bluuebunny/crossref_metadata_2025 huggingface dataset:
The structure and adhesion of coatings deposited by wire explosion spraying
Authors: Suhara Toshiro , Kitajima Kazunori , Fukuda Shigehisa , Ito Hiroshi , Fukunaga Hiroku
Published: July 2002

The coating method and the characteristics of wire explosion spraying, as developed in our laboratory, are described. A study of the mechanism of adhesion between the coating and substrate in two metal systems, W-mild steel and W–Cu which differ in mutual solubility, is discussed. Metallographic observations using electron probe and soft x ray confirmed the presence of a solid solution boundary layer in the case of the mild steel substrate, with a critical shearing stress of adhesion measured by our method ranging from 20 to 26 kg/mm2, which is nearly equal to the shearing strength of the tungsten coating itself of 24 kg/mm2; fracture propagated within the coating itself. In the case of the copper substrate the critical shearing stress of adhesion was from 9 to 13 kg/mm2 which is much weaker than the shearing strength of copper, 28 kg/mm2; the fracture propagated along the boundary between the coating and substrate. Theoretical considerations attempt to explain the mechanisms of formation of the structures and the adhesion properties. It is concluded that the high adhesion strengths obtained by this method are attributable to the characteristics of the particles sprayed by wire explosion, i.e., the small size (average 5 μ), the high temperature (near the boiling point of materials), the high impinging velocity (500–600 m/sec), and furthermore, the uniformity of the size, velocity and temperature of the sprayed particles.
High-rate evaporation/deposition processes of metals, alloys, and ceramics for vacuum metallurgical applications
Authors: Bunshah R. F.
Published: July 2002

This is a review on high-rate evaporation/deposition processes for metals, alloys, and ceramics. These processes are described. The influence of process variables on the microstructure and mechanical properties of the deposits is discussed. Present and potential applications are presented.
Growth of fcc Metals on Lead Sulfide
Authors: Green A. K. , Dancy J. , Bauer E.
Published: July 2002

The growth of evaporated Au and Ag films on air- and vacuum-cleaved natural galena is studied in situ by RHEED, LEED, and with conventional electron microscopy after removal from the PbS substrates. Au was observed to grow with two equivalent (110) orientations. This predominant orientation occurs over the entire substrate temperature range studied (25 °–400 °C). Ag forms with a (111)-one deg orientation at 25 °C; (100)-oriented Ag becomes evident at 100 °C and increases with temperature to nearly perfect epitaxy at 200 °C. The orientation of both Au and Ag is the same on air- and vacuum-cleaved surfaces and is not influenced by electron irradiation.
Anomalous Fine Structure in the Soft X-Ray Appearance Potentials of Nonmetals
Authors: Houston J. E. , Park Robert L.
Published: July 2002

A simple, nondispersive spectrometer has been used to study the binding energies of core electrons at solid surfaces. The spectrometer consists of a photomultiplier which measures the soft x-ray fluorescence of an electron-bombarded surface. The derivative of the multiplier current as a function of target potential rises abruptly at the threshold energies at which core electrons can be excited to unoccupied states. This produces a comparatively simple spectrum for metals with each level being represented by a sharp peak, followed by an abrupt step. For nonmetals, however, the spectrum of a single level can consist of a series of sharp peaks spread over as much as 30 eV.
Thick Epitaxial Films of Pb1−xSnxTe
Authors: Bis R. F. , Dixon J. R. , Lowney J. R.
Published: July 2002

During the past several years attempts have been made to grow thick epitaxial films of PbS, PbTe, PbSe, and their alloys with tin on alkali halide substrates. The thickest films which have been achieved using conventional evaporation techniques were limited to 10–15 μ m. We have developed a quasiequilibrium system which has yielded thick films of Pb1−xSnxTe ranging up to 328 μm. When combined with appropriate substrate preparations, this technique yields films having optical quality surfaces and good adherence to the substrate. In addition, the films may be easily removed from their substrates, intact and undistorted, by dissolving the substrates. Various electrical, optical, and thermal measurements on these thick films show that they are homogeneous. X-ray data indicate that the films are of high crystalline quality.
Mass Spectra Generated by a Graphite Field Ionizer
Authors: Gutshall P. L. , Bryant P. J.
Published: July 2002

The mass spectra, formed by field ionization utilizing a graphite filament source, have been determined for a number of gases including heptane, a long chain hydrocarbon. The spectrum for each molecule studied was notably free of a cracking pattern. The spectra were also found to be free of anonymous mass peaks at one atomic mass unit greater than the parent molecule. Such anonymous peaks often occur when metallic field ionizers are employed. Thus, the mass spectra produced by a graphite field ionizers are characterized by a single peak corresponding to the mass of the parent molecule. The graphite field ionizer has produced sufficient ions to operate a mass spectrometer at potentials as low as 3 kV. Data taken using both the quadrupole and the magnetic sector type mass spectrometers are presented.
The effects of oxygen adsorption on the positive secondary ion yield of stainless steel
Authors: Schubert Rudolf
Published: July 2002

The positive secondary ion yields of Fe and Cr in 301 stainless steel vs oxygen exposure are studied using secondary ion mass spectrometry. It is shown that there are large amounts of Fe in the surface layer, although it is enriched with Cr. Both elements readily and reversibly form surface oxides. Furthermore, it is shown that the absolute elemental yields cannot be used to calculate alloy compositions at the present time.
Effect of metal–insulator–semiconductor structure derived space charge field on the tip vibration signal in electrostatic force microscopy
Authors: Hong Seungbum , Woo Jungwon , Shin Hyunjung , Kim Eunah , Kim Keun-Ho , Jeon Jong Up , Pak Y. Eugene , No Kwangsoo
Published: July 2002

The role of metal–insulator–semiconductor structure derived space charge field in the tip vibration signal of electrostatic force microscopy was studied using boron doped Si tip and Pt film sputtered on Si substrate. The ohmic contact between the tip and the film was confirmed by current–voltage characterization. Then the tip was held at a position so that an air gap of 100 nm existed between the tip and the film. The tip deflection and the tip vibration signals were examined by applying dc voltage to the film and ac voltage to the tip. The asymmetry in both signals supports the existence of the space charge field, and the direction of the field at zero dc bias field is from the tip to the sample as expected from the band bending theory.
Crystallization of nanostructured silicon films deposited under a low-pressure argon–silane pulsed-glow discharge: Correlation with the plasma duration
Authors: Hadjadj A. , Beorchia A. , Boufendi L. , Huet S. , Roca i Cabarrocas P.
Published: July 2002

In this work, we compare the thermal crystallization and the laser crystallization of hydrogenated nanostructured silicon (ns-Si:H) films in relation with their deposition conditions. The samples are grown in a low-pressure pulsed radio-frequency glow discharge of an argon–silane mixture. The laser crystallization shows a decrease of the crystallization threshold (Ecryst) and an increase of the induced crystalline fraction when the plasma duration (Ton) used for the deposition increases. No correlation with Ton is observed in the case of the thermal annealing, indicating that the modifications of the bulk structure of the film with Ton are not the main parameter in the determination of Ecryst. The role of the surface roughness in the lowering of the laser crystallization threshold is then emphasized.
Deposition of electronic quality amorphous silicon, a-Si:H, thin films by a hollow cathode plasma-jet reactive sputtering system
Authors: Pribil G. , Hubička Z. , Soukup R. J. , Ianno N. J.
Published: July 2002

High quality hydrogenated amorphous silicon, a-Si:H, thin films were deposited by means of a dc hollow cathode plasma-jet with magnetic field confinement. Single-crystal silicon nozzles were reactively sputtered in a high density hollow cathode discharge. Only nontoxic gases, argon and hydrogen, were used for this purpose. Different configurations of the dc hollow cathode were used for the deposition process. Electronic quality a-Si:H thin films were achieved with light to dark conductivity ratios >106, with light conductivity near 10−5 S/cm and dark conductivity between 10−11 and 10−12 S/cm. This was accomplished with a specific configuration of the hollow cathode discharge in the silicon nozzle. Our best films have a Tauc band gap near 1.8 eV and an atomic hydrogen concentration of about 14%. The growth rate achieved for the electronic quality a-Si:H films was in the range of 2–3 μm/h.
Diamond-based composite layers as protective coatings for ion beam extraction systems
Authors: Terranova M. L. , Sessa V. , Piccirillo S. , Rossi M. , Valeri S. , Materassi M.
Published: July 2002

W-containing polycrystalline diamond films were produced by a hybrid chemical vapor deposition- powder flowing technique, in order to test the feasibility of using composite diamond-based materials as protective coatings for acceleration grids subjected to ion bombardment. The morphology and structure of the composite layers, deposited on Mo substrates, were investigated by scanning electron microscopy and reflection high-energy electron diffraction. It is found that W insertion substantially lowers the resistivity of the diamond-based layers (around 10−2Ω cm) but does not modify the lattice parameters of the host diamond matrix. The performance of such coatings for shielding Mo grids from ion-induced sputtering was tested using 1 keV Ar+ beams. The Auger electron spectroscopy spectra indicated that the dose of 6×1019 ions/cm2 employed was not sufficient for complete erosion of the composite layers, for which sputtering yields in the range of 0.6–0.9 atoms/ion were measured. The secondary electron emission induced by 1.5–4.0 keV Ar+ ions was investigated and compared with the emission from uncoated Mo samples.
“NANOJET”: Tool for the nanofabrication
Authors: Rangelow I. W. , Voigt J. , Edinger K.
Published: July 2002

A tool for pattern generation and microfabrication based on scanning micro/nanonozzle is presented. Electrically neutral radicals created in a plasma discharge are pumped through a small tube tapered to a nozzle. A small distance between the nozzle and the surface of the substrate allows a localized interaction. A description of the tool and principles of this technology, such as transport of free radicals through a high aspect ratio hollow tip, localized etching and high etching rates without ion bombardment are demonstrated in this work. This article presents the fundamental aspects and the experimental proofs of the outlined nanofabrication technique.
Intermittent chemical vapor deposition of thick electrically conductive diamond-like amorphous carbon films using i-C4H10/N2 supermagnetron plasma
Authors: Kinoshita Haruhisa , Murakami Toichi
Published: July 2002

Electrically conductive diamond-like amorphous carbon (DAC) films with nitrogen (DAC:N) were deposited on Si and SiO2 wafers using the i-C4H10/N2 supermagnetron plasma chemical vapor deposition (CVD) method. Resistivity and hardness decreased with increase of upper electrode rf power (UPRF) under constant lower electrode rf power (LORF). Film thickness increased linearly to over 0.3 μm with deposition time via intermittent deposition. The film exhibited good adhesion to the substrate. Low-resistance thick films were deposited using alternating multilayer CVD at UPRF/LORFs of 1 kW/1 kW and 300 W/300 W. In the deposited alternating multiple layers, resistivity significantly decreased with the increase of H layer (1 kW/1 kW) thickness, and film thickness significantly increased with the increase of L layer (300 W/300 W) thickness. By the deposition of H/L multiple layers, a film of 2.1 μm thickness and 0.14 Ω cm resistivity was obtained.
Solution of Clausing’s Integral Equation for Molecular Flow
Authors: Helmer John C.
Published: July 2002

A new solution of Clausing’s equation has been obtained by iterative methods. In long cylindrical tubes it is found that the gradient of the molecular density is higher in the ends of the tube than in the center. Relations are developed for the measurement of the molecular flow rate by pressure gauges mounted in the wall of the tube. A simple function closely approximates the density distribution for both long and short tubes. The gauge position is calculated for the measurement of pumping speed at the end of the tube. The molecular transmission probability is found to agree with the results of Berman to within 0.1%.
Simultaneous Adsorption of Hydrogen and Nitrogen on Tungsten at 300 °K
Authors: Singleton J. H.
Published: July 2002

The simultaneous adsorption of pure hydrogen and nitrogen on polycrystalline tungsten, at. 300 °K, has been compared with the adsorption of the pure gases on the same surface. The results are consistent with a model which assumes a single set of adsorption sites, equally accessible to either gas, with only weak interaction between the two adsorbed species. The sticking probability and rate of adsorption of each gas is primarily determined by the fraction of the adsorption rates covered and is relatively independent of the particular species in the adsorption sites. There was no evidence of the replacement of one gas by the other at 300 °K.
Analysis of grain boundary diffusion in bimetallic thin film structures using Auger electron spectroscopy
Authors: Wildman H. S. , Howard J. K. , Ho P. S.
Published: July 2002

The feasibility of using Auger electron spectroscopy (AES) for solute grain boundary diffusion measurements in thin films is explored in this investigation. Diffusion couples of a sandwiched Al/Cu/Al structure were prepared by sequential deposition in the same pumpdown. The composition profile was determined before and after annealing with an AES system which employed argon sputtering for thin film sectioning. It is shown that both the lattice and grain boundary diffusivities can be extracted from the solute profile based on the Whipple analysis of grain boundary diffusion. At 175°C, the grain boundary diffusivity αDbδ for Cu in Al was determined to be 4.3×10−20 cm3/sec with an estimated error of ±7% from the ion etching damage. The agreement between our measured lattice diffusivity and radioactive tracer data is satisfactory. Some of the problems associated with the AES method for diffusion studies are discussed.
Phase stability of chrome-carbide Ni–Cr coatings in low-oxygen environments
Authors: Taylor Thomas A.
Published: July 2002

The thermal stability of the phases in chrome-carbide-based, wear-resistant coatings, applied by plasma and detonation gun (D-gun) devices, was investigated for applications in low-oxygen environments. It was found that current coatings using the Cr3C2 carbide in a Ni–Cr binder decomposed to lower carbides, and consumed Cr from the binder upon long-term exposure at elevated temperature. Two new coatings based on the Cr23C6 carbide were found to have excellent thermal stability, as well as excellent wear properties.
Electrical and metallurgical examination of Pb1−xSnxTe/PbTe heterojunctions
Authors: Bicknell R. W.
Published: July 2002

Vapor-phase heterojunctions between Pb0.8Sn0.2Te and PbTe epitaxial layers have been examined for tin diffusion and the electrical effects of dislocations. Tin has been shown to diffuse across the junction as an approximately symmetrical error function and growth dislocations were shown to be electrically inactive. Scanning laser microscopy and I–V characteristics show that slip dislocations caused by surface damage were responsible for deterioration in the electrical characteristics of infrared mesa diodes fabricated from the grown layers. Laser microscopy used on chemically prepared taper sections gave carrier diffusion lengths of 15 μm and p-n junction depths accurate to ∠0.1 μm.
Focusing and dispersing properties of a stigmatic crossed-field energy analyzer
Authors: Galejs A. , Kuyatt C. E.
Published: July 2002

The electron-optical properties of a stigmatic crossed-field energy analyzer (double-focusing Wien filter) have been obtained from exact trajectory calculations. The results are given in the form of focusing and dispersing coefficients to the second order. These coefficients enable the device designer or potential user to calculate the total beam transfer and evaluate the resulting beam quality without additional ray tracing. The specific device for which calculations are made employs a uniform electric field and a toroidal magnetic field. This analyzer is of special interest in our laboratory because it can be constructed with a very small stray magnetic field, and in addition to its dispersive properties it also rotates the spin of a polarized electron beam.
Application of a double-pass CMA to ion scattering from some actinide materials
Authors: Ellis W. P. , Taylor T. N.
Published: July 2002

Surfaces of polycrystalline U, Th, and single-crystalline UO2(111) have been examined with He+, Ne+, and Ar+ at incident beam energies Ei?650 eV. For this study we used a double-pass cylindrical mirror analyzer in a custom vacuum system intended primarily for UPS chemisorption studies. The incident ion beam was perpendicular to the axis of the analyzer. Our approach was to determine if the instrument could serve in a complementary ISS capacity and, if so, what the ion scattering conditions are for detecting both surface oxygen and the actinides. Data are presented illustrating definitive results. But severe limitations in resolution are evident, the energies do not correspond exactly to a simple binary-collision model, and with He+ the scattering intensities from actinide materials are quite low by comparison with a Au reference.
Interface characteristics of thermal Si02 on SiC
Authors: Kee R. W. , Geib K. M. , Wilmsen C. W. , Ferry D. K.
Published: July 2002

The interface between a thermally grown silicon dioxide and a vapor epitaxial layer of cubic silicon carbide has been investigated. Initial studies have concentrated on an Auger analysis of the interface region. The interface region is considerably wider for the unannealed oxide than that between Si and Si02. The Si KLL peak shift occurs over a region of some 130 Å, while the compositional profile indicates a transition region about 210 Å wide. No buildup of free carbon is found at the interface. The Si KLL peak changes indicate that the interface is composed primarily of Si02 and SiC. The cause of the wide interface is discussed in terms of the reaction products of carbon.
Applications of ion implantation to magnetic bubble devices
Authors: North J. C. , Wolfe R. , Nelson T. J.
Published: July 2002

Ion implantation has become an important part of magnetic bubble technology. The damage produced by implantation places the implanted layer in a state of in-plane compression. This can change the easy axis of magnetization from perpendicular to parallel to the surface in a material having a negative magnetostriction coefficient. Several magnetic effects result from the creation of a thin layer of in-plane magnetization at the top of the magnetic bubble supporting material. These include flux capping of the bubbles, control of the allowable magnetic bubble states, formation of bubble guiding rails at the boundaries of implanted areas, and creation of a moving magnetic pole pattern for bubble propagation in an external rotating in-plane magnetic field. Other observed effects include increases in lattice parameter up to ∠2% and enhancement of the etching rate of the material by as much as a factor of 1000. Implantation is now widely used to suppress hard bubbles, and there is the possibility that ion implantation will be used to produce the drive patterns of the next generation of high-density magnetic bubble memories.
Ionization of liquid metals, gallium
Authors: Culbertson R. J. , Sakurai T. , Robertson G. H.
Published: July 2002

Field ionization of a liquid metal, such as Ga or In, has attracted considerable interest since it could become a source of strong focused ion emission. We have studied this phenomenon using the improved magnetic-sector atom-probe field ion microscope. The energy distributions of field ionization of Ga and critical energy deficits are measured as a function of surface temperature and electric field. The field ionization of Ga can be divided into a low and a high emission region. In the low emission region Ga+ ions are emitted at a field of approximately 0.5 V/A when the emitter is heated to approximately 600 °C. The intensity of this Ga+ emission is sufficient to yield a desorption image of the emitter surface. This implies that the ion flux is ∠103 ions/atomic site/second. When the emitter is kept at low tempertures (78 K) the emission is predominately Ga++. In both cases the ions display a sharp energy distribution (?1.5 eV FWHM) and a small energy deficit (?2.1 eV). In the high emission regime Ga++ ions are produced with a broad energy distribution (?12 eV FWHM). The total current ranges from 10−8 A or less in the low emission regime up to or greater than 10−5 A in the high emission regime.
Study of the properties of GaAs–anodic Al2O3 interfaces
Authors: Bayraktaroglu B. , Schuermeyer F. L. , Grant J. T.
Published: July 2002

For its possible use as a stable insulator passivating the surface of GaAs we have studied anodically grown Al2O3 films and their interfacial properties with GaAs. The particular aim of the passivation scheme was directed towards the neutralization of some of the long term instabilities of GaAs MeSFET’s due to the traps near the bare surface of GaAs not covered by the gate metal. Al2O3 films were grown on the surface of GaAs by the anodization of a thin film of evaporated Al in an electrolyte consisting of ammonium pentaborate and ethylene glycol. As grown, films are essentailly water free and show excellent high temperature (?800 °C) and chemical stability. The Al2O3–GaAs interface thickness was estimated to be ∠80 Å. The electrical properties of the Al2O3–GaAs interface seem to depend strongly on the type of GaAs used with superior results on p-type GaAs. However, all MOS devices showed reduced insulator charging effects compared to those employing anodic native oxides. Annealing Al2O3 on GaAs in an oxygen atmosphere at temperatures above 450 °C promotes the formation of a semi-insulating GaAs surface.
High resolution, steep profile resist patterns
Authors: Moran J. M. , Maydan D.
Published: July 2002

High resolution and steep profile patterns have been generated in a 2.6 μm thick organic layer which conforms to the steps on a wafer surface and is planar on its top. This thick organic layer (a photoresist in the present experiments) is covered with an intermediate layer of SiO2 and a top, thin layer of x-ray or photoresist. After exposure and development of the top resist layer, the intermediate layer is etched by CHF3 reactive ion etching. The thick organic layer is then etched by O2 reactive ion etching. Submicron resolution with essentially vertical walls in the thick organic material was achieved. The technique is also applicable to photo and electron lithography. It reduces the need for thick resist patterns for the lithography step and, at the same time, ensures high resolution combined with good step coverage.
Combined ion beam deposition and etching for thin film studies
Authors: Harper J. M. E. , Gambino R. J.
Published: July 2002

A dual ion beam system is used to deposit thin films in the presence of ion bombardment. This technique provides a measurement of sputter yields of elements in alloy films. Material is deposited by ion beam sputtering using a high current focused beam, while a second ion beam bombards the growing film. The film composition is modified by preferential resputtering of the high sputter yield component, analogous to the effect of substrate bias in diode sputtering. The advantage of the ion-beam technique is that ion energies, currents and angles may be directly measured and controlled. We have studied the sputter yield ratio of Gd to Co in binary Gd–Co films deposited with simultaneous ion bombardment by an argon beam of typically 500 eV ion energy. Gd is preferentially resputtered with a yield ratio which increases from 2 to 6 with increasing Co concentration in the film. This dependence of yield ratio on film composition is consistent with a model in which surface binding energy dominates the sputter yields.
Mixtures of poly (2,3−dichloro−1−propyl acrylate) and poly (Glycidyl methacrylate−co−ethyl acrylate) as an x-ray resist with improved adhesion
Authors: Moran J. M. , Taylor G. N.
Published: July 2002

Improved adhesive properties for poly (2,3-dichloro-1-propyl acrylate) x-ray resist have been obtained by the addition of small quantities of an adherent electron sensitive resist, poly (glycidyl methacrylate-co-ethyl acrylate). The mixture is novel in that it appears to be compatible over broad compositional ranges, affords improved resolution in thick films, and offers superior resistance to wet etching. Sensitivity and contrast are decreased for the mixtures. Resolution is limited to 2 μm (gap) in 0.5 μm-thick films by swelling encountered upon development. With some modification in exposure conditions, higher resolution is obtainable.
Optical imaging for microfabrication
Authors: Bruning J. H.
Published: July 2002

As time progresses, integrated circuit feature-sizes along with alignment tolerances are shrinking while wafer sizes are getting larger. This trend has made life difficult for contact and proximity printers and has made projection printing of an entire wafer within a single lens field no longer possible. The present practical upper limit to the number of resolution elements within a single lens field is ∠108, whereas 1 μm resolution over a 4 in. wafer is the equivalent of 2×109. Partitioning of the optical field by scanning or step-and-repeat printing permits the maximum number of resolution elements on a wafer to grow. Thus the 108 element limit, at least for step-and-repeat printing, applies to the chip. And, in principle, the field of the chip could itself be partitioned by scanning or image stepping. The practical limits to optical lithography will be determined by resolution, overlay, and the characteristics of photoresists. This latter area has received a recent resurgence of effort with the introduction of multilevel and inorganic resists. One distinct benefit of these new classes of resists is the complete elimination of the degrading effects of standing waves and topography. These are key factors for photolithography below 1–1.5 μm. The end of the road for photolithography will probably be somewhere in the range of 0.4–0.8 μm depending on how well we exploit the potentials of deep-UV, image partitioning, and optical design.
Effects of oxygen and chlorine on the interfacial crystallization of amorphous selenium films
Authors: Jansen Frank
Published: July 2002

The interfacial crystallization of vapor deposited selenium films has been investigated. It is shown that the interfacial crystalline layer does not form immediately upon condensation of the vapor on aluminum substrates held at 80 °C but forms by crystallization of the condensed amorphous phase. This transformation gives rise to a highly imperfect crystalline layer. Trace amounts of oxygen which can not easily be detected analytically increase the interfacial crystallization rate of selenium. The addition of chlorine to selenium is shown to have the opposite effect. Films fabricated from selenium containing more than 1000 ppmw of chlorine do not show any crystalline formation at the interface. The relationship between our findings and earlier work on the crystallization behavior of melt quenched selenium is discussed.
Ion-beam-induced-current (IBIC) monitoring of uniform and selective ion-etching processes in layered structures
Authors: Sakaki H. , Sekiguchi Y. , Yokoyama K.
Published: July 2002

Electrical current induced in a sample during ion-etching processes is found to depend sensitively on constituent materials of the sample surfaces. This induced current (IBIC), when measured as a function of etching time, is shown to exhibit a step-like change whenever a new interface is reached in the etching process of layered structures. Consequently, the IBIC measurement provides a new powerful real-time method to monitor the evolution of etched-surface profiles; this simple method is successfully applied to optimize the fabrication process of highly-efficient gold gratings with the periodicity of 0.26 μm.
VLSI Metallization: Some problems and trends
Authors: Vossen J. L.
Published: July 2002

The paper summarizes the most probable course of the evolution of device metallization for VLSI circuits based on considerations of contact resistance, junction depth, feature size and density, step coverage and radiation damage. Materials and technologies requiring further investigation are highlighted.
A method to reduce deflection aberrations in electron-beam lithography systems
Authors: Knauer W.
Published: July 2002

An imaging and deflection method is described which is intended for high-speed, submicron lithography. The basic electron-optical approach is similar to one described by Pfeiffer, comprising a large-bore lens and an in-lens deflection element. A saddle coil rather than toroidal deflector is utilized in order to facilitate the simultaneous reducton of deflection aberrations and beam deflection offset due to eddy currents and skin effect. Deflection aberrations usually are minimized by varying the relative positions of lenses and deflection elements against each other. In this paper, an optimization approach is described in which the shape of the deflection coil is varied. By changing the length of the coil wires, their radial and lateral positions, and by adjusting the axial coil position in the lens, low levels of field curvature, astigmatism, and distortion are reached. To minimize eddy currents, saddle-type deflection coils can be surrounded by secondary coils which generate the same magnetic dipole moment as the primary coils, but provide opposing polarity. This approach has been described earlier by Wardly; its extension to the correction of beam deflection offset due to skin effect is presented in this paper. Experimental tests of these concepts have been conducted. A specific result obtained is that all geometrical aberrations and all eddy current related effects are reduced to about 0.1 μm in the corners of a 2 mm scan field.
E-beam fabrication of 1.25 micron 4 K static memory
Authors: Shah P. , Pollack G. , Miller R. , Varnell G. , Lee W. , Love R. , Wood S. , Robbins R.
Published: July 2002

Fast, high density 4 K-bit static RAM’s (SRAM’s) have been fabricated utilizing electron beam direct slice writing and dry etch processes to demonstrate 1.25 μ VLSI MOS device technology. Access times of 15 ns were obtained for these scaled memories with channel lengths of 1.0 μ on a chip size of only 6 K mil2 vs the standard production 4 K SRAM with 35–45 ns access times, a 2.5 μ channel length and a chip size of 20 K mil2. All levels were patterned using a vector-scanned electron-beam exposure system with a capability of 1 μ resolution, ±0.2 μ level-to-level registration, and automatic chip-by-chip alignment. High speed, high resolution positive and negative electron beam resists were used for all patterning steps. All implanted, 250 Å gate oxide, scaled MOS processes with dry etching techniques for Si, SiO2, and Si3N4 were used to realize these static memories functional over full temperature.
Electron beam direct writing of capacitor coupled GaAs FET logic circuits
Authors: Dix C. , Flavin P. G. , Hendy P. , Jones M. E.
Published: July 2002

Capacitor coupled logic circuits using depletion-mode Schottky-gate GaAs transistors are being made by direct electron beam exposure with a Cambridge Instruments EBMF-1. Etched active mesas are defined using either a negative working polystyrene based resist or positive working PMMA. The use of PMMA is possible following the development of a tone reversal program for the PDP 11/34 EBMF-1 control computer. The chips have 2 mm sides and each is written in a single field. Automatic registration of the FET electrodes is accomplished using topographic marks for the source/drain level and metal marks for the gate and subsequent layers. The source/drain and gate metallizations are defined by liftoff using PMMA. Software to correct the intraproximity effect within individual exposure features has been developed, and applied to the 1.5 μm gate structures. The dose given to a feature and its dimensions are simultaneously adjusted to obtain the correct feature size and resist profile for liftoff metallization. In subsequent steps a polyimide insulation layer and a metal interconnect level are defined to complete the circuit.
A multibeam scheme for electron-beam lithography
Authors: Sasaki T.
Published: July 2002

The most important requirement for the direct-writing scheme of electron-beam lithography is to increase the throughput. The throughput is severely impacted by the space–charge effect in the single-beam schemes. This paper proposes a multibeam scheme in which the space–charge effect is not serious and investigates the feasibility of the scheme.
Fabrication of polyimide x-ray masks with high dimensional stability
Authors: Wada T. , Sakurai S. , Kawabuchi K.
Published: July 2002

A technique has been developed for fabricating polyimide x-ray masks of high durability and excellent dimensional stability. It is found that the most serious factor causing the distortion of the polyimide membrane is the nonuniformity of the back-etching rate. Improvements were effected to the etching apparatus and wafer holder to ensure a high uniformity of the etching rate of 3% over an 80 mm diam window. In addition, a gold layer was inserted between the polyimide membrane and the silicon wafer, and it is found that this etching stopper is very effective in reducing distortion. In addition, the distortion of the polyimide membrane is reduced, increasing the thickness of polyimide film and also decreasing the window size. As a result, polyimide x-ray masks having a 4-μm-thick membrane and a 40-mm-diam window have been obtained with a distortion less than 0.15 μm (σ). They have shown excellent dimensional stability against a high-level x-ray irradiation amounting to 40 J/cm2 over one week.
A wide-range alignment system for x-ray lithography
Authors: Nelson D. A. , Dimilia V. , Warlaumont J. M.
Published: July 2002

A new wafer alignment mark is introduced which, when used in conjunction with a linear Fresnel zone plate on the mask, results in an alignment method with a wide range while retaining the high resolution implicit in the method. This new mark eliminates the need for several separate marks with different alignment ranges and/or accurate prealignment of the mask−wafer system. If a large mark is used, as is needed for the initial alignment in a step and repeat system, a unique point of alignment is determined even if the initial misalignment is as large as the mark, in this case initial misalignment as large as ±1 mm. When it is desirable to occupy less wafer area with alignment marks, the alignment signal can be attained by using a portion of this configuration with a range of ±50 μm. The optimum operating conditions which result from theoretical analysis of this alignment system are discussed, and the results of experiments using this technique are given.
Frequency-sweeping interferometer develops new aspects in pattern generator
Authors: Nishizawa J. , Kasai S. , Aoyama Y. , Fukase M.
Published: July 2002

An attempt was made to develop a new type of laser interferometer which sweeps the oscillation frequency of the laser so as to improve the position control accuracy in microfabrication process. By knowing the wave lengths at which the interference intensity takes the extreme values, the optical path difference between the reference path and the object path was obtained without moving the object. In experiment, one resonator mirror of a He–Ne laser was oscillated by a piezoelectric transducer to oscillate the laser wave length. Four-figures resolution was obtained experimentally.
The use of bias in electron beam lithography for improved profile quality and linewidth control
Authors: Rosenfield M. G. , Neureuther A. R. , Ting C. H.
Published: July 2002

As in optical lithography, the use of a bias, or difference in linewidth between the exposed pattern and developed resist profile, in electron beam lithography will lead to improved resist profile shape quality and linewidth control. Simulation is used to study the key aspects of choosing the proper bias for vertical resist profiles and to illustrate the advantages of using a bias in electron beam lithography. The use of a bias is also shown to aid in proximity correction. The techniques of dose correction, bias and/or exposure position correction, and a combination of bias and dose correction are investigated by means of a comparison of developed resist profile shape quality and linewidth sensitivity.
Optimization techniques for proximity effect compensation
Authors: Carroll Allen M.
Published: July 2002

The most important tool in computing proximity effect compensation for electron-beam lithographic patterns is a powerful and general facility for correcting small subpatterns. In this paper, we propose a solution method for the subpattern correction problem which has significant advantages over the techniques currently in use. The problem is shown to be amenable to the techniques of mathematical optimization. This permits proximity effect compensation to be adapted to the needs of a particular resist, device pattern, process step, or lighographic equipment.
Determination of surface space–charge capacitance using a light probe
Authors: Kamieniecki E.
Published: July 2002

A new technique for the characterization of semiconductors, surface photovoltage measured capacitance (SPMC) is introduced. This technique permits the semiconductor surface space-charge capacitance to be determined by simple measurements of the intrinsic surface photovoltage (ISPV) induced by chopped light. ISPV transients for a semiconductor under depletion conditions are discussed. Both theoretical and experimental results are presented demonstrating the existence of two limiting dependences of the ISPV on the ratio Φ/f (photon flux divided by the chopping frequency of the incident light). It is shown that ISPV induced by low-intensity, high-frequency chopped light is proportional to the reciprocal of the semiconductor surface space-charge capacitance. This dependence is fundamental to the SPMC method whose capabilities are illustrated using GaAs. Using a three-electrode electrochemical cell, the doping concentration, the flat band potential and the energy of surface states which are responsible for the Fermi level pinning have been determined.
Low-temperature chemical vapor deposition of tungsten from tungsten hexacarbonyl
Authors: Vogt Gerald J.
Published: July 2002

Chemical vapor deposition (CVD) of tungsten from W(CO)6 has been investigated below 670 K as an alternate process to WF6 CVD for coating glass microspheres. The major advantages of W(CO)6 CVD are the elimination of the HF damage to the glass microspheres and potentially a lower deposition temperature for coating DT-filled microspheres. W(CO)6 CVD can be utilized, in principle, to coat the microspheres with 1 to 5 μm of tungsten or to flash coat the microspheres for further coating by WF6 CVD. Test coatings were deposited in a fluidized-bed reactor with a hydrogen carrier gas. The coatings were found to contain nearly equal portions of carbon and oxygen, ranging from 16 to 25 at.% for each element. The high carbon and oxygen concentrations are believed to result principally from the physical entrapment of chemisorbed CO molecules at the surface of the growing deposit. The general quality and adhesion of the W(CO)6-derived coatings are unsatisfactory at this time for ICF applications.
Self-consistent calculations in InAs–GaSb heterojunctions
Authors: Bastard G. , Mendez E. E. , Chang L. L. , Esaki L.
Published: July 2002

Self-consistent calculations, in the electric quantum limit, of GaSb–InAs–GaSb heterostructures show the existence of a semiconductor-to-semimetal transition when the InAs thickness exceeds 100 Å, as a result of electron transfer from GaSb. Under the effect of an intense magnetic field a reverse electron transfer leads to a semimetal-to-semiconductor transition which occurs at a thickness-dependent critical field.
Interfacial reactions between Au and hydrogenated amorphous Si
Authors: Tsai C. C. , Nemanich R. J. , Thompson M. J.
Published: July 2002

Solid state reactions at the interface between thin films of Au and hydrogenated amorphous Si are probed by interference enhanced Raman scattering, TEM, scanning Auger microprobe, and Schottky electrical measurements. It is found that crystalline Si islands with a dimension of ∠1 μm grow dendritically after annealing to temperatures above 150 °C. The islands apparently grow laterally due to diffusion of Si through Au. This formation of Si crystallites occurs at a temperature much lower than the normal crystallization temperature of ≳650 °C for the hydrogenated amorphous Si. Through this process the Schottky barrier is not destroyed. A model is proposed to describe the formation process, which includes the low-temperature Si diffusion into Au to form a Au–Si intermixed phase, and the agglomeration of the Au-rich regions.
High resolution trilevel resist
Authors: Namatsu H. , Ozaki Y. , Hirata K.
Published: July 2002

A detailed study of film formation and directional etching for high-resolution trilevel resist was performed. The top layer was CMS and AZ-1350. The intermediate layer was ion beam sputter- deposited SiO2. The bottom layer was AZ-1370. High-temperature baking of the bottom layer prevents crack generation in the SiO2 intermediate layer. Reactive ion etching in O2 gas plamsa with a carbon electrode was used to pattern the bottom layer and gave a residue-free etched surface. A study was made of undercutting during O2 etching with power, temperature, and pressure varied over wide ranges. The results agree with spectroscopic observations of the variation in the ratio of excited neutral species to ionic species in the plasma. Low pressure and low substrate temperature during the bottom layer etching were found to be necessary for a low undercut. The viability of the trilevel resist for submicron patterning was verified.
Laser diagnostics of plasma etching: Measurement of Cl+2 in a chlorine discharge
Authors: Donnelly V. M. , Flamm D. L. , Collins G.
Published: July 2002

Laser-induced fluorescence has been used to determine the relative density of Cl+2 in a chlorine radio frequency discharge as a function of pressure, flow, power, frequency, and distance from the electrodes. The conditions studied correspond closely to those used in anisotropic plasma etching of materials such as Si and InP. This technique provides quantitative data on ion densities over a wide range of parameters, as contrasted with qualitative methods, such as optical emission.
Fast pressure measurements for the TMX-U fusion experiment
Authors: Hunt A. L. , Coffield F. E. , Pickles W. L.
Published: July 2002

The pressure on the boundary of the Lawrence Livermore National Laboratory’s (LLNL) Tandem Mirror Plasma Experiment-Upgrade (TMX-U) is difficult to measure for several reasons: (1) the TMX-U boundary is in the high vacuum range (10−5 to 10−6 Pa) and requires an ionization gauge; (2) the boundary includes high energy neutral particles and radiation, so the gauge must be optically baffled from the plasma; (3) the gauge must be shielded from the magnetic flux density of 0.03 T; (4) maximum conductance to the gauge must be preserved so that the time response remains about 1 ms; (5) a fast electrical circuit is required to measure the small ion current changes at a rate consistent with the geometrical and experimental time constant of 1 ms. We have developed solutions to these limitations, including fast ionization gauge (FIG) circuitry for the remote gauge operation and the CAMAC system for recording the pressure–time history in the TMX-U computer data base. We also give some examples of actual fast pressure histories during plasma operation.
Plasma etching of III-V compound semiconductors
Authors: Donnelly V. M. , Flamm D. L. , Ibbotson D. E.
Published: July 2002

Plasma etching techniques for III-V compound semiconductors are reviewed, emphasizing design considerations in the choice of gases, discharge parameters, and substrate temperature. Mechanisms are proposed for anisotropic, isotropic, and crystallographic chemical etching. Applications of plasma etching in device fabrication are given.
Homogeneous chemical vapor deposition
Authors: Scott B. A. , Olbricht W. L. , Meyerson B. A. , Reimer J. A. , Wolford D. J.
Published: July 2002

In homogeneous chemical vapor deposition (HOMOCVD), reactive radicals are created in a relatively unreactive gas maintained at a much higher temperature than that of the substrate, allowing films to be deposited at low growth temperatures. In this paper, we review the basic aspects of the method and its application to amorphous hydrogenated silicon and germanium growth. HOMOCVD chemistry and reactor dynamics are treated to illustrate the most important parameters of the method, and to examine its potential usefulness in ‘‘low temperature processing.’’ In this context, the connection between HOMOCVD and current silicon CVD growth models is also explored.
Grain structure variation with temperature for evaporated metal films
Authors: Hentzell H. T. G. , Grovenor C. R. M. , Smith D. A.
Published: July 2002

Metallic films are today used in various technological applications. The grain structures of these films influence many properties including the hardness, corrosion resistance, and the electrical conductivity reactivity of thin films in electrical devices. It is therefore important to understand how the films grow and the mechanisms by which grain structures are developed during deposition . In this paper the role of the substrate temperature (Ts) during deposition is the variable that is discussed in the greatest detail. Earlier work has shown that it is possible to classify the structure of the thick films into four characteristic zones which depend on the substrate temperature.