bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle formation during low-pressure chemical vapor deposition from silane and oxygen: Measurement, modeling, and film properties
Authors: Kim T. , Suh S-M. , Girshick S. L. , Zachariah M. R. , McMurry P. H. , Rassel R. M. , Shen Z. , Campbell S. A.
Published: July 2002

Particle generation in thermal chemical vapor deposition (CVD) processes can lead to the formation of contaminant particles that affect film properties and eventually device performance. This article reports on measurements of particle formation during low-pressure CVD of SiO2 from silane and oxygen. Measurements of aerosol size distributions were made using a particle beam mass spectrometer (PBMS) and were carried out at pressures and temperatures ranging from 0.5 to 2.0 Torr (67–267 Pa) and 200–800 °C, using an O2/SiH4 ratio of 20. We found that within this parameter space, there are three different particle formation regions and a particle-free region. The particle formation regions include an explosion region [200–300 °C, P≳1.0 Torr (∼80 Pa)], an unsteady region [400–600 °C, P≳0.8 Torr (∼107 Pa)], and a steady region [700–800 °C, P≳0.6 Torr (∼67 Pa)]. PBMS size analysis in the steady region shows that the size distributions are bimodal with one mode around 7 nm in diameter and the other around 20 nm, which is in reasonable agreement with transmission electron microscopy measurements. A numerical model was developed to simulate particle nucleation and growth in this system. The model predicts that for a given temperature, there exists a critical pressure above which abundant particle formation occurs and below which particle production is insignificant. The pressures for which particle formation was measured with the PBMS are in good agreement with model predictions, and measured and calculated particle sizes are in reasonable agreement. It is also found that there is a correlation between particle concentration and film surface morphology, dielectric constant, and current–voltage characteristics of the film.
Investigation of Sputtered β-Tantalum Thin Films
Authors: Cook H. C.
Published: July 2002

Sputtered β-tantalum thin films were produced in a two-chamber vacuum system (entrance chamber and sputtering chamber) with typical background pressure of 1×10−7 Torr. Both the resistivity and sheet-resistance uniformity were almost entirely dependent on cathode voltage; a sheet resistance uniformity of ±1% over a 3 in. by 4 in. substrate was achieved. The application of negative-anode bias voltage was found to control β-tantalum film resistivity; a 53% reduction in resistivity was caused by a −200-V anode bias voltage applied during a 4-kV cathode sputtering run. A relationship between resistivity and plasma potential was found, which unifies both cathode voltage and anode-bias voltage effects. The electrostatic environment of the substrate appears to control the resulting β-tantalum film properties. Continuous sputtering over a period of several days was required to initially achieve equilibrium conditions in the sputtering chamber. The application of direct-substrate negative bias voltage during cleanup reduced the β-tantalum resistivity and, in some cases, produced a mixed structure of both bcc and β tantalum.
Characterization, Control, and Use of Dielectric Charge Effects in Silicon Technology
Authors: Szedon J. R. , Handy R. M.
Published: July 2002

The charge behavior of dielectric films on silicon is particularly important in device and integrated circuit technology because of surface effects. Models for ionic migration, fixed-interface charge, and injection trapping are reviewed for insulators used in silicon technology: thermally-grown silicon dioxide and chemical vapor-deposited silicon dioxide and silicon nitride. The distinctive characteristics of insulator charge related to these mechanisms are applied in the case of reactively sputtered SiO2 and Ta2O5. Ion migration and injection-trapping behavior are found under certain conditions of preparation for both materials. A degree of interface charge control is indicated in the study of sputtered silicon dioxide. More work is needed to establish the future utility of these materials.
Multicomponent Getter Films for Getter-Ion Pumps
Authors: Hall Lewis D.
Published: July 2002

Since the first commercial application of getter-ion pumping, a single metal, such as titanium, has usually been employed for this purpose. However, data obtained several years ago for bulk gettering, i.e., volume absorption of gases by heated materials, showed considerable increases in gettering rates for certain binary alloy compositions over the rate for either component alone. These results suggest that comparable effects might be observed in getterion pumps. This paper reports the results of experiments on the use of two reactive metals in a sputter-ion pump. Residual gas analyses are given and conclusions stated for titanium-zirconium and certain gases. The data indicate the superiority of two-component films, compared with titanium, for pumping in the milliTorr range. The differences in base pressures and residual gas spectra were minor.
Nucleation Studies Using Electron Transparent NaCl Substrates
Authors: Miller R. F. , Hoffman R. W.
Published: July 2002

A technique has been developed for fabricating NaCl substrates sufficiently thin to be used as transmission substrates for electron microscopy. These small cleavage flakes, a few microns on a side, have been generally found in (100) orientations, and were placed on carbon-coated grids for observation in the microscope. A preliminary study has been made of the observed diffraction contrast features, in relation to the nucleation of gold on the rocksalt surfaces.
Impurity Effects on Heterogeneous Nucleation from the Vapor III—Mercury on Pyrex Glass
Authors: Kinawi Anwar A. , Hudson John B.
Published: July 2002

The thermal accommodation coefficient (TAC) and critical supersaturation for nucleation (αcr) of mercury vapor on Pyrex glass have been studied over a wide range of vapor pressure and temperature conditions for both rigorously outgassed blown Pyrex surfaces, and for the same surfaces contaminated by the adsorption of water vapor or CO. Measurements were made by observing mass spectrometrically the mercury vapor flux leaving a substrate exposed to a flux of mercury atoms from a static vapor at fixed temperature and pressure. By appropriate manipulation of the substrate temperature both the TAC and αcr could be measured at essentially the same time and under identical conditions of vapor pressure, vapor temperature, and substrate contamination. Observed values of the TAC ranged from 0.6 to 1.0 depending on substrate condition. The αcr ranged from sightly more than unity to about seven over the temperature range from 263 °K to 225 °K. Impurity adsorption generally increased αcr, but not greatly. Results are interpreted in terms of the effect of impurity adsorption on the TAC and the substrate-nucleus contact angle.
Nonequilibrium Chemical Reactivity of Polycrystalline Iron Foils
Authors: Gabor T. , Blocher J. M.
Published: July 2002

It is shown that continuous oxide films form on iron specimens in contaminated hydrogen atmospheres in which the metal is the thermodynamically favored phase; the explanation being that (1) oxygen in the gas does not come to equilibrium with the hydrogen but reacts with the iron, (2) the high activation energy of nucleation prevents reduction at the oxide-gas interface, and (3) hydrogen cannot diffuse through the continuous oxide film to the oxide-metal interface. The nonequilibrium nature of the oxidation is demonstrated by the finding that simultaneously with the formation of the continuous oxide films, bulk iron oxides on iron specimens become reduced. Also, reduction of the continuous oxide films proceeds readily when iron nuclei are formed by the addition of small quantities of iron carbonyl to the hydrogen stream.
Partial Pressure Calibration For Residual Gas Analyzers
Authors: Morrison Charles F.
Published: July 2002

The method of reference transfer is applied to the full range partial pressure calibration of residual gas analyzers (RGA). Partial pressures are transferred across the upper orifice of a 10× pressure divider in such a way that a mathematically interrelated series of increasing partial pressures is generated. A gas flow measurement is used to establish the value of the partial pressure when it is in the 10−5 to 10−7 Torr region. For gases not residual to the vacuum system, calibration can begin at pressure levels limited primarily by electronic sensitivity and noise. Independence of RGA peak heights from interference by certain other gases was observed over a wide range of partial pressures of the several gases. Using this same equipment, inert gas fixed leaks were calibrated for just the inert gas components of their effluent.
Magnetic “Ternary Permalloy” Memory Films
Authors: Uno Frank M. , Vieth Robert F.
Published: July 2002

Ternary paramagnetic additions to Permalloy have been used to produce magnetic films with salient modifications of the coercive and anisotropy properties. Films from 4000 Å to 12 000 Å were deposited on glass substrates by application of electron-beam evaporation techniques. Vanadium, Gadolinium, Cobalt, Titanium, and Chromium are shown to be the most advantageous additions for selectively controlling memory characteristics (coercive force, hard axis anisotropy, and dispersion). Nondestructive readout (NDRO) and destructive readout (DRO) memory subsystems have been designed and built using these films in conjunction with a ferrite keeper. The NDRO memory employs an ultralow dispersive read film which utilizes vanadium, and a storage film with high coercivity containing cobalt. The DRO memory eliminates the storage film and operates with a modified read film.
Complex Impedance Characteristics of Low-Resistance Bismuth Films
Authors: Howard Lorn L.
Published: July 2002

A structure-determined electrical impedance in the infrared region between 2 and 15 μ was postulated for thin bismuth films a few years ago and an equivalent circuit was determined for films having initial resistances of 90 Ω/square. The circuit was derived from resistance and infrared transmission measurements. Theory developed subsequently indicated that if reflectance measurements also could be made and if these measurements gave values falling within a certain range, the postulated impedance could be established with certainty. These measurements have been made; the theory and the data are presented. In addition, equivalent circuits are given for films having initial resistance values lying between 34 and 300 Ω/square.
Inverse Pressure Dependence of the Quadrupole Ionization Gauge
Authors: Schwarz Helmut , Tourtellotte H. A.
Published: July 2002

A nonmagnetic ionization gauge has been developed in which electrons are oscillating back and forth along the axis of the tube as in a Penning type ion gauge. The electrons are emitted from a hot hairpin filament at one side of a cylindrical tube and are accelerated by a dc potential of 27 V towards the other end. At the other end there is a disk-shaped electrode which has the same potential as the cathode. This causes the electrons to travel back and forth between the ends until they suffer a collision. A quadruple system serves to keep the electrons from reaching the electrodes and the wall. The system is excited by a rf oscillator of 200 MHz and 165 V peak voltage which is tuned in such a way that only electrons will not deviate from stable trajectories along the center of the tube. A closed screen surrounds the whole electrode structure. It is at a slightly negative potential and serves as the ion collector. Within the pressure range p=10−5 to 10−10 Torr the ion current i follows the relationship pin=c. n was found to be 1.31 ± 0.02 for electron emissions of 10, 50, 100, and 500 μA. The constant c was c=2.88×10−17 for 10 μA, 2.63×10−16 for 50 μA, and in the case of 100 μA it was 5.37×10−15.
Buried Collector Gauge for Measurements in the 10−11 Torr Pressure Range
Authors: Melfi, Leonard T.
Published: July 2002

A nude ionization gauge is described in which a shielded collector is used to lower the x-ray current. Pressures as low as 4×10−12 Torr have been indicated with an estimated x-ray current corresponding to a pressure below 2.6×10−12 Torr. Calibration of the gauge on an orifice flow-rate system in the pressure range between 10−6 and 10−9 Torr with 4-mA emission and a collector to filament voltage of −300 V, yielded a gauge constant of 20 Torr−1. For pressure below 10−9 Torr the buried collector gauge was compared to the bent-beam Helmer gauge. Data from tests performed on the bent beam Helmer gauge are also given. These include a calibration and a plot of gauge constant as a function of emission current in the range between 0.1 and 10 mA.
Fractionation of Antimony Triselenide
Authors: Efstathiou A. , Hoffman D. M. , Levin E. R.
Published: July 2002

Optical density, dark conductivity, and photoconductivity of evaporated antimony triselenide thin films were studied as a function of deposition conditions. The film properties may vary appreciably with both source temperature and time at which the deposition is made. Initial deposits exhibit abnormal bandgap energies, as high as 1.7 eV with a source operated 20 deg below the Sb2Se3 melting point. The bandgap energy decreases monotonically with time during a long evaporation, finally approaching a constant value in the 1.1–1.2 eV range if the boat is maintained at or above the Sb2Se3 melting point (611 °C). The data suggest that initially stoichiometric Sb2Se3 fractionates during the early stages of evaporation, the Se-Sb ratio of the melt decreasing until a composition range producing films with constant bandgap energy is reached. Spectrographic analyses of different fractions from the vapor stream support this explanation.
Influence of the Wall Potential on Pumping Effects in Ionization Gauges
Authors: Konjevic R. , Farrell G. , Grant W. A.
Published: July 2002

The internal wall of a diode tube was held at either a high positive potential or near to zero (cathode) potential. The trapping of positive inert gas ions in this wall was investigated by measuring the rate of gas removal from the tube and, following trapping, by the release of gas during thermal treatment of the tube. The experimental results indicate that the gas trapped during tube operation with the wall at the high potential, is located more deeply within the wall than would be expected from consideration of the energy of the ions striking the wall. An explanation on the basis of the formation of multiply charged ions, before their acceleration into the tube walls, is presented.
Abstract: Low-aberration deflection system for microfabrication
Authors: Owen G. , Nixon W. C.
Published: July 2002

A theoretical design has previously been proposed for a low-aberration magnetic deflection system.1 This has now been translated into practice. Specially shaped interleaved deflection coils have been constructed that give rise to low values of all the aberration coefficients except for distortion and field curvature. The latter aberration is corrected electrically. Since the sole effect of distortion is to destroy the linearity between coil excitation and beam deflection, no correction for this aberration has been incorporated at present. A combined electrical and mechanical centering procedure has been developed and implemented. The deflection system has been tested and found to increase the diameter of an on-axis spot by a maximum of 1.2 μm over a 3×3-mm working field at an angular aperture of 8 mrad. This compares well with the theoretically predicted value of 1.3 μm. The spot diameter has been taken as the 1% to 99% rise distance of the transmitted beam current as the spot was scanned across an edge.

The theoretical work has been extended to show that under certain conditions it is, in principle, possible to eliminate the noncorrectable aberrations completely.
Design of fast deflection coils for an electron-beam microfabrication system
Authors: Amboss K.
Published: July 2002

The design of improved postlens deflection coils for electron-beam microfabrication is described. These coils were made for use in a Cambridge Instrument Co. model S-4 scanning-electron-microscope column. These new coils permit a 0.8-nA 20-kV beam to cover a 2-mm-square scan field with a theoretical resolution of 0.1 μm.
Abstract: Theory of lenslet interactions in a fly’s eye lens
Authors: Harte K. J.
Published: July 2002

In an electron-optical fly’s eye lens, comprised of several parallel plates with arrays of aligned holes, the field at each lenslet is distorted by the fields of the surrounding lenslets. This interaction sets a limit on how closely packed the array can be (or how large the lenslet holes can be for a given spacing) and therefore has a direct bearing on performance. In this paper a method is developed for calculating the effect of the interaction for arbitrary lens geometry.

First, from the symmetry of the environment of each lenslet, Neumann boundary conditions are derived on the bounding polygon between lenslets. These boundary conditions are expanded in a Fourier-perturbation series about the circle which is the zeroth harmonic of the polygon. Laplace’s equation is then solved within the bounding circle for each harmonic to first-order in the perturbation theory, for example by numerical relaxation. Second- and higher-order solutions can be similarly obtained if necessary. From the zeroth Fourier component of the resulting axial potential, Gaussian properties of the lenslet are obtained, along with the spherical aberration coefficient. The next nonvanishing harmonic (fourth for a square array of lenslets, sixth for an hexagonal array) determines a corresponding aberration coefficient, which describes the major effect of lenslet interactions on the focused spot. Higher-order aberration coefficients are calculated from higher-harmonic potentials, if needed.

Finally, as an example, the method is applied to a three-element einzel lens with a square array of lenslets. Fourfold aberrations, which are the dominant interaction effect, are found to be significant if the hole diameter in the center element is greater than about 70% of the lenslet spacing, in rough agreement with experimental results. At this diameter such aberrations amount to roughly one tenth of the spherical aberration.
A contribution to explain the deep penetration of high-power-density electron beams in metals
Authors: Schebesta W.
Published: July 2002

Contrary to the widespread opinion that an electron beam evaporates the material when used as a tool, observations are described which can be explained more satisfactorily with an explosion mechanism. When the electron beam penetrates deeply into the material, regular oscillations of the target current are observed. The main features of these oscillations for various materials are described. These oscillations are explained by intermittent thermionic emissivity and explosions of the energy transfer zone.
Abstract: Controlled-energy micropositioning system for high-vacuum applications
Authors: Wojtaszek M. R. , Hassan J. K. , Haire D. F.
Published: July 2002

The operation of a high-performance positioning system within a high-vacuum environment poses several restraints on configuration and materials selection. To overcome these physical design limitations and reduce their effect on the dynamic performance of the positioning system, a technique for achieving optimum energy usage during stepping has been developed and evaluated. Principles used in developing this technique are reviewed; their application is illustrated through the use of simulation techniques and actual test results. System design requirements, control system configuration, and simulation will be discussed. Dynamic performance and accuracy objectives are emphasized.
Abstract: Fabrication of microelectronic devices with electron-beam lithography
Authors: Ting C. H. , Hatzakis M. , Leone R. A.
Published: July 2002

A variety of semiconductor devices have been fabricated by scanning-electron-beam lithography to demonstrate not only high resolution lithography but also to show that adequate associated processes exist for making properly functioning devices. The resist used was poly-methyl-methacoylate (PMMA) (DuPont, Elvacite 2010) developed in methyl iso-butyl ketone. The devices include npn bipolar transistors with As emitters,1 n- and p-channel MOS FET’s with gate lengths from 1.25 to 7.5 μm,2–4 n-channel ring oscillators with 1-μm gate lengths,5 CMOS ring oscillators with minimum linewidths of 1.25 μm, and a three-phase CCD with 3-μm-long electrodes and 1-μm gaps. By combining state of the art electron optics6,7 with newly developed electron resists, scanning-electron-beam lithography could be an attractive technique for making devices and circuits.
Replication of 0.1-μm geometries with x-ray lithography
Authors: Feder R. , Spiller E. , Topalian J.
Published: July 2002

The effective range of secondary electrons generated by Al Kα radiation is measured in polymethylmethacrylate (PMMA) as 400 Å. Lines with 0.1-μm linewidth with high aspect ratios are successfully replicated with x rays. Problems connected with the replication of very low contrast masks are discussed. Carbon Kα radiation is proposed as the radiation to be used for the replication of very fine geometries around or below 0.1 μm.
Novel microfabrication process
Authors: Faris S. M. , Gustafson T. K.
Published: July 2002

A process for fabricating metallic microstructures having submicron dimensions is discussed. Based on simple electrochemical etching of sputtered metallic strips on substrates, the process is potentially useful for making mechanically stable point-contact devices.
Abstract: Determination of ion-implanted profiles using the MOS capacitance–voltage technique
Authors: Edwards J. R. , Marr G.
Published: July 2002

In this paper, the application of the MOS capacitance–voltage technique for the determination of ion-implanted impurity profiles is described experimentally and theoretically for moderate (1011–1012 ions/cm2) ion implants.

The experimental vehicle was a large-geometry p-channel IGFET (250×250 μm) which was implanted with boron ions at an energy of 120 keV through the gate region (500 Å Al2O3 + 1000 Å SiO2). This results in a doping profile with a peak approximately 1700 Å beneath the Si–SiO2 interface and an effective Debye length the order of 500 Å. Since the application of a gate voltage results in a maximum surface depletion width which is less than the boron profile depth, a reverse bias was applied between the source-drain diffusions and the substrate in order to sweep out the inversion electrons that otherwise would shield the surface electric field. The resulting gate to source-drain capacitance curve in the surface depletion region was used to determine the implanted profile with the Kennedy–O’Brien majority carrier correction factor included. This was also compared to a theoretical Gaussian implant profile based on theoretical values for range and straggle.

To examine the validity of the experimental results, a theoretical study was made using the following method: (1) Assume a Gaussian profile. (2) From the above, calculate the semiconductor capacitance. (3) Use the capacitance to calculate an ’’effective’’ profile. (4) Compare the ’’effective’’ profile with the Gaussian profile. This comparison showed that the measured profile can be determined with resolution substantially less than a Debye length.

Based on this work, it is concluded that the substrate-biased MOS transistor capacitance of an ion-implanted depletion-mode IGFET is a practical method which can be used for process control of the peak of the implant to an accuracy which is better than a Debye length.
Molecular fluxes from a spacecraft measured with quartz microbalances
Authors: Scialdone John J.
Published: July 2002

A technique has been developed to obtain a characterization of the self−generated environment of a spacecraft and its variation with time, angular position, and distance. The density, pressure, outgassing flux, total weight loss, and other important parameters were obtained from data provided by two mass measuring crystal microbalances, mounted back to back, at a distance of 1 m from the spacecraft equivalent surface. The main results from this thermal model of a spacecraft indicate the following: The strongest source appeared to be caused by a material diffusion process which produced a directional density at 1 m distance of about 1.6×1011 molecules cm−3 after 1 h in vacuum and decayed to 1.6×109 molecules cm−3 after 200 h. Self contamination of the spacecraft was equivalent to that which occurs in a 300−km altitude orbit.
Design and synthesis of a neurological electrode
Authors: Martin Patrick Lyle , Bunshah R. F. , Dymond Anthony M.
Published: July 2002

Depth electrodes for implantation in the central nervous system of man are used for basic research and diagnosis of disease. Conventional large electrodes cause damage when used in the brain. Two materials systems and synthesis techniques were chosen for study in an attempt to fabricate an electrode smaller than 150 μm (8 mils). Titanium conductors, with a titanium-dioxide insulator between, were produced in a coaxial configuration using physical vapor deposition (PVD) techniques. The dielectric strength of the oxide and the overall stiffness of the electrode were found to be marginal. Tungsten conductors, with a mixed alumina–silica insulator between them, were produced using chemical vapor deposition (CVD) techniques. The resistivity of the Al2O3⋅SiO2 mixture was found to be approximately 1012 Ω-cm, while its dielectric strength was greater than 105 V/cm. The feasibility of fabrication of the composite electrode was demonstrated but it will require further work to control the variables of the deposition process and the deposit properties.
Preparation of Si3N4 coatings by ion plating
Authors: Chin J. , Elsner N. B.
Published: July 2002

Ion plating experiments have been used to deposit silicon-nitride coatings on n- and p-type 85 Si–15 Mo. The presence of phosphorus in n-type 85 Si–15 Mo (which is doped beyond its solubility limit) influenced the grain size of the deposit. Mass spectrographic analyses of uncoated and coated substrates yielded phosphorus and SiO partial pressures above these substrates when they were held at 1100 °C. All coatings were hyperstoichiometric in silicon relative to Si3N4. Rates of evaporation for these coatings are plotted as a function of time at 1100 °C and 10−9 Torr. Sample weight loss rates were highest in uncoated controls and lowest in Si3N4-coated p-type 85 Si–15 Mo.
Corrugated laser structures
Authors: Katzir A. , Yariv A. , Yen H. W. , Nakamura M. , Aiki K. , Umeda Jun-ichi
Published: July 2002

GaAs–GaAlAs double-heterostructure injection lasers consist of several epilayers of GaAs and GaAlAs grown on a GaAs substrate. The need for cleaved end mirrors may be eliminated in these lasers by incorporating internal periodic corrugation which provide feedback. This distributed feedback relies on Bragg reflection from the periodic perturbation, and thus the lasing wavelength is directly proportional to the corrugation period. Such corrugated laser structures are compatible with the fabrication of monolithic optical circuits and seem to be most suitable as light sources for integrated optics. Our group prepared corrugated structures by ion milling or chemical etching through a photoresist mask which was generated by the interference of two laser beams. We observed laser emission from GaAs–GaAlAs double heterostructures with internal corrugation when pumped electrically at 77 °K. Theoretical considerations indicate that such lasers should have a very low threshold current and a good wavelength selectivity. Further experimental work on these devices is now in progress.
Resistivity of Al metal films at microwave frequencies
Authors: Roberts W. G. , Jennings T. A. , Chen S. T.
Published: July 2002

This paper reports on the resistivity of vacuum-deposited thick films at frequencies ranging from 300 MHz to 1 GHz. The process used to prepare the films is described and the metal film thickness was varied between 5000 and 40 000 Å. The films were prepared in the form of an inductor whose self-resonant frequency approached 2 GHz. The resistivity of the films at a given frequency was determined by a sweep frequency technique. This method permits the measurement of Q and the inductance of coils within the desired range of frequencies.
Influence of hydrogen and water vapor on the oriented growth of copper on muscovite mica
Authors: Reichelt K.
Published: July 2002

The growth of continuous copper films deposited under UHV conditions onto mica substrates was studied. It was found that epitaxial films are only formed if the mica is cleaved in a gaseous atmosphere. The orientation of the films grown under these conditions corresponds to the smallest misfit between copper and mica. Furthermore, it was observed that an adsorption layer of water causes a twist of 30 deg in azimuthal orientation of the copper single-crystal film. This twisted azimuthal orientation is explained by the agreement of the symmetry of the copper monocrystal films with the water layer assumed to be adsorbed in ice structure on the mica substrate. No epitaxial growth was observed on vacuum-cleaved mica.
Secondary−ion mass spectrometry and its use in depth profiling
Authors: Liebl Helmut
Published: July 2002

During the past decade, since commercial instruments have become available, secondary−ion mass spectrometry has been increasingly applied as a very sensitive technique for surface characterization. Depth−concentration profiling has emerged as one of the most important applications, owing to the high−depth resolution obtainable. The intrinsic depth resolution of some 10 Å is degraded by uneven erosion, sample mixing owing to the atomic collisions, and at very low concentration, profiling by the sample consumption required. Quantitative analyses are more difficult than with other techniques, but are feasible. The utilization of chemical signal enhancement by oxygen flooding or oxygen bombardment is very helpful.
Thermal desorption of gases from aluminum alloy Al 6061, their rates and activation energies
Authors: Halama H. J. , Herrera J. C.
Published: July 2002

The use of Al in the construction of the vacuum chamber of intersecting proton storage rings has several advantages over the use of stainless steel. We have, therefore, undertaken UHV studies on long pipes made of Al alloy 6061 to see whether this material could be used in the proposed proton intersecting storage accelerator facility ISABELLE at Brookhaven. The outgassing rates, measured by two different methods, are compared for several surface treatments and three bakeout temperatures. The lowest outgassing rate of less than 1×10−14 Torr l s−1cm−2 was obtained with Ar and O2 discharge cleaning. The residual gas in the pipe contained more than 99% H2 with traces of CO and CO2. By observing the temperature dependence of the desorption of these gases, we have measured the heat of diffusion of H2 (EH2=10.5±1.0 kcal/mole) and the thermal activation energies of CO (ECO=29±2 kcal/mole) and CO2 (ECO2=25±2 kcal/mole). Ar, with a peak desorption at 280°–300 °C, also appears to be embedded in the metal. Since all commercially available UHV equipment uses stainless steel flanges, we have investigated the behavior of the stainless steel to Al transitions up to 350°C.
Survey of low temperature rf plasma polymerization and processing
Authors: Havens M. R. , Biolsi M. E. , Mayhan K. G.
Published: July 2002

Plasma-induced polymerization of both conventional and unconventional monomers has produced materials of unique properties suitable for applications in diverse fields. These fields include permselective and biological membranes, barrier coatings, dielectric layers, antireflection optical coatings, light guides, and adhesive bonding of otherwise incompatable materials. The science behind these applications is developing into predictions of properties based on defined variables but has not resolved some basic questions (such as reaction mechanism or residual activity within the films). Solutions to these problems will expand the applications horizon.
Effects of high temperature and e-beam irradiation on the stability of refractory thin films
Authors: Lee Eal H. , Poppa Helmut
Published: July 2002

Refractory thin films of Al2O3, ZrO2, MgO, ThO2, and BN have been investigated in situ in an UHV transmission electron microscope. The electron transparent refractory films were prepared by e-beam evaporation, anodization, rf sputtering, and thinning of bulk crystal materials. The study concentrates on monitoring the thermal and mechanical stability of the films, phase and structural changes, and electron irradiation effects as a function of film-preparation conditions. With increasing temperatures, five different crystallographic phases were observed for both anodized and e-beam-evaporated alumina films. Zirconia films exhibited two phase transitions upon heating to 1200°C and electron-irradiation-induced crystallization of ZrO2 even at room temperature. MgO, ThO2, and BN films did not undergo any noticeable phase transformation but ruptured due to sintering below 1200°C. In general it was found that crystalline forms of thin films exhibited higher thermal and radiation stability than amorphous films. The results show that the radiation damage is mainly due to beam-induced dissociation and is enhanced in nonstoichiometric materials.
Ion-induced secondary-electron emission from MgO films
Authors: Chou N. J.
Published: July 2002

A pulsed-beam technique has been developed to measure the ion-induced secondary-electron emission from insulating films. The technique, which circumvents conventional specimen heating, consists in determining the target and collector currents in a pulsed ion beam at a varied retarding collector potential, followed by neutralizing the surface change at each pulse interval with a beam of low-energy electrons. Measurements have been made with this technique on MgO films on conductive substrate, using neon and argon ions at 200-eV energy. The secondary-electron yield γi for the electronspectroscopically clean MgO films was found to be 0.45 and 0.05 for Ne+ and Ar+, respectively.
Oxygen sorption and excitonic effects on GaAs surfaces
Authors: Chye P. W. , Pianetta P. , Lindau I. , Spicer W. E.
Published: July 2002

It is now clear that excitations from the Ga-3d core level into the empty surface states are highly excitonic in nature. These transitions can be studied by partial yield or low-energy electron-loss spectroscopy, and in the past their disappearance with oxygen exposure has been attributed to oxygen bonding on surface Ga atoms and destroying the empty surface states. By combining partial yield, ultraviolet photoemission, and soft x-ray photoemission data, it is shown that this disappearance is not due to oxygen bonding on Ga atoms but due to exciton extinction from oxygen-induced changes in the surface electronic structure at very low coverages.
Raman scattering studies of the GaAs native oxide interface
Authors: Cape J. A. , Tennant W. E. , Hale L. G.
Published: July 2002

Oxide films grown by heat treatment on the 100 and 111 faces of GaAs have been studied by Raman backscattering. A spectrum consisting of the bulk LO and TO lines of GaAs and two additional lines labeled R1 and R2 is observed on all samples prepared at temperatures above 435° C. The additional modes are attributed to an interface region of perhaps several hundred angstroms thickness beneath the oxide film. This structure appears to be made unstable by chemical removal of the film. After the film is removed, the spectrum is annealed (returns to that of GaAs) in a matter of weeks at room temperature and in about 1 h at 400° C whether the annealing atmosphere is N2, O2, or forming gas. One of the modes, R2, appears to scatter as a scalar, i.e., a diagonal Raman matrix element. Spectra by the R1 mode on the other hand appear to be largely unpolarized or possibly slightly nondiagonal in character. Some speculations about the possible nature of the interface region are presented.
Convolution and deconvolution in Auger electron spectroscopy with application to silicon
Authors: Onsgaard J. H. , Morgen P. , Creaser R. P.
Published: July 2002

Auger electrons emitted from the valence band in solids carry information on the local density of states in this band in the surface region. The emitted Auger electron intensity distribution is a convolution product of the transition densities of the two valence-band electrons involved in the Auger process in the ionized solid, multiplied with the probability of escape of the outgoing electron. In a first-order approximation the transition density is proportional to the density of states. A comparison between a theoretical, or a directly measured, density of states and Auger spectra must rely on mathematical convolution/deconvolution techniques. Here it is proposed to use spline functions to represent the densities of states to be convolved. This method is unconstrained with respect to form of the density of states. The same representation is used to deconvolve experimental kinetic energy distributions of Auger electrons, in a nonlinear least-squares fitting of a convolution square of a trial density-of-states function. As an example, the Auger spectrum of Si is considered and compared with a calculated density of states.
Field electron emission from dense array of microneedles of tungsten
Authors: Okuyama F. , Aoyagi M. , Kitai T. , Ishikawa K.
Published: July 2002

Characteristics of field electron emission from the dense array of microneedles of tungsten prepared on a 10-μm tungsten filament were measured at an environmental pressure of ∠1×10−8 Torr (1.33×10−6 Pa). Electron emission was not uniform over the filament surface, but the variation of emission current with applied voltage explicitly obeyed the Fowler–Nordheim relationship. At an emission current of ∠10−4 A, a vacuum arc was induced that led to a permanent change in current–voltage characteristic. Current fluctuation was dependent on emitter temperature and applied voltage, and the lowest fluctuation of about 4% was routinely obtained at ∠550 K and at applied voltages several percent lower than the arc-inducing voltage. Macroscopic current density amounted to ∠20–80 mA/cm2 at the best stability.
Absorption coefficient measurements for vacuum-deposited Cu-ternary thin films
Authors: Sun L. Y. , Kazmerski L. L. , Clark A. H. , Ireland P. J. , Morton D. W.
Published: July 2002

The absorption coefficients, α, of polycrystalline CuInS2 and CuInSe2 thin films have been determined at room temperature using transmission measurements. For each of these semiconductors, an absorption edge corresponding to the direct band-gapl transition (1.54±0.02 eV for CuInS2 and 1.00±0.02 eV for CuInSe2) is observed in the α vs hν spectrum. In p-type CuInS2 thin films, another edge is evident at lower energies (1.41×1.42 eV) and is attributed to transitions from a copper vacancy band to the conduction band. The effects of annealing on the absorption coefficient spectra of these chalcopyrite materials are presented. An additional absorption region, appears in the CuInSe2 spectra at higher energies (hν∠1.28 eV), and is critically dependent on the Se concentration of the films. This effect is discussed in terms of band structure, film stoichiometry and structural characteristics of the films.
Ultraviolet photoelectron spectroscopy investigation of the interaction of Te with Zn (0001)
Authors: Abbati I. , Braicovich L. , Ciucci G. , Perfetti P.
Published: July 2002

We give photoelectron spectroscopy results (hν?21.2 eV) on 1/4 and 1 Te monolayers deposited onto the (0001) Zn face. It is shown that a surface compound is formed whose density of states shows an increasing similarity to that of bulk amorphous ZnTe when the Te coverage increases. No ordered structures due to Te deposition have been detected with LEED.
Identification of S and S2− states from Auger line shapes
Authors: Losch Wolfgang
Published: July 2002

Experimental results of sulfur line shape variations observed from various metal–sulfur compounds (Cu5FeS4, Cu2S, FeS) show that Auger fine structure analysis is able to separate chemical states of sulfur. Atomic sulfur presents a single Auger line at 149 eV whereas sulfur in the S2− oxidation state is characterized by a peak at 147 eV.
Rate controlling and composition analysis of Si/Al–Si processes by electron impact emission spectroscopy (EIES)
Authors: Gogol C. A.
Published: July 2002

The technique of electron impact emission spectroscopy (EIES) has been used to control the rate of silicon evaporation in both sequential and codeposition processes with aluminum. The evaporant flux is allowed to pass through a sensor where it is excited by electron bombardment. The specific emission line for each component is selected either with a narrow band optical filter, or a monochromator. Experimental results on these systems show the technique to have sufficient sensitivity and selectivity to control Si and low percentage Si alloys.
Wall conditioning by low power discharge in the ISX-A tokamak
Authors: Gomaya) Y. , Clausing R. E. , Colchin R. J. , Emerson L. C. , Heatherly L. , Namkung W. , Simpkins J. E.
Published: July 2002

The effects of low power discharge cleaning (Te=9–18 eV, ne=1010–1011 cm−3) on wall conditions in the ISX-A tokamak have been studied in detail by means of Auger electron spectroscopy and residual gas analysis. It was found that discharge cleaning caused very little transport of metals and reduced the surface oxygen content on stainless steel samples located between the limiter and the wall to substoichiometric levels. This oxygen was probably removed from the samples as H2O molecules. On the other hand carbon, in the form of a metallic carbide, increased during discharge cleaning. The cleanliness of tokamak plasmas (Zeff=1.6–2) obtained after about three weeks of discharge cleaning was clearly correlated with improvements in the wall conditions and with the reduced level of residual gas species.
Molecular wake shields of various shapes
Authors: Moore B. C.
Published: July 2002

A satellite in orbit is moving at a much higher velocity than most of the ambient molecules, so that it leaves a wake swept nearly free of gas. A concave shield with a large opening into this wake can thus contain a region of low pressure for experiments and provide a high speed pump for experiment outgassing. Potential experiments in this environment include the production of ultrapure materials and deposition of thin films. It is possible to set bounds on the flux density within a wake shield relative to the externally incident flux density on the shield opening. The upper bound of this ratio, for an aft-facing shield, is simply 1.0, corresponding to a Maxwellian incident flux. The lower bound for a hemispherical shield is 0.5, when the incident flux is all concentrated on the edge around the opening. The lower bound for cylinders of various L/R ratios with the same edge concentration is also very near 0.5. The total flux on a hemisphere from an internal isotropic point source is 1.0 to 1.5 times the flux leaving the point, depending on its location.
Alternating and direct current ion pumping up to 30 kV
Authors: Ames Elizabeth E. , Graneau Peter , Silevitch M. B.
Published: July 2002

The ion pumping characteristics of high voltage 60 Hz ac and dc crossed field discharges, using permanent magnets, are compared. Vacuum insulation, it is suggested, becomes a low cost alternative to permanently sealed equipment.(AIP)
New hybrid (e-beam/x-ray) exposure technique for high aspect ratio microstructure fabrication
Authors: Hatzakis M. , Hofer D. , Chang T. H. P.
Published: July 2002

A new lithographic technique will be described in this paper which makes it possible to increase the height-to-width (aspect) ratio of electron-beam-exposed patterns in the resist layer, without significantly increasing proximity effects. The technique consists of applying two resist layers on the substrate, separated by a thin metal film. The pattern is electron-beam exposed on the top resist layer, and after development, a thin (2000–3000 Å) gold or other x-ray absorbing material is used to form an in situ x-ray mask to expose a much thicker bottom resist layer in an x-ray exposure system. It is shown that with this technique, lines of 0.25-μm wide with vertical walls, can be obtained in 2-μm-thick PMMA resist or an aspect ratio of eight can be easily achieved. It is also shown that the in situ mask can be registered to a previous level on the workpiece with accuracy better than 0.1 μm.
UHV compatible chopper system
Authors: Voss Donald E. , Cohen Samuel A.
Published: July 2002

A time-of-flight system utilizing a novel mechanical chopper has been developed to measure the energy spectrum of neutral deuterium atoms emitted from a tokamak plasma. The chopper system consists of a motor, a magnetically levitated shaft, and a chopper disk. The disk is rigidly attached to a 159 g shaft assembly and the set is supported against gravity in vacuum by permanent magnets and a stabilizing servosystem (patented by Cambridge Thermionic Corp., Cambridge, MA). All components are UHV compatible to avoid contamination to the tokamak and to the electron multiplier detector. The 25.4-cm-o.d., 0.005-cm-thick, 20 g, 301 stainless-steel chopper disk has 24 0.025-cm-wide slots photoetched at an 11.4-cm radius. An effective aperture time of 0.55 μs is achieved during typical steady-state operation at 22500 rpm with a vacuum pressure of 2×10−8 Torr.
A safer procedure to handle semiconductor devices in SEM examination
Authors: Lavallée P.
Published: July 2002

Procedures are described to avoid breakdown of semiconductor devices during SEM examination as a result of gas discharges. (AIP)
Intrinsic and extrinsic interface states at lattice matched interfaces between III–V compound semiconductors: The InAs/GaSb(110) system
Authors: Madhukar A. , Sarma S. Das
Published: July 2002

In this paper we report the first results on band gap levels associated with cation and anion vacancies at lattice matched III–V compound semiconductor interfaces. These results are contrasted with the absence of intrinsic interface states found in earlier studies of these systems. Specific results for such vacancies in bulk GaSb and InAs and in the GaSb–InAs(110) thin superlattice are reported. The behavior of both the cation and anion vacancy induced levels at the interface is significantly different from the corresponding behavior in the bulk. A study of the influence of the interface geometry on the vacancy induced levels is presented. Such effects, it is found, can be quite significant.