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Nov 1998

Volume 16, Issue 6, pp. 2915-3953


Electrical transport and far-infrared transmission in a quantum wire array

J. Lefebvre, J. Beerens, Y. Feng, Z. Wasilewski, J. Beauvais, and E. Lavallée

J. Vac. Sci. Technol. B 16, 2915 (1998); http://dx.doi.org/10.1116/1.590368 (13 pages) | Cited 1 time

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A wide set of data obtained on a two-dimensional electron gas submitted to a tunable lateral modulation, induced using a split-gate technique, is presented. Owing to a unique design of the sample, it has been possible to combine in a single experimental run, far-infrared transmission measurements and electrical transport measurements in both directions parallel and perpendicular to the lateral modulation. The discussion of the results emphasizes the correspondence between various features observed in both types of measurements. Based on these features, three regimes of modulation are clearly identified, namely the weak, intermediate and strong modulation regimes. Far-infrared transmission data show that each of these regimes is characterized by plasmon modes with a distinctive behavior. These behaviors are analyzed further with the use of transport data, which allow to determine the electron concentration in the structure for every condition of gate voltage. In the weak modulation regime, a quantitative analysis shows that the collective mode energy is consistent with that of a classical 2D plasmon at q=2π/a (where a is the period of the split gate), using the average electron concentration under the gate as the relevant parameter. In the intermediate regime, the collective modes are confined plasmons. The observation of “confined Bernstein modes” indicates that the bare confinement potential is nonparabolic in this regime. In the strong modulation regime, the observation of a far-infrared resonance energy which does not depend on the modulation amplitude, while the effective 2D electron concentration (within each wire) varies with gate voltage, shows that the collective mode is a Kohn mode. © 1998 American Vacuum Society.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Luminescence from erbium implanted silicon–germanium quantum wells

M. Q. Huda, J. H. Evans-Freeman, A. R. Peaker, D. C. Houghton, and A. Nejim

J. Vac. Sci. Technol. B 16, 2928 (1998); http://dx.doi.org/10.1116/1.590320 (6 pages) | Cited 4 times

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We have investigated the luminescence emitted at 1.54 μm from erbium-implanted strained ultrahigh vacuum chemical vapor deposition-grown (UHVCVD-grown) Si1−xGex quantum wells. Germanium fractions of up to 13% were used, and all well widths were below the critical thickness for pseudomorphic growth. A preliminary study was carried out on Si1−xGex quantum wells implanted with amorphizing doses of silicon at 77 K in order to study the regrowth across the interfaces, and subsequent structural and optical recovery. After amorphization and regrowth by a two stage anneal process, transmission electron microscopy (TEM) clearly showed the presence of the quantum wells, with sharp contrast. X-ray diffraction (XRD) studies showed that good regrowth has been achieved, with line widths very similar to the original material. However, the photoluminescence (PL) was found to be dependent upon the duration of the first anneal. Increasing the anneal time resulted in PL spectra being dominated by broad signals between 0.9 and 0.97 eV associated with structural defects. High concentrations of erbium were incorporated into the strained Si1−xGex quantum wells by implantation and solid phase epitaxial regrowth. TEM and XRD studies showed that the quantum wells retained their structure, with negligible segregation or diffusion of the germanium during the recrystallization. Erbium-related emission centered at 1.54 μm was observed in the implanted Si1−xGex layers after regrowth, and generally found to be of similar intensity as that in bulk silicon implanted with more than an order of magnitude higher dose of erbium. © 1998 American Vacuum Society.
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78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors
61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing
81.15.Np Solid phase epitaxy; growth from solid phases

Optical absorption of Ag nanoclusters in Ag+-implanted c-SiO2

Xiao-Dong Feng, Min-Bo Tian, and Zheng-Xin Liu

J. Vac. Sci. Technol. B 16, 2934 (1998); http://dx.doi.org/10.1116/1.590321 (4 pages) | Cited 2 times

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c-SiO2 samples were implanted with Ag+ at an energy of 200 keV to doses in the range of 2.3–9×1016 ions/cm2 at room temperature. At a dose of 6.7×1016 ions/cm2, the transmission electron microscopy image shows that the implanted layer consists of two major sizes of nanoclusters: the large clusters, found in the deeper layer, are about 20 nm in diameter; the smaller clusters, found near the surface, are about 5 nm in diameter. At the relatively low dose of 2.3×1016 ions/cm2, there is only one optical absorption band caused by surface plasmon resonance. At a higher dose, a splitting of the absorption band and the redshift are attributed to a dipole interaction between nanoclusters for a high density of nanoclusters. © 1998 American Vacuum Society.
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78.40.Ha Other nonmetallic inorganics
61.46.-w Structure of nanoscale materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.72.up Other materials

Silicon nanopillars formed with gold colloidal particle masking

P. A. Lewis, H. Ahmed, and T. Sato

J. Vac. Sci. Technol. B 16, 2938 (1998); http://dx.doi.org/10.1116/1.590322 (4 pages) | Cited 20 times

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Silicon nanopillars were fabricated by a novel natural lithography technique utilizing a gold colloidal particle monolayer as an etch mask. Using SiCl4 based reactive ion etching (RIE), silicon nanopillars with high density and uniformity in height and shape were obtained with 15 and 10 nm diam gold colloidal particles. The uniform pillars obtained from the 15 nm colloidal gold etch mask were subsequently sharpened to less than 5 nm diam tips by oxidation. 5 nm diam colloids were used to obtain nonuniform 5 nm diam pillars directly by RIE, but with 2 nm colloids the limit of pillar formation was reached. The pillars were also fabricated in selected areas by lithographic patterning of the substrate. © 1998 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer
81.65.Mq Oxidation
81.65.Cf Surface cleaning, etching, patterning

Detection and control of ferroelectric domains by an electrostatic force microscope

J. W. Hong, D. S. Kahng, J. C. Shin, H. J. Kim, and Z. G. Khim

J. Vac. Sci. Technol. B 16, 2942 (1998); http://dx.doi.org/10.1116/1.590323 (5 pages) | Cited 20 times

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An electrostatic force microscopy (EFM) method has been used for the detection and control of the microdomain in ferroelectric single crystal [triglycine sulfate (TGS)] and thin film piezoelectric transducer (PZT). In this method, EFM is operated in a dynamic contact mode that allows a simultaneous measurement of the topographic and domain contrast images. Through the analysis of the force between the tip and ferroelectric surface, the surface charge density of TGS single crystal is obtained. Polarization charge density of TGS obtained in this method is 2.7 μC/cm2 at room temperature. A complex pattern was written on a PZT film by the polarization reversal. The line shape or the intensity of the reoriented domain does not show any noticeable dependence on the writing speed. The threshold bias for writing on a PZT film studied in this work was 4 V. © 1998 American Vacuum Society.
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77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.84.Jd Polymers; organic compounds
07.79.Lh Atomic force microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
77.22.Ej Polarization and depolarization
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.55.-g Dielectric thin films

Atomistic study of nickel silicide structures on Si(100) by tunneling microscopy

Izumi Ono, Masamichi Yoshimura, and Kazuyuki Ueda

J. Vac. Sci. Technol. B 16, 2947 (1998); http://dx.doi.org/10.1116/1.590324 (5 pages) | Cited 2 times

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Surface structures of Ni-deposited Si(100) have been investigated using scanning tunneling microscopy (STM). After heating at 670 °C, NiSi2 islands consisting of patch features grow on the (2×n) substrate. We have proposed a new structure model for NiSi2 island by taking account of the correlation of heights and lateral positions between top-layer atoms in the NiSi2 and Si dimers in the substrate. In the model, the top-layer atoms, with a nearest neighbor distance of 0.38 nm, are located at bridge sites on the Ni layer of NiSi2. Patch features consist of two equivalent anti-phase sites shifted by half the unit length of 1×1 along both [011] and [01̄1] directions. In addition, it is found in the empty-state STM images that the center atoms make pairs two by two. © 1998 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
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.40.Ns Metal-nonmetal contacts

Growth of silicon oxide on hydrogenated silicon during lithography with an atomic force microscope

F. Marchi, V. Bouchiat, H. Dallaporta, V. Safarov, D. Tonneau, and P. Doppelt

J. Vac. Sci. Technol. B 16, 2952 (1998); http://dx.doi.org/10.1116/1.590325 (5 pages) | Cited 20 times

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We present an experimental study of growth of silicon oxide strips drawn on hydrogenated silicon under the voltage biased tip of an atomic force microscope operating in ambient atmosphere. Oxide formation was found to occur at negative tip biases above a voltage threshold around ∣−2∣V, corresponding to the minimum electric field required for hydrogen removal from the substrate surface. We show the influence of tip-sample distance and of the chemical composition of the atmosphere on the growth. An ozone enriched atmosphere leads to a growth kinetics enhancement. © 1998 American Vacuum Society.
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81.65.Mq Oxidation
85.40.Hp Lithography, masks and pattern transfer
81.05.Cy Elemental semiconductors
07.79.Lh Atomic force microscopes

Plasma polymer films for 532 nm laser micromachining

M. S. Silverstein, I. Visoly, O. Kesler, M. Janai, and Y. Cassuto

J. Vac. Sci. Technol. B 16, 2957 (1998); http://dx.doi.org/10.1116/1.590326 (11 pages) | Cited 3 times

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Laser micromachining with a frequency doubled Nd:YAG laser (532 nm) can replace more complex microlithographic processes for rapid turnaround in the development of prototype application-specific integrated circuits. Plasma polymerization is a rapid, dry, environmentally friendly process that yields crosslinked pinhole-free films. Plasma polymerized films of ethylene and an additional gas [PP(gas/E)] were investigated for their micromachining potential. The deposition rates, molecular structures, physical properties and optical properties of the polymers were characterized. PP(Ar/E), with relatively little oxygen and no nitrogen, with superior substrate adhesion and with no debris generated on laser micromachining was chosen as the optimal laser micromachining film. The PP(Ar/E) coefficient of optical absorption at 532 nm (α532), related to unsaturated group concentration, increased with the ratio of plasma power to ethylene mass flow rate [W/Fm(E)]. α532 reached an asymptote of 2.9 μm−1 at high W/Fm(E) and could be enhanced slightly using postpolymerization ultraviolet exposure. The optimum conditions were using Ar/E=1/1 and 75 W to produce a 0.6 μm thick film for micromachining at 2 J/cm2 focused 0.25 μm beneath the surface. The laser pulse in a 1.2 μm thick film was not fully developed at 2 J/cm2 and exhibited rounded corners at 4 J/cm2, indicating that multiple low energy pulses would be preferable. A complicated and densely packed pattern with several different pulse sizes in which neighboring holes from pulses in close proximity do not merge was accurately reproduced in PP(Ar/E) using laser micromachining. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
82.35.-x Polymers: properties; reactions; polymerization
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
85.40.Sz Deposition technology
81.65.Cf Surface cleaning, etching, patterning

Nonstatistical degradation and development characteristics of poly(methylmethacrylate) based resists during electron beam exposure

A. Uhl, J. Bendig, J. Leistner, U. Jagdhold, L. Bauch, and M. Böttcher

J. Vac. Sci. Technol. B 16, 2968 (1998); http://dx.doi.org/10.1116/1.590327 (6 pages) | Cited 1 time

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We present an investigation to study the degradation of poly(methylmethacrylate) (PMMA) based resists during electron beam exposure and their development characteristics. After exposure to the electron beam we detect for ARP 610 resist (PMMA 74%, PMAA 26%) and for a homopolymeric PMMA resist, a similar bimodal respectively multimodal molecular weight distribution curve characterized by a shift of the maximum from 105 to 103 g/mol and an increase of low molecular weight fractions (≈103 g/mol) with increasing exposure dose. The model of Greeneich can only be applied to lower deposited energy densities (ARP 610<4 eV/nm3, homopolymeric PMMA <8 eV/nm3). The difference found between experimental data and modeling values at higher deposited energy densities for both resists, results from a formation of stable low molecular weight fractions. Comparing the measured dissolution rate with the calculated one, the determined difference proves the nonapplicability of the empirical formula for the dissolution rate given by Greeneich. The low molecular weight fractions influence the dissolution rate significantly more than given by their portion in the molecular weight distribution. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Electrical conductivity measurement for quantitative evaluation of development speed of a photoresist

T. Takeda and M. Saka

J. Vac. Sci. Technol. B 16, 2974 (1998); http://dx.doi.org/10.1116/1.590328 (3 pages) | Cited 1 time

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In a previous article, we reported on the possibility of predicting the development speed of a photoresist by measuring its electrical conductivity in an organic solvent [T. Takeda and M. Saka, J. Vac. Sci. Technol. B (submitted)]. The electrical conductivity of the organic solution of a photoresist base polymer at various frequencies was found to have a positive correlation with the dissolution speed of photoresist base polymers into an alkaline developer. In addition, the influence of the measurement temperature and the concentration of polymer solution on conductivity was investigated. Based on the collected data, this article derives the calibration equation, which was influenced neither by measurement temperature nor by the concentration of the solution. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
82.35.-x Polymers: properties; reactions; polymerization

Fabrication of submicron suspended structures by laser and atomic force microscopy lithography on aluminum combined with reactive ion etching

A. Boisen, K. Birkelund, O. Hansen, and F. Grey

J. Vac. Sci. Technol. B 16, 2977 (1998); http://dx.doi.org/10.1116/1.590329 (5 pages) | Cited 13 times

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We report a simple fabrication method for suspended submicron silicon and silicon oxide structures. The structures are defined by laser and atomic force microscopy (AFM) writing on a 7-nm-thick aluminum film. For laser writing the minimum obtained linewidth is 500 nm, whereas for AFM it is approximately 100 nm. During AFM writing, aluminum oxide is formed, whereas during laser writing, a compound containing aluminum and silicon is formed. For both processes the nonpatterned aluminum can be dissolved selectively in a wet chemical etch leaving the patterned areas as an etch mask. Alternatively, the aluminum oxide can be etched to form a positive etch mask. Aluminum and aluminum oxide are both excellent etch masks for reactive ion etching (RIE) of silicon and silicon oxide. Hence, by combinations of RIE processes, a variety of structures can be fabricated from the aluminum based masks. To illustrate the flexibility of this technique we demonstrate fabrication of submicron cantilevers and bridges defined in silicon and silicon oxide. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.10.Cm Micromechanical devices and systems
81.65.Cf Surface cleaning, etching, patterning
07.79.Lh Atomic force microscopes
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

Submicrometer transmission mask fabricated by low-temperature SF6/O2 reactive ion etching and focused ion beam

H. Y. Sheng, D. Fujita, T. Ohgi, H. Okamoto, and H. Nejoh

J. Vac. Sci. Technol. B 16, 2982 (1998); http://dx.doi.org/10.1116/1.590330 (4 pages) | Cited 2 times

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A novel technique is presented to fabricate a silicon submicrometer transmission mask for nanofabrication. One of the applications of the mask is to fabricate a single electron transistor using an ultrahigh vacuum scanning tunneling microscope. The mask fabrication processes involve KOH wet etching, electron beam lithography, low-temperature SF6/O2 plasma-assisted reactive ion etching and focused ion beam techniques. Using this method, we fabricated masks with pattern sizes of 2.5×2.5 mm2 and opaque parts of submicrometer scale. After the evaporation, by using the mask a submicrometer gap on the metal pattern can be obtained. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Cleaning of CHF3 plasma-etched SiO2/SiN/Cu via structures using a hydrogen plasma, an oxygen plasma, and hexafluoroacetylacetone vapors

Kazuyoshi Ueno, Vincent M. Donnelly, and Yasuaki Tsuchiya

J. Vac. Sci. Technol. B 16, 2986 (1998); http://dx.doi.org/10.1116/1.590331 (10 pages) | Cited 8 times

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Cleaning processes for CHF3 reactive ion etched Cu vias, consisting of exposure to a hydrogen plasma, an oxygen plasma, and hexafluoroacetylacetone [H(hfac)] vapors have been investigated. After each step in the cleaning process, the dielectric surface and the Cu surface of via structures were analyzed by in situ by angle-resolved x-ray photoelectron spectroscopy. A hydrogen plasma was effective in removing carbon and fluorine deposits on all of the surfaces, and CuO and Cu2O on the Cu surface at the via bottom. It was not effective, however, in removing the Cu deposited on the dielectric surfaces. An oxygen plasma is effective in removing all the carbon and some fluorine deposits. Cu deposits on the dielectric surfaces were not removed, however, and the Cu surface was oxidized. Exposure to H(hfac) vapors reduced some of the Cu deposits on the dielectric, however Cu diffusion into SiO2 possibly occurred during this exposure at the elevated temperature of 200 °C. CuO and Cu2O were removed by the H(hfac) exposure above 150 °C. A three-step cleaning sequence was devised which consists of a brief oxygen-plasma exposure, a dilute-HF solution dip, followed by exposure to H(hfac) vapors. The cleaning sequence is effective in obtaining a clean dielectric surface and an oxide-free Cu surface at the via bottom that allows low contact resistances of 5.8–6.8×10−11 Ω cm2. © 1998 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Endpoint uniformity sensing and analysis in silicon dioxide plasma etching using in situ mass spectrometry

J. J. Chambers, K. Min, and G. N. Parsons

J. Vac. Sci. Technol. B 16, 2996 (1998); http://dx.doi.org/10.1116/1.590332 (7 pages) | Cited 5 times

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Mass spectroscopy is used to characterize the endpoint uniformity of silicon dioxide etching in an electron cyclotron resonance (ECR) plasma etch process. Etch products are observed using a two stage differentially pumped mass spectrometry system attached to the ECR process chamber. Specifically, using CF4 and D2 etch gases, the partial pressure of CO-containing etch products decays near the endpoint, and the rate of signal decay is directly correlated with the uniformity determined from optical interferometry thickness measurements. To correlate the mass spectrometer signal with the etch rate variation across the wafer, etch uniformity is altered by changing the ECR electromagnet geometry and by modifying the initial oxide uniformity. A COF2 etch product material balance is developed to model the observed concentration versus time data, resulting in a quantitative correlation between change in endpoint slope and uniformity. The ability to utilize a process-state sensor, such as a mass spectrometer, for wafer-state information will result in new approaches for sensing, optimizing, and controlling integrated circuit fabrication processes. © 1998 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
07.75.+h Mass spectrometers

BCl3/Ar reactive ion etching for gate recessing of GaInP/InGaAs/GaAs pseudomorphic high electron mobility transistors

C. W. Kuo, Y. K. Su, H. H. Lin, and C. Y. Chin

J. Vac. Sci. Technol. B 16, 3003 (1998); http://dx.doi.org/10.1116/1.590369 (5 pages)

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BCl3 reactive ion etching for gate recessing of GaInP/InGaAs/GaAs pseudomorphic high electron mobility transistors (PHEMTs) is found improved by the addition of an appropriate amount of Ar to the gas flow. The influence of the BCl3/Ar gas flow ratio on GaAs to GaInP etch selectivity, surface roughness, and surface damage was studied. The results indicate that the conditions for minimum plasma damage, as determined by photoreflectance (PR) spectroscopy, corresponded with the conditions for minimum surface roughness, as determined by atomic force microscopy (AFM). The optimal BCl3/Ar gas flow ratio for minimum surface damage and roughness was found to be 6:4. Two BCl3:Ar flow rate ratios, 6:4 (optimal ratio) and 10:0 (pure BCl3) were used for gate recess etching in the fabrication of GaInP/InGaAs/GaAs PHEMTs. From drain–source current to gate–source voltage (Ids–Vgs) measurements, it was found that the plasma-induced damage for the sample Sc dry etched with 6:4 BCl3/Ar is less than that of the sample Se dry etched with pure BCl3. The dc and small signal rf characteristics of PHEMT Sc were superior to those of the wet-etched PHEMT S0 and PHEMT Se dry etched with pure BCl3. The improvement is attributed to the lower parasitic source resistance associated with the tighter recess geometry of the BCl3 plasma recess device. These results show that photoreflectance spectroscopy is a powerful tool for investigating surface damage and can be used to improve the performance of PHEMTs. © 1998 American Vacuum Society.
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85.30.Tv Field effect devices
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Interaction between gas rarefaction and metal ionization in ionized physical vapor deposition

S. M. Rossnagel

J. Vac. Sci. Technol. B 16, 3008 (1998); http://dx.doi.org/10.1116/1.590333 (5 pages) | Cited 19 times

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The process known as ionized physical vapor deposition, or I-PVD, consists of the physical sputtering of metal atoms into a dense, inert gas plasma, ionization of the sputtered metal atoms, and subsequent deposition of the films from these metal ions. Measurements have shown a decrease in electron temperature coupled with an unexpected decrease in plasma density as a function of increasing metal flux. Recent plasma modeling work has suggested gas rarefaction as the underlying factor in these declines. Measurements of neutral gas density in the plasma region reported here confirm this model and are consistent with earlier studies of sputtered atom induced gas heating and rarefaction. © 1998 American Vacuum Society.
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81.15.Cd Deposition by sputtering
85.40.Sz Deposition technology

Atomically flat gold film surfaces deposited on Si (111) surfaces at room temperature

H. Okamoto and H. Nejo

J. Vac. Sci. Technol. B 16, 3013 (1998); http://dx.doi.org/10.1116/1.590334 (2 pages) | Cited 2 times

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We have observed atomically flat gold surfaces deposited on Si (111) 7×7 surfaces. These films are deposited by conventional evaporative deposition at a pressure below 2×10−6 Pa. The surface topography was taken by scanning tunneling microscopy. Atomically flat terraces as large as 100 Å separated by steps were observed. This surface should provide a good substrate for scanning tunneling microscopy studies. © 1998 American Vacuum Society.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
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

Correlation between the early stage of copper metal organic chemical vapor deposition and the material properties of thin film

Eui Seong Hwang and Jihwa Lee

J. Vac. Sci. Technol. B 16, 3015 (1998); http://dx.doi.org/10.1116/1.590335 (6 pages) | Cited 9 times

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Cu metal organic chemical vapor deposition has been performed on TiN/Si(100) substrates using Cu(I)(hfac)(vtms) at various substrate (110⩽Ts⩽300 °C) and bubbler temperature (0⩽Tb⩽30 °C) conditions, in which the early stage of film formation characterized by scanning electron microscopy and in situ laser beam (λ=6328 Å) reflectance measurement could be well correlated with the surface roughness and the electrical resistivity of the copper films developed in a later stage. All the reflectance versus deposition time curves showed a qualitatively similar shape consisting of three sequential parts: a rapid initial decrease to a minimum, an increase to a maximum, and a gradual decay to almost zero, in which the minimum and maximum roughly correspond to the onset and completion of island coalescence, respectively. As the Ts is raised and/or the Tb is lowered, larger islands were formed in a smaller density at the onset of island coalescence due to a lower nucleation rate. The surface roughness gradually develops with increasing film thickness after forming a continuous film, but it does not saturate at a thickness of ∼2 μm and shows a correlation with the average island size in the earlier coalescence stage, i.e., the smaller islands evolves to a smoother surface. Above the threshold temperature (Ts∼230 for Tb=30 °C) the copper islands begin to show facets and at even higher Ts large truncated polyhedron-shaped copper islands are formed, which upon coalescing leave many interfacial voids to result in a film with a very rough surface and a high electrical resistivity. The copper films deposited at 150⩽Ts⩽200 °C have a very low value of ρ≈2 μΩ cm, which increases by a factor of ∼2 when Ts is lowered to 110 °C. The latter was accompanied by the formation of smaller islands at the onset of coalescence, and therefore the increase in ρ at Ts⩽150 °C was attributed to the electron scattering at the grain boundaries. © 1998 American Vacuum Society.
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81.05.Bx Metals, semimetals, and alloys
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.61.At Metal and metallic alloys
78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Properties of sputtered Cr–O and reactively sputtered Cr–N–O as passivation layers against copper oxidation

Jui-Chang Chuang and Mao-Chieh Chen

J. Vac. Sci. Technol. B 16, 3021 (1998); http://dx.doi.org/10.1116/1.590336 (6 pages)

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Passivation layers of 200 Å sputtered Cr–O as well as reactive sputtered Cr–N–O were studied with respect to the passivation capability against thermal oxidation of Cu in flowing nitrogen and flowing oxygen ambients. In a flowing N2 ambient, both Cr–O and Cr–N–O passivation layers were able to prohibit oxidation of Cu at temperatures up to 700 °C. In an O2 ambient, the passivation capability of Cr–N–O layer was found to be 500 °C, which is 150 °C higher than that of Cr–O layer. The superiority of the passivation capability of the Cr–N–O layer is presumably due to decoration of the surface defects and grain boundaries with nitrogen, which provide fast paths for oxygen and copper diffusion. © 1998 American Vacuum Society.
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81.65.Rv Passivation
81.65.Mq Oxidation
81.15.Cd Deposition by sputtering

Role of V-shaped stacking faults in Au/n-type ZnMgSSe:Cl Schottky diodes

Ching-Wu Wang

J. Vac. Sci. Technol. B 16, 3027 (1998); http://dx.doi.org/10.1116/1.590337 (5 pages)

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The microstructural, optical, and electronic characteristics of both Cl-doped ZnMgSSe epilayers and Schottky diodes grown by the molecular beam epitaxy method on n+-type GaAs (100) substrates with different thicknesses of Cl-doped ZnSe buffer layers were investigated via three measurements: transmission electron microscopy, photoluminescence, and deep level transient spectroscopy. The V-shaped stacking faults, originating at or near the ZnSe:Cl (buffer layer)/GaAs interface and extending into the ZnMgSSe:Cl epilayer, were discovered to have the evident inclination to exist in samples with thicker ZnSe:Cl buffer layers and higher growth temperatures. Evidence also revealed that the stacking faults not only produced poor optical quality of ZnMgSSe:Cl thin film, but also created more interface state densities at the Au/n-type ZnMgSSe:Cl Schottky junction. Such results are the main factors to damage the I–V characteristics of Au/n-type ZnMgSSe:Cl Schottky diode, including the less forward conduction current density, the bigger turn-on voltage, and the larger reverse leakage current followed by the smaller reverse breakdown voltage. © 1998 American Vacuum Society.
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85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes
61.72.Nn Stacking faults and other planar or extended defects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Interface characterization of Si3N4/Si/GaAs heterostructures after high temperature annealing

Dae-Gyu Park, Zhonghui Wang, Hadis Morkoç, Samuel A. Alterovitz, David J. Smith, and S.-C. Y. Tsen

J. Vac. Sci. Technol. B 16, 3032 (1998); http://dx.doi.org/10.1116/1.590338 (9 pages) | Cited 4 times

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We present data on interface characteristics of Si3N4/Si/GaAs metal–insulator–semiconductor (MIS) structures and correlate electrical properties with spectroscopic ellipsometry, x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) observations. The interface of Si3N4/Si/GaAs heterostructures was electrically characterized by a combination of capacitance–voltage and conductance methods. The nature of an insulator/GaAs interface and the microstructure of Si3N4/Si/GaAs interfaces after high temperature annealing were investigated by variable angle spectroscopic ellipsometry and high resolution TEM, respectively. The evolution of chemical species in Si3N4/Si/GaAs heterostructures was examined using in situ angle-resolved XPS. The interface trap density (Dit) of the Si3N4/Si MIS capacitor was in the 2×1010 eV−1 cm−2 range near the Si midgap after rapid thermal annealing at 550 °C in N2. However, this density increased to high 1010 eV−1 cm−2 with annealing at 800 °C. The interface characteristics of Si3N4/Si/GaAs structures with Dit in the 7×1010 eV−1 cm−2 range also degraded after annealing at 750 °C in N2 with Dit increasing to 5×1011 eV−1 cm−2 near the GaAs midgap. The spectroscopic ellipsometry results together with high resolution TEM observations appear to suggest that the degradation is due in part to the interface changing from crystalline to amorphous through chemical reaction. XPS measurements revealed that the as-deposited Si interlayer is nitridated during the initial stages of silicon nitride deposition, thus the thinned Si cannot prevent the outdiffusion of Ga and As species. We circumvented thermally induced interface degradation of Si3N4/Si/GaAs structures by employing a novel ex situ/in situ growth approach. © 1998 American Vacuum Society.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing
73.20.At Surface states, band structure, electron density of states
68.35.Fx Diffusion; interface formation
84.32.Tt Capacitors
85.30.Tv Field effect devices

Reduction of oxygen contamination in InGaP and AlGaInP films grown by solid source molecular beam epitaxy

W. E. Hoke, P. J. Lemonias, and A. Torabi

J. Vac. Sci. Technol. B 16, 3041 (1998); http://dx.doi.org/10.1116/1.590339 (7 pages) | Cited 6 times

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Oxygen contamination has been observed in In0.5Ga0.5P and (Al0.23Ga0.77)0.5In0.5P films grown by solid source molecular beam epitaxy with elemental phosphorus. Using a conventional P4 cracking zone temperature of 950 °C, spike contamination levels as high as 1×1019 cm−3 were observed at growth interrupted interfaces with the resultant deactivation of silicon doping pulses. By reducing the phosphorus cracking temperature to 700 °C, the oxygen level in InGaP was reduced to below the secondary ion mass spectrometry background level of 3×1016 cm−3. No measurable accumulation of oxygen was observed at growth interrupted interfaces and efficient silicon pulse doping was obtained. InGaP films grown at the lower cracking temperature exhibited improved mobilities and enhanced photoluminescence intensities. An oxygen level in (Al0.23Ga0.77)0.5In0.5P of less than 1.5×1017 cm−3 was obtained with good mobilities and luminescence. Efficient silicon pulse doping in AlGaInP was demonstrated. The oxygen contamination is in the phosphorus flux and is likely a volatile phosphorus oxide such as P4O6. © 1998 American Vacuum Society.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
78.55.Cr III-V semiconductors

Surface chemistry of II–VI semiconductor ZnSe studied by time of flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy

J. Zhao, M. H. Na, E. H. Lee, H. C. Chang, J. A. Gardella, and H. Luo

J. Vac. Sci. Technol. B 16, 3048 (1998); http://dx.doi.org/10.1116/1.590340 (7 pages) | Cited 6 times

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The composition and chemical state of the native oxide of single-crystalline ZnSe and the effect of HCl (18.5%)/H2O wet etching have been studied by time of flight secondary ion mass spectrometry (TOF-SIMS) and x-ray photoelectron spectroscopy (XPS). TOF-SIMS depth profile measurements show that the oxide layer of ZnSe is removed by etching in this solution for one minute, followed by a subsequent one minute rinse in deionized H2O. XPS depth profile measurements of the untreated ZnSe surface show that Se oxide only exists at the topmost surface (within the top 10% of the oxide layer). The change of Zn Auger parameter with depth of the untreated ZnSe specimen indicates that the remaining oxygen is chemically associated to Zn. High resolution XPS measurements of the etched ZnSe show no detectable Se oxide at the surface. Meanwhile, the Zn Auger parameter is similar to that of the unetched ZnSe after its oxide layer being removed by Ar+ sputtering. Both experiments show longer wet etching times result in Zn deficiency and more Cl contamination at the sample surface.© 1998 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Dz II-VI semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Evaluation of development speed of a photoresist by means of electrical conductivity measurement

T. Takeda and M. Saka

J. Vac. Sci. Technol. B 16, 3055 (1998); http://dx.doi.org/10.1116/1.590341 (4 pages) | Cited 1 time

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A method was examined for evaluating the electrical conductivity of a photoresist to predict its development speed. The conductivity of organic solutions of the photoresist base polymer at various frequencies was found to have a positive correlation with the dissolution speed of the photoresist base polymer into an alkaline developer. In addition, the influence of the measurement temperature and of the concentration of the polymer solution on the conductivity was investigated. It is shown that a prediction of development speed of a photoresist by measuring its conductivity is possible. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Investigation of Ta–RuO2 diffusion barrier for high density memory capacitor applications

Dong-Soo Yoon, Hong Koo Baik, Sung-Man Lee, Chang-Soo Park, and Sang-In Lee

J. Vac. Sci. Technol. B 16, 3059 (1998); http://dx.doi.org/10.1116/1.590342 (6 pages) | Cited 8 times

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The properties of both oxygen indiffusion and oxidation resistance in a Ta+RuO2 layer for high density memory devices were investigated by using Rutherford backscattering spectroscopy, four point probe, x-ray diffraction, x-ray photoelectron spectroscopy, and planar transmission electron microscopy. The Ta+RuO2/Si system sustained up to 800 °C without an increase in resistivity. The Ta+RuO2 diffusion barrier showed a Ta amorphous microstructure and an embedded RuOx nanocrystalline structure in the as-deposited state. The Ta+RuO2 film showed the formation of RuO2 phase by reaction with the indiffused oxygen from atmosphere after annealing in an air ambient. The Ta+RuO2 diffusion barrier showed that Ta is sufficiently bound to oxygen in the as-deposited state, but RuO2 consists of Ru and Ru–O binding state. The Ta–O bonds showed little change compared to the as-deposited state with increasing annealing temperature, whereas Ru–O bonds significantly increased and transformed to conductive oxide, RuO2. Therefore, the Ta layer deposited by RuO2 addition effectively prevented the indiffusion of oxygen up to 800 °C and its oxidation resistance was superior to various barriers reported by others. © 1998 American Vacuum Society.
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68.35.Fx Diffusion; interface formation
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.30.Sk Pulse and digital circuits
66.30.Ny Chemical interdiffusion; diffusion barriers
81.65.Mq Oxidation
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Ct Interface structure and roughness
81.40.Gh Other heat and thermomechanical treatments

Nonerratic behavior of overerased bits in flash EEPROM

F. D. Nkansah, E. Prinz, and M. Hatalis

J. Vac. Sci. Technol. B 16, 3065 (1998); http://dx.doi.org/10.1116/1.590343 (4 pages)

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We report the effects of flash “channel” programming, or severe gate disturb, on the threshold voltage of fast or overerased bits. Experiments have been performed to establish that this class of fast bits are nonerratic and remain fast after 250 °C bake. These fast bits exhibit identical subthreshold characteristics similar to that of a normal bit after ultraviolet erase, thus establishing that the initial charge stored on the floating gate is the same for both normal and fast bits. Polysilicon grain boundary enhanced electric fields which result in impact ionization by tunneling electrons, thus generating trapped positive charges in the grain boundary oxide ridges are believed to play an important role in the generation of fast bits. © 1998 American Vacuum Society.
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84.30.Sk Pulse and digital circuits

Vacuum properties of a new panel structure for field emission displays

Y. R. Cho, H. S. Kim, J. D. Mun, J. Y. Oh, H. S. Jeong, and S. Ahn

J. Vac. Sci. Technol. B 16, 3069 (1998); http://dx.doi.org/10.1116/1.590344 (4 pages) | Cited 2 times

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A new field emission display (FED) panel structure with an auxiliary space was developed in order to increase the conductance of the system for evacuation and help evacuate the cavity inside the FED more effectively. Gas molecules in the main space of the panel can move easily into the auxiliary space through the multiple openings in the base plate and can then be pumped out through the exhaust tube at the auxiliary tank. For the very thin panel, in which the space between the face plate and base plate is 58 μm, pressure drop characteristics during evacuation are very sensitive to the number of openings in the base plate. The main purpose of multiple openings in shortening evacuation time is to reduce pressure gradient inside the cavity. Additionally, the auxiliary space makes it easy to place various getters inside the FED panel and to maintain high vacuum for a prolonged lifetime of the FED. © 1998 American Vacuum Society.
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85.45.Fd Field emission displays (FEDs)

Effect of CH4 on the electron emission characteristics of active molybdenum field emitter arrays

Babu R. Chalamala, Robert M. Wallace, and Bruce E. Gnade

J. Vac. Sci. Technol. B 16, 3073 (1998); http://dx.doi.org/10.1116/1.590444 (4 pages) | Cited 7 times

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Exposing active Spindt-type molybdenum field emission microcathode arrays to CH4 resulted in increased electron emission. Exposures of 250 and 2500 L result in electron emission enhancement of 106.2±41.0% and 200.1±20.7% and a decrease in tip work function by 10.2±5.6% and 17.6±1.7%, respectively. The measured work function changes indicate the formation of molybdenum carbides on the field emitter tips. © 1998 American Vacuum Society.
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85.45.Db Field emitters and arrays, cold electron emitters

Easy and reproducible method for making sharp tips of Pt/Ir

J. Lindahl, T. Takanen, and L. Montelius

J. Vac. Sci. Technol. B 16, 3077 (1998); http://dx.doi.org/10.1116/1.590445 (5 pages) | Cited 9 times

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We have investigated a simple yet powerful method for making sharp scanning tunneling microscopy tips of Pt/Ir. It consists of three electrochemical polish/etch steps, not requiring any special micropolishing. The tips, as seen by high-resolution transmission electron microscopy, are sharper than 20 Å. Furthermore, they are smooth, without mini tips and covered with an oxide layer not much thicker than the native one (as seen from a freshly cut wire) when all three steps are applied. © 1998 American Vacuum Society.
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07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.65.Ps Polishing, grinding, surface finishing
81.65.Cf Surface cleaning, etching, patterning

Microelectron gun with silicon field emitter

Yasuhiro Endo, Ichiro Honjo, and Shunji Goto

J. Vac. Sci. Technol. B 16, 3082 (1998); http://dx.doi.org/10.1116/1.590495 (4 pages) | Cited 5 times

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We evaluated the characteristics of single Si field emitters (Si-FEs) from the perspective of their use in electron guns. Since the current fluctuation of Si-FEs strongly depends on the product of vacuum pressure P and emission current I, just as it does for conventional cold field emitters (CFEs), the mechanism of fluctuation was assumed to be similar to that of CFE. Such fluctuations are divided into two regions, the boundary was virtually equal to CFEs, at approximately 3×10−12 Pa A. However, unlike as for CFEs, the emission current of Si-FEs drops abruptly after a certain duration. We found that the integral of PI with the duration time (PIT integral) is almost constant (approximately 1×10−8 Pa A s) in various conditions and therefore assume that it correlates with the emission area of the emitter tip. The current leakage between emitter and gate electrode was found to be caused because of their small size. Responsible for this leakage are hydrocarbon contamination layers that were generated by emitted electrons or backscattered electrons on the surface of the insulating layer. Finally, we fabricated a miniaturized electron gun with Si-FEs and succeeded in obtaining SEM images with electrons that were emitted from the Si-FEs. © 1998 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
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
68.35.Dv Composition, segregation; defects and impurities

Self-heating effects in a InP/CdS/LaS cold cathode

Aashish Malhotra, Yamini Modukuru, and Marc Cahay

J. Vac. Sci. Technol. B 16, 3086 (1998); http://dx.doi.org/10.1116/1.590446 (11 pages) | Cited 7 times

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We analyze the importance of self-heating effects in a new cold cathode emitter which consists of a thin region of cadmium sulfide (CdS) sandwiched between a heavily doped indium phosphide (InP) substrate and a low work function lanthanum sulfide (LaS) semimetallic thin film. We identify the mechanisms leading to power dissipation in a cathode with an emission window of rectangular geometry, including the effects of inelastic scattering in the CdS and LaS layers. The latter are modeled using a temperature dependent mean-free path approach. The analysis includes the effects of current crowding in the emission window due to the finite resistivity of the LaS layer. We determine the cathode parameters which minimize current crowding and self-heating effects in the cathode. We also calculate the relative contribution of the ballistic and inelastic portions of the electron current emitted into vacuum. © 1998 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
73.40.Gk Tunneling

Experimental demonstration of the validity of accelerated radiation damage testing of x-ray mask materials

R. E. Acosta and R. Rippstein

J. Vac. Sci. Technol. B 16, 3097 (1998); http://dx.doi.org/10.1116/1.590447 (2 pages) | Cited 2 times

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85.40.Hp Lithography, masks and pattern transfer
61.80.Cb X-ray effects
61.82.Fk Semiconductors
06.60.Mr Testing and inspecting procedures

Sputtering rate change and surface roughening during oblique and normal incidence O2+ bombardment of silicon, with and without oxygen flooding

Charles W. Magee, Gary R. Mount, Stephen P. Smith, Brad Herner, and Hans-J. Gossmann

J. Vac. Sci. Technol. B 16, 3099 (1998); http://dx.doi.org/10.1116/1.590370 (6 pages) | Cited 20 times

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A sample of low-temperature epitaxial Si grown with five B delta-doped layers 5.4 nm apart has been profiled using secondary ion mass spectrometry under a variety of O2 bombardment conditions. Energies from 400 eV to 1.5 keV were used with angles of incidence from 0° to 70°. Analyses were performed using oxygen flooding of the sample surface during analysis, as well as without using oxygen flooding. The apparent spacing between the B delta layers was used to determine the magnitude and extent of increased sputtering rate at the beginning of an analysis. Changes in depth resolution due to sputter-induced surface roughening are reflected in variations in the apparent width of the B delta layers. It was found that sputtering with 500 eV O2 at an angle of 50° while flooding with oxygen produced no measurable change in sputtering rate and resulted in no unexpected shift towards the surface of the B delta layers. These analysis conditions also resulted in a depth resolution which was as good as that obtained using 400 eV O2 bombardment at 0° incidence without oxygen flooding. The 0° method of analysis, however, resulted in a 1.1 nm shift of the topmost B delta layer toward the surface, and the 0° method had a sputtering rate only 1/5 that of the 50° method of analysis. © 1998 American Vacuum Society.  
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.uf Ge and Si
61.72.S- Impurities in crystals
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
68.55.Nq Composition and phase identification

Ohmic contacts to p-type GaN using a Ni/Pt/Au metallization scheme

Ja-Soon Jang, Kyung-Hyun Park, Hong-Kyu Jang, Hyo-Gun Kim, and Seong-Ju Park

J. Vac. Sci. Technol. B 16, 3105 (1998); http://dx.doi.org/10.1116/1.590448 (3 pages) | Cited 17 times

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We report a new Ni/Pt/Au trilayer metallization scheme for the formation of ohmic contact to p-GaN. Metal thin films with a thickness of 20 nm for Ni, 30 nm for Pt, and 80 nm for Au were deposited on the p-GaN layer (Na=9.4×1016 cm−3) by electron beam evaporation. The samples, annealed at 500 °C for 30 s in a rapid thermal anneal system, showed a high quality ohmic contact with a low specific contact resistance of 2.1×10−2 Ω cm2. Auger electron spectroscopy analysis of the contact layers suggests that Pt plays an important role in the formation of ohmic contact, indicating that a Ni/Pt/Au trilayer can be used and that it is a promising material system for ohmic contact to p-GaN. © 1998 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
07.50.-e Electrical and electronic instruments and components
73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts

Thermally induced interface degradation in (100) and (111) Si/SiO2 analyzed by electron spin resonance

A. Stesmans and V. V. Afanas’ev

J. Vac. Sci. Technol. B 16, 3108 (1998); http://dx.doi.org/10.1116/1.590449 (4 pages) | Cited 19 times

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A comparative electron spin resonance (ESR) study was performed on thermal (111) Si/SiO2 and (100) Si/SiO2 of the vacuum postoxidation-induced interface degradation in terms of interfacial trivalent Si dangling bond creation (ESR-active Pb, Pb0, and Pb1 defects). In (111) Si/SiO2, the degradation mechanism was isolated as pronounced permanent Pb (∘Si�Si3) creation from ∼640 °C onward in densities Nc monotonically increasing with anneal temperature; at ∼1100 °C, about 1.1×1013 Pbs cm−2 are created in addition to the as-oxidized state value No∼4.9×1012 cm−2. The (100) Si/SiO2 interface is found to be much less vulnerable. Only electrically harmless Pb1’s are additionally created, the density reaching Nc(Pb1)∼4.4×1012 cm−2 at ∼1100 °C. By contrast, the density of the electrically adverse Pb0 trap tends to decrease. Together with the recently established electrical irrelevance of Pb1, the results add to provide a fundamental reason for the preference of the (100) Si face in devicing. © 1998 American Vacuum Society.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
76.30.Mi Color centers and other defects
61.72.Cc Kinetics of defect formation and annealing

Enabling in situ atomic-scale characterization of epitaxial surfaces and interfaces

J. B. Smathers, D. W. Bullock, Z. Ding, G. J. Salamo, P. M. Thibado, B. Gerace, and W. Wirth

J. Vac. Sci. Technol. B 16, 3112 (1998); http://dx.doi.org/10.1116/1.590496 (3 pages) | Cited 17 times

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A custom designed sample handling system which allows the integration of a commercially available scanning tunneling microscope (STM) facility with a commercially available molecular beam epitaxy (MBE) facility is described. No customization of either the STM imaging stage or the MBE is required to implement this design.© 1998 American Vacuum Society.
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68.55.-a Thin film structure and morphology
06.60.Ei Sample preparation (including design of sample holders)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness

Atom technology project: Recent activities

Kazunobu Tanaka

J. Vac. Sci. Technol. B 16, 3127 (1998); http://dx.doi.org/10.1116/1.590450 (5 pages)

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The “Atom Technology” project started in fiscal 1992 as one of MITI’s 10 year projects, aims at systematically establishing technology for handling individual atoms and molecules on a solid surface or in a three-dimensional space, as a generic technology for various fields of industry. This project, closely adjacent to science, emphasizes the following three key focuses: atom manipulation, nanoscale self-organization, and critical-state phase control, with two basic approaches of in situ dynamical observation (experimental) as well as ab initio calculation (theoretical). In this article, several topics were picked up from recent activities at the Joint Research Center for Atom Technology (JRCAT) for Phase I of the initial 6 years (1992–1997) and some technical details were described: (1) ultrathin SiO2 on Si(001) surfaces; layer-by-layer oxidation, its kinetics, scanning reflection electron microscopy observation, and scanning tunneling microscopy observation of leakage sites; (2) growth and transport of structure-controlled SinHx+ clusters for deposition using a novel ion trap; and (3) colossal magnetoresistance and related phenomena in perovskite-type manganese oxides. Research plans for phase II (1998–2001) of the project will be also touched upon. © 1998 American Vacuum Society.
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68.00.00 Surfaces and interfaces; thin films and nanosystems (structure and nonelectronic properties)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.65.Mq Oxidation
36.40.-c Atomic and molecular clusters
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
72.15.Gd Galvanomagnetic and other magnetotransport effects
72.20.My Galvanomagnetic and other magnetotransport effects

Nanofabrication in cellular engineering

C. D. W. Wilkinson, A. S. G. Curtis, and J. Crossan

J. Vac. Sci. Technol. B 16, 3132 (1998); http://dx.doi.org/10.1116/1.590451 (5 pages) | Cited 31 times

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Biological cells are strongly influenced by the topography of the surface on which they live, both in cell culture and in an animal. They are guided along micron sized grooves and change their shape becoming more elongated. On the other hand, cells do not adhere to surfaces that are covered in small nanometrically sized pillars. These effects can be used for cellular engineering purposes to determine the behavior of cells and in particular to make prostheses for medical purposes. The differences in micro and nanofabrication techniques necessary to adapt normal semiconductor technology for these purposes are discussed. Patterning of plastics using mechanical methods (embossing and molding) is shown to have excellent resolution, can be used on biodegradable material and a large enough area of patterned material can be produced at a reasonable cost. An application of this technology to the repair of broken tendons is discussed in some detail. It is shown that a biodegradable membrane patterned by embossing with a fused silica master can be used to effect tendon repair. Not only does the tendon reheal, but the synovial channel that should surround the tendon and provide lubrication to the tendon, is reformed correctly. © 1998 American Vacuum Society.
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87.17.-d Cell processes
87.90.+y Other topics in biological and medical physics (restricted to new topics in section 87)
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

Challenges and progress in x-ray lithography

Jerome P. Silverman

J. Vac. Sci. Technol. B 16, 3137 (1998); http://dx.doi.org/10.1116/1.590452 (5 pages) | Cited 26 times

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X-ray lithography (XRL) is a very promising technique with the potential to be available for integrated circuit manufacturing as early as the 130 nm generation. As a result of many years of development, the technology is relatively mature. Synchrotron sources have demonstrated performance and reliability; preproduction aligners are available from multiple vendors; significant improvements are being made in mask fabrication; and high resolution imaging has been demonstrated at 100 nm and below. Established vendors already have experience with almost all of the tools that are needed, although improved performance is required for most in order to satisfy the error budgets at 130 nm and below. Significant development activities are continuing in both the United States and Japan, and numerous complex integrated circuits have been fabricated using XRL for one or more critical levels. Nonetheless, there are challenges still to be met. Among the most important are the development and commercial availability of an improved e-beam mask writer; the ability to fabricate defect-free masks satisfying the image placement and critical dimension control requirements with good yields; the stability of the masks in usage (including the issue of possible radiation damage); the ability to correct for magnification errors; and the ability to satisfy the industry’s desire for a technology extendible to 70 nm ground rules. These issues are primarily manufacturing issues, as opposed to issues related to demonstrating proof-of-concept or feasibility, although demonstrating extendibility is still needed before the industry can commit to using XRL at 70 nm ground rules. Because of the existing XRL facilities and experience, effective work to address these and other issues can be accomplished in a timely manner. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Extreme ultraviolet lithography

C. W. Gwyn, R. Stulen, D. Sweeney, and D. Attwood

J. Vac. Sci. Technol. B 16, 3142 (1998); http://dx.doi.org/10.1116/1.590453 (8 pages) | Cited 90 times

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An extreme ultraviolet (EUV) lithography tool using 13.4 nm radiation is being developed by a consortium of integrated circuit (IC) manufacturers to support 100 nm imaging for integrated circuit production. The 4×, 0.1 NA alpha tool has a >1 μm depth of focus, all reflective optics, a xenon laser plasma source, and robust reflective masks. The technology is expected to support feature scaling down to 30 nm. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Ion projection lithography: Status of the MEDEA project and United States/European cooperation

Gerhard Gross, Rainer Kaesmaier, Hans Löschner, and Gerhard Stengl

J. Vac. Sci. Technol. B 16, 3150 (1998); http://dx.doi.org/10.1116/1.590454 (4 pages) | Cited 5 times

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Structure and targets of the European MEDEA project on ion projection lithography as well as related U.S./European cooperation are explained. By assuming 10 μm virtual source size and 1 eV (full width half maximum) energy spread calculations for a multielectrode electrostatic ion–optical system (1.25 m between ion source and stencil mask, ≈1.8 m between mask and wafer) we realize the possibility of 100 nm resolution (line and space) over an exposure field of 22×22 mm2 even when using the MONTEC model for calculating the stochastic blur and when running 3.3 μA He+ ion beam current through the ion–optical column, thus more than twice exceeding target specifications. Thus, for 100 nm resolution and 50% pattern density the raw throughput is ≈12 cm2/s corresponding to >75 WPH (pattern within 80% of 300 mm wafer area). © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
41.85.-p Beam optics
89.20.Bb Industrial and technological research and development

Critical issues in 157 nm lithography

T. M. Bloomstein, M. Rothschild, R. R. Kunz, D. E. Hardy, R. B. Goodman, and S. T. Palmacci

J. Vac. Sci. Technol. B 16, 3154 (1998); http://dx.doi.org/10.1116/1.590455 (4 pages) | Cited 29 times

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Projection lithography at 157 nm is a candidate technology for the 100–70 nm generations, and possibly beyond. It would provide an evolutionary extension to the current primary photolithographic processes and components: excimer lasers, refractive optics, and transmissive masks. This article presents data on the transmission of optical materials at 157 nm, the performance of optical coatings, the issues that must be faced by photomasks, and the considerations related to engineering resists at this wavelength. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.70.-a Optical materials
42.79.Wc Optical coatings

Electron beam lithography process for advanced optical masks

Naoya Hayashi, Masa-aki Kurihara, Toshikazu Segawa, Toshifumi Yokoyama, and Tsukasa Abe

J. Vac. Sci. Technol. B 16, 3158 (1998); http://dx.doi.org/10.1116/1.590456 (6 pages)

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The requirements for advanced optical masks have been tightened according to the accelerated lithography roadmap for semiconductor manufacturing. The accuracy of the optical mask may be affected by the pattern exposure tools, the materials, and the processes. Higher acceleration voltage e-beam pattern exposure was evaluated with a chemically amplified resist. With the higher acceleration voltage e-beam system, proximity effect correction is needed to control the critical dimension (CD). CD linearity is maintained down to 400 nm for different kinds of patterns by adopting the 50 kV e-beam system and proximity effect correction. The results show that the method is an attractive candidate for fabrication of next generation optical masks. Dry etching is effective in achieving small feature sizes, such as optical proximity correction (OPC), with high pattern fidelity. Loading effects were evaluated, and inductively coupled plasma dry etching was found to be stable against those effects. Fabrication of the OPC pattern designed for a 0.15 μm rule device was demonstrated with these methods. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

EL5: One tool for advanced x-ray and chrome on glass mask making

M. A. Sturans, J. G. Hartley, H. C. Pfeiffer, R. S. Dhaliwal, T. R. Groves, J. W. Pavick, R. J. Quickle, C. S. Clement, G. J. Dick, W. A. Enichen, M. S. Gordon, R. A. Kendall, C. A. Kostek, D. J. Pinckney, C. F. Robinson, et al.

J. Vac. Sci. Technol. B 16, 3164 (1998); http://dx.doi.org/10.1116/1.590457 (4 pages) | Cited 3 times

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The state-of-the-art for mask making continues to be driven by 1× x-ray masks. The IBM EL4+ e-beam mask writer at the Advanced Mask Facility in Burlington, Vermont, was originally designed for 0.35 μm ground rules (GRs) direct write at 50 kV, but delivered at 75 kV operation to achieve 0.25 μm GR performance for 1× mask making. Over the next 2 years, with optimization and improvements in each of the subsystems, its performance was enhanced beyond the 0.18 μm GR requirements. It is clear, however, that for 0.13 and 0.1 μm GR mask manufacturing, a new tool is required. It has also become apparent that because of the very high development and tool build costs, and small number of required x-ray mask makers, the same technology must be applicable for chrome on glass (COG) mask making. Based on the experience with EL4+, IBM is designing an EL5 tool which will provide the 0.13/0.1 μm GR performance for 1×, and easily convert to 4× COG exposure for 9 in. glass as well as 300 mm wafer direct write operation. As with previous IBM EL series e-beam systems, it is anticipated that EL5 performance will be extendable beyond 0.1 μm GR. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Distributed, multiple variable shaped electron beam column for high throughput maskless lithography

T. R. Groves and R. A. Kendall

J. Vac. Sci. Technol. B 16, 3168 (1998); http://dx.doi.org/10.1116/1.590458 (6 pages) | Cited 20 times

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The ultimate resolution obtainable with focused electron beams is, for practical purposes in lithography, unlimited. Existing e-beam lithography systems are too slow to be practical for high volume manufacturing of semiconductor devices, however. The usable current in probe forming systems is limited by the stochastic Coulomb interaction in the beam path, which causes loss of resolution at high current. This is due to the need to pass all of the writing current through an aperture. Distributed systems, by contrast, do not suffer from this problem, as the current is spread over a large volume. The purpose of this article is to propose a distributed system, employing multiple, variable shaped beams for direct write (maskless) lithography. We call this system DiVa, to emphasize the key attributes of distributed writing current, and variable beam shaping. It utilizes a planar cathode, patterned with a rectilinear array of square emitters. Focusing is accomplished by a uniform, axial magnetic field, oriented along the optic axis. This transfers a one-to-one image of the emitters onto the writing surface. Deflection plates between adjacent rows of beamlets effect motion in one Cartesian axis, while mechanical translation of the stage effects motion in the orthogonal axis. Theoretical resolution is diffraction limited to 4.6 nm at 50 kV. Experimental results are presented which demonstrate the first order optics using a rudimentary apparatus. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Multiplexed blanker array for parallel electron beam lithography

G. I. Winograd, L. Han, M. A. McCord, R. F. W. Pease, and V. Krishnamurthi

J. Vac. Sci. Technol. B 16, 3174 (1998); http://dx.doi.org/10.1116/1.590345 (3 pages) | Cited 3 times

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Alternative electron beam technologies to conventional single beam systems have the potential to increase beam current by an order of magnitude, into the 1–10 μA range. The technique we are investigating is to insert an aperture array at an object plane in a lithography system, thus creating an array of beamlets which are imaged as a dot matrix. Each aperture is surrounded by an independently controlled electrostatic microblanker which can modulate the beamlet passing through the aperture in conjuction with a blanking aperture placed at a crossover further down the column. An existing 20 kV shaped beam column with a LaB6 source providing 5 μA of illumination current over a 150 μm×150 μm square area is used as a test stand. The column is used to test prototype microblanker chips. Power dissipation calculations show less than a 10 K temperature rise over the prototype chips. Work has begun on a second generation prototype blanker array which will overcome many of the processing difficulties encountered with the first prototype. Specifically, the new all-silicon process will allow fabrication of smaller apertures which require less demagnification and a shorter electron-optical column. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

High throughput electron lithography with the multiple aperture pixel by pixel enhancement of resolution concept

P. Kruit

J. Vac. Sci. Technol. B 16, 3177 (1998); http://dx.doi.org/10.1116/1.590346 (4 pages) | Cited 6 times

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A new lithography concept for the sub-100 nm generations is proposed. The bulk of the machine is a traditional deep ultraviolet demagnification scanner–stepper. The mask is illuminated by 106–108 almost diffraction limited subbeams formed by a microlens array. After demagnification these subbeams are focused on a photon–electron converter plate. Each photon subbeam triggers the emission of a narrow beam of electrons. The electron beams are focused individually on the wafer, which is at a distance of about 1 mm from the converter plate. By scanning both mask and wafer through the many beams, the whole wafer is exposed. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.79.Bh Lenses, prisms and mirrors
41.85.-p Beam optics

Experimental evaluation of a miniature electrostatic thin-foil electron optical column for high current and low-voltage operation

Dieter Winkler, Claus-D. Bubeck, Andreas Fleischmann, Guido Knell, Yvonne Lutsch, and Erich Plies

J. Vac. Sci. Technol. B 16, 3181 (1998); http://dx.doi.org/10.1116/1.590347 (4 pages) | Cited 4 times

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A miniaturized electrostatic electron optical column, consisting of thin commercial electron-microscope apertures as electrodes [Burstert, Winkler, and Lischke, Microelectron Eng. 31, 95 (1996)] has been successfully constructed and evaluated. An electron probe with a current of 300 nA and a spot size of 0.6 μm is achieved at 3 keV. The system is operated with beam energies as low as 300 eV, yielding 600 nA in a 2 μm spot size. Long term stability and reproducibility are achieved over operation times of several months. This demonstrates that the column is suitable for testing purposes where a high signal-to-noise ratio is required. © 1998 American Vacuum Society.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.85.Ne Electrostatic lenses, septa
41.75.Fr Electron and positron beams

Micromachined ultrasharp silicon and diamond-coated silicon tip as a stable field-emission electron source and a scanning probe microscopy sensor with atomic sharpness

I. W. Rangelow, F. Shi, P. Hudek, P. Grabiec, B. Volland, E. I. Givargizov, A. N. Stepanova, L. N. Obolenskaya, E. S. Mashkova, and V. A. Molchanov

J. Vac. Sci. Technol. B 16, 3185 (1998); http://dx.doi.org/10.1116/1.590348 (7 pages) | Cited 7 times

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A novel combination of silicon micromachining and deposition on silicon whiskers on (111) oriented silicon substrates shows promise for stable field emission electron emitters and sensors for scanning probe microscopy. As a field emission electron emitters show promise for high-density and high-resolution electron beam applications owing to a small (within 3°) divergence half angle of emitted electrons. Due to the sharpening of the diamond coated Si tips the threshold voltage, which is necessary to create a stable emission current (nanoampers) is decreased from the initial 1300 V to about 150 V. The diamond coating stabilizes the field-emission current as large as about 100 μA from a single tip. Training of the emitter at a current of about 10−7 A for several hours results in an additional improvement of the current stability with an additional slight current increase. Second application of vapor–liquid–solid grown silicon whiskers described here is the recent progress toward high aspect ratio (>100) probes and relates a technique for preparation of cantilevers for atomic force microscopy with atomic resolution on the very end of the tip. The radii are less than 2 nm for silicon tips and the angles at the ends are less than 20°. In the case of diamond, the tip radius is 10 nm. © 1998 American Vacuum Society.
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85.45.Db Field emitters and arrays, cold electron emitters
07.79.Lh Atomic force microscopes
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
79.70.+q Field emission, ionization, evaporation, and desorption
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
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)

Patterned negative electron affinity photocathodes for maskless electron beam lithography

J. E. Schneider, P. Sen, D. S. Pickard, G. I. Winograd, M. A. McCord, R. F. W. Pease, W. E. Spicer, A. W. Baum, K. A. Costello, and G. A. Davis

J. Vac. Sci. Technol. B 16, 3192 (1998); http://dx.doi.org/10.1116/1.590349 (5 pages) | Cited 8 times

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This work focuses on two issues crucial to achieving high throughput with a negative electron affinity semiconductor photocathode source. Monte Carlo simulations indicate that for a 50 kV system, as much as 8 μA of current may be delivered to the wafer to achieve a raw throughput of 20 8 in. wafers per hour with 0.1 μm minimum feature size (assuming a resist sensitivity of 10 μC/cm2). In order to achieve the throughput potential of this approach, suboptical emission areas are required; this suggests the use of cathode patterning. Two patterning alternatives have been investigated experimentally, and both approaches have been used to generate arrays of more than 100 electron beams with source sizes as small as 150 nm. However, each type of patterned cathode presents unique challenges to fabrication and performance in a practical multibeam system. Different source configurations (number of beams, beam current, beam spacing, etc.) create a system-level tradeoff between resolution and throughput. Results from patterned cathode experiments and system modeling are presented. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.60.Ha Photomultipliers; phototubes and photocathodes
41.85.Ja Particle beam transport
02.70.Rr General statistical methods
41.85.Ew Particle beam profile, beam intensity

Critical dimension control at stitched subfield boundaries in a high-throughput SCALPEL® system

Stuart T. Stanton, J. Alexander Liddle, Warren K. Waskiewicz, and Anthony E. Novembre

J. Vac. Sci. Technol. B 16, 3197 (1998); http://dx.doi.org/10.1116/1.590350 (5 pages) | Cited 1 time

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Scattering with angular limitation projection electron-beam lithography (SCALPEL®) is a stitching lithography system, using a segmented mask pattern which is assembled on the wafer by dynamic imaging. Critical objects may lie on the original pattern segment boundaries (seams), but their stitched images must adhere to conservatively interpreted +/−10% critical dimension (CD) control requirements. Stitching with butted (touching) spatial image parts requires an aggressive placement-error allocation of approximately +/−CD/20, along with allowed values for dose control, mask, resist, and process in the CD control budget. Further analysis has shown that a seam-blending scheme increases the stitching-error tolerance by as much as five times, and allows redistribution of all values in the CD error budget. The seam-blending approach provides overlapped image portions in a small area common to neighboring segments which receive complementary illumination dose portions. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
41.85.Ja Particle beam transport

Pattern dependent alignment technique for mix-and-match electron-beam lithography with optical lithography

Yasuko Gotoh, Yasunari Sohda, Norio Saitou, Tsutomu Tawa, Takashi Matsuzaka, Naoko Asai, Katsuya Hayano, and Norio Hasegawa

J. Vac. Sci. Technol. B 16, 3202 (1998); http://dx.doi.org/10.1116/1.590351 (4 pages)

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An alignment technique for electron-beam (EB) lithography that corrects the writing pattern to match the pattern-dependent lens distortion of an optical stepper is proposed. In mix-and-match EB and optical lithography, precise measurement of positional distortion caused by the stepper lens is necessary. However, recent research in optical lithography has shown that the lens distortion differs depending on the pattern features. Thus, we have enhanced the measurement method to reflect the pattern-feature dependence of positional distortion in optical lithography. To measure the various types of distortions more effectively, we modified the marks used for distortion and overlay measurement. The measured pattern dependence of the lens distortion was in good agreement with our simulation results and the overlay accuracy in mix-and-match lithography was improved with this method. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Electron-optical optimization for Gaussian, high-current, high-dose columns

Marian Mankos, Lee H. Veneklasen, Rudy Garcia, and Henry Pearce-Percy

J. Vac. Sci. Technol. B 16, 3206 (1998); http://dx.doi.org/10.1116/1.590352 (5 pages)

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This article demonstrates the electron-optical optimization of a high-current, high-dose column operating at 10 keV. The goal is to increase the available dose to the resist, which requires increasing the current density to more than 800 A/cm2. Our calculations use the MEBS Ltd. BOERSCH program. We model the complete column as a set of thin lenses, separated by field-free drift spaces. Monte Carlo simulation propagates discrete bunches of electrons through the column, taking into account the mutual repulsion between pairs of electrons. Gaussian spot size and current density in the column were calculated for three beam currents: 314, 75, and 35 nA. The results show that to achieve a higher current density, it is necessary to change the electron gun and the column. Specifically, a low aberration gun and a significantly shorter column are required. At 10 keV, the column performance at high beam currents (∼300 nA) is almost entirely dominated by electron–electron interactions. Major improvements in gun performance only yield minor improvement in total column performance, and a significant decrease in column length is required to reduce the electron–electron interactions enough to meet the design specification. A new, low aberration gun operating in an accelerating lens mode gun was chosen. A major effort was focused on redesigning the middle column to reduce electron–electron interactions. The combination of the low-aberration electrostatic gun and a shorter middle column provides the key improvement in the current density (dose) performance of the column. Results of experimental measurements on the optimized columns are in good agreement with the presented Monte Carlo simulations. © 1998 American Vacuum Society.
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02.70.Rr General statistical methods
85.40.Hp Lithography, masks and pattern transfer
41.85.Ew Particle beam profile, beam intensity

Simulation of Coulomb interactions in electron beam lithography systems—A comparison of theoretical models

W. Stickel

J. Vac. Sci. Technol. B 16, 3211 (1998); http://dx.doi.org/10.1116/1.590353 (4 pages) | Cited 11 times

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The Loeffler effect (trajectory displacement) has been calculated for a magnetic lens doublet electron-optic system considered to represent the basic configuration for next generation lithography. The results of two analytic and two numeric (Monte Carlo) models are compared and presented graphically as well as by analytic approximations, revealing significant quantitative differences within the parameter space considered relevant. Less severe discrepancies in the trends appear to be useful as a guide for system design, but experimental verification is needed to determine the validity of any of the approaches compared. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
02.70.Rr General statistical methods
41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
41.75.Fr Electron and positron beams

Performance investigation of Coulomb interaction-limited high throughput electron beam lithography based on empirical modeling

Liqun Han, Mark A. McCord, Gil I. Winograd, and R. F. W. Pease

J. Vac. Sci. Technol. B 16, 3215 (1998); http://dx.doi.org/10.1116/1.590354 (6 pages) | Cited 5 times

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Multibeam direct writing and projection strategies have been proposed for high throughput electron beam lithography; however, the large beam current required may cause severe beam blur due to the stochastic Coulomb interaction effects between the electrons. From viewpoint of both concept proof and practical system design, evaluation of the fundamental system limits and the optimum performance in a large range of multiple system parameter variable space is critical for such high throughput tools. Based on the response surface design approach, well-fitted empirical models of image beam size as a function of various system parameters have been extracted from Monte Carlo simulations of electron interactions for different proposed multi-beam systems. The blurred imaging beam size is examined in a wide range of system parameters: beam currents from 1 to 100 μA, acceleration voltages from 25 to 100 kV, column lengths from 1 to 100 cm, field sizes from 0.5 to 2 mm, and demagnification from 4 to 16. Two general tendencies for such systems were observed: the nonuniformity of image defocusing due to the inhomogeneous interbeamlet space charge effect at large field sizes, and the high sensitivity of maximum beam current to column length at a fixed image beam size. Finally, the throughput versus acceleration voltage is evaluated under different assumptions of resolution, resist thickness, and column length. It is concluded that to achieve the throughput required by manufacturing beyond 0.1 μm resolution, very aggressive design of a short column along with thin resist will be required. © 1998 American Vacuum Society.  
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85.40.Hp Lithography, masks and pattern transfer
02.70.Rr General statistical methods

Rigorous simulation of statistical electron–electron interactions with fast multipole acceleration and a network of workstations

Victor S. H. Wen, Owen T. Carmichael, Hiroshi Yamashita, and Andrew R. Neureuther

J. Vac. Sci. Technol. B 16, 3221 (1998); http://dx.doi.org/10.1116/1.590355 (6 pages)

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Rigorous simulation, which in concept is nearly linear in CPU time with microampere beam currents, has been developed for analyzing statistical electron–electron interactions in lens free regions joined by ideal lenses and apertures. The simulation method is based on combining fast multipole acceleration (FMA) with modifications to a message passing interface for use on a multiprocessor and on a network of workstations. As test cases, the distribution of scattered electrons versus deviation from focus is given as well as results for the interaction between simultaneously imaged spots. The performance improvement per level of spatial division was only about a factor of 2 instead of the expected factor of 8 due to the pencil shape nature of the beam. A FMA method that is adaptable to beam density and geometry is needed. It is projected that it will be possible to simulate a 30 μA beam current on a quad-Pentium Pro machine in half a day and in matter of hour on a network of workstations. © 1998 American Vacuum Society.
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41.75.Fr Electron and positron beams
85.40.Hp Lithography, masks and pattern transfer
07.05.Tp Computer modeling and simulation

Mask electron modeling for Coulomb interaction by mask-scattered electrons in electron-beam projection lithography

Hiroshi Yamashita, Victor S. H. Wen, Andrew R. Neureuther, and Eiichi Nomura

J. Vac. Sci. Technol. B 16, 3227 (1998); http://dx.doi.org/10.1116/1.590356 (5 pages) | Cited 3 times

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A rigorous statistical Coulomb interaction simulator that can take into account mask electrons was developed. In electron-beam (EB) projection lithography, many electrons incident to an absorber or a scatterer pass through the EB mask. These mask electrons, however, have not been considered in a simulation of Coulomb interaction. In a novel simulation approach, an assessment has been made of the effects of mask electrons on image quality and flare due to electron–electron interactions. The statistical electron–electron interactions from mask electrons under various conditions are simulated by injecting them into a simulation domain and using the fast multipole accelerated method to rigorously follow all interactions as a function of time. It was found that mask electrons contribute to the trajectory displacement effect and increase the number of deviated electrons in the pattern area by four to five times when the accelerating voltage is 125 kV, the beam current density is 0.1 A/cm2, the mask thickness is 10 μm, and the electron transmittance is 95%. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Optical data storage in LiF using electron beam encoding

E. J. Caine and S. D. Miller

J. Vac. Sci. Technol. B 16, 3232 (1998); http://dx.doi.org/10.1116/1.590357 (5 pages) | Cited 10 times

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Electron beam generated color centers in LiF are presented as the basis for a new optical data storage scheme. Data are “read” with a confocal microscope. The alkali halide medium is capable of gray scale and multilevel or volumetric storage demonstrating a thermally stable coloration. This initial investigation shows that data can be resolved to less than 0.25 μ resolution with at least three orders of magnitude data scaling. An assessment is made for future work. © 1998 American Vacuum Society.
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42.70.Ln Holographic recording materials; optical storage media
61.80.Fe Electron and positron radiation effects
61.72.J- Point defects and defect clusters
61.82.Ms Insulators
42.79.Vb Optical storage systems, optical disks

Fabrication of electron beam generated, chirped, phase mask (1070.11–1070.66 nm) for fiber Bragg grating dispersion compensator

R. C. Tiberio, D. W. Carr, M. J. Rooks, S. J. Mihailov, F. Bilodeau, J. Albert, D. Stryckman, D. C. Johnson, K. O. Hill, A. W. McClelland, and B. J. Hughes

J. Vac. Sci. Technol. B 16, 3237 (1998); http://dx.doi.org/10.1116/1.590358 (4 pages) | Cited 8 times

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We report on the fabrication of a chirped, phase mask that was used to create a fiber Bragg grating (FBG) device for the compensation of chromatic dispersion in longhaul optical transmission networks. Electron beam lithography was used to expose the grating onto a resist-coated quartz plate. After etching, this phase mask was used to holographically expose an index grating into the fiber core [K. O. Hill, F. Bilodeau, D. C. Johnson, and J. Albert, Appl. Phys. Lett. 62, 1035 (1993)]. The linear increase in the grating period, “chirp,” is only 0.55 nm over the 10 cm grating. This is too small to be defined by computer aided design and a digital deflection system. Instead, the chirp was incorporated by repeatedly rescaling the analog electronics used for field size calibration. Special attention must be paid to minimize any field stitching and exposure artifacts. This was done by using overlapping fields in a “voting” method. As a result, each grating line is exposed by the accumulation of three overlapping exposures at 1/3 dose. This translates any abrupt stitching error into a small but uniform change in the line-to-space ratio of the grating. The phase mask was used with the double-exposure photoprinting technique [K. O. Hill, F. Bilodeau, B. Malo, T. Kitagawa, S. Thériault, D. C. Johnson, J. Albert, and K. Takiguchi, Opt. Lett. 19, 1314 (1994)]: a KrF excimer laser holographically imprints an apodized chirped Bragg grating in a hydrogen loaded SMF-28 optical fiber. Our experiments have demonstrated a spectral delay of −1311 ps/nm with a linearity of +/−10 ps over the 3 dB bandwidth of the resonant wavelength of the FBG. The reflectance, centered on 1550 nm, shows a side-lobe suppression of −25 dB. Fabrication processes and optical characterization will be discussed. © 1998 American Vacuum Society.
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42.81.Dp Propagation, scattering, and losses; solitons
42.79.Dj Gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer

Experimental verification of the TEMPTATION (temperature simulation) software tool

Sergey Babin and Igor Yu. Kuzmin

J. Vac. Sci. Technol. B 16, 3241 (1998); http://dx.doi.org/10.1116/1.590359 (7 pages) | Cited 7 times

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Predicting the temperature rise during electron-beam lithography (EBL) is an important practical problem in the development of new EBL systems and in the optimization of new exposure processes. The TEMPTATION software tool was developed. This software uses an analytic solution of heat propagation in a multilayered substrate. The software attains both high speed and good accuracy. Experimental verification of the software was done. Simulated data were verified versus experiments made with variably shaped EBL systems using three different resists. Change of effective absorbed energy due to heating was simulated and compared to published data. Good agreement of predicted and measured data for both long-range and short-range resist heating was shown. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Lie algebraic aberration theory and calculation method for combined electron beam focusing-deflection systems

Kangyan Hu and T.-T. Tang

J. Vac. Sci. Technol. B 16, 3248 (1998); http://dx.doi.org/10.1116/1.590371 (8 pages)

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Lie algebraic deflection aberration theory is presented and applied to combined magnetic focusing-deflection systems. Employing this new algebraic tool, all third- and fifth-order canonical aberrations (including canonical position and momentum aberrations at arbitrary observation planes) for combined systems are derived. The results are complete with concise forms. An example of an in-lens deflection system is calculated for high-order geometric aberrations through fifth order. This article lays the groundwork for further studies on the computation and optimized design for higher-order aberrations of scanning probe systems. © 1998 American Vacuum Society.
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41.85.Gy Chromatic and geometrical aberrations
41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
85.40.Hp Lithography, masks and pattern transfer
02.10.Ud Linear algebra
02.10.Xm Multilinear algebra
07.05.-t Computers in experimental physics

Characterizing GHOST proximity effect correction effectiveness by determining the worst-case error

G. Patrick Watson, Steven D. Berger, and J. Alexander Liddle

J. Vac. Sci. Technol. B 16, 3256 (1998); http://dx.doi.org/10.1116/1.590360 (6 pages)

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Background proximity effect corrections such as GHOST and the proposed SCALPEL correction technique have been analyzed to determine how well they can perform in situations where the correction dose distribution is not ideal. A technique has been developed that evaluates the largest possible correction dose error by determining the worst-case exposure pattern. This pattern is found to be unlikely to occur in integrated circuit patterns, so that the dose errors found in realistic situations are expected to be much smaller. For Gaussian shaped GHOST correction energy distributions, the worst-case pattern resembles a disk or a bull’s eye. The optimal correction dose distribution has a width parameter of about 90% of the backscatter width. The worst-case background dose error is less than +/−2% for a backscatter coefficient of 0.40. For a correction dose that resembles a disk of constant intensity, the worst-case error is typically larger than the case of a Gaussian shape. The smallest worst-case error occurs with a correction disk radius of 1.2 times the backscatter range for a backscatter coefficient of 0.50. The smallest worst-case error is +/−10% or one half of that, +/−5%, for practical pattern density ranges. The SCALPEL correction dose profile is ring shaped and the worst-case background error can be nearly as large as the backscatter coefficient. The worst-case error concept is used to search for the optimum ring shape; a worst-case error as small as +/−3% is possible with the appropriate correction ring characteristics. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Accuracy and efficiency in electron beam proximity effect correction

S. J. Wind, P. D. Gerber, and H. Rothuizen

J. Vac. Sci. Technol. B 16, 3262 (1998); http://dx.doi.org/10.1116/1.590361 (7 pages) | Cited 9 times

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We present a suite of electron beam proximity effect correction algorithms which incorporate elements of various shape-to-shape techniques as well as field-based techniques. They are applied to a set of prototypical pattern data at simulated electron beam exposure conditions ranging from 25 to 100 keV on bulk substrates. The results are compared in terms of correction accuracy and computational efficiency. In addition, we show how these algorithms, when used in combination with one another, can be applied to hierarchical pattern design data such that the correction can be obtained with a high degree of accuracy without requiring unnesting of the hierarchy. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Adaptive selection of control points for improving accuracy and speed of proximity effect correction

Soo-Young Lee and Jayesh Laddha

J. Vac. Sci. Technol. B 16, 3269 (1998); http://dx.doi.org/10.1116/1.590362 (6 pages) | Cited 1 time

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A large class of the proximity effect correction schemes being currently used employ so-called control points in their implementation. Control points are the pixel locations in a circuit pattern at which energy received, referred to as exposure, is estimated. Depending on the exposure estimates at control points, the dose to be given to each feature (or subfeature) or the amount of shape modification for each feature is determined. Many proximity correction schemes including the first version of our scheme (PYRAMID 1.0) adopt a fixed selection of control points, which may not be optimal especially for high density, finely feature circuit patterns. Selection of control points greatly affects the accuracy and speed of correction. We have designed a simple but effective method for adaptively selecting control points. In this article we describe the scheme for adaptive control point selection with simulation results showing the successful correction of high-density, fine-feature circuits in less time. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Parallel and hierarchical postprocessing for variable spot electron beam lithography

Gregory J. Dick, Abigail S. Ganong, Chising Lai, Mary L. Merillat, and John W. Pavick

J. Vac. Sci. Technol. B 16, 3275 (1998); http://dx.doi.org/10.1116/1.590363 (4 pages)

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Chip designs, for both logic and memory, are becoming increasingly large and complex. It is not unusual for the postprocessing of these designs to be one of the biggest bottlenecks in the mask order processing pipeline. To address this bottleneck a parallel postprocessing system was developed. It was named P5 for practically perfect parallel postprocessor. This system is in use for production processing of designs to be written on IBM’s EL4+ electron beam lithography tool located in the Advanced Mask Facility in Essex Junction, VT. In addition the system is being enhanced with the addition of hierarchical data handling capability. Early results of this enhancement work are presented in this article. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Mask bias requirement for 0.13 μm e-beam block exposure lithography

Kimitoshi Takahashi, Hiroyuki Kanata, and Yasuo Nara

J. Vac. Sci. Technol. B 16, 3279 (1998); http://dx.doi.org/10.1116/1.590364 (5 pages) | Cited 2 times

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Coulomb interactions have been discussed as an obstacle for 0.13 μm line and space (L/S) resolutions in the block exposure or the cell projection lithography. In this article, effects of the Coulomb interactions are experimentally analyzed in the 50 kV block exposure lithography system. Blurs of the e-beam profiles, which characterize the Coulomb interactions, were obtained by knife-edge experiments. From the results, the following theoretically predicted facts have been clarified. The blur increases with the increasing current monotonously. We have obtained linear relationships, δ=0.03×Ib+0.05 (μm) between the blurs and an e-beam current. The dynamic refocusing technique can suppress the Coulomb interactions only partially. In order to resolve 0.13 μm L/S, practical methods to reduce the Coulomb interactions by reducing the current are needed. It is clarified that mask biasing, where widths of the mask openings are narrowed, is more effective to achieve high contrast than current density reduction or shot size reduction. It is also clarified that the mask biasing is effective to resolve 0.13 and 0.10 μm L/S patterns. We have applied the current reduction techniques and have successfully obtained fine 0.13, 0.12 and 0.10 μm L/S patterns. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
84.30.Sk Pulse and digital circuits

Comparative study of AZPN114 and SAL601 chemically amplified resists for electron beam nanolithography

Zheng Cui, Annamaria Gerardino, Massimo Gentili, Enzo DiFabrizio, and Phil D. Prewett

J. Vac. Sci. Technol. B 16, 3284 (1998); http://dx.doi.org/10.1116/1.590365 (5 pages) | Cited 5 times

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With the minimum feature dimension of integrated circuits (ICs) shrinking to below 130 nm, the IC industry has to choose one among a number of nonoptical lithography tools. Electron beam direct write or mix-and-match lithography is an attractive choice because of the maturity of the technology and the potential of using the tool for several generations of ICs. The low throughput associated with e-beam direct writing of wafers can be significantly reduced by using chemically amplified resists. Two commercially available negative tone chemically amplified resists, AZPN114 and SAL601, were investigated and compared for their performance in e-beam direct writing of wafers at 150, 100, and sub-50 nm resolutions. A number of factors influencing the throughput issue were evaluated. The latitudes of postexposure bake and postexposure delay were compared. It is found that both resists are of high resolution and high contrast, with the highest resolution, 30 nm, achieved for AZPN114. AZPN114 has higher sensitivity and is more stable during postexposure delay than SAL601 but less stable during postexposure bake. A 6 in. industrial wafer was exposed with AZPN114 at gate level at 150 nm resolution using e-beam lithography and it showed feature uniformity across the entire wafer. © 1998 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

Comparison of negative resists for 100 nm electron-beam direct write and mask making applications

K. J. Nordquist, D. J. Resnick, and E. S. Ainley

J. Vac. Sci. Technol. B 16, 3289 (1998); http://dx.doi.org/10.1116/1.590366 (5 pages) | Cited 2 times

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A new negative tone, chemically amplified deep ultraviolet resist, Shipley UVN-2, and a negative electron-beam (e-beam) resist, Sumitomo NEB-22A5, have been investigated for use in direct write and mask fabrication applications. The Sumitomo NEB-22A5 material has shown superior high resolution capabilities with excellent exposure latitude for both isolated and line/space features. Line and space gratings and isolated lines of 100 nm were resolved in a 400 nm film of NEB-22 using a 40 kV e-beam exposure tool. UVN-2 resist has shown resolution down to 150 nm line/space features with excellent etch selectivity and postexposure bake critical dimension control. Both resists perform well with respect to delay stability before and after exposure. This article will discuss the process development of the two resists and compare the performance characteristics including resolution, exposure latitude, linearity, and etch selectivity in various chemistries. Effects relating to pre-exposure and postexposure bake delay will also be considered because of the susceptibility of many chemically amplified resists to contaminants in the air. Finally, the application of these resists for both direct write and advanced mask making applications will be discussed. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
82.50.Kx Processes caused by X-rays or γ-rays

Masked ion beam lithography with highly charged ions

J. D. Gillaspy, D. C. Parks, and L. P. Ratliff

J. Vac. Sci. Technol. B 16, 3294 (1998); http://dx.doi.org/10.1116/1.590367 (4 pages) | Cited 12 times

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Masked ion beam lithography using highly charged ions is demonstrated for the first time by producing an array of hundreds of ordered micrometer wide dots using Xe44+ on poly(methylmethacrylate) resist. At low dose, exposure of the resist is incomplete and isolated single-ion impact sites can be seen within the exposed areas. Atomic force microscope images of the single-ion impact sites show craters with a width of 24 nm. At high dose, the exposure is complete and the dot morphology is consistent with limitations from the mask. Scanning electron microscope images indicate that the sidewall slope is steeper than four. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Electronic desorption of alkyl monolayers from silicon by very highly charged ions

T. Schenkel, M. Schneider, M. Hattass, M. W. Newman, A. V. Barnes, A. V. Hamza, D. H. Schneider, R. L. Cicero, and C. E. D. Chidsey

J. Vac. Sci. Technol. B 16, 3298 (1998); http://dx.doi.org/10.1116/1.590372 (3 pages) | Cited 10 times

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Self-assembled alkyl monolayers on Si (111) were exposed to low doses of slow (v≈6.6×105 m/s≈0.3vBohr), highly charged ions, like Xe41+ and Th73+. Atomic force microscope images show craters from single ion impacts with diameters of 50–63 nm. Emission of secondary ions by highly charged projectiles was monitored by time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS data give insights into the dependence of electronic desorption effects on the projectile charge state. We discuss the potential of highly charged projectiles as tools for materials modification on a nanometer scale. © 1998 American Vacuum Society.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Red luminescence from a focused ion beam modified silicon surface

L. E. Erickson, P. Schmuki, and D. J. Lockwood

J. Vac. Sci. Technol. B 16, 3301 (1998); http://dx.doi.org/10.1116/1.590373 (4 pages) | Cited 1 time

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We present a new principle and technique that can be used to create light emitting porous silicon submicron patterns of arbitrary shape on silicon wafers. We demonstrate that porous silicon growth can be preferentially initiated at surface defects created by maskless focused ion beam implantation into n-type silicon. During electrochemical polarization, the implanted areas show a significantly lower threshold potential for pore formation than the nonimplanted areas [0.25 V vs 3.8 V standard calomel electrode (SCE)]. For samples electrochemically polarized at potentials below 3.8 V SCE, implanted areas show the typical red-orange photoluminescence of porous silicon while the areas that are not implanted show only the band gap infrared photoluminescence from silicon. © 1998 American Vacuum Society.
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78.55.Ap Elemental semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.uf Ge and Si
81.05.Rm Porous materials; granular materials

In situ Ga+ focused ion beam definition of high current density resonant tunneling diodes

P. See, E. H. Linfield, D. D. Arnone, P. D. Rose, D. A. Ritchie, and G. A. C. Jones

J. Vac. Sci. Technol. B 16, 3305 (1998); http://dx.doi.org/10.1116/1.590374 (6 pages) | Cited 1 time

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Results are presented for small embedded tunnel area (<100 μm2), high current density resonant tunneling diodes (RTDs) fabricated using a combination of in situ Ga+ focused ion beam (FIB) implantation with molecular beam epitaxial regrowth. In such devices, the tunnel current path is defined by the highly resistive disordered lattice (from the Ga+ FIB lithography) and confined to the undamaged regions. Postgrowth optical processing is then straightforward to perform. The success of this novel technique is demonstrated by systematically varying the wet etched mesa dimensions, the FIB defined tunneling area, and the ion implantation dose, with experimental data discussed in each case. Furthermore, it is shown that this approach allows a common and easy connection to an array of individual RTDs, which is of considerable interest for microwave and millimeter wave power combining applications. © 1998 American Vacuum Society.  
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Kk Junction diodes
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Study of precursor gases for focused ion beam insulator deposition

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

J. Vac. Sci. Technol. B 16, 3311 (1998); http://dx.doi.org/10.1116/1.590497 (4 pages) | Cited 9 times

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The electrical properties of insulators formed by focused ion beam induced deposition of various siloxane precursor gases have been compared. Leakage current and breakdown field have been measured by forming metal-insulator-metal structures. It was found that the focused ion beam induced deposition of metal on top of the insulator can substantially degrade the quality of the insulator. We found that the resistivity of the insulator material depends on the deposition yield (e.g., the amount of Ga implantation) as well as on the chemical nature of the precursor gas. From the precursor gases studied, the new compound pentamethylcyclopentasiloxane shows the best performance. Compared to the commercially used tetramethylcyclotetrasiloxane compound, an improvement in resistivity by two orders of magnitude (∼8×1011 versus ∼6×109 Ω cm) and a factor of about 1.5 in breakdown field (650 vs 440 V/μm) could be achieved. © 1998 American Vacuum Society.
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81.15.Cd Deposition by sputtering
73.40.Rw Metal-insulator-metal structures
73.61.Ng Insulators

Influence of edge roughness in resist patterns on etched patterns

Hideo Namatsu, Masao Nagase, Toru Yamaguchi, Kenji Yamazaki, and Kenji Kurihara

J. Vac. Sci. Technol. B 16, 3315 (1998); http://dx.doi.org/10.1116/1.590375 (7 pages) | Cited 54 times

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We report on the linewidth fluctuations in resist patterns and their influence on etched patterns. The linewidth fluctuations observed as line edge roughness are mainly caused by polymer aggregates in the resist materials. Polymer aggregates more than 30 nm in diameter are observed in both the positive and negative resist films. Because the polymer aggregates are not dissolved but extracted during development, they remain stuck on the pattern sidewall and cause linewidth fluctuations. When substrates, such as Si, are etched using resist patterns as a mask, the linewidth fluctuations of the resist patterns are faithfully transferred to the substrate. This means that the linewidth fluctuations in device patterns are originally due to the polymer aggregates in the resist films. The linewidth fluctuation is also found to decrease through substrate etching, depending on resist thickness loss. This possibly results from degradation of the resist patterns in lateral directions through etching. However, it does not provide a sufficient decrease in linewidth fluctuations because the large thickness loss of the resist during etching results in critical dimension loss. Therefore, the reduction of the effect of the aggregate size, for example, by using the resist with small aggregates, such as hydrogen silsesquioxane, is necessary. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning

Dry development in an O2/SO2 plasma for sub-0.18 μm top layer imaging processes

A. M. Goethals, F. Van Roey, T. Sugihara, L. Van den hove, J. Vertommen, and W. Klippert

J. Vac. Sci. Technol. B 16, 3322 (1998); http://dx.doi.org/10.1116/1.590376 (12 pages) | Cited 11 times

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Dry development using thin layer imaging (TLI) in either a bilayer approach or top surface imaging are currently investigated as viable alternatives to extend optical lithography to 0.13 μm and below. This article describes a systematic study of dry development in a LAM TCP9400SE inductively coupled plasma etcher for both a single layer TLI resist process and for a bilayer resist process using O2 and SO2/O2 chemistries. The effect of the important machine parameters such as TCP power, bias power, O2 and SO2 gas flows, on the process characteristics (etch rate, selectivity, uniformity, anisotropy) and on the lithographic performance (resolution, profile control, proximity) of a TSI process at 248 has been investigated by means of statistically designed experiments. As line edge roughness (LER) is a critical issue for TSI, the effect of the dry development conditions on LER have been quantified. The effect of temperature on profile control is also presented. In a second part of this article, these trends have been applied to the process optimization for a bilayer resist process at 193 nm. With an optimized dry development process, good profile control is demonstrated down to 0.12 μm L/S resolution. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Can dry-etching systems be designed for low damage ab initio?

L. G. Deng, M. Rahman, S. K. Murad, A. Boyd, and C. D. W. Wilkinson

J. Vac. Sci. Technol. B 16, 3334 (1998); http://dx.doi.org/10.1116/1.590377 (5 pages) | Cited 6 times

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Photoluminescence intensity measurements from GaAs/AlGaAs and InGaAs/InAlAs quantum well probe structures have been used to study dry-etch damage inflicted in low power reactive ion etching environments. Selective etching has been employed to accumulate damage in the materials under these relatively low damage conditions. The measured data are consistent with calculations for channeling effects of atomic ion species, using a microscopic ion channeling theory. The results indicate that atomic as opposed to molecular ion channeling may be the main mechanism for deep dry-etch damage in these environments, which suggests that gases can be selected as likely to cause low damage. © 1998 American Vacuum Society.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
61.82.Fk Semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Observation of the trajectories of particles in process equipment by an in situ monitoring system using a laser light scattering method

Natsuko Ito, Tsuyoshi Moriya, Fumihiko Uesugi, Hiroshi Doi, Shingo Sakamoto, and Yuji Hayashi

J. Vac. Sci. Technol. B 16, 3339 (1998); http://dx.doi.org/10.1116/1.590378 (5 pages) | Cited 8 times

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An in situ scattered laser light measurement system, which can detect individual particles and observe their trajectories, has been produced experimentally and has been used with tungsten (W) etchback reactive ion etching (RIE) equipment. The particles which are smaller than 100 nm in size can be detected during plasma emission if the stray light that is caused by the laser light is properly suppressed. The trajectories of the particles are successfully observed in the W etchback RIE chamber by using this system under mass production conditions. Not only the appearance of the particle but also the direction of particle trajectory correlate distinctly with the specific operating state of the equipment. When the rf power was turned off, many of the particles that were observed seemed to be drawn towards the wafer. On the other hand, during injection of the N2 purge gas to the process chamber, the few particles that were frequently observed seemed to fall down, away from the wafer. © 1998 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.65.Cf Surface cleaning, etching, patterning
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Fabrication of Cu interconnects of 50 nm linewidth by electron-beam lithography and high-density plasma etching

Y. Hsu, T. E. F. M. Standaert, G. S. Oehrlein, T. S. Kuan, E. Sayre, K. Rose, K. Y. Lee, and S. M. Rossnagel

J. Vac. Sci. Technol. B 16, 3344 (1998); http://dx.doi.org/10.1116/1.590379 (5 pages) | Cited 4 times

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The feasibility of building Cu interconnects with a linewidth as small as 50 nm embedded in insulating SiO2 has been explored using the damascene process. Fine line test structures, designed for evaluating effects of small linewidth on metal line electric resistivity, were written on a poly(methylmethacrylate) resist layer and then transferred to the underlying SiO2 layer by high-density plasma etching. Using a CHF3 etching gas and an inductive power of 400 W, we were able to produce 50-nm-wide and 150-nm-deep trenches in SiO2. These trenches were then filled with a thin (5–10 nm) TaSiN or TaN liner and a thick Cu layer by the ionized physical vapor deposition technique. The field Cu was removed by a chemical-mechanical polishing process, leaving narrow damascene Cu in the oxide trenches. Direct current resistance measurements have indicated a wide distribution of resistivity in these fine lines. The low end of the distribution is close to the effective resistivity of a perfect Cu line. The high values are indicative of severe necking or other imperfections induced during the fabrication process. © 1998 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Hp Lithography, masks and pattern transfer
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Patterning of thin film NiMnSb using inductively coupled plasma etching

J. Hong, J. A. Caballero, E. S. Lambers, J. R. Childress, and S. J. Pearton

J. Vac. Sci. Technol. B 16, 3349 (1998); http://dx.doi.org/10.1116/1.590380 (5 pages) | Cited 6 times

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Several plasma chemistries based on fluorine (SF6, NF3), Cl2/Ar, BI3/Ar, or BBr3/Ar were compared for etching NiMnSb under inductively coupled plasma (ICP) conditions. ICP source power, radio frequency chuck power, and plasma composition were found to have strong effects on the etch rate. SF6/Ar discharges provided the fastest etch rates for NiMnSb (>1 μm min−1) even with small amounts of source power (100 W) addition. On the other hand, NF3/Ar showed net deposition rather than etching at source powers >100 W or at high NF3 percentages. Cl2/Ar showed a similar trend, with net deposition at low dc self-bias (−100 V), but net etching above this threshold. BBr3/Ar discharges produced deposition under all the conditions investigated while relatively high etch rates (⩾3000 Å min−1) were obtained with BI3/Ar at halide percentages ⩾70%. In terms of etched surface morphology, SF6/Ar provided the best surfaces, with root-mean-square roughness of 2.5 nm and vertical etched profiles. Surfaces etched in plasma chemistries other than SF6/Ar revealed Mn enrichment, an indication of involatile Mn etch products. The SF6 chemistry has the further advantage of the absence of the corrosion noted with Cl2-based mixtures. © 1998 American Vacuum Society.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance

Metallization-induced damage in III–V semiconductors

Ching-Hui Chen, Evelyn L. Hu, Winston V. Schoenfeld, and Pierre M. Petroff

J. Vac. Sci. Technol. B 16, 3354 (1998); http://dx.doi.org/10.1116/1.590381 (5 pages) | Cited 3 times

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Damage introduced from sputtering deposition, electron-beam evaporation, and thermal evaporation were investigated with an InGaAs/GaAs strained quantum well structure. This strained quantum well structure was found to be a more sensitive probe of damage, revealing metallization-induced damage where none was found using comparable lattice-matched quantum wells. The damage was found to vary with deposition method, deposition rates, or even different metal sources used. Noticeable degradation of the photoluminescence of the strained quantum well was observed after a thin layer (∼100 Å) of metal was deposited. © 1998 American Vacuum Society.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
73.40.Ns Metal-nonmetal contacts
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.55.Cr III-V semiconductors
85.30.-z Semiconductor devices
81.15.Cd Deposition by sputtering

Electrical and optical characteristics of etch induced damage in InGaAs

E. W. Berg and S. W. Pang

J. Vac. Sci. Technol. B 16, 3359 (1998); http://dx.doi.org/10.1116/1.590459 (5 pages) | Cited 10 times

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The effects of etch induced damage on the electrical and optical properties of AlGaAs/InGaAs quantum wells (QWs) were studied. From the variations in the photoluminescence (PL) intensity and the conductivity of etched gratings, the optical cutoff width was found to be 33 nm whereas the electrical cutoff width was 136 nm. The PL intensity of the gratings indicated that increased stage power during etching causes more damage. Comparisons were also made between the sheet resistivity (ρs) of transmission lines and the conductivity of wires after etching of AlGaAs/InGaAs and AlInAs/InGaAs QWs grown on GaAs and InP substrates, respectively. The AlGaAs/InGaAs QW transmission lines showed reduced ρs after etching with higher stage power, although the ρs was still higher than that of the unetched control sample. The AlInAs/InGaAs QW transmission lines had a higher ρs as the stage power was increased. The two material systems also showed different etch time and sidewall damage characteristics. The AlInAs/InGaAs QW structure degraded more severely at a shorter etch time and had a larger cutoff width as extracted from etched conducting wires. © 1998 American Vacuum Society.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
78.55.Cr III-V semiconductors
72.80.Ey III-V and II-VI semiconductors

Kinetics of Si growth by an electron-beam-irradiation technique using a Si2H6 source

F. Hirose and H. Sakamoto

J. Vac. Sci. Technol. B 16, 3364 (1998); http://dx.doi.org/10.1116/1.590304 (3 pages)

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Room-temperature selective Si growth is possible by irradiating an electron beam on a Si surface in a Si2H6 ambient. The growth has an apparent substrate temperature dependence, such that the selective growth of Si is allowed at substrate temperatures only below 330 °C. We have found by the H2 thermal desorption experiments that the Si surface during the growth is covered with higher Si hydrides such as: SiH2, SiH3, and Si2H6 molecules. This indicates that the selective Si growth is caused by the higher Si hydrides. The reaction schemes of the Si growth are discussed in this article. © 1998 American Vacuum Society.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.20.Hf Product distribution

Plasma source for ion and electron beam lithography

Y. Lee, R. A. Gough, K. N. Leung, J. Vujic, M. D. Williams, N. Zahir, W. Fallman, M. Tockler, and W. Bruenger

J. Vac. Sci. Technol. B 16, 3367 (1998); http://dx.doi.org/10.1116/1.590460 (3 pages) | Cited 6 times

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A new plasma source configuration, coaxial source, has been developed at the Lawrence Berkeley National Laboratory suitable for ion and electron beam lithography applications. The axial ion energy spread and electron temperature of the multicusp ion source have been reduced considerably from 2 and 0.3 eV to a record low of 0.6 eV by employing a coaxial source arrangement. Results of ion projection lithographic exposure at the Fraunhofer Institute demonstrate that feature size less than 65 nm can be achieved by using a filter-equipped multicusp ion source. Langmuir probe measurements also show that very low energy spread electron beams can be obtained with the multicusp plasma generator. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
52.50.Dg Plasma sources

Characteristics of focused beam spots using negative ion beams from a compact surface plasma source and merits for new applications

S. K. Guharay, E. Sokolovsky, and J. Orloff

J. Vac. Sci. Technol. B 16, 3370 (1998); http://dx.doi.org/10.1116/1.590461 (4 pages) | Cited 5 times

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The characteristics of H− beams from a compact Penning-type surface plasma source have been studied with the goal of evaluating their merits for improved focused ion beam (FIB) systems. As a proof-of-the principles experiment to demonstrate the beam quality a simple, prototype source was developed without any special cooling arrangement of the electrodes. The source is operated in a pulsed mode with a maximum duty factor of 1%; and the operation can be extended to the dc mode by using water cooling. The beam brightness is estimated to be ∼0.5×105 A cm2 sr−1 at a beam energy of 7 kV, and the energy spread of the beam for angular beam intensity of ∼40 mA/sr is ⩽3 eV. The beam at an energy of 7 keV has been focused by a lens with a magnification factor of M∼0.1, and the spot size is determined by scanning a Si knife edge over the beam as well as by poly(methylmethacrylate) resist exposures. A focused spot, with diameter of ∼6 μm and current density of ∼10 mA/cm2, has been achieved. The dependence of the spot characteristics with the beam intensity from the source has been studied. The results suggest that a submicron size spot with a current density of ⩾1 A/cm2 can be generated using these beams for M∼0.01. The source, with its simple, robust technology, seems an attractive choice for FIB applications. © 1998 American Vacuum Society.
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07.77.Ka Charged-particle beam sources and detectors
41.75.Cn Negative-ion beams
41.85.Ew Particle beam profile, beam intensity
52.50.Dg Plasma sources
41.85.Ja Particle beam transport

OS3: Photoemission from gold thin films for application in multiphotocathode arrays for electron beam lithography

Xinrong Jiang, C. N. Berglund, Anthony E. Bell, and William A. Mackie

J. Vac. Sci. Technol. B 16, 3374 (1998); http://dx.doi.org/10.1116/1.590462 (6 pages) | Cited 14 times

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Photoemission is a promising approach to electron sources for electron beam lithography because of the ease with which various shapes or arrays of independently modulated sources can be fabricated. However, most high-quantum-efficiency photoemitters are extremely sensitive to even partial monolayers of contamination, and therefore require some combination of differential pumping systems and photoemitter surface protection after activation. Here we propose to use a high-power 257 nm laser in combination with the relatively high work function and low quantum efficiency of gold films to produce practical multicathode electron sources for electron beam lithography. Gold films have the offsetting advantages that their photoemission characteristics are relatively reproducible and stable even in contaminating environments. It is possible, therefore, to prepare and handle them in air as well as operate them in less demanding vacuum environments. It is shown that a back-illuminated 15 nm gold film on a quartz or sapphire substrate exhibits a quantum efficiency of approximately 10−4 at 257 nm, producing photocurrents greater than 1 μA at a laser power of under 200 mW. The quantum efficiency is very reproducible and relatively stable under a variety of environmental and operational conditions. Slow changes, by as much as a factor of 3, over time periods of several weeks following sample preparation have been observed, consistent with variations of the gold work function of approximately 0.2 eV. The results are in good agreement with a straightforward extension of existing photoemission models for bulk material. © 1998 American Vacuum Society.
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85.60.Ha Photomultipliers; phototubes and photocathodes
79.60.Bm Clean metal, semiconductor, and insulator surfaces
85.40.Hp Lithography, masks and pattern transfer

Lifetime and reliability results for a negative electron affinity photocathode in a demountable vacuum system

P. Sen, D. S. Pickard, J. E. Schneider, M. A. McCord, R. F. Pease, A. W. Baum, and K. A. Costello

J. Vac. Sci. Technol. B 16, 3380 (1998); http://dx.doi.org/10.1116/1.590463 (5 pages) | Cited 12 times

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Negative electron affinity photocathodes may have useful applications as electron sources for high-throughput microlithography [A. Baum et al., J. Vac. Sci. Technol. B 15, 2707 (1997)]. However, the nature of such a system has raised questions about the lifetime and reliability of a cathode during operation. In this article, we report on the lifetime and reliability of cathode operation under various conditions applicable to lithography. To perform these measurements, a 632 nm laser was focused onto a spot smaller than 10 μm in diameter on the back surface of the cathode (active area 0.5–2.0 μm thick). The emitted electrons were accelerated to 5 kV to form a magnified image of the cathode on a phosphor screen 1 m away. The 1/e lifetime of the cathode was measured as a function of the cathode current, which turned out to be an inverse relationship. Additionally, a wafer coated with SAL-601 resist was substituted for the phosphor screen to determine if resist outgassing induced by exposure affected operating lifetime. It was found that the cathode had a lifetime (75 h at 165 nA) that was the same as that obtained without the wafer under similar conditions. Lifetime was also found to be a function of initial level of cesiation of the surface and cesium levels during activation. In particular, when the cathode was initially overcesiated, the Faraday cup current (in the plane of the phosphor) was found to be stable to 2% for up to 3 days at 200 nA, indicating that the cesium level that optimizes lifetime is not necessarily the same level that optimizes quantum efficiency. © 1998 American Vacuum Society.
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85.60.Ha Photomultipliers; phototubes and photocathodes
85.40.Hp Lithography, masks and pattern transfer
07.77.Ka Charged-particle beam sources and detectors

Electron scattering and transmission through SCALPEL masks

M. M. Mkrtchyan, J. A. Liddle, A. E. Novembre, W. K. Waskiewicz, G. P. Watson, L. R. Harriott, and D. A. Muller

J. Vac. Sci. Technol. B 16, 3385 (1998); http://dx.doi.org/10.1116/1.590464 (7 pages) | Cited 9 times

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Electron scattering in thin solid films used for the fabrication of masks for electron projection lithography, e.g., SCALPEL®, is investigated. We have developed an analytical model to calculate electron transmission through the mask membrane and image contrast due to different scattering properties of the patterned area and the membrane. The model utilizes cross sections for electron elastic and inelastic scattering on an atom with exponentially screened Coulomb potential of the nucleus derived in the first Born approximation. The variety and controversy of theoretical and empirical adjustments of the screening parameter are briefly analyzed and attributed to the misinterpretation of experimental data ignoring the effects mostly due to plural scattering of electrons and dense packing of atoms in thin solid films. This model frees us from the computational limitations of Monte Carlo simulations and proves to be effective for the straightforward characterization of various alternative materials for SCALPEL mask membrane and scatterer. The model includes the appropriate effects of the projection optics and back-focal plane aperture. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
79.20.Kz Other electron-impact emission phenomena
41.75.Fr Electron and positron beams

Imaging interferometric lithography: A wavelength division multiplex approach to extending optical lithography

Xiaolan Chen and S. R. J. Brueck

J. Vac. Sci. Technol. B 16, 3392 (1998); http://dx.doi.org/10.1116/1.590465 (6 pages) | Cited 8 times

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The critical dimension (CD) limits of conventional optical lithography follow directly from the low-pass filter characteristics of the imaging optical system (∣k∣≲2πNA/λ where λ is the optical wavelength and NA the numerical aperture). In contrast, the linear systems limits of optics extend to spatial frequencies of 4π/λ (interference between counterpropagating beams at grazing incidence). Imaging interferometric lithography is introduced as a technique to approach this linear systems limit while retaining the arbitrary pattern capability of an imaging optical system. Multiple, wavelength-division-multiplexed exposures are used, each exposure recording a different portion of frequency space. A conventional, coherent illumination exposure provides the low frequency information, within the lens passband. Offset exposures provide the high spatial frequency information. Off-axis illumination shifts a portion of the high spatial frequency diffraction from the mask into the lens passband and interference with a reference beam resets the frequencies once they are transmitted through the optical system. For a typical x-y geometry pattern, offset exposures in the x and y directions provide a sufficient coverage of frequency space. Model calculations illustrate that the imaging capabilities of imaging interferometric lithography (IIL) for dense features extend to ∼λ/3 (130 nm at I line; 65 nm at an ArF exposure wavelength). Initial experiments are reported at I line with a modest (NA=0.04) optical system. The results are in good agreement with the model calculations. A resolution enhancement of ∼3× from dense 6 μm CDs for a conventional, coherent illumination exposure to ∼dense 2 μm CDs for an IIL exposure sequence is demonstrated. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.60.Ly Interferometers
42.15.Eq Optical system design
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Bh Lenses, prisms and mirrors

0.18 μm KrF lithography using optical proximity correction based on empirical behavior modeling

Alexander Tritchkov, John Stirniman, Hareen Gangala, and Kurt Ronse

J. Vac. Sci. Technol. B 16, 3398 (1998); http://dx.doi.org/10.1116/1.590466 (7 pages) | Cited 1 time

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We present the characterization of optical proximity effects and their correction for 0.18 μm deep-ultraviolet (UV) lithography processes using a semiempirically derived “behavior” model. Since critical dimension (CD) measurement data for deriving the model are taken after resist pattern transfer into the underlying layer (α-Si), the model incorporates all of the different proximity effect contributors: optics, mask, resist bake, etching, etc. The modeling technology we use allows for user defined model forms. It was empirically determined that the CD behavior could be adequately described by the diffusion of the aerial image with one Gaussian, and an adjustment to the signal threshold based on signal slope. The validity of the model for random geometry was confirmed by comparing contours drawn on Prospector™ with two-dimensional configurations of the uncorrected and corrected parts of a 0.18 μm test circuit. The model is then used for proximity effects correction of the gate level of a 0.18 μm test design and for the feasibility study for printing 0.15 μm features using deep-UV (λ=248 nm) lithography. Also, some process window enhancement techniques are evaluated in the correction recipe to enlarge the limited process window for printing 0.175 μm features. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Influences of off-axis illumination on optical lens aberration

Bruce W. Smith and John S. Petersen

J. Vac. Sci. Technol. B 16, 3405 (1998); http://dx.doi.org/10.1116/1.590467 (6 pages) | Cited 3 times

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Through modification of the illumination system of optical lithography tools, resolution and focal depth improvements can allow for near diffraction limited imaging. Most often, lens aberrations are evaluated assuming full use of a lens pupil. With off-axis illumination (OAI), diffraction information is distributed selectively over the lens pupil, influencing the impact of aberrations on imaging. This article describes these effects through a modified set of aberration coefficients and their variance over a pupil illuminated using OAI. Results in general show that astigmatic effects can worsen while spherical aberration and defocus effects can be improved. Coma induced image placement can be further aggravated with OAI unless rebalanced with tilt. The analysis presented here can also be extended to phase-shift masking approaches. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.15.Fr Aberrations
42.79.Bh Lenses, prisms and mirrors

Evaluation of a two-mask resolution enhancement technique

D. L. White and O. R. Wood

J. Vac. Sci. Technol. B 16, 3411 (1998); http://dx.doi.org/10.1116/1.590468 (4 pages)

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We have evaluated the performance of an optical projection lithography camera employing a two-mask resolution enhancement technique proposed by Matsumoto et al. [K. Matsumoto et al., Proc. SPIE 2197, 844 (1994)] and Kamon et al. [K. Kamon et al., Jpn. J. Appl. Phys., Part 1 33, 6848 (1994)] in 1994 that automatically provides a different illumination for every feature on the reticle. Our simulations show that such a system can provide better imaging performance than a system that employs ordinary quadrupole illumination and can enhance the depth of focus by more than 50% in specific cases. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Investigation of new overlay measurement marks for optical lithography

Takashi Saito and Hisashi Watanabe

J. Vac. Sci. Technol. B 16, 3415 (1998); http://dx.doi.org/10.1116/1.590469 (4 pages)

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New overlay measurement marks that consider the influence of coma aberration have been investigated. The concept behind the marks is the use of patterns that correspond to the actual device pattern rules, because the effect of coma aberration depends on the pattern size and pitch. Registration errors within one layer and overlay errors between two layers have been measured with the marks. The registration measurement results showed that the displacement of the marks with fine line patterns was different from that of the large box pattern. The difference was more than 20 nm. Then the overlay measurement marks were adapted to measure the displacement between a polysilicon gate pattern and an etched oxide layer. The results were compared to the scanning electron microscopy measurement of actual patterns and they showed good agreement. The repeatability of the marks was less than 5 nm and this is sufficient for quarter micron device fabrication. Overlay measurement marks having fine patterns can precisely measure the overlay errors of the actual fine patterns and can improve the overlay accuracy. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.15.Fr Aberrations
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Thermal annealing of deep ultraviolet (193 nm) induced compaction in fused silica

Fan Piao, William G. Oldham, and Eugene E. Haller

J. Vac. Sci. Technol. B 16, 3419 (1998); http://dx.doi.org/10.1116/1.590470 (3 pages) | Cited 2 times

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Different 1995–1996 ultraviolet (UV) grade experimental fused silica samples were evaluated for their resistance to UV-induced compaction at 193 nm under elevated sample temperature conditions. We found that the compaction rate decreases with increasing sample temperature. Compaction recoveries were observed at temperatures as low as 120 °C, this suggests that the recovery of UV-induced compaction in fused silica is a thermally excited process with a low activation energy. Isothermal annealing experiments were performed on two different sets of precompacted fused silica samples. An activation energy of 0.13 eV was found for both cases. © 1998 American Vacuum Society.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Cc Kinetics of defect formation and annealing

Light-coupling masks: An alternative, lensless approach to high-resolution optical contact lithography

Heinz Schmid, Hans Biebuyck, Bruno Michel, Olivier J. F. Martin, and Nicolas B. Piller

J. Vac. Sci. Technol. B 16, 3422 (1998); http://dx.doi.org/10.1116/1.590471 (4 pages) | Cited 14 times

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We describe an approach to optical lithography using light-scattering contact masks with protruding elements that couple light into a photoresist. This method differs from conventional contact lithography in two important ways. First, because portions of the light-coupling mask (LCM) are made from a polymer, intimate contact with the resist occurs over large areas without additional load. This contact is readily reversible, and causes no observable damage or contamination of the LCM or substrate. Second, the structure formed by the protruding parts of the LCM in contact with the resist can define local optical modes that impart directionality to the light propagating through the LCM and amplify its intensity. We provide an experimental realization and theoretical description of the method, demonstrating its use for the formation of 100 nm features with light having a wavelength of 256 nm. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.70.Jk Polymers and organics

Zone-plate-array lithography in the deep ultraviolet

Ihsan J. Djomehri, T. A. Savas, and Henry I. Smith

J. Vac. Sci. Technol. B 16, 3426 (1998); http://dx.doi.org/10.1116/1.590472 (4 pages) | Cited 9 times

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We describe initial steps we have taken in the development of zone-plate-array lithography (ZPAL), a proposed new paradigm for sub-100 nm lithography. The optimal implementation of ZPAL would employ an undulator emitting soft x rays of 4.5 nm wavelength. However, we have opted to concentrate initially on the major uncertainties associated with ZPAL: (1) fabrication of a large array of zone plates with a center-to-center spacing accuracy finer than the minimum zone width, (2) multiplexing of input beams to the individual zone plates, and (3) coordination of that multiplexing with precision motion of a substrate stage. We fabricated arrays of pure-phase zone plates suitable for the 193 nm output of an ArF laser, and conducted exposure tests using a modified Michelson configuration for focusing the zone plate array on the substrate. We also show the first example of simplistic writing. We show that the micromirror array manufactured by Texas Instruments, for use in projection displays, has dimensions and switching characteristics close to those needed for an ultimate ZPAL system. © 1998 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

At-wavelength detection of extreme ultraviolet lithography mask blank defects

Seongtae Jeong, Mourad Idir, Yun Lin, Lewis Johnson, Seno Rekawa, Michael Jones, Paul Denham, Phil Batson, Rick Levesque, Patrick Kearney, Pei-Yang Yan, Eric Gullikson, James H. Underwood, and Jeffrey Bokor

J. Vac. Sci. Technol. B 16, 3430 (1998); http://dx.doi.org/10.1116/1.590473 (5 pages) | Cited 8 times

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We report the design and operation of an at-wavelength system for extreme ultraviolet lithography mask blank defect detection. Initial results demonstrate sensitivity to submicron size phase defects. The performance of the system is compared with the practical requirements for a mask blank inspection system in terms of the sensitivity and scanning time. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

High-accuracy interferometry of extreme ultraviolet lithographic optical systems

Kenneth A. Goldberg, Patrick Naulleau, Sang Lee, Cynthia Bresloff, Craig Henderson, David Attwood, and Jeffrey Bokor

J. Vac. Sci. Technol. B 16, 3435 (1998); http://dx.doi.org/10.1116/1.590498 (5 pages) | Cited 3 times

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Recent improvements in extreme ultraviolet (EUV) lithographic imaging with Schwarzschild objectives have come as a direct result of at-wavelength interferometric characterization with the phase-shifting point diffraction interferometer. High accuracy system wave front characterization has led to the determination of the best Schwarzschild objective and subaperture configuration. These investigations and the results of imaging experiments are discussed. Two pinhole null tests have provided an in situ method of demonstrating reference wavefront accuracy of ∼λEUV/300.
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85.40.Hp Lithography, masks and pattern transfer
07.60.Ly Interferometers
42.87.Bg Phase shifting interferometry

Thermal–mechanical performance of extreme ultraviolet lithographic reticles

Steven E. Gianoulakis and Avijit K. Ray-Chaudhuri

J. Vac. Sci. Technol. B 16, 3440 (1998); http://dx.doi.org/10.1116/1.590474 (4 pages) | Cited 1 time

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Thermal deformation of reticles will likely become an important consideration for all advanced lithography techniques targeting 130 nm features and below. Such effects can contribute to image placement errors and blur. These issues necessitate the need to quantify the reticle distortion, induced by the absorption of illumination power, for candidate substrate and coating materials. To study the impact of various substrate and coating materials on reticle performance, detailed three-dimensional transient thermal and solid mechanical models have been developed and extensively applied to predict total placement errors, residual placement errors, and blur on an extreme ultraviolet lithography (EUVL) reticle during scanning. The thermal model includes a bidirectional scanning heat source representative of the illumination incident on the reticle. The heat loads on the reticle are characteristic of an EUVL engineering test stand with a wafer throughput of twenty 200 mm wafers per hour (assuming 80% die coverage and 68% exposure time). This article includes the results which describe the impact of (1) different substrate materials, (2) various degrees of contact conductance between the reticle and chuck, (3) pattern density and arrangement, and (4) temperature variations across the chuck. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Imaging properties of the extreme ultraviolet mask

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

J. Vac. Sci. Technol. B 16, 3444 (1998); http://dx.doi.org/10.1116/1.590475 (5 pages) | Cited 10 times

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The reflective mask used in extreme ultraviolet lithography is based on a multilayer stack reflector, overcoated with a suitable absorber. We show that in order to predict correctly the reflected field it is necessary to describe in detail the diffraction and multiple reflection processes that the propagating field undergoes in the multilayer stack. The finite thickness of the absorber causes the incoming field to diffract before being incident on the multilayer stack and is reflected many times in the stack before re-emerging. The fact that the effective reflecting surface of the multilayer stack is below its physical surface, adds complexity to the reflection process. An absorber line would thus appear wider and a space narrower, i.e., a diffraction bias is introduced in this process. If the incoming field is not incident normally, an asymmetry is observed in the reflected field that is angle dependent. Thus, off-axis illumination results in both an imaging bias and a feature displacement due to the image asymmetry. These effects are highly predictable and can be taken into account when writing the mask pattern. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Rigorous simulation of mask corner effects in extreme ultraviolet lithography

Thomas V. Pistor, Konstantinos Adam, and Andrew Neureuther

J. Vac. Sci. Technol. B 16, 3449 (1998); http://dx.doi.org/10.1116/1.590476 (7 pages) | Cited 4 times

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A windowing and multilayer acceleration methodology for rigorous electromagnetic analysis of extreme ultraviolet masks in three dimension is introduced and used to explore strong feature asymmetries associated with off-axis illumination. Specifically synthesizing large features from smaller simulation domains and replacement of the multilayer substrate by upward radiating equivalent sources are used and allow mask corner effects to be analyzed in about 10 h on a 200 MHz workstation. Windowing synthesizes the fields for a large mask feature from simulation of smaller domains such as corners. With off-axis illumination at angles of even a few degrees, hot spots in the near field occur at edges of the mask which face the illumination. This effect is associated with diffraction of the upward reflected light and its propagation in the presence of the side wall of the mask edge profile. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.05.Tp Computer modeling and simulation

Aspheric collimator for a point source x-ray lithography system

S. Singh-Gasson, Y. Vladimirsky, and F. Cerrina

J. Vac. Sci. Technol. B 16, 3456 (1998); http://dx.doi.org/10.1116/1.590477 (6 pages)

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X-ray point sources are an interesting alternative to synchrotrons for small to medium scale production. These sources are by nature highly divergent, and thus require the use of collimation for delivering an acceptable lithographic illumination. We present the design of an aspheric collimator for a point source such as a dense plasma focus system. Designing a collimating mirror for a point source presents different challenges than designing one for a synchrotron source, although both cases require that the radiation be condensed and collimated to deliver the radiation with 1%–2% uniformity and acceptable runout over a large field area. The collimator is 3 cm wide and 31 cm long, accepts 20 mrad in the vertical and 70 mrad in the horizontal, and delivers the x-ray flux to a 3 cm×3 cm field on a mask located 3 m from the source with a runout of 6 mrad. The figure is an asphere, not dissimilar to those developed previously. The scanning mechanism, however, is radically different, since the virtual rotation point is located at the source, rather than at the mirror pole. This design provides excellent uniformity since the mirror is always scanned inside the radiation cone while maintaining a constant nominal incidence angle. The design principles and predicted performance are discussed in detail, together with a consideration of the manufacturing challenge for such a mirror. The collimator design presented has the capability of delivering the required power density and collimation from an x-ray point source to satisfy the requirements of x-ray lithography. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Design study of compact beam lines for x-ray lithography

Eijiro Toyota

J. Vac. Sci. Technol. B 16, 3462 (1998); http://dx.doi.org/10.1116/1.590382 (4 pages) | Cited 3 times

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This article presents a design study of compact and high-performance beam lines for synchrotron-radiation-based x-ray lithography. The optical system is composed of a single toroidal scanning mirror and a movable beryllium window synchronized with the mirror motion. Usually the use of a toroidal scanning mirror tends to cause excessive deformation of beam shape and degradation of the focusing property of the mirror. This problem has been improved by placing the oscillating center of the mirror near the light source. The arc-shaped beam forms a concave dose distribution along the scanning centerline. A beryllium window foil with a specified curvature is used to create a uniform dose distribution. A series of analytical studies and computer simulations have been carried out to define the curvature. For example, the design study shows a compact beam line of 7 m length with a brightness of 159 mW/(cm2 A) within ±1% of dose uniformity at an exposure field of 50×50 mm. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
41.60.Ap Synchrotron radiation
41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
42.15.Eq Optical system design

Advanced synchrotron radiation stepper alignment system performance

Koichi Sentoku and Takahiro Matsumoto

J. Vac. Sci. Technol. B 16, 3466 (1998); http://dx.doi.org/10.1116/1.590478 (5 pages) | Cited 1 time

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Canon has been developing a synchrotron radiation stepper system for volume production known as the XR1. The system incorporates many-original technologies. In this article, the key features of the XR1 alignment system and its performance will be discussed. To align the mask and wafer, the alignment system uses Fresnel zone plates as alignment marks. Our alignment is based on an advanced dual grating lens method. In order to attain high alignment accuracy and large process latitude, we improved the design of alignment marks and optics of the alignment scope. The alignment marks are optimized to minimize alignment error resulting from changing the gap distance between the mask and wafer, which is called telecentricity. Using these newly designed alignment marks, we have evaluated alignment accuracy. We obtained alignment accuracy 3σ of 11.9(X) and 10.2 nm(Y) using etched SiN patterns on a Si substrate. Furthermore, the alignment scope is designed with multiwavelength light sources to illuminate the alignment marks. Selectable three laser diodes are applied in the optics. Multiwavelength light sources compensate each other and achieve robustness for various lithography processes. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
84.30.Sk Pulse and digital circuits
41.60.Ap Synchrotron radiation

Nanometer scattered-light alignment system using SiC x-ray masks with low optical transparency

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

J. Vac. Sci. Technol. B 16, 3471 (1998); http://dx.doi.org/10.1116/1.590479 (5 pages) | Cited 6 times

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Previously we described a video-based scattered-light alignment (SLA) system, capable of nanometer-scale alignment accuracy. In order to meet highly accurate alignment with low optical transparency in x-ray masks, we performed the modifications of alignment marks and an optical microscope imaging system on the conventional SLA system. The advanced SLA system has achieved a high alignment accuracy of 10.2–15.7 nm (∣mean∣+3σ) using a silicon carbide (SiC) x-ray mask of 18% optical transparency, coated with 5 nm thick chrome (Cr) film as an etching stop, with four different processed wafers: nitride, oxide, poly-Si, and aluminum. The different SiC membranes of 2–5 μm in thickness did not have an effect on the alignment accuracy in the nitride wafer. © 1998 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

Wafer chuck for magnification correction in x-ray lithography

M. Feldman and D. Smith

J. Vac. Sci. Technol. B 16, 3476 (1998); http://dx.doi.org/10.1116/1.590480 (4 pages) | Cited 3 times

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Magnification correction has emerged as a critical issue in x-ray lithography for very large scale integrated circuits. We have developed a simple and robust method to correct the magnification, which is suitable for use in a collimated x-ray beam from a storage ring. In our technique the wafer is bent to conform to a chuck whose surface is a portion of a sphere of adjustable radius. Both increases and decreases in the pattern size may be accommodated by using convex and concave spherical surfaces, respectively. The radius of the chuck can be set to achieve desired corrections of up to several parts per million. The maximum attainable correction is determined by the permissible out of plane distortion which accompanies the wafer bending, and is dependent upon the wafer thickness and the field size. The change in the wafer pattern is expected to be very nearly an isotropic magnification; however a limited one-dimensional magnification correction may also be added by differentially scanning the mask and wafer. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Mask membrane deflection caused by mask tilt during the wafer stepping motion in x-ray steppers

Norio Uchida

J. Vac. Sci. Technol. B 16, 3480 (1998); http://dx.doi.org/10.1116/1.590481 (5 pages)

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A new analysis method for deflection of the mask membrane during the wafer stepping motion in x-ray steppers has been developed. The deflection is caused by the wedge action of the gas film between the mask and the wafer if the mask tilts slightly relative to the plane on which the wafer is traveling. The deflection is not only detrimental to the throughput of x-ray steppers, it may also damage the mask membrane. Lees’ difference approximation method is applied to Reynolds’ equation for the gas film and the equation of motion for the membrane. The results calculated show good agreement with the experimental results (Ref. 1) obtained by Canon Inc. (1) The larger the tilt angle of the mask and the narrower the mask-to-wafer gap, the larger the deflection of the mask membrane. (2) In order to maintain the deflection of the membrane within 1 μm in the calculated mask, the tilt angle of the mask must be within 20 μrad under conditions of a 15 μm mask-to-wafer gap, a 30 mm stepping distance, and a wafer velocity of 100 mm/s. If the stepping distance becomes longer, the tilt angle must be more strictly controlled. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Overlay modeling for proximity x-ray lithography

Alek C. Chen

J. Vac. Sci. Technol. B 16, 3485 (1998); http://dx.doi.org/10.1116/1.590482 (6 pages) | Cited 1 time

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Proximity x-ray lithography is one of the most promising manufacturing technologies for the fabrication of future electronics devices with ground rules of 100 nm and less because of its wide exposure latitude and processing simplicity. However, the ability to make 1× x-ray masks, with high pattern placement accuracy, has continued to be one of the main technical challenges preventing the wide use of this technology by the semiconductor industry. A model has recently been developed to examine the parameters affecting the overall lithographic system overlay performance, such as the mask pattern placement error as well as the error sources from the x-ray aligner. The model treats all of the error sources statistically. The major assumption of the model is that all the error sources are statistically independent. This is a fairly accurate assumption for the error sources under consideration. For example, the mask pattern placement error is and should be independent of the aligner wafer stage stepping errors. Furthermore, the model can simulate error sources that do not follow the normal statistics. The model has three major components: (1) the x-ray aligner machine model that simulates all the major aligner error sources such as mask and wafer alignments, (2) the application parameter component that considers any application-specific setup tool parameters such as the number of wafer alignment marks and the number and location of global alignment sites, and (3) the mask component that accounts for the effects of pattern placement accuracy on alignment marks and overlay metrology targets. A detailed description of the model and the experimental data used to verify its validity will be given. The relative impact of the various subcomponent error contributions on the overall overlay performance will be provided. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Properties of sputtered TaReGe used as an x-ray mask absorber material

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

J. Vac. Sci. Technol. B 16, 3491 (1998); http://dx.doi.org/10.1116/1.590483 (4 pages) | Cited 2 times

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We have investigated the characteristics of Ta-based amorphous alloy films for use in an x-ray mask absorber. The stress in the TaReGe film can be controlled by changing the concentration of Re, making it easy to obtain low-stress films through deposition with any sputtering system followed by annealing. A required mask contrast can be obtained with a TaReGe film thinner than other Ta-based alloy films because the TaReGe film has a high density and a high mass absorption coefficient. We have achieved 0±10 MPa stress control for a TaReGe film by annealing. The TaReGe films showed high durability against various strong acids and developers, and against O2 plasma. We also demonstrated the fine patterning capability (0.1μm) of a TaReGe absorber. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.05.Bx Metals, semimetals, and alloys
68.60.Bs Mechanical and acoustical properties
81.15.Cd Deposition by sputtering
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.65.Cf Surface cleaning, etching, patterning

Characteristics of Ta-based amorphous alloy film for x-ray mask absorbers

Yoshihisa Iba, Fumiaki Kumasaka, Takashi Iizuka, Hajime Aoyama, and Masaki Yamabe

J. Vac. Sci. Technol. B 16, 3495 (1998); http://dx.doi.org/10.1116/1.590484 (5 pages) | Cited 2 times

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We examined Ta-based amorphous alloy films and studied their characteristics for application in an x-ray mask with dimensions of the 0.1 μm design rule. From the viewpoint of x-ray absorption, Ge is a suitable element for a compound with Ta. We found that a Ge inclusion atomic ratio of 20%–30% in a Ta–Ge compound film was suitable with respect to stress control and stress stability. It was possible to adjust the stress of the Ta–Ge film after deposition by annealing it at high temperature while maintaining control as good as 0.56 MPa/ °C. During pattern fabrication by dry etching, it was possible to successfully etch the Ta–Ge film with a single-layer resist using a chroline based plasma, and scale patterns of 0.1 μm were obtained. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Cd Deposition by sputtering
85.40.Sz Deposition technology

Temperature gradients during absorber etching and their effect on x-ray mask patterning

S. V. Pendharkar, D. J. Resnick, M. F. Laudon, W. J. Dauksher, P. J. S. Mangat, P. A. Seese, and K. D. Cummings

J. Vac. Sci. Technol. B 16, 3500 (1998); http://dx.doi.org/10.1116/1.590485 (4 pages)

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Pattern transfer in x-ray mask absorbers is often accomplished by reactively etching in chlorine containing plasmas. In this article, we show that the etch rate of one such absorber, TaSi, is a strong function of substrate temperature. We also show that the etch rate versus temperature behavior of TaSi is a result of the Ta in the film. Hence, other Ta based absorbers (Ta, Ta4B, TaGe, etc.) may also exhibit a similar behavior. We use finite element modeling to demonstrate that under certain conditions, significant temperature variations can exist on a National Institute Standards and Technology (NIST) x-ray mask which in turn can lead to etch rate variations. We also present experimental verification of these modeling results. Finally, through modeling, we discuss the effect of this etch rate variation on the pattern placement accuracy of NIST x-ray masks. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Low-dose exposure technique for 100-nm-diam hole replication in x-ray lithography

K. Fujii, Y. Tanaka, T. Taguchi, M. Yamabe, K. Suzuki, Y. Gomei, and T. Hisatsugu

J. Vac. Sci. Technol. B 16, 3504 (1998); http://dx.doi.org/10.1116/1.590486 (5 pages) | Cited 6 times

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In this article, we describe a new exposure technique for printing hole patterns with diameters of 100 nm or below in x-ray lithography. By using mask patterns approximately twice the size of the required resist patterns, 100-nm-diam holes can be replicated with doses less than those required to clear a large exposed area (D0) with a 20–30 μm gap. A 540-nm-thick UVII-HS resist was used for the exposure experiment. With a proximity gap of 20 μm, a 100-nm-diam hole was replicated with a 200-nm-diam mask pattern by exposing it with 0.56 D0 dose. Both the experimental and the simulation results indicated that this technique provides a higher resolution and a larger exposure latitude compared to normal-dose exposure. In terms of mask biasing, this technique corresponds to the mask bias optimization at doses below D0. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

130 nm and 150 nm line-and-space critical-dimension control evaluation using XS-1 x-ray stepper

Y. Tanaka, T. Taguchi, K. Fujii, S. Tsuboi, M. Yamabe, K. Suzuki, Y. Gomei, T. Hisatsugu, M. Fukuda, and H. Morita

J. Vac. Sci. Technol. B 16, 3509 (1998); http://dx.doi.org/10.1116/1.590487 (6 pages) | Cited 7 times

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Critical-dimension (CD) control for 130 and 150 nm line-and-space (L/S) patterns printed with the XS-1 x-ray stepper was evaluated using two kinds of resists: SAL606 and TDUR-N908. The largest factor in the CD variation was the nonuniformity of the x-ray dose, which was ±4.4% in a 20 mm×20 mm field. In replicated resist patterns, the CD variation due to mask-CD variation dropped to less than half the mask-CD variation because of Fresnel diffraction. For 130 nm L/S patterns, the CD variation for an 8-in.-diam wafer was 7.9 nm (3σ) for SAL606, and 12.0 nm (3σ) for TDUR-N908. For 150 nm L/S patterns, the values were 10.5 nm (3σ) and 14.6 nm (3σ), respectively. Although the major factors causing CD variation are dose nonuniformity and mask-CD variation, different resist materials reflect the effects of these factors to different degrees. The CD variation of 150 nm L/S patterns among seven wafers exposed on the same day was ±2.8 nm for SAL606 and ±3.7 nm for TDUR-N908, which is most likely due to fluctuations in the exposure dose of ±2.7%. The total CD variation for SAL606 was roughly estimated to be 9.0 nm (3σ) for 130 nm L/S patterns and 11.9 nm (3σ) for 150 nm L/S patterns. These values are within ±10% of the design rule. © 1998 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

Characterization of pattern geometrical effect on line end shortening in x-ray lithography

M. Yi, Y. Seo, E. Seo, J. Yang, K. Lee, B. K. Choi, and O. Kim

J. Vac. Sci. Technol. B 16, 3515 (1998); http://dx.doi.org/10.1116/1.590488 (6 pages)

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Line end shortening in x-ray proximity lithography was characterized from the viewpoint of the pattern geometry. Mask patterns from 0.1 to 0.3 μm linewidth with different pattern density were fabricated by e-beam lithography and subsequent gold electroplating. The mask patterns were printed in commonly well known chemically amplified resists using the Satellite-800 x-ray stepper developed by Sumitomo Heavy Industry with the synchrotron storage ring at the Pohang Accelerator Laboratory at Postech. A former study [J. R. Maldonado et al., J. Vac. Sci. Technol. B 13, 3094 (1995)] had shown the effect of the absorber thickness and the gap between mask and wafer on line end shortening. In this article, the effect on line end shortening of the geometry of a neighboring pattern, such as pattern shape, pattern density and position of the neighboring pattern, was considered. Several resists with different postexposure bake (PEB) temperatures and different gaps between mask and wafer were examined to characterize their effect on line end shortening. The closer neighboring pattern induced larger line end shortening and also higher PEB temperature and larger gap caused larger line end shortening. A perpendicular neighbor pattern to the test pattern induced different line end shortening than a parallel neighbor pattern. In addition, two dimensional aerial image simulations were performed and line end shortening was extracted from the calculated aerial image. Simulation results showed good agreement with the experimental results. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Edge diffraction enhanced printability in x-ray nanolithography

Y. Chen, G. Simon, A. M. Haghiri-Gosnet, F. Carcenac, D. Decanini, F. Rousseaux, and H. Launois

J. Vac. Sci. Technol. B 16, 3521 (1998); http://dx.doi.org/10.1116/1.590489 (5 pages) | Cited 8 times

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We study the edge diffraction enhanced printability in x-ray nanolithography under both proximity and soft-contact printing conditions. Theoretical modeling shows that the gap dependence of the edge diffraction is closely related to that of the minimum linewidth described by the common Fresnel formula and that the edge diffraction can significantly enhance the image contrast of nanometer scale features. Experimental results are also presented to show high resolution and high aspect ratio printability. Furthermore, a method for fabricating ultrahigh resolution and dense structure is discussed based on edge diffraction enhanced printability with very thin absorber masks. © 1998 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

Recent developments in deep x-ray lithography

Wolfgang Ehrfeld and Andreas Schmidt

J. Vac. Sci. Technol. B 16, 3526 (1998); http://dx.doi.org/10.1116/1.590490 (9 pages) | Cited 30 times

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Deep x-ray lithography (DXRL) with synchrotron radiation represents the technological core of the Lithographie, Galvanoformung, Abformung (LIGA) microfabrication process, thus defining the lateral shape and the accuracy of the final product. High aspect ratio microcomponents with a height of some micrometers up to several millimeters can be manufactured with submicron precision. We report on recently performed theoretical investigations on the structure transfer accuracy in the shadow printing process. Model calculations revealed the importance of photoelectron emission compared to Fresnel diffraction and beam divergence for typical DXRL conditions. The parameters used to model the effects correspond to the spectral distribution of the BESSY I wavelength shifter, Berlin (0.8 GeV, 5 T) equipped with several vacuum windows and a mask membrane made of beryllium with a thickness of 500 μm. A poly(methylmethacrylate) resist layer of 300 μm thickness with a bottom dose of 5 kJ cm−3 is assumed. The calculated dose profiles are supplemented by a detailed experimental analysis confirming the calculation results which indicate a microstructure precision of less than 0.05 μm per 100 μm resist height. Additionally, advanced irradiation techniques like multiple tilted exposures and aligned double exposures are discussed with respect to their technological capacity. Resist side walls exposed under an inclination angle of 45° turned out to follow an accuracy of approximately 1 μm over a height of up to 500 μm, where overlay accuracy for multiple aligned irradiations can be achieved within submicron scale using an internal alignment system in the DEX2 JENOPTIK scanner. Both specially treated beryllium masks and optically transparent LIGA masks made of thin silicon nitride membranes have been utilized. Finally, novel applications of microproducts using DXRL as a prerequisite for mass production will be given. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.85.Qe Synchrotron radiation instrumentation

Surface photochemistry induced by x-ray irradiation

Richard A. Rosenberg, Qing Ma, Barry Lai, and Derrick C. Mancini

J. Vac. Sci. Technol. B 16, 3535 (1998); http://dx.doi.org/10.1116/1.590491 (4 pages) | Cited 11 times

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The high-intensity, high-energy x rays produced by third-generation synchrotron radiation sources have made possible many new applications, such as deep x-ray lithography, that take advantage of the long penetration lengths of the x rays in lower-Z materials. Recently, we have initiated a program to evaluate the prospects for using x rays for materials processing by performing surface photochemistry induced by x-ray irradiation (SPIXI). The x rays induce reactions on the surfaces of solids immersed in potentially reactive liquids or gases. In this article we present results that demonstrate the feasibility of the SPIXI approach for both etching and deposition. Using a fluorochlorocarbon-based solvent and a Mo substrate we find indications of an etching-type reaction. Au and Ag films and nanocrystalline particles were produced from the irradiation of a Mo substrate immersed in their respective salt solutions. A Au film was also deposited on Kapton by back irradiation. These preliminary results indicate that this approach has great potential for room-temperature, atmospheric, patterned, materials processing. © 1998 American Vacuum Society.
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82.50.Kx Processes caused by X-rays or γ-rays
81.65.Cf Surface cleaning, etching, patterning
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.05.Bx Metals, semimetals, and alloys
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.07.-b Nanoscale materials and structures: fabrication and characterization

Enhanced adhesion buffer layer for deep x-ray lithography using hard x rays

Francesco De Carlo, Joshua J. Song, and Derrick C. Mancini

J. Vac. Sci. Technol. B 16, 3539 (1998); http://dx.doi.org/10.1116/1.590492 (4 pages) | Cited 5 times

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The first step in the fabrication of microstructures using deep x-ray lithography (DXRL) is the irradiation of an x-ray sensitive resist like polymethylmethacrylate (PMMA) by hard x rays. At the Advanced Photon Source, a dedicated beamline allows the proper exposure of very thick (several mm) resists. To fabricate electroformed metal microstructures with heights of several mm, a PMMA sheet is glued onto a metallic plating base. An important requirement is that the PMMA layer must adhere well to the plating base. The adhesion is greatly reduced by the penetration of even a small fraction of hard x rays through the mask absorber into the substrate. In this work we will show a novel technique to improve the adhesion of PMMA onto high-Z substrates for DXRL. Results of the improved adhesion are shown for different exposure/substrate conditions. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Adhesion promotion between poly(methylmethacrylate) and metallic surfaces for LiGA evaluated by shear stress measurements

C. G. Khan Malek and S. S. Das

J. Vac. Sci. Technol. B 16, 3543 (1998); http://dx.doi.org/10.1116/1.590493 (4 pages) | Cited 5 times

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The fabrication of high-aspect-ratio microelectromechanical structures (HI-MEMS) using the LiGA process [German acronym for Lithography, Galvanoplasty, and molding (Abformung)] requires both sufficient lithographic and mechanical adhesion of thick microstructures to the substrate. The interfacial bond strength between poly(methylmethacrylate) and various metal surfaces (Ti, Cu, and Au), in the preliminary stages of the LiGA process, was evaluated by shear stress measurement. In addition, adhesion promotion processes have been investigated. A mechanical type of adhesion was promoted by modifying the morphology of surfaces. Ti or Cu were microroughened by chemical oxidation and acrylic resist sheets thermally processed. The largest increase in adhesion was obtained with a combination of both substrate and resist treatments. The use of Novolak resists as interfacial layers enhanced adhesion, independently of the nature of the substrates. Severalfold increases in bond strengths were also obtained using various primers, such as 3-aminopropyl-triethoxysilane on Au and Cu substrates. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
68.35.Gy Mechanical properties; surface strains
07.10.Cm Micromechanical devices and systems
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Mq Oxidation
81.05.Bx Metals, semimetals, and alloys
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Influence of developer temperature and resist material on the structure quality in deep x-ray lithography

F. J. Pantenburg, S. Achenbach, and J. Mohr

J. Vac. Sci. Technol. B 16, 3547 (1998); http://dx.doi.org/10.1116/1.590494 (5 pages) | Cited 18 times

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Deep x-ray lithography is a fabrication method for the production of microstructures with aspect ratios of up to 100 in up to several millimeter thick resist layers. Usually, poly(methylmethacrylate) is used as the resist layer. We have measured the molecular weight and developing rates of crosslinked and noncrosslinked PMMA foils at different GG developer temperatures for dose values between 0.1 and 8 kJ/cm3. The determined developing rates cover a region of 7 orders of magnitude: With decreasing temperature the contrast of the resist-developer system and the limit of the developing dose are increased. Crosslinked PMMA has a higher contrast compared to noncrosslinked material. These effects lead to an enhanced quality of microstructures, which is demonstrated by the grating of the LIGA microspectrometer. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Metrology study of structural transfer accuracy in fabrication of high-aspect-ratio microelectromechanical systems: From optical mask to polished electroplated parts

C. Khan Malek, R. Wood, B. Dudley, and P. Genova

J. Vac. Sci. Technol. B 16, 3552 (1998); http://dx.doi.org/10.1116/1.590305 (6 pages) | Cited 3 times

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This article focuses on some fabrication issues and characterization at various steps of the LIGA [German acronym for Lithorgraphy, Galvanoplasty, and molding (Abformung)] process, in particular on the acuity of pattern transfer through the various steps of the process, from the optical mask to planarized electroplated parts for basic LIGA processing (single level). Metrology data on the accuracy of the LIGA process as currently applied in the high-aspect-ratio microelectromechanical systems (HI-MEMS) Alliance at various stages of the process are presented and the sources of process biases are investigated. Some potential areas for improvement with respect to dimensional control will also be highlighted. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.10.Fq Growth from melts; zone melting and refining
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.10.Cm Micromechanical devices and systems
81.20.Wk Machining, milling

Assessment of thermal loading-induced distortions in optical photomasks due to e-beam multipass patterning

Bassam Shamoun, Roxann Engelstad, and David Trost

J. Vac. Sci. Technol. B 16, 3558 (1998); http://dx.doi.org/10.1116/1.590306 (5 pages) | Cited 1 time

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Thermal loading-induced distortion in the photomask during e-beam patterning has recently received special attention due to its significant contribution to overlay errors. Multipass e-beam writing, a strategy proposed to reduce the heating effects and associated distortions, was simulated using three-dimensional finite element models. Thermal responses of the photomask during multipass patterning were determined and global in-plane distortions were calculated. For the given system exposure conditions of 40 μC/cm2 at 50 keV, the average value of the 3σ pattern placement error due to the bulk heating of the photomask obtained from multipass writing was found to be ≈3.5 nm which is 28% lower than that of single pass writing. Parametric studies showed that thermal radiation has a large influence on the mask cooling. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
02.70.Dh Finite-element and Galerkin methods

Aerial image slope and proximity effects on critical dimensions in mask lithography

Allan Sagle, M. Gesley, H. Kao, and R. Innes

J. Vac. Sci. Technol. B 16, 3563 (1998); http://dx.doi.org/10.1116/1.590307 (4 pages)

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Critical dimension (CD) control for isolated lines has been experimentally studied as a function of aerial image slope and proximity effects on a photomask. The aerial image slope was controlled by defocusing a 50 kV shaped beam. Isolated crosses of 0.2, 0.3, 0.5, and 1.0 μm were written on a chrome on glass mask. When all of the features are written at the same dose a nonlinearity of 100 nm and a uniformity of 3σ=65 nm were observed for an aerial image slope of 120 nm. These were reduced to a nonlinearity of 20 nm and a uniformity of 3σ=18 nm when a dose correction was performed for each feature size. This suggests that proximity correction and not small aerial image slope is the most critical improvement needed to achieve good CD control. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Improving pattern placement using through-the-membrane signal monitoring

F. K. Perkins, C. R. K. Marrian, and M. C. Peckerar

J. Vac. Sci. Technol. B 16, 3567 (1998); http://dx.doi.org/10.1116/1.590499 (5 pages) | Cited 2 times

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We describe here a means of improving pattern placement accuracy in the electron-beam lithographic manufacture of membrane masks. Our method is based on collection of the beam transmitted through the membrane with a detector fixed to the mask assembly. A fiducial grid overlaid onto the detector is used to provide a global reference for measurement of the beam position during lithographic patterning. We give results from recent experiments with components of such a system, and estimate 1σ accuracy in our method to be on the order of 1.5 nm. We discuss the effect of beam scattering on our technique, and possible improvements in our implementation.  
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85.40.Hp Lithography, masks and pattern transfer
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Pattern transfer on mask membranes

A. H. Fisher, R. L. Engelstad, E. G. Lovell, and D. M. Puisto

J. Vac. Sci. Technol. B 16, 3572 (1998); http://dx.doi.org/10.1116/1.590308 (5 pages) | Cited 1 time

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Pattern specific emulation is facilitated by the prediction of the distortions due to pattern transfer. Using finite element (FE) methods along with equivalent modeling techniques, it is possible to determine the distortions due to the fabrication of actual mask patterns. This article presents the results of the FE simulation on x-ray lithography masks. Employing the IBM Talon mask design as an example case, the distortions in the pattern area due to the fabrication of the absorbers on the mask membrane were determined. Results are presented for both a uniformly stressed absorber layer and an absorber layer with a unidirectional linear stress gradient. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
02.70.Dh Finite-element and Galerkin methods

Etching processes and characteristics for the fabrication of refractory x-ray masks

Michael J. Lercel, Cameron J. Brooks, Douglas E. Benoit, and Maheswaran Surendra

J. Vac. Sci. Technol. B 16, 3577 (1998); http://dx.doi.org/10.1116/1.590309 (5 pages) | Cited 5 times

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Refractory x-ray masks for a wide variety of pattern types were fabricated using tantalum silicon as the absorber material. Both positive (Shipley UVIII®) and negative (Shipley SNR200®) chemically amplified electron beam resists were exposed and the patterns transferred into a silicon oxynitride hardmask. The amorphous TaSi absorber was then etched using a Cl2/O2 reactive ion etch (RIE). From a mask manufacturing standpoint, the challenge is etching the wide variety of feature types that commonly occur in device processing. The overall etch process was characterized for the formation of both freestanding lines (using negative electron beam resist) and narrow trenches (using positive resist). RIE lag, feature shape dependence, and cross-mask uniformity in the etch bias were characterized for feature sizes down to 125 nm. The etch process has been implemented in a pilot line environment and is being used to produce product masks. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Commercialization of SCALPEL masks

R. C. Farrow, A. E. Novembre, M. Peabody, R. Kasica, M. Blakey, J. A. Liddle, K. Werder, R. DeMarco, L. Ocola, L. Rutberg, T. Saunders, J. Unruh, F. Qian, and M. Smith

J. Vac. Sci. Technol. B 16, 3582 (1998); http://dx.doi.org/10.1116/1.590310 (5 pages) | Cited 4 times

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To investigate the viability of large scale manufacture of SCALPEL masks, key components of the SCALPEL mask process have been performed by commercial suppliers. SCALPEL mask blanks have been fabricated by MCNC to specifications supplied by Lucent and have been delivered, patterned, and utilized. Patterning, inspection, and metrology have been performed by DuPont Photomask and Photronics using the standard set of tools used for photomasks. A wet chemical pattern transfer process has been developed that is compatible with the processing tools in the mask shops and is extensible to the 0.1 μm generation of integrated circuits. SCALPEL masks that have been fabricated using these processes and tools exhibit excellent pattern fidelity and feature edge quality. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Dynamic analysis of a SCALPEL mask during electron-beam exposure

W. H. Semke, R. L. Engelstad, E. G. Lovell, and J. A. Liddle

J. Vac. Sci. Technol. B 16, 3587 (1998); http://dx.doi.org/10.1116/1.590311 (5 pages) | Cited 3 times

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Projection electron-beam lithography, specifically the scattering with angular limitation projection electron lithography (SCALPEL) system, is a viable technology for the production of semiconductor devices with feature sizes in the sub-0.13 μm regime. A step-and-scan approach is used to expose the patterned membrane areas within the grillage structure on the SCALPEL mask. Finite element methods were employed to determine the dynamic distortions caused by an acceleration duty cycle and by various mounting techniques. The transient response of a SCALPEL mask with and without a support ring has been analyzed. Results for both an electrostatic chuck and a “3-2-1” kinematic mount are presented. They show the electrostatic mount produces significantly lower distortions than the 3-2-1 kinematic mount with a support ring. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
02.70.Dh Finite-element and Galerkin methods

p-n junction-based wafer flow process for stencil mask fabrication

I. W. Rangelow, F. Shi, B. Volland, E. Sossna, A. Petrashenko, P. Hudek, R. Sunyk, I. Kostic, J. Butschke, F. Letzkus, R. Springer, A. Ehrmann, G. Gross, R. Kaesmaier, A. Oelmann, et al.

J. Vac. Sci. Technol. B 16, 3592 (1998); http://dx.doi.org/10.1116/1.590500 (7 pages) | Cited 8 times

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The development of stencil masks is considered to be critical to the success of the new ion projection lithography technology. We present here a p-n junction wafer flow process where all fabrication steps are realized on a bulk Si wafer except the final trench etching through the 2–4-μm-thick Si membrane. Stencil masks were produced in a conventional complementary metal-oxide-semiconductor 150 mm wafer line, using an e-beam direct writing tool for patterning. The resist patterns were transferred by standard reactive ion etching (RIE) into a stress-controlled SiON hard mask layer. Subsequent to depositing an Al metal layer for contact to the n-doped wafer surface, the membrane was realized by a wet chemical etch which implemented well established reverse biased p-n junction etch stop techniques. Then, openings through the Si membrane were etched by RIE or inductively coupled plasma etching. Finally, the remaining hard mask layer was removed in BHF. The realized Si membrane diameter was 120 mm with a stencil pattern field of 60 mm×60 mm. Results from LMS-IPRO placement measurements are in agreement with the simulation of the stencil mask fabrication process using finite element methods. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Fabrication of silicon stencil masks with vitreous carbon ion-absorbing coatings

P. Ruchhoeft, J. C. Wolfe, J. Wasson, J. Torres, H. Wu, H. Nounu, N. Liu, M. Herbordt, M. D. Morgan, and R. C. Tiberio

J. Vac. Sci. Technol. B 16, 3599 (1998); http://dx.doi.org/10.1116/1.590385 (3 pages) | Cited 2 times

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We show how to integrate a vitreous carbon ion-absorbing coating with current silicon stencil mask technology to create a mask for ion beam lithography with dramatically improved radiation resistance. The masks were formed by first sputtering a graphitic carbon film onto the nonplanar side of a patterned silicon stencil mask. The carbon film was subsequently vitrified by He+ ion implantation and patterned by O2 reactive ion etching using the silicon mask itself as an etching template. In the example reported herein, the thicknesses of the silicon mask and carbon film were 0.7 and 1.0 μm, respectively. Silicon mask openings as small as 80 nm were faithfully replicated in the carbon, making a 20:1 aspect ratio in the bilayer mask. The mean stress of these multilayer masks is extremely stable when lithography ions are stopped within the carbon layer: stress change is less than experimental error (0.5 MPa) for at least 500 000 proximity exposures. Compared to silicon stencil masks, which wrinkle after only 100 exposures, these masks represent a breakthrough in nanostructure manufacturing. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.15.Cd Deposition by sputtering
85.40.Sz Deposition technology

Optimization of the temperature distribution across stencil mask membranes under ion beam exposure

B. Kim, R. Engelstad, E. Lovell, A. Chalupka, E. Haugeneder, G. Lammer, H. Löschner, J. Lutz, and G. Stengl

J. Vac. Sci. Technol. B 16, 3602 (1998); http://dx.doi.org/10.1116/1.590312 (4 pages) | Cited 2 times

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The pattern placement accuracy of a stencil mask is affected by thermomechanical distortion induced during ion beam exposure. Any temperature gradient across the mask membrane could result in thermal distortions which contribute to the stringent error budget. Therefore, a concept has been proposed to control the temperature across the mask membrane by using radiation heat transfer between exposure station components. This work extends previous efforts by including the effects of the backside radiation loss of the exposure area, the aperture, etc. Here the exposure station which has been proposed by IMS-Ion Microfabrication Systems is investigated and simulated with finite element models. Parametric studies have been performed in order to optimize design variables such as material properties, and the temperature settings of the cooled lens electrodes and aperture. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
02.70.Dh Finite-element and Galerkin methods

Optically induced mask critical dimension error magnification in 248 nm lithography

John N. Randall and Alexander Tritchkov

J. Vac. Sci. Technol. B 16, 3606 (1998); http://dx.doi.org/10.1116/1.590313 (6 pages) | Cited 2 times

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One form of optical proximity effect that further complicates lithography is the unexpected response of the printed image to small perturbations [critical dimension (CD) errors] in the reticle. In this way mask CD errors are actually magnified (they are reduced by less than the reduction factor of the optics) during the optical transfer to the wafer. This effect will require even tighter specifications for mask CD control when the error magnification factor is significantly above unity. The effect is particularly pronounced for tight pitches of small features, but can also impact the printing of small isolated lines. Both resist and optical nonideal responses are involved in this mask error factor (MEF). This article discussed the optical effects that produce the MEF. This article will show where the MEF due to optical effects can be ignored and where they cannot when using 248 nm lithography with a high numerical aperture (NA) tool. We will demonstrate how the NA, partial coherence, and variations in focus can effect the mask error magnification factor. We will also show that resolution enhancement techniques can be used to reduce the mask error magnification factor. In particular, Levenson phase shift masks show particularly low mask error magnification factors for small lines. For some applications it should be possible to design the mask so that the mask error magnification factor of the smallest features is significantly below unity. This would allow loosened reticle CD specifications and/or better CD control of the lithography process. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Characteristics of plasma enhanced chemical vapor deposition-grown SiNx films prepared for deep ultraviolet attenuated phase-shifting masks

H. L. Chen, L. A. Wang, and C. W. Hsu

J. Vac. Sci. Technol. B 16, 3612 (1998); http://dx.doi.org/10.1116/1.590314 (6 pages) | Cited 1 time

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Suitable SiNx films for constructing attenuated phase-shifting masks (APSMs) to be operated in the deep ultraviolet (DUV) regime are obtained by varying the gas flow ratios in a plasma enhanced chemical vapor deposition process. Characteristics of the films such as optical constants, optical band gaps, material compositions, irradiation stability, etching selectivity, and adhesion strength are experimentally analyzed in detail. Subquarter micron patterns on SiNx films are obtained by utilizing DUV lithography and silylation technique for the proof of feasibility. These results indicate that the SiNx films thus fabricated can meet all the requirements for building such APSMs working at wavelengths of 248 and 193 nm. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Nk Insulators
61.82.Ms Insulators
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.65.Cf Surface cleaning, etching, patterning
68.35.Gy Mechanical properties; surface strains
68.55.Nq Composition and phase identification

Graphite-based x-ray masks for deep and ultradeep x-ray lithography

Philip Coane, Robert Giasolli, Francesco De Carlo, Derrick C. Mancini, Yohannes Desta, and Jost Göttert

J. Vac. Sci. Technol. B 16, 3618 (1998); http://dx.doi.org/10.1116/1.590315 (7 pages) | Cited 1 time

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The cost-effective fabrication of high-aspect-ratio microstructures using x rays largely depends on the availability and quality of x-ray masks. The architecture of a mask is mainly determined by the photon energy of the synchrotron source, the x-ray flux, and the thickness of the resist. Typically, the mask membrane is made from a low-atomic-number material and can either be a frame-supported, several microns thin membrane (carbon, silicon carbide, silicon nitride, or silicon) or a bulk material (beryllium) with a thickness of up to 1 mm. The absorber pattern is formed from high atomic number materials such as gold, tungsten, or tantalum, and the final pattern geometry can be defined either with additive (electroplating) or subtractive (etching, milling) processes. One approach that is designed to reduce cost and turn-around time is the fabrication of x-ray masks using graphite sheet stock for the mask membrane. Rigid graphite offers unique properties, such as moderate x-ray transmission, relatively low cost, and the ability to be used with either subtractive or additive processes. This article will report details on the lithographic fabrication of graphite x-ray masks using intermediate x-ray masks for pattern transfer. First experimental results will be presented for synchrotron x-ray exposures performed at the Center for Advanced Microstructures and Devices synchrotron in Baton Rouge and the Advanced Photon Source at Argonne National Laboratory. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
41.60.Ap Synchrotron radiation

Optical probing of flip chip packaged microprocessors

Mario Paniccia, R. M. Rao, and Wai Mun Yee

J. Vac. Sci. Technol. B 16, 3625 (1998); http://dx.doi.org/10.1116/1.590316 (6 pages) | Cited 10 times

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A method to optically probe flip chip packaged complementary metal–oxide–semiconductor (CMOS) microprocessors is described. The technique utilizes an infrared laser with a wavelength of 1064 nm to probe the electric field and the free carrier induced absorption modulation that occurs in a reverse biased P-N junction. This absorption modulation is related directly to the voltage across the junction. The mode-locked laser, which generates a train of 35 ps optical pulses at a repetition rate of 100 MHz, is focused through the heavily doped silicon onto the diffusion regions of the CMOS chip. The small modulations in laser power riding on the reflected optical beam are detected and recovered to measure the voltage across the junction. Time resolution is achieved by making the measurement stroboscopically, by phase locking the mode-locked laser to the tester driving the chip. Results from the flip chip packaged microprocessor have been measured and are presented. © 1998 American Vacuum Society.
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84.30.Sk Pulse and digital circuits
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Application of interferometric broadband imaging alignment on an experimental x-ray stepper

Euclid E. Moon, Jawoong Lee, Patrick N. Everett, and Henry I. Smith

J. Vac. Sci. Technol. B 16, 3631 (1998); http://dx.doi.org/10.1116/1.590317 (6 pages) | Cited 9 times

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A series of experiments were performed with an interferometric-broadband imaging (IBBI) alignment system on an experimental x-ray lithography stepper. These experiments demonstrated sub-1 nm consistency of independent IBBI measurements and the ability to feedback lock the mask relative to a wafer to within a mean of 0.0 nm and a standard deviation of 1.4 nm. Comparisons of displacement measurements made with IBBI and closed-loop piezo drives confirmed scale consistency to within about 1.5%. In the absence of feedback control, spurious relative displacements were observed, due to temperature gradients and the nonrigid mechanics. This argues in favor of feedback control during exposure. The robustness of IBBI in allowing nanometer-level alignment measurements during x-ray exposure, with remotely located long-working-distance, low-cost microscopes should enable it to be used as a stand-alone alignment system or as an adjunct to global alignment. © 1998 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
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.60.Ly Interferometers

Performance of adaptive alignment method on asymmetric signals

X. Chen, A. A. Ghazanfarian, M. A. McCord, and R. F. W. Pease

J. Vac. Sci. Technol. B 16, 3637 (1998); http://dx.doi.org/10.1116/1.590318 (5 pages) | Cited 1 time

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Common problems in alignment include signal asymmetry from a nominally symmetric mark and variation across the wafer, from wafer to wafer and from mask level to mask level. Signal asymmetry arises from many sources, including uneven coating of overlayers, smearing effects of chemical mechanical polishing, or aberration and uneven illumination in the optical alignment systems. All reported alignment algorithms assume symmetric alignment signals. These alignment algorithms perform poorly when the signal is asymmetric. In previous publications [X. Chen, A. A. Ghazanfarian, M. A. McCord, and R. F. W. Pease, J. Vac. Sci. Technol. B 15, 2185 (1997); A. A. Ghazanfarian, X. Chen, M. A. McCord, and R. F. W. Pease, Proc. IEEE 4, 1913 (1998)], we proposed a new alignment method that incorporates prior knowledge by building a model for the asymmetry and process variations using alignment signals and overlay data from prior wafers. In this article, we present experimental results that convincingly demonstrate the viability of the adaptive alignment method. The experiments are carried out using deliberately distorted alignment marks placed alongside undistorted marks. It is shown that even under conditions when conventional alignment systems fail altogether, the mean-plus-three-sigma value of the alignment errors is less than 50 nm when the proposed algorithm is used. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Exploiting structure of wafer distortion in global alignment

Amir A. Ghazanfarian, Xun Chen, Mark A. McCord, R. Fabian, W. Pease, Khanh Nguyen, and Harry Levinson

J. Vac. Sci. Technol. B 16, 3642 (1998); http://dx.doi.org/10.1116/1.590319 (5 pages) | Cited 1 time

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One of the most critical emerging challenges in lithography is achieving rapid and accurate alignment. The problem is exacerbated by wafer and stage distortions. Thus, an effective learning process is needed to rapidly acquire the best possible positional information from an array of marks across the wafer. An algorithm based on a neural network model of global alignment was presented [A. A. Ghazanfarian et al., Proc. SPIE 3051, 629 (1997); J. Vac. Sci. Technol. B 15, 2146 (1997)], which incorporated both wafer and stage distortion. Yet in almost all cases, the stepper machines are precalibrated and the stage distortion is well controlled. Therefore, the aforementioned methods need to be revisited to specifically address the wafer distortion problem. In this article, we propose a new global alignment algorithm based on array processing techniques [J. Rissanen et al., Automatica 14, 465 (1978); M. Wax et al., IEEE Trans. Acoust., Speech, Signal Process], which exploits the structure of the overlay data from prior wafers to characterize the wafer distortion for a new wafer. The algorithm has been applied to overlay data from Advanced Micro Devices, Inc., Overlay error has been measured on 9(3×3) sites, with five measurements per site. We have used data for two pairs of lots, each pair belonging to the same process. The model obtained from the first lot of each pair is used in global alignment of the wafers in the second lot. Results indicate more than 70% improvement in alignment accuracy compared to the current global alignment algorithm, with the average error reduced by about 30 nm. It is also faster than the site-by-site alignment algorithm; simulation results from a bowing distortion example show that the proposed algorithm requires measurement from only six sites. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Phase shift microscopes

M. Feldman

J. Vac. Sci. Technol. B 16, 3647 (1998); http://dx.doi.org/10.1116/1.590383 (4 pages)

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We report on a new class of scanning optical microscopes with twice the resolution of conventional microscopes. The new microscopes use standard components to produce high intensity images, with large working distances and large depths of focus, without additional mechanical complexity. The microscopes scan a focused laser beam which has passed through a pattern of phase shifts arranged in a spiral staircase. These phase shifts generate a narrow dark spot in the center of the focused beam. The width of this central dark spot is about half the diffraction limit. The signal from this “phase shifted” beam is subtracted from the signal produced by a conventional Gaussian beam which is simultaneously scanned. The difference between the two detected signals corresponds to the signal from a bright beam of width equal to the width of the dark central area. Since only linear operations on observed optical signals are used, there is a useful improvement in resolution of about a factor of 2. This improves both the accuracy with which feature edges may be located, as well as the resolution of small features such as the corners of narrow lines. © 1998 American Vacuum Society.
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07.79.Fc Near-field scanning optical microscopes
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Quantitation of latent resist images using photon tunneling microscopy

J. A. Liddle, J. A. Johnson, R. Cirelli, M. M. Mkrtchyan, A. E. Novembre, and M. L. Peabody

J. Vac. Sci. Technol. B 16, 3651 (1998); http://dx.doi.org/10.1116/1.590384 (4 pages)

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Photon tunneling microscopy (PTM) is an optical microscopy technique that can, by using frustrated total internal reflection, be sensitive to changes in surface topography as small as 1 nm. We have developed a simple calibration technique that generates plots of sample reflectivity as a function of topography. This empirical data is then used to convert a gray-scale image of a specimen into an accurate topographic image. Errors, such as accurate magnification calibration and detector nonlinearity, lead to only small differences between the empirical data and our theoretical prediction. We have used PTM to study the evolution of latent images in a chemically amplified resist, ARCH2, as a function of dose, both after exposure and after postexposure bake, and have obtained good agreement between the topography measured in the PTM with thickness changes determined by ellipsometry from large exposed areas. Comparison of the results of the PTM with those obtained by near-field scanning optical microscopy demonstrate that changes in topography on the order of 3–5 nm are visible in the PTM. The topography that appears to develop in a latent image is a function of feature size. This effect occurs before the lateral resolution limit of the microscope is reached, and is a result of the mechanical constraint arising from unexposed resist material around the exposed features. Techniques such as adjusting the polarization and wavelength of the illumination can improve the sensitivity of the technique to small changes in topography, while in the case of materials that undergo changes in refractive index, contrast can be seen even in the absence of topography. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.79.Fc Near-field scanning optical microscopes

Economical sampling algorithm using Fourier analysis for mapping wafer critical dimension variations

Xu Ouyang, C. N. Berglund, Mark A. McCord, R. F. W. Pease, Chris Spence, and Hua-Yu Liu

J. Vac. Sci. Technol. B 16, 3655 (1998); http://dx.doi.org/10.1116/1.590386 (6 pages) | Cited 3 times

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Characterizations of critical dimension (CD) errors on wafers are usually based on the assumption that the errors are random and normally distributed, and that they therefore can be fully described by a mean and 3σ value. However many sources of CD errors are known to be primarily systematic and are often spatially correlated. In order to establish an efficient measurement sampling scheme and data analysis algorithm that accounts for such nonrandom errors, we collected 900 CD data points using electrical test structures on each of nine wafers that were fabricated in two different fabrication facilities. Wafers using both phase-shifting mask and conventional mask lithography were measured. Fourier analysis was then used to study the errors in the spatial frequency domain. It was found that in all cases systematic and spatially correlated errors, in particular a set of errors that were largely repetitive with stepper field periodicity, dominated over random CD errors. By taking advantage of the correlated nature of these errors, an economical two-step sampling algorithm is defined that significantly reduces the amount of sampling needed (by approximately fourfold). By combining the results of the two-step sampling in the spatial frequency domain, an accurate map of actual error spatial distribution can be extracted. The accuracy of the scheme is verified by using subsets of the 900 data point measurements, and comparing the results to those from the full set of data. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
02.30.Nw Fourier analysis

Evaluation of total uncertainty in the dimension measurements using critical-dimension measurement scanning electron microscopes

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

J. Vac. Sci. Technol. B 16, 3661 (1998); http://dx.doi.org/10.1116/1.590387 (7 pages) | Cited 1 time

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Total uncertainty can be discussed in terms of bias and reproducibility. We have studied bias and reproducibility in the critical dimension measurement scanning electron microscope and measurements have derived expressions of them, and discussed the parameters which determine them by making a comparison with measurement data. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.20.Dk Measurement and error theory

Whole film inspection using an extended source

Arun Aiyer and Henry Chau

J. Vac. Sci. Technol. B 16, 3668 (1998); http://dx.doi.org/10.1116/1.590388 (4 pages)

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Currently, one measures dielectric thin film thickness on a wafer surface by sampling a predetermined number of points across the wafer. Point measurements do not provide accurate information on the trend in thickness variation across the wafer surface. Such information could be quite useful while developing new coating, deposition, etching, or polishing processes. Hence, a system that can map single layer film thickness across the whole wafer or a large area of the wafer will be very useful to process developers. In this article, we will discuss a technique that can map film thickness across a large area in a relatively short amount of time. It takes about 4 s to determine about 23 000 thickness values across the wafer. The approach has been breadboarded and demonstrated. Using a single wavelength, this technique makes it possible to characterize single layer film thickness without having to know optical constants of the substrate material.© 1998 American Vacuum Society.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.60.Hv Refractometers and reflectometers
81.65.Ps Polishing, grinding, surface finishing
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Scintillating global-fiducial grid for electron-beam lithography

James Goodberlet, James Carter, and Henry I. Smith

J. Vac. Sci. Technol. B 16, 3672 (1998); http://dx.doi.org/10.1116/1.590389 (4 pages) | Cited 8 times

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An organic scintillator has been developed for use in electron-beam lithography. The scintillator can be deposited in a thin film (<200 nm) on the substrate, and can be patterned by an ultraviolet-interferometric exposure to produce a uniformly thick, scintillating, fiducial grid. When scanned with the electron beam, the scintillating pattern produces a high-contrast (>2) optical signal. It is expected that the signal from this type of grid will improve the pattern-placement precision to within 1 nm when used in conjunction with spatial-phase-locked electron-beam lithography. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Resist processes for hybrid (electron-beam/deep ultraviolet) lithography

S. Tedesco, T. Mourier, B. Dal’zotto, A. McDougall, S. Blanc-Coquant, Y. Quéré, P. J. Paniez, and B. Mortini

J. Vac. Sci. Technol. B 16, 3676 (1998); http://dx.doi.org/10.1116/1.590390 (8 pages) | Cited 5 times

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This article describes the different mix and match writing strategies using both an optical deep ultraviolet (DUV) stepper (ASML/90) and an electron-beam (e-beam) system (LEICA VB6HR) with both positive and negative tone chemically amplified resists. These resists, mainly developed for DUV applications, have shown very good performance under e-beam exposure. Negative tone resists such as the Shipley XP90166 and UVN2, and positive tone resists such as the Shipley UVIII and UV5 have been optimized in terms of soft bake temperatures, postexposure bake temperatures, and development process. Resolutions in the range of 40–50 nm have been obtained using a 50 keV accelerating voltage. Delay time effect has been quantified and different behaviors under vacuum and in air have been pointed out. © 1998 American Vacuum Society.  
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85.40.Hp Lithography, masks and pattern transfer

Negative electron-beam nanofabrication resist using acid-catalyzed protection of polyphenol provided by phenylcarbinol

Shou-ichi Uchino, Jiro Yamamoto, Sonoko Migitaka, Kyoko Kojima, Michiaki Hashimoto, and Hiroshi Shiraishi

J. Vac. Sci. Technol. B 16, 3684 (1998); http://dx.doi.org/10.1116/1.590391 (5 pages) | Cited 7 times

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A high-resolution negative electron-beam (EB) lithography resist based on an acid-catalyzed protection reaction of a polyphenol enabled by a phenylcarbinol has been developed for nanofabrication. Polyphenol-3, which is synthesized by condensation of α,α,α′-tris(4-hydroxyphenyl)1-ethyl-4-isopropylbenzene with m-cresol, was selected as the most suitable matrix resin for the resist. 1,3,5-tris[1-(1-hydroxyethyl)]benzene (Triol-2) was found to be the best protection reagent among the six phenylcarbinols evaluated. Line-and-space patterns of 80 nm with edge roughness of less than 10 nm were delineated by using a resist composed of Triol-2, diphenyliodonium triflate, and polyphenol-3 in conjunction with an EB writer (20 μC/cm2 at 50 kV). Spectroscopic studies clearly showed that the acid-catalyzed protection reaction of the polyphenol brought about by Triol-2 is responsible for the resist insolubilization. © 1998 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
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.35.-x Polymers: properties; reactions; polymerization

Deep-ultraviolet interferometric lithography as a tool for assessment of chemically amplified photoresist performance

W. Hinsberg, F. A. Houle, J. Hoffnagle, M. Sanchez, G. Wallraff, M. Morrison, and S. Frank

J. Vac. Sci. Technol. B 16, 3689 (1998); http://dx.doi.org/10.1116/1.590392 (6 pages) | Cited 77 times

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The precise control of the exposure step provided by interferometric photolithography facilitates studies of chemically amplified resist physics, chemistry, and functional properties that are difficult using more conventional exposure techniques. We describe here the design and operating characteristics of a deep-ultraviolet interferometric lithography tool designed specifically for the study of high resolution chemically amplified resists. We provide an example of its use to evaluate resist response to controlled variations in aerial image contrast. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Nanolithography in polymethylmethacrylate: An atomic force microscope study

Elizabeth A. Dobisz, Susan L. Brandow, Robert Bass, and Loretta M. Shirey

J. Vac. Sci. Technol. B 16, 3695 (1998); http://dx.doi.org/10.1116/1.590501 (6 pages) | Cited 7 times

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This work addresses the formation and development of very dense nanolithographic resolution patterns in polymethylmethacrylate (PMMA) of two molecular weights (MWs), 950 and 50 K. The patterns were lithographically defined by a JEOL JBX-5DII e-beam lithography system operated at 50 kV with a Gaussian probe standard deviation of 8–10 nm. The lithographic patterns consisted of pads of widths from 1 to 20 μm with a 50 nm gap of exposure in the center and single pass line gratings of periods 40, 60, 80, and 100 nm. Atomic force microscope images were acquired. Latent images of the 50 nm gap were observed over a much larger range in dose and pad size, than observed in developed samples. The morphologies of the two unpatterned resists were comparable exhibiting a granular type structure with average particle diameters of 52–53 nm and root mean square surface roughness of 0.2–0.3 nm. In developed patterns, the morphologies and resolution of the two MW resists were very different. The 950 K resist exhibited better resolution and contrast than the 50 K resist. The results are discussed in the context of the exposure and development of macromolecular resists.
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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

Copolymer approach to charge-dissipating electron-beam resists

Maggie A. Z. Hupcey and Christopher K. Ober

J. Vac. Sci. Technol. B 16, 3701 (1998); http://dx.doi.org/10.1116/1.590393 (4 pages) | Cited 1 time

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During electron-beam lithographic exposure on insulating substrates, pattern distortions and displacements are observed due to charging of the surface. To alleviate these displacements, conducting polymers have been investigated in the past decade as negative-tone resists and as unimageable top or bottom layers in a multilayer stack. Our approach uses a graft copolymer: an acrylic backbone for the imaging performance of the resist and a conducting polymer grafted onto the backbone for the charge-dissipating performance. By using this system, the respective properties of the two components can be individually optimized for such properties as speed, etch resistance, solubility, and conductivity. This system also permits positive-tone single-layer imaging, which has not been achievable previously. High-resolution features (<0.10 μm), minimal pattern distortions, and no change in the clearing dose, were observed for graft copolymers containing <1% of the charge-dissipating component that were processed identically to commercially available PMMA resist. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Negative chemically amplified resist characterization for direct write and SCALPEL nanolithography

L. E. Ocola, C. J. Biddick, D. M. Tennant, W. K. Waskiewicz, and A. E. Novembre

J. Vac. Sci. Technol. B 16, 3705 (1998); http://dx.doi.org/10.1116/1.590394 (4 pages) | Cited 7 times

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Despite the common link of using high energy electrons as exposure probes in direct write and SCALPEL lithography, the imaging systems in both are different. The question arises then if an optimal process for direct write lithography will provide optimal results in SCALPEL. Characterization of a series of negative tone chemically amplified resists for use in direct write (at 50 kV) and projection electron beam (at 100 kV) nanolithography is reported. The current work has explored modifying the postapplied bake and postexposure bake temperatures and times to find an optimum process for direct write nanolithography and then verify it is applicable to SCALPEL. Results, using NEB-22A (Sumitomo Chemical Co.), show that this is possible. We have demonstrated that in direct write, the NEB-22A resist has excellent resolution (36 nm in 125-nm-thick resist, 75 nm in 500-nm-thick resist) and process latitude (>20%), with a sensitivity of about 14 μC/cm2 at 50 kV exposure. The etch resistance is 3 nm/s and is being used for gate level e-beam lithography of single level field-effect transistors. The optimal bake conditions are found to be longer than usual postapplied and postexposure bake times. We have also demonstrated that the optimal bake conditions can be transferred to a SCALPEL exposure with similar process latitude and resolution. © 1998 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
82.50.Kx Processes caused by X-rays or γ-rays

Chemically amplified resist processing with top coats for deep-ultraviolet and e-beam applications

Karen Petrillo, James Bucchignano, Marie Angelopoulos, Kathleen Cornett, and William Brunsvold

J. Vac. Sci. Technol. B 16, 3709 (1998); http://dx.doi.org/10.1116/1.590395 (7 pages) | Cited 2 times

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Protective top coats and top antireflective coatings (ARCs) are frequently used in conjunction with chemically amplified resists. Top coats provide resistance to airborne contamination, and are particularly important where charcoal filtration is not available in the processing area. They are also useful in environments where delay times between process steps are not precisely controlled. Conductive top coats can be used for e-beam applications to reduce charging and image placement errors. Top ARCs are used to reduce reflections at the resist/air interface, thereby lowering the amplitude of the swing curve. All of these materials are applied on top of the photoresist after the postapply bake. In this article we report that depending on the subsequent processing conditions, top coatings can significantly impact the lithographic performance of the photoresist. Alterations in development rate, optical proximity effects, resist profile, and postexposure bake latitude have been observed as a result of processing with an additional top film. The primary mechanism responsible for these changes is an alteration of the diffusion characteristics of the photo acid generator during the deprotection step. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

193 nm single layer resist strategies, concepts, and recent results

O. Nalamasu, F. M. Houlihan, R. A. Cirelli, A. G. Timko, G. P. Watson, R. S. Hutton, J. M. Kometani, E. Reichmanis, A. Gabor, A. Medina, and S. Slater

J. Vac. Sci. Technol. B 16, 3716 (1998); http://dx.doi.org/10.1116/1.590396 (6 pages) | Cited 2 times

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Matrix resins used in conventional resists are not suitable for use at 193 nm due to their opacity. Hence new materials that are functionally similar to but structurally different from novolac and poly(hydroxy styrene) are required for 193 nm lithography. We report on the use of alternating copolymers of cycloolefins with maleic anhydride as effective 193 nm matrix resins, with or without dissolution inhibitors based on polyfunctional cholates, for 193 nm lithography. Due to their structural diversity, the required high transparency and etch stability, compatibility with industry standard 0.262 N tetramethyl ammonium hydroxide (TMAH) can be built into the polymer by conventional free redical polymerization techniques. A correlation between the molecular properties of the resist components (matrix resin, dissolution inhibitor, photoacid generator, and base additive) and resist lithographic performance parameters is illustrated. The formulations containing dissolution inhibitors currently show 0.13 μm line/space (L/S) pair and 0.11 μm isolated line resolution at 20–30 mJ/cm2 photospeeds with good process latitude, etch resistance, and environmental stability. These materials are completely compatible with 0.262 N TMAH development, show poly and oxide etch rates comparable to that of deep-ultraviolet resists used in manufacturing today, and exhibit postexposure delay stabilities of greater than 2 h for 0.16 μm features at 13 ppb concentrations of ammonia or N-methyl pyrrolidone. The importance of reflectivity control at the 193 nm imaging wavelength and how it can be handled by a multilayer dielectric antireflective coating (ARC) has been elucidated. An optimized resist and ARC system shows 0.14 μm l/s pair resolution over 100 nm poly topography and exhibits a resolution of 60 nm isolated lines and 80 nm with >0.8 μm depth of focus using a Levenson phase shift mask. The design and utility of photoacid generators that serve both the photoacid generation and amine additive functions in low activation energy resist systems and the base additive function in high activation energy system are also described. The use of these photodecomposable bases (PDBs) has been shown to dramatically alleviate the outgassing during exposure in low activation energy chemically amplified (CA) resists. In high activation energy CA resists, use of a PDB that is basic but generates an acid upon exposure to light or radiation provides some relief in designing 193 nm resists that are fast, yet stable, to environmental and substrate contamination effects. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Top surface imaging process and materials development for 193 nm and extreme ultraviolet lithography

Veena Rao, John Hutchinson, Susan Holl, Joseph Langston, Craig Henderson, David R. Wheeler, Greg Cardinale, Donna O’Connell, John Goldsmith, John Bohland, Gary Taylor, and Roger Sinta

J. Vac. Sci. Technol. B 16, 3722 (1998); http://dx.doi.org/10.1116/1.590397 (4 pages) | Cited 2 times

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The maturity and acceptance of top surface imaging (TSI) technology have been hampered by several factors including inadequate resist sensitivity and line edge roughness. We have found that the use of a chemically amplified resist can improve the sensitivity in these systems by 1.5– 2× without compromising the line edge roughness. In addition, we have shown improved line edge roughness by increasing the molecular weight of the polymeric resin in the resist. Using these materials approaches, we have been able to show excellent resolution images with the TSI process for both 193 nm and extreme ultraviolet (13.4 nm) patterning. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Dissolution characteristics of chemically amplified 193 nm resists

Toshiro Itani, Hiroshi Yoshino, Shuichi Hashimoto, Mitsuharu Yamana, Mami Miyasaka, and Hiroyoshi Tanabe

J. Vac. Sci. Technol. B 16, 3726 (1998); http://dx.doi.org/10.1116/1.590502 (4 pages) | Cited 2 times

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The dissolution kinetics of two types of chemically amplified positive 193 nm resists were investigated; a ter-polymer resist consisting of poly(tricyclodecylacrylate-co-tetrahydrodpyranyl-methacrylate-co-methacrylicacid) and triphenylsulfonium triflate as a photoacid generator, and a copolymer resist consisting of poly(carboxytetracyclododecylmethacrylate-co-tetrahydro-pyranyloxy-carbonyl-tetracyclododecylmethacrylate) and triphenylsulfonium triflate as a photoacid generator. The dissolution rate contrast was higher and the slope of dissolution rate curve was steeper for the ter-polymer resist than those for the copolymer resist. However, the Arrhenius plots of the dissolution rates were straight lines for both resists irrespective of the exposure doses. This indicates that only one mechanism determines the dissolution of both resists, and it is believed that the dominant rate-determining step in both resists is the tetramethylammoniumhydroxide penetration into the resist films. The resolution capability of the ter-polymer resist was very high, 0.14 μm lines and spaces pattern. The resolution capability of the copolymer resist was moderate, 0.16 μm lines and spaces in spite of its lower dissolution contrast and smaller slope value. In addition, the dry-etch resistance of both resists was close to that of a conventional polyhydroxystyrene base KrF resist. These results indicate that both the ter-polymer and the copolymer resists are candidates for practical use. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
64.75.-g Phase equilibria

Single layer chemical vapor deposition photoresist for 193 nm deep ultraviolet photolithography

Mike Nault, Tim Weidman, Dian Sugiarto, David Mui, Carol Lee, and John Yang

J. Vac. Sci. Technol. B 16, 3730 (1998); http://dx.doi.org/10.1116/1.590398 (4 pages)

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The chemical vapor deposition resist film plasma polymerized methyl silane (PPMS) can be used as a single layer photoresist for optical lithography at 248 and 193 nm wavelengths. Upon exposure, the PPMS undergoes efficient photo oxidation in the presence of air to yield a siloxane network (PPMSO) giving patterns that can be dry developed using a chlorine-HBr plasma. After dry development, the PPMSO can be used to transfer a pattern through organic low κ materials, or can be converted to a silicon dioxide hardmask using a conventional resist stripper, then used to transfer patterns into polysilicon. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.35.-x Polymers: properties; reactions; polymerization

Resist design for resolution limit of KrF imaging towards 130 nm lithography

T. Azuma, D. Kawamura, K. Matsunaga, E. Shiobara, S. Tanaka, and Y. Onishi

J. Vac. Sci. Technol. B 16, 3734 (1998); http://dx.doi.org/10.1116/1.590399 (5 pages) | Cited 4 times

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A strategy of resist design for the resolution limit of KrF imaging is investigated, and then the possibility of 130 nm lithography using KrF imaging is discussed. An extremely thin resist in a thickness of less than 150 nm was developed for KrF imaging at the resolution limit. The resist could overcome crucial problems of nanoedge roughness as well as degraded resist profiles without sacrificing resolution capability even when reducing the resist thickness to extreme limits. Moreover, a resist thickness of 80 nm could narrowly perform 130 nm lithography using an unconventional KrF imaging system featuring a numerical aperture of 0.6 and a partial coherency of 0.75 with 2/3 annular aperture, without using any phase shift mask technologies. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Reduction of line edge roughness in the top surface imaging process

Shigeyasu Mori, Taku Morisawa, Nobuyuki Matsuzawa, Yuko Kaimoto, Masayuki Endo, Takahiro Matsuo, Koichi Kuhara, and Masaru Sasago

J. Vac. Sci. Technol. B 16, 3739 (1998); http://dx.doi.org/10.1116/1.590409 (5 pages) | Cited 22 times

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This article presents a novel top surface imaging (TSI) process that is highly sensitive and reduces line edge roughness (LER). We found that LER and residue decreased when we used a chemically amplified (CA) resist, consisting of a base polymer with a high molecular weight and a photo-acid generator producing an acid with a high molecular weight. The top thin silylated layer of the exposed region on the CA resist causes the LER. A breakthrough step in the dry-development process improves the silylation contrast between the exposed and unexposed regions. We then apply a novel step in the dry-development process which involves a predry development bake at a temperature above the glass transition temperature of the silylated polymer. This step is effective in rolling and smoothing the edge of silylated layer by thermal flow. By applying the predry-development bake step above the glass transition temperature, we were able to reduce the LER to less than 6 nm. We have demonstrated a novel TSI process for achieving highly sensitive and improved LER. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Pattern collapse in the top surface imaging process after dry development

Shigeyasu Mori, Taku Morisawa, Nobuyuki Matsuzawa, Yuko Kaimoto, Masayuki Endo, Takahiro Matsuo, Koichi Kuhara, and Masaru Sasago

J. Vac. Sci. Technol. B 16, 3744 (1998); http://dx.doi.org/10.1116/1.590400 (4 pages) | Cited 6 times

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In this article the pattern collapse in a 193 nm top surface imaging process after dry development is described. We dry developed the resist with O2 and SO2 plasmas at low temperature in order to replicate a fine pattern profile. Pattern collapse occurred because of stress from neighboring patterns when SO2 was added at low substrate temperatures and the line/space binary pattern was below 0.15 μm. We found, using Auger electron spectroscopy analysis, that a sulfuric compound covered the side walls of the pattern when SO2 was used. We propose a pattern collapsing mechanism caused by the reaction of H2O with the evaporation of water adsorbed by the sulfuric compound on the resist pattern. It is therefore effective to decrease the sulfuric compound on the patterns before the wafer is removed from the etching chamber. Finally, we successfully replicated a sub-0.10 μm line and space pattern without pattern collapse. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Process dependence of roughness in a positive-tone chemically amplified resist

D. He and F. Cerrina

J. Vac. Sci. Technol. B 16, 3748 (1998); http://dx.doi.org/10.1116/1.590401 (4 pages) | Cited 38 times

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Line edge roughness becomes an important factor in linewidth control as lithographic dimensions approach the 0.1 μm region. In order to understand different contributions to roughness, we explored the relationship between roughness and deprotection in the case of a positive chemically amplified resist. Experiments show that the roughness of the remaining resist depends on process history and it is not a simple function of the degree of deprotection. Scaling analysis of atomic force microscopy images shows that an equal degree of deprotection yields a self-affine rough surface with constant fractal dimensions which imply a similar surface morphology, but with a different standard deviation. The correlation between sidewall and top surface roughness is also discussed. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Novel methodology for postexposure bake calibration and optimization based on electrical linewidth measurement and process metamodeling

Luigi Capodieci, Ramkumar Subramanian, Bharath Rangarajan, William D. Heavlin, Jiangwei Li, Doug A. Bernard, and Victor V. Boksha

J. Vac. Sci. Technol. B 16, 3752 (1998); http://dx.doi.org/10.1116/1.590402 (7 pages) | Cited 4 times

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By combining electrical linewidth measurements and neural-network (NN) process metamodeling, lithography simulators can be calibrated in an efficient way. In this work we present a novel methodology for characterizing postexposure bake using a very large experimental data set, so that the calibrated model can be used as a truly predictive tool. The adoption of a special test reticle mask allowed us to collect more than 700 000 critical dimensions CDs from 24 silicon wafers for a matrix of postexposure bake (PEB) time, and temperature conditions. The lithographic patterns included isolated, semidense and dense lines for structures of 0.25, 0.20, 0.175, and 0.15 μm nominal size replicated across the exposure field and across the wafer. As a result of this particular metrology, each measured CD was associated with both topological (position on the wafer and position within the field) and process information (exposure dose, PEB time, and temperature). Database management techniques were implemented in order to extract and analyze such a massive data set. Process metamodeling (PMM) was used for the calibration of a PEB model describing the joint effect of photoacid diffusion and photoacid loss, coupled with a deprotection reaction. PMM creates a NN model of the PEB original model (a “model of a model”) so that the diffusion coefficient, the acid loss, and the deprotection rates can be estimated by inversion of the NN mapping. The comparisons between experimental and simulated data show excellent agreement that is maintained across the entire process space. © 1998 American Vacuum Society.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.40.Hp Lithography, masks and pattern transfer
07.05.Mh Neural networks, fuzzy logic, artificial intelligence

Real-time Fourier transform infrared spectroscopy study of the kinetics of acid-catalyzed negative-tone resists based on hexamethoxymethylmelamine and phenolic resins

Paul M. Dentinger and James W. Taylor

J. Vac. Sci. Technol. B 16, 3759 (1998); http://dx.doi.org/10.1116/1.590403 (8 pages) | Cited 2 times

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The kinetics of the acid-catalyzed reaction in the novolac-based, negative-tone resist SAL 605 (Shipley Co.) and similar formulations were studied with Fourier transform infrared spectroscopy with an in situ hot plate. Real-time measurements of the reaction kinetics were made in a matrix identical to the lithographic conditions and without interference from the development step. The reaction order in the acid concentration was measured to be 1.2±0.15 at 113 °C, and the overall activation energy was measured to be 113±11 kJ/mol for SAL 605. A kinetic model was explored to explain the observed results. The model invoked the general acid catalysis shown in a prior publication [P. M. Dentinger, K. G. Knapp, G. W. Reynolds, J. W. Taylor, T. H. Fedynyshyn, and T. A. Richardson, Proc. SPIE 3331, 568 (1998)], and that the rate constant for the first link of a hexamethoxymethylmelamine (HMMM) was significantly greater than the rate constant for a second link. This model can be simplified to aid in chemically amplified resist modeling efforts and all parameters may be determined experimentally under similar conditions as the lithography and without interference from the dissolution process. A direct comparison of novolac-based and poly(4-hydroxy)styrene (PHS)-based negative resist formulations showed that the reaction rate was slightly faster for the PHS resin near lithographic bake times. The PHS system also appeared more able to form additional links per HMMM than novolac. However, a difference in dose to print between similar formulations of the two phenolic resins appears to arise largely from a reaction of the resin/HMMM matrix to the developer and is only a small function of the postexposure bake kinetics. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

On-wafer photoacid determination and imaging technique for chemically amplified photoresists

Paul M. Dentinger, Bing Lu, James W. Taylor, Scott J. Bukofsky, Gilbert D. Feke, Dan Hessman, and Robert D. Grober

J. Vac. Sci. Technol. B 16, 3767 (1998); http://dx.doi.org/10.1116/1.590404 (6 pages) | Cited 6 times

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A fundamental task of chemically amplified photoresists is to record the incident radiation by generating catalyst concentration gradients within the film. In many resists, the catalyst is a strong Brönsted acid which yields a latent image of pH within the exposed film. A number of mechanistic questions remain about acid generator efficiency and its mobility once generated and heated. We have developed a technique in which a pH-dependent fluorophore is incorporated into the resist (an undyed version of SAL 605 from the Shipley Company and similar formulations). The localized acid concentrations generated by exposure to x-rays are analyzed and imaged using fluorescence spectroscopy and microscopy. Initial experiments, the spectroscopic apparatus, and initial far-field imaging are reported elsewhere [S. J. Bukofsky, G. D. Feke, Q. Wu, R. D. Grober, P. M. Dentinger, and J. W. Taylor, Appl. Phys. Lett. 73, 3 (1998)]. In this article, several fluorophores are evaluated, and various criteria for successful imaging within the photoresist matrix are established. These criteria include pKa of the fluorophore, photostability, and functional groups that affect the performance of the acid within the film. The technique is used to show the relative efficiency of two photoacid generators in otherwise identical matrices, and the method has the potential for rapid photogenerated acid yield determination among a variety of photoacid generators. This technique can be used in thin imaging films and, due to the low level of fluorophore required (0.01–0.1 wt. %), for photoacid yield determination in optical photoresists without significantly altering the absorbance characteristics of the film. Initial near-field scanning optical microscopy images are shown and the potential of the technique for several lithographic applications, including measurement of the actual spread of the acid distribution during postexposure bake, is discussed. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Electron-beam nanolithography, acid diffusion, and chemical kinetics in SAL-601

Elizabeth A. Dobisz, Theodore N. Fedynyshyn, David Ma, Loretta M. Shirey, and Robert Bass

J. Vac. Sci. Technol. B 16, 3773 (1998); http://dx.doi.org/10.1116/1.590405 (6 pages) | Cited 3 times

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The work presents a unique investigation of the role of postexposure bake (PEB) on resist insolubility, PEB reaction kinetics, and the high resolution behavior of Microposit™ SAL-601. Patterns of 20–100 μm rectangles and single pass isolated lines were written on a JEOL JBX-5DII e-beam lithography system operated at 50 kV. The effects of PEB temperatures of 90–110 °C for periods of 1–11 min on resist insolubility and linewidth were examined. The samples were developed in MF-322 or acetone. The range of patterns allowed measurement of both the resist exposure curves and the line spread for each PEB condition. Insolubility in MF-322 can result from protection reactions and/or crosslinking reactions. Acetone insolubility, a characteristic of crosslinked resist, was observed at PEB temperatures of 100 °C and above. At 90 °C, acetone insolubility (crosslinking) was observed only after a PEB of 11 min. From the resist exposure curves for a sequence of PEB times, reaction orders for the PEB processes that led to resist insolubility were determined. At temperatures of 100–110 °C, reaction orders of 2.4 and 2.1 were obtained for reactions that led to insolubility in MF-322 and acetone, respectively. At 90 °C the order of reaction leading to MF-322 insolubility was 1.8. PEBs at 90 °C for 3 and 6 min produced the finest lines, with linewidths ⩽50 nm over an order of magnitude range in dose. An acid diffusion mth order reaction model, which allows for H+ loss to the surface, was introduced to analyze the linewidth measurements. In the 105–110 °C temperature range, the model best fit the data with diffusion coefficients of 4–8 nm2/s and acid loss rates of 0.003–0.005%/s. © 1998 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
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Modeling solvent diffusion in photoresist

C. A. Mack, K. E. Mueller, A. B. Gardiner, J. P. Sagan, R. R. Dammel, and C. G. Willson

J. Vac. Sci. Technol. B 16, 3779 (1998); http://dx.doi.org/10.1116/1.590406 (5 pages) | Cited 2 times

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A semi-empirical study into the effects of residual casting solvent on the lithographic properties of photoresist is described. Solvent content of a commercial i-line photoresist after postapply bake has been measured using a quartz crystal microbalance and using radio-labeled solvent with scintillation counting. Analysis of this data has led to a calibrated model of solvent diffusivity as a function of solvent content which can then predict solvent content as a function of depth into the photoresist for a given bake. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
64.75.-g Phase equilibria

Shot-noise and edge roughness effects in resists patterned at 10 nm exposure

Nicholas Rau, Fred Stratton, Charles Fields, Taro Ogawa, Andrew Neureuther, Randy Kubena, and Grant Willson

J. Vac. Sci. Technol. B 16, 3784 (1998); http://dx.doi.org/10.1116/1.590407 (5 pages) | Cited 24 times

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The experimental shot-noise effects and line-edge roughness are reported for two positive and two negative tone chemically amplified resists (IBM Apex-E, Shipley UVIIHS, IBM ENR, and Shipley SAL-601, respectively) produced by high resolution (10 nm) focused ion-beam exposure. Scanning electron micrographs at the resolution limit for each resist (50–70 nm) showed that the positive resists became negative in tone and that edge roughness was reasonable. Shot-noise effects causing arrays of 10 nm posts to print or not to print at exposure events of 7, 14, and 28 average ions per post were observed in SAL-601 and agree with Poisson statistics. Single exposure events were not observed in any resist possibly owing to the fact that the working minimum exposure level at the resolution limit of the resist material required several overlapping events to print. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Coulomb blockade devices fabricated by liquid metal ion source droplet deposition

C. Vieu, A. Pepin, J. Gierak, C. David, Y. Jin, F. Carcenac, and H. Launois

J. Vac. Sci. Technol. B 16, 3789 (1998); http://dx.doi.org/10.1116/1.590408 (6 pages) | Cited 10 times

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The fabrication of two-dimensional multiple tunnel junction (MTJ) devices by deposition of Au droplets from a liquid metal ion source is reported. By adjusting the emission parameters of the source and the final landing voltage of the droplets we have been able to deposit 1 nm size islands with a good reproducibility and with a sufficient density to allow tunneling between islands. Our devices exhibit a Coulomb gap up to a temperature of 200 K and show nonlinear current–voltage characteristics up to room temperature. The thermal behavior of these devices was investigated and shows the absence of a Kosterlitz–Thouless–Berezenskii transition. The charging energy of the islands is as high as 240 meV opening interesting perspectives for the integration of these MTJ devices in single electron memory cells working at high temperature. © 1998 American Vacuum Society.
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85.35.Ds Quantum interference devices
85.40.Sz Deposition technology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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

Demonstration of a functional quantum-dot cellular automata cell

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

J. Vac. Sci. Technol. B 16, 3795 (1998); http://dx.doi.org/10.1116/1.590410 (5 pages) | Cited 5 times

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We report an experimental demonstration of a functional cell for quantum-dot cellular automata (QCA), a transistorless approach to implement logic functions. The four-dot QCA cell is defined by a pair of series-connected, capacitively coupled input and output double dots. We demonstrate that, at low temperature, an electron switch in the input double dot induces an opposite electron switch in the output double dot, resulting in a complete polarization change of the QCA cell. Switching is verified by electrometer signals which are coupled to the output double dot. Experimental results suggest that electron motion in the coupled double dots is strongly correlated and can support high operating frequencies. Agreement between theoretical predictions and experimentally measured values of the dot potentials is excellent. © 1998 American Vacuum Society.
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85.35.Ds Quantum interference devices
73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Rw Metal-insulator-metal structures
03.67.Lx Quantum computation architectures and implementations

Fabrication of self-aligned metallic Coulomb blockade devices on Si nanowires

E. M. Ford and H. Ahmed

J. Vac. Sci. Technol. B 16, 3800 (1998); http://dx.doi.org/10.1116/1.590411 (4 pages) | Cited 2 times

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A self-aligned metallic single-electron tunneling transistor was fabricated on a Separated by Implanted Oxygen substrate. An array of 10–50 gold islands of 1–3 nm diameter was isolated between source and drain electrodes on a silicon nanowire. This design reduces the number of transport paths by restricting the number of active nanodots between source and drain. The islands were deposited by a retarding field single ion deposition method, whereby the island sizes and separations could be varied by adjusting landing energy and dose. An undercut beneath the nanowire was used to separate the side gates from the multiple tunnel junction. Coulomb blockade was observed in the source drain characteristics at 77 K. © 1998 American Vacuum Society.
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85.35.Gv Single electron devices
73.23.Hk Coulomb blockade; single-electron tunneling
85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.35.Ds Quantum interference devices
81.65.Cf Surface cleaning, etching, patterning
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Direct patterning of single electron tunneling transistors by high resolution electron beam lithography on highly doped molecular beam epitaxy grown silicon films

T. Koester, F. Goldschmidtboeing, B. Hadam, J. Stein, S. Altmeyer, B. Spangenberg, H. Kurz, R. Neumann, K. Brunner, and G. Abstreiter

J. Vac. Sci. Technol. B 16, 3804 (1998); http://dx.doi.org/10.1116/1.590412 (4 pages) | Cited 3 times

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We present a fabrication method for a single electron tunneling transistor (SETT) in silicon. The process is based on bonded and etched back silicon on insulator material with a 40 nm thick highly n-doped Si layer grown by molecular beam epitaxy. The nanometer structure of the SETT is defined by electron beam lithography in combination with a two-layer resist system. The pattern is transferred by anisotropic reactive ion etching. The devices are passivated by low temperature remote plasma enhanced chemical vapor deposition of high quality silicondioxide. An extended region of low conductivity is observed even at T=130 K in the current–voltage characteristics, outside of which a strong Coulomb staircase is visible. The Coulomb blockade is significantly affected by the applied gate voltage. Coulomb oscillations of the blockade width with gate potential are observed. © 1998 American Vacuum Society.
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85.35.Gv Single electron devices
85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.35.Ds Quantum interference devices
81.65.Rv Passivation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Double electron layer tunneling transistors by dual-side electron beam lithography

J. R. Wendt, J. A. Simmons, J. S. Moon, M. A. Blount, W. E. Baca, and J. L. Reno

J. Vac. Sci. Technol. B 16, 3808 (1998); http://dx.doi.org/10.1116/1.590413 (4 pages) | Cited 1 time

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We describe the first demonstration of small-area double electron layer tunneling transistors (DELTTs) fabricated by dual-side electron beam lithography. The DELTT is a planar quantum device which operates by modulating the two-dimensional (2D)-to-2D tunneling between two coupled quantum wells. The fabrication technique utilizes the epoxy-bond and stop-etch process to remove the substrate material which allows the backside gates to be placed in close proximity (less than 1 μm) to the frontside gates. The use of electron beam lithography provides precise alignment of the front and back features to each other. We have applied this technique to the fabrication of DELTTs on coupled AlGaAs/GaAs double quantum wells. Low temperature electrical characterization yields source-drain current–voltage curves that exhibit negative differential resistance with peak-to-valley ratios of up to 8:1. The height and position of the resonant peak varies strongly with gate bias, demonstrating transistor action. © 1998 American Vacuum Society.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Fabrication and characterization of buried subchannel implant n-metal–oxide–semiconductor transistors

W. Wang, D. McCarthy, D. Park, D. Ma, C. Marrian, M. Peckerar, N. Goldsman, J. Melngailis, and I. L. Berry

J. Vac. Sci. Technol. B 16, 3812 (1998); http://dx.doi.org/10.1116/1.590414 (5 pages)

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The shrinking of the gate length is not only a challenge for lithography but also for device performance. Subthreshold current increases, so short channel transistors are hard to turn off. In order to reduce the subthreshold current, transistors with buried subchannel implants were modeled and then fabricated by a self-aligned process. This article describes the buried implant metal–oxide–semiconductor field effect transistor (MOSFET) model, fabrication, and measured performance. The simple analytic model developed predicts less short channel effects in the buried implant MOSFETs. A novel self-aligned process has been applied to fabricate the subchannel implants directly under the gate. Identical devices of various gate lengths down to 0.25 μm were fabricated with and without the buried p+ implant. The devices with the p+ implant exhibited a slower threshold voltage roll-off and less subthreshold swing. © 1998 American Vacuum Society.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
85.30.De Semiconductor-device characterization, design, and modeling

Microdisk laser structures for mode control and directional emission

S. A. Backes, J. R. A. Cleaver, A. P. Heberle, and K. Köhler

J. Vac. Sci. Technol. B 16, 3817 (1998); http://dx.doi.org/10.1116/1.590415 (4 pages) | Cited 7 times

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GaAs microdisk laser structures with modified resonator geometry have been investigated. Device fabrication employs electron-beam lithography and etch procedures for generating disks with notches, projections, and holes, and a novel ring-laser structure. Directional emission from the notched microdisk lasers has been investigated using external scattering structures, which may also be used as couplers for the laser emission. © 1998 American Vacuum Society.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Measurement of nanomechanical resonant structures in single-crystal silicon

D. W. Carr, L. Sekaric, and H. G. Craighead

J. Vac. Sci. Technol. B 16, 3821 (1998); http://dx.doi.org/10.1116/1.590416 (4 pages) | Cited 50 times

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We have used electron beam lithography to make very small (<30 nm linewidth) mechanical structures in single-crystal silicon. These structures can be driven capacitively by applying a voltage between the suspended portion and the underlying substrate. Optical interference techniques are used to detect and measure the motion of the structures with resonant frequencies above 40 MHz. We employed a design consisting of a square mesh with a 315 nm period, which results in a low mass (∼1×10−13 g) and large relative surface area (10−6 cm2). Also, by making suboptical-wavelength features, the optical properties can be altered, leading to an improved measurement sensitivity. We measured the oscillations at small amplitudes where the detected change in the optical reflection is proportional to the drive amplitude. © 1998 American Vacuum Society.
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07.10.Cm Micromechanical devices and systems
85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.60.Ly Interferometers

Large area high density quantized magnetic disks fabricated using nanoimprint lithography

Wei Wu, Bo Cui, Xiao-yun Sun, Wei Zhang, Lei Zhuang, Linshu Kong, and Stephen Y. Chou

J. Vac. Sci. Technol. B 16, 3825 (1998); http://dx.doi.org/10.1116/1.590417 (5 pages) | Cited 68 times

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A new low-cost, high throughput method was developed for fabricating large area quantized magnetic disks (QMDs) using nanoimprint lithography (NIL), electroplating, and chemical mechanical polishing. Perpendicular QMDs with a density of 18 Gbit/in.2 and good uniformity over an area of 4 cm×4 cm (total 45 Gbit) have been achieved, as well as longitudinal QMDs of 30 Gbit/in.2 The NIL molds for the perpendicular QMDs were fabricated using double NIL with a grating mold. The magnetic properties of both types of QMDs were studied by magnetic force microscopy. © 1998 American Vacuum Society.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
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

Fabrication of magnetic submicron-wire channels for the investigation of magnetization reversal

Y. Chen, V. Kottler, F. Carcenac, J. F. René, N. Essaidi, C. Chappert, and H. Launois

J. Vac. Sci. Technol. B 16, 3830 (1998); http://dx.doi.org/10.1116/1.590418 (5 pages) | Cited 5 times

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We have demonstrated a process for fabricating magnetic structures with feature sizes ranging from 50 nm to several hundred microns using high-resolution electron beam lithography with 50 keV electrons followed by Ti evaporation and liftoff. The Ti was used as an etch mask for ion milling and then removed by SF6 reactive ion etching. A variety of magnetic fine structures were fabricated on (CoNi/Pt)6 multilayer substrates. In particular, submicron-wire channels, which connect a number of microscopic squares to a large reservoir area, were obtained. The magnetization reversal processes in submicron wire channels were studied with a conventional magneto-optical Kerr microscope. We found that the switching field for magnetization and the reversal behavior of the connected microscopic squares strongly depend on the channel wire width, thereby providing a way to study domain wall motion in a subwavelength scale with diffraction limited methods. © 1998 American Vacuum Society.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure

Monolithic nanofluid sieving structures for DNA manipulation

S. W. Turner, A. M. Perez, A. Lopez, and H. G. Craighead

J. Vac. Sci. Technol. B 16, 3835 (1998); http://dx.doi.org/10.1116/1.590419 (6 pages) | Cited 58 times

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A new technique for fabricating two-dimensional artificial gels for DNA electrophoresis is presented. The technique differs from previous approaches in that the entire device is fabricated as a monolithic unit using exclusively planar processing techniques adapted from semiconductor electronics fabrication. The height of the fluid gap between the dielectric floor and ceiling is determined by the thickness of a sacrificial layer which is removed by a wet chemical etch. This allows precise control and excellent uniformity of the gap over an entire silicon wafer. Floor-to-ceiling height control better than 5 nm has been demonstrated over a 1.5 cm device. Electron beam lithography is used to define a square array of 100 nm obstructions in the sacrificial layer. Chemical vapor deposition silicon nitride is applied over the sacrificial layer. Reactive ion etching (RIE) is used to create access holes in the nitride layer, so that the sacrificial layer can be removed with a wet chemical etch. After the wet etch, the access holes are resealed with very low temperature oxide (VLTO) silicon dioxide. Finally, loading widows are opened with RIE at both ends of the device so that DNA in aqueous solution can be introduced and its motion under the influence of an electric field can be observed. The DNA molecules are labeled with a fluorescent dye and observed through the dielectric top layers with an optical microscope. The electrophoretic mobility is measured for two different DNA chain lengths, 43 and 7.2 kbase. The velocity for both DNA lengths is reported for an applied potential between 2 and 20 V over the 15 mm device. At some voltages the velocities differed by nearly a factor of 2. © 1998 American Vacuum Society.
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87.15.Nn
87.80.-y Biophysical techniques (research methods)
82.70.Gg Gels and sols
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
82.45.-h Electrochemistry and electrophoresis

Using neutral atoms and standing light waves to form a calibration artifact for length metrology

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

J. Vac. Sci. Technol. B 16, 3841 (1998); http://dx.doi.org/10.1116/1.590420 (5 pages) | Cited 1 time

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Beams of neutral metastable atoms can be patterned by spatially dependent deexcitation in a standing wave of laser light. Metastable atoms which hit a substrate transfer their internal energy (10–20 eV) to the surface and activate the formation of a durable carbonaceous resist from a vapor precursor. The resist can be used as an etch mask to transfer patterns into the substrate material. In this work, we report a recent experimental demonstration of this “standing wave quenching” (SWQ) patterning technique. We also present an analysis of the accuracy to which atom lithography and SWQ can form a periodic reference array for length metrology. We find that, with some modification of the experimental setup and parameters, the absolute period across a 1 mm2 patterned area can be known to one part in 106. © 1998 American Vacuum Society.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
06.20.F- Units and standards
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
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
07.60.Ly Interferometers
32.50.+d Fluorescence, phosphorescence (including quenching)

Sharp edged silicon structures generated using atom lithography with metastable helium atoms

Weijian Lu, Kenneth G. H. Baldwin, Maarten D. Hoogerland, Stephen J. Buckman, T. J. Senden, T. E. Sheridan, and R. W. Boswell

J. Vac. Sci. Technol. B 16, 3846 (1998); http://dx.doi.org/10.1116/1.590421 (4 pages) | Cited 13 times

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By combining atom lithography and plasma etching technology in a two-step process, we demonstrate the transfer of sharp edged structures into silicon with a depth of 580 nm and an inclination of better than 86°. A self-assembled monolayer resist deposited on a Au-coated Si surface is damaged by a beam of metastable helium atoms through a physical mask. A wet etching process removes Au in the damaged regions, resulting in an intermediate mask of patterned Au on Si. Low-pressure plasma etching is then used to transfer the pattern of the Au mask into the Si. This plasma etching process shows a selectivity greater than 19 with respect to the Au mask. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Absorptive masks of light: A useful tool for spatial probing in atom optics

Claudia Keller, Roland Abfalterer, Stefan Bernet, Markus K. Oberthaler, Jörg Schmiedmayer, and Anton Zeilinger

J. Vac. Sci. Technol. B 16, 3850 (1998); http://dx.doi.org/10.1116/1.590422 (5 pages) | Cited 2 times

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We demonstrate periodic localization of neutral atoms of better than 65 nm behind amplitude, i.e., absorptive masks made of light. With these masks, produced by a standing on resonant light wave, it is possible to create and to probe spatially well-defined atomic distributions. Applications of such absorptive masks range from atom lithography to fundamental atom optical experiments. As two examples we show how to use these gratings as a tool to measure the evolution of an atomic wave field behind a static Bragg crystal and its dependence on the incidence angle of the atomic beam and how to demonstrate the frequency shift of atoms diffracted at a modulated Bragg crystal in a beating experiment. © 1998 American Vacuum Society.
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03.75.Be Atom and neutron optics
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
31.50.Df Potential energy surfaces for excited electronic states
61.05.Np Atom, molecule, and ion scattering (for structure determination only)
42.40.Eq Holographic optical elements; holographic gratings
37.20.+j Atomic and molecular beam sources and techniques

Atomic beam holography for nanofabrication

J. Fujita, T. Kisimoto, M. Morinaga, S. Matsui, and F. Shimizu

J. Vac. Sci. Technol. B 16, 3855 (1998); http://dx.doi.org/10.1116/1.590423 (4 pages) | Cited 5 times

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Atomic beam holography is a unique technique by which to fabricate a nanoscale object by using the interference of matter waves of ultracold atoms. The atomic de Broglie wave coming through a hologram interferes with and reconstructs a desired structure on a substrate. We first demonstrated holographic manipulation of metastable Ne atoms of 7 nm wavelength, where we showed the reconstruction of an “F” pattern and improvement of it. In this article, we propose and show techniques to manipulate three-dimensionally cooled Ne atoms. Atomic beam holography has the potential to make atomic-size objects, and the freedom in designing the hologram enables us to make not only a binary pattern but also an analog (gray scale) pattern. The resolution demonstrated in this experiment was about 60μ, but the minimum feature size expected is theoretically the same as the wavelength, i.e., several nanometers. © 1998 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
03.75.Be Atom and neutron optics

Particle manipulation and surface patterning by laser guidance

Michael J. Renn and Robert Pastel

J. Vac. Sci. Technol. B 16, 3859 (1998); http://dx.doi.org/10.1116/1.590424 (5 pages) | Cited 15 times

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Laser-induced forces are used to manipulate atoms, clusters, and micron-sized particles in hollow optical fibers. Laser light (400 mW, 800 nm) is guided in a low-order grazing incidence mode in glass capillaries. The optical field in the fiber generates gradient and scattering forces which simultaneously draw particles to the center of the hollow region and push them along the fiber axis. Dielectric, semiconductor, and metal particles in the size range of 9 μm–50 nm have been guided in gas- and liquid-filled fibers. Rb atoms are guided in evacuated fiber for up to 15 cm. Used alone or in conjunction with traditional methods, laser guidance is attractive for direct-write lithography. Arbitrary surface patterns can be created under ambient conditions with potential write speeds exceeding 106 particles/s and placement accuracy approaching 50 nm (assuming a 1 W laser, 100 nm Ge particles, and fiber filled with Ar at 760 Torr). Anisotropic optical forces resulting from particle shape anisotropy act to orient particles in the fiber. In initial experiments NaCl and KI crystals in aerosol suspension have been funneled into a hollow fiber using optical forces. The crystals have been directed onto a glass surface and lines as narrow as 0.5 μm drawn. This linewidth is 30 times smaller than the inner fiber diameter and illustrates the strong focusing produced by optical forces. Atomic force microscopy images show a high degree of alignment between crystals suggesting that anisotropic optical forces act to orient the crystals during deposition. © 1998 American Vacuum Society.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.81.Wg Other fiber-optical devices
37.10.De Atom cooling methods
37.10.Gh Atom traps and guides

Electron beam and scanning probe lithography: A comparison

Kathryn Wilder, Calvin F. Quate, Bhanwar Singh, and David F. Kyser

J. Vac. Sci. Technol. B 16, 3864 (1998); http://dx.doi.org/10.1116/1.590425 (10 pages) | Cited 25 times

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Electron beam lithography (EBL) and scanning probe lithography (SPL) are electron exposure techniques capable of high resolution patterning of organic resists. This article compares the exposure properties of these two systems. We consider the resist sensitivity to EBL and SPL electrons, exposure tolerances, patterning linearity, and proximity effects. It is possible to print sub-50 nm features using both systems, but SPL has a wider exposure latitude at these small feature sizes. SPL requires a significantly higher incident electron dose for exposure than does EBL. In EBL, lithography control is most limited by proximity effects which arise from backscattered electrons whose range is considerably larger than the forward scattering range in the resist film. As a result, the exposed feature dimension depends strongly on the local feature density and size, leading to unacceptable linewidth variations across a wafer. These limitations are alleviated in the case of SPL exposures. We demonstrate improved linearity and reduced proximity effects with SPL. We have patterned 200 nm pitch grids with SPL where all individual features are resolved. The linewidth of features in these grids is the same as the width of an isolated line at the same dose. Finally, we suggest that the SPL exposure mechanism may be different than that for EBL. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Approaches to nanofabrication on Si(100) surfaces: Selective area chemical vapor deposition of metals and selective chemisorption of organic molecules

G. C. Abeln, M. C. Hersam, D. S. Thompson, S.-T. Hwang, H. Choi, J. S. Moore, and J. W. Lyding

J. Vac. Sci. Technol. B 16, 3874 (1998); http://dx.doi.org/10.1116/1.590426 (5 pages) | Cited 23 times

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The selective removal of hydrogen from a passivated Si(100) surface with an ultrahigh vacuum scanning tunneling microscope (STM) allows nanometer-sized “templates” of clean Si(100) to be defined on an otherwise unreactive surface. Such depassivated areas have already been shown to react selectively with O2 and NH3 in preference to the surrounding H-terminated surface. This selectivity suggests two more sophisticated approaches to fabricating nanostructures with this technique: (1) selective metallization by thermal chemical vapor deposition, and (2) formation of ordered organic monolayers by reaction with specific organic molecules. In the first case, an intrinsic difference in the reaction rate of a metal precursor with the clean and H-terminated Si(100) surface results in selective deposition of a metal on the STM-patterned area. In order to prevent hydrogen desorption and loss of selectivity, the metal precursor must dissociate its ligands at relatively low temperatures. In the second case, the patterned surface is exposed to an organic molecule expected to react in a site specific manner with unsaturated Si dimer sites. An example of this site selective reaction is the [2+2] cycloaddition reaction between carbon–carbon double bonds and the Si dimer bond. Such reactions can result in the formation of spatially resolved nanometer-sized regions containing organic monolayers. In this article we describe progress toward the fabrication of nanostructures utilizing these two techniques. First, we discuss the use of a new amidoalane precursor for the selective chemical vapor deposition of aluminum on STM-patterned Si(100) surfaces, as well as the selective patterning of a nucleation promoter, TiCl4, commonly used to initiate aluminum film growth. We also discuss the selective chemisorption of norbornadiene (bicyclo[2.1.1] hepta-2,5-diene) on STM-patterned areas. STM images reveal the formation of a norbornadiene adlayer with indications of local ordering. Both of these methods show promise as techniques for the fabrication of nanostructures on Si(100) surfaces. © 1998 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
81.65.Cf Surface cleaning, etching, patterning
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
81.65.Rv Passivation
81.05.Cy Elemental semiconductors

Nanolithography of metal films using scanning force microscope patterned carbon masks

T. Mühl, H. Brückl, D. Kraut, J. Kretz, I. Mönch, and G. Reiss

J. Vac. Sci. Technol. B 16, 3879 (1998); http://dx.doi.org/10.1116/1.590435 (4 pages) | Cited 8 times

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Recently, we have shown that small trenches in amorphous carbon films can be produced by a field induced local oxidation with a voltage biased cantilever tip in a scanning force microscope. The depth of the holes and the trenches corresponds to the total thickness of the carbon film while the width was found to be as small as 30 nm. Amorphous carbon films as resist masks for lithography show some advantageous properties, e.g., the stability against halogen plasma etching, negligible chemical reactivity with most substrates and the possibility of removing the mask by oxygen reactive ion etching. In this article, we demonstrate the transfer of the carbon patterns into metal films by argon ion beam etching. By this new method, we produced 10-nm-wide trenches in thin AuPd films. Furthermore, we made small gaps in narrow AuPd lines which have been predefined by conventional e-beam lithography. In order to control and minimize the width of the gaps, the resistance of the conducting lines was controlled in situ during ion beam etching. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.79.Lh Atomic force microscopes
81.05.Bx Metals, semimetals, and alloys
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation

Modification of YBa2Cu3O7−δ wires using a scanning tunneling microscope: Process and electrical transport effects

G. Bertsche, W. Clauss, F. E. Prins, and D. P. Kern

J. Vac. Sci. Technol. B 16, 3883 (1998); http://dx.doi.org/10.1116/1.590427 (4 pages) | Cited 8 times

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Wires of the high temperature superconductor YBa2Cu3O7−δ (YBCO) were fabricated by electron beam lithography and were subsequently modified further on a sub-100 nm scale using the scanning tunneling microscope (STM). The process responsible for this modification has been shown to be field enhanced corrosion of the YBCO surface in the presence of CO2 and H2O. The intention of this work is to investigate the effect of the STM induced modifications on the electrical transport behavior of the YBCO wires with current–voltage characteristics (CVCs) measured at 77 and 4.2 K. Different types of CVCs can be distinguished, depending on the size of the cut into the wire generated by the STM. The measured characteristics will be explained by thermal self-heating at locations of the wire induced by the STM. Thus, the STM modifications initiate thermal domains in the wire where the Joule heat emission generated at sufficient high current values raise the temperature of the wire above its critical temperature. Furthermore, a steplike structure in the CVC of a STM fabricated nanobridge is detected, which we attribute to an increase of the number of vortex trajectories as the transport current through the wire is increased. © 1998 American Vacuum Society.
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84.71.Mn Superconducting wires, fibers, and tapes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.65.Cf Surface cleaning, etching, patterning
74.72.-h Cuprate superconductors
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Fabrication of high-density nanostructures by electron beam lithography

O. Dial, C. C. Cheng, and A. Scherer

J. Vac. Sci. Technol. B 16, 3887 (1998); http://dx.doi.org/10.1116/1.590428 (4 pages) | Cited 25 times

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We demonstrate a fabrication method to define high-density, uniform nanostructures by electron beam lithography at conventional beam voltages (<40 kV). Here we optimize the exposure and development conditions needed to generate such nanostructure arrays using polymethylmethacrylate as positive resist and isopropyl alcohol as a developer. Arrays of 12 nm dots with 25 nm period and 20 nm lines with 40 nm period were fabricated to show the resolution of this optimized process. © 1998 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

Small aperture fabrication for single quantum dot spectroscopy

D. Park, C. R. K. Marrian, D. Gammon, R. Bass, P. Isaacson, and E. Snow

J. Vac. Sci. Technol. B 16, 3891 (1998); http://dx.doi.org/10.1116/1.590429 (3 pages) | Cited 1 time

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A simple fabrication method for submicron diameter metallic apertures using negative electron beam resist and metal lift-off has been developed. In general, the lift-off process is beneficial for semiconductor quantum dot spectroscopy, since the original surface condition of the substrate is not altered or destroyed as it may be in a conventional dry or wet etching processes to form apertures in a subtractive process. With an optimum combination of process parameters, such as higher pre- and postexposure bake temperatures for longer times, longer developing time and with optimal mixtures of developers, high aspect ratio resist posts were obtained. Using 20 kV single dot e-beam exposure, a reentrant profile can be obtained directly. While this profile is not obtained with 50 kV single dot e-beam exposure, a higher aspect ratio (∼7:1) and sub-100 nm diam resist posts are possible. High vertical sidewall 100 nm diam resist posts are obtained using 50 kV area e-beam exposures. Taking advantage of these characteristics: high aspect ratio, high vertical resist sidewall, and resist undercut at the bottom of post, sub-100 nm diam apertures in 100 nm thick metallic films are obtained by evaporation of metal on the sample and dissolving the resist post in solvent. For sub-100 nm apertures, a significant improvement in aperture edge smoothness was achieved by applying an oxygen plasma. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
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

25 nm pitch GaInAs/InP buried structure: Improvement by calixarene as an electron beam resist and tertiarybutylphosphine as a P source in organometallic vapor phase epitaxy regrowth

Y. Miyamoto, A. Kokubo, T. Hattori, H. Hongo, M. Suhara, and K. Furuya

J. Vac. Sci. Technol. B 16, 3894 (1998); http://dx.doi.org/10.1116/1.590430 (5 pages) | Cited 4 times

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To achieve a fine periodic semiconductor structure by electron beam (EB) lithography, calixarene was used as an EB resist. A 25 nm pitch InP pattern was formed successfully and 40 nm pitch InP structures were achieved with good reproducibility. A shorter developing time, precise stage motion, accurate control of the widths of lines and spaces, and slight O2 ashing were important to obtain a fine InP pattern by a two-step wet chemical etching process. Furthermore, the fabricated periodic InP pattern was buried in a GaInAs structure by organometallic vapor phase epitaxy. The introduction of tertiarybutylphosphine as the phosphorus source prevented the fine structure from deforming when the temperature was raised and a 25 nm pitch periodic structure was buried successfully. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
61.72.uj III-V and II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.61.Ey III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning

Focused ion-beam patterning of nanoscale ferroelectric capacitors

A. Stanishevsky, S. Aggarwal, A. S. Prakash, J. Melngailis, and R. Ramesh

J. Vac. Sci. Technol. B 16, 3899 (1998); http://dx.doi.org/10.1116/1.590431 (4 pages) | Cited 21 times

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A 50 kV Ga+ focused ion beam was applied for milling submicron Pt-(La0.5Sr0.5)CoO3–Pb(NbxZryTiz)O3–(La0.5Sr0.5)CoO3–Pt-based ferroelectric capacitor heterostructures prepared by pulsed laser and sol-gel deposition techniques. The milling yields were found to be 0.22±0.02 μm3/nC for Pb(NbxZryTiz)O3, 0.3.4±0.01 μm3/nC for (La0.5Sr0.5)CoO3, and 0.34±0.06 μm3/nC for Pt layers. The influence of the ion beam current and its scan strategy, as well as depth of milling, on the quality of fabricated structures was studied. The minimum sizes down to 0.017 μm2 for the top electrode, and 0.04 μm2 for the capacitor structures milled to the bottom electrode were achieved without an additional sacrificial layer. A scanning probe microscopy technique was employed to test the properties of the milled capacitor structures. © 1998 American Vacuum Society.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
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

Artificial dielectric optical structures: A challenge for nanofabrication

C. Giaconia, R. Torrini, S. K. Murad, and C. D. W. Wilkinson

J. Vac. Sci. Technol. B 16, 3903 (1998); http://dx.doi.org/10.1116/1.590432 (3 pages) | Cited 5 times

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Diffractive optical components can be made using multiple level kinoforms or single level artificial dielectric structures. The latter require the fabrication of pillars of equal depth but differing width and spacing. As a demonstration device, the diffractive optic equivalent of a wedge has been made in GaAs for use at 1.15 μm. The need for all pillars to have the same height was met by using a selective etch and a very thin etch-stop layer on AlGaAs. The experimental diffraction efficiency was 87.8%, among the best ever obtained and close to the theoretical maximum of 97.6%. © 1998 American Vacuum Society.
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42.79.Dj Gratings
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.82.Cr Fabrication techniques; lithography, pattern transfer

InGaAsP photonic band gap crystal membrane microresonators

A. Scherer, O. Painter, B. D’Urso, R. Lee, and A. Yariv

J. Vac. Sci. Technol. B 16, 3906 (1998); http://dx.doi.org/10.1116/1.590433 (5 pages) | Cited 24 times

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We have microfabricated two-dimensional (2D) photonic band gap structures in a thin slab of dielectric material to define reflectors and high-Q microresonators. By selectively omitting holes from the 2D photonic crystal, optical microcavities, and in-plane microresonator switches can be defined. We have designed this structure with a finite difference time domain approach, and demonstrate the effect of lithographic 2D band gap tuning on the emission spectra of InGaAs/InGaAsP multiple quantum well material emission wavelength of 1.55 μm. © 1998 American Vacuum Society.
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42.70.Qs Photonic bandgap materials
42.82.Et Waveguides, couplers, and arrays
78.55.Cr III-V semiconductors
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Bh Lenses, prisms and mirrors

Nanoscale freestanding gratings for ultraviolet blocking filters

J. T. M. van Beek, R. C. Fleming, P. S. Hindle, J. D. Prentiss, M. L. Schattenburg, and S. Ritzau

J. Vac. Sci. Technol. B 16, 3911 (1998); http://dx.doi.org/10.1116/1.590434 (6 pages) | Cited 8 times

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Ultraviolet (UV) blocking filters are needed for atomic flux imaging in environments where high levels of ultraviolet radiation are present. Freestanding gratings are a promising candidate for UV filtering. They have a high aspect ratio (∼13), narrow (∼40 nm) slots, and effectively block UV radiation. The grating fabrication process makes use of several etching, electroplating, and lithographic steps and includes an optional step to plug pinholes induced by particles during processing. Gratings were successfully manufactured and tested. Measured UV transmissions of ∼10−5 and particle transmissions of ∼10% are in agreement with theoretical predictions. © 1998 American Vacuum Society.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.82.Cr Fabrication techniques; lithography, pattern transfer

Problems of the nanoimprinting technique for nanometer scale pattern definition

H.-C. Scheer, H. Schulz, T. Hoffmann, and C. M. Sotomayor Torres

J. Vac. Sci. Technol. B 16, 3917 (1998); http://dx.doi.org/10.1116/1.590436 (5 pages) | Cited 53 times

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We have tested nanoimprint lithography, a new and promising technique for nanometer-scale pattern definition. Preliminary experiments reveal that, besides severe sticking and adhesion problems, the problem of material transport is one inherent to this technique. There are clear indications that most of the effects found may be understood in terms of material transport. We performed experiments within a well defined pressure and temperature window which ranged from 60 to 100 bar and from 50 to 90 °C above the glass transition temperature of the poly(methylmethacrylate)-like polymer used. As a result, the quality of imprint is evaluated with respect to full area pattern transfer, based on a qualitative scanning electron microscope investigation of the fully imprinted area of 2 cm × 2 cm patterned with features of different size and shape. Optimum conditions for imprint quality are found around 100 bar and 90 °C above Tg for the specific polymer used. Although material transport will limit nanoimprint performance in general, it is found that periodic patterns and isolated or small area negative stamp relief patterns are most suitable for high quality nanoimprinting. © 1998 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer

Multilayer resist methods for nanoimprint lithography on nonflat surfaces

Xiaoyun Sun, Lei Zhuang, Wei Zhang, and Stephen Y. Chou

J. Vac. Sci. Technol. B 16, 3922 (1998); http://dx.doi.org/10.1116/1.590437 (4 pages) | Cited 32 times

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Five multilayer resist methods (three positive tones and two negative tones) have been devised for nanoimprint lithography on nonflat surfaces. Three of the methods have been demonstrated experimentally on a SiO2 surface with 100 nm deep sharp steps. The advantages and disadvantages of each method are discussed. Our results should be applicable to nanoimprint lithography with 10 nm feature size on nonflat surfaces. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning

Roller nanoimprint lithography

Hua Tan, Andrew Gilbertson, and Stephen Y. Chou

J. Vac. Sci. Technol. B 16, 3926 (1998); http://dx.doi.org/10.1116/1.590438 (3 pages) | Cited 64 times

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An alternative approach to flat nanoimprint lithography (NIL)—roller nanoimprint lithography (RNIL) is demonstrated. Compared with flat NIL, RNIL has the advantage of better uniformity, less force, and the ability to repeat a mask continuously on a large substrate. Two methods for RNIL are developed: (a) rolling a cylinder mold on a flat, solid substrate; (b) putting a flat mold directly on a substrate and rolling a smooth roller on top of the mold. Using our current roller nanoimprint system, sub-100 nm resolution pattern transfer has been achieved. © 1998 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer
81.10.Fq Growth from melts; zone melting and refining

Nanolithography using wet etched silicon nitride phase masks

M. M. Alkaisi, R. J. Blaikie, and S. J. McNab

J. Vac. Sci. Technol. B 16, 3929 (1998); http://dx.doi.org/10.1116/1.590439 (5 pages) | Cited 3 times

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A new technique for performing chromeless phase shift optical nanolithography is presented. Phase masks have been wet etched into silicon nitride membranes, using either hot H3PO4 or HF. Contact exposure through these masks results in developed photoresist features as small as 90 nm, even for masks with shallow sidewall slopes. The observed effect is attributed to the presence of an abrupt phase step at some point on the wet etch profile, although this does not need to correspond to a π phase shift in order to obtain good contrast exposures. Simulations have been performed for typical wet-etching profiles, and it is found that good contrast is expected for a very wide range of etch depths. In addition, the width of the null in the near-field intensity profile varies with etch depth, indicating that control of feature size is possible. This technique is simple and inexpensive, making it an attractive candidate for nanopatterning a wide variety of substrates. © 1998 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning

Regular array of Si nanopillars fabricated using metal clusters

Tetsuya Tada and Toshihiko Kanayama

J. Vac. Sci. Technol. B 16, 3934 (1998); http://dx.doi.org/10.1116/1.590440 (4 pages) | Cited 8 times

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We have developed a fabrication process of Si nanopillars using metal clusters arranged by electron beam (e-beam) lithography. This process forms nanopillars by taking advantage of the fact that metal clusters deposited on Si substrates act as nuclei for self-formation of etch masks during electron cyclotron plasma etching with SF6 if the substrate is kept at ∼−135 °C. The clusters are placed on the substrate by an e-beam lift-off technique following a small amount of deposition of metal vapors. Arrays of Si pillars with a regular spacing of 100 nm were actually fabricated using Au, Ag, and Fe clusters. Au clusters yielded 70 nm high pillars with an average diameter of 10 nm and a standard deviation of 1.3 nm, which is exceedingly better than the resolution of the lithography used (∼30 nm). Ag and Fe clusters produced pillars 20 nm in diameter. These results demonstrate that the pillar size is controlled by species of the metal clusters, whereas the position is defined by the e-beam lithography. We have also found that Fe clusters are very durable in the etching process and can produce pillars with a very high aspect ratio: 280 nm high and 20 nm in diameter. © 1998 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning

Oxidation properties of silicon dots on silicon oxide investigated using energy filtering transmission electron microscopy

C. Single, F. Zhou, H. Heidemeyer, F. E. Prins, D. P. Kern, and E. Plies

J. Vac. Sci. Technol. B 16, 3938 (1998); http://dx.doi.org/10.1116/1.590441 (5 pages) | Cited 10 times

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We used a side view transmission electron microscopy (TEM) technique which allows us to study the oxidation process of Si dots on SiO2 systematically for different dot sizes, oxidation times, and temperatures. Using energy filtering TEM (EFTEM) an excellent contrast between Si and SiO2 is achieved, independent from the crystal orientation. Si dots on SiO2 with initial diameters from 10 to 60 nm were oxidized with different oxidation times at 850 °C. The resulting shapes of the SiO2 and the embedded Si cores were determined from the EFTEM micrographs. A strong retardation of the oxidation process compared to planar oxidation as well as a self-limiting effect for long oxidation times are reported. Furthermore a pattern dependent oxidation is observed, depending on the aspect ratios of the dots. © 1998 American Vacuum Society.
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81.65.Mq Oxidation
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Fabrication of metallic point contacts: A new approach for devices with a multilayer or a heterointerface

N. N. Gribov, S. J. C. H. Theeuwen, J. Caro, E. van der Drift, F. D. Tichelaar, T. R. de Kruijff, and B. J. Hickey

J. Vac. Sci. Technol. B 16, 3943 (1998); http://dx.doi.org/10.1116/1.590442 (5 pages) | Cited 3 times

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Thin silicon membranes on silicon on insulator substrates are used to fabricate point contacts with a well-defined interface in the nanoconstriction between the two metal electrodes. Transmission electron microscope images of heterointerfaces in conjunction with energy dispersive x-ray analysis of the interfacial region show the capabilities of the process and its limitations. The latter involve material-specific phenomena on a nanoscale, such as an interfacial reaction between a metal film and SiO2 and metal diffusion across the heterointerface. These adverse effects can be avoided by a proper choice of the metals and the deposition temperature, as demonstrated with results of electrical measurements on a Au/Cu heterocontact. © 1998 American Vacuum Society.
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73.40.Jn Metal-to-metal contacts
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.05.Bx Metals, semimetals, and alloys
68.35.Ct Interface structure and roughness
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.65.Mq Oxidation
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer

Fabrication of multipurpose piezoresistive Wheatstone bridge cantilevers with conductive microtips for electrostatic and scanning capacitance microscopy

T. Gotszalk, J. Radojewski, P. B. Grabiec, P. Dumania, F. Shi, P. Hudek, and I. W. Rangelow

J. Vac. Sci. Technol. B 16, 3948 (1998); http://dx.doi.org/10.1116/1.590443 (6 pages) | Cited 10 times

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The fabrication and performance of a microprobe with multipurpose capabilities for scanning probe microscopy is presented in this article. Atomic force microscopy (AFM), scanning capacitance microscopy, and electrostatic force microscopy measurements can be simultaneously performed with the probe in which a silicon tip is integrated with a piezoresistive cantilever. Fabrication of the microprobe is based on double side bulk/surface micromachining of silicon on insulator (SOI) substrates. The novelty of this device is a highly doped silicon tip with a curvature radius of about 20 nm which is electrically isolated from the silicon cantilever by the buried oxide layer of the SOI substrate. At the beam supporting point a piezoresistive Wheatstone bridge is fabricated to allow the deflection of the microtip to be monitored. This cantilever displacement detection system enables measurements in vacuum and simplifies the design of the AFM head. Experimental measurements agree well with theoretical estimates of the sensitivity of the microprobe. © 1998 American Vacuum Society.
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07.79.-v Scanning probe microscopes and components
07.10.Pz Instruments for strain, force, and torque
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
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