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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 15 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 18 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 6 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 4 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 11 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 3 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 20 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 29 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 43 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 36 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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