment on asymmetrical signals

Xun Chen, Amir A. Ghazanfarian, Mark McCord, and R. Fabian W. Pease

J. Vac. Sci. Technol. B 15, 2185 (1997); http://dx.doi.org/10.1116/1.589610 (4 pages) | Cited 1 time

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Existing alignment algorithms all assume that the alignment signal is symmetrical about the correct center position. When the signal becomes asymmetrical, these algorithms inevitably result in alignment error. We describe a general approach to align accurately on asymmetrical signals. This is achieved by incorporating learning and utilization of a priori information. The proposed algorithm looks at some sample alignment signals with known centers. The latter are provided by metrology data or some other means. The algorithm builds a linear space model of the asymmetry that is present in the sample signals. It then uses the built model to extract the symmetrical part of alignment signals that come from the same, well-controlled process. The extracted nearly symmetrical signal is then used to determine the alignment position. A detailed algorithm is provided for each of the three steps. Computer simulation implementing the algorithms shows that the alignment performance, both in terms of the mean and variance of the alignment error, is significantly improved compared to two examples of alignment algorithm that do not incorporate learning. The two example alignment algorithms used for comparison are phase detection and center of mass detection. A physical interpretation of the linear asymmetry model is provided. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Wall angle measurement with a scanning probe microscope employing a one-dimensional force sensor

J. E. Griffith, L. C. Hopkins, C. E. Bryson, A. Berghaus, E. J. Snyder, J. J. Plombon, L. A. Vasilyev, M. Hecht, and J. B. Bindell

J. Vac. Sci. Technol. B 15, 2189 (1997); http://dx.doi.org/10.1116/1.589611 (4 pages) | Cited 3 times

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To measure the angle of a wall, the probe of a stylus profiler must be able to reach the wall. Sample tilting substantially expands the range of wall angles accessible to a profiler. Tilting also allows flared probe tip characterizers to be used more efficiently. The balance beam force sensor used for this work was designed to permit significant sample tilting. © 1997 American Vacuum Society.
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07.79.Lh Atomic force microscopes
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Design and characterization of a high numerical aperture lens system for scanned laser lithography

P. C. Allen, M. J. Bohan, and P. D. Buck

J. Vac. Sci. Technol. B 15, 2193 (1997); http://dx.doi.org/10.1116/1.589612 (4 pages) | Cited 1 time

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Over the past decade, three generations of scan lens systems have been developed, culminating in a 33×, 364 nm, 0.8 numerical aperture lens system for 0.25 μm generation mask writing. The specifications and design performance of this latest lens from Tropel are compared with measurements made on a lens test bench and on a scanned laser writing system. A full-width at half-maximum spot size of 270 nm, and linearity performance under 20 nm have been measured. CD linearity data shows deviations less than 20 nm down to 0.3 μm feature sizes. Corner rounding data shows marked improvement over previous generation imaging optics with a minimum radius of 253 nm. These lens distortion and resolution measurements confirm that the new lens system has the imaging performance required for 0.25 μm generation masks. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.79.Bh Lenses, prisms and mirrors

Metrology of scattering with angular limitation projection electron lithography masks

J. A. Liddle, M. I. Blakey, T. Saunders, R. C. Farrow, L. A. Fetter, C. S. Knurek, R. Kasica, A. E. Novembre, M. L. Peabody, D. M. Tennant, D. L. Windt, and M. Postek

J. Vac. Sci. Technol. B 15, 2197 (1997); http://dx.doi.org/10.1116/1.589613 (7 pages) | Cited 2 times

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Mask metrology is a vital part of any lithographic technology, both for control of the mask patterning process and also for ensuring that the contribution of the mask to the system error budget is within acceptable limits. For design rules of 0.13 μm and below, errors arising from metrology must be kept to less than 1 nm. We have examined the potential for achieving this, in the case of scattering with angular limitation projection electron lithography (SCALPEL) masks, by using high-energy (100 keV) electron transmission measurements. We have also performed extensive metrology using conventional scanning electron microscope techniques. These results show that the SCALPEL mask has the potential to meet the specifications necessary for lithography at the 0.13 μm generation and beyond. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Design and implementation of a real-time hierarchical parallel postprocessor for 100 keV electron beam lithography

Lawrence P. Muray, Erik H. Anderson, and Volker Boegli

J. Vac. Sci. Technol. B 15, 2204 (1997); http://dx.doi.org/10.1116/1.589614 (5 pages) | Cited 2 times

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A farm of off-the-shelf microprocessors is evaluated for use as a real-time parallel postprocessing subsystem of the Lawrence Berkeley National Laboratory datapath, including backscatter proximity correction. The native data format is GDSII with embedded control. Data storage is fully hierarchical with no intermediate binary pattern data formats. Benchmarks of a four Pentium Pro™ farm, after optimization, demonstrate compatibility with exposure rates of 25 MHz for 32% area fill on a vector scan Gaussian beam e-beam tool. Scalability of the architecture is discussed in detail. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
84.30.Sk Pulse and digital circuits

Measurement of resist heating in photomask fabrication

Sergey Babin

J. Vac. Sci. Technol. B 15, 2209 (1997); http://dx.doi.org/10.1116/1.589615 (5 pages) | Cited 12 times

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High-throughput photomask fabrication using 50 kV variably shaped electron-beam lithography was examined for resist heating distortions. Effective absorbed energy changes in the resist due to heating were measured using beam current density and subfield time sequences as parameters. Absorbed energy changes due to short-range heating inside a subfield were also determined. Corresponding linewidth variations caused by resist heating were measured. This showed that the 1 μm gaps had become completely broken. The sublimation of resist during exposure was investigated, and the subsequent reduction in resist thickness was measured as a function of exposure dose. The highly sensitive resist PBS [poly(butene-1 sulfone)], which is used widely for photomask manufacturing, was used for the heating measurements. It was concluded that high-throughput variably shaped electron-beam lithography with a high current density (20–80 A/cm2) may not be suitable for reticle fabrication without taking precautions for heating effects. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Ion absorbing stencil mask coatings for ion beam lithography

J. R. Wasson, J. L. Torres, H. R. Rampersad, J. C. Wolfe, P. Ruchhoeft, Martin Herbordt, and H. Löschner

J. Vac. Sci. Technol. B 15, 2214 (1997); http://dx.doi.org/10.1116/1.589616 (4 pages) | Cited 14 times

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The implantation of ions into the silicon membrane masks of ion beam lithography is known to create compressive stress which leads to very serious distortion after only a few tens of exposures. In this article, we describe a new, dimensionally stable, protective coating for silicon membranes which meets the exacting requirements of very large scale integrated manufacturing. The coating is formed by first depositing a low density, low stress graphitic carbon film which is subsequently amorphized by He+ ion bombardment with a dose of about 125 mC/cm2. We show that the stress of these bilayer membranes is stable to within experimental error (±1 MPa) for 20 keV He+ ion doses up to 0.53 C/cm2, corresponding to about 8.5 million exposures in a 4×-ion projector. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Novel technique for improving pattern placement in membrane mask making

F. Keith Perkins, Christie R. K. Marrian, and Martin C. Peckerar

J. Vac. Sci. Technol. B 15, 2218 (1997); http://dx.doi.org/10.1116/1.589617 (6 pages) | Cited 3 times

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Pattern placement errors pose a serious problem in the manufacture of masks for proximity x-ray lithography. Many of these errors are attributable to long term drifts in beam position relative to external fiducials. To address this problem we have developed a technique based on through-the-membrane monitoring of the electron beam position. This technique uses as a detector a reverse biased Schottky diode with high bandwidth and gain. In use this detector is mounted near the back surface of the membrane. An accurately patterned overlayer on the detector provides the fiducial reference. The overlayer is designed to modulate the electron-hole pair current generated in the diode by absorbing the incident beam. Position information is obtained by analyzing the image created from recording the digitized diode current during patterning. The phase in a Fourier transform of the data at the spatial frequency of the patterned absorber gives a measure of the position of the incident beam. Changes in the observed phase from one frame to the next can then be used to correct position errors of the beam in real time. We report results from tests of various components of this system. Initial results indicate that the system will be sufficiently fast and accurate for use in pattern placement correction for 130 nm ground rule mask production. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Conductive polyaniline: Applications in x-ray mask making

M. S. Lawliss, J. M. Rocque, M. Angelopoulos, D. M. Puisto, and R. W. Henry

J. Vac. Sci. Technol. B 15, 2224 (1997); http://dx.doi.org/10.1116/1.589618 (4 pages) | Cited 1 time

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Image-placement control with electron-beam lithography is directly influenced by charging effects during exposure. One of the primary charging sources is the buildup of electrons in the nonconductive resist film. We have evaluated the use of a conductive-polyaniline film as a topcoat over the resist during exposure. Critical parameters including image-size variation, image placement, and defect density were compared for masks with and without the conductive-polyaniline topcoat. It was found that the performance is dependent on the resist exposure dose. For a low-sensitivity resist (i.e., a resist requiring high exposure dose), significant improvements for image size and image placement can be achieved with the implementation of a conductive topcoat. For a high-sensitivity resist (i.e., a resist requiring low exposure dose) with single-pass writing, preliminary results show that charging is currently not the primary driver of image-placement errors. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Low-stress sputtered chromium–nitride hardmasks for x-ray mask fabrication

Shinji Tsuboi, Setsu Kotsuji, Takuya Yoshihara, and Katsumi Suzuki

J. Vac. Sci. Technol. B 15, 2228 (1997); http://dx.doi.org/10.1116/1.589619 (4 pages) | Cited 6 times

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We have developed low-stress chromium nitride (CrN) films as hardmasks for x-ray absorber etching. The stress in the CrN films is 3 MPa and its distribution (gradient) is less than 10 MPa in a 25×25 mm area. In addition, the CrN film is electrically conductive (1.4 Ω/□). We have fabricated 0.10 μm line-and-space patterns in 0.4-μm-thick tantalum germanide using a 75-nm-thick CrN hardmask. The results demonstrate that a sputtered CrN film is an excellent hardmask material for x-ray mask fabrication. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Cd Deposition by sputtering
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Uniform low stress oxynitride films for application as hardmasks on x-ray masks

W. J. Dauksher, D. J. Resnick, S. M. Smith, S. V. Pendharkar, H. G. Tompkins, K. D. Cummings, P. A. Seese, P. J. S. Mangat, and J. A. Chan

J. Vac. Sci. Technol. B 15, 2232 (1997); http://dx.doi.org/10.1116/1.589620 (6 pages) | Cited 5 times

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A low stress silicon oxynitride deposition process has been developed in which the average stress level can be tailored by adjusting silane flow in the plasma enhanced chemical vapor deposition reactor. Stress gradients, as might be caused by nonuniform heating or gas distribution, were not found to exist. By volume, the SiON films were found to be approximately 81% silicon dioxide and 19% silicon nitride. Because the films are easily removed in hydrofluoric acid, this composition is ideally suited for use as a hardmask patterning layer on x-ray masks. A reactive ion etch process employing CHF3, O2, and Ar gases has demonstrated selectivity to Shipley SNR 200 resist of better than 3:1. Smooth pattern transfer into TaSi and TaSiN absorber layers of test features as small as 0.1 μm has been achieved using SiON as the hardmask layer. Image placement distortions on the order of 15 nm (3σ) occur from etching the SiON films on 64 Mbit SRAM x-ray test masks. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Sz Deposition technology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Automatic mask generation in x-ray lithography

B. S. Bollepalli, M. Khan, and F. Cerrina

J. Vac. Sci. Technol. B 15, 2238 (1997); http://dx.doi.org/10.1116/1.589621 (5 pages) | Cited 2 times

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It is well known that diffraction plays an important role in image formation in any photon-based lithographic system. Some of the consequences of diffraction are reduction in contrast of the aerial image and phenomenon such as line-end shortening. In this article we explore some computational schemes which modify the mask pattern so as to minimize the diffractional effects. Several papers have been written on this problem for the case of optical lithography. Here, we consider the case of x-ray lithography only. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Practical approach to separating the pattern generator-induced mask CD errors from the blank/process-induced mask CD errors using conventional market measurements

Liqun Han, Weidong Wang, Mark A. McCord, C. N. Berglund, R. F. W. Pease, and L. Suzanne Weaver

J. Vac. Sci. Technol. B 15, 2243 (1997); http://dx.doi.org/10.1116/1.589622 (6 pages) | Cited 4 times

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With the continuing reduction of minimum feature sizes for semiconductor wafers, the manufacturing tolerances for photomask CD errors were reduced proportionately. As a result, it has become increasingly important to separate the major sources of mask CD errors so that they can be quantified and appropriately addressed. In this article we describe a reliable, convenient and inexpensive technique for separating the blank, and process CD errors from the pattern generator CD errors using conventional market measurements on cross arrays and two-dimensional spatial frequency Fourier analyses. By taking advantage of the fact that the blank/process-induced CD error spatial distributions are known to be fixed relative to the mask blank, while the pattern generator CD error distributions are known to be fixed relative to the pattern generator, a spatial frequency domain analysis of multiple sets of CD measurements on the masks, each set printed by displacing the mask relative to the previous set, is shown to allow a simple and unambiguous separation of the two types of CD errors. These measurements also directly verify the expected result that the blank/process CD error contributors tend to have mainly low-spatial-frequency components, while the pattern generator tends to mainly have higher-spatial-frequency components. Furthermore, by utilizing this result, it is shown that a simple low-pass filter applied to a single set of market measurements provides a surprisingly accurate estimate of the relative sizes of these two error contributors. Results are presented from masks printed on two commercial mask-making systems, one optical and one e-beam. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Pattern placement errors in mask membranes

A. H. Fisher, M. F. Laudon, R. L. Engelstad, E. G. Lovell, and F. Cerrina

J. Vac. Sci. Technol. B 15, 2249 (1997); http://dx.doi.org/10.1116/1.589623 (6 pages) | Cited 3 times

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X-ray and ion-beam lithographic processes require the use of advanced masks with free-standing thin membranes. In the fabrication of these masks, the pattern transfer process involves the deposition or removal of a thin layer of material (or portions of a layer), which can produce relatively large pattern placement errors. The stress-induced distortions of both x-ray and stencil mask membranes (due to the individual fabrication processes) have been simulated by finite-element procedures. For patterned areas of both mask membrane types, equivalent models with uniform characteristics have also been developed and assessed for validity. These models facilitate the calculation of global in-plane distortions needed to perform pattern specific emulation. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
02.70.Dh Finite-element and Galerkin methods

Revisiting phase shifting masks in x-ray lithography

Mumit Khan, Srinivas Bollepalli, and Franco Cerrina

J. Vac. Sci. Technol. B 15, 2255 (1997); http://dx.doi.org/10.1116/1.589624 (4 pages) | Cited 2 times

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In this article, we describe a framework for selecting the materials for phase shift masks (PSMs) in x-ray lithography to yield the optimal exposure latitude. Traditional design of PSMs involves choosing the thickness of the material to produce a π phase shift, as in the case of clear phase shifting masks, or to produce the sufficient contrast needed for imaging with a requisite phase shift to improve linewidth control, as in the cases of attenuated phase shifting masks and half-tone phase shifting masks. We instead find the optical constants of a theoretical material that yield optimal exposure latitude, and try to find combinations or alloys of various materials that have the requisite optical constants. © 1997 American Vacuum Society.  
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85.40.Hp Lithography, masks and pattern transfer

Plasma reactive ion etching of 193 nm attenuated phase shift mask materials

B. W. Smith, C. Fonseca, L. Zavyalova, Z. Alam, and A. Bourov

J. Vac. Sci. Technol. B 15, 2259 (1997); http://dx.doi.org/10.1116/1.589625 (4 pages) | Cited 10 times

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This article gives details on plasma etch process development for potential attenuated phase shift masking materials for use at 193 nm. Masking films investigated include materials based on aluminum nitride, zirconium nitride, molybdenum–silicon oxide, tantalum–silicon nitride, and tantalum–silicon oxide. A variety of halogenated etch plasmas were investigated, including fluorine-based chemistries (CF4 and SF6) and chlorine-based chemistries (Cl2, CCl4) combined with oxygen, argon, and hydrogen. Thin films of TaN, MoSiO, SixNy, and TaO that allow for sufficient volatility in fluorine plasma and processes using SF6 were chosen for optimization. Fluorides of aluminum and zirconium exhibit very low vapor pressure so Cl2+Ar mixtures were chosen for study. Al and Zr chlorides can be made volatile but ion assistance is generally needed to produce sufficiently high etch rates. Because of this, selectivity to resist is generally poor. Of all the materials evaluated, attenuated phase shift mask films of TaN/Si3N4 etched with SF6 allow the largest etch selectivity to both fused silica and resist. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Effects of accelerating voltage and pattern size on electron scattering by electron-beam mask

Hiroshi Yamashita, Eiichi Nomura, and Hiroshi Nozue

J. Vac. Sci. Technol. B 15, 2263 (1997); http://dx.doi.org/10.1116/1.589626 (6 pages) | Cited 5 times

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Electron scattering by electron-beam (EB) masks has been studied by a Monte Carlo simulation to investigate the influence of increasing accelerating voltage, of decreasing pattern size, and of using a thinner mask for a practical engineering application. The simulation study has revealed that there are two different exiting angle distributions; whether the most frequent exiting angle depends on L/S size or not. These are named interfeature scattering and intrafeature scattering, respectively. In order to analyze the electron scattering phenomena, we investigated the electron transmittance and absorbance by normalizing the mask thickness, using a Grün range. As a result, the EB mask was found to be categorazible into four function categories defined by the normalized mask thickness. They are pure absorber, scattering absorber, absorbing scatterer, and pure scatterer. This classification gives us important information for engineering design of the EB mask and for column design. For the EB mask, whose normalized mask thickness is more than 0.2, the transmitted electrons are scattered enough not to contribute to imaging in the angular and the energy distributions and high contrast can be obtained with some optimization of the angular limiting aperture. When the normalized mask thickness is less than 0.2, the limiting angle of the aperture may need to be decreased due to high electron transmittance, but optimization for different pattern sizes is not necessary in the case of the intrafeature scattering. The combination of thinner mask and an appropriate limiting aperture seems to be feasible and promising for future EB cell projection lithography to achieve higher resolution. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
02.70.Rr General statistical methods

Resistless electron beam lithography process for the fabrication of sub-50 nm silicide structures

D. Drouin, J. Beauvais, E. Lavallée, S. Michel, J. Mouine, and R. Gauvin

J. Vac. Sci. Technol. B 15, 2269 (1997); http://dx.doi.org/10.1116/1.589627 (5 pages) | Cited 2 times

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We report on a study of the fabrication of submicron silicide structures with a resistless lithography technique. Several different metals can be used as a basis for producing silicide using this method; in this work, results will be discussed for both platinum and nickel silicide. The feasibility of producing nanostructures using polycrystalline silicon as a base growth layer for metal–oxide–semiconductor, and other device applications have also been demonstrated. Threshold doses for this method for submicron lines (<50 nm) and square areas were obtained in order to establish a framework for the fabrication of more complex devices. Preliminary electrical measurements were carried out which indicate that the resistivity of the silicide is 45 μΩ cm, and that the barrier height of the silicide/(high resistivity silicon) interface is 0.56 eV. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Process development of sub-0.5 μm nonvolatile magnetoresistive random access memory arrays

K. Nordquist, S. Pendharkar, M. Durlam, D. Resnick, S. Tehrani, D. Mancini, T. Zhu, and J. Shi

J. Vac. Sci. Technol. B 15, 2274 (1997); http://dx.doi.org/10.1116/1.589628 (5 pages) | Cited 10 times

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The fabrication of magnetoresistive random access memory (MRAM) devices requires full characterization of the giant magnetoresistive ratio (GMR) permalloy films at the sub-0.5 μm feature dimensions. Future memory arrays of the 1 and 4 Gb density require GMR bit cells of a 0.25 μm and below in configurations which will require close proximity of cells. Since the cells are magnetic and act like tiny magnets, the switching field of a cell may be influenced by the polarization direction of the neighboring cell. This article describes the development of sub-0.5 μm MRAM devices using current e-beam microfabrication techniques and the implementation of the latest chemically amplified deep ultraviolet resists. Etch processing is also discussed as well as the testing results for the 0.25 μm arrays. Testing the GMR material at these dimensions consists of evaluating the single magnetic domain behavior and observing the effect of cell size on the magnetoresistance ratio. Array testing will consist of measuring switching field variations on a 0.25 μm 5×5 array to determine if there is field coupling with neighboring cells. © 1997 American Vacuum Society.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance

Electron optical system for the x-ray mask writer EB-X2

Kenichi Saito, Hirofumi Morita, Junichi Kato, and Nobuo Shimazu

J. Vac. Sci. Technol. B 15, 2279 (1997); http://dx.doi.org/10.1116/1.589629 (5 pages) | Cited 3 times

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An electron optical system that yields a beam voltage of 100 kV and a beam edge resolution of 20 nm was developed for a variably shaped electron beam writing system, the EB-X2. In order to improve the beam edge resolution, the objective lens and main deflector were designed on the basis of the uniform field concept, and the optimum beam half-angle was determined by beam profile calculations. The optimized design provides a beam edge resolution of 20 nm for a 650-μm-square deflection field and a beam current of 250 nA. Given the high acceleration voltage, it is possible that the electron optical column could be too high to fit into a clean room. To shorten the height of the electron optical column, the lens configuration was carefully examined. The results show that the height of the column is a minimum when the first shaping aperture is placed in the principal plane of the illumination lens. This finding enabled us to reduce the height of the column to 880 mm. The electron optical column was constructed and the beam edge resolution was measured. The measured values agree well with the calculated ones, which confirms that the constructed column has the performance expected of the EB-X2 electron optical system. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
41.85.Ct Particle beam shaping, beam splitting

Performance of Zr/O/W Schottky emitters at reduced temperatures

H. S. Kim, M. L. Yu, M. G. R. Thomson, E. Kratschmer, and T. H. P. Chang

J. Vac. Sci. Technol. B 15, 2284 (1997); http://dx.doi.org/10.1116/1.589630 (5 pages) | Cited 5 times

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Experimental measurements of emission stability and energy distributions from a Schottky emitter have been conducted at a tip temperature range from 1330 to 1800 K. The changes of emission properties have been observed at reduced tip temperatures. Noise fluctuations of the probe current increase with decrease of the tip temperature at a constant extraction voltage. The work function of the Schottky emitter increases with decrease of tip temperature. The energy distribution measurements show that the energy width at a given temperature increases with increasing angular emission current density. The energy width also increases with decreasing tip temperature at a given angular emission current density. The results indicate that the energy broadening is mainly contributed by electron tunneling. A comparison of the measured energy width with the theoretical predictions is discussed. © 1997 American Vacuum Society.
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07.77.Ka Charged-particle beam sources and detectors
73.30.+y Surface double layers, Schottky barriers, and work functions
79.40.+z Thermionic emission

Blanked aperture array for parallel electron beam lithography

G. I. Winograd, R. F. W. Pease, and M. A. McCord

J. Vac. Sci. Technol. B 15, 2289 (1997); http://dx.doi.org/10.1116/1.589631 (4 pages) | Cited 4 times

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The blanked aperture array (BAA) is a technique for improving the throughput of electron beam lithography tools by utilizing a much larger fraction of the electron source current than single probe forming systems. The fabrication of a BAA employs standard MEMS processing. Equations are derived which optimize the blanker performance under specified constraints on source emittance and brightness and blanker modulation frequency. An electron optics column is designed to illuminate the BAA and image it onto the target. For 0.1 μm lithography at 50 kV, an objective working distance of 30 mm and a 5 mrad convergence angle, a total current of 1 μa can be delivered to the target before beam blurring due to Coulomb interactions becomes unacceptable. An electron source of brightness 2×106 A/cm2/Ω and emittance 24 μm mrad can deliver this current through a 660 beamlet BAA at a 100 MHz modulation rate. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Spatial-phase-locked electron-beam lithography with a delay-locked loop

J. Goodberlet, J. Ferrera, and Henry I. Smith

J. Vac. Sci. Technol. B 15, 2293 (1997); http://dx.doi.org/10.1116/1.589632 (5 pages) | Cited 13 times

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A delay-locked loop is used in a one-dimensional demonstration of the global-fiducial-grid mode of spatial-phase-locked electron-beam lithography. A pattern-placement precision of σ∼5 nm is demonstrated under nonideal conditions. Results compare well with numerical simulations. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Energy dependence of proximity parameters investigated by fitting before measurement tests

L. I. Aparshina, S. V. Dubonos, S. V. Maksimov, A. A. Svintsov, and S. I. Zaitsev

J. Vac. Sci. Technol. B 15, 2298 (1997); http://dx.doi.org/10.1116/1.589633 (5 pages) | Cited 5 times

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Some years ago a method for fast and accurate experimental evaluation of the proximity parameters α, β, η was suggested [S. V. Dubonos et al., Microelectron. Eng. 21, 293 (1993)]. The method, called the fitting before measurement procedure, is used for regular measurements of β and η in a wide energy range for different bulk substrates (Si, SiO2, mica, ZrO2, Al2O3, InAs, GaAs) and of α as function of resist thickness and energy. An empirical relation from the fitting procedure allows one to extrapolate the β and η values to other substrates and energies. It is demonstrated that a resist of micron thickness can remarkably reduce the resolution of e-beam lithography. It is important that the reducing could not be improved by accurate focusing of the beam but could be overcome only by using a higher accelerating voltage. A phenomenological relation helps to predict resolution as function of resist thickness and electron energy. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
02.60.Ed Interpolation; curve fitting

Dose, shape, and hybrid modifications for PYRAMID in electron beam proximity effect correction

Brian D. Cook and Soo-Young Lee

J. Vac. Sci. Technol. B 15, 2303 (1997); http://dx.doi.org/10.1116/1.589634 (6 pages) | Cited 3 times

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As the dimensions of circuit primitives are reduced, the proximity effect becomes an increasingly important limiting factor in the fabrication of high density integrated circuits using electron beam (e-beam) lithography. In the past, proximity effect correction schemes have in general utilized one of two different approaches: dose or shape modification. Previously, PYRAMID, a hierarchical, rule-based proximity effect correction scheme which has been demonstrated to be able to correct circuit patterns with a minimum feature size of 0.1 μm was successfully presented. Although PYRAMID has been implemented with a pattern shape modification technique, its correction algorithms are not limited to this approach. In this article, the two approaches are compared in details in terms of CD error (edge placement error) and edge contrast, using the two corresponding versions of PYRAMID. A hybrid approach, i.e., combination of dose and shape modifications, is also considered. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.05.Dz Control systems

Dose modification proximity effect correction scheme with inherent forward scattering corrections

G. Patrick Watson, Linus A. Fetter, and J. Alexander Liddle

J. Vac. Sci. Technol. B 15, 2309 (1997); http://dx.doi.org/10.1116/1.589635 (4 pages) | Cited 3 times

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A new approach to dose modification proximity effect correction (PEC) has been proposed that accounts for both short range and long range scatter in advanced direct-write electron beam lithography systems. This scheme can be applied to device writing and to optical mask making where critical dimension (CD) control is of increasing importance. This technique is unique because detailed knowledge of the short range scatter dose distribution is unnecessary; by correcting only for long range scatter, both short and long range compensation is obtained. The new approach is based on the fact that if the characteristic distance of short range scatter is about one third or less of the smallest feature, and if each feature is at least five addressable pixels in the beam writer, then the feature can be printed at its coded dimension if the resist clearing or threshold dose is at the midpoint of the dose profile. Si wafers coated with a positive tone e-beam resist were exposed to a test pattern using no PEC, conventional dose modification PEC and the new scheme. Results show that CD control is maintained over a larger pattern density variation and over a larger exposure dose range by the new technique when compared to the older method and to the uncorrected patterns. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Deep submicron resist profile simulation and characterization of electron beam lithography system for cell projection and direct writing

Young-Mog Ham, Changbuhm Lee, Soo-Hwan Kim, and Kukjin Chun

J. Vac. Sci. Technol. B 15, 2313 (1997); http://dx.doi.org/10.1116/1.589636 (5 pages) | Cited 5 times

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In this article we report the experimental data of chemically amplified resists (CARs) used in fabrication of deep submicron pattern delineation using electron beam lithography, and propose a reliable simulation method that fits the experiment results well. CAR is proven to have high resolutions of 150 nm for a 70 nm diameter Gaussian beam at 30 keV, and 125 nm for various shaped beams at 50 keV. The sensitivity to process parameters of CAR can be reduced by finding the optimum experiment condition for the best resist profiles. To make the simulation results more realistic, we applied the ray tracing method to the development simulator especially appropriate for CAR. Also, we modified the conventional hybrid scattering model to include the inelastic scattering and to take the low energy lithography into account. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Atomic force microscope studies of nanolithographic exposure and development of polymethylmethacrylate

Elizabeth A. Dobisz, Susan L. Brandow, Eric Snow, and Robert Bass

J. Vac. Sci. Technol. B 15, 2318 (1997); http://dx.doi.org/10.1116/1.589637 (5 pages) | Cited 14 times

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Atomic force microscopy was employed to study e-beam exposure and pattern development of polymethylmethacrylate (PMMA) in molecular weights (MWs) of 950 and 50 K. The work focuses on the development of dense high resolution patterns. PMMA was found to have a nodular morphology with an average particle diameter of ∼53 nm. Submersion of unexposed PMMA in both water and mixtures of isopropanol (IPA) and 0–33% methylisobutylketone (MIBK) did not change the surface morphology. IPA mixtures with ⩾50% MIBK roughened the surface. Latent images of exposed resist were consistent with Monte Carlo simulations. The particle size limited the ability to resolve a 40 nm grating. A pillar type morphology was observed between the lines in the 40 nm period grating in 950 K MW PMMA developed in 25% and 50% MIBK. The particle size was not reduced in 50 K MW PMMA. In fact, the ability to define a 40 nm grating in 50 K molecular weight PMMA was worse. Patterns of large pads and 100 nm gratings did not exhibit the pillar morphology nor a difference in morphology between the two molecular weight resists. © 1997 American Vacuum Society.  
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Resist processes for low-energy electron-beam lithography

K.-D. Schock, F. E. Prins, S. Strähle, and D. P. Kern

J. Vac. Sci. Technol. B 15, 2323 (1997); http://dx.doi.org/10.1116/1.589638 (4 pages) | Cited 8 times

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Low-energy electron-beam lithography processes have been studied, a new resist system has been proposed, and preliminary tests have been performed. The interaction between electrons and e-beam resist and its effect on the exposure dose and the penetration depth of the electrons have been studied as a function of electron energy. A silylation process for low energy e-beam lithography has been tested and applied to a new bilayer resist scheme for low-energy electron-beam exposure. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Control in sub-100 nm lithography in SAL-601

Elizabeth A. Dobisz and Christie R. K. Marrian

J. Vac. Sci. Technol. B 15, 2327 (1997); http://dx.doi.org/10.1116/1.589639 (5 pages) | Cited 8 times

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This article focuses on e-beam nanolithography in SAL-601, a negative tone, chemically amplified resist from the Shipley Corporation. It examines the role of exposure conditions and the postexposure bake (PEB) on the ability to define features of critical dimensions of 100 nm and below. Lithography was performed with a 50 kV e beam and 140 nm thick resist, where forward scattering of the e beam is expected to be minimal. Common PEB conditions of 105 °C for 1, 3, and 10 min and 110 °C for 1 min were investigated. Although the different PEB conditions produced a factor of up to 2.4× increase in sensitivity, no change was observed in the contrast, 5.8±0.1, or the minimum linewidths, ∼60 nm. The measured line spread function forward Gaussian widths were characterized by standard deviations, σ=27–33 nm, depending on PEB conditions. These are compared to σ of 19 nm for PMMA and the expected σ of 11 nm for the incident probe (σ=10 nm) convoluted with a Monte Carlo code generated point spread function. The measured backscatter coefficient was 0.51, in agreement with our Monte Carlo simulation results. In the analysis of dose latitude to form critical dimension gaps (±10% precision) between a series of pads of differing sizes, the different PEB conditions produced no observed difference. The feature size, however, had a large effect on the ability to form the critical dimension gap. Furthermore, the dose latitude was much smaller than calculated by integration of Monte Carlo derived line spread functions. A semiempirical model is introduced in which the forward Gaussian width of a measured line spread function (LSF) in developed resist is convoluted with the Monte Carlo code LSF. The calculated exposure profiles based on the semiempirical LSF show much better agreement with the experiment than those based on the expected, σ=11 nm, forward Gaussian width. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Minimum emission current of liquid metal ion sources

J. C. Beckman, T. H. P. Chang, A. Wagner, and R. F. W. Pease

J. Vac. Sci. Technol. B 15, 2332 (1997); http://dx.doi.org/10.1116/1.589640 (5 pages) | Cited 1 time

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The inability of liquid metal ion sources (LMIS) to operate at low dc emission currents limits their performance. We briefly describe a model that explains why LMIS have a minimum dc emission current (Imin) and also predicts Imin as a function of the temperature and the properties of the liquid metal. The model predicts that Imin=217+0.744T(nA) for gallium LMIS, where T is the temperature (K). Measurements of Imin for gallium LMIS between 30 and 890 °C are in reasonable agreement with the model. A better fit to this data, however, is given by Imin=1187 exp(−0.026/kT)(nA) where k is Boltzmann’s constant (eV/K). Below 30 °C, Imin drops precipitously—values as low as 380 nA have been measured at temperatures as low as 25.8 °C. This drop is attributed to a supercooling effect that is not accounted for in the model. Imin is also calculated for 17 pure-elemental LMIS at their melting points, and found to vary from 10 nA for mercury to 1.0 μA for aluminum. Imin is measured to be much lower for bismuth LMIS than for gallium LMIS, as predicted by the model, although difficulties with the bismuth LMIS have allowed only an upper limit of Imin⩽77 nA to be measured. The model also suggests possibilities for improving ion sources by reducing or eliminating Imin. © 1997 American Vacuum Society.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative

Fabrication of in situ Ohmic contacts patterned in three dimensions using a focused ion beam during molecular beam epitaxial growth

P. J. A. Sazio, G. A. C. Jones, E. H. Linfield, and D. A. Ritchie

J. Vac. Sci. Technol. B 15, 2337 (1997); http://dx.doi.org/10.1116/1.589641 (5 pages) | Cited 2 times

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Focused ion beam doping during molecular beam epitaxial (MBE) growth is a novel technique that allows the in situ fabrication of unique three-dimensional semiconductor structures with doping profiles unobtainable using standard planar lithography. Conventional MBE growth uses a thermal Si effusion cell as the dopant source during two-dimensional layer growth of III–V semiconductor material. In the technique described here, a scanning Si focused ion beam (FIB) has been added onto the growth chamber to introduce the dopant atoms selectively in a maskless lithographic process. As the FIB is rastered in the xy plane under computer control during crystal growth in the z direction, it is possible to generate specific three-dimensional dopant patterns embedded within the semiconductor. Furthermore, the patterned semiconductor crystal requires no post growth anneal as the dopant ions are decelerated by a retarding electric field on the sample. The dopant is thus deposited on the epilayer surface rather than impinging at high energy, minimizing crystal damage. In this article, we report the successful fabrication and electrical measurements of highly doped GaAs/AlGaAs structures, directly written by focused ion MBE (FIMBE). The scanning Si FIB has been used to form both lateral and vertical, low resistance Ohmic contacts to two-dimensional electron gases at low temperatures. Lateral patterning was initially exploited to form extended contacts to an electrostatically induced electron gas. This was achieved by FIMBE using both selective modulation doping (forming two-dimensional electron gas sheet contacts to the induced gas) and selective n+ doping directly in the quantum well. Field-effect transistor action and Shubnikov de Haas oscillations were observed, thus demonstrating that the conventionally difficult constraint of self-alignment in undoped GaAs/AlGaAs field-effect transistor structures can be eliminated. Vertical patterning was used to form degenerately doped n+ columns embedded within a conventional high electron mobility transistor structure. The resulting I–V characteristics, recorded at room temperature and at 1.5 K in the presence of a 5 T magnetic field, will be discussed. The ability to introduce specific doping within a structure opens the possibility of forming three-dimensional integrated conducting pathways which would not be possible by any other means. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
85.40.Hp Lithography, masks and pattern transfer

N channel metal–oxide–semiconductor field-effect transistor with 0.15 μm gate delineated by focused ion beam lithography

Kohei Suzuki, Motoji Yamashita, Nobuyuki Kawakami, and Akimitsu Nakaue

J. Vac. Sci. Technol. B 15, 2342 (1997); http://dx.doi.org/10.1116/1.589642 (4 pages)

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An N channel metal–oxide–semiconductor field-effect transistor (MOSFET) with a 0.15 μm gate was fabricated by using focused ion beam lithography for gate level and its electrical characteristics were investigated. The choice of the ion species and the gate structure were designed to avoid contamination and damage due to ion penetration. The MOSFET showed an excellent junction leakage current and subthreshold swing. The impact of the ion irradiation on the thin gate oxide quality was also investigated. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Focused ion beam sputter yield change as a function of scan speed

D. Santamore, K. Edinger, J. Orloff, and J. Melngailis

J. Vac. Sci. Technol. B 15, 2346 (1997); http://dx.doi.org/10.1116/1.589643 (4 pages) | Cited 22 times

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In many of the applications of focused ion beams, such as integrated circuit sectioning and TEM sample preparation, considerable volume of materials may need to be removed. Thus optimizing the sputter yield is important. For very rapid scan speeds at normal incidence, each pass of the beam removes a thickness of material which is much smaller than the beam diameter. In this case, this milling yield corresponds to the yield at normal incidence. However, if the scan speed is slowed down so that the thickness removed per pass is comparable to the beam diameter, then locally under the beam the ions are not normally incident even though the beam is normal to the surface. The milling yield of Si and SiO2, for example, increases by a factor of seven to eight in going from normal incidence at 0° to 75°–85°. Thus the material removal rate can be significantly increased by reducing the scan speed. We have measured the milling yield of Si and SiO2 as a function of scan speed in one axis by milling boxes, typically 7 μm×9 μm using 30 keV Ga+ ions. In the other axis, the scan speed is many orders of magnitude faster so that the beam can be thought of as a sheet or “blade.” To measure the dependence of yield on scan speed, we milled the boxes with a single scan in the slow direction, and then measured the depth of the boxes with an atomic force microscope. The beam currents used were 1 and 2.9 nA. At the slowest single-axis speeds, the sputter yield increased by a factor of two. The observed dependence on scan speed agrees with existing models, which assume a single local angle of incidence under the beam. We also measured the redeposition on the bottom of the pit and found that it increased as the scan speed was decreased. In many applications, a small amount of redeposition would be unimportant. © 1997 American Vacuum Society.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.20.Wk Machining, milling

Focused ion beam milling: Depth control for three-dimensional microfabrication

M. J. Vasile, Z. Niu, R. Nassar, W. Zhang, and S. Liu

J. Vac. Sci. Technol. B 15, 2350 (1997); http://dx.doi.org/10.1116/1.589644 (5 pages) | Cited 23 times

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Ion milling with a focused ion beam (FIB) is a potential method for making micromolds, which will then be the primary elements in the mass production of micro- or mini-objects by embossing or injection molding. The challenge lies in controlling the ion milling to produce cavities with predefined, arbitrary geometric cross-sections. This work involves programming variations as a function of position into the algorithm that generates the dwell times in the pixel address scheme of a FIB. These variations are done according to whether an axis of symmetry or a plane of symmetry determines the final geometry, and the result is 26 new cross-sectional shapes, such as hemispherical pits, parabolic pits, hemispherical domes, etc. The ion milling control programs were used to generate parabolic cross-section trenches, sinusoidal trenches, sinusoidal cross-section rings on an annulus, and hemispherical domes. We observed reasonable agreement between the shapes ion milled in Si(100) and the expected geometry. The dwell times are generated assuming each pixel has a unique dose and the ion yield is constant with angle of incidence. Deviations from ideality are ascribed to the variation in sputter yield with changing angle of incidence, and to the dwell time control algorithm. Redeposition also compounds the deviation from ideality, but it is difficult to estimate the magnitude of this effect. © 1997 American Vacuum Society.
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81.20.Wk Machining, milling
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)
07.10.Cm Micromechanical devices and systems
07.05.Dz Control systems

Chemically amplified deep ultraviolet resist for positive tone ion exposure

W. H. Bruenger, M. Torkler, L.-M. Buchmann, and W. Finkelstein

J. Vac. Sci. Technol. B 15, 2355 (1997); http://dx.doi.org/10.1116/1.589645 (3 pages) | Cited 4 times

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The positive tone deep ultraviolet resist UV II HS-0.6 (Shipley) has been evaluated for ion exposure in the ion projector at the Fraunhofer Institute in Berlin. The chemically amplified resist showed extremely high sensitivity of 1×1012 H+ ions/cm2 at an ion energy of 75 keV. The contrast number was 11. Smallest lines with 65 nm linewidth could be delineated in 140-nm-high resist. At higher resist thickness of 370 nm, lines down to 70 nm were stable showing aspect ratios of >4. The exposure latitude at 100 nm nominal linewidth was ±10% dose variation for a ±10% linewidth change. © 1997 American Vacuum Society.  
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85.40.Hp Lithography, masks and pattern transfer

Printing halftone photographic images on diamond by focused silicon ion implantation

L. E. Erickson, H. G. Champion, J. W. Fraser, R. Hussey, P. Schmuki, and C. Porco

J. Vac. Sci. Technol. B 15, 2358 (1997); http://dx.doi.org/10.1116/1.589646 (4 pages) | Cited 4 times

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A process for creating archival records on a very long-lived durable material is demonstrated. Optical and scanning electron microscope viewable photographs were printed into the surface of a chemical vapor deposition diamond wafer by silicon ion implantation. The damage caused by the implant converts the transparent diamond to visible (black) forms of carbon. The photographs were printed using both halftone and gray-scale encoding. The halftone encoding was accomplished by implanting an area proportional to the desired optical density within the 1 μm square pixel at a fixed area dose. This photograph may optionally be “fixed” by annealing the sample at 1000 °C. This transforms the amorphous carbon to graphite. For the gray-scale encoded image, an 800 nm square is implanted with an ion dose proportional to the optical density of each pixel. © 1997 American Vacuum Society.
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07.68.+m Photography, photographic instruments; xerography
42.70.Gi Light-sensitive materials
42.79.Vb Optical storage systems, optical disks
61.72.up Other materials

Nanoparticle impact micromachining

A. Gruber and J. Gspann

J. Vac. Sci. Technol. B 15, 2362 (1997); http://dx.doi.org/10.1116/1.589647 (3 pages) | Cited 8 times

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Nanoparticles of about 1000 molecules of CO2 accelerated to 20 km/s are used for surface micromachining. Isolated impacts are found to generate hillocks of about 0.5 nm in height and 20 nm in radius on silicon. The cluster material penetrates up to 20 nm into the target, suggesting the initial formation of transitory craters that relax by elastic rebound. © 1997 American Vacuum Society.
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61.46.-w Structure of nanoscale materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.20.Wk Machining, milling

Development of a high brightness gas field ion source

Klaus Edinger, Victor Yun, John Melngailis, Jon Orloff, and Gerald Magera

J. Vac. Sci. Technol. B 15, 2365 (1997); http://dx.doi.org/10.1116/1.589648 (4 pages) | Cited 7 times

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We have investigated the emission properties of gas field ionization emitters built up from electrochemically dc-etched W〈111〉 and W〈100〉 single crystal wires. A standard thermal field method was used to confine the ion emission to a single spot at the apex of the emitter. The angular current density obtained for these kinds of tips with a small end radius (100–200 nm) is in the range of 5 μA/sr. For H2 and Ne, maximum ion current was observed in the temperature range between 18 and 21 K. We have measured the ion current density for different gases (H2, He, and Ne) as a function of extraction voltage and gas pressure. The linear dependence of the angular current density on the gas pressure shows that current densities of 10 μA/sr and above can be expected with this type of emitter. © 1997 American Vacuum Society.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative
79.70.+q Field emission, ionization, evaporation, and desorption

Stochastic Coulomb interactions in ion projection lithography systems with aberration-broadened crossover

P. Kruit, J. E. Barth, G. Lammer, A. Chalupka, H. Vonach, H. Löschner, and G. Stengl

J. Vac. Sci. Technol. B 15, 2369 (1997); http://dx.doi.org/10.1116/1.589649 (4 pages) | Cited 2 times

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The allowable current in ion beam projection lithography is limited by stochastic Coulomb interactions. Theories for the dependence of these interactions on the parameters of the system, i.e., length, beam energy, print size, crossover diameter, etc. are thus important to guide the design of future machines. All existing theories on blur from stochastic Coulomb interaction assume a homogeneous current distribution in the crossover, where a large part of the blur is produced. However, in actual lithography machines, the crossover may be substantially broadened by the spherical aberration of the ion lenses, thus giving a very inhomogeneous current distribution in the crossover. In most analytical theories, the stochastic blur is independent of the radius of the homogeneously field crossover rc for very small crossovers, and relates to rc as (1/rc)1/2 or (1/rc)1/3 for larger ones. If aberration broadening could do the same, the effect of broadening the crossover from rc=1.5 to 50 μm would decrease the blur by a factor as much as 6, without the negative effect of increasing the curvature-of-field blur. We find physical arguments that such a large factor is impossible. Monte Carlo simulations first of all show that the blur reduction is larger near the edges of the image field than in the center, near the optical axis. For the simulated model system, the reduction on axis can be increased to a factor 2 at very large aberration coefficients. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
41.85.Gy Chromatic and geometrical aberrations
02.70.Rr General statistical methods

Optimization of experimental operating parameters for very high resolution focused ion beam applications

J. Gierak, C. Vieu, M. Schneider, H. Launois, G. Ben Assayag, and A. Septier

J. Vac. Sci. Technol. B 15, 2373 (1997); http://dx.doi.org/10.1116/1.589650 (6 pages) | Cited 14 times

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We report an experimental procedure to optimize the current profile of a focused ion beam probe, with a special emphasis on high resolution applications. The optimized operating conditions are given for three specific cases: specimen thinning for electron microscopy, nanoetching, and nanolithography. We present high quality membranes for transmission electron microscopy, arrays of nanoholes with reproducible dimensions of 17 nm etched on a nickel membrane, and finally nanolithography operations with a 10 nm resolution. Due to the conventional design of our focused ion beam system, the operating conditions that we have established for each nanofabrication application, should be successfully applied to a wide variety of ion columns. © 1997 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
06.60.Ei Sample preparation (including design of sample holders)
07.77.Ka Charged-particle beam sources and detectors

Fabrication of high-temperature superconductor Josephson junctions by focused ion beam milling

C.-H. Chen, Z. Trajanovic, Z. W. Dong, C. J. Lobb, T. Venkatesan, K. Edinger, J. Orloff, and J. Melngailis

J. Vac. Sci. Technol. B 15, 2379 (1997); http://dx.doi.org/10.1116/1.589651 (3 pages) | Cited 1 time

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We have fabricated high-critical-temperature Josephson junctions using a focused ion beam (FIB) milling to define the gap, in a-axis oriented YBa2Cu3O7 (YBCO) films. A good quality normal metal/YBCO interface is obtained by in situ Au deposition. The effect of FIB milling has been studied with different milling conditions and the resulting devices exhibit different I–V characteristics, i.e., flux flow or superconductor/normal/superconductor Josephson junction behavior. The junctions exhibit Shapiro steps in their I–V characteristics under microwave irradiation. The critical current and normal resistance product (IcRn) of the order of 1 mV has been obtained. We also show that there is a voltage modulation in the superconducting quantum interference devices as a function of an applied magnetic flux up to 80 K. © 1997 American Vacuum Society.
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85.25.Cp Josephson devices
85.25.Dq Superconducting quantum interference devices (SQUIDs)
81.20.Wk Machining, milling
74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures

Programmable aperture plate for maskless high-throughput nanolithography

I. L. Berry, A. A. Mondelli, J. Nichols, and J. Melngailis

J. Vac. Sci. Technol. B 15, 2382 (1997); http://dx.doi.org/10.1116/1.589652 (5 pages) | Cited 7 times

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One of the most serious challenges to extending lithography (by whatever radiation) into the sub-100 nm regime is mask manufacturing technology. We propose and analyze a pattern writing concept somewhat like a dot matrix printer that can expose resist with 25 nm pixels at rates needed for production lithography. It consists of a programmable aperture plate which defines an array of 3000×3000, 5 μm×5 μm apertures on 20 μm centers which is illuminated by a collimated beam of either ions or electrons. Each aperture can be blanked off by suitable electrodes and is individually addressed. The image of the array is demagnified on the wafer by 200×. The pattern is entered into the array from one edge only and is toggled across the array by shift registers. The wafer is moved in synchronism. Each pixel on the wafer is exposed 750 times by 750 different pixels to accumulate the total dose. If ions are used (e.g., H+) and a total maximum current of 3 μA is passed down the ion optical column, consistent with space charge limits, then the writing speed with 25 nm×25 nm pixels on the wafer is 1 cm2/s for an ion resist sensitivity of 3 μC/cm2. The aperture plate can be fabricated from a sandwich of 3 Si membranes and will exploit the high aspect ratio etching of 〈110〉 Si to achieve the structures that hold the blanking plates. The aperture array will measure 6 cm×6 cm. The shift register circuits clocking at about 10 MHz will be built in the spaces between the apertures and are feasible with state of the art devices. © 1997 American Vacuum Society.  
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Data analysis methods for evaluating lithographic performance

Richard A. Ferguson, Ronald M. Martino, and Timothy A. Brunner

J. Vac. Sci. Technol. B 15, 2387 (1997); http://dx.doi.org/10.1116/1.589653 (7 pages) | Cited 2 times

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Lithographic improvements obtained from process modifications or application of optical enhancement techniques can often be obscured within experimental noise and inconsistent data analysis techniques. At IBM, the need for a common platform for the accurate analysis of lithographic data led to the development of a new software analysis package entitled LEOPOLD. In this article, the exposure-defocus methodology taken by LEOPOLD for accurate calculation of the total lithographic process window in the presence of experimental noise is outlined; the extension of this method to the evaluation of the common process window through applications in the areas of optical proximity effects, analysis of optical enhancement techniques, and across-field exposure tool characterization is also demonstrated. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling
07.05.Kf Data analysis: algorithms and implementation; data management

Algorithm for shifter placement with flexible order prioritizing

Tamae Haruki, Junji Tomita, Satoru Asai, and Isamu Hanyu

J. Vac. Sci. Technol. B 15, 2394 (1997); http://dx.doi.org/10.1116/1.589654 (5 pages)

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Alternating phase shifting masks have been investigated as a method for forming the devices of 0.18 μm or less. To design these mask patterns, the phase difference between adjacent apertures should be 180°. However, it is theoretically impossible to accomplish this without phase conflicts. Therefore, design modifications at each conflicting portion is necessary after the shifter placement. On the basis of our investigations, modifying the design layout can be facilitated by reflecting the designers’ various demands in the shifter layout that is designed by the automated computer-aided design (CAD). We formulated an evaluation function by taking the priorities for designers’ demands into account and developed a model of the design layout and a resolution method implemented by a genetic algorithm. Then, a shifter placement CAD was made available on the layout editor. We confirmed that the various demands of designer are satisfied and that the computational performance is satisfactory for practical use. © 1997 American Vacuum Society.  
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85.40.Hp Lithography, masks and pattern transfer
02.10.Ab Logic and set theory

Characterizing partial coherence uniformity in a deep ultraviolet step and repeat tool

G. Patrick Watson, Raymond A. Cirelli, Masis Mkrtchyan, and Richard J. Travers

J. Vac. Sci. Technol. B 15, 2399 (1997); http://dx.doi.org/10.1116/1.589655 (5 pages)

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In recent literature the partial coherence uniformity of a lithography tool has been suspected to be a cause of critical dimension control and pattern placement problems. A direct measurement of the uniformity of partial coherence has been developed to determine the magnitude and distribution of this problem. Apertures have been fabricated that block illumination everywhere except for a small angular range and in one quadrant. The illumination reaching the wafer plane of the stepper is measured with a photodetector on the wafer chuck designed to measure exposure uniformity. The intensity distribution can vary across a chip field by as much as ±20% for large off-axis illumination (OAI) angles. However, if no aperture is inserted, the field is uniform to within ±1.5%. The consequences of this nonuniformity are surprisingly subtle; at best focus, there is no difference between the aerial image of a feature with or without the uneven angular distribution. The combination of defocus with the nonuniform OAI leads not only to image shifts, but to feature dimension variations as well. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.25.Kb Coherence

Photolithography at 0.10 and 0.13 μm using ArF excimer laser lithography in combination with resolution enhancement techniques

M. Chan, R. R. Kunz, S. P. Doran, and M. Rothschild

J. Vac. Sci. Technol. B 15, 2404 (1997); http://dx.doi.org/10.1116/1.589656 (8 pages) | Cited 2 times

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ArF (193 nm) excimer laser lithography was evaluated for production of 0.10- to 0.15-μm-size line widths. For near-term (0.13- to 0.15-μm line widths) work, an emphasis was placed on resolution enhancement strategies not requiring new mask processes or materials and was limited to consideration of binary masks in combination with annular (σi=0.4, σ0=0.6) illumination. Using a 0.5 numerical aperture lens, silylation resist, and a binary mask, a 0.8-μm depth of focus was obtained for 0.14-μm dense lines and 1.0 μm for 0.15-μm lines. However, the lack of resist linearity required almost 50% lower dose for the isolated lines, suggesting the need for optical proximity correction. For smaller features (0.10- to 0.12-μm line widths), chromeless phase-shifting masks were used. Using a partial coherence of 0.6, a 1.8-μm depth of focus and ∼3% exposure latitude was achieved for 0.11-μm isolated lines at spatial periods as small as 0.24 μm. However, aerial image modelling suggests a limitation in this approach is focus-dependent image distortion as a result of lens aberrations. These aberration-induced effects may limit the practical depth of focus for this approach and must be considered for extension of optical lithography to near the Rayleigh resolution limit. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Optimal coherent decompositions for radially symmetric optical systems

R. M. von Bünau, Y. C. Pati, Y.-T. Wang, and R. F. W. Pease

J. Vac. Sci. Technol. B 15, 2412 (1997); http://dx.doi.org/10.1116/1.589657 (5 pages) | Cited 2 times

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In this article, we discuss the application of the optimal coherent decompositions introduced by Pati and Kailath [J. Opt. Soc. Am. A 11, 2438 (1994)] to radially symmetric optical systems. We show that for such systems, both the point spread functions and the pupil functions corresponding to each term in the expansion are separable in polar coordinates. We derive analytical expressions for their angular dependence and an integral equation for the radial dependence. Our results reduce the task of computing optimal coherent decompositions from a two-dimensional integral eigenvalue problem to a one-dimensional one. © 1997 American Vacuum Society.  
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42.30.Lr Modulation and optical transfer functions
85.40.Hp Lithography, masks and pattern transfer

Fresnel diffraction mask for optical projection lithography

Hisashi Watanabe and Yoshimitsu Okuda

J. Vac. Sci. Technol. B 15, 2417 (1997); http://dx.doi.org/10.1116/1.589658 (5 pages) | Cited 1 time

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A photomask technology, Fresnel diffraction mask (FDM) is developed in order to extend the usable depth of focus (DOF) in optical lithography on topographic substrates. By using FDM, a focal plane can be controlled. The Fresnel diffraction image near the photomask is reconstructed on a wafer through a projection lens. The ring-shaped aperture is used as a FDM to form a bright spot. The focal plane of the spot images can be successfully shifted more than 1 μm from the nominal focal plane of the optical system. The FDM produces two light intensity maxima at both sides of the nominal focal plane in the optical axis. By replacing the mask patterns on the highest and/or lowest wafer topography with FDM, the usable DOF on a topographic substrate can be extended because the original mask and FDM have different optimum focal planes. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.79.Ci Filters, zone plates, and polarizers

Towards 280 nm i-line random logic lithography with off-axis illumination and optical proximity correction

I. Grodnensky, G. P. Watson, J. Garofalo, D. Castro, L. Zych, and W. Lee

J. Vac. Sci. Technol. B 15, 2422 (1997); http://dx.doi.org/10.1116/1.589659 (4 pages)

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The feasibility of imaging 280 nm features for random logic using i-line technology is examined. Theoretical and experimental studies are carried out to evaluate the effects of subresolution assist lines on the printing of an isolated 280 nm line. Optical proximity effect bias corrections for the 280 nm gaps were investigated as well. Simulations and experiments are conducted to study the exposure field nonuniformity and to evaluate the capability of modern i-line high numerical aperture (NA) exposure tools for 280 nm patterning. It is found that for NA=0.63, independent of illumination conditions, the optimum position and width of assist lines are in the range of 260–320 and 140–160 nm, respectively. The 2/3 annular off-axis illumination shows good performance and provides a greater than 1.6 μm depth of focus (DOF) for the assisted 280 nm isolated line. For the 280 nm gap, with the appropriate mask correction features (“hammerheads”), the 2/3 annular illumination also offers more than 1 μm DOF. The image uniformity studies show that the level of variations of the spatial partial coherence factor σ and the coma aberration in modern tools have practically no effect on the across field linewidth variation (AFLV) under the 2/3 annular condition. For the isolated 280 nm assisted line, an AFLV as small as 10 nm was observed over a 17×17 mm2 exposure field. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Optical proximity correction for intermediate-pitch features using sub-resolution scattering bars

J. Fung Chen, Tom Laidig, Kurt E. Wampler, and Roger Caldwell

J. Vac. Sci. Technol. B 15, 2426 (1997); http://dx.doi.org/10.1116/1.589660 (8 pages) | Cited 9 times

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Using our original scattering bar implementation as a starting point, we identify two major discontinuities in the CD versus pitch curve. The first discontinuity occurs at the pitch where two standard scattering bars will no longer fit between features at the proper optical distance and must be replaced by a single shared bar. The second discontinuity occurs at the pitch where a single shared bar no longer fits between features at the proper optical distance, and must be deleted. We propose several techniques that can be used in the pitch range around these discontinuities that allow us to decompose them into a finer series of smaller discontinuities, in effect smoothing out the curve. We introduce the concepts of “placement elasticity” and “optical weight modulation,” and two new classes of scattering bars: thin scattering bars and binary halftone scattering bars. We combine all of these elements in a hybrid optical proximity correction strategy, recommending actual dimensions for i-line, KrF (248 nm) and ArF (193 nm) reticles. We report both simulated and actual results for an i-line embodiment of this approach, demonstrating a greater than 50% improvement in overlapped depth-of-focus for both on-axis and off-axis illumination. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Viability of conventional KrF imaging for 150 nm lithography

T. Azuma, K. Matsunaga, D. Kawamura, S. Mimotogi, and Y. Onishi

J. Vac. Sci. Technol. B 15, 2434 (1997); http://dx.doi.org/10.1116/1.589661 (5 pages) | Cited 4 times

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Viability of conventional KrF imaging featuring a numerical aperture of 0.6 for 150 nm lithography is investigated by applying a novel process to reduce resist thickness down to around 100 nm. Both simulation data of aerial image contrast and resist development are applied to understand a degradation model of clear process window predicted by the aerial image contrast calculations. Comparing simulation results of the process windows’ dependencies on the resist thickness, which are derived from combinations of aerial image contrast and resist development calculations, experimental results respecting the process windows’ dependencies on the resist thickness are then discussed to elucidate how the aerial image contrast could be degraded. It is found that the minimum requirements of the process windows of 150 nm equal lines and spaces for the early stage of 1 Gbit dynamic random access memory development could narrowly be guaranteed in the case of the thickness range of less than 300 nm, and also that a great advance in the process window would be obtained when using an unconventional imaging system with 2/3 annular aperture. Further improvement of the degraded resist profiles is demonstrated in order to obtain a more stable pattern fabrication process. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.62.-b Laser applications

Methods for fabricating arrays of holes using interference lithography

A. Fernandez, J. Y. Decker, S. M. Herman, D. W. Phillion, D. W. Sweeney, and M. D. Perry

J. Vac. Sci. Technol. B 15, 2439 (1997); http://dx.doi.org/10.1116/1.589662 (5 pages) | Cited 17 times

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Optical interference lithography provides a robust patterning technology capable of achieving deep submicron resolution over extremely large field sizes (∼1 m2). Here, we compare two approaches for fabricating arrays of holes using interferometric techniques. We first show that, by applying an image reversal process to standard two-beam interference lithography, arrays of high aspect ratio holes (2:1) can be generated. This process scales well to submicron periods and allows holes as small as 0.1 μm to be patterned. Next, we present an analysis of the multiple-beam approach for patterning holes. This technique offers a potentially higher throughput process compared to other techniques. We demonstrate that, while the formation of higher contrast intensity profiles is possible by interfering four or more beams, the shape and modulation depth of such profiles are sensitive to relative phase variations. This dependence complicates the application of multiple-beam techniques for patterning large uniform arrays of resist structures. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Investigation into excimer laser radiation damage of deep ultraviolet optical phase masking films

B. W. Smith, L. Zavyalova, A. Bourov, S. Butt, and C. Fonseca

J. Vac. Sci. Technol. B 15, 2444 (1997); http://dx.doi.org/10.1116/1.589663 (4 pages)

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A variety of materials based on various oxides, nitrides, fluorides, and composites have been found to be potentially suitable for use as attenuated phase masking materials for use at excimer laser wavelengths. Presented here are results from the investigation into 193 nm excimer laser radiation of zirconium–nitride-based, aluminum–nitride-based, chrome–fluoride, amorphous-carbon, and tantalum–silicon–nitride (TaN/Si3N4) attenuated phase-shift mask materials at fluence levels mask materials experience during wafer exposure. Spectroscopic photometric and ellipsometric methods were utilized to quantify damage through measurement of transmission and reflection properties and extraction of optical constants. Results show that understoichiometric zirconium– and aluminum–nitride materials are susceptible to radiation-induced modification through oxidation effects while tantalum–silicon–nitride and chrome–fluoride films are able to withstand exposure to several thousand J/cm2 without significant degradation. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.79.Wc Optical coatings
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Use of attenuated phase masks in extreme ultraviolet lithography

O. R. Wood, D. L. White, J. E. Bjorkholm, L. E. Fetter, D. M. Tennant, A. A. MacDowell, B. LaFontaine, and G. D. Kubiak

J. Vac. Sci. Technol. B 15, 2448 (1997); http://dx.doi.org/10.1116/1.589664 (4 pages)

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We have used an attenuated phase mask, a mask with a π-phase shifting attenuator, in extreme ultraviolet lithography at 13.9 nm wavelength to produce resist profiles with sharper, more vertical sidewalls. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Mask blanks for extreme ultraviolet lithography: Ion beam sputter deposition of low defect density Mo/Si multilayers

P. A. Kearney, C. E. Moore, S. I. Tan, S. P. Vernon, and R. A. Levesque

J. Vac. Sci. Technol. B 15, 2452 (1997); http://dx.doi.org/10.1116/1.589665 (3 pages) | Cited 9 times

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We report on the growth of low defect density Mo/Si multilayer (ML) coatings. The coatings were grown in a deposition system specifically designed for extreme ultraviolet lithography mask blank fabrication. Complete, 81 layer, high reflectance Mo/Si ML coatings were deposited on 150 mm diam (100) oriented Si wafer substrates using ion beam sputter deposition. Process added defect densities correspond to 2×10−2/cm−2 larger than 0.13 μm as measured by optical scattering. This represents a reduction in defect density of Mo/Si ML coatings by a factor of 105. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Cd Deposition by sputtering
85.40.Sz Deposition technology

At-wavelength interferometry for extreme ultraviolet lithography

Edita Tejnil, Kenneth A. Goldberg, SangHun Lee, Hector Medecki, Phillip J. Batson, Paul E. Denham, Alastair A. MacDowell, Jeffrey Bokor, and David Attwood

J. Vac. Sci. Technol. B 15, 2455 (1997); http://dx.doi.org/10.1116/1.589666 (7 pages) | Cited 10 times

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A phase-shifting point diffraction interferometer is being developed for at-wavelength testing of extreme ultraviolet lithographic optical systems. The interferometer was implemented to characterize the aberrations of a 10× Schwarzschild multilayer-coated reflective optical system at the operational wavelength of 13.4 nm. Chromatic vignetting effects are observed and they demonstrate the influence of multilayer coatings on the wave front. A subaperture of the optic with a numerical aperture of 0.07 was measured as having a wave front error of 0.090 wave (1.21 nm) root mean square (rms) at a 13.4 nm wavelength. The wave front measurements indicate measurement repeatability of ±0.008 wave (±0.11 nm) rms. Image calculations that include the effects of the measured aberrations are consistent with imaging performed with the 10× Schwarzschild optic on an extreme ultraviolet exposure tool. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.87.Bg Phase shifting interferometry
07.60.Ly Interferometers
42.15.Fr Aberrations

At-wavelength characterization of an extreme ultraviolet camera from low to mid-spatial frequencies with a compact laser plasma source

A. K. Ray-Chaudhuri, K. D. Krenz, and C. H. Fields

J. Vac. Sci. Technol. B 15, 2462 (1997); http://dx.doi.org/10.1116/1.589667 (5 pages) | Cited 2 times

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The final alignment and characterization of an extreme ultraviolet (EUV) lithographic projection optics system must be performed at the operating wavelength in order to account for errors associated with the combined effect of multilayer coating and substrate fabrication error. Two complementary metrology techniques have been developed which can operate on a compact laser plasma source: EUV lateral shear interferometry (LSI) and aerial image monitoring (AIM). LSI quantifies residual low spatial frequency wave front errors associated with the “figure” of each optical element. To characterize the effect of mid-spatial frequency errors that lead to scatter in the image plane, an EUV aerial image monitor was employed. EUV interferometry was compared to visible light interferometry measurements of the optical system and was found to be in reasonable agreement for low spatial frequency errors. The contrast as measured by AIM and photoresist exposures indicates an additional reduction of contrast associated with scatter due to large mid-spatial frequency errors. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.68.+m Photography, photographic instruments; xerography
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
07.60.Ly Interferometers

Minimum critical defects in extreme-ultraviolet lithography masks

Yun Lin and Jeffrey Bokor

J. Vac. Sci. Technol. B 15, 2467 (1997); http://dx.doi.org/10.1116/1.589668 (4 pages) | Cited 8 times

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We have performed aerial image simulations to characterize critical defects on extreme-ultraviolet lithography masks based on their interactions with typical mask patterns. Instead of the conventional critical dimension criteria, an exposure–defocus process window allowing a 10% critical dimension variation was used as the criteria for defining the critical defects. We also carried out aerial image simulations of isolated defects to obtain information for future reticle blank defect inspection needs. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Evaluation of alignment accuracy in processed wafers and SiC masks on a scattered-light alignment system for x-ray aligners

Tsutomu Miyatake, Masaoki Hirose, Tsutomu Shoki, Ryo Ohkubo, and Kuniaki Yamazaki

J. Vac. Sci. Technol. B 15, 2471 (1997); http://dx.doi.org/10.1116/1.589669 (5 pages) | Cited 3 times

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The alignment performances of the video-based scattered-light alignment (SLA) system for 0.1 μm lithography are described in this article. The SLA system has high sensitivity to the silicon carbide (SiC) mask without an antireflection coating (ARC). This article especially focuses on the alignment accuracy in processed wafers and the dependency of the alignment accuracy on the SiC membrane thickness. A series of alignment tests was done on a lab-based vertical wafer stage using the SiC masks. In order to evaluate the alignment accuracy in processed wafers, we prepared four processed wafer types: nitride, oxide, poly-Si, and aluminum. The high position sensing repeatability in the range of 4.8–6.4 nm (3σ) was obtained using the combination of the four processed wafers and a 2-μm-thick SiC membrane without the ARC. We also obtained the alignment accuracy using the wafer alignment marks only, resulting in an alignment accuracy of 10.0, 8.8, 9.1, and 35.7 nm (3σ) for the nitride, oxide, poly-si, and aluminum wafers, respectively. In addition, the dependency of the alignment accuracy on the SiC membrane thickness was obtained using the membranes with thicknesses of 2, 3, 4, and 5 μm. An improvement of the alignment accuracy in the aluminum is discussed. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.05.Pj Image processing
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.85.Qe Synchrotron radiation instrumentation

Overlay performance of 180 nm ground rule generation x-ray lithography aligner

A. C. Chen, A. L. Flamholz, R. Rippstein, R. H. Fair, D. A. Heald, and R. J. Amodeo

J. Vac. Sci. Technol. B 15, 2476 (1997); http://dx.doi.org/10.1116/1.589670 (7 pages) | Cited 5 times

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The 180 nm ground rule production prototype x-ray lithography aligner was developed for the Defense Advanced Lithography Program (DALP) and installed in IBM’s Advanced Lithography Facility (ALF) in 1995. This aligner is designed to satisfy the manufacturing requirement for 250 and 180 nm ground rule electronic devices, such as 256 Mbit and 1 Gbit dynamic random access memories. The acceptance evaluation of this aligner was presented elsewhere (Ref. 12). The aligner uses an innovative x-ray image sensor (XRIS) to align the mask by detecting its x-ray actinic image and uses an off-axis alignment system, similar to the alignment system used in Micrascan-II™ (a trademark of Silicon Valley Group Lithography), to align the wafer. From subsystem testing, the alignment repeatability of XRIS is not a significant contributor to the aligner’s contribution of overlay error. As a result, the x-ray alignment sensor technology can be used for future generations of x-ray lithography aligners. This article will specifically focus on the overlay performance of the aligner. The overlay evaluation consisted of careful wafer stage and alignment system calibration, off-line subsystem testing, and extensive exposure tests. The exposure tests were designed to measure the alignment performance of the aligner across a wide range of wafer structure types. A detailed discussion is given on the test methodology and the aligner contribution to the total overlay error. On the better levels (e.g., etched Si), the tool-to-itself aligner contribution to overlay error is in the range of 35–40 nm (mean+3σ) and approaches the overlay error budget for a 180 nm ground rule generation x-ray aligner. An overlay model was also developed to include the error contributions of the aligner as well as the image placement accuracy of the mask. The modeling results show that the aligner, with image placement errors of current x-ray masks, can satisfy the overlay requirement (mean+3σ<70 nm) for 1 Gbit device demonstration programs. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Origin of stress distribution in sputtered x-ray absorber film

Yoshihisa Iba, Fumiaki Kumasaka, Hajime Aoyama, Takao Taguchi, and Masaki Yamabe

J. Vac. Sci. Technol. B 15, 2483 (1997); http://dx.doi.org/10.1116/1.589671 (6 pages) | Cited 3 times

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To eliminate distortion in x-ray masks, not only lower average stress but also uniformity of the stress distribution in the x-ray absorber film are very important. We investigated the cause of stress distribution in sputtered x-ray absorber films both theoretically and experimentally. Our investigation clarified that stress distribution is determined by the distribution of the average velocity of sputtered and working gas atoms and/or the arrival frequency of incident working gas atoms when arriving at the wafer in sputtering systems. These determinants are strongly influenced by the geometry of the sputtering apparatus, i.e., the shape of the erosion area of the target and the substrate-to-target distance. We obtained a good uniformity of stress by optimizing the sputtering equipment configuration taking the erosion area of the target into consideration. Two ways to accomplish this are by adjusting the gap between the target and the substrate and by achieving uniformity of the erosion area. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Cd Deposition by sputtering

Sub-20 nm x-ray nanolithography using conventional mask technologies on monochromatized synchrotron radiation

G. Simon, A. M. Haghiri-Gosnet, J. Bourneix, D. Decanini, Y. Chen, F. Rousseaux, H. Launois, and B. Vidal

J. Vac. Sci. Technol. B 15, 2489 (1997); http://dx.doi.org/10.1116/1.589672 (6 pages) | Cited 9 times

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The optimal wavelength range for x-ray lithography is usually estimated between 0.8 and 1.4 nm. In this work, the use of a monochromator working at 1.1 nm on synchrotron radiation is reported. Replication results in this monochromatic mode are compared with results obtained for a polychromatic synchrotron radiation centered at 0.8 nm in terms of resolution and image contrast. Two conventional mask technologies are used for this study. The influence of the mask contrast is also studied. A nondestructive soft contact system was chosen to lower the gap below 1 μm. An ultimate resolution of 20 nm is shown in PMMA resist as well as 35 nm in PMMA/MAA (8.5%) resist for the monochromatic mode. The effect of photoelectrons created in the substrate is also investigated by replications on Si substrates coated with a Cr/Au bilayer. In addition, the daughtering of high resolution masks at 1.1 nm is successfully performed in the 20 nm range by Au electroplating. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.85.Qe Synchrotron radiation instrumentation

X-ray micro- and nanofabrication using a laser–plasma source at 1 nm wavelength

I. C. E. Turcu, R. M. Allot, C. M. Mann, C. Reeves, I. N. Ross, N. Lisi, B. J. Maddison, S. W. Moon, P. Prewett, J. T. M. Stevenson, A. W. S. Ross, A. M. Gundlach, B. Koek, P. Mitchell, P. Anastasi, et al.

J. Vac. Sci. Technol. B 15, 2495 (1997); http://dx.doi.org/10.1116/1.589673 (8 pages) | Cited 6 times

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A picosecond excimer laser–plasma source has been constructed, which generates an x-ray average power of 2.2 and 1.4 W at the wavelengths required for proximity x-ray lithography: 1.4 nm (steel target) and 1 nm (copper target), respectively. The plasma source could be scaled to the 50–75 W x-ray average power required for industrial lithographic production by scaling the total average power of the commercial excimer laser system up to 1 kW. The 1 nm x-ray source is used to micromachine a 2.5 THz microwave waveguide–cavity package with a 48 μm deep, three-dimensional structure, using the LIGA technique. The 1 nm x-ray source is also used to print 180 nm long transistor gates in the fabrication process of field-effect transistors. © 1997 American Vacuum Society.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Novel illumination system of synchrotron radiation stepper with full field exposure method

Yutaka Watanabe, Shinichi Hara, Nobutoshi Mizusawa, Yasuaki Fukuda, and Shunichi Uzawa

J. Vac. Sci. Technol. B 15, 2503 (1997); http://dx.doi.org/10.1116/1.589674 (6 pages) | Cited 6 times

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We estimate the pattern distortion and the critical dimension (CD) variation due to the thermal distortion under a large exposure field for the full field exposure method. We verify that the effect of the thermal distortion of the mask and wafer on the pattern distortion and the CD variation is small enough under the condition of mass production of devices of 0.1 μm design rule. We present a design of the novel two mirror illumination system which can improve the throughput both by exposing a field as large as 50 mm square and by condensing synchrotron radiation (SR) spread in the horizontal plane. The effects of the variation of the position of the SR source and the mirrors and the size of the SR source on the performance of the stepper are investigated. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.85.Qe Synchrotron radiation instrumentation

Direct measurement of the effect of substrate photoelectrons in x-ray nanolithography

D. J. D. Carter, A. Pepin, M. R. Schweizer, H. I. Smith, and L. E. Ocola

J. Vac. Sci. Technol. B 15, 2509 (1997); http://dx.doi.org/10.1116/1.589675 (5 pages) | Cited 10 times

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We measure the dissolution rate of poly(methylmethacrylate) (PMMA) as a function of height above substrates of silicon and thin films suitable as bases for gold electroplating: a “thick-gold” film (10 nm Ti/10 nm Au), and a “thin-gold” film (10 nm Ti/1.8 nm Au). For the thick-gold film, a dramatic increase is seen in the PMMA dissolution rate starting approximately 50 nm above the substrate. This is attributed to increased x-ray absorption and photoelectron generation in the thick gold. An increased dissolution rate is not seen for the other two substrates. Our measurements are compared with simulations and with our experience in replicating sub-50-nm device structures. We point out two consequences of this increased exposure due to substrate-generated electrons. The first is an increased exposure rate near the resist/substrate interface which can lead to development at the interface in the dark areas. The second is an increase in exposure near a resist/substrate interface at the boundary between shadowed and unshadowed regions, leading to an undercut in the resist profile. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

X-ray fabrication of nonorthogonal structures using “surface” masks

V. White, C. Herdey, D. D. Denton, and J. Song

J. Vac. Sci. Technol. B 15, 2514 (1997); http://dx.doi.org/10.1116/1.589676 (3 pages) | Cited 1 time

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Standard x-ray lithographic techniques allow great flexibility of geometry in two dimensions. Typically, the third dimension is limited to depth, which is purely orthogonal to the surface. We have been developing a relatively simple technique using x-ray lithography and have fabricated a whole family of precisely controlled nonorthogonal structures such as tapers, bridges and various “leaning” or blazed structures. Traditional soft x-ray masks, create the modulation required to print into x-ray resists by having the absorbing elements of the x-ray mask patterned on a thin membrane. This technique involves the creation of the gold absorbing elements of the x-ray mask directly on the surface of the photoresist, i.e., a “surface” mask. These surface masks can create nonorthogonal exposures creating blazed structures as well as “bridges” by tilting the sample with respect to the x-ray beam during exposure. The exposures can also be done while having the tilted sample rotated, creating tapered exposure profiles. In addition to the novel geometries, a potentially useful feature of the rotated exposures is that the sidewalls have nanometer scale smoothness, due to the averaging of intensities during rotation. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

X-ray lithography for ⩽100 nm ground rules in complex patterns

Scott Hector, Victor Pol, Azalia Krasnoperova, Juan Maldonado, Alex Flamholz, Dave Heald, Carl Stahlhammer, Dan Galburt, Ralph Amodeo, Tom Donohue, Shalom Wind, James Buchigniano, Raman Viswanathan, Mumit Khan, Srinivas Bollepalli, et al.

J. Vac. Sci. Technol. B 15, 2517 (1997); http://dx.doi.org/10.1116/1.589677 (5 pages) | Cited 9 times

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Complex patterns with 75–125 nm feature sizes exposed with x-ray lithography are shown. Lithographic results for 75–125 nm lines with varying pitch are compared to simulations of image formation and resist dissolution, showing good qualitative agreement. Exposure dose latitude, nested-to-isolated print bias, image shortening, linewidth change with gap, and linearity of printed linewidth versus mask linewidth are quantified for 11–22.5 μm gaps. Critical dimension control error budgets for resist linewidth uniformity are determined for logic patterns at 75 and 100 nm ground rules. Image shortening is quantified for 75–125 nm ground rule static random access memory-like patterns, indicating hammerheads added to line ends reduce shortening to acceptable levels for ⩾100 nm ground rules at ⩽17.5 μm gaps. With tight gap control and tight mask linewidth control, 100 nm ground rule complex patterns can be printed with good latitude using x-ray lithography. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Design and fabrication of Fresnel zone plates with large numbers of zones

Z. Chen, Y. Vladimirsky, M. Brown, Q. Leonard, O. Vladimirsky, F. Moore, F. Cerrina, B. Lai, W. Yun, and E. Gluskin

J. Vac. Sci. Technol. B 15, 2522 (1997); http://dx.doi.org/10.1116/1.589678 (6 pages) | Cited 5 times

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The advent of high-brightness x-ray sources in the 10–40 keV region opens new possibilities of experiments with microbeams. Techniques to form these focused beams may be based on glancing mirrors, phase elements, or diffractive optics, in particular Fresnel zone plates (FZPs). Because of the long focal length and large acceptance, FZPs designed to work in the hard x-ray region tend to have quite large diameters and large numbers of zones. For instance, the zone plate described in this article has a 1860 μm diam, a focal length of f=3 m (for 8 keV), and 1860 zones. On a standard pattern generator, circular shapes are always approximated as simpler structures. The tolerance requirement for shape and positions of zones depends on the number of zones, and it is necessary to guarantee that the circular structures are approximated to the required degree of accuracy while keeping the size of the data structure to a reasonable size for processing by the exposure system. For instance, if polygons are used to approximate circular zones, a formula for the minimum acceptable number of polygon sides can be derived. An x-ray mask for a Fresnel phase zone plate (FPZP) with 1860 zones was designed directly in Cambridge source pattern data format and fabricated using the Leica Cambridge e-beam tool installed in the CXrL. The zone plates presented in this article were designed for hard x rays, and multilevel x-ray lithography was employed as a fabrication technique to form absorber thickness sufficient to provide the necessary phase shift. Minimum gold features of 0.25 μm with thicknesses of 1.6 and 3 μm, were formed to be used with 8 and 20 keV photons, respectively. Finally, in order to estimate the quality of the zone plates during fabrication, a scanning electron microscope based moiré method was used. © 1997 American Vacuum Society.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Ci Filters, zone plates, and polarizers
42.86.+b Optical workshop techniques

Resist design concepts for 193 nm lithography: Opportunities for innovation and invention

E. Reichmanis, O. Nalamasu, F. M. Houlihan, T. I. Wallow, A. G. Timko, R. Cirelli, G. Dabbagh, R. S. Hutton, A. E. Novembre, and B. W. Smith

J. Vac. Sci. Technol. B 15, 2528 (1997); http://dx.doi.org/10.1116/1.589679 (6 pages) | Cited 8 times

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Photolithography using 193 nm radiation is the leading candidate for the manufacture of 0.18–0.13 μm design rule devices. The optical absorption of materials such as novolacs, and functionalized poly(hydroxystyrenes) and styrene-acrylate copolymers which are the matrix materials of choice for G line, I line, and 248 nm lithography is significantly higher than one at 193 nm making them too opaque to be useful at this shorter wavelength. The opacity of the current photoresists at 193 nm requires innovation in designing alternative materials and processes to realize the full potential of 193 nm (ArF) lithography. From a materials standpoint, this challenge must be addressed by new chemistries and process schemes capable of providing resists with the aqueous base solubility, etching resistance, resolution, photospeed, and process latitude required for large-scale manufacturing. In addition, regulatory constraints on volatile organic chemical emissions have spurred efforts to design revolutionary resist platforms that address these concerns while providing the performance required for sub-0.18 μm device manufacture. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Specific behavior of chemically amplified systems with low activation energy under electron-beam exposure: Implementation of 248 and 193 nm resists

B. Mortini, S. Tedesco, B. Dal’Zotto, and P. Paniez

J. Vac. Sci. Technol. B 15, 2534 (1997); http://dx.doi.org/10.1116/1.589680 (7 pages) | Cited 3 times

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Low activation energy resists are studied through two formulations representative of these systems, namely, Shipley 248 nm XP9493 and MCC 193 nm TER-1 resists. It is shown that their specific behavior can be easily demonstrated by using differential scanning calorimetry techniques at different steps of the lithographic process. As these resists present a low activation energy for their deprotection, the postexposure bake (PEB) is not necessary so a comparison between processes with and without a PEB step can be made. Processes without PEB are interesting as they allow deconvolution and an emphasis on different phenomena (evaporation, diffusion, and recompaction) which are of tremendous importance for chemically amplified resists. Finally, processes without PEB can allow a correlation of the mechanisms involved in the resists to lithographic performance. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Polymer structure effect on dissolution characteristics and acid diffusion in chemically amplified deep ultraviolet resists

Toshiro Itani, Hiroshi Yoshino, Shuichi Hashimoto, Mitsuharu Yamana, Norihiko Samoto, and Kunihiko Kasama

J. Vac. Sci. Technol. B 15, 2541 (1997); http://dx.doi.org/10.1116/1.589681 (4 pages) | Cited 10 times

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The role of molecular weight dispersion (Mw/Mn) of base phenolic resin was investigated in chemically amplified positive KrF resists. The resists consisted of tert-butoxycarbonyl (t-BOC) blocked polystyrene as base resin and 2,4-dimethylbenzenesulfonic acid derivative as photoacid generator, and the Mw/Mn value was changed as 1.2, 4.0, and 9.0. Not only dissolution rate contrast, but also the slope m of log(dissolution rate)-log(exposure dose) plots increased with decreasing Mw/Mn. In the case of low Mw/Mn, the molecular structure becomes more homogeneous, so resist film could be dissolved uniformly via constant developer penetration into film. This uniform dissolution characteristics may be attributable to the origin of dispersion effects mentioned above. Furthermore, higher acid diffusion property and smooth pattern side wall were obtained without side wall roughness in lower Mw/Mn. This fact indicates that acid diffusion length is also uniform within resist film in the case of low Mw/Mn. Based on the experimental analysis, the clear relationship among Mw/Mn, dissolution characteristics and acid diffusion behavior in resist film was obtained. Moreover, it was found that lower Mw/Mn has advantage for improving inherent resist performance. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
64.75.-g Phase equilibria
66.30.J- Diffusion of impurities
61.41.+e Polymers, elastomers, and plastics

Latent image characterization of postexposure bake process in chemically amplified resists

L. E. Ocola, F. Cerrina, and Tim May

J. Vac. Sci. Technol. B 15, 2545 (1997); http://dx.doi.org/10.1116/1.589682 (5 pages) | Cited 4 times

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The demand of smaller device dimensions drives the need to improve the lithographic and the metrology tools to produce them. Characterization of the image formation during the lithography process is key to any process control effort. Scanning probe microscopy (SPM) on exposed, unbaked and baked, undeveloped photoresist shows morphological details of the image formation process unachievable with other techniques. The use of micro-Fourier transform infrared (μ-FTIR) spectroscopy will be investigated for latent image chemical analysis. Both of these techniques will be used in the study of the dependence of the latent image of a negative novolac-based chemically amplified resist, SAL 605 (Shipley), with postexposure bake (PEB) conditions. The objective of the experiment is to understand how the thermal properties of the resist and the linking reaction taking place are related to each other during PEB. Experimental results indicate that resist from unexposed regions diffuse into the exposed resist during PEB. SPM results show that this diffusion increases as the PEB temperature rises above the glass transition temperature of the unexposed resist. μ-FTIR results show that the linker component of the resist, hexamethoxymethylmelamine, has been identified as one of the resist components that diffuses into the exposed regions during PEB. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Deep ultraviolet resists AZ DX-561 and AZ DX-1300P applied for electron beam and masked ion beam lithography

P. Hudek, I. Kostic, M. Belov, I. W. Rangelow, F. Shi, G. Pawlowski, W. Spiess, H. Buschbeck, E. Cekan, S. Eder, and H. Löschner

J. Vac. Sci. Technol. B 15, 2550 (1997); http://dx.doi.org/10.1116/1.589683 (5 pages) | Cited 1 time

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This article reports work on two positive-tone deep ultraviolet chemically amplified resist (CAR) systems from HOECHST AG that were applied in two different lithographic processes: (i) the AZ DX-561 resist in serial working direct-write scanning electron-beam lithography, and (ii) AZ DX-1300P resist in a novel parallel working masked ion beam lithography. The main parameters of both CARs under the optimized processing conditions for both lithographic processes were generally determined. The contrast of these resists was found to be >10. The sensitivity of AZ DX-561 was about 12 μC/cm2 for 30 keV electrons. For AZ DX-1300P, a sensitivity of 9 μC/cm2 was found for 30 keV electrons and 0.3 μC/cm2 for 80 keV He+ ions. Both resists showed excellent performance for subsequent reactive ion etching. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Low energy electron beam top surface image processing using chemically amplified AXT resist

C. S. Whelan, D. M. Tanenbaum, D. C. La Tulipe, M. Isaacson, and H. G. Craighead

J. Vac. Sci. Technol. B 15, 2555 (1997); http://dx.doi.org/10.1116/1.589684 (6 pages) | Cited 4 times

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High resolution processes are demonstrated with a positive-mode chemically amplified AXT top surface imaging resist system exposed with a low energy electron beam. Top surface imaging is an ideal match to low energy electron beam lithography because it allows thick resist layers to be patterned despite the limited penetration depth of the electron beam. The three key steps of the process are exposure, silylation, and etch development. All three steps influence the final process sensitivity, contrast, and resolution. The AXT has a poly(hydroxy styrene) base resin, and has been formulated both with and without a dye used to enhance optical absorption. We have achieved sub 100 nm resolution both with and without a postexposure bake. Critical area doses below 1 μC/m2 are demonstrated. The edge roughness and density of etch residue from silylation defects have been compared for a variety of oxygen plasma etch systems. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Theoretical discussion of diffusion effects in negative chemically amplified resists based on contrast curve simulation

G. P. Patsis, G. Meneghini, N. Glezos, and P. Argitis

J. Vac. Sci. Technol. B 15, 2561 (1997); http://dx.doi.org/10.1116/1.589685 (4 pages) | Cited 3 times

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Gel formation theory is discussed in the case of chemically amplified resists (CARs) and a specific epoxy-based resist is used in order to model the results. It is found that existing gel formation models may be classified in four classes and there are two important parameters (inhibitor activity and maximum number of available crosslinkable sites) which must be specially interpreted in order to account for chemical amplification and diffusion mechanisms in CARs. It is also proved that a Charlesby–Pinner representation of the gel-dose relationship reveals qualitative characteristics of the process and composition changes. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
61.80.Fe Electron and positron radiation effects
61.82.Pv Polymers, organic compounds
82.70.Gg Gels and sols

Stress dependent silylation model and two-dimensional profile simulation

Marco A. Zuniga and Andrew R. Neureuther

J. Vac. Sci. Technol. B 15, 2565 (1997); http://dx.doi.org/10.1116/1.589686 (5 pages)

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A new model for polymer silylation is proposed that takes into account three mechanisms: The relaxation of the polymer during silylation, a diffusivity of the silylating agent which increases with resist matrix expansion, as well as a local reaction rate retardation due to stress induced by resist swelling. These mechanisms capture changes in profile shape during silylation. The resulting nonlinear differential equations are solved two-dimensional (2D) using the finite element method and the influence of the main parameters is studied as a function of feature size and feature type, illustrating the effects of initial aerial image and processing conditions on the final resist image. The simulation profiles reproduce the silylation depth reduction with feature size and abrupt encroachment heretofore unexplained in various experimental studies. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
02.70.Dh Finite-element and Galerkin methods
82.35.-x Polymers: properties; reactions; polymerization
82.20.Wt Computational modeling; simulation
85.40.Bh Computer-aided design of microcircuits; layout and modeling
82.50.-m Photochemistry

C60-incorporated nanocomposite resist system for practical nanometer pattern fabrication

T. Ishii, H. Nozawa, T. Tamamura, and A. Ozawa

J. Vac. Sci. Technol. B 15, 2570 (1997); http://dx.doi.org/10.1116/1.589687 (5 pages) | Cited 7 times

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We propose a nanocomposite resist system that incorporates sub-nm size fullerene C60 molecules into a highly sensitive and moderately dry-etching resistant electron-beam positive resist, ZEP520. C60 incorporation leads to carbon reinforcement in the original resist material and enhances resist performance for nanometer pattern fabrication. 10 wt % C60 incorporated ZEP520 shows enhancements of etching resistance (∼15%), thermal resistance (∼30 °C), and mechanical resistance (3.5–5.5 in the aspect ratio). By applying this new resist system to x-ray mask fabrication, an ultrafine mask with the minimum dimension of 45 nm has been successfully fabricated. © 1997 American Vacuum Society.  
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer

Increasing plasma etch resistance of resists using fullerene additives

Paul M. Dentinger and James W. Taylor

J. Vac. Sci. Technol. B 15, 2575 (1997); http://dx.doi.org/10.1116/1.589688 (7 pages) | Cited 3 times

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We utilize a new class of additive, Fullerenes, which appear to impart superior plasma etch resistance to resist films compared to other additives reported in the literature. [R. R. Kunz, S. C. Palmateer, A. R. Forte, R. D. Allen, G. M. Wallraff, R. A. DiPietro, and D. C. Hofer, Proc. SPIE 2724, 365 (1996).] The plasma etch resistance of PMMA impregnated with [60]Fullerenes was compared directly to pure PMMA; adamantane- and 1-chloroadamantane-impregnated PMMA; the novolac-based, e-beam/x-ray photoresist SAL 605 (The Shipley Co.); APEX-E (IBM Corp.); and an experimental, 193 nm resist, XP96545-7A (The Shipley Co.). These comparison experiments were done under CF4 and Cl2 reactive ion etch conditions. The plasma etch rate of PMMA decreased linearly with concentration of [60]Fullerenes in the film up to at least 11 wt %. When 10.8 wt % C60 (≈7.3 vol %) versus total solids were added to PMMA, the etch rate ratio to SAL 605 dropped from 1.80 to 1.38 in CF4 and from 2.5 to 1.55 in Cl2. Improvements in etch resistance with Fullerenes added to PMMA were similar for both Cl2 plasmas and CF4 plasmas, which was contrary to the results of the unmodified XP96545-7A resist and that reported for alicyclic additives, [R. R. Kunz, S. C. Palmateer, A. R. Forte, R. D. Allen, G. M. Wallraff, R. A. DiPietro, and D. C. Hofer, Proc. SPIE 2724, 365 (1996)]. [60]Fullerenes were also successful at improving the plasma etch durability of pure polystyrene films, showing that these additives have the potential to improve etch resistance of films to better than novolac, provided solubility limitations can be overcome. The absorptivity of [60]Fullerenes at 193 nm can be reduced by derivatizing the C60 to C60H36, C60F40, or C60F48. The fluorinated Fullerenes show high solubility in propylene glycol methyl ether acetate and 1-methoxy-2-propanol. On a mole basis, fluorinated Fullerenes improve the etch resistance of PMMA as well as [60]Fullerenes showing the potential of derivatized Fullerenes for various photoresist applications, including 193 nm imaging materials. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Radiation-induced reactions of chemically amplified x-ray and electron-beam resists based on deprotection of t-butoxycarbonyl groups

T. Kozawa, S. Nagahara, Y. Yoshida, S. Tagawa, T. Watanabe, and Y. Yamashita

J. Vac. Sci. Technol. B 15, 2582 (1997); http://dx.doi.org/10.1116/1.589689 (5 pages) | Cited 53 times

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Radiation-induced reactions in chemically amplified resists based on deprotection of t-butoxycarbonyl groups have been investigated by both time-resolved (the pulse radiolysis methods) and steady-state optical absorption spectroscopy. Upon exposure of a partially tBOC-protected novolak by electron and synchrotron radiation beams, the yields of the intermediates contributing to the acid generation (phenoxyl radical and proton adducts of base resin) decreased with increasing the protection ratio of hydroxyl groups. Therefore, the efficiency of the acid generation is closely related with the protection ratio. The relation of the acid generation mechanism with the protection ratio was discussed. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
82.50.Kx Processes caused by X-rays or γ-rays

Optimizing the resist to the aerial image in a chemically amplified system

T. H. Fedynyshyn, C. R. Szmanda, and G. J. Cernigliaro

J. Vac. Sci. Technol. B 15, 2587 (1997); http://dx.doi.org/10.1116/1.589690 (9 pages)

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For KrF based lithographic systems, resist design philosophy focuses on methods to maximize resist performance while providing both a reliable and cost effective lithographic process. Such systems will, out of necessity, be high sensitivity and high contrast. A key evaluation criterion for resists is the lithographic process window, as defined by the focus and exposure latitudes of the resist. As the process window is dependent on the type of feature being printed, the overlap of resist process windows between isolated and dense lines is often employed to define the overall resist process window. Two general methods can be employed to manipulate the lithographic performance. One way is to manipulate the image through the numerical aperture of the lens, coherence of the source and bias of the mask. The second is to manipulate the latent image by changing the relative response of the resist to changes in the energy dose. Both methods will directly influence the lithographic performance of the resist and will be feature dependent. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Nanolithography performances of ultraviolet III chemically amplified positive resist

L. Grella, M. Gentili, E. Di Fabrizio, M. Baciocchi, L. Mastrogiacomo, R. Maggiora, and L. Scopa

J. Vac. Sci. Technol. B 15, 2596 (1997); http://dx.doi.org/10.1116/1.589691 (5 pages) | Cited 1 time

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Devices for future microelectronics shall demand lithographic performance that fall within the nanometer region (100 nm and below). Chemically amplified resists (CARs) offer a substantial gain in speed compared to conventional ones, and thus are attractive for the ultradense layouts of such future devices. However, before they can be selected for advanced microelectronics device production, nanolithography performances have to be proven. Ultraviolet (UV) III is a novel CAR from Shipley Corp. which was reported to possess fine-line lithographic capabilities. In this work, the UV III resist is characterized for the e-beam exposure. A commercial e-beam lithography machine was employed as exposure tool at 50 kV accelerating voltage. A process description for resolution below 100 nm is given, and resist performance was proven on layouts meaningful of actual devices. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Investigation of the notching effect for single layer deep ultraviolet resist processing

Hiroshi Yoshino, Toshiro Itani, Shuichi Hashimoto, Mitsuharu Yamana, Tsuyoshi Yoshii, Norihiko Samoto, and Kunihiko Kasama

J. Vac. Sci. Technol. B 15, 2601 (1997); http://dx.doi.org/10.1116/1.589692 (4 pages)

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In order to extend the application limit of single layer resist processing to 0.25 μm pattern formation, the influence of resist thickness on reflective notching effects was investigated, using a two-dimensional resist profile simulator with the vector model. As the resist thickness increased, the reflective notching was varied periodically. Resist profile degradation due to reflective notching was maximum at the resist thickness where resist sensitivity was maximum (Emax), and was minimum at the resist thickness where resist sensitivity was minimum (Emin). The reflective notching was strongly dependent on the effective exposure dose Eeff at the bottom of the resist film, defined as the product of resist transmittance and optimum exposure dose Eopt. These simulation results were verified experimentally. It was concluded that the resist thickness should be set to minimize exposure dose for the reduction of reflective notching effects. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Top surface imaging process at and below quarter-micron resolution and pattern transfer into metal

Mathias Irmscher, Bernd Höfflinger, Christian Reuter, Reinhard Springer, Craig Stauffer, and Mark Puttock

J. Vac. Sci. Technol. B 15, 2605 (1997); http://dx.doi.org/10.1116/1.589693 (5 pages) | Cited 1 time

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The use of top surface imaging processes pushes the limits of both deep ultraviolet lithography and e-beam direct writing. However, the flow effect due to silylation with monofunctional aminosilanes prevents the creation of a faithful resist mask of a high resolution. The application of mixed mono- and bifunctional agents causes crosslinking of the silylated resist and eliminates the flow. We investigated details of the silylation of novolak-based chemically amplified resists with a mixture of bis(dimethylamino)methylsilane and dimethylsilydiethylamine. After mixing, new materials evolved until a stable ratio of all components was reached. During silylation the ratio changes again and requires a continuous adaptation of the silylation parameters. The optimized process enables the realization of a 0.15 μm pattern in 0.7 μm thick resist. An inductively coupled plasma etcher was evaluated for transferring of the resulting resist structures into typical aluminium alloys. The developed process enables the etching of subquarter-micron features into 0.6 μm thick AlSiCu layers. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

T-top forming simulation using percolation theory

K. Kamon, K. Nakazawa, A. Yamaguchi, N. Matsuzawa, T. Ohfuji, K. Kanzaki, and S. Tagawa

J. Vac. Sci. Technol. B 15, 2610 (1997); http://dx.doi.org/10.1116/1.589694 (6 pages) | Cited 4 times

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In KrF or ArF resist processing, a chemically amplified resist is widely used for ultralarge scale integrated device fabrication. Decomposition (positive resist) or cross linking (negative resist) is amplified by an acid catalytic reaction during post-exposure baking (PEB). T-top forming becomes a serious problem in these resists. In resist simulation, to take these characteristics into account, percolation theory is introduced. The acid and product distributions during PEB are iteratively calculated. Thus, we can conclude that the acid and product distribution in resist films are time dependent. Moreover, a resist simulator that can take into account macroscopic feature changes from microscopic molecular structural change is necessary. From resist surface observation and slow positron annihilation measurements, free volume generation is confirmed. A new resist process model, including prebake, PEB, and development for chemically amplified resists is established by the cluster model. CPU time is 1 min each for a three dimensional image and for development, which is fast enough for practical evaluation use. The defocus dependence of the resist profile agrees well with the experiment. For chemically amplified resists, decomposition or cross linking proceeds vertically rather than horizontally. Thus, a rectangular resist profile can be obtained. Simulation results based upon this model can describe T-tops or resist bridges. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Developer temperature effect on negative deep ultraviolet resists: Characterization, modeling, and simulation

Paul Isaac Hagouel, Ioannis Karafyllidis, and Andrew R. Neureuther

J. Vac. Sci. Technol. B 15, 2616 (1997); http://dx.doi.org/10.1116/1.589695 (5 pages) | Cited 6 times

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We consider the effect of developer (solvent) temperature in the dissolution of both the exposed and unexposed parts of the resist. The spin-formatted resist film tends to have macromolecules oriented parallel to the substrate surface. The orientation of the resist macromolecules introduces an anisotropic component to the etch rate: higher in the direction parallel to the substrate surface and lower in the perpendicular one. We performed a series of experiments on resist-coated Si wafers using a stepper and a deep ultraviolet source at 248 nm using SNR-248 negative resist. We obtained scanning electron micrographs for various developer temperatures. The variation of the lateral etch rate manifested itself in sidewall profile slopes and is compatible with the entropy directional flow. Simulation using the Cellular Automata model predicted identical results. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Ultrasonic and dip resist development processes for 50 nm device fabrication

K. L. Lee, J. Bucchignano, J. Gelorme, and R. Viswanathan

J. Vac. Sci. Technol. B 15, 2621 (1997); http://dx.doi.org/10.1116/1.589696 (6 pages) | Cited 9 times

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A comparison between the conventional dip development process and resist development with ultrasonic agitation at 40 kHz has been conducted for the development of high-resolution resist nanostructures with dimension down to 50 nm. High-resolution commercially available ZEP520 positive electron resist and an in-house epoxy-based negative resist were used in the study. For large area exposure with ultrasonic agitation for resist development, improved resist sensitivity (≈4%) over a dip development process was observed for positive resist and no sensitivity improvement was seen with negative resist. There was also no observable improvement in the measured resist contrast for both positive and negative resist with and without ultrasonic agitation. For resist development in dense arrays or isolated nanostructures, ultrasonic agitation for positive and negative resist development offered faster development rate, more uniformity in resist development and a larger window for exposure dose variation in resist nanostructures. For negative resist, it was also observed that the descum rate with ultrasonic agitation was more than a factor of 3 faster than for dip development. Experiments on the relative merits of ultrasonic agitation for resist development with cavitation at 25 kHz and a narrowly focused acoustic beam at 400 kHz indicated that faster development rate and resist contrast were obtained with cavitation for the experimental conditions used. © 1997 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

Quarter-micron chemically amplified reaction image determination using arrested development

Steven J. Rhyner and James W. Taylor

J. Vac. Sci. Technol. B 15, 2627 (1997); http://dx.doi.org/10.1116/1.589697 (5 pages) | Cited 1 time

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An experimental technique is described to determine the reaction image in the negative-tone, chemically amplified resist, Shipley SAL 605, for a specific set of exposure and thermal processing conditions. Isolated 0.25-μm line formation at varying arrested development times is used in this study to assign an “effective” dose to locations within the resist through bulk dissolution rate data. This method was validated under different development conditions resulting in calculated and experimental line width agreement with an average deviation of 27 nm, and sidewall angle within 4° for developer puddle times between 20 and 113 s. End-on development provides unique access to determine chemically amplified reaction processing effects by diminishing the role of development. A comparison between the arrested development and end-on developed cross-sections indicates a strong development effect contributing to the sidewall angle at various puddle times. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Quantification of the extent of reaction in a negative, novolac-based, chemically amplified resist

Paul M. Dentinger and James W. Taylor

J. Vac. Sci. Technol. B 15, 2632 (1997); http://dx.doi.org/10.1116/1.589698 (7 pages) | Cited 7 times

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A technique for determining the extent of reaction and the molar absorptivity of the Fourier transform infrared (FTIR) peak created during the postexposure bake (PEB) reaction of the negative e-beam/x-ray Shipley resist, SAL 605, is described. Wafers were oven baked within a gas-tight bomb. The product of the linking reaction, methanol, was quantified from the gas in the bomb and within the resist film after the PEB. The ether peak, corresponding to the reaction between hexamethoxymethylmelamine (HMMM) and novolac was measured on the same wafer using FTIR. In addition, the absolute number of HMMM molecules reacted was measured by gel permeation chromatography to yield the number of moles methanol produced/HMMM reacted. The molar absorptivity for the ether peak, resulting from a reaction between an HMMM and a phenolic site on the novolac is 3.14±0.53×105 cm2/mole. Under conditions sufficient for imaging in a 0.5 μm thick film, the average number of reactions/HMMM molecule is 1.27±0.24. From previous work on the acid concentration in this resist [P. M. Dentinger, C. M. Nelson, S. J. Rhyner, J. W. Taylor, T. H. Fedynyshyn, and M. F. Cronin, J. Vac. Sci. Technol. B 14, 4239 (1996)] each acid moiety created was found to catalyze an average of 26±8 events during the PEB process. It appears that no more than 1.5%–2% of the available phenolic sites in the film need to be reacted for the required differential dissolution rate, and that the film does not crosslink. The ramifications of this work on modeling this type of resist will also be discussed. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Bg Chromatography

0.1 μm WSiN-gate fabrication of GaAs metal-semiconductor field effect transistors using electron cyclotron resonance ion stream etching with SF6–CF4–SiF4–O2

Yoshito Jin, Chiharu Takahashi, Kazumi Nishimura, Toshiro Ono, and Seitaro Matsuo

J. Vac. Sci. Technol. B 15, 2639 (1997); http://dx.doi.org/10.1116/1.589699 (4 pages) | Cited 4 times

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We investigate etching characteristics of WSiN gates using electron cyclotron resonance ion stream etching with a SF6–CF4–SiF4–O2 gas mixture, and we fabricate 0.1 μm WSiN gates for ultrahigh speed GaAs metal-semiconductor field effect transistors (MESFETs). A vertical WSiN gate etched pattern is obtained as a result of CF4 addition. Moreover, uniform etching over the entire wafer can be attained with high selectivity between the WSiN and the GaAs and with accurate control of the gate length. A current-gain cutoff frequency (fT) of 131.4 GHz with a 3σ value of 5.0 GHz in whole wafer has been obtained for 0.1 μm gate GaAs MESFETs. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Time dependence of etch-induced damage generated by an electron cyclotron resonance source

E. W. Berg and S. W. Pang

J. Vac. Sci. Technol. B 15, 2643 (1997); http://dx.doi.org/10.1116/1.589700 (5 pages) | Cited 4 times

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The effects of etch time on the damage induced during dry etching have been studied. GaAs- and InP-based materials were etched for different times in an electron cyclotron resonance source and the electrical and optical characteristics were measured. Variations in Schottky diode ideality factor (n) and barrier height (ϕb) were used to measure dry-etch-induced electrical damage at the surface of GaAs after different etch times. The contact resistance of In0.53Ga0.47As, extracted from transmission line measurements, was also investigated for different etch times and compared to the etch time dependence of GaAs. Capacitance–voltage (C–V) measurements from Schottky diodes and photoluminescence (PL) intensity from GaAs/Al0.30Ga0.70As multiple quantum well (MQW) structures were used to investigate the time dependence of the etch damage farther below the surface. The damage in GaAs as shown by n and ϕb shows marked deterioration after 10 s of etching but improves after longer etching. The contact resistance of In0.53Ga0.47As was found to increase fastest in the first 10 s, but the electrical characteristics did not improve with etch time as the GaAs did. There was no etch time dependence in the C–V measurements from the diodes or the PL spectra from the MQWs, indicating that variations in dry-etch-induced damage with etch time are mostly confined to the surface. Using wet chemical etching, the damage profile was investigated and the most damage was found within ∼15 nm from the surface for GaAs while In0.53Ga0.47As did not return to the original value after removing 20 nm of the surface. This indicates that the damage generation, removal, diffusion, and channeling mechanisms or rates may be different for the two materials. By changing the temperature of the stage during etching from −130 to 350 °C, the etch time dependence of the n and ϕb of GaAs was affected, indicating that diffusion of defects may be mainly responsible for the variations in electrical characteristics with etch time. © 1997 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.05.Ea III-V semiconductors

Characterization of the radiation-enhanced diffusion of dry-etch damage in n-GaAs

Ching-Hui Chen, Yi-Jen Chiu, and Evelyn L. Hu

J. Vac. Sci. Technol. B 15, 2648 (1997); http://dx.doi.org/10.1116/1.589701 (4 pages)

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Radiation-enhanced diffusion of dry-etch damage observed from experiments has been further characterized with Schottky diodes and deep level transient spectroscopy (DLTS) measurements. The use of DLTS spectra to monitor the effects of changes in ion dose rate and the application of laser radiation shows that the ion-induced defects having high diffusivities during ion-assisted processes are basically associated with the components of primary point defects, such as interstitials and vacancies. The properties of ion-induced traps obtained from DLTS measurements may provide us with some information to refine our model on the low-energy ion-induced damage. © 1997 American Vacuum Society.
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61.82.Fk Semiconductors
81.65.Cf Surface cleaning, etching, patterning
71.55.Eq III-V semiconductors
66.30.Lw Diffusion of other defects
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.05.Ea III-V semiconductors
61.72.J- Point defects and defect clusters
61.80.Jh Ion radiation effects
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
73.30.+y Surface double layers, Schottky barriers, and work functions

Ion induced damage in strained CdZnSe/ZnSe quantum well structures

L. M. Sparing, P. D. Wang, A. M. Mintairov, S. Lee, U. Bindley, C. H. Chen, S. S. Shi, J. K. Furdyna, J. L. Merz, and G. L. Snider

J. Vac. Sci. Technol. B 15, 2652 (1997); http://dx.doi.org/10.1116/1.589702 (4 pages) | Cited 1 time

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A study of the effects of reactive ion etching on molecular beam epitaxy grown (CdxZn1−xSe/ZnSe) strained quantum well (QW) samples using low temperature photoluminescence reveals a blue shift in the characteristic peak position of the 8 nm QW when exposed to plasmas of H2, D2, or He. Based on experimental results we suggest that this blue shift is a result of ion induced damage interacting with strain present in the as-grown QW. The QW is compressively strained at the interface with additional local strains in the QW lattice due to its random ternary alloy composition. The shallowest QW samples exhibit a peak in the blue shift as a function of bias voltage, with a reduced blue shift seen at high voltages. © 1997 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.05.Dz II-VI semiconductors

Low damage thermally assisted electron cyclotron resonance etch technology for wide bandgap II-VI materials

T. Kümmell, G. Bacher, A. Forchel, J. Nürnberger, W. Faschinger, G. Landwehr, B. Jobst, and D. Hommel

J. Vac. Sci. Technol. B 15, 2656 (1997); http://dx.doi.org/10.1116/1.589703 (5 pages) | Cited 4 times

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A flexible and low damage dry etch technology for the fabrication of ZnSe-based nanostructures is presented. Thermally assisted electron cyclotron resonance etching using gas mixtures of chlorine compounds and Ar and N2, respectively, combines plasma etching at low ion energies with process temperatures between 60 and 250 °C. With increasing process temperatures, rising etch rates and reduced surface roughness indicate a thermal activation of the etching process. The etch profile can be controlled by varying the plasma power causing a transition from partially physical to prevailing chemical etch properties. High quantum efficiencies in CdZnSe/ZnSe quantum wires with lateral sizes down to 20 nm were obtained, indicating a significantly reduced etch damage compared to conventionally dry etched II-VI nanostructures. The potential of the etch technology is demonstrated by realizing quantum wires with a blue shift of the photoluminescence signal (e.g., 8 meV for 20-nm-wide wires) caused by lateral carrier confinement effects. © 1997 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.05.Dz II-VI semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Hf II-VI semiconductors

High reflectivity micromirrors fabricated by coating high aspect ratio Si sidewalls

W. H. Juan, Y. H. Kao, and S. W. Pang

J. Vac. Sci. Technol. B 15, 2661 (1997); http://dx.doi.org/10.1116/1.589704 (5 pages) | Cited 2 times

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Micromachined Si vertical structures were sputter coated with Au onto sidewalls as reflective mirrors. These vertical micromirrors were integrated with comb drives as optical switching arrays. The micromirrors were first etched in a Cl2 plasma generated by an electron cyclotron resonance source, followed by a short B diffusion and a wet etch with ethylenediamine pyrocatechol to reduce sidewall roughness and to separate the mirrors from the substrate. The sputter-deposited Au films have nearly uniform thickness along the sidewalls of the micromirrors. There was only a 6% thickness variation from the top to the bottom of the mirror sidewalls. Reducing the sputtering pressure from 30 to 4 mTorr improved the coating uniformity for high aspect ratio, closely spaced mirrors. For 30-μm-tall micromirrors with 6 μm spacing, the Au thickness close to the bottom of the sidewalls decreased by 52% compared to the top of the sidewalls when sputtered at 4 mTorr. The roughness along the micromirror sidewalls was found to change from 7.7 to 16.1 nm as the pressure during sputtering was varied from 4 to 30 mTorr. The resultant reflectivity for these vertical micromirrors decreased from 85% to 70% at a wavelength of 1.55 μm. For high reflectivity micromirrors with smooth sidewalls and uniform thickness, sputter deposition of 400-nm-thick Au at 4 mTorr should be used. © 1997 American Vacuum Society.
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42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Wc Optical coatings
81.15.Cd Deposition by sputtering

Layer-by-layer sputtering of Si(111) and (001) surfaces mediated by surface vacancy diffusion: Surface physics and application for nanofabrication

Heiji Watanabe and Masakazu Ichikawa

J. Vac. Sci. Technol. B 15, 2666 (1997); http://dx.doi.org/10.1116/1.589705 (6 pages) | Cited 2 times

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Layer-by-layer sputtering of Si surfaces by low-energy Ar ions is studied by using scanning reflection electron microscopy. Two types of layer-by-layer etching (reversal of step-flow growth and two-dimensional vacancy-island nucleation) are observed. These results imply that vacancies created by ion impact can diffuse on the surface, and are annihilated at step edges. The diffusion length of vacancies are estimated from the denuded zone width of vacancy islands formed along steps by thermal heating after the vacancy introduction. The obtained activation energies of vacancy diffusion are 3.0±0.2 and 2.3±0.2 eV for Si(111) and (001) surfaces, respectively. We also propose an application of vacancy islands in nanofabrication, where vacancy islands are used as a self-organized template to provide nucleation sites of quantum dots. © 1997 American Vacuum Society.
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68.35.Fx Diffusion; interface formation
81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.35.Rh Phase transitions and critical phenomena
68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Role of defect diffusion in the InP damage profile

D. G. Yu, C.-H. Chen, A. L. Holmes, S. P. DenBaars, and E. L. Hu

J. Vac. Sci. Technol. B 15, 2672 (1997); http://dx.doi.org/10.1116/1.589706 (4 pages) | Cited 1 time

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Channeling of incident ions and radiation-enhanced diffusion of the ion-created defects have been shown to be major components of the ion damage profile. Our earlier results showed a deeper damage profile in InP, compared to GaAs, when subjected to the same ion bombardment conditions. Computer simulations demonstrated that this can partially be attributed to the greater ion channeling range in InP. In this article the role of defect diffusion in InP, through experiments coupled with simulations, is delineated. The multiple quantum well (MQW) probe technique is used to determine the amount of damage by measuring the change in low temperature photoluminescence of quantum wells before and after argon ion bombardment. A blocking superlattice is added to the MQW heterostructure and is proven effective in preventing damage from propagating into the material below it. By correlating the experimental results with computer modeling, an estimate of the defect diffusion constant is obtained and it is found to be in the range of 4×10−15–1×10−14 cm2/s. These high values for diffusion are justified with experimental results that illustrate the presence of radiation-enhanced diffusion mechanisms during ion bombardment. © 1997 American Vacuum Society.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
66.30.Lw Diffusion of other defects
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Interactive effects in reactive ion etching of W1−xGex

E. van der Drift, B. Q. Dinh, P. A. Verhoeven, E. J. M. Fakkeldij, M. R. Zuiddam, and T. Zijlstra

J. Vac. Sci. Technol. B 15, 2676 (1997); http://dx.doi.org/10.1116/1.589707 (6 pages) | Cited 1 time

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Reactive ion etching characteristics of chemical vapor deposition-deposited W1−xGex alloys in Cl2, SF6, and SF6/O2/He plasmas were investigated. The interactive role of the germanium component in the overall etch process was unraveled. To this aim etch rates were studied as a function of the Ge content and at different temperatures. Etched profiles give useful additional information about the nature of the etch mechanism. The underlying surface reactions were more quantitatively identified by x-ray photoelectron spectroscopy on dry etched surfaces. © 1997 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Deposition of silicon nitride by low-pressure electron cyclotron resonance plasma enhanced chemical vapor deposition in N2/Ar/SiH4

S. A. Moshkalyov, J. A. Diniz, J. W. Swart, P. J. Tatsch, and M. Machida

J. Vac. Sci. Technol. B 15, 2682 (1997); http://dx.doi.org/10.1116/1.589708 (6 pages) | Cited 8 times

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Plasma deposition of silicon nitride on silicon substrates in a microwave electron cyclotron resonance N2/Ar/SiH4 discharge was studied as a function of gas pressure (1–5 mTorr), gas composition, and discharge power (250–1000 W). The dependencies of deposition parameters on discharge characteristics obtained at 1 mTorr appear to be essentially different from those at higher pressures. Optical emission spectroscopy was used for plasma characterization. A high degree of ionization and dissociation of gas molecules was observed under present plasma conditions. It is shown that the contribution of ionized species to film deposition is comparable with that of neutral ones under high power and low pressure conditions. The best quality of films was obtained at a moderate rather than the highest available dissociation degree of silane. © 1997 American Vacuum Society.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
85.40.Sz Deposition technology
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Protective film by magnetic plasma polymerization on a Y–Ba–Cu–O superconductor

Jin Xinyu, Zhang Yu, Wang Rui, Chen Kangsheng, and Liang Suzhen

J. Vac. Sci. Technol. B 15, 2688 (1997); http://dx.doi.org/10.1116/1.589709 (4 pages)

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A new method of deposition of an organosilicon thin film by magnetic-controlling plasma polymerization has been successfully used to protect a YBa2Cu3O7−δ (YBCO) superconductor from corrosion. The organosilicon (hexamethyldisilane-HMDS) protective film obtained is homogeneous, compact, pinhole free, and highly crosslinked. The deposition rate of the polymer film increases rapidly first and then decreases, as radio frequency input power and HMDS monomer pressure increase, respectively. The deposition rate of a plasma polymer film with magnetic controlling is 20 times higher than that without magnetic controlling. The YBCO superconductor covered with an organosilicon film by magnetic-controlling plasma polymerization has been protected from corrosion in water over 48 h. © 1997 American Vacuum Society.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Kn Corrosion protection
74.72.-h Cuprate superconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
82.35.-x Polymers: properties; reactions; polymerization

Electron and ion optical design software for integrated circuit manufacturing equipment

Eric Munro

J. Vac. Sci. Technol. B 15, 2692 (1997); http://dx.doi.org/10.1116/1.589710 (10 pages) | Cited 4 times

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This article describes methods for the computer aided design of electron and ion beam columns for the integrated circuit (IC) manufacturing industry. The techniques described include computation of field distributions in electron lenses and deflectors, electron trajectories and aberrations, dynamic corrections, effects of discrete Coulomb interactions, design of electron guns, treatment of diffraction effects, optimization, and tolerancing of complete columns. These techniques are illustrated with examples relevant to the IC manufacturing industry, including systems for high-throughput electron beam lithography, nanolithography systems, and electron beam systems for inspection, metrology, and voltage testing. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.05.Tp Computer modeling and simulation
41.85.-p Beam optics
06.60.Mr Testing and inspecting procedures
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Compact electrostatic lithography column for nanoscale exposure

Tom Chisholm, Haoning Liu, Eric Munro, John Rouse, and Xieqing Zhu

J. Vac. Sci. Technol. B 15, 2702 (1997); http://dx.doi.org/10.1116/1.589711 (5 pages) | Cited 2 times

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This article introduces an all-electrostatic electron-beam column which uses conventional electrode assemblies, resulting in a system which is very much smaller than a magnetic lens column. Computer modeling of the electron-optical performance of the column has shown that the concept has promise as a lithography tool. Beam broadening due to electron–electron interactions and aberrations of the final accelerating lens are both small enough to give a resolution which matches that of present-day magnetic columns. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.85.Ne Electrostatic lenses, septa
41.85.Gy Chromatic and geometrical aberrations

Semiconductor on glass photocathodes for high throughput maskless electron beam lithography

A. W. Baum, J. E. Schneider, R. F. W. Pease, M. A. McCord, W. E. Spicer, K. A. Costello, and V. W. Aebi

J. Vac. Sci. Technol. B 15, 2707 (1997); http://dx.doi.org/10.1116/1.589712 (6 pages) | Cited 9 times

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Previous results obtained from negative electron affinity (NEA) photocathodes have shown high brightness (1×108 A/cm2sr at 3 kV), energy spreads as low as 50 meV at room temperature, uniform sensitivity to red and infrared light over cm2 areas, picosecond-scale switching, and low emission noise. These properties make possible a number of new electron beam tools, including a high-throughput multibeam maskless wafer exposure tool. Simulations show that up to 10 μA of current at 50 kV can be delivered to the wafer in such a system with a total spot diameter of 70 nm. The main obstacle to the use of NEA photocathodes in lithography instruments is the issue of cathode stability and lifetime. An ultrahigh system vacuum was built to activate and evaluate NEA photocathodes in a demountable system that includes areas with poorer vacuum. In this system a low quantum efficiency photocathode (<0.1%) was maintained at constant emission up to 190 nA with no discernible decay. A higher-efficiency cathode provided a brightness estimated at 2.2×107 A/cm2sr at 5 kV. Lifetime measurements on this cathode showed no measurable effect from resist exposure, and stable emission of 375 nA for 15 h, followed by a steady decay of ∼1.5%/h with no re-cesiation. Higher current results (3.75–1.3 μA) show a decay rate of ∼6%/h without re-cesiation. The use of cesium in a feedback loop was shown as an effective way to stabilize emission. Furthermore, the decay is limited to an area 2.6 mm in diameter, as the rest of the cathode is shielded by nonevaporable getter material. This result indicates that the source lifetime can be extended hundreds of times by simply moving the cathode to expose a fresh area. A moveable NEA photocathode in combination with a cesium source in a feedback loop promises to be a highly reliable, long-lifetime electron source. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.60.Ha Photomultipliers; phototubes and photocathodes

Micromachined single-crystal silicon electron lenses

Wolfgang Hofmann and Noel C. MacDonald

J. Vac. Sci. Technol. B 15, 2713 (1997); http://dx.doi.org/10.1116/1.589713 (5 pages) | Cited 3 times

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We report on the design, simulation, and fabrication of micromachined single-crystal silicon electrostatic lenses and lens arrays. The lenses consist of two or three high-aspect-ratio silicon tubes, which are fabricated from a single silicon substrate using a self-aligned process. The tubes are isolated from each other and the substrate by long (>20 μm) thermal silicon oxide spacers. Single microlenses, multipole lens elements, and microlens arrays have been fabricated with tube diameters ranging from 5 to 50 μm and lengths from 5 to 240 μm. After a brief review of scaling considerations for electron microsource and microlenses, a detailed description of the fabrication process is presented. This process is also applicable to a wide variety of other multiple level (array) structures. The electron-optical properties of the microlenses are discussed. Numerical simulation results are used to predict the spherical and chromatic aberration coefficients and to investigate the effects of mechanical tolerances (misalignment, tilt, ellipticity). © 1997 American Vacuum Society.
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41.85.Ne Electrostatic lenses, septa
41.85.Gy Chromatic and geometrical aberrations
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Filter design methodology for defect detection in wafer inspection

Robert J. Socha and Andrew R. Neureuther

J. Vac. Sci. Technol. B 15, 2718 (1997); http://dx.doi.org/10.1116/1.589714 (7 pages) | Cited 2 times

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A methodology for the design of a filter to image the bottom of a contact is developed through simulation. Without a filter, the topography of the hole causes normally incident light to refract out of the hole. By conditioning the light with a filter, however, light is launched into the hole that is capable of propagating down the hole and imaging the bottom. When using this filter, the reflected aerial image differs by as much as 10% when the contact hole is under etched by 0.05 μm. Although, this initial success shows that the filter is capable of imaging the bottom of the hole, the introduction of process variations such as a larger hole diameter or a thinner oxide cause large deviations in the aerial image. © 1997 American Vacuum Society.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis
85.40.Hp Lithography, masks and pattern transfer
42.79.Ci Filters, zone plates, and polarizers

Electrostatic deflection aberrations revisited: Solution proposed to an old problem

Michael Retsky

J. Vac. Sci. Technol. B 15, 2725 (1997); http://dx.doi.org/10.1116/1.589715 (4 pages) | Cited 1 time

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The deflection of charged particle beams into large angles is more often done with magnetic fields than with electric fields. One reason is that magnetic deflection aberrations are two to three times lower than electrostatic deflection aberrations. Electrostatic deflection aberrations have been re-examined in an attempt to design a 4 k by 5 k pixel cathode ray tube display suitable for digital mammography workstations. Using a novel ray trace program, it has been determined that electrostatic deflection aberrations can be reduced ten-fold by injecting the electron beam at an optimized offset position into a conventional deflection plate assembly. The surprising result is that the “sweet spot” is not near the center where it would be expected based upon looking at the fringe fields. The optimum injection position is offset almost halfway towards the attracting plate. This result has been confirmed in one test configuration. While the mammography application provided the initial motivation to reduce deflection aberrations, the technology may be useful in electron or ion beam lithography, especially so since the design readily accommodates four discrete beams. © 1997 American Vacuum Society.
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41.85.Gy Chromatic and geometrical aberrations
87.59.E- Mammography
07.07.Hj Display and recording equipment, oscilloscopes, TV cameras, etc.

Micro-extraction spectrometer structures for voltage contrast in the scanning electron microscope

A. R. Dinnis

J. Vac. Sci. Technol. B 15, 2729 (1997); http://dx.doi.org/10.1116/1.589716 (3 pages)

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This work aims at the achievement of efficient extraction of secondary electrons from the surface of the specimen, with the least possible corruption of the information which they contain. The method adopted is to use a system of microelectrodes very close to the conductor under investigation to extract the electrons and to act as a retarding-field spectrometer system. In the present case, the first extraction electrode structure was added to the integrated circuit specimen at an appropriate point by the use of focused ion beam technology. © 1997 American Vacuum Society.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.81.+a Electron and ion spectrometers

Spherical aberration corrector using space charge

L. C. Chao, J. Orloff, and Li Wang

J. Vac. Sci. Technol. B 15, 2732 (1997); http://dx.doi.org/10.1116/1.589717 (5 pages) | Cited 1 time

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We have investigated the use of space charge for the correction of spherical aberration in focused ion beam systems. A negative space charge cloud can be formed to reduce the spherical aberration of a lens for ions or for electrons, depending on the details of the space charge distribution. Spherical aberration is important in focused ion beam applications where large aperture angles are needed to obtain high beam currents used for milling or deposition, because it results in large tails on the current density distribution. A space charge distribution (cloud) can be produced with a small electron gun inside an electrostatic lens that can reduce this problem. We report on the properties of one such design. © 1997 American Vacuum Society.
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41.85.Gy Chromatic and geometrical aberrations
41.85.Ne Electrostatic lenses, septa

Novel objective lens for low voltage electron beam imaging

W. Liu, M. McCord, and R. F. Pease

J. Vac. Sci. Technol. B 15, 2737 (1997); http://dx.doi.org/10.1116/1.589718 (5 pages) | Cited 1 time

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Low energy electron beams are increasingly being used in semiconductor manufacturing for wafer and mask inspection because of their low level of damage to the sample, and the reduced charging effects when the electron energy is close to EII where secondary electron yield is unity. Also due to the short range of the electrons with the sample and the reduced proximity effect, electron beams with even lower energies are attractive for a variety of other applications such as surface studies, thin film microscopy, and lithography. However, achieving high resolution and high secondary electron detection efficiency at 100 eV landing energy and below meets serious electron optical challenges. To address this issue, we describe a low aberration objective lens that is combined with an efficient secondary electron detector. The objective lens has a final electrode just in front of the sample to minimize the electric field at the sample surface. We have optimized the design for minimum beam diameter and high secondary electron collection efficiency, subject to constraints imposed by practical concerns, such as arcing. The lens was fabricated using a combination of conventional machining and silicon micromachining. By inserting the lens into the sample chamber of a traditional scanning electron microscope (SEM), we obtained images of many kinds of samples at landing energies as low as 20 eV. Resolution of better than 30 nm is achieved at 100 eV landing energy. The degradation from the expected resolution (17 nm) is in part due to limitations imposed by the SEM resulting in a nonoptimal convergence angle. At these very low energies the image is seen to be very sensitive to contamination on the sample surface; this illustrates its possible application for viewing ultrathin films. We have calibrated the magnification versus landing energy relationship for the lens and carried out detailed signal and noise analyses for the electronics system. © 1997 American Vacuum Society.
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41.85.Ne Electrostatic lenses, septa
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.77.Ka Charged-particle beam sources and detectors
85.40.Hp Lithography, masks and pattern transfer

Miniature electron beam column with a silicon micro field emitter

Ichiro Honjo, Yasuhiro Endo, and Shunji Goto

J. Vac. Sci. Technol. B 15, 2742 (1997); http://dx.doi.org/10.1116/1.589719 (7 pages) | Cited 6 times

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Silicon micro field emitters (Si-MFEs) are expected to be promising as electron sources for their high brightness and ease in making arrayed microcolumns due to small physical size. We have developed a Si-MFE electron gun assembly that produces an electron beam of 1 keV. All components including the Si acceleration electrode are mounted on an integrated circuit (IC) package stem (TO-8) by anodic and eutectic bonding. A high brightness (75 μA/sr) and a long lifetime (>1000 h) have been observed. To overcome the intrinsic emission instability of Si-MFEs, we developed a simple feedback circuit which controls an extraction voltage. The source position shift and the aberration coefficient change caused by stabilization were evaluated analytically and found to be negligible due to the scaling law as applied to micron size. We confirmed that the total emission fluctuation could be stabilized to less than 1% by detecting the absorption current but also found that this detection should be done in the electron beam column to stabilize the probe current due to the instability of the emission angle. Using the Si-MFE electron gun along with a miniature electron beam column 5 cm in length, we evaluated the electron optical properties and succeeded in demonstrating a scanning electron microscope operation with a resolution less than 0.5 μm. © 1997 American Vacuum Society.
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41.75.Fr Electron and positron beams
85.45.Db Field emitters and arrays, cold electron emitters
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Fabrication of multiple microcolumn array combined with field emission array

Jeong-Young Park, Jared D. Lera, M. A. Yakshin, S. S. Choi, Y. Lee, K. J. Chun, J. D. Lee, D. Jeon, and Young Kuk

J. Vac. Sci. Technol. B 15, 2749 (1997); http://dx.doi.org/10.1116/1.589720 (5 pages) | Cited 7 times

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We made a multiple electron microcolumn array. The electron source was made of either a Si based field emission array or a nickel coated array to keep the distances among sources equal. Laser micromachining was used to obtain a self-aligned microcolumn with five lenses: an extractor, an accelerator, and an Einzel lens. The aberration of each column was greatly improved compared to anodically bonded Si lens microcolumns. The field emission electron beam pattern was obtained from a multiple microcolumn. Its I–V dependence and possible application to the electron beam lithography with high throughput is discussed. © 1997 American Vacuum Society.
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85.45.Db Field emitters and arrays, cold electron emitters
85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams
07.77.Ka Charged-particle beam sources and detectors
81.20.Wk Machining, milling
42.62.Cf Industrial applications

Optimization of field-emission columns for next-generation MEBES® systems

H. Pearce-Percy, F. Abboud, R. Garcia, and M. Mankos

J. Vac. Sci. Technol. B 15, 2754 (1997); http://dx.doi.org/10.1116/1.589721 (6 pages) | Cited 1 time

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To support device generations below 250 nm mask writing systems must improve productivity for smaller design address grids and simultaneously provide higher dose to support high resolution processes. Combining multipass writing techniques with higher pixel rate provides improved productivity and increased dose; however, many high resolution processes require even higher dose delivery. The optimization of field-emission systems for maximum effective brightness has been discussed previously, but the inclusion of electron-electron (e-e) interactions in the optimization process is a significant complication. There is little discussion in the general literature, except for Brodie and Meisburger [A. D. Brodie and W. D. Meisburger, Microelectron. Eng. 17, 399 (1992)] about the impact of e-e interactions on the design of columns for electron-beam lithography systems. This article discusses several formulations of the problem and the solutions. Closed-form solutions for particular special cases (spherical- and chromatic-aberration limited systems) have been derived using the computer algebra code Mathematica and will be presented. The design of an improved field-emission gun and column is described, based on these general considerations, and on an acceleration-mode gun lens with particularly low chromatic aberration. Several improvements in the column design are discussed. These include optimization of the gun and the column for highest dose (800 A/cm2) without increasing the beam energy of 10 keV. Although the transmission-line beam blanker design in the current MEBES column is sufficient for higher pixel rate requirements, the blanker driver rise and fall times need improvement. Early results from the new driver have been described previously [A. Muray, D. Colby, R. Teitzel, and M. Gesley, J. Vac. Sci. Technol. B 13, 2488 (1995)]. Later improvements and experimental results are discussed, including 250 ps rise and fall times and leading as well as trailing edge TAP settings. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams
41.85.Gy Chromatic and geometrical aberrations

Fabrication of nanoelectromechanical systems in single crystal silicon using silicon on insulator substrates and electron beam lithography

D. W. Carr and H. G. Craighead

J. Vac. Sci. Technol. B 15, 2760 (1997); http://dx.doi.org/10.1116/1.589722 (4 pages) | Cited 57 times

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We have demonstrated a process for fabricating nanometer-scale electromechanical structures of diverse geometries in single crystal silicon, using silicon on insulator substrates. We pattern the substrate using high resolution electron beam lithography with 100 keV electrons followed by Al evaporation and liftoff. The Al is used as an etch mask in CF4 reactive ion etching to pattern the top silicon layer. We then undercut structures using a buffered oxide etch. The structures were made from substrates having a top silicon thickness of 200 or 50 nm, and a buried oxide thickness of 400 nm. With this process we have made a variety of movable structures. We describe the performance of an electrostatically driven Fabry–Perot interferometer that consists of a μm sized pad suspended by wires that are 100–200 nm wide. We have also made much smaller mechanical structures such as suspended silicon beams as narrow as 30 nm. © 1997 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.10.Cm Micromechanical devices and systems
85.40.Hp Lithography, masks and pattern transfer
07.60.Ly Interferometers

New fabrication techniques for high quality photonic crystals

Chuan C. Cheng, Axel Scherer, Rong-Chung Tyan, Yeshayahu Fainman, George Witzgall, and Eli Yablonovitch

J. Vac. Sci. Technol. B 15, 2764 (1997); http://dx.doi.org/10.1116/1.589723 (4 pages) | Cited 37 times

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We have developed new methods for the fabrication of high quality two-dimensional (2D) and three-dimensional (3D) photonic crystals. These techniques involve anisotropic etching and steam oxidation of AlAs mask layers. We have made manufacturable 2D photonic crystals with high aspect ratios for use as micropolarizers and have measured extinction ratios larger than 800 to 1 between TE and TM modes transmitted through these structures. The new Al2O3 mask fabrication technique also allows us to fabricate 3D structures with up to six repeating layers in depth and over 90% attenuation in the band gap region. Here, we show the fabrication details and performance of 2D and 3D photonic crystals. © 1997 American Vacuum Society.
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42.70.Qs Photonic bandgap materials
42.86.+b Optical workshop techniques
42.79.Ci Filters, zone plates, and polarizers

Surface micromachined membranes for tunnel transducers

Joyce Wong, Axel Scherer, and Thomas George

J. Vac. Sci. Technol. B 15, 2768 (1997); http://dx.doi.org/10.1116/1.589724 (5 pages)

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We have developed low-temperature surface micromachining procedures for the fabrication of suspended SiO2/Si3N4 membranes. This fabrication method was integrated with electron beam lithography, anisotropic ion etching, and electroplating to construct electrostatically deflectable tunnel transducers. We show the structures and some preliminary measurements on the performance of these monolithic devices. © 1997 American Vacuum Society.
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07.07.Mp Transducers
07.10.Cm Micromechanical devices and systems
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)

Fabrication and behavior of nanoscale field emission structures

A. A. G. Driskill-Smith, D. G. Hasko, and H. Ahmed

J. Vac. Sci. Technol. B 15, 2773 (1997); http://dx.doi.org/10.1116/1.589725 (4 pages) | Cited 4 times

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Novel field emission devices with dimensions an order of magnitude less than the elastic mean free path of electrons in air have been fabricated and tested at atmospheric pressure. It is well known that the operating voltage of field emission devices may be decreased by reducing the radius of the emitter tip and the distance between the emitter tip and extractor electrode. We have developed and tested a nanoscale-tip field emission system consisting of multiple emitter tips with radii of about 1 nm within an extractor aperture 50 nm in diameter. All nanopillar tips were less than 30 nm from the extractor electrode in both the horizontal and vertical directions, so field-emitted electrons traveled ballistically from the nanopillar tips to the extractor electrode even at atmospheric pressure. The extractor turn-on voltage was approximately 7 V; field-emitted currents of about 10 nA were collected typically at an extractor voltage of 9 V. © 1997 American Vacuum Society.
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85.45.Db Field emitters and arrays, cold electron emitters
85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Field emission from gated Si emitter tips with precise gate–tip spacing, gate diameter, tip sharpness, and tip protrusion

M. R. Rakhshandehroo and S. W. Pang

J. Vac. Sci. Technol. B 15, 2777 (1997); http://dx.doi.org/10.1116/1.589726 (5 pages) | Cited 3 times

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A self-aligned process was developed to control the gate–tip spacing, gate diameter, tip sharpness, and tip protrusion of Si field emission devices (FEDs). Such control is needed for the fabrication of FEDs with low turn-on voltage and high emission current. Using the mask erosion technique, 2-μm-tall Si emitter tips were initially etched in a Cl2 plasma generated by an electron cyclotron resonance source. Plasma oxides with different thicknesses were grown on the Si emitters as a sacrificial layer which creates close spacing between gate and tips, as well as sharpens the tip when removed in wet etchant. Sharp emitters with 8 nm tip radius and 80 nm gate–tip spacing were formed using plasma oxidation. Polyimide was used as the insulator and Mo was sputtered to form the self-aligned gate. By changing the polyimide thickness, gate diameter ranging from 220 to 880 nm and tip apex position ranging from 320 nm below the gate (nonprotruding) to 930 nm above the gate (protruding) were demonstrated. Emission current from an array of 100 tips increased from 261 to 598 μA when the tips radii were decreased from 67 to 8 nm by sharpening. By decreasing the gate–tip spacing from 500 to 193 nm, the gate turn-on voltage was reduced from 91 to 38 V. In addition, highest emission current was found to occur when the tip apex was positioned 70 nm above the gate level. © 1997 American Vacuum Society.
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85.45.Db Field emitters and arrays, cold electron emitters
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation

Field emission displays based on linear horizontal field emission cathodes

Huei Pei Kuo, S. F. Burriesci, J. Lin, and D. J. Miller

J. Vac. Sci. Technol. B 15, 2782 (1997); http://dx.doi.org/10.1116/1.589727 (4 pages) | Cited 3 times

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We have developed a linear horizontal wedge field emission cathode for field emission displays. The cathode consists of a horizontal wedge with a diameter of curvature ∼10 nm. A self-aligned sloping gate is positioned at a distance of ∼10 nm above the wedge. Computer simulation shows that the wedge cathode can operate at a gate voltage of ⩽15 V to allow the use of complementary metal–oxide semiconductor drivers to modulate the electron emission. Coplanar focusing electrodes are incorporated without additional processing steps to collimate the electron beam to a dimension of ∼50 μm onto a high voltage phosphor screen ∼1 mm away. We have fabricated wedge cathodes operating at a gate voltage of ∼60 V with a relatively uniform emission from an area of ∼5 mm×5 mm. The wedge cathode was developed to be fabricated with mainstream large-area equipment for flat panel displays. © 1997 American Vacuum Society.
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85.45.Fd Field emission displays (FEDs)
07.07.Hj Display and recording equipment, oscilloscopes, TV cameras, etc.
85.45.Bz Vacuum microelectronic device characterization, design, and modeling

Optical manipulation of a lasing microparticle and its application to near-field microspectroscopy

Keiji Sasaki, Hideki Fujiwara, and Hiroshi Masuhara

J. Vac. Sci. Technol. B 15, 2786 (1997); http://dx.doi.org/10.1116/1.589728 (5 pages) | Cited 10 times

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A novel probe of a near-field scanning optical microscope (NSOM) is proposed. The probe is composed of a micrometer-sized spherical particle doped with laser dye, that acts as an optical cavity for lasing, and of a nanometer-sized particle attached to the microsphere. The high-intensity evanescent field is generated just outside of the lasing microsphere and scattered with the nm particle, which forms a minute light source for NSOM. Three-dimensional positioning control of the probe is performed with the accuracy of <10 nm by a laser manipulation technique. Photon tunneling from the lasing microsphere to an object was demonstrated as a drastic change of an emission spectrum depending on the microsphere-object distance. The lasing microspherical probe has the advantage of high sensitivity due to intracavity enhancement of the tunneling loss. © 1997 American Vacuum Society.
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07.79.Fc Near-field scanning optical microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.62.Fi Laser spectroscopy
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
37.10.Mn Slowing and cooling of molecules
37.10.Pq Trapping of molecules
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Wire-channel and wrap-around-gate metal–oxide–semiconductor field-effect transistors with a significant reduction of short channel effects

Effendi Leobandung, Jian Gu, Lingjie Guo, and Stephen Y. Chou

J. Vac. Sci. Technol. B 15, 2791 (1997); http://dx.doi.org/10.1116/1.589729 (4 pages) | Cited 14 times

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Metal–oxide–semiconductor field-effect transistors (MOSFETs) with a wire-channel and wrap-around-gate (WW) structure were fabricated using electron beam lithography and reactive ion etching. The smallest devices have a 35 nm channel width, a 50 nm channel thickness, and a 70 nm channel length. Measurements showed that as the channel width of WW MOSFETs decreased from 75 to 35 nm short channel effects were significantly reduced: the subthreshold slope decreased from 356 to 80 mV/dec and the drain-induced barrier lowering decreased from 988 to 129 mV. Furthermore, the reduction of channel width increases the drive current per unit channel width. A multichannel WW MOSFET with a high current driving capability is discussed. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices

New complimentary metal–oxide semiconductor technology with self-aligned Schottky source/drain and low-resistance T gates

S. A. Rishton, K. Ismail, J. O. Chu, K. K. Chan, and K. Y. Lee

J. Vac. Sci. Technol. B 15, 2795 (1997); http://dx.doi.org/10.1116/1.589730 (4 pages) | Cited 9 times

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A new experimental complimentary metal–oxide semiconductor (CMOS) technology is presented, fabricated with Schottky source and drain and a T-shaped gate. The process results in a significant reduction in the number of steps required to fabricate CMOS, and no longer relies on implantation of the source and drain. The gate resistance and the source/drain contact resistance are very low compared to conventional designs. Performance of 0.25 and 0.15 μm channel length devices has been measured and the technology is readily scalable to sub-0.1 μm dimensions. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices

Gate technology for 70 nm metal–oxide–semiconductor field-effect transistors with ultrathin (<2 nm) oxides

D. Tennant, F. Klemens, T. Sorsch, F. Baumann, G. Timp, N. Layadi, A. Kornblit, B. J. Sapjeta, J. Rosamilia, T. Boone, B. Weir, and P. Silverman

J. Vac. Sci. Technol. B 15, 2799 (1997); http://dx.doi.org/10.1116/1.589731 (7 pages) | Cited 6 times

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Results are described for a gate level technology module developed to produce metal–oxide–semiconductor transistors with physical gate lengths of 70 nm and below. Lithography is performed by direct write e-beam lithography (EBL) using a thermal field-emission EBL system in SAL 601 resist. Critical dimension (CD) control, as measured by several methods, is found to depend not only on dose control but also on writing parameters such as pixel spacing. The pattern transfer using a silicon dioxide hard mask is shown to exhibit a trade-off between anisotropy and selectivity. Transmission electron microscopy cross sections reveal that two atomic layers are removed even when the gate oxide stopping layer is completely intact. We report results for gate lengths down to 60 nm with edge roughness on the order of 5 nm, within the acceptable limits for threshold requirements, while stopping the etch process on oxides as thin as 1.2 nm. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Fabrication of 30 nm gate length electrically variable shallow-junction metal–oxide–semiconductor field-effect transistors using a calixarene resist

T. Sakamoto, H. Kawaura, T. Baba, J. Fujita, and Y. Ochiai

J. Vac. Sci. Technol. B 15, 2806 (1997); http://dx.doi.org/10.1116/1.589732 (3 pages) | Cited 6 times

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We have fabricated electrically variable shallow-junction metal–oxide–semiconductor field-effect transistors (EJ-MOSFETs) with an ultrafine gate for the first time. The gate length was reduced to 32 nm by using electron-beam lithography with a calixarene resist, which has an under 10 nm resolution with a sharp pattern edge. Moreover, normal transistor operation of 32 nm gate-length EJ-MOSFETs was confirmed. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Lateral tunnel junction produced by electron-beam-induced deposition

Masanori Komuro and Hiroshi Hiroshima

J. Vac. Sci. Technol. B 15, 2809 (1997); http://dx.doi.org/10.1116/1.589733 (7 pages) | Cited 4 times

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Electron-beam-induced deposition using a WF6 precursor molecule was applied to making metal/insulator/metal tunnel junctions for single-electron transport devices. Single wires 8 nm high and about 13 nm wide were produced on a SiO2 substrate with Au/Cr electrode pads and their conductance showed a rapid increase of about five orders of magnitude as electron-beam (EB) doses increased between 5 and 15 pC shot. To estimate the deposit thickness distribution, spatial thickness distribution in spot exposure was defined and obtained for specified EB doses. From this function, a single-wire resistivity at 230 and 300 K was determined to be 6×10−4 Ω cm at doses exceeding 15 pC/shot. Single-tunnel junctions, where space with a 2.5 nm increment was at the center of single wire, were produced. The electrical characteristics of these single junctions were fitted to a Fowler–Nordheim plot the absolute value of whose gradient gradually increased with increasing space width. The barrier height of this junction was estimated to be 0.17–0.2 eV, lower than that for SiO2/W junctions. This might be caused by the change from the metallic deposit to the insulator for the single wire as a function of the EB dose. This deposition technique enabled us to fabricate a transistor structure where dots were located in space and a side gate electrode was also deposited. The structure showed Coulomb oscillation even at 230 K and Monte Carlo simulation of this device showed reasonable agreement with the experiment, assuming appropriate circuit parameters of gate capacitance and tunnel resistance. © 1997 American Vacuum Society.
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73.40.Rw Metal-insulator-metal structures
73.40.Gk Tunneling
81.15.Jj Ion and electron beam-assisted deposition; ion plating
85.35.Gv Single electron devices

Self-aligned subchannel implant complementary metal–oxide semiconductor devices fabrication

W. Wang, C. Chang, D. Ma, M. Peckerar, I. Berry, N. Goldsman, and J. Melngailis

J. Vac. Sci. Technol. B 15, 2816 (1997); http://dx.doi.org/10.1116/1.589734 (5 pages) | Cited 1 time

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High-speed and low-power complementary metal–oxide semiconductor devices with subchannel implants have been proposed and demonstrated recently. In subchannel implant devices, the alignment of the gate and the buried implant region is a critical issue. In this article, a fully self-aligned gate and subchannel implant fabrication method is proposed using either focused-ion-beam or conventional ion implantation. This method defines the gate and produces the subchannel implant in the same step. By doing this, the buried implant region and gate are automatically aligned. By exposing the resist with a B+ ion beam, we verified that the dose needed to produce the subchannel implant matches the dose needed to expose the resist (1013 ion/cm2). We have simulated the implant profile and the expected device performance. The subthreshold current was found to be decreased by 1–2 orders of magnitude. Since the process requires implantation through the gate oxide, capacitors were built over the gate oxide for C–V measurement and implanted over a range of doses. Proper postimplantation treatment has been developed to prevent increasing of the interface state density. © 1997 American Vacuum Society.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology

Fabrication and transport study of finite lateral superlattices

M. Hannan, R. Grundbacher, P. Fay, I. Adesida, R. W. Giannetta, C. J. Wagner, and M. R. Melloch

J. Vac. Sci. Technol. B 15, 2821 (1997); http://dx.doi.org/10.1116/1.589735 (4 pages)

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Transport measurements are reported for a two-dimensional electron gas subject to a finite lateral superlattice potential. Devices are fabricated in high mobility GaAs/AlGaAs heterostructures with modulation periods in the range of 2000–3000 Å and differing numbers of gates. Conductance plateaus are observed at gate voltages where the thermopower is stationary. These features indicate the possible formation of effective one-dimensional conductance channels through the potential landscape formed by the lateral gates. The plateau conductances are much less than the basic quantum unit (2e2/h). © 1997 American Vacuum Society.
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73.61.Ey III-V semiconductors
73.50.Lw Thermoelectric effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Fabrication of planar silicon nanowires on silicon-on-insulator using stress limited oxidation

Jakub Kedzierski, Jeffrey Bokor, and Christian Kisielowski

J. Vac. Sci. Technol. B 15, 2825 (1997); http://dx.doi.org/10.1116/1.589736 (4 pages) | Cited 33 times

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A new method is proposed for the fabrication of planar single crystal silicon nanowires down to 8 nm in diameter. In this method silicon lines are defined on silicon-on-insulator with electron beam lithography followed by a metal liftoff process and a silicon plasma etch. Low temperature oxidation is then used to shrink these lines to a sub-10 nm diameter. Normal stress generated by the expansion of the viscous oxide during oxidation eventually stops the reaction, leaving a small silicon core at the center of the line. The effect of the crystallographic orientation of the line and the stress complications caused by the substrate are investigated. © 1997 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.Mq Oxidation
85.40.Hp Lithography, masks and pattern transfer
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Cy Elemental semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Low voltage electron-beam lithography based InGaAs/GaAs quantum dot arrays with 1 meV luminescence linewidths

K. H. Wang, A. Pecher, E. Höfling, and A. Forchel

J. Vac. Sci. Technol. B 15, 2829 (1997); http://dx.doi.org/10.1116/1.589737 (3 pages) | Cited 6 times

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We have developed InGaAs/GaAs quantum dots with diameters down to about 50 nm on shallow quantum wells using low voltage electron-beam lithography and wet chemical etching. Due to the low energy of the e-beam of 2.5 keV the proximity effect is negligible and arrays of quantum dots with a homogeneous diameter could be fabricated. By using low excitation photoluminescence spectroscopy we observe a clear shift of the dot emission to higher energy due to lateral quantization that amounts to 6 meV in the smallest structures. The linewidth of the luminescence of the dot arrays of about 1.5 meV is almost independent of the dot size, i.e., the inhomogeneous broadening due to the patterning induced lateral size fluctuation is found to be negligible in the present structures. © 1997 American Vacuum Society.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
85.40.Hp Lithography, masks and pattern transfer

Differential charge detection for quantum-dot cellular automata

Islamshah Amlani, Alexei O. Orlov, Gregory L. Snider, and Gary H. Bernstein

J. Vac. Sci. Technol. B 15, 2832 (1997); http://dx.doi.org/10.1116/1.589738 (4 pages) | Cited 2 times

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We report direct measurements of the charging diagram of a nanoscale series double-dot system at low temperatures. Our device consists of four metal dots, with two of them in series forming a double-dot, and the other two serving as electrometers for the double-dot system. This configuration allows us to externally detect all possible charge transitions within a double-dot system. Specifically, we can detect charge redistribution in the double-dot, which corresponds to shift of an electron between two dots, using differential signal from the two electrometers. We discuss possible applications as an output stage for quantum-dot cellular automata architecture. © 1997 American Vacuum Society.
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73.23.Hk Coulomb blockade; single-electron tunneling
07.68.+m Photography, photographic instruments; xerography
85.35.Gv Single electron devices
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Metal–oxide–semiconductor-compatible silicon based single electron transistor using bonded and etched back silicon on insulator material

T. Köster, B. Hadam, K. Hofmann, J. Gondermann, J. Stein, S. Hu, S. Altmeyer, B. Spangenberg, and H. Kurz

J. Vac. Sci. Technol. B 15, 2836 (1997); http://dx.doi.org/10.1116/1.589739 (4 pages) | Cited 4 times

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We present a fabrication method for a single electron transistor in silicon. The process is based on bonded and etched back silicon on insulator material with a very thin silicon top layer. Tunnel junctions are realized by electron beam lithography in combination with a two layer resistsystem. The pattern is transferred by anisotropic reactive ion etching and the lateral dimensions are reduced further by thermal oxidation. The process technology is, apart from the e-beam lithography, fully metal–oxide–semiconductor compatible. We electrically characterized samples with four tunnel junctions in series. At 6 K the I/U characteristics reveals a Coulomb blockade as well as a Coulomb staircase, which can be attributed to the asymmetry in the system. Additionally, the temperature dependence and the variation of the background electrostatic potential of the islands were investigated. © 1997 American Vacuum Society.
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85.35.Gv Single electron devices
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.05.Cy Elemental semiconductors

Fabrication and characterization of room temperature silicon single electron memory

Lingjie Guo, Effendi Leobandung, Lei Zhuang, and Stephen Y. Chou

J. Vac. Sci. Technol. B 15, 2840 (1997); http://dx.doi.org/10.1116/1.589740 (4 pages) | Cited 12 times

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A single electron memory was demonstrated in crystalline silicon that has a transistor channel width of ∼10 nm and a nanoscale floating gate of dimension ∼(7 nm × 7 nm × 2 nm), patterned by electron beam lithography, lift-off, and reactive ion etching. Quantized shift in the threshold voltage and self-limited charging process have been observed at room temperature. Analysis has shown that these quantized characteristics are the results of single electron charging effect in the nanoscale floating gate. © 1997 American Vacuum Society.
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85.35.Gv Single electron devices
85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Single-electron transistor as a charge sensor for semiconductor applications

David Berman, Nikolai B. Zhitenev, Raymond C. Ashoori, Henry I. Smith, and Michael R. Melloch

J. Vac. Sci. Technol. B 15, 2844 (1997); http://dx.doi.org/10.1116/1.589741 (4 pages) | Cited 8 times

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We describe the use of aluminum single-electron transistors (SETs) to measure, with extremely high sensitivity, the fluctuation of charge in semiconductor quantum dots. Our method of fabricating SETs results in excellent reliability and reproducibility. © 1997 American Vacuum Society.
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85.35.Gv Single electron devices
07.50.-e Electrical and electronic instruments and components
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.40.Rw Metal-insulator-metal structures
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Cell attachment on silicon nanostructures

S. Turner, L. Kam, M. Isaacson, H. G. Craighead, W. Shain, and J. Turner

J. Vac. Sci. Technol. B 15, 2848 (1997); http://dx.doi.org/10.1116/1.589742 (7 pages) | Cited 44 times

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Advances in neural probe technology are currently hindered by a lack of understanding of the cues and mechanisms responsible for rejection and isolation of probes implanted in the central nervous system. To gain additional insight into this topic, the attachment of astrocytes on nanoscale textured silicon surfaces was investigated. Silicon surfaces were textured using a reactive ion etch process designed to produce nanometer-scale columnar structures in silicon (“silicon grass”). Standard photolithographic techniques were used to pattern the surface thereby allowing selective modification of the surface texture by a wet chemical etch for silicon. The resulting surface allowed a side-by-side presentation of different surface textures to cells grown in culture. The silicon surfaces were characterized by scanning electron microscopy (SEM) and scanning Auger electron microscopy. The cell attachment and morphology were observed with laser scanning confocal microscopy and SEM. Transformed astrocytes from a continuous cell line showed a preference for wet-etched regions over grassy regions. In contrast, primary cortical astrocytes from neonatal rats showed a preference for silicon grass over the wet-etched surface. For the transformed astrocytes cells, the degree of response was continuous with the degree of wet-etch modification. © 1997 American Vacuum Society.
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87.17.-d Cell processes
87.80.-y Biophysical techniques (research methods)
81.65.Cf Surface cleaning, etching, patterning

Comparative study of gated single crystal silicon and polysilicon field emitters

S. E. Huq, G. H. Grayer, and P. D. Prewett

J. Vac. Sci. Technol. B 15, 2855 (1997); http://dx.doi.org/10.1116/1.589743 (4 pages) | Cited 9 times

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Both single crystal silicon and polysilicon are attractive emitter materials for displays using cold field emission. Although single crystal silicon has been under investigation for some time, by contrast, interest in polysilicon is more recent. Using state of the art fabrication techniques including high resolution electron beam lithography and plasma dry etch both single crystal silicon and polysilicon have been processed to fabricate sharp and uniform gated emitter arrays. We report in this article a comparative study of material aspects, processing, and emission properties of the two materials. © 1997 American Vacuum Society.
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85.45.Db Field emitters and arrays, cold electron emitters

Efficient diffractive optics made by single-step electron beam lithography in solid PMMA

David R. S. Cumming, Iman I. Khandaker, Stephen Thoms, and Brendan G. Casey

J. Vac. Sci. Technol. B 15, 2859 (1997); http://dx.doi.org/10.1116/1.589744 (5 pages) | Cited 4 times

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Diffractive optics are of increasing interest as they can be used to make compact optical components of great complexity. However, they require precision of fabrication on a scale significantly below the operating wavelength in order to achieve high efficiency. We describe a new technique for making multilevel diffractive optics in a single step by the patterning of solid poly methyl methacrylate (PMMA) as opposed to conventional thin films. We have characterized the process to optimize it for development, dose, and beam current. Using the technique we have made blazed diffraction gratings for use in transmission or reflection with efficiencies as high as 83% at a wavelength of 514 nm. The method is excellent for rapid prototyping of designs and we anticipate that it may be used to make embossing masters for lens fabrication into other materials. © 1997 American Vacuum Society.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Dj Gratings

Application of amorphous silicon subwavelength gratings in polarization switching vertical-cavity surface-emitting lasers

Stephen Y. Chou, Steven J. Schablitsky, and Lei Zhuang

J. Vac. Sci. Technol. B 15, 2864 (1997); http://dx.doi.org/10.1116/1.589745 (4 pages) | Cited 3 times

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Amorphous silicon subwavelength gratings have been fabricated. Their use as quarter-wave plates in polarization switching vertical-cavity surface-emitting lasers with tunable oscillation frequency as high as several terahertz is proposed. The substantial increase in frequency comes from a reduction in the oscillator cavity length due to the small thickness of the grating (only about one-third of the wavelength thick). The frequency tuning is provided by fabricating the wave plate and a partial reflector monolithically on a movable microcantilever. © 1997 American Vacuum Society.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems

Accurate critical dimension control by using an azide/novolak resist process for electron-beam lithography

Jiro Yamamoto, Shou-ichi Uchino, Hiroya Ohta, Toshiyuki Yoshimura, and Fumio Murai

J. Vac. Sci. Technol. B 15, 2868 (1997); http://dx.doi.org/10.1116/1.589746 (4 pages) | Cited 4 times

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Nanofabrication with accurate critical dimension control was investigated with a nonchemically amplified resist. The resist consists of 3,3′-dimethoxy-4,4′-diazidobiphenyl and cresol novolak (novolak). By using novolak with a small weight-average molecular weight (Mw), small resist surface roughness (nano edge roughness) was significantly suppressed down to 3 nm. Nanofabrications of 20-nm lines and spaces (L and S) and 20-nm dot patterns had been demonstrated with the resist. The pattern line-width linearity, the minimum size that the fabricated patterns width were equal to the designed ones, was also preserved down to 30-nm L and S. We investigated use of electron-beam/optical lithography to enhance throughput in nanofabrication. Fine gate structure of 70 nm with a large pad was demonstrated with the hybrid exposure. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Process optimization for production of sub-20 nm soft x-ray zone plates

S. J. Spector, C. J. Jacobsen, and D. M. Tennant

J. Vac. Sci. Technol. B 15, 2872 (1997); http://dx.doi.org/10.1116/1.589747 (5 pages) | Cited 49 times

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We report here the optimization of processes for producing sub-20 nm soft x-ray zone plates, using a general purpose electron beam lithography system and commercial resist technologies. We have critically evaluated the failure point of the various process steps and where possible chosen alternate methods, materials, or otherwise modified the process. Advances have been made in most steps of the process, including the imaging resist, pattern conversion for electron beam exposure, and pattern transfer. Two phase shifting absorber materials, germanium and nickel, were compared. Zone plates with 30 nm outer zones have been fabricated in both germanium and nickel with excellent quality using polymethyl methyl accrylate and zones as small as 20 nm have been fabricated in nickel using the calixarene resist. The total efficiency as well as the efficiency of different regions of the zone plates were measured. All zone plates have demonstrated good efficiencies, with nickel zone plates performing better than germanium zone plates. © 1997 American Vacuum Society.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Ci Filters, zone plates, and polarizers

Influence of secondary electrons in proximal probe lithography

B. Völkel, A. Gölzhäuser, H. U. Müller, C. David, and M. Grunze

J. Vac. Sci. Technol. B 15, 2877 (1997); http://dx.doi.org/10.1116/1.589748 (5 pages) | Cited 15 times

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This article describes the limitations of proximal probe lithography due to electrons that are mirrored by the electric field between the tip and the surface. The incident beam generates two kinds of electrons at the sample surface: primary electrons which are elastically backscattered and secondary electrons which are produced in the resist/substrate system. The electric field confines the electrons emanating from the surface. The electron trajectories are bent in such a way that the electrons impinge on the sample surface in the vicinity of their origin. These reflected electrons contribute to the exposure of the resist and therefore, limit the resolution. For hexadecanethiol monolayers on gold substrates, we have measured the energy distribution of the mirrored electrons and the secondary electron yield as a function of the primary energy. With near edge x-ray absorption fine structure spectroscopy, we have investigated the relevance of low energy electrons in the exposure of hexadecanethiol films. Simulations of secondary electron trajectories can explain the occurrence of triple line structures observed in field emission proximal probe lithography. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
79.20.Hx Electron impact: secondary emission

Ion trap for mass-selective production of nanoclusters

Toshihiko Kanayama and Hirohiko Murakami

J. Vac. Sci. Technol. B 15, 2882 (1997); http://dx.doi.org/10.1116/1.589749 (5 pages) | Cited 12 times

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To form nanoclusters with a specified atomic structure, an electrical trapping technique of charged particles was developed that allows us to confine, grow, and mass selectively eject cluster ions. Theoretical calculations and experiments using inert gas ions indicate that the developed ion trap can confine ions with a wide range of mass values using the external field of an ac quadrupole, and send out the ions mass selectively through the internal region of the quadrupole. To demonstrate performance, Si6H12+ clusters were selectively grown using SiH4 as a starting material. In the trap, confined SiHx+ ions were allowed to react with neutral SiH4 molecules or SiHy radicals, and SinHx+ clusters were grown, from which Si6H12+ clusters were automatically ejected by tuning trapping parameters. © 1997 American Vacuum Society.
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61.46.-w Structure of nanoscale materials
37.20.+j Atomic and molecular beam sources and techniques
81.07.-b Nanoscale materials and structures: fabrication and characterization
36.40.-c Atomic and molecular clusters
07.77.Ka Charged-particle beam sources and detectors

Nanochannel fabrication for chemical sensors

Margaret B. Stern, Michael W. Geis, and Jane E. Curtin

J. Vac. Sci. Technol. B 15, 2887 (1997); http://dx.doi.org/10.1116/1.589750 (5 pages) | Cited 36 times

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In a novel chemical sensor, the chemical charge coupled device (CCD), electrostatic fields in nanocapillary channels smaller than a Debye length will be used to separate and concentrate ions in solution with a predicted detection limit of <1× 10−13 M. Conventional integrated circuit techniques are used to deposit thin dielectric and amorphous-Si films on a Si substrate and to lithographically define channel and reservoir structures. Hollow Si3N4 nanochannels with heights between 20 and 100 nm, widths between 0.5 and 20 μm, and lengths up to 5 mm have been fabricated by wet chemical etching of a sacrificial amorphous-Si layer in tetramethylammonium hydroxide. Initial modeling of a three-phase chemical CCD predicts the ability to select and concentrate ionic constituents by many orders of magnitude, according to their diffusion coefficients. © 1997 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning

Nanometer biodevice fabrication by electron beam lithography

Enzo Di Fabrizio, Luca Grella, Marco Baciocchi, Massimo Gentili, Cesare Ascoli, Brunero Cappella, Carlo Frediani, and Piero Morales

J. Vac. Sci. Technol. B 15, 2892 (1997); http://dx.doi.org/10.1116/1.589751 (5 pages) | Cited 11 times

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A conventional electron beam lithography machine operated at 50 kV is used in this work to fabricate devices and structures for biophysical and molecular electronics applications featuring critical dimensions down to the nanometer region. Such nanostructures are used for deposition and manipulation of organic molecules; fabricated devices include fine pitch self-standing meshes for laser deposition of molecules, a bimetallic miniaturized glucose sensor and nanogaps for molecular trapping and probing. The developed process is described in detail and by means of Monte Carlo simulation, the various electron scattering processes are modelled. Critical issues, such as fabrication of nanogaps with dimension down to 5 nm, are also addressed. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
87.80.-y Biophysical techniques (research methods)
85.65.+h Molecular electronic devices

Sub-10 nm imprint lithography and applications

Stephen Y. Chou, Peter R. Krauss, Wei Zhang, Lingjie Guo, and Lei Zhuang

J. Vac. Sci. Technol. B 15, 2897 (1997); http://dx.doi.org/10.1116/1.589752 (8 pages) | Cited 325 times

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New developments, further details, and applications of imprint lithography are presented. Arrays of 10 nm diameter and 40 nm period holes were imprinted not only in polymethylmethacrylate (PMMA) on silicon, but also in PMMA on gold substrates. The smallest hole diameter imprinted in PMMA is 6 nm. All the PMMA patterns were transferred to a metal using a liftoff. In addition, PMMA mesa’s of a size from 45 nm to 50 μm were obtained in a single imprint. Moreover, imprint lithography was used to fabricate the silicon quantum dot, wire, and ring transistors, which showed the same behavior as those fabricated using electron (e)-beam lithography. Finally, imprint lithography was used to fabricate nanocompact disks with 10 nm features and 400 Gbits/in.2 data density—near three orders of magnitude higher than current critical dimensions (CDs). A silicon scanning probe was used to read back the data successfully. The study of wear indicates that due to the ultrasmall force in tapping mode, both the nano-CD and the scanning probe will not show noticeable wear after a large number of scans. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning

Nanolithography with neutral chromium and helium atoms

B. Brezger, Th. Schulze, U. Drodofsky, J. Stuhler, S. Nowak, T. Pfau, and J. Mlynek

J. Vac. Sci. Technol. B 15, 2905 (1997); http://dx.doi.org/10.1116/1.589393 (7 pages) | Cited 9 times

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We describe two experiments that use neutral atomic beam techniques to write nanostructures. In the chromium experiment, we have used neutral chromium atoms to write one- and two-dimensional periodic nanometer-scale structures in a direct way. The periodic structure is given to the atomic beam by a laser light mask. In a second experiment, we have used a self-assembling monolayer as a resist for metastable helium atoms in a proximity printing experiment. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
37.20.+j Atomic and molecular beam sources and techniques

New approaches to atomic force microscope lithography on silicon

K. Birkelund, E. V. Thomsen, J. P. Rasmussen, O. Hansen, P. T. Tang, P. Møller, and F. Grey

J. Vac. Sci. Technol. B 15, 2912 (1997); http://dx.doi.org/10.1116/1.589753 (4 pages) | Cited 8 times

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We have investigated new approaches to the formation of conducting nanowires on crystalline silicon surfaces using atomic force microscope (AFM) lithography. To increase processing speed and reduce wear of the AFM tip, large-scale structures are formed with a direct laser write setup, while the AFM is used to add the finer nanostructures. Both methods are based on selective oxidation of hydrogen-passivated silicon and subsequent etching to define conducting regions on the surface. This combined technique has previously been implemented on amorphous Si on oxide. To extend the technique to form crystalline silicon nanowires, we have used an arsenic implanted crystalline silicon layer on p-type Si, where the nanostructures are isolated from the substrate electrically due to p-n junction formation. Improvements in the reliability of the AFM lithography technique were achieved by using all-metal tips, which do not wear out as rapidly as metal-coated Si3N4 tips. © 1997 American Vacuum Society.  
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85.40.Hp Lithography, masks and pattern transfer
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
07.79.Lh Atomic force microscopes

“Safe” solvent resist process for sub-quarter micron T-gates

D. Via, C. Bozada, C. Cerny, G. DeSalvo, R. Dettmer, J. Ebel, J. Gillespie, T. Jenkins, K. Nakano, C. Pettiford, T. Quach, and J. Sewell

J. Vac. Sci. Technol. B 15, 2916 (1997); http://dx.doi.org/10.1116/1.589754 (5 pages) | Cited 1 time

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With the advent of the “green” revolution, the semiconductor industry must develop alternative processes that utilize environmentally friendly products. As a first step toward this end we have demonstrated an electron beam patterned sub-quarter micron T-gate process using safe resists manufactured by Microlithography Chemical Corp. (MCC). Instead of the more conventional chlorobenzene based poly methyl methacrylate (PMMA) and 2-ethoxyethanol copolymer solutions, new anisole based PMMA and an ethyl lactate based copolymer are used. In addition to replacing the non-environmentally friendly resists, we sought to increase gate yield by improving the shape of the resist profile. Focused ion beam (FIB) cross-sectional analysis of 0.2 μm T-gates fabricated using our conventional process showed metal discontinuity at the stem-to-cap transition. This was attributed to a sharp transition in the resist from the bottom layer of PMMA to the copolymer. With the safe resists we sought to grade the transition between the stem and cap to improve metal continuity. Multiple techniques were used to evaluate and characterize the safe resist process. FIB cross sectioning provided a rapid and less destructive method for resist profile inspection. In addition, metal deposition was examined prior to liftoff to view evaporation buildup. Scanning electron microscopy and atomic force microscopy were used to give comparative measures of gate length. A safe resist process for sub-quarter micron T-gate fabrication is described. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Influence of electron-beam induced microporosity on masking properties of polymethylmethacrylate in wet etching of nanometer structures

I. Maximov, A. L. Bogdanov, and L. Montelius

J. Vac. Sci. Technol. B 15, 2921 (1997); http://dx.doi.org/10.1116/1.589755 (4 pages) | Cited 1 time

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The masking properties of nanometer scale polymethylmethacrylate (PMMA) features used for definition of sub-100-nm-wide bridges in InP/Ga0.25In0.75As two-dimensional electron gas heterostructures by wet etching were investigated. Bridges untreated after the development of PMMA showed very poor masking ability due to a substantial exposure by backward scattered electrons from the surrounding exposed areas. However, if the resist was post-baked after development at a temperature higher than the glass transition temperature, Tg, the masking properties were restored and wet etched nanobridges of a sufficient quality were obtained. The post-development bake temperature and time were optimized to provide enough resist “packing” and yet not to cause resist flowing resulting in unacceptable alteration of the pattern geometry. © 1997 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning
85.35.Ds Quantum interference devices
73.23.-b Electronic transport in mesoscopic systems

Fabrication and near-room temperature transport of patterned gold cluster structures

L. Clarke, M. N. Wybourne, Mingdi Yan, S. X. Cai, L. O. Brown, J. Hutchison, and J. F. W. Keana

J. Vac. Sci. Technol. B 15, 2925 (1997); http://dx.doi.org/10.1116/1.589756 (5 pages) | Cited 7 times

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Ligand stabilized metal clusters are becoming of considerable interest for possible nanoscale electronics applications. In this article, we report the fabrication and near-room temperature electrical transport properties of structures made from the gold-cluster material Au55[P(C6H5)3]12Cl6. While other strategies to produce cluster arrays have been reported, this work is the first to use electron-beam lithography to laterally define the structures. We compare the current–voltage characteristics of nonpatterned and patterned structures, and show that in both cases the nonlinear behavior observed is consistent with Coulomb blockade dominated transport. We argue that charging of individual Au55 cores is responsible for the effects observed. © 1997 American Vacuum Society.
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61.46.-w Structure of nanoscale materials
73.23.Hk Coulomb blockade; single-electron tunneling
85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Characterization of Si-doped layer in GaAs fabricated by a focused ion beam/molecular beam epitaxy combined system

Junichi Yanagisawa, Hiromasa Nakayama, Kenji Oka, Masaya Nakai, Fujio Wakaya, Yoshihiko Yuba, Sadao Takaoka, Kazuo Murase, and Kenji Gamo

J. Vac. Sci. Technol. B 15, 2930 (1997); http://dx.doi.org/10.1116/1.589757 (4 pages) | Cited 2 times

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Effect of the regrowth temperature of the cap layer grown successively on a Si focused ion beam (FIB) implanted GaAs surface on the dopant activation was investigated using a FIB/molecular beam epitaxy combined system. Indication of the reevaporation of the implanted Si was observed at high regrowth temperature and the fabrication process was improved by using low regrowth temperature. A high doping efficiency was obtained for the ion dose at about 1×1013 cm−2. Present results indicate the importance of controlling the regrowth condition to obtain high doping efficiency. © 1997 American Vacuum Society.  
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Direct epitaxial growth of thin-film structures

Gyula Eres, Frank Y. C. Hui, T. Thundat, and D. C. Joy

J. Vac. Sci. Technol. B 15, 2934 (1997); http://dx.doi.org/10.1116/1.589758 (6 pages) | Cited 1 time

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In this article we describe a method for direct epitaxial growth of thin-film structures using a combination of resistless electron beam lithography and supersonic molecular beam epitaxy. Electron beam irradiation of a surface hydride layer on silicon induces hydrogen desorption and hence alters the surface reactivity of the exposed area. Introduction of a source gas concurrently with, or immediately following electron beam exposure results in a pattern formation on the exposed area. Continuous silicon oxide patterns with linewidths below 0.1 μm have been achieved. The resulting pattern can be also used as a mask for subsequent selective growth on the unexposed area. Supersonic molecular beam epitaxy is a highly nonequilibrium film growth method that uses translationally hot source gas species generated by a high pressure gas expansion. Since the reactivity of the source gas molecules depends exponentially on the incident kinetic energy, the chemical selectivity of the film growth process can be altered by tuning the incident kinetic energy. Arbitrary patterns with linewidths on the order of 0.1 μm have been achieved with Si, Ge, and SiC epitaxy on Si (100) and Si epitaxy on Ge (100). © 1997 American Vacuum Society.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
85.40.Hp Lithography, masks and pattern transfer

Super-smooth x-ray reflection grating fabrication

A. E. Franke, M. L. Schattenburg, E. M. Gullikson, J. Cottam, S. M. Kahn, and A. Rasmussen

J. Vac. Sci. Technol. B 15, 2940 (1997); http://dx.doi.org/10.1116/1.589759 (6 pages) | Cited 12 times

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Blazed, grazing incidence x-ray reflection gratings are an important component of modern high resolution spectrometers and related x-ray optics. These have traditionally been fabricated by diamond scribing in a ruling engine, or more recently by interferometric lithography followed by ion etching. These traditional methods result in gratings which suffer from a number of deficiencies, including high surface roughness and poor control of the groove profile. These deficiencies lead to poor diffraction efficiency and high levels of scattered light. We have developed a novel fabrication method for fabricating blazed x-ray reflection gratings which utilizes silicon wafers that are cut 0.7° off of the (111) plane. In solutions such as potassium hydroxide (KOH), silicon is etched in 〈111〉 directions orders of magnitude slower than in other directions, resulting in extremely smooth {111} facets. The gratings are patterned using interferometric lithography with 351.1 nm wavelength and transferred into the substrate using tri-level resist processing, reactive-ion etching (RIE), and silicon nitride masking during the KOH etch. The narrow (<0.1 μm) ridge of silicon which supports the nitride mask is removed using a chromium lift-off step followed by a CF4 RIE trench etch. The result is a grating with extremely smooth blaze facets which is suitable for x-ray reflection after evaporative coating with thin Cr/Au. Atomic force microscope images confirm that fabricated gratings have less than a 0.4 nm rms roughness—much smoother than conventional gratings which have over ∼1 nm roughness. Theory predicts that reduced blaze facet roughness increases diffraction efficiency. Experiments and simulations performed at the Lawrence Berkeley Laboratory and Columbia University confirm that efficiency is increased; in fact, measured peak efficiencies reach ∼80% of calculated theoretical limits. Peak grating efficiencies were achieved that are ∼35% greater than that of the best available ruled masters of comparable design. © 1997 American Vacuum Society.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Dj Gratings
81.65.Cf Surface cleaning, etching, patterning
42.86.+b Optical workshop techniques

Subwavelength, binary lenses at infrared wavelengths

J. R. Wendt, G. A. Vawter, R. E. Smith, and M. E. Warren

J. Vac. Sci. Technol. B 15, 2946 (1997); http://dx.doi.org/10.1116/1.589760 (4 pages) | Cited 16 times

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We describe the nanofabrication of subwavelength, binary lenses in GaAs for operation in the infrared. Subwavelength surface relief structures create an artificial material with an effective index of refraction determined by the fill factor of the binary pattern and can be designed to yield high-efficiency diffractive optical elements. In this work, we designed and fabricated a circular-aperture, off-axis lens with a deflection angle of 20°, focal length of 110 μm, and diameter of 80 μm, for operation at 975 nm. The off-axis lens design has a theoretical efficiency of 92% and the fabricated lens exhibits a diffraction efficiency into the first order of 72% and 59% of the transmitted power for TE and TM polarization, respectively. A significant advantage of these subwavelength structures is that fabrication requires only a single-lithography-and-etch-step process, in this case, electron-beam lithography and reactive-ion-beam etching. © 1997 American Vacuum Society.
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42.79.Bh Lenses, prisms and mirrors
42.86.+b Optical workshop techniques
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
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