bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and characterization of ultrathin Pb and In films on PbTe and Te
Authors: Miller D. L.
Published: July 2002

Ultrathin 10–300-Å films of Pb and In have been prepared by evaporation in ultrahigh vacuum onto single crystal PbTe and Te substrates at low temperatures. Epitaxial growth was obtained for both metals deposited on PbTe (100) at 77 K, but not on Te (101̄0). Low energy electron diffraction, Auger electron spectroscopy, and low energy electron energy loss measurements were used to characterize substrates and films. Values of low energy electron escape depths through Pb, In, and PbTe were also obtained.
The rf glow-discharge sputtering model
Authors: Logan J. S. , Keller J. H. , Simmons R. G.
Published: July 2002

A model of rf sputtering systems is qualitatively described. The model allows simulation of an entire system so that the deposition process can be related to externally measured parameters. The steps in deriving the model are outlined, with some key equations and underlying assumptions given. The model is based on the physical processes that occur in the chamber, such as ionization, sputtering, and material transport. This model relates these processes to electrical-circuit parameters and to resultant film-deposition conditions. Theory and experiment are compared for a system at 40 MHz to show reasonable agreement with the model. As an example of use of the model, the effects of phase and reemission on secondary electron energy are calculated, showing that the damaging effects of high-energy electrons incident on the substrate can be minimized by use of zero-phase and high reemission levels.
Evidence for a superlattice at Si–SiOx interface
Authors: Stiles P. J. , Cole Teresa , Lakhani Amir A.
Published: July 2002

Evidence is presented for periodic structure at the Si–SiOx interface in MOSFET’s in which the interface is a vicinal plane of (100). The results are discussed in terms of their relevance to interface technology.
Time dependence of the chemical composition of the surface film on the metastable tin–nickel alloy studied with x-ray photoelectron spectroscopy
Authors: Tompkins H. G. , Wertheim G. K. , Sharma S. P.
Published: July 2002

X-ray photoelectron spectroscopy is used to study the change in the chemical composition of the surface film of the metastable tin–nickel alloy as a function of age. As-plated samples as well as HCl-etched samples are studied from very young (6 h and 2 min old, respectively) to about 60 days old. The change in the spectra caused by heating in vacuum is also shown. The film which exists on the as-plated samples which are reasonably young (e.g., 14 days old) is significantly different from the film which grows after this native film has been removed. In all samples studied, the film contains primarily tin components. A small amount of nickel hydroxide forms as the samples age. The change of the film on the etched sample would be described as growth. For the as-plated sample some change in thickness probably occurs over very long times, but the major change is in the chemical composition.
Selective resputtering-induced anisotropy in amorphous films
Authors: Gambino R. J. , Cuomo J. J.
Published: July 2002

A model will be presented to explain the bias voltage dependence of magnetic anisotropy in sputtered amorphous films of gadolinium cobalt alloys. It has been found that the magnetic anisotropy increases with bias voltage up to a critical bias voltage (∠150 V depending on the sputter gas) then decreases precipitously at higher voltages. The model used to explain this behavior is based on selective resputtering of atoms in different surface sites causing an anisotropic distribution of Gd and Co atoms with respect to the growth direction. For example, a Gd adatom in contact with three surface atom neighbors can have 0, 1, 2, or 3 cobalt neighbors. The sputtering threshold for each type of Gd adatom will be different so those with a low threshold will be selectively removed giving a structural anisotropy. This anisotropic atomic distributions can cause different kinds of anisotropy with respect to the growth direction depending on the type of amorphous film. For example, both easy-axis (GdCo) and hard-axis (GdFe) magnetic anisotropies have been observed. It may be possible to extend this model to other types of anisotropy in amorphous films.
Modeling charge storage in electron-beam-accessed MOS memories
Authors: Rockstad Howard K.
Published: July 2002

MOS capacitors have been subjected to 10-kV elecron irradiation at different gate biases, resulting in charge storage in the oxide. C–V translations vs bias are given for various accumulated electron doses extending from 10−4 to 0.1 C/cm2. To explain the essential features of the data, a single-layer model for the charge distribution is proposed. The model comprises several stages which depend upon the irradiation bias. For the first stage, a characteristic charge layer thickness is independent of bias; this thickness varies from less than 300 Å early in the radiation history to over 800 Å for an accumulated dose of 0.1 C/cm2. A critical interfacial electric field and a trap density are incorporated in the model to directly account for other features of the data.
Surface bands in relaxed cleavance surface of GaP
Authors: Bertoni C. M. , Bisi O. , Manghi F. , Calandra C.
Published: July 2002

We have studied the dependence of the surface states upon relaxation in GaP (110) surface. Calculations were performed using a tight binding model with an approximate treatment of the self-consistency. Different relaxation models, involving both rotation and stretching of the bonds were considered. The location and orbital composition of the surface bands their dispersion and the local density of states at the surface are presented for the various models. Unlike the other III–V compounds, we find that the relaxation does not remove the empty surface states from the band gap. Such a conclusion agrees with the experimental information on the pinning of the Fermi level in n-doped samples of GaP. A comparison with partial-yield photoemission data and a theoretical estimate of the surface excitonic binding energy are also given.
Surface final-state effects in core electron transition energies
Authors: McMenamin J. C. , Bauer R. S.
Published: July 2002

The empty states of semiconductor surfaces have been probed by exciting surface core electrons and measuring the constant-final-state partial yield. We have previously reported the wavefunction symmetry and atomic composition of semiconductor surface states deduced from these data. Here we discuss the determination of the energy of these surface states relative to the bulk conduction bands. The surface transition-energy is always less than the separation of the energy levels measured in direct photoemission. We show that the experimental uncertainties in applying this additivity principle always result in a lower limit for that difference. Although the empty surface states cannot yet be located precisely, analysis of our experimental data has revealed a definite trend toward increasing surface-state final-state shift with decreasing semiconductor polarizability. This trend is not observed for conduction band states at the surface or in the bulk, thereby allowing us to pose arguments concerning the relative contributions to the observed final-state shifts of relaxation, electron-hole interactions, and dielectric function discontinuity at the surface.
Magnetic sector atom-probe field ion microscope with a retarding potential analyzer
Authors: Culbertson Robert J. , Sakurai Toshio
Published: July 2002

A combination of a magnetic sector atom-probe field ion microscope and a filter-lens-type retarding potential analyzer makes possible the investigation of the energy distribution of field desorption as well as field ionization and the field ion energy deficit with respect to the emitter potential on an absolute energy scale. The performance of this analyzer was evaluated using various imaging gases, and its resolution is estimated to be better than 100 meV out of a 2000 eV primary energy.
Properties and applications of saddle-field ion sources
Authors: Franks J.
Published: July 2002

The operation of these dc-energized cold cathode sources is based on the effect that electrons describe long oscillatory paths in the presence of an electrostatic saddle potential field. A high probability thus exists of ionizing any gas present in the source, to maintain a discharge at considerably lower pressures (10−4–10−3 Torr) than in conventional cold cathode tubes without a magnetic field. Depending on the symmetry of the saddle-field, beams of various cross-sections are obtained: an axial field produces a high-intensity pencil beam (2 mm diameter), planar fields give rise to divergent beams (e.g.,extending to 25 cm diameter at 10 cm from the source operating at 20 mA, 2 keV). The beam contains a high proportion of energetic neutrals, or may be fully neutralized on emerging from the cathode aperture, depending on source geometry and applied field. Neutralization may be due to the recombination of ions with slow secondary electrons from the edges of the aperture. The operating pressure is compatible with filament and electron beam gun evaporation. Evaporation on a surface exposed to a saddle-field beam combines rapid deposition with strong adhesion characteristic of sputtered films. Other applications include preparation of specimens for TEM and SEM, cleaning and profiling for surface analysis, ion beam machining and sputtering. At present there appears no obstacle to further increasing the size and output of saddle-field ion sources.
Energetic binary collisions in rare gas plasmas
Authors: Robinson R. S.
Published: July 2002

Calculations have been made of cross sections for energy and momentum transfer in binary collisions between like pairs of Ar, Kr, and Xe atoms in the energy range from about 1 to 1000 eV. These calculations were made using a classical model with pair interaction potentials for the rare gases developed from experimental sources, e.g., investigations of specific heats, viscosities, solid-state parameters, and scattering data. Cross sections in this energy range have not been available. The cross sections exhibit a rapid decrease from accepted values at thermal energies as the interaction energy increases. This behavior can be used to understand directed beam propagation limits as well as particle propagation within a plasma. Experimental data have also been fit to a theoretical expression for the Ar resonance charge exchange cross section over the same energy range.
Photoillumination effect on silicon field ion microscopy
Authors: Sakurai Toshio , Culbertson R. J. , Melmed A. J.
Published: July 2002

The photoillumination effect which occurs during the field ion microscopy of silicon is investigated in detail using an UHV magnetic-sector atom-probe field ion microscope equipped with a retarding potential energy analyzer. It is shown that the observed enhancement of image intensity and field evaporation rate which occurs upon illumination with red light is due to the presence of an oxide layer. Measurements of energy deficits indicate that (1) the oxide layer causes a large potential drop at the emitter cap and (2) red light illumination drastically reduces or completely eliminates the reduction in potential.
Surface composition and characteristics of oxide-free Ga1–xAlxAs (110) Schottky barriers
Authors: Lee B. W. , Jou L. , Mark P. , Yeh J. L. , So E.
Published: July 2002

Surface composition of a Ga1–xAlxAs (110) face with different aluminum concentrations (0.2?x?0.8) were studied by Auger electron spectroscopy (AES). Native oxide layers of ∠30 Å were found on the surfaces. The surface oxide-layer thickness is very insensitive of aluminum concentration. Crystals of different aluminum content have the same native oxide layers. Oxygen exists at the crystal surfaces in the form of aluminum oxide Al2O3. Ultrahigh vacuum (UHV) technologies and ion sputtering are combined to fabricate oxide-free Schottky barriers and the I–V characteristics were analyzed. A leakage current in the μA range and breakdown voltage above 107V m−1 were observed.
Review of binary alloy formation by thin film interactions
Authors: Ottaviani G.
Published: July 2002

Formation and properties of binary compounds made by thin film interactions at temperatures well below the melting point of the various components were recently studied. Several aspects concerning such compounds are still, however, unclear; among which are (a) the mechanism responsible for the growth, (b) which phase is formed first, and (c) why not all the compounds predicted by the phase diagram were observed. We review the literature and suggest that the processes occurring at the interfaces control the phase formed. This conclusion is supported by new experimental data concerning the stability of the various phases as a function of the temperature and/or the sample composition.
Transverse acoustoelectric voltage (TAV) spectroscopy of gallium phosphide, indium arsenide and cadmium sulphide–nickel chloride
Authors: Das P.
Published: July 2002

When a semiconductor sample is placed in the proximity of a piezoelectric surface acoustic wave (SAW) delay line, the propagating electric field interacts with the carriers in the semiconductor surface. The manifestation of this interaction occurs among other things, through the appearance of a dc transverse acousto-electric voltage (TAV) accross the semiconductor sample. It is known that this voltage is a function of semiconductor surface conductivity. The magnitude reduces to zero for very high and low conductivities and peaks at an intermediate value. Thus, when the semiconductor is illuminated with monochromatic radiation, the photoenhanced acousto-electric voltage can be used to study the electrical properties of semiconductors. TAV spectroscopy of GaP and InAs has been performed at different temperatures ranging from 77 to 300 K. Some of the special features of this experimental data are (i) a deep chromium level around 1.4 eV in GaP. (ii) a very strong transition at 1.5 eV for InAs. Also the magnitude of TAV for InAs is the largest ever observed to our knowledge. The main advantage of this SAW method is that it is contactless and requires no special sample preparation. It can also be extended to include the study of the semiconductor-electrolyte interface. Some preliminary results on this interface study (CdS–NiCl2) are included.
Carrier generation and trapping in n-InP/SiO2 capacitors
Authors: Stannard J.
Published: July 2002

Zerbst and DLTS measurements indicate the level active for hole generation in samples of n-InP is located near Ev+0.5 eV, and has a cross section for electron emission at least 108 times that for holes. While the Zerbst technique does not establish the presence of a surface inversion layer, the present data in combination with other work indicates the C–V response of this structure under negative bias is controlled by hole trapping at the interface or in the oxide. Interface trapping of electrons becomes less severe as deposition temperature is lowered.
Impact of electron scattering on linewidth control in electron-beam lithography
Authors: Greeneich J. S.
Published: July 2002

The importance of electron-scattering on pattern fidelity in electron-beam lithography is examined using computer simulation of the exposure and development of resist images. It is found that electron scattering can be treated in terms of an effective Gaussian half-width which is the quadrature sum of the incident Gaussian half-width and the characteristic width for forward-scattered electrons. Linewidth control is improved by reducing the effective half-width; this is accomplished by using higher beam energies, thinner resists and smaller spot sizes. Developer simulation shows that using 2 pixels per minimum linewidth with a spot size equal to half the pixel size gives better developed images than the more conventional writing strategy which uses four pixels per minimum linewidth and a spot size equal to the pixel size.
Spatial variation of lifetime distributions due to inert ion damage from low- and room-temperature implantation
Authors: Possin G. E. , Kirkpatrick C. G.
Published: July 2002

The lifetime depth distribution in silicon due to Ar ion implantation prior to annealing has been measured. The lifetime is profiled by the quantitative electron-beam-induced current technique (QEBIC). For silicon with high P-doping levels (≳1018 cm−3) and or high oxygen content the lifetime distribution is essentially Gaussian with an exponential tail of slope <0.03 μm. For lightly doped and low oxygen content <111≳ and <100≳ float zone silicon the slope is much larger and extended beyond 0.45 μm for Ar ion fluences of 1012 cm−2. It is suggested that these deep defect depths are due to the room temperature diffusion of vacancies and the formation of V–O or V–P complexes.
Inorganic resist for dry processing and dopant applications
Authors: Chang M. S. , Hou T. W. , Chen J. T. , Kolwicz K. D. , Zemel J. N.
Published: July 2002

Evaporated As2S3 thin films are employed as inorganic resists in microlithography. Its sensitivity is enhanced by overcoating with a AgCl layer to form a composite. The approach combines the silver halide technology well known to the photographic industry with the newly developed chalcogenide resist technology to yield higher sensitivity and resolution. A CF4 plasma process is developed for pattern generation in these inorganic resists. Since the resist contains arsenic, a dopant for silicon device fabrication, a diffusion process is developed and silicon p–n diodes are fabricated and characterized. A complete dry process of silicon device fabrication is discussed. Possible mechanisms of the photostructural change in As2S3 and the silver photodissolution into As2S3 are mentioned.
Characterization of commercial black chrome coatings
Authors: Fell D. M. , Tongson L. L. , Krishnaswamy S. V. , Messier R. , Tsong I. S. T.
Published: July 2002

A comparative study of the optical properties and chemical composition of three commercially prepared black chrome solar absorber coatings has been made. In all these samples, the visible and IR spectra were nearly the same and showed no peaks corresponding to hydrated chromium oxides. The chemical composition was obtained by AES and sputter-induced photon spectrometry (SIPS). The hydrogen profiles by SIPS indicated the presence of H (or OH) at varying levels in these coatings. Although the AES and SIPS analyses showed significant compositional profile differences among samples, their optical properties were quite comparable.
High rate reactive ion etching of Al2O3 and Si
Authors: Heiman Neil , Minkiewicz Vincent , Chapman Brian
Published: July 2002

The reactive ion etch rate (RIE) of Al2O3-based ceramics, in a plasmax reactor with a gas mixture of 5 μm Ar and 2 μm Cl2, is temperature sensitive. The etch rate at room temperature (∠2600 Å/min) is essentially all physical sputtering. For T=250 °C, the etch rate increase to ∠8200 Å/min. This increase in etch rate is the ’’chemical’’ component of the total etch rate. By means of the same technique, etch rates up to 2.0 μm/min were obtained for Si. In contrast to physical sputtering, RIE of these materials has the advantage that the reaction products are volatile compounds. Redeposition problems should therefore be minimized. In addition, the increase in etch rate obtained by RIE can be used as a trade-off to optimize other process parameters.
Refractory silicides for integrated circuits
Authors: Murarka S. P.
Published: July 2002

Transition metal silicides have, in the past, attracted attention because of their usefulness as high temperature materials and in integrated circuits as Schottky barrier and ohmic contacts. More recently, with the increasing silicon integrated circuits (SIC) packing density, the line widths get narrower and the sheet resistance contribution to the RC delay increases. The possibility of using low resistivity silicides, which can be formed directly on the polysilicon, makes these silicides highly attractive. The usefulness of a silicide metallization scheme for integrated circuits depends, not only on the desired low resistivity, but also on the ease with which the silicide can be formed and patterned and on the stability of the silicides throughout device processing and during actual device usage. In this paper, various properties and the formation techniques of the silicides have been reviewed. Correlations between the various properties and the metal or silicide electronic or crystallographic structure have been made to predict the more useful silicides for SIC applications. Special reference to the silicide resistivity, stress, and oxidizability during the formation and subsequent processing has been given. Various formation and etching techniques are discussed.
Structure and composition of interfaces between Ga1−xAlxAs and GaAs layers grown by liquid phase epitaxy (LPE)
Authors: Petroff P. M. , Logan R. A.
Published: July 2002

The structural perfection and composition of interfaces between LPE grown Ga1−xAlxAs and GaAs layers have been analyzed for a large variety of crystal growth conditions. A combination of scanning transmission electron microscopy (STEM) and cathodoluminescence (CL) analysis in the scanning and spectral analysis model has shown the existence of several interfacial features. A compositional grading of the interface was found for LPE interfaces formed by isothermal growth from a saturated melt in the temperature range 750 °–850 °C. The Al concentration in the interface transition region shows variations on a scale of 10–50 μm in the plane of the interface. Its origin is attributed to the fast Al redistribution during the substrate dissolution period which initiates the growth of the LPE layer. Other interfacial features observed correspond to: (a) deep levels associated with the Ge doped Ga1−xAlxAs layers, and (b) meniscus lines which correspond to variations in the Al concentration and impurity segregation producing recombination centers. The role of these interfacial features on the electronic properties of devices should be important for devices which require good carrier confinement and uniform injection.
Chemical reactions of oxide layers on GaAs
Authors: Langer D. W. , Schuermeyer F. L. , Johnson R. L. , Singh H. P. , Litton C. W. , Hartnagel H. L.
Published: July 2002

The interface of GaAs and its native oxide is shown to exhibit a region of excess As. The amount of this excess is increased by laser annealing of the oxide layers with a corresponding change of the depletion layer capacitance being observed. The migration of As out of the surface of GaAs is clearly observed when Al is deposited on GaAs but not when Ga is deposited. MOS structures, formed by a series of new processing steps, avoid the formation of excess As in the insulator region and As vacancy related traps in the semiconductor region of the interface. The C–V characteristics of these structures show improvements over those produced by conventional oxidation methods.
Atomic reconstruction at polar interfaces of semiconductors
Authors: Martin Richard M.
Published: July 2002

Polar interfaces between semiconductors are shown to have a tendency to form reconstructed compensated interfaces with no free carriers. The conditions for stability of such interfaces are given in terms similar to that for self-compensation in bulk cases, and it is shown that all GaAs–Ge interfaces are expected to obey the conditions. Electronic calculations are given for reconstructed (100) interfaces. The reconstructions can be described by atomic substitutions in the interface layers, which are shown to be examples of general models for order–disorder in two dimensions. The nature of the order is discussed for (100) and (111) interfaces, and it is predicted that there will be ordered charges but disordered dipoles in the interface layers.
Metal/silicon interface formation: The Ni/Si and Pd/Si systems
Authors: Grunthaner P. J. , Grunthaner F. J. , Madhukar A. , Mayer J. W.
Published: July 2002

The valence level spectra of the Ni/Si and Pd/Si systems have been investigated using high resolution x-ray photoelectron spectroscopy. Temperature dependence studies for Ni deposited on thin thermal SiO2 demonstrate the importance of metal aggregation effects in the interpretation of binding energies as chemical shifts. Temperature studies for the Ni/Si system indicate that substantial chemical interaction occurs at the interface at temperatures as low as 100 K. These studies also show the presence of Ni in interstitial voids in the Si near the interface. A comparative study of the core and valence band features for the Ni and Pd silicides provides many valuable insights and a self-consistent picture of the attendent valence charge redistribution and its influence on the observed chemical shifts.
Shallow and parallel silicide contacts
Authors: Tu K. N.
Published: July 2002

Ways of making silicide contacts to Si which have a contact depth of about 10 nm are reviewed. Both Si alloys and refractory metal alloys have been explored for shallow silicide formation, and both high (0.85 to 0.75 eV) and low (0.50 to 0.40 eV) Schottky contacts have been demonstrated. Shallow contacts may not be uniform over the entire contact area due to nonuniform interfacial reaction, so nonuniform contacts consisting of a high barrier silicide and a low barrier silicide in parallel have been analyzed.
Reactive ion beam etching of silicon compounds with a saddle–field ion source
Authors: Revell P. J. , Goldspink G. F.
Published: July 2002

Previous work using cold cathode ion sources of the saddle-field type has indicated that they are suitable for the reactive ion beam etching of many materials. Using a B93 source with a nominal beam current density of 0.16 mA cm−5 (neutral beam ion equivalent for argon), targets of Si, SiO2, and Si3N4 have been etched with a beam produced by injecting the source with Ar, CF4, and CHF3. Data are presented which show the etch rate dependence on beam current density for various combinations of etchant and target material. There is evidence to indicate that silicon was etched by free radical species which were produced at low beam energy (0.6 kV anode potential). Test patterns etched in SiO2 and Si3N4 by ’’CF4 and CHF3 beams’’, which have been examined by Scanning Electron Microscopy, reveal no evidence of redeposition, trenching, or lateral etching. Lines and troughs etched in SiO2 with a ’’CHF3 beam’’ to a depth of approximately 1 μm are shown to be vertical and free of undercutting.
Silicon transfer layer for multilayer resist systems
Authors: Kruger J. B. , Rissman P. , Chang M. S.
Published: July 2002

Thin film silicon is found to be a desirable interlayer material for e-beam lithography with multilayer resist systems. It is easily etched in CF4 plasma (Si/PMMA: 30/1) yet resists O2 reactive ion etch (Si/HPR: 1/300). It is sufficiently conductive to avoid charging effects, both during lithography and SEM inspection. High optical contrast aids in inspection. Monte Carlo calculations show that a 2.5 μm bottom layer of polymer can substantially alleviate the proximity effect, even with an 80 nm Si interlayer. Pattern transfer with less than 100 nm linewidth loss is demonstrated. Lines as narrow as 200 nm in 2 μm of Hunt positive resist were holographically produced.
CdSe1−xOy films prepared by reactive planar magnetron sputtering
Authors: Maniv S. , Westwood W. D. , Shepherd F. R. , Scanlon P. J. , Plattner H.
Published: July 2002

A hot-pressed CdSe planar magnetron target was dc and rf sputtered in Ar and Ar/O2 mixtures. In the Ar case, the deposition rate increased linearly with dc or rf average power P. When O2 was added, it was efficiently gettered until a critical flow rate  f2D which increased linearly with P. For 0< f2<  f2D, the deposition rate was given by (r−bf2/P)(P−P0) where r, b, and P were 0.011 μm min−1, 0.032 μm min−1 W−1 and 25 W; the value of  f2D/P was 0.04 ml min−1 W−1. In this range, there was a continuous increase in the oxygen content of the film until an equivalent composition of CdSe0.8O4.5 was reached at  f2D. For  f2≳ f2D, there was no further change in either the deposition rate or film composition. The behavior of the discharge pressure and impedance also indicate that the equivalent oxygen-rich phase was formed on the target surface at  f2D. The film compositions were determined from Rutherford Backscattering and O16(d,p)O17 reaction analysis. The resistivity of the films increased with  f2/P from 100 Ω cm at  f2 = 0 to greater than 106 Ω cm at  f2/P = 0.01 ml min−1 W−1 and this was associated with a decrease of 1% in the value of the hexagonal lattice parameter of the CdSe wurtzite structure but an oxygen-rich amorphous phase must be present to account for the 25 at.% oxygen in the films. All the films deposited at  f2/P≳0.02 ml min−1 W−1 were amorphous.
Hg1−xCdxTe native oxide reduction by CVD SiO2
Authors: Rhiger David R. , Kvaas Robert E.
Published: July 2002

An interfacial reaction is shown to occur between the native oxide on Hg1−xCdxTe and a CVD SiO2 overlayer. Native oxides were grown by anodizing and coated with SiO2 by the reaction of SiH4 and O2 at 100 °C. The structure was analyzed by sputter-XPS profiling. The chemically split components of the Te(3d5/2) line indicate a much greater ratio of reduced to oxidized Te compared to the anodic oxide without SiO2. The reduced material is equivalent to roughly 15 Å of anodic oxide. Calculations indicate that reactions in which oxide compounds of Hg, Cd, and Te are reduced by SiH4, Si, and SiO are thermodynamically favored.
Bound and resonant surface states at the (110) surfaces of AlSb, AlAs, and AlP
Authors: Beres Richard P. , Allen Roland E. , Buisson Jean Pierre , Bowen Marshall A. , Blackwell George F. , Hjalmarson Harold P. , Dow John D.
Published: July 2002

The dispersion curves E(?) have been calculated for bound and resonant (110) surface states of AlSb, AlAs, and AlP. AlSb is predicted to have no surface states within the bulk fundamental band gap, but AlAs and AlP are predicted to have surface state band minima which are very near the conduction band edge, and could lie either within the gap or immediately above the edge.
SIMS investigation of very shallow implanted Si layers
Authors: Shepherd F. R. , Robinson W. H. , Brown J. D. , Phillips B. F.
Published: July 2002

This paper reports comparative analyses of low energy (≤50 keV) B and As implants in Si using ion microscope (Cameca IMS 3-f) and quadrupole SIMS (Perkin–Elmer Physical Electronics SIMS II) instrumentation. For B implants, the measured profiles indicate that channeling of the B during implantation is primarily responsible for the non-Gaussian distributions, rather than ion beam mixing effects. For very shallow (15 keV) As implants, the mean range and peak concentration measured by SIMS and recent RBS measurements are in reasonable agreement with the calculated distribution.
Surface chemistry and friction behavior of Ti-implanted 52100 steel
Authors: Singer I. L. , Jeffries R. A.
Published: July 2002

Auger spectroscopy, EDX, and optical microscopy have been used to analyze the friction and wear behavior of 52100 steel couples, one modified by Ti implantation (5–50×1016/cm2 at 190 keV). A low friction coefficient, μk=0.3, was measured on surfaces that were carburized by high fluence (>16×1016 Ti/cm2) implantation. A fully carburized layer, produced at 50×1016 Ti/cm2, resisted wear and retained the low friction coupling. Partially carburized layers, produced at 16 and 20×1016 Ti/cm2, gave an initially low friction coupling, μk=0.3; but after 6–10 passes, the partially carburized layer was sheared off exposing the underlying Fe–Ti alloy layer, and the friction coefficient rose to μk=0.8. A high friction coefficient, μk=0.8, was also measured on initial sliding contact with a surface implanted to a low fluence (5×1016 Ti/cm2). High friction is attributed to high adhesion between Fe in the slider and the Fe–Ti alloy found in the surface. Continued sliding contact (in air) against the Fe–Ti surface oxidized the Ti and Fe, and the friction coefficient dropped to a value of μk=0.6, characteristic of the nonimplanted sliding couples.
High rate planar magnetron deposition of transparent, conducting, and heat reflecting films on glass and plastic
Authors: Brett M. J. , McMahon R. W. , Affinito J. , Parsons R. R.
Published: July 2002

Films of indium tin oxide (ITO) and ZnO have been deposited by dc reactive planar magnetron sputtering of metal targets in an Ar/O2 atmosphere. Control of film stoichiometry was achieved through an applied rf bias to the substrate, a reactive gas baffle surrounding the target, and computer control of all parameters in the sputtering process, such as cathode voltage, gas flow, and substrate bias. Films were deposited on cold glass substrates as well as on rolls of polyester sheet. Both the ITO and ZnO films were highly conducting, visually transparent, and infrared reflecting. The success of this deposition technique applied to ZnO films identifies ZnO as a new candidate for transparent, heat reflecting coatings.
Two different species of deuterium implanted into a pyrolytic graphite observed by XPS–SIMS
Authors: Ashida Kan , Ichimura Kenji , Watanabe Kuniaki
Published: July 2002

Trapped states of deuterium implanted into a pyrolytic graphite with 5 keV were investigated by means of the x-ray photoelectron spectroscopy and the secondary ion mass spectrometry. Chemical shift and broadening of C 1s peak were observed in the XPS spectra due to deuterium-ion implantation at room temperature. The shift and the broadening increased with the deuterium fluence to reach constant values. In the SIMS spectra, CD− and C2D− peaks appeared due to the deuterium implantation. The intensity of the CD− peak increased with the fluence to reach a constant value, whereas that of the C2D− peak passed through a maximum to decrease to a constant value. A linear relation was observed between the chemical shift and the CD− peak. The chemical shift and the CD− peak disappeared after annealing the sample at 600 °C for 5 min, whereas the broadening of the C 1s peak and the C2D− peak disappeared after annealing the sample at 900 °C for 5 min. On the basis of these observations, it is concluded that at least two different species of the deuterium are formed in the graphite due to the deuterium implantation.
XPS characterization of erbium sesquioxide and erbium hydroxide
Authors: Swami G. T. K. , Stageberg F. E. , Goldman A. M.
Published: July 2002

The low temperature antiferromagnetic transition of Er2O3 is being investigated by studying the tunneling characteristics of superconducting junctions fabricated with artificial barriers of the oxide. To develop techniques for the semiquantitative determination of the relative concentrations of Er2O3 and Er(OH)3 in tunneling barriers, XPS studies have been carried out on standard samples of Er, Er2O3, and Er(OH)3.
Role of GaAs surface cleaning in plasma deposition of silicon nitride films for encapsulated annealing
Authors: Valco G. J. , Kapoor V. J.
Published: July 2002

The role of GaAs surface cleaning and plasma reactor cleaning prior to deposition of silicon nitride films for encapsulated annealing has been investigated. X-ray photoelectron spectroscopy was employed to determine the surface characteristics of GaAs treated with HCl, HF, and NH4OH solutions preceded by a degreasing procedure. The HCl clean left the least amount of oxygen on the surface. Fluorine contamination resulting from the CF4 plasma used to clean the reactor was found to be located at the film-substrate interface by Auger electron spectroscopy with argon-ion sputtering. A modified deposition procedure was developed to eliminate the flourine contamination. Plasma deposition of silicon nitride encapsulating films was found to modify the I-V characteristics of Schottky diodes subsequently formed on the GaAs surface. The reverse current of the diodes was slightly reduced. Substrates implanted with Si at 100 keV and a dose of 5×1012/cm2 showed a peak electron concentration of 1.7×1017/cm3 at a depth of 0.1 μm with 60% activation after encapsulation and annealing at 800 °C for 7 min.
Field adsorption of inert gas atoms on the tungsten surface—A pulsed-laser atom-probe study
Authors: Kinkus T. J. , Tsong T. T.
Published: July 2002

On a solid surface, inert gas atoms can be field adsorbed to the surface under the influence of a strong electric field. The probability of field adsorption was measured as a function of temperature for He, Ne, and Ar on the W(112) surface. Although it was assumed that gas atoms field adsorb only on top of surface atoms, experimental evidence indicates that secondary sites also exist, such as on bridge sites, between surface atoms, or second layer adsorption sites. A simplified calculation of the binding energy assumes an isolated dipole pair model and significantly overestimates the binding energy at 0.20, 0.19, and 0.24 eV for He, Ne, and Ar at a field of 4.5, 3.9, and 2.5 V/Å, respectively. The measured values were 0.17, 0.14, and 0.12 eV. Including a correction for the depolarizing field caused by the layer of polarized adatoms gives a reasonable agreement with the experimental values at 0.18, 0.16, and 0.13 eV.
High-end computer packaging—VLSI scaling and materials science
Authors: Grobman W. D.
Published: July 2002

This paper reviews the nature of the package which supports a high-end general purpose computer. It describes the functions provided by the package, and then focuses on a central theme: namely that the level of complexity and density of the chip interconnections, power distribution network, and channels in the package depends on the areal density of circuits on the chips in the system. Consequently, the materials and processes used in fabricating the package must develop in new directions to satisfy the needs imposed on the package by the chip level of integration. This theme is developed by first describing the logic design scaling rules that relate the number of random logic circuits in any subset of the system to the number of interconnections which must be provided to support this subset of the system and connect it to the rest of the computer. Next, the topology of packages is described, and then a particular example, the IBM 2-dimensional high-end package, is described. The definition and application of a simple scaling model to the IBM package predicts the dimensional aggressiveness of future packages as chip circuit density increases. Finally, the consequences of these results for materials and processes goals in future packaging technology are sketched. This set of ideas should form a useful introduction to the papers which follow in this issue, for these ideas are the link between performance-driven computer system design and the physical design of the package.
Modeling of interface reaction products with high-resolution core-level photoemission
Authors: Grioni M. , del Giudice M. , Joyce J. J. , Weaver J. H.
Published: July 2002

High-resolution photoemission studies make it possible to distinguish different atomic configurations at evolving interfaces by monitoring chemical shifts. Hence, it is possible to determine the coverage at which reactions are triggered and are effectively completed, the species that outdiffuses into the metal overlayer, and the bonding of surface-segregated species. Core-level deconvolutions and plots of the concentration of substrate, reacted, and segregated species as a function of coverage are discussed for Ce/Si(111), Ce/GaAs(110), and Cr/GaAs(110). Our results show that distinct Ce/As and Ce/Si species form but that no distinct Cr/Ga bonding configuration is established at the interface.
Overlayer-induced enhanced oxidation of GaAs surfaces
Authors: Chang S. , Rizzi A. , Caprile C. , Philip P. , Wall A. , Franciosi A.
Published: July 2002

Thin metal overlayers deposited on GaAs(110) cleavage surfaces enhance the surface oxidation rate several orders of magnitude above the clean surface value. The magnitude of this effect depends on the chemistry of the overlayer, on the local morphology of the overlayer–semiconductor interface region, and on the nature of the gaseous reactants. We present a synchrotron radiation photoemission investigation of the GaAs surface interaction with oxygen in the presence of Ag, Au, and Cr overlayers, and of the GaAs–H2O reaction in the presence of Cr overlayers. We find that the promotion effect is maximum in the presence of Cr overlayers, and that the nature of the surface reaction products changes if oxygen or water is employed. In particular, in the case of oxygen, Ga and As-oxide phases are found with high atomic oxidation states present. If water is employed, only Ga oxide/hydroxyl phases are found at the surface, on top of a Cr–As subsurface layer that remains largely unaffected by oxidation.
Kinetic theory of laser photochemical deposition
Authors: Chen C. Julian
Published: July 2002

A kinetic theory of laser photochemical deposition is developed, which includes the following parts: (1) an analytic formalism for the deposition profile due to gas phase decomposition, (2) a theorem which relates the ballistic case and the diffusion-dominated case, (3) a detailed account of adsorbed phase photodeposition, and (4) six dimensionless quantities to characterize various deposition processes. The theory is used to analyze and gain insights to a number of recent photodeposition experiments.
Far-infrared magnetoabsorption in HgTe–CdTe and Hg1−xMnxTe–HgTe superlattices
Authors: Dobrowolska M. , Yang Z. , Luo H. , Furdyna J. K. , Harris K. A. , Cook J. W. , Schetzina J. F.
Published: July 2002

We report far-infrared (FIR) magnetoabsorption measurements on two Hg-based superlattices: HgTe/CdTe and Hg0.90Mn0.10 Te/HgTe grown by molecular-beam epitaxy. The latter one is novel and unique in that it is a superlattice of a zero-gap semiconductor and a narrow-gap diluted magnetic semiconductor. The FIR experiments were carried out at discrete photon energies between 2.5 and 12.8 meV in the temperature range 1.6 K<T<200 K. Rich spectra of inter- and intraband transitions were observed, the intensities and positions of the transitions showing a dramatic temperature dependence associated with the thermal redistribution of electrons within the energy level scheme of the superlattices.
Photoemission studies of core level shifts in HgCdTe, CdMnTe, and HgZnTe
Authors: Shih C. K. , Spicer W. E. , Furdyna J. K. , Sher A.
Published: July 2002

We report here the photoemission studies of core level shifts in Hg1−xCdxTe, Cd1−xMnxTe, and Hg1−xZnxTe alloys. The cation core level binding energies relative to the valence-band maximum (VBM) are measured as a function of composition. In Hg0.7Cd0.3Te, the Hg 5d level shifts to lower binding energy by 0.1 eV whereas the Cd 4d levels shift to higher binding energy by 0.25 eV upon alloying (relative to their binaries). In Cd1−xMnxTe and Hg1−xZnxTe, such behavior is not observed: the binding energies of the Cd 4d level in CdTe and Cd0.55Mn0.45Te are the same; the binding energies of the Hg 4d level in HgTe and Hg0.84Zn0.16Te are the same also. By using the Born–Haber cycle, we have calculated core level binding energies relative to the VBM in the context of tight-binding theory. Compared to our measurements the calculated core level shifts upon alloying in HgCdTe are too small to account for the observed values. We attribute the discrepancy to the existence of natural valence-band offset between HgTe and CdTe, which has been considered to be zero in our calculation. The natural valence-band offset between HgTe and CdTe deduced from our experiment is 0.35 eV. Following the same line of argument, the natural valence-band offsets between CdTe and the hypothetical zinc-blende MnTe, and between HgTe and ZnTe, are small.
New cathode material for sputter ion pumps: Aluminum mixed rare-earth alloy
Authors: Lu Ming , Fang Ping Wei
Published: July 2002

Cathodes for sputter ion pumps have usually been made of pure titanium and used for Penning discharge. A new cathode material—aluminum mixed rare-earth alloy (AlRE)—can be now used as a substitute for pure Ti as a result of experimental research. The comparative tests were made against cathodes made of pure Ti and some rare-earth alloys, respectively, under the same conditions (same pump body, same pumping elements, and same test conditions). It has been found that the pumping speed for dry air increased by 40% when AlRE alloy cathode was used. The AlRE alloy can be stably obtained through a novel process. Experiments demonstrate that AlRE alloy is an excellent cathode material for sputter ion pumps.
Performance test of a ceramic rotor developed for turbomolecular pumps for fusion use
Authors: Murakami Y. , Abe T. , Morii S. , Nakaishi N. , Hata S.
Published: July 2002

Turbomolecular pumps with a metallic rotor have been widely used to pump out gases from plasma confinement devices. However, high magnetic fields produced by magnet coils and plasmas cause eddy current heating and rotation speed reduction of the rotor of the pumps, and as a result serious problems take place in the rotor strength and pump performance. In order to overcome these problems, the authors have been developing a ceramic turbomolecular pump and, as a first step, have manufactured a test machine. The test machine consists of a ceramic rotor assembly with high electrical resistivity, gas bearings, a gas turbine, and a spiral-groove seal. The ceramic material is silicon nitride. Using the material strength of the actual components, rupture probability of the rotor assembly was estimated at various rotation speeds. Rotational tests of the test machine were successfully performed in both stationary and pulsed magnetic fields (0.046 T and 0.02 T/ms, respectively) at the required speed of 30 000 rpm. The leak rate through the spiral-groove seal was measured for two different seal gaps and at various rotation speeds.
The thermodynamic treatment of the cryosorption process in a cryopump
Authors: Liu Bingkun , Xie Jue , Ren Jiasheng , Cui Xiuhua
Published: July 2002

The cryocondensation and cryosorption dominate the whole pumping process in a cryopump. Thus, it is prudent to study the cryosorption phenomenon from the thermodynamic viewpoint to enhance understanding of cryopumping. On the basis of the equilibrium between gas phase and adsorption phase, this paper has tried to deduce the relevant thermodynamic functions involving enthalpy, adsorption heat, entropy, Gibbs free energy, and the interrelations of the various parameters existing in the cryosorption process. These authors established an experimental system by using the ZDB-150 cryopump with the closed cycle refrigerator, and conducted the experimental study of cryosorption for hydrogen on the ZX-15 charcoal at the temperature of 18–22 K and in the pressure range of 10−4–10−7 Torr. Deducing from the experimental data, the above thermodynamic functions and the relationship among themselves in the cryosorption process were presented. It shows that this work is useful to the investigation of the cryosorption process in a cryopump.
Pumping of hydrocarbons using nonevaporable getters
Authors: Emerson L. C. , Knize R. J. , Cecchi J. L.
Published: July 2002

Pumping speed measurements have been obtained for a number of gaseous hydrocarbons including members of the alkene, alkadiene, and cycloalkane groups as a function of temperature using a Zr–Al alloy getter. Pumping speeds were obtained by analysis of an exponential least-squares fit to the pressure decay curve following introduction of each gas. It was found that these pumping speeds are relatively high (up to 400 l/s) and exhibit, with only a few exceptions, little temperature dependence. This is in contrast to the earlier reported results for the alkane series.