bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent tests of negative electron affinity photocathodes as source for electron lithography and microscopy
Authors: Arcuni P. , Presley S. , Aebi V. , Spicer W. E.
Published: July 2002

We report recent results from tests of laser driven and modulated negative electron affinity photocathodes as high-brightness electron sources. Preliminary tests used an electron column that could image the cathode surface with a resolution of less than 100 nm. We measured a current density of 2.4(±0.2) A/cm2 from an emission area with a diameter [full width at half maximum (FWHM)] of 3.5 μm. However, unwanted field emission in the gun (aided by the presence of Cs) limited the extraction field to about 1 kV/mm and negatively affected quantum efficiency and emission stability. A curve fit of the source angle with accelerating voltage gave a typical transverse energy spread of 44(±2) meV, for an extrapolated brightness at 50 kV of 1.7×106 (±0.2) A/cm2 sr. Indications that space charge above the flat cathode limited the current density are presented; a possible model is discussed. The electron gun has been redesigned for electric fields up to 7 kV/mm (where space-charge effects are unlikely) with no field emission. Lack of access to an imaging column has prevented subsequent measurements of current density and brightness. In a nonimaging column an emission current of 200(±0.4) nA, from a single emission area, has been maintained for more than a week, with no reapplication of cesium. As with other photocathodes, variations of quantum efficiency after sudden changes in illumination intensity are usually present. We suggest that competing effects of Cs mobility and electron trapping explain this behavior. Transverse energy spreads (FWHM) have been studied as a function of extracted current; 20(±5) meV at small currents (<10 nA) and 70 meV at large currents (700 nA), both from an illumination area of less than 2 μm diameter, are typical.
Simulation of time-dependent charging of resist on Si under electron-beam irradiation
Authors: Kotera Masatoshi
Published: July 2002

The time-dependent charging mechanism of an electrically insulating resist film on a Si substrate under electron-beam irradiation is proposed based on results obtained by a numerical simulation. The primary electron trajectory and the secondary electron cascade multiplication in the resist are calculated by Monte Carlo simulation, and spatial distributions of the electron deposition and the energy deposition in the resist are obtained. The potential distribution in and above the resist is obtained by solving the Poisson equation. The electron trajectory bending due to the electric field is calculated. The electron-beam-induced conduction is calculated based on the energy deposited. The potential distributions obtained in the resist show quite good agreement with the experimental results.
Band offsets of AlxGa1−xSbAs/InGaAs heterojunctions
Authors: Cai W. Z. , Miller D. L.
Published: July 2002

By applying van de Walle and Martin’s model solid theory (MST), we have investigated the compositional dependence of the band-edge alignment at the AlxGa1−xSbAs/InGaAs and AlxGa1−xSbAs/InAlAs heterointerfaces lattice-matched to InP. A comparison between theoretical calculations and previously published experimental values on ternary extremes of AlxGa1−xSbAs yields a discrepancy of 0.1–0.2 eV for GaSbAs/InAlAs and GaSbAs/InGaAs, and 0.3 eV for AlSbAs/InAlAs and AlSbAs/InGaAs. For all four heterostructures, it has been found that the MST results shift the valence band edge of the (Sb, As) alloy downward relative to that of InAlAs and InGaAs as compared to experimental data, and possible causes of the disagreement are analyzed. Furthermore, the band offset values have been obtained from a current–voltage measurement on InGaAs/AlxGa1−xSbAs/InGaAs semiconductor–insulator–semiconductor diodes. The carrier transport mechanism in these diodes is discussed and the measured offset values are shown to be in qualitative agreement with the MST predictions.
Dry etch process optimization for small-areaa-Si:H vertical thin film transistor
Authors: Chan I. , Nathan A.
Published: July 2002

This article reports the investigation of dry etch processes suitable for small-area amorphous silicon (a-Si:H) vertical thin film transistor (VTFT) fabrication. SF6/O2 and CF4/H2 gas mixtures were experimented on for the anisotropic etching of an n+a-Si:H/a-SiNx:H/n+a-Si:H trilayer to give a self-aligned vertical drain–source stacked structure that is desirable for subsequent deposition of the VTFT channel layers. The results show that the trilayer profiles formed with the SF6/O2 plasma for different O2 concentrations suffered different degrees of undercutting of the composite layers under overetching condition, leading to misaligned etch profiles. On the other hand, the CF4/20%H2 plasma provides a self-aligned vertical trilayer profile even after 1 min of overetching.
Simulation and dielectric characterization of reactive dc magnetron cosputtered (Ta2O5)1−x(TiO2)x thin films
Authors: Westlinder J. , Zhang Y. , Engelmark F. , Possnert G. , Blom H.-O. , Olsson J. , Berg S.
Published: July 2002

New capacitor material with high dielectric constant is needed for future integrated capacitor structures. Tantalum pentoxide (Ta2O5) is considered as one of the most promising candidates. In this article, thin films of (Ta2O5)1−x(TiO2)x were grown utilizing reactive dc magnetron cosputtering of tantalum and titanium in an argon/oxygen atmosphere. By varying the input power at the targets, the composition of the thin film is easily controlled. The composition of the films was analyzed with elastic recoil detection analysis revealing the titanium oxide content (x ranging from 0 to 0.40). The presented results indicate that reactive sputter deposited tantalum pentoxide, with or without the addition of titanium, exhibits the properties required to meet the demands for future dielectric materials in integrated capacitors. The dielectric constant for metal-insulator-semiconductor structures is about 20 and the leakage current density is below 10 nA/cm2 at 0.5 MV/cm, if the annealing temperature does not exceed 600 °C. Annealing at 800 °C leads to ∼50% increase in dielectric constant with a cost of a severe increase in leakage current.
Diffusion Pump Oil Deposition Measurements Utilizing Radioactive Tracers
Authors: Carter J. G. , Elder J. A. , Birkhoff R. D. , Roecklein A. K.
Published: July 2002

A radioactive tracer technique is proposed as a quick, simple, nondestructive method for measuring the deposition of diffusion pump oil and as a possible means of evaluating the efficiency of vacuum components. A simple bell jar vacuum system was assembled consisting of a 4-in. oil diffusion pump, a multicoolant baffle, a 4-in. gate valve, and a bell jar with associated gauges. Ten milliliters of Dow Corning 704 oil were irradiated in the low intensity test reactor at ORNL for 2.6 h. The Si1430, comprising 0.54% by weight of the oil, becomes activated to Si1431. The system utilizing various baffle coolants, was operated for certain time intervals. The results indicate the presence of an initial backstreaming surge and also show the relative effectiveness of air-, water-, and liquid-nitrogen-cooled baffles. Deposition rates of a few Å/h were measured.
Combustion of Diffusion-Pump Fluids in Oxygen Atmospheres
Authors: Solbrig C. W. , Jamison W. E.
Published: July 2002

The use of oxygen as an emergency pressurizing and life-support gas in man-rated space chambers presents a combustion hazard with oil diffusion pumped systems. This study determined the ignition characteristics of five commonly used pump fluids in pure oxygen atmospheres at low pressures in combustion-bomb experiments. The results were verified in tests in diffusion pumped systems. Spontaneous ignition studies were conducted with DC-705, DC-704, Convalex 10, Convoil 20, and tricresyl phosphate in the temperature range 600 ° to 900 °F at pressures from 0.01 to 400 Torr, and concentrations from fuel rich to fuel lean. Verification tests were conducted with DC-705, DC-704, and Convalex 10 in a 6-in. diffusion-pumped system by pressurizing the system to 8 psia with pure oxygen and observing for spontaneous and spark initiated combustion. Additional verification tests with DC-705 and DC-704 were conducted in a 35-in. diffusion pump.
Calibration of Low Pressure Penning Discharge Type Gauges
Authors: Lange W. J. , Singleton J. H. , Eriksen D. P.
Published: July 2002

Two cold cathode discharge gauges have been calibrated from 10−4 to 10−12 Torr for argon and hydrogen and to 10−10 Torr for helium, nitrogen, and carbon monoxide. With minor exceptions the sensitivity decreases with pressure; for example, the sensitivity for argon for one gauge was ∼3.5 A/Torr at 10−4 Torr, ∼1.5 A/Torr at 10−10 Torr, and ∼0.1 A/Torr at 10−12 Torr. The calibration may be represented by a series of linear segments which probably correspond to stable discharge modes in the gauge. In addition, overlap of stable modes occurs and hence the accuracy of pressure measurement is difficult to predict even with a detailed calibration of a specific gauge.
Pumping Speeds of Getter-Ion Pumps at Low Pressures
Authors: Dallos Andras , Steinrisser Fortunat
Published: July 2002

Pumping speeds of commercial diode and triode type getter-ion pumps were measured for the gases H2, He, and N2 over the pressure range from below 10−10 Torr to 10−6 Torr. At 10−10 Torr, the pumping speed was about 20% of the speed at 10−6 Torr, where the pumps attained approximately the rated speed. Pumping speed measurements as a function of time showed that the pumping speed decreased generally less than 25% over a period of one day. Strong saturation was found only for He at pressures above 10−7 Torr. No significant differences between diode and triode in the pumping speed vs time or pressure curves were observed. In the diode, pump currents were measured. The quantity P·S/I was found to be pressure independent for short pumping times. The numbers (in molecules or atoms pumped per charge) are: 0.5 (H2), 0.6 (He), and 0.2 (N2).
Surface Smoothness in Thermal Transpiration at Very Low Pressures
Authors: Hobson J. P.
Published: July 2002

The thermal transpiration ratio for helium has been measured by the absolute method with a leached pyrex tube joining the cold and hot regions. Cold temperature was T1=77.4 °K, hot temperature T2=295 °K, pressure range 10−7 to 100 Torr. The results agreed closely with those obtained when an aperture joined the cold and hot regions. In particular, the ideal limiting law P1/P2=(T1/T2)1/2 was found at very low pressures, P1 and P2 being the pressures at T1 and T2 respectively. This result is in contrast to that found with smooth Pyrex tubes where unpredictable deviations from the ideal law were found. It is concluded that leaching the surface produces atomic roughness which forces all reflections to be cosine reflections, leading to the ideal law. The use of a leached tube permits precise thermal transpiration corrections in simple glass apparatus. The glass was leached for 100 h at 100 °C in 0.05 N HCl.
Observations of Reactions in Solids and Formation of Surface Layers with the Emission Electron Microscope
Authors: Zaminer Ch. , Graber R. , Wegmann L.
Published: July 2002

In an emission electron microscope the grain growth of a tungsten wire and the reaction with oxygen and hydrocarbons at high temperatures are observed using thermionic emission. Below the thermionic temperature range the reaction between evaporation layers of thin films was studied with photoemission micrographs.
Synthesis of dispersion-strengthened alloys by the activated reactive evaporation process from a single rod-fed electron beam source
Authors: Nimmagadda R. , Bunshah R. F.
Published: July 2002

Oxide-dispersion-strengthened alloys have better high-temperature properties but poorer low-temperature strength compared to Ni-base super alloys. Relative to these alloys, dispersion-strengthened alloys of titanium carbide dispersed in a Ni-base alloy matrix have been found to have good low- as well as high-temperature strength. This investigation was concerned with the synthesis of dispersion-strengthened alloys of TiC particles in a Ni matrix using the activated reactive evaporation (ARE) process. A Ni–Ti alloy rod was evaporated from an electron beam source in the presence of C2H2, all of the vapor species being activated or partially ionized using the ARE process. The deposits were characterized by x-ray diffraction, electron microprobe analysis, microhardness, and transmission electron miscroscopy of carbon replicas. It was established that Ni–TiC dispersion-strengthened alloys were produced by ARE process. The microhardness of the alloys decreased when annealed at high temperatures due to particle coarsening.
Technology of low-pressure systems−establishment of optimum conditions to obtain low degassing rates on 316 L stainless steel by heat treatments
Authors: Nuvolone R.
Published: July 2002

Heat treatment procedures for obtaining reproducible low degassing rates in 316L stainless steel high vacuum systems are presented and evaluated. (AIP)
Study of ESD from type 304 stainless steel in relation to CTR first wall applications
Authors: Drinkwine M. J. , Lichtman D.
Published: July 2002

Electron stimulated desorption (ESD) of adsorbed species from type 304 stainless steel (S.S.) was studied, primarily from the standpoint of controlled thermonuclear fusion reactor ’’first wall’’ applications. H+ and F+ were, by far, the most predominant ESD ion species observed from ’’as is’’ S.S. surfaces. O+, Cl+, and other ESD ions were also observed, but normally in much smaller quantities. The origin of the ESD ion signals are attributed to adsorbed H2 and/or H2O for ESD of H+, and fluorocarbon and/or alkali halide contaminants in the case of ESD of F+. Little or no temperature effects on the H+ and F+ ESD ion signals were observed over the S.S. sample temperature range from 23° to ∠450°C. The total cross section for ESD of hydrogen was found to be ∠10−16 cm2 while that for ESD of fluorine was found to be ∠10−17 cm2. The ion energy distributions of both H+ and F+ ions were obtained and no observable changes were found over the bombarding electron energy range 300–4000 eV. The total cross section for ESD of hydrogen from S.S. was investigated as a function of bombarding electron energy over the energy range 200–4000 eV. Relative cross sections for ESD of H+ and F+ were investigated over the bombarding electron energy range 50–6000 eV. The cross-section behavior for ESD vs electron energy was found to be very similar to the behavior for electron–gas-phase molecule interaction cross sections vs electron energy. The ESD cross-section maximum was observed to occur at an electron energy of several hundred eV. Above this energy the cross section slowly decreased with increasing electron energy. The observed behavior of ESD cross section vs electron energy is attributed to the interaction of both primary and secondary electrons with the surface adsorbates.
Synthesis and physical properties of superconducting compound films formed by the electron-beam codeposition of the elements
Authors: Hammond R. H.
Published: July 2002

Electron-beam codeposition of the elements to form certain high critical temperature superconducting materials, in particular A-15 compounds, has proven to be very useful in research directed at understanding and improving their superconducting properties. This work has used the close control of three or more evaporant sources to reproducibly make specimens that permit studies across selected regions of composition and phase space. The effect of composition and phase, together with the temperature and rate of deposition, on the growth morphology and superconducting properties has been studied. The superconducting properties measured include the critical temperature, ac loss, critical current density, and tunnel junction characteristics. The particular compounds studied include Nb3Sn, Nb3Ge, and V3Si.
Large-scale sputtering of indium–tin oxide
Authors: Gillery F. Howard
Published: July 2002

The development of a reactive dc diode sputtering system for the deposition of indium oxide coatings by scanning large substrates will be described. Coatings of 5 Ω/sq, with 86% light transmission, having a specific resistivity of less than 2.5×10−4Ω cm are routinely produced on curved and flat substrates up to 5 ft2. Effects particularly noticeable in large sputtering systems, such as secondary electron emission, plasma focusing, imperfections due to cathode nonuniformity, arcing caused by cathode contamination, and substrate temperature gradients, will be emphasized.
Molecular-beam apparatus for the study of gas–surface interactions
Authors: Cardillo M. J. , Ching C. S. Y. , Greene E. F. , Becker G. E.
Published: July 2002

An ultrahigh vacuum apparatus has been developed to study the dynamics of gas–surface interactions utilizing modulated supersonic molecular-beam techniques, angle-resolved mass spectrometry, Auger electron spectroscopy, and low-energy electron diffraction. Nearly monoenergetic beams of atoms and molecules in the form of narrow pulses or square waves are sent with a variable incident angle at a crystal. The wave forms of the scattered species or reaction products are monitored as a function of desorption or reflection angle. The initial experiments have examined the scattering of atoms and simple molecules from a Pt(111) surface. The results are in the form of angular and time-of-flight distributions for a range of incident beam energies, angles, and crystal temperatures.
Oxygen uptake on epitaxial PbTe(111) surfaces
Authors: Sun T. S. , Byer N. E. , Chen J. M.
Published: July 2002

The uptake of oxygen on Ar+-cleaned (111) surfaces of PbTe epitaxial films was studied by means of UPS and XPS. Two distinct stages of uptake process were observed and they were separated by a phaselike change at an exposure of 105 L. The first stage, characteristic of an adsorption process, has a high oxygen uptake rate. In this stage, weak bonding between oxygen and the substrate is suggested by the observation of the relatively narrow linewidth of the Pb 5d5/2 core level. The most important feature, however, is the lowering of the Fermi level with oxygen coverage, which confirms the band bending model developed by previous studies, based on electrical measurements. The second stage, characteristic of an oxidation process, has a lower uptake rate. Strong bonds between oxygen and individual Pb and Te ions appear to prevail in this stage, as is evident from the broadening of the Pb 5d5/2 level and the appearance of the Te oxide species in the XPS spectra. The Fermi level stops lowering and in fact rises slightly at high oxygen coverages.
Design and optimization of directly heated LaB6 cathode assemblies for electron-beam instruments
Authors: Schmidt P. H. , Longinotti L. D. , Joy D. C. , Ferris S. D. , Leamy H. J. , Fisk Z.
Published: July 2002

A description is given of the design and testing of a directly heated, stable, electron source utilizing a single-crystal lanthanum hexaboride (LaB6) cathode. The emitter mounting fixture consists of an adjustable molybdenum base unit supported on gas-impervious alumina or machinable glass. Single-crystal cathode rods are securely clamped and positioned between vitreous carbon jaws that are resistively heated. The complete assembly is designed to be a direct ’’plug-in’’ substitute for the conventional tungsten thermionic filaments used in electron-beam instruments. The cathode current density for 〈110〉 axial orientations is found to be ten times higher than that for 〈100〉 orientations under equivalent conditions, a value of 50 A cm−2 being measured at 1500°C with an observed lifetime in excess of 300 h. Optimum vacuum conditions for high lifetime and stable operation are in the range 1×10−6 Torr and lower. Comparison values for the emission at various temperatures from other borides, and tungsten, are also given.
Kinetics data for diffusion of outgassing species from RTV 560 silicone rubber
Authors: Liu C. K. , Glassford A. P. M.
Published: July 2002

A detailed analytical and experimental study has been made of the outgassing behavior of RTV 560 silicone rubber. Outgassing rate measurements were made by collection of outgassed species on a cooled quartz crystal microbalance (QCM). The four outgassing species which predominate in the temperature range of 285 to 425 K have been separately identified. The initial concentration of these species in the parent material has been determined, while the diffusion coefficients and activation energy for diffusion of the two major species have been deduced from outgassing rate data. It is shown that using these data in a diffusion theory model, the outgassing rates of these major species can be predicted for arbitrary sample thickness, and for any temperature within the range studied.
Turbomolecular pumps for high gas flow applications
Authors: O’Hanlon J. F.
Published: July 2002

Turbomolecular pumps used for maintaining a sputtering chamber in the 0.5–10 Pa region must be able to pump a large flow of gas as well as be able to exhaust the system to a suitable base pressure. This paper discusses the effects of turbomolecular-to-forepump speed ratio, or staging ratio, and the rotational velocity on the pumping performance in both the high-vacuum and high-gas-flow regions. It concludes that pumps having a low compression ratio for hydrogen require a low staging ratio, as low as 20:1, to maintain high hydrogen pumping speed in the high-vacuum region, and that the light gas compression ratio is increased in the presence of flowing argon. The favorable economic advantage of the turbomolecular pump relative to the diffusion pump and the cryogenic pump is discussed.
Preferential sputtering of Ta2O5 by argon ions
Authors: Holloway P. H. , Nelson G. C.
Published: July 2002

X-ray photoelectron spectroscopy has been used to show that Ar+ preferentially sputters O from the surface to Ta2O5. In addition, x-ray photoelectron, Auger electron, ion scattering, and secondary ion mass spectroscopies were used to show that more reduction of Ta2O5 is caused by 0.5 keV Ar+ than by 5 keV Ar+. This dependence of preferred sputtering upon energy is attributed to changes in the sputtering mechanisms.
Oxidation of ordered and disordered GaAs(110)
Authors: Chye P. W. , Su C. Y. , Lindau I. , Skeath Perry , Spicer W. E.
Published: July 2002

The adsorption of nonexcited molecular oxygen on ordered and disordered(110) surfaces of GaAs was studied using photoemission techniques. On the ordered surface, only one chemically shifted level was observed for the As3d core level up to 1013 exposure. The Ga3d core level exhibits an asymmetrical broadening towards higher binding energy for the same exposure, indicating the presence of a shifted component. The percentages of shifted Ga and shifted As appear to be about equal. However, when a sputtered (disordered) surface was exposed to oxygen, there was preferential adsorption on the Ga. Implications of these data are discussed.
Local atomic and electronic structure of oxide/GaAs and SiO2/Si interfaces using high-resolution XPS
Authors: Grunthaner F. J. , Grunthaner P. J. , Vasquez R. P. , Lewis B. F. , Maserjian J. , Madhukar A.
Published: July 2002

The chemical structures of thin SiO2 films, thin native oxides of GaAs (20–30 Å), and the respective oxide–semiconductor interfaces, have been investigated using high-resolution x-ray photoelectron spectroscopy. Depth profiles of these structures have been obtained using both argon ion bombardment and wet chemical etching techniques. The chemical destruction induced by the ion profiling method is shown by direct comparison of these methods for identical samples. Fourier transform data-reduction methods based on linear prediction with maximum entropy constraints are used to analyze the discrete structure in oxides and substrates. This discrete structure is interpreted by means of a structure-induced charge-transfer model (SICT).
Magnitude of the atom shielding effect of oxygen in ion scattering spectrometry of magnesium silicate (forsterite)
Authors: McCune R. C.
Published: July 2002

Ion scattering spectrometry (ISS) of the compounds magnesium silicide (Mg2Si) and forsterite (Mg2SiO4) yields as much as a fivefold difference in the Si/Mg ratios as measured from spectral intensities. The relative attenuation of ion scattering from silicon in forsterite is explained in terms of an oxygen shielding model in which silicon is more effectively shielded in the oxygen matrix than is magnesium. By reacting the surface of Mg2Si with oxygen it was possible to show a variation in the Si/Mg ratio of from 0.56 in the clean condition to 0.24 in an oxidized condition. The shielding susceptibility model is used to explain the effect of fluorine contamination on the appearance of ISS spectra for MgAl2O4 (spinel).
Importance of the interface in noncrystalline (poly and amorphous) conductor–insulator–semiconductor (CIS) solar cells
Authors: Singh R. , Rajkanan K.
Published: July 2002

In recent years a new class of photovoltaic device, namely the conductor–insulator–semiconductor (CIS) solar cell, has emerged. The top layer in these devices may be a transparent metal film, oxide-semiconductor or a combination of them leading to a wide variety of metal-insulator-semiconductor (MIS) and semiconductor–insulator–semiconductor (SIS) solar cells. Due to improved understanding of the interface between the top layer and the single crystal base semiconductor, efficiencies above 17% have been realized in these structures. However, CIS-type solar cells made on nonrecrystallized poly and amorphous semiconductors are usually of low efficiency. In this paper we show that the native grown oxide may not be capable of forming a good interface and deposited dielectrics are required for noncrystalline CIS solar cells. We present the criteria for selecting the insulating layer.
Oxidation properties of II–VI compound surfaces studied by low-energy electron-loss spectroscopy and 21 eV photoemission spectroscopy
Authors: Ebina A. , Asano K. , Suda Y. , Takahaski T.
Published: July 2002

Oxidation properties of ZnSe, ZnTe, CdSe, and CdTe surfaces were studied. The following combinations of experimental techniques were used: electron-energy-loss spectroscopy on vacuum-cleaved ZnSe(110) surfaces and on Ar+ bombarded-annealed surfaces of ZnSe, ZnTe, CdSe, and CdTe. Photoemission spectroscopy also was used on a vacuum cleaved ZnTe(110) surface. The oxygen uptake is very slow with exposures to molecular oxygen. Thus oxide overlayers were prepared by an electron-beam irradiation technique which greatly enhanced the oxygen uptakes. Changes in loss spectrum detected on oxidation of CdTe can be explained by formation of TeO2. For the case of ZnTe, the shifted Te 4d loss due to TeO2 appears at the oxygen coverage, ϑ, of about 0.5 of a monolayer, and losses characterizing formation of ZnO are seen at ϑ≳1. The oxide overlayer on ZnTe is composed of TeO2 and ZnO and, in addition, an unidentified complex oxide for the heavily oxidized surface. On further oxygen exposures and beam irridation of this oxide, tellurium oxides sublime away from the surface, leaving an oxide layer rich in ZnO. In the case of the Se compounds, the oxygen adsorbs on the surface Se atoms without breaking the back bonds at the initial stages of oxidation (ϑ≳0.5). For ϑ≳0.5, back bonds are broken, resulting in the formation of the bulklike cation oxide and, perhaps, the anion oxide, SeO2. Because of its high vapor pressure, the SeO2 may sublime away from the surface, leaving the overlayer rich in ZnO for ZnSe and rich in CdO for CdSe. Thus, for very heavy oxidation, the following oxides were found; TeO2 on CdTe, CdO on CdSe, and ZnO on ZnTe and ZnSe. For each II–VI the single oxide listed above was that with the largest heat of formations.
Infrared dyes for optical storage
Authors: Jipson V. B. , Jones C. R.
Published: July 2002

There is current interest in developing optical storage materials that can be written with GaAlAs lasers. Dyes which absorb strongly at those wavelengths are potential candidates for this application due to their attractive thermal properties. Through optical and thermal modelling, the properties that are necessary if they are to be writeable at energies of ?1 nJ are examined. A specific class of infrared absorbing dyes, squarylium, is discussed and preliminary data on optical characteristics, writing energy, and stability are presented.
Studies of surface, thin film and interface properties by automatic spectroscopic ellipsometry
Authors: Aspnes D. E.
Published: July 2002

This paper qualitatively describes the principles and presents some applications of the rapidly developing technique of automatic spectroscopic ellipsometry, as applied to the analysis of the properties of surfaces and interfaces of materials in bulk or thin film form. Examples include composition and density measurements of polycrystalline and amorphous Si films, the determination of the best-quality surfaces of bulk materials, oxidation of Si, optical profiling of microscopic surface roughness, determination of interface widths in semiconductor–oxide systems and CVD heterostructures, and nucleation of a-Si films.
A nonevaporable low temperature activatable getter material
Authors: Boffito C. , Ferrario B. , della Porta P. , Rosai L.
Published: July 2002

Nonevaporable getters have been widely used for many years in sealed vacuum or controlled atmosphere devices. They are also finding applications in other fields, where specific characteristics are required and tailor-made getters are requested, in some cases sacrificing speed in favor of lower activation temperatures, or lower operating temperature, while still maintaining an adequate sorption capacity. With these objectives, a decade long research project was undertaken which involved investigation of Zr–V–Fe alloys. The physico-chemical properties and the gettering characteristics (speed and capacity) of this family of alloys for some main gases usually present in vacuum devices (H2, CO, N2) have therefore been studied in a range of activation temperatures of less than about 700°C. The equilibrium pressure of H2 on these materials has also been studied as a function of concentration and temperature in a range of pressures less than ∠10 Pa. The results obtained, showing the efficiency of this type of alloy as a getter in a range of activation temperatures of about 500°C, are also discussed in comparison with some other well-known getter materials.
MBE-grown fluoride films: A new class of epitaxial dielectrics
Authors: Farrow R. F. C. , Sullivan P. W. , Williams G. M. , Jones G. R. , Cameron D. C.
Published: July 2002

The deposition of cubic fluorite structure group II fluorides onto several well known semiconductors has been studied under clean, controlled, monitored conditions in an MBE system. The fluoride beams were generated from a single Knudsen effusion oven for each fluoride. Modulated beam mass spectrometry (MBMS) confirmed that the fluorides sublimed as group II molecules. Fluoride films therefore grow by a simple process of molecular condensation from the fluoride beam. BaF2 films deposited onto semiconductor surfaces held at room temperature were polycrystalline. However, growth at temperatures≳200 °C onto ion-bombarded, annealed InP and CdTe surfaces resulted in twin-free epitaxial films with the parallel epitaxial relation: (001)BaF2∥(001)InP, CdTe, [100]BaF2∥[100]InP, CdTe. Growth onto InP(001) surfaces subjected to no ion-bombardment annealing treatment also resulted in twin free epitaxial films with the same epitaxial relation. In situ electron diffraction studies during fluoride film growth combined with ex situ studies suggest that film growth occurs by a 2D mechanism rather than a 3D island mechanism. Electrical measurements of BaF2 and CaF2 films show typical film resistivities of ≳1013 Ω cm at 77 and 300 K. Typical breakdown fields are ∠5×105 V cm−1 and promising interface properties for MIS (BaF2 insulator) structures on p-type Si and n-type Hg0.79Cd0.21Te have been achieved. Cubic fluorite structure group II fluorides form a promising new class of epitaxial dielectrics which can be grown at low (∠200 °C) substrate temperatures.
Interfacial chemical reactivity of metal contacts with thin native oxides of GaAs
Authors: Kowalczyk Steven P. , Waldrop J. R. , Grant R. W.
Published: July 2002

X-ray photoemission spectroscopy (XPS) was used to investigate the chemical reactivity and band-bending variation of native oxide covered surfaces of GaAs (100) during Schottky-barrier formation. The GaAs surfaces prior to metal deposition had thin ∠10 Å overlayers of either As2O3 and Ga2O3 or only Ga2O3. A variety of metals, some chemically inert (Au, Cu, and Ag) and some chemically reactive (Al, Mg, Cr, and Ti), were studied on both types of oxide surfaces. The chemical reactions occurred at room temperature and were well predicted by bulk thermodynamic free energies of formation.
Recent developments in two-level resist technology
Authors: Griffing B. F.
Published: July 2002

High resolution optical lithography requires a sophisticated photoresist technology. In the micron and submicron linewidth regime, the shallow depth of focus characteristic of optical systems gives rise to the need for multilevel resists. Recent work in this area has concentrated on both two-and three-level systems. An example is a two-layer resist (TLR) technique 1 which uses a thin top layer of positive resist over a thick layer of PMMA. The pattern formed in the thin top layer serves as a mask for a deep UV blanket exposure of the thick PMMA bottom layer. Recently a new deep UV source 2 was described for use with this technology. This paper will describe the exposure/development characteristics of the thick PMMA layer for the combination of this novel UV source and a new development chemistry. The paper will compare the complexity of several multilevel resist processes to point up the advantages of simplicity that the TLR technique provides. A comparison of the step coverage ability of this particular TLR technology with that of conventional positive resists is also made. Using the new development chemistry and lamp, (PMMA) structures of 0.4 μ width having 3.5:1 vertical: horizontal aspect ratios have been fabricated.
Experimental evaluation of interferometric alignment techniques for multiple mask registration
Authors: Lyszczarz T. M. , Flanders D. C. , Economou N. P. , DeGraff P. D.
Published: July 2002

An interferometric alignment technique, which is capable of achieving 200 Å overlay accuracy has been described previously. This scheme utilizes matching grating type alignment marks located on mask and sample. In this paper, an experimental evaluation of this alignment scheme is presented. A breadboard alignment system has been constructed which allows coarse and fine control of mask and substrate position in x, y, z, and ϑ. This breadboard system is used to study the alignment marks, signals, and signal processing. The alignment strategy involves an operator-assisted coarse alignment once per wafer and automated fine alignments at each die site. The coarse alignment is based upon moiré fringe patterns, and the fine alignment is based upon the grating scheme. A vernier scheme is used to extend the capture range of the fine alignment. Experimental results are presented for the grating scheme both in transmission and in reflection. The sensitivity of the alignment signals in reflection to variations in gap is analyzed. A modified grating mark is presented as a solution to the sensitivity problem.
Effect of x-ray flux on polytetrafluoroethylene in x-ray photoelectron spectroscopy
Authors: Wheeler D. R. , Pepper S. V.
Published: July 2002

The effect of the x-ray flux in x-ray photoelectron spectroscopy (XPS) on the constitution of the polytetrafluoroethylene (PTFE) surface has been examined. The radiation dose rate for our specimen was ∠107 rad/s. We observed the structure, magnitude and binding energy of the C(1s) and F(1s) features of the XPS spectrum and the mass spectrum of gaseous species evolved during irradiation. The strong time dependence of these signals over a period of several hours indicated that the surface constitution of PTFE is greatly affected by this level of radiation dose. The results are consistent with the development of a heavily cross-linked or branched structure in the PTFE surface region and the evolution of short chain fragments into the gas phase.
Comparison of AES and XPS analysis of thin passive films
Authors: Baer D. R. , Petersen D. A. , Pederson L. R. , Thomas M. T.
Published: July 2002

The surface composition and elemental depth profiles of native oxide films formed on amorphous FeCrNiPB alloys have been studied using both Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). Although both AES and XPS are surface sensitive techniques, differences in electron escape depths for various Auger and photoelectron peaks result in different sample volumes being analyzed by the two methods. This is found to be significant for specimens that have thin surface films with a varying elemental depth composition such as passive layers. Standard XPS and AES analysis of the data from the surface films using either published or bulk normalized sensitivity factors gave different results for the film composition from the two techniques. In addition, AES and XPS sputter profiles were dissimilar. A ’’true’’ depth profile was constructed using an iterative method, considering escape depth broadening effects and the measured profiles. Model calculations of XPS and AES film compositions based on this profile reproduce the differences observed in the experimental XPS and AES data, showing that it is difficult to determine the content of a complex film without some type of depth analysis.
Modeling ion beam milling
Authors: Youngner D. W. , Haynes C. M.
Published: July 2002

Ion beam milling is a dry etching process capable of anisotropically transferring lithographic patterns from photoresist (or other mask material) into an underlying substrate. The process is conceptually simple, experimentally controllable, and therefore relatively easy to simulate on a computer. In this paper, the results of an attempt to construct a physically realistic model of ion beam milling are reported. The model explicitly demonstrates the effects of redeposition and reflected ion beam milling on the sample surface. Several comparisons of simulated profiles with real sample profiles are presented.
A combined instrument for the investigation of catalytic reactions by means of gas chromatography, secondary ion and gas phase mass spectrometry, Auger and photoelectron spectroscopy, and ion scattering spectroscopy
Authors: Ganschow O. , Jede R. , An L. D. , Manske E. , Neelsen J. , Wiedmann L. , Benninghoven A.
Published: July 2002

A combined instrument has been developed which couples a microreactor operated with technical catalysts with a combined surface analytical instrument. The microreactor is equipped with gas chromatography and gas phase mass spectrometry for continuous control of the reaction parameters. The surface analytical part of the instrument incorporates secondary ion and thermal desorption mass spectrometry, Auger and photoelectron spectroscopy, and ion backscattering spectroscopy, all of which have been developed to their full versatility and efficiency. The transfer of the catalyst from the reactor to the surface analysis station is performed by a valveless lock within about one minute in a vacuum free of organic contaminations. The whole system can be operated fully under computer control. First applications of this instrument have been devoted to the oxidation of methanol to formaldehyde on silver catalysts.
Comparison of optically modulated absorption and photoconductivity decay lifetime measurements on HgCdTe
Authors: Radford W. A. , Shanley J. F. , Doyle O. L.
Published: July 2002

The optically modulated absorption (OMA) effect has been examined in p-type (NA−ND≊2×1015 cm−3) Hg0.785 Cd0.215Te. The effect has been used to measure the excess hole lifetime for temperatures between 85 and 250 K. The measured lifetimes agree with the results of photoconductivity (PC) decay measurements performed on the same samples. The measured lifetimes also indicate that an Auger process is the dominant recombination mechanism at temperatures above about 150 K, while a Shockley–Read–Hall process controls the lifetime below this temperature. In addition, it was found that the OMA signal exhibits extremely large phase-interference effects when coherent radiation is used for the probe beam. These effects have been both experimentally and theoretically investigated.
Effect of temperature and preconditioning on the outgassing rate of double aluminized mylar and dacron net
Authors: Glassford A. P. M. , Osiecki R. A. , Liu C-K
Published: July 2002

Measurements have been made to determine the effect of temperature and elevated-temperature preconditioning on the outgassing rate of double-aluminized mylar (DAM) and dacron net (DN), two materials used in multilayer insulation systems. The outgassing rate of DAM was measured at seven constant temperatures between 219 and 394 K, while that of DN was measured at six temperatures between 275.7 and 399 K for 7 days each. The isothermal DAM measurements permitted analytical expressions to be derived for the outgassing rate, from which diffusion coefficient and activation energies could be derived. The effect of elevated-temperature preconditioning on long-term outgassing rate at 298 K was determined in a series of tests on both DAM and DN, in which the samples were heated for 24 h in vacuum to various elevated temperatures between 298 and 423 K, then returned to 298 K, at which temperature their outgassing rate was measured for the next 6 days. It was found that there is an optimum preconditioning temperature for DAM in the region of 343 to 363 K. Preconditioning above this temperature actually increases the long-term outgassing rate at 298 K. For DN, raising the preconditioning temperature steadily lowers the long-term 298 K outgassing rate. In general, elevated temperature preconditioning is more effective for DN than DAM.
Comments on the history of vacuum pumps
Authors: Hablanian M. H.
Published: July 2002

A brief outline of the development of methods for pumping of fluids is presented, emphasizing parallel progress of conceptual understanding and technological achievement. Early experiments with vacuum pumping in the 17th and 18th centuries are reviewed, but the main discussion is reserved for the developments made during the last 100 years when vacuum technology became an industrial practice. Accelerated progress in the development of new pumping methods and in the design of vacuum pumps was made in response to requirements of industrial applications. These include incandescent lamps, vacuum tubes, vacuum distillation, vacuum instruments such as mass spectrometers, electron microscopes, particle accelerators and cathode ray tubes, nuclear energy, vacuum metallurgy, space simulation, thin film deposition for microelectronics, and surface analysis. Each of the above led to some progress in vacuum pump technology ranging from mechanical pumps and diffusion pumps to turbopumps, cryopumps, and ion-getter pumps. A brief history of the development of high vacuum pumps in the United States, written by B. B. Dayton, is included in the Appendix.
The development of valves, connectors, and traps for vacuum systems during the 20th century
Authors: Singleton J. H.
Published: July 2002

The components used in vacuum systems have undergone profound change during the 20th century. The development has been driven both by the needs of research and of commercial manufacturing. It is, however, remarkable that the sealing wax and string era persisted through the 1940’s even in large research establishments. The present wide range of reliable commercial components became available only with the demand for ultrahigh vacuum capability, and with the development of helium leak detection techniques which permit rapid assessment of vacuum integrity. This paper provides a historical perspective of the evolution of: (a) sealing techniques for feedthroughs and for connections between components, (b) valves for isolation and for control of gas flow, and (c) traps to minimize the backstreaming of pumping fluids.
Vacuum pump fluids
Authors: O’Hanlon John F.
Published: July 2002

Organic fluids are used in rotary vane and piston, lobe blowers, turbomolecular, and diffusion pumps. They lubricate, seal, cool, or transfer momentum. We review the properties of pump fluids, why they are important, and how they are (or are not) characterized. The fluids currently used in vacuum pumps are highly refined mineral oils, and synthetic esters, silicones, ethers, fluorosilicones, and fluorocarbons. We describe the properties, types, and selection of fluids for several applications including pumping of oxygen and hazardous gases.
Determination of hydrogen concentration profiles in titanium using SIMS
Authors: Bastasz R.
Published: July 2002

A SIMS technique to measure the H content in the near surface region of Ti is developed. It consists of monitoring positive, secondary ion emission of each of the five, adjacent mass isotopes along with their corresponding monohydrides during Ar+ bombardment. A specialized analysis method identifies the atomic and hydride ion components in the observed signals and gives the hydride ion fraction, which is a relative measure of H content. Depth profiles of in situ H implants obtained using this technique are in good agreement with calculated implantation profiles.
Texturing of poly(ethylene terephthalate) film surfaces by sputter etching
Authors: Cross J. H. , LeMay M. W. , McClure D. J.
Published: July 2002

Poly(ethylene terephthalate) surfaces become microtextured during sputter etching due to differences in the etch rates for the crystalline and amorphous regions. Texture development depends on the selectivity and directionality of the etch chemistry used. We report on the etch rate, the selectivity, the directionality of etch, and loading effects for etching of PET in oxygen. Results of etching in argon, nitrogen, and air are also reported. As a result of a higher selectivity and directionality of etch, argon etching generates microtexture features more rapidly than oxygen etching, even though the etch rate in oxygen is four times larger than that in argon.
Glow discharge cleaning of stainless steel accelerator beam tubes
Authors: Hseuh H. C. , Chou T. S. , Christianson C. A.
Published: July 2002

Glow discharge cleaning has been employed successfully in the CERN ISR to eliminate beam induced pressure bumps and had been adopted as a final surface treatment for the beam vacuum system of CBA. A glow discharge cleaning facility for beam tubes up to 5.5 m in length has been constructed and is in operation. To ensure efficient and thorough cleaning of the long tubes, a residual gas analyzer was used to monitor the exhaust during cleaning. Quantitative studies of the glow discharge process were performed on several tubes by using Ar or Ar/O2 mixture (0.1 to 10 Pa) and by varying the discharge density (≤30 μA/cm2). The results of the studies, such as the desorption yields of H2O, CO, and CO2 with respect to the accumulated dosage, the depletion of O2 in Ar/O2 mixture, will be reported here. The effect of venting to air and CO2, as well as plasma deposition of carbon will also be discussed.