bluuebunny/crossref_metadata_2025 huggingface dataset:
Yaw corrected precision X-Y stage for high-throughput electron-beam lithography systems
Authors: Moriyama Shigeo , Ozasa Susumu , Saitou Norio
Published: July 2002

Overhead time associated with a work stage is an important factor determining the throughput of step-and-repeat-type electron-beam lithography systems. In addition to increasing stage speed, utilization of large field electron optics contributes to reduction of such overhead time. However, when using large field optics, the stage is required to have minimal yaw to prevent field stitching error. Accordingly, a high-speed, high-precision work stage with a piezodrive yaw correction function has been developed for construction of high-throughput e-beam systems. To avoid leakage, magnetic field variation, and vacuum contamination, only the work table is located in the vacuum chamber. The table is driven by X,Y-drive mechanisms located outside the chamber. To achieve high speed positioning, a unique, light-weight X-Y table structure using a PTFE slide bearing has been incorporated. To correct yaw error at the stage, the work table can be rotated ±8 arcsec with a piezoactuator. Positioning and yaw correction for the table are carried out with a closed-loop control system that utilizes three-axis (X,Y, and yaw) laser interferometers. A maximum velocity of 100 mm/s, ±2 μm positioning accuracy, 130 ms movement time including vibration settling for a 6.5 mm step, and a yaw of less than ±0.3 arcsec has been achieved.
Investigation of kinetic mechanism for the ion-assisted etching of Si in Cl2
Authors: McNevin S. C. , Becker G. E.
Published: July 2002

This paper reports the results of a modulated ion beam study of the ion-assisted etching of Si using Cl2 gas and Ar+ ions. These experiments were designed to study the kinetic mechanism of the ion-enhanced surface reaction of Si with Cl2, which is thought to be responsible for anisotropic etching of Si in practical plasma systems. Pulses of Ar+ ions (typically 12 ms long) were incident on the surface with ion fluxes ranging up to 4.5×1014 ions/cm2 s and ion energies between 0.3 and 3 keV. Chlorine fluxes were varied between 2×1012 and 4×1014 molecules/cm2 s. Products were detected with a quadrupole mass spectrometer and a comparison of the resulting modulated signals with the cracking pattern of SiCl4 under the same conditions indicated that most of the Si left the surface in the form of SiCl4. The amount of Si removed from the surface depended linearly on the incident ion and increased with increasing chlorine up to a saturation limit. The time dependence of the product signals, measured by signal averaging, is not consistent with physical sputtering. A kinetic mechanism is discussed for this reaction.
Etching of Si by SF6 in a radio frequency double cathode
Authors: Boswell R. W. , Bouchoule A.
Published: July 2002

Experimental measurements in a modified reactive-ion etching system using SF6 show that the inclusion of an electrode connected to the cathode dramatically reduces the self-bias voltage and peak-to-peak radio frequency (rf) voltage on the cathode. Etch rates with silicon of 0.3 μm min−1 were obtained at pressures of 0.1 Pa with a self-bias voltage of around 100 V. The variation of etch rates, self-bias, and peak-to-peak voltages are presented for a pressure range of 0.1 to 10 Pa and various cathode configurations.
Fabrication and characterization of one- and zero-dimensional electron systems
Authors: Lee K. Y. , Smith T. P. , Arnot H. , Knoedler C. M. , Hong J. M. , Kern D. P. , Laux S. E.
Published: July 2002

One- and zero-dimensional electron systems confined in GaAs/GaAlAs have been fabricated. The starting material consisted of a modulation doped and a double barrier diode heterostructure grown by molecular-beam epitaxy. Very high resolution electron beam lithography and reactive ion etching were used to pattern lines and dots with widths ranging from 100 to 400 nm. Two measurement techniques have been applied: capacitance measurements of density of states—a novel technique for observing quantum effects in these structures—and resonant tunneling measurements. We have observed oscillations in capacitance spectroscopy which reflect discrete energy levels associated with one- and zero-dimensional electron systems. Preliminary tunneling measurements are presented.
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u observation on electron beam induced chemical vapor deposition by transmission electron microscopy
Authors: Ichihashi Toshinari , Matsui Shinji
Published: July 2002

Electron beam induced chemical vapor deposition of W and Si has been studied in a transmission electron microscope. WF6 and SiH2Cl2 were used as gas sources. Si and W clusters were initially formed. The W clusters, ∼3 nm in size, were β-W crystal, while the Si clusters were amorphous. Deposition rates can be directly calculated, by using these techniques. For example, a 120-kV electron beam at 100 A/cm2 current density will deposit W at ∼5 nm/min at 5×10−7 Torr, and Si at 2 nm/min at 5×10−5 Torr. A W rod, 15 nm in diameter, has been deposited using a 3-nm-diam focused electron beam.
Raman study of order and disorder in SiGe ultrathin superlattices
Authors: Menéndez J. , Pinczuk A. , Bevk J. , Mannaerts J. P.
Published: July 2002

We present a Raman scattering study of ultrathin SiGe superlattices. The spectra show evidence for the formation of superlattice structures with disordered interfaces. We explain the Raman peak energies in terms of strain and confinement effects and present a simple model for the Raman spectrum, from which we obtain semiquantitative information on the degree of superlattice ordering.
Oxygen adsorbed on GaAs(110) surfaces: The effect of temperature on band bending
Authors: Stiles K. , Mao D. , Kahn A.
Published: July 2002

GaAs surfaces cleaved in ultrahigh vacuum and cooled to 100 K [low temperature (LT)] were exposed to molecular oxygen. Band bending as a function of exposure was measured with ultraviolet photoemission spectroscopy. Band bending on LT p-GaAs is very small up to exposures >106 L, whereas the same exposures give considerable band bending at room temperature (RT). Band bending on LT n-GaAs is as fast as at RT. This situation is therefore opposite to that of metals/LT GaAs reported last year at this conference, but is analogous to that produced by Cl/GaAs at RT. These results can be interpreted in terms of simple adsorption of electronegative species which introduce an acceptor level deep in the GaAs gap. As for metals on LT GaAs, the nature of the surface states induced by the adsorption of single species dominates the position of EF at low coverage. Metallicity dominates at high coverages of metals; oxidation-induced defects dominate at RT or at higher exposures for O2/GaAs.
Spectroscopic studies of fluorescent emission in plasma etching of silicon nitride
Authors: Field D. , Klemperer D. F. , Wade I. T.
Published: July 2002

Basic chemical processes involved in etching of silicon nitride with a CF4 /O2 radio frequency plasma have been investigated using optical emission spectroscopy. Spectra have been recorded in the range 2400–7050 Å and comparison has been made of the intensity of more than 60 atomic and molecular lines in the presence and absence of silicon nitride coated wafers. We identify a number of species as important etching agents including metastable F(4 P), CF2, and metastable F+ (1D,1S). Our results are consistent with the principle of spin conservation in surface reactions set out in earlier work on Si(100). Our conclusions extend and broadly confirm the results of a previous mass spectrometric study of the same system.
Structural and electronic properties of Bi/GaAs(110)
Authors: Ludeke R. , Taleb-Ibrahimi A. , Feenstra R. M. , McLean A. B.
Published: July 2002

Ordered Bi overlayers on GaAs(110) were investigated with scanning tunneling microscopy (STM), STM spectroscopy, low-energy electron diffraction (LEED) studies, and with angle-integrated and angle-resolved photoemission spectroscopies. Two-dimensional (2D) layer growth occurs to ∼1 monolayer (ML), thereafter three-dimensional (3D) growth dominates. A Bi phase pseudomorphic with the GaAs is observed to ∼10 ML. Interdiffusion or chemical reactions between the components were not detected. STM images for coverages of 0.5 and 1 ML reveal the Bi structure to consist of chains of atoms aligned above and in between the Ga–As zigzag surface chains. Additional evidence for dual bonding sites of the Bi suggests that the Bi chains exhibit a zigzag structure similar to the Sb/GaAs system. Near 1 ML the Bi chains are interrupted by a periodic array of dislocations, ∼25 Å apart, that consist of missing Bi atoms. STM spectroscopy reveals that the Bi ML is semiconductorlike with a 0.7-eV band gap, and that the dislocations generate a band of empty, acceptorlike states within this gap. Band bending measurements indicate that the position of the Fermi level on n-type GaAs is determined by these acceptor states. Gap states were also associated with Bi terrace edges for coverages <1 ML. The position of the Fermi level for Bi on p-type GaAs is determined by the top of the Bi valence band, which overlaps that of GaAs by 0.4 eV. The dispersion of this band and another lower Bi band were measured using angle resolved photoemission spectroscopy.
Surface rotational phonons on the cleavage faces of tetrahedrally coordinated compound semiconductors
Authors: Duke C. B. , Wang Y. R.
Published: July 2002

Surface rotational phonons associated with atomic displacements about the relaxed minimum-energy surface geometry are shown to be responsible for a new branch in the surface excitation spectra of GaAs(110) observed via inelastic helium atom scattering. These phonons are associated with the rehybridization-induced surface reconstructions on the cleavage surfaces of both zincblende and wurtzite structure compound semiconductors. For zincblende structure materials, the frequencies of these phonons are predicted for the (110) surfaces of GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, and CdTe. For wurtzite structure materials, the frequencies are predicted for the (101̄0) surfaces of ZnO, ZnS, ZnSe, CdS, and CdSe. A discussion is given on the role of tetrahedral symmetry in determining the nature and consequences of these phonons.
Mask fabrication for projection electron-beam lithography incorporating the SCALPEL technique
Authors: Liddle J. A. , Huggins H. A. , Berger S. D. , Gibson J. M. , Weber G. , Kola R. , Jurgensen C. W.
Published: July 2002

The choice of mask materials and fabrication route for a projection electron-beam lithography system is subject to a variety of constraints. Some are encountered in most lithographic techniques, while some are unique to the scattering with regular limitation for projection electron lithography SCALPEL technique. We have developed methods for analyzing the performance of potential mask materials and constructions. These have been used to determine the composition of a prototype mask. Results from such a mask are presented.
Crystalline lattice for metrological applications and positioning control by a dual tunneling-unit scanning tunneling microscope
Authors: Kawakatsu Hideki , Hoshi Yasuo , Higuchi Toshiro , Kitano Hitoshi
Published: July 2002

A dual tunneling-unit (DTU) scanning tunneling microscope (STM) was built to verify the potential of crystalline lattices to metrological applications and positioning control. As an example of metrological application, imaging crystals for XY scale calibration of the other image was proposed. Two highly oriented pyrolitic graphite (HOPG) chips were imaged for comparison. Apparent lengths of lines defined within the images were measured by counting the number of lattices. The measurements matched to 99.7%. Different thermal drift rates of the two tips to the samples were confirmed to be the dominant factor of calibration accuracy, while effects of errors due to geometric asymmetry (e.g., Abbe’s error) were evaluated to be less. Lateral dither vibrations [amplitude 14 to 70 pm (p–p), frequency 3.3 kHz] were applied to the XY scanners to implement feedback control of the XY scanners. The gradient signals obtained through application of dither vibrations were fed back to the XY scanners. Two active positioning functions implemented were: (i) tip to atom positioning for a duration of several minutes; and (ii) a well defined stepping action of the tip to the crystalline lattice. Both functions were confirmed to be robust and stable.
Micropattern measurement with an atomic force microscope
Authors: Fujii T. , Suzuki M. , Miyashita M. , Yamaguchi M. , Onuki T. , Nakamura H. , Matsubara T. , Yamada H. , Nakayama K.
Published: July 2002

The atomic force microscope (AFM) can profile both the surfaces of conductors and insulators with nanometer resolution. One of the most promising applications of the AFM is micropattern measurement of semiconductor devices such as linewidth. An AFM with high precision positioning stages using monolithic, parallel spring mechanisms with flexture hinges has been applied to the measurement of nonconducting surfaces. The X-Y scanner is equipped with the two-dimensional optical interferometer to measure displacements of the scanner. The sensing lever is a microfabricated V-shaped Si3N4 cantilever with a tip made using electron beam deposition. Distortion-free images of a polycarbonate compact disk nonconducting surfaces with details around the pits have been successfully obtained.
Resolution limits of optical lithography
Authors: Okazaki Shinji
Published: July 2002

The development of optical lithography has promoted the development of ultralarge scale integration (ULSI) devices. However, optical lithography is now facing serious obstacles due to the limitations in wavelength. Higher resolution with sufficient depth of focus is the most important requirement for ULSI engineers. To satisfy this requirement, many technologies for resolution improvement and new optical image formation technologies such as phase shifting and focus latitude enhancement exposure (FLEX) are reviewed, and a future perspective on optical lithography is also discussed in this paper.
Stability and electronic adjustment of ion images projected at 10×reduction
Authors: Brünger W. H. , Torkler M. , Buchmann L. M.
Published: July 2002

An ion projection system was tested to demonstrate the long-term stability of lithographic properties. By exposing a resist to He+ ions, the pattern from an open stencil mask was transferred by a surface imaging process into the resist. Even after 12 min exposure the resolution capability still gave patterns of a minimum linewidth of 150 nm. Shifts of the pattern with high accuracy and reproducibility were performed by an octopole deflection unit. A projection mode, which consists of multiple exposures each with a different pattern displacement, was established by activating electric dipole fields. A deflection factor of 3.3 μm/V was obtained. Inducing a quadrupole field, changes in demagnification of opposite signs in x and for y directions (anamorphism) were generated which can be used to compensate for different types of distortion. A relative compression as well as expansion factor of 1.7×10−4 V−1 was determined. Simple two-dimensional simulation of quadrupole induced pattern displacements were carried out and compared with experiments.
In situ distortion measurement of an ion projector with 5× ion-optical reduction
Authors: Stengl G. , Bösch G. , Chalupka A. , Fegerl J. , Fischer R. , Lammer G. , Löschner H. , Malek L. , Nowak R. , Traher C. , Wolf P. , Vonach H.
Published: July 2002

In situ distortion measurements of an ion projector with 5× ion-optical reduction were performed. At optimum conditions the measured minimum distortion was less than 0.15 μm within an exposure field of 8 mm×8 mm. This result is in excellent agreement with fifth order ion-optical calculations.
Planar-processed tungsten and polysilicon vacuum microelectronic devices with integral cavity sealing
Authors: Mei Q. , Tamagawa T. , Ye C. , Lin Y. , Zurn S. , Polla D. L.
Published: July 2002

Solid-state micromachining and planar lithography have been applied in the formation of vacuum microdiode devices. These devices are fabricated with an on-chip vacuum cavity through directional material sealing techniques initiated at vacuum pressure of ∼2×10−6 T. Both tungsten and polycrystalline silicon have been used as cold-cathode emitter materials. The resulting current–voltage characteristics are stable and show good Fowler–Nordheim characteristics to operating currents in excess of 50 μA for wedge-shaped emitter tips. Electrical noise measurements carried out indicate a dominance of flicker noise at low frequencies for both tungsten and polycrystalline silicon microdiodes with the tungsten devices exhibiting excellent characteristics.
Phenomenological modeling of ion-enhanced surface kinetics in fluorine-based plasma etching
Authors: Gray David C. , Tepermeister I. , Sawin Herbert H.
Published: July 2002

A multiple beam apparatus has been constructed to facilitate the study of ion-enhanced fluorine chemistry on undoped polysilicon and silicon dioxide surfaces by allowing the fluxes of fluorine (F) atoms and argon (Ar+) ions to be independently varied over several orders of magnitude. The chemical nature of the etching surfaces has been investigated following the vacuum transfer of the sample dies to an adjoining x-ray photoelectron spectroscopy facility. The etching ‘‘enhancement’’ effect of normally incident Ar+ ions has been quantified over a wide range of ion energy through the use of Kaufman and electron cyclotron resonance-type ion sources. The increase in per ion etching yield of fluorine saturated silicon and silicon dioxide surfaces with increasing ion energy (Eion) was found to scale as (Eion1/2−Eth1/2), where Eth is the etching threshold energy for the process. Simple near-surface site occupation models have been proposed for the quantification of the ion-enhanced etching kinetics in these systems. Acceptable agreement has been found in comparison of these Ar+/F etching model predictions with similar Ar+/XeF2 studies reported in the literature, as well as with etching rate measurements made in F-based plasmas of gases such as SF6 and NF3.
Fermi-level variation on GaAs(110) surface with Sb overlayer studied with a photoelectron microscope
Authors: Kim Changyoung , Cao Renyu , Pianetta Piero
Published: July 2002

Bare and Sb covered GaAs(110) surfaces were studied with a photoelectron microscope. For the cleaved surfaces, maximum band bendings of 0.85 and 0.50 eV was observed for n- and p-type GaAs, respectively. For n-type, evaporation of Sb reduces the band bending from 0.85 to 0.55 eV. Annealing p-GaAs at 350 °C almost restored the flatband condition for an initially unpinned area. A reduction of band bending was observed for an initially heavily pinned area. This suggests that the cleavage defects originate partly from surface strain which can be removed by relaxing the strain with the formation of an ordered Sb overlayer. Sb desorbs from the GaAs surfaces when annealed at 560 °C. The Fermi level on this surface is at 0.35 eV above the valence-band maximum regardless of initial band bending conditions. The new surface is attributed to the destructive process of Sb desorption.
Molecular-beam epitaxy growth of high-performance midinfrared diode lasers
Authors: Turner G. W. , Choi H. K. , Calawa D. R. , Pantano J. V. , Chludzinski J. W.
Published: July 2002

Recent advances in the performance of GaInAsSb/AlGaAsSb quantum-well diode lasers have been directly related to improvements in the quality of the molecular-beam epitaxy (MBE)-grown epitaxial layers. These improvements have been based on careful measurement and control of lattice matching and intentional strain, changes in shutter sequencing at interfaces, and a generally better understanding of the growth of Sb-based epitaxial materials. By using this improved MBE-grown material, significantly enhanced performance has been obtained for midinfrared lasers. These lasers, which are capable of ∼2-μm emission at room temperature, presently exhibit threshold current densities of 143 A/cm2, continuous wave powers of 1.3 W, and diffraction-limited powers of 120 mW. Such high-performance midinfrared diode lasers are of interest for a wide variety of applications, including eye-safe laser radar, remote sensing of atmospheric contaminants and wind turbulence, laser surgery, and pumping of solid-state laser media.
Neutral transport in high plasma-density reactors
Authors: Kilgore M. D. , Wu H. M. , Graves D. B.
Published: July 2002

The direct simulation Monte Carlo method is used to study neutral species transport in cylindrical, high plasma-density systems. This technique is well suited for the transition flow regime in which these reactors operate. The ground state neutral density is depleted in the volume of the chamber due to ionization and is enhanced at bounding walls due to ion–electron surface recombination. In addition, electron–neutral and ion–neutral collisions heat the neutrals resulting in further neutral density depletion. The influence of chamber geometry and fractional degree of ionization on neutral density profiles is explored for an electron cyclotron resonance system. Results for an extended source/downstream chamber and for a compact source chamber are compared.
Piezoelectric sliding–pushing micropositioner in a scanning tunneling microscope
Authors: Yao Xiaowei , Xu Lei , Zhang Lanping , Hu Jun , Ge Guoqing , Gong Peirong , Xu Yaoliang , Lu Sonling , Li Minqian
Published: July 2002

A piezoelectric micropositioner for coarse sample translation in a scanning tunneling microscope (STM) has been designed. The mechanical construction for the positioner is very simple, and it can be separated from the sample carriage during STM imaging. The coarse sample movement is obtained via a sliding–pushing mechanism, and a displacement speed of 0.1 mm/s has been attained. The performance of the STM is tested by imaging a highly oriented pyrolytic graphite sample.
High power modulator for plasma ion implantation
Authors: Goebel Dan M.
Published: July 2002

The treatment of metal and polymer materials by plasma ion implantation (PII) requires high-voltage, high average-power modulators to process relatively large-size parts in a reasonable amount of time. CROSSATRON-switch-based modulators provide all of the features desired for large-scale PII. The fast opening and closing capability of the switch eliminates the need for pulse-forming networks and high-voltage thyratrons, and allows arbitrary pulse width adjustment over the range of 2 to 100 μs of interest for PII. The CROSSATRON switch is capable of modulating high peak currents, which permits rapid charging of the relatively high capacitance of the PII load to provide fast switching times. The CROSSATRON switch requires only a low-voltage (≤1 kV) pulsed biasing of the control grid to close and open, and has switching times of 1 μs or less. CROSSATRON switches are cold-cathode, plasma discharge devices that also eliminate the need for large filament-heater power supplies and higher grid-drive power required for hard-vacuum-tube switches. A 100-kV modulator, built at Hughes Research Laboratories for the PII program, has demonstrated reliable operation at up to 100 kW of average power, limited only by the existing power supply. The modulator is based on the 120-kV, 8455H CROSSATRON switch, which provides hard-tube-like modulation at peak currents of up to 1000 A and pulse repetition frequencies (PRFs) of over 1 kHz.
Overview of plasma source ion implantation research at University of Wisconsin–Madison
Authors: Malik Shamim M. , Sridharan K. , Fetherston R. P. , Chen A. , Conrad and J. R.
Published: July 2002

In the last five years, plasma source ion implantation (PSII) research at the University of Wisconsin–Madison, has encompassed work in the areas of plasma physics, diagnostics, ion-material interactions’ modeling, materials science issues, and a broad spectrum of industrial applications of PSII technology. The third generation PSII system is presently under construction. Three methods of plasma generation, namely, electron impact method, glow discharge, and radio frequency have been successfully employed. In the following article the highlights of the above facets of PSII research activities have been presented.
Multilayer facilities required for extreme-ultraviolet lithography
Authors: Windt D. L. , Waskiewicz W. K.
Published: July 2002

We have developed a magnetron sputtering system for the deposition of Mo/Si multilayer (ML) coatings onto large-area, figured optics, as required for the imaging system in a practical, extreme-ultraviolet (EUV) lithography tool. Coating uniformity on figured optics is adjusted by implementing contoured, shaped baffles during ML deposition. We have also developed an EUV reflectometer that is capable of measuring the reflectance versus wavelength across the surface of these optics, so that the coating uniformity can be determined with the required precision. We discuss the ML coating uniformity requirements for a practical EUV lithography tool, describe the facilities and techniques we have developed, and present some recent results wherein these facilities and techniques have been used to deposit high-reflectance coatings onto a variety of spherical and aspherical substrates.
Reliability of nitrided Si–SiO2 interfaces formed by a new, low-temperature, remote-plasma process
Authors: Lee David R. , Parker Christopher G. , Hauser John , Lucovsky Gerald
Published: July 2002

Controlled amounts of nitrogen atoms have been incorporated at Si–SiO2 interfaces by a new, low-temperature (300 °C), remote-plasma process, and corresponding improvements in device reliability are reported. Interfacial nitrogen-atom concentrations, up to 1×1015 cm−2, were obtained by a predeposition, remote plasma-assisted oxidation using mixtures of N2O and O2. Auger electron spectroscopy and secondary ion mass spectrometry studies to analyze N-atom concentrations at Si–SiO2 interfaces are discussed. Also, the results of electrical testing of submicron, n-channel metal–oxide–silicon field-effect transistors fabricated with this new process technology are reported. We found that the incorporation of N atoms at the Si–SiO2 interface increased current drive capability at high gate voltages but did not affect the threshold voltage of devices or the peak channel transconductance, gm. Device reliability, as measured by resistance to peak gm degradation after hot-carrier stressing, was found to increase with increasing N-atom concentrations at the Si–SiO2 interface.
Field emission characteristics of diamond coated silicon field emitters
Authors: Liu J. , Zhirnov V. V. , Myers A. F. , Wojak G. J. , Choi W. B. , Hren J. J. , Wolter S. D. , McClure M. T. , Stoner B. R. , Glass J. T.
Published: July 2002

Single crystal silicon field emitters have been modified by surface deposition of diamond using bias-enhanced microwave plasma chemical vapor deposition. Polycrystalline diamond with a high nucleation density (1010/cm2) and small grain size (<20 nm) was achieved on silicon field emitters. Field emission from these diamond coated emitters exhibited significant enhancement both in total emission current and stability compared to pure silicon emitters. A large effective emitting area comparable to the tip surface area was obtained from a Fowler–Nordheim analysis. The effective work function of the polycrystalline diamond coated emitter surface was found to be larger than that of a pure silicon emitter surface.
Fabrication of ultrasmall magnets by electroplating
Authors: Xu W. , Wong J. , Cheng C. C. , Johnson R. , Scherer A.
Published: July 2002

We use high voltage electron beam lithography followed by electroplating to define small metal features on semiconductor substrates. These have been used to form high resolution etch masks, dense nanomagnet arrays, and highly anisotropic metal nanostructures. To reproducibly obtain uniform arrays of such structures, we have developed an end-point detection technique, which is based on in situ observation of the electrodeposition process.
Reaction-diffusion modeling and simulations in positive deep ultraviolet resists
Authors: Zuniga M. , Neureuther A. R.
Published: July 2002

This article examines the effects of acid diffusion in APEX-E through the quantitative modeling of resist top loss in unexposed samples due to acid diffusion from a top-to-top contact bake with an exposed sample. Top-loss measurements are reported for 90 and 95 °C postexposure bake (PEB) temperatures ranging from 60 to 360 s bake times, resulting in 0.12 and 0.29 μm top loss, respectively, after 360 s PEB times. Results of systematically changing the diffusion constant, the kinetic reaction rates, and the deprotection level for dissolution in a Fickean diffusion model show that this model cannot account for the experimental observations. A better fit of the data and a near linear top-loss dependence with bake time are obtained with a deprotection dependent diffusion model, suggesting nonlinear diffusion mechanisms are important in modeling lithographic performance in positive deep ultraviolet resists.
Quantitative chemical topography of polycrystalline Si anisotropically etched in Cl2/O2 high density plasmas
Authors: Guinn K. V. , Cheng C. C. , Donnelly V. M.
Published: July 2002

The spatially resolved surface chemical composition or ‘‘chemical topography’’ of submicron features [polycrystalline silicon (poly-Si) masked with photoresist (PR) lines] etched in high density, low pressure helical resonator Cl2/O2 plasmas has been quantitatively determined using angle resolved x-ray photoelectron spectroscopy (XPS). The chemical topography of plasma etched microelectronic materials is important in understanding how impinging ions and neutrals interact with surfaces to influence etched profiles. The spatial origin of XPS signals was determined from a combination of geometric shadowing of photoelectrons by adjacent features, electrostatic charging of insulating surfaces, XPS signal calibration versus take-off angle, x-ray attenuation, and geometric modeling. Equal line and space width (0.75–2.0 μm) features, unmasked poly-Si, and unpatterned PR surfaces were examined following plasma etching and vacuum sample transfer. For pure Cl2 plasmas, Cl surface concentration was found to be similar for horizontal and vertical surfaces of the poly-Si and PR. Only a small amount of Si was found on the PR sidewall, and similarly, little C or O was observed on the side of the poly-Si features, indicating that sidewall passivation is not occurring. O coverage on all surfaces increased with O2 addition to the plasma. For Cl2/5% O2 plasmas, a small amount of O was found on the poly-Si trench bottom, and more (but still submonolayer) on the poly-Si sidewall. Also, more Cl, O, and Si were found on the PR sidewall with 5% O2. For Cl2/10% O2 plasmas, rough surfaces were observed by scanning electron microscopy (SEM). On poly-Si trench bottoms, O coverage is comparable to Cl at roughly a monolayer. On poly-Si sidewalls, O and Cl coverages are again comparable, but the O coverage is about double that found on the trench bottoms. The most dramatic effect by far at 10% added O2 is the formation of a thick SiOx Cly layer (where x≊y≊1) on the side of the PR, detected by both XPS and SEM. The quantitative analysis method developed in this study is readily applicable to other etching gases and materials.
Influence of the substrate doping level on spreading resistance profiling
Authors: Vandervorst W. , Clarysse T. , Smith H. E.
Published: July 2002

A study has been performed of spreading resistance probe measurements on a series of 200-nm-deep boron implants into p-type substrates with varying doping levels ranging from 3×1014 up to 4×1017/cm3. All implants were performed under the same conditions and with the same dose. However, routinely generated spreading resistance carrier profiles from different sites consistently indicate abnormally high doses and shoulder peak artifacts at the back side of the implant profile for the more highly doped substrates. It is proposed that these artifacts can be related to pressure-enhanced carrier spilling effects underneath the probes. When performing a Laplace-based correction and hence neglecting any carrier spilling effects, the correction factor scheme reacts upon the position of the on-bevel junction position instead of on the vertical junction position which can be considerably deeper in the presence of pressure-enhanced spilling. The observed artifacts can be reduced within Laplace calculations by allowing for more barrier resistance and consequently a larger contact radius.
Nanoimprint lithography
Authors: Chou Stephen Y. , Krauss Peter R. , Renstrom Preston J.
Published: July 2002

Nanoimprint lithography, a high-throughput, low-cost, nonconventional lithographic method proposed and demonstrated recently, has been developed and investigated further. Nanoimprint lithography has demonstrated 25 nm feature size, 70 nm pitch, vertical and smooth sidewalls, and nearly 90° corners. Further experimental study indicates that the ultimate resolution of nanoimprint lithography could be sub-10 nm, the imprint process is repeatable, and the mold is durable. In addition, uniformity over a 15 mm by 18 mm area was demonstrated and the uniformity area can be much larger if a better designed press is used. Nanoimprint lithography over a nonflat surface has also been achieved. Finally, nanoimprint lithography has been successfully used for fabricating nanoscale photodetectors, silicon quantum-dot, quantum-wire, and ring transistors.
High-brightness ion source for ion projection lithography
Authors: Guharay S. K. , Wang W. , Dudnikov V. G. , Reiser M. , Orloff J. , Melngailis J.
Published: July 2002

A Penning-type surface plasma source has been developed with the goal to achieve the beam requirements for ion projection lithography (IPL). The present source, with simple, forced air cooling runs up to a duty factor of 1% (pulse length of 1 ms and repetition rate of 10 Hz); a cw Penning source is being planned for IPL. H− emission current density of more than 2 A/cm2 has been obtained with negligibly low noise. The perpendicular temperature is about 0.6 eV for emission current density of about 1 A/cm2—this yields normalized beam brightness of more than 1012 A/(mrad)2. The energy spread full width at half-maximum (FWHM) for a 5 kV beam with angular current density of 33 mA/sr is about 3.3 eV (close to instrumental resolution). The energy spread increases with beam intensity. In preliminary experiments on positive ion extraction, noiseless H+ beams with emission current density of about 150 mA/cm2 have been achieved.
Emission stability and high current performance of diamond-coated Si emitters
Authors: Zhirnov V. V. , Voronin A. B. , Givargizov E. I. , Meshcheryakova A. L.
Published: July 2002

Silicon field emitters were coated with polycrystalline diamond using the hot-filament chemical vapor deposition technique. Maximum emission currents of 300–500 μA were achieved from single-tip emitters. Current fluctuations have been found to be between 3% and 16%. Temporal dependence of emission current was studied over 36 h at initial current of 100 μA. At the end of the testing, the current had decreased by 20%. Diamond-coated silicon emitters demonstrated favorable emission properties, as compared with uncoated silicon emitters.
Application of time-resolved scanning electron microscopy to the analysis of the motion of micromechanical structures
Authors: Ogo I. , MacDonald N. C.
Published: July 2002

We applied a time-resolved scanning electron microscope to the analysis of the movement of micromechanical structures. A detector signal modulation method is used in our experiment. The major advantage of this method is that no hardware modifications are required to a commercially available scanning electron microscope. The test devices are simple cantilever beams fabricated from silicon dioxide with and without an aluminum coating. These cantilever beams are electrostatically excited at resonance under several conditions. Both time-resolved images and precise resonant frequency measurements of these microcantilever beams are obtained. We found that electrically floating silicon dioxide beams without an aluminum coating can also be excited stably by an ac driving voltage at resonance under scanning electron microscopy observation. Accumulated charge on the cantilever beam caused by the electron beam irradiation is found to be positive and this charge results in a driving force between the cantilever beam and the driving electrode. A time-resolved scanning electron microscopy method is proved to be a useful technique to determine the resonant frequencies and resonant mode shapes of micromechanical systems.
Measurement of N in nitrided oxides using spectroscopic immersion ellipsometry
Authors: Irene E. A. , Liu Q. , Paulson W. M. , Tobin P. J. , Hegde R. I.
Published: July 2002

An ellipsometric method is demonstrated for the assessment of the amount of N in nitrided silicon oxides. The method utilizes the immersion of the film covered sample in a liquid that refractive index matches to the bulk film index. Thus, the overlayer is optically removed yielding greater measurement sensitivity to the interface region where the N is concentrated and is therefore optically distinct. A simple optical model is used and the ellipsometric results are compared with and found in concordance with secondary ion mass spectroscopy N profile measurements made on nitrided oxides that were prepared using N2O and NO. In addition, the interfacial roughness has been found to decrease with increasing N content also in agreement with a literature report. The new method called ‘‘spectroscopic immersion ellipsometry’’ is compared with conventional spectroscopic ellipsometry for the same samples and found to be superior.
Well surface roughness and fault density effects on the Hall mobility of InxGa1−xAs/InyAl1−yAs/InP high electron mobility transistors
Authors: Peiró F. , Ferrer J. C. , Cornet A. , Morante J. R. , Beck M. , Py M. A.
Published: July 2002

In this work, we present a correlation between the morphological characterization of InyAl1−yAs/InxGa1−xAs heterostructures grown on InP substrates for high electron mobility transistors (HEMTs) applications as determined by transmission electron microscopy, and the electrical behavior of the two-dimensional electron gas (2DEG) confined in the InGaAs channel. Our main goal is to analyze the origin of the low and anisotropic values of 2DEG Hall mobilities, discussing the effect of the density and asymmetric distribution of stacking faults and the surface undulation induced by a three-dimensional (3D) growth mode, depending on the growth temperature (Tg) and thickness (tw) of the InxGa1−xAs well. Our results have shown that a high mobility for a matched channel is obtained if the In0.53Ga0.47As layer is grown at 530 °C. Lower temperatures reduce the mobility values and lead to higher mobilities for [11̄0] due to the surface corrugation along [110] induced by lateral decomposition of the InGaAs at low growth temperatures. For HEMT structures with strained In0.75Ga0.25As channels grown at 530 °C, within the range of the well thickness considered (5–10 nm), Hall mobilities are also more influenced by the surface roughness than by fault distribution. However, in this case, the observed roughness is not driven by alloy decomposition but by a strain-induced 3D growth mode.
Development of a piezoelectric self-excitation and self-detection mechanism in PZT microcantilevers for dynamic scanning force microscopy in liquid
Authors: Lee Chengkuo , Itoh Toshihiro , Ohashi Takahiro , Maeda Ryutaro , Suga Tadatomo
Published: July 2002

We report on the first successful operation of a cyclic contact scanning force microscope (SFM) using a self-excited cantilever in liquid. Based on a new structure including a PZT reference pattern and a free-standing PZT cantilever, the piezoelectric self-excitation and self-detection mechanism for a PZT microcantilever was developed successfully. The topography is recorded by measuring the piezoelectric current variation, which corresponds to the vibration. Since the acoustic excitation from the external oscillator no longer exits, a clear single resonance peak can be obtained by using this self-excited force sensing PZT cantilever. Clear grating imaging in liquid was demonstrated, and it is compatible with the image taken in air. The future potential of applying this piezoelectric SFM to the characterization of biological samples in liquid is very promising.
X-ray photoelectron spectroscopy study of GaAs(110) cleaved in alcoholic sulfide solutions
Authors: Bessolov Vasily N. , Konenkova Elena V. , Lebedev Mikhail V.
Published: July 2002

X-ray photoelectron spectroscopy has been used to study chemical bonds which appeared on the (110) surface of GaAs after cleavage of the crystal in solutions of sodium sulfide in different alcohols. It has been shown that after such treatment the sulfur atoms are almost exclusively bonded only to gallium atoms. This is conditioned by the electrostatic interaction of sulfur ions in the solution with the surface ions of the crystal lattice of the semiconductor.
Polarization-dependent contrast in near-field optical microscopy
Authors: Kobayashi Kiyoshi , Watanuki Osaaki
Published: July 2002

This article presents a simple modeling and simulation of experiments with a near-field optical microscope or a photon scanning tunneling microscope (PSTM) in the sub-100-nm range. The simulation employs a semimicroscopic and perturbative approach based on field propagator and linear response theory. A probe tip and sample are approximated as nanometric spheres in order to clarify the behavior of the near-field and far-field signal intensities, I, and the contrast, i.e., visibility, (Imax−Imin)/(Imax+Imin), for s and p polarization of incident light and three scanning methods: constant height, constant intensity, and constant distance. The signal intensity then becomes a function of the taper angle of the fiber probe tip θ or the numerical aperture of the collecting lens, in addition to the variables mentioned above. Note that the signal intensity I(θ=90°) corresponds to that for the near-field. The simulated polarization-dependent intensity and contrast are in good qualitative agreement with the experimental results. At the same time, for each polarization and scanning method, there is an optimal angle θ for maximizing the contrast and maintaining a high signal intensity. This result indicates that the taper angle and scanning method are very important factors in the polarization-dependent contrast and resolution of near-field optical microscopy.
Effects of accelerating voltage and pattern size on electron scattering by electron-beam mask
Authors: Yamashita Hiroshi , Nomura Eiichi , Nozue Hiroshi
Published: July 2002

Electron scattering by electron-beam (EB) masks has been studied by a Monte Carlo simulation to investigate the influence of increasing accelerating voltage, of decreasing pattern size, and of using a thinner mask for a practical engineering application. The simulation study has revealed that there are two different exiting angle distributions; whether the most frequent exiting angle depends on L/S size or not. These are named interfeature scattering and intrafeature scattering, respectively. In order to analyze the electron scattering phenomena, we investigated the electron transmittance and absorbance by normalizing the mask thickness, using a Grün range. As a result, the EB mask was found to be categorazible into four function categories defined by the normalized mask thickness. They are pure absorber, scattering absorber, absorbing scatterer, and pure scatterer. This classification gives us important information for engineering design of the EB mask and for column design. For the EB mask, whose normalized mask thickness is more than 0.2, the transmitted electrons are scattered enough not to contribute to imaging in the angular and the energy distributions and high contrast can be obtained with some optimization of the angular limiting aperture. When the normalized mask thickness is less than 0.2, the limiting angle of the aperture may need to be decreased due to high electron transmittance, but optimization for different pattern sizes is not necessary in the case of the intrafeature scattering. The combination of thinner mask and an appropriate limiting aperture seems to be feasible and promising for future EB cell projection lithography to achieve higher resolution.
Effects of arsenic in gas-source molecular beam epitaxy
Authors: Zhao Y. , Deng F. , Lau S. S. , Tu C. W.
Published: July 2002

The role of arsenic in gas-source molecular beam epitaxy of GaN(As) was investigated. We found that arsenic mainly acts as a surfactant which dramatically improves the surface morphology of GaN when the growth temperature is over 700 °C, while it is incorporated into GaN as high as 1% at lower growth temperature. The optical absorption of the sample GaN0.99As0.01 shows a direct-band gap optical absorption edge, but smaller band gap compared to that of GaN.
Size distribution of SiGeC quantum dots grown on Si(311) and Si(001) surfaces
Authors: Jonczyk R. , Hits D. A. , Kulik L. V. , Kolodzey J. , Kaba M. , Barteau M. A.
Published: July 2002

Quantum dots of Si1−x−yGexCy alloys with high Ge contents were grown on Si(311) and Si(001) substrates by solid source molecular beam epitaxy and were measured by atomic force microscopy. The quantum dot layers had a nominal thickness (equivalent two-dimensional) of 4 nm. The smallest quantum dots occurred for the composition Si0.09Ge0.9C0.01 on Si (311), and had a 40 nm mean diameter, an 8 nm mean height, and a density of 3.3×1010 cm−2. Quantum dots on Si(001) were larger and had less regular spacing than quantum dots on Si(311) with the same composition. Carbon decreased both the mean size and spacing of SiGe quantum dots and the ratio of size deviation to mean diameter. The presence of small uniform quantum dots for particular compositions is attributed to a reduction in the surface migration of adatoms due to decreased atomic surface diffusivity. These results suggest that quantum dot organization is controlled by composition, substrate orientation, strain, and surface diffusion.
Control of wet-etching thickness in the vertical cavity surface emitting laser structure by in situ laser reflectometry
Authors: Cho H. K. , Lee J. Y. , Lee B. , Baek J. H. , Han W. S.
Published: July 2002

We have investigated the use of in situ laser reflectometry for etch depth control in vertical cavity surface emitting laser (VCSEL) structures. We can obtain the precise etch depth by simply counting the number of oscillations during the wet-etching process. After calibration on an AlGaAs/GaAs 20-period distributed Bragg reflector (DBR) structure, this technique was applied to the monolithic 1.55 μm VCSEL device process that is required to etch epilayers of several μm thickness. In the 1.55 μm VCSEL structure, the mesa was generated by monitoring the number of peaks in the bottom DBR that corresponded to an etch depth of about 11 μm. The overall spatial uniformity of the etched sample was within a layer (1000 Å) by the distinction between layers. This process offers the possibility of precise control of etch depth for any multilayer structure.
Comparison of metrology methods for quantifying the line edge roughness of patterned features
Authors: Nelson C. , Palmateer S. C. , Forte A. R. , Lyszczarz T. M.
Published: July 2002

Comparisons are made of two atomic force microscopes in different modes of operation, and two scanning electron microscopes, one high and one lower resolution for quantifying the edge roughness of patterned features in resist and silicon. Definitions of the edge roughness magnitude and spatial frequency are given. For each metrology method, the parameters that limit the edge roughness measurement and how they compare to the parameters that limit the critical dimension measurement are addressed. An attempt to quantify the edge roughness spatial frequency is also discussed. For the two best metrology methods the repeatability of the measurements was determined, and measurements were made to understand the correlation between them.