bluuebunny/crossref_metadata_2025 huggingface dataset:
The electronic structure of Ge:GaAs(110) interfaces
Authors: Mönch W. , Bauer Robert S. , Gant H. , Murschall R.
Published: July 2002

Ge:GaAs heterostructures were investigated by photoemission from core levels excited with soft x rays. Epitaxial and amorphous films were grown by condensing Ge on surfaces cleaved from n- GaAs held at 300 and 20 °C, respectively. On the GaAs side of the heterostructure, the Fermi level is pinned (0.75±0.1) eV above the valence band edge, regardless of whether the Ge overgrowth was crystalline or amorphous. This may be caused by chemisorption-induced defects. The valence band discontinuity depends on the structure of the Ge film and amounts to 0.42 with epitaxial and to 0.65 eV with amorphous overgrowths. Half a monolayer of As (most probably bound as GeAs) and ∠0.03 monolayer of Ga were found to be segregated at the crystalline film surfaces.
Theory of heterostructures: A reduced Hamiltonian method with evanescent states and transfer matrices
Authors: Chang Yia-Chung , Schulman J. N.
Published: July 2002

A new theoretical technique for calculating the electronic properties of heterostructures is presented. This method is computationally more efficient than any current technique and has physically intuitive clarity. Furthermore, it can be applied to heterostructures with arbitrary perturbations varying in the direction perpendicular to the interface, such as smoothly varying electrostatic potentials caused by doping, compositional grading disruptions, and long range lattice relaxations. Using this method, we have studied several semiconductor surfaces, interfaces, and superlattices, including doping and relaxation effects in a realistic tight-binding model. The results for the Si (111)–(2×1) surface and the GaAs/AlAs interface with doping are presented.
Ion beam sputter-deposited diamondlike films
Authors: Banks Bruce A. , Rutledge Sharon K.
Published: July 2002

A single argon ion beam source was used to sputter deposit carbon films on fused silica, copper and tantalum substrates under conditions of sputter deposition alone and sputter deposition combined with simultaneous argon ion bombardment. Simultaneously deposited and ion bombarded carbon films were prepared under conditions of carbon atom removal to arrival ratios of 0, 0.36, and 0.71. Deposition and etch rates were measured for films on fused silica substrates. Resulting characteristics of the deposited films are: electrical resistivity of ≳1011 Ω cm, densities of 2.1 g/cm3 for sputter-deposited films and 2.2 g/cm3 for simultaneously sputter-deposited and Ar ion-bombarded films. For ∠1700-Å thick films deposited by either process and at 5550 Å wavelength light the reflectance was 0.2, the absorptance was 0.7, the absorption coefficient was 6.7×104 cm−1, and the transmittance was 0.1.
X-ray and XPS studies of evaporated CuxS thin films
Authors: Uppal P. N. , Burton L. C.
Published: July 2002

The structural changes in CuxS films have been monitored by x-ray diffraction and correlated to the chemical changes taking place on the CuxS surface, the latter monitored by XPS. The results show: evaporated CuxS films contained chalcocite, free copper phases, and probably a third phase (of sulfur); resistivity is related to the amounts of free Cu and S in the film; air heat treatments converted chalcocite to Cu deficient phases and resulted in the disappearance of the sulfide and predominance of CuSO4⋅nH2O and CuO; argon heat treatment tended to react Cu and S to form CuxS; Cd is detected on the surface of CuxS deposited onto CdS and is significantly increased in amount by heat treatments. These results can be related to chemical processes occurring on CuxS/CdS and CuxS/(Zn,Cd)S solar cells. For the CdS cell, oxides and sulfates of Cu and Cd are found on the CuxS surface and the sulfates are enhanced by the heat treatment in moist air. CuO and CuSO4 are formed in the absence of Cd, and dominate the CuxS surface.
A comparison of AES and RBS analysis of the composition of reactively sputtered TiSix films
Authors: Blom H. O. , Stridh B. , Berg S. , Sundgren J.-E.
Published: July 2002

By reactive sputtering of Ti in a gas mixture of Ar/SiH4 it is possible to form TiSi2. The influence of rf bias to the target on film composition is investigated. The dependence of partial pressure of SiH4 on film composition TiSix is also demonstrated. A phenomenological description of the physical processes mainly responsible for film composition is outlined. Analysis of the film composition of the TiSix films have been performed by using both Rutherford back scattering (RBS) and quantitative Auger electron spectroscopy (AES). The results obtained from a wide range of stoichiometries show that the composition data obtained from AES analysis deviate from the bulk stoichiometry obtained by RBS analysis. The conclusion is that the surface modification, caused by precleaning the TiSix films prior to AES analysis changes the surface composition significantly. There are, however, other effects which make quantitative AES analyses of the films difficult, i.e., the difference in escape depths for Auger electrons originating from silicon and titanium. There may also be a matrix effect in the sensitivity factors Prel(Si,Ti).
Thermal stability of diffusion barriers for aluminum alloy/platinum silicide contacts
Authors: Merchant P. , Amano Jun
Published: July 2002

Thin metal films of Cr, Ti, Mo, and W–Ti (10 wt.%) have been investigated for their effectiveness in preventing the Al–PtSi reaction which occurs during the post-metallization alloy treatment of Ohmic contacts and Schottky diodes on integrated circuits. The metal films were deposited by two different dc magnetron sputtering systems. The processed structures were compared for their electrical and metallurgical stability as a function of alloy temperature up to 550 °C for 30 min, as well as for effects of a sputter-etch versus a wet chemical dip prior to the barrier metal and aluminum alloy deposition. Degradation of the electrical behavior of the contact structures at the higher alloying temperatures is correlated with structural alterations of the layered structures by MeV He ion backscattering and Auger electron spectroscopy with Ar ion sputter-depth profiling. Conditions under which each barrier metal is useful are presented.
Kinetics of electron-stimulated oxidation of GaAs(1̄1̄1̄)
Authors: Alonso M. , Soria F. , Sacedón J. L.
Published: July 2002

Kinetics and current dependence of the electron-stimulated oxidation (ESO) of GaAs (1̄1̄1̄) surfaces are obtained by means of a quantitative Auger numerical formalism for oxide layers applied to new experimental data. The kinetics presents two stages: a linear growth with time, and a saturation region. The rate of growth and the saturation thickness for the oxide layer show simultaneous maxima as a function of the current density. The amount of oxygen adsorbed in the preoxidation stage (two monolayers of atomic height) and its independence of the current density is also obtained. The minimum diameter of the oxide spots made with our conventional Auger gun is about 20 μm. The possibility of a classical interpretation of ESO effects in GaAs (1̄1̄1̄) looks controversial.
Silicide formation in lateral diffusion couples
Authors: Zheng L. R. , Hung L. S. , Mayer J. W.
Published: July 2002

Silicide formation, growth kinetics, and phase sequences have been investigated with lateral-diffusion, thin-film couples formed by overlapping deposited layers of Ni and Si on an inert substrate. The lateral extent (3 to 100 μm) of the silicide region is determined by electron microscope and microprobe measurements. For annealing temperatures between 400 and 800 °C, the growth of the silicides follows a (time) 1/2 dependence at a growth rate similar to that in conventional (planar) thin-film couples. In Ni-Si lateral diffusion couples, Ni2Si is the first phase formed; it grows to a length of about 25 μm (at 600 °C) and then multiple phases appear with the same sequence as that found in bulk diffusion couples. Lateral-diffusion couples thus provide the transition between thin-film and bulk behavior.
An investigation of the interaction of polycrystalline zirconium with O2, N2, CO, and N2O. Part I
Authors: Hoflund Gar B. , Cox David F. , Gilbert Richard E.
Published: July 2002

The adsorption of O2, N2, CO, and N2O on polycrystalline zirconium has been studied using ESCA and AES over a wide temperature range from room temperature to nearly the melting point of zirconium. The gases adsorb dissociatively at all temperatures studied, and the room temperature sticking coefficients are low (<0.01). Heating causes migration of the adsorbate species into the bulk zirconium. Two distinct surface phases (states) of zirconium are identified. State 1 exists when the sample has not been heated above the hcp↔bcc transition temperature of 1135 K for prolonged periods while state 2 occurs after prolonged heating (the time is a function of temperature) above the transition temperature. The AES spectra and chemisorption properties of the two states are very different. State 1 AES spectra show a prominent 175 eV peak which is nearly gone in state 2 AES spectra. State 1 readily adsorbs CO and N2 at room temperature while state 2 adsorbs relatively small amounts of CO and is almost inert to N2. Therefore, the valence electrons responsible for the AES 175 eV peak play a significant role in the chemisorption properties of zirconium.
On baking a cryopumped UHV system
Authors: Kubiak R. A. A. , Leong W. Y. , King R. M. , Parker E. H. C.
Published: July 2002

The problems of the thermal loading of cryopumps during bakeout of UHV systems are considered. A simple design of thermal baffle is presented which permits baking at temperatures of 200 °C without compromising the high speed of the pump during normal system operation.
Relation between the electronic states and structural properties of Hg1−xCdxTe
Authors: Chen A.-B. , Sher A. , Spicer W. E.
Published: July 2002

Physical reasons are presented for the coherent potential approximation (CPA) calculation method’s abillity to predict little band gap bowing or alloy scattering, while at the same time predicting large deviation from virtual crystal behavior in other energy ranges. Accurate treatment of structural properties requires that calculations be doubly self-consistent: a density functional method plus CPA is needed. Experimental values of bond energies are greater than those predicted by simple theories. Weakened HgTe bonds in alloys help to explain the loss of Hg when the materials undergo surface treatments.
Comparative studies of mercury cadmium telluride single crystal and epitaxial
Authors: Raccah Paul M. , Lee U.
Published: July 2002

We have carried out a systematic study of mercury cadmium telluride (MCT), bulk single crystal and epilayers, using electrolyte electroreflectance (EER). Our results, and others discussed here, suggest that much of the unusual properties of this material are due to structural microdomains. Under mechanical stresses or chemical attack, the walls of these domains tend to move via the generation and propagation of defects associated with cationic diffusion. A typical consequence is the creation of n-type zones within a p-type matrix. We have calibrated our etch rate so as to be able to apply EER to the study of the profiles of epilayers with a depth resolution of 200 Å. The technique was applied to more than 100 samples of all origins. The results are summarized here in qualitative terms, such as typical profile features, as well as in quantitative terms, such as compositional variations and defect densities. EER results are integrated within the conceptual framework introduced above and compared to SIMS and microprobe results.
Nondestructive analysis of Hg1−xCdxTe (x=0.00, 0.20, 0.29, and 1.00) by spectroscopic ellipsometry. I. Chemical oxidation and etching
Authors: Aspnes D. E. , Arwin H.
Published: July 2002

Chemical oxidation and etching reactions are studied using the real-time analytic capabilities of spectroscopic ellipsometry to avoid ambiguities arising from air exposure or delays between processing and measurement. We show that bromine–methanol treatments leave the surfaces of these materials covered with an optically identifiable Te layer about 7 Å thick. Previous XPS measurements indicating TeO2 as a reaction by-product of Br exposure can be understood as an artifact of air oxidation and the inability to resolve the 3d core-level signal of metallic surface Te from that of semiconductor substrate Te. The Te layer can be removed from the Hg-containing compounds by oxidizing and stripping freshly polished samples with HNO3 or by reducing them with NaBH4. The Te layer cannot be completely removed in this way from CdTe. Chemical oxidations of these materials with H2O2 solutions of different pH values show that the oxide on CdTe is a single stoichiometric compound, probably the tellurite CdTeO3, while that formed on HgTe is a physical mixture of TeO2 and probably HgTeO3. The H2O2-grown oxides can be removed with HCl, but a Te residue remains. No evidence is found for chemically induced bulk damage in any of the compounds studied.
Structure study of Au–GaAs(001) interfaces by HEIS, XPS, and RHEED
Authors: Narusawa Tadashi , Watanabe Nozomu , Kobayashi Keisuke L. I. , Nakashima Hisao
Published: July 2002

MeV He+ ion scattering/channeling (HEIS), angle resolved XPS, and RHEED have been applied to study the Au and MBE-grown GaAs(001)-c(4×4) interface structures in the Au film thickness range of ≲70 Å and the annealing temperature range from room temperature up to ∼300 °C. The results show release of the As atoms and epitaxial growth of the Au film even at room temperature. The shrinked Au film after annealing displays selective registry to the [1̄10] direction, which is believed to result from a strong Au–GaAs(001) interaction.
Evaporative coating of a sphere from a point source
Authors: Strayer D. M. , Jackson H. W. , Gatewood J. R.
Published: July 2002

To optimize the procedure for evaporating a metal film onto a sphere, calculations of the film thickness distribution for various motions of the sphere have been carried out. These calculations, including shadowing effects of sphere support rods, are presented in this paper. Also, an apparatus and procedure for the evaporative coating of a sphere are described. A comparison of measured thickness with the calculated values is made for one example of sphere motion. The implications of the calculated results for coating techniques are discussed.
An angle-resolved UPS study of the oxygen-induced reconstruction of Cu(110)
Authors: DiDio R. A. , Zehner D. M. , Plummer E. W.
Published: July 2002

Angle-resolved ultraviolet photoemission spectroscopy (ARUPS) has been used to study the p(2×1) oxygen-induced reconstruction of Cu(110). While there is agreement between experimental groups that the O atoms sit in the long-bridge site along the 〈001〉 Cu directions, there are two proposed models for the reconstruction: the missing-row model, in which alternating 〈001〉 rows of Cu atoms are missing, and the buckled-row model, in which the O-containing 〈001〉 rows are displaced outwards from their bulk position. Our ARUPS data show oxygen-induced changes in the Cu d-band photoemission features that are inconsistent with the missing-row model, thus favoring the buckled-row picture. In addition, the O–Cu bond appears to be highly directional and oriented along the 〈001〉 Cu rows, consistent with O sitting in the long-bridge site. Moreover, the O–Cu bond is primarily a result of the O(2pxy)–Cu(3dx2−y2) interaction.
Radio frequency magnetron sputtering of multicomponent ferroelectric oxides
Authors: Krupanidhi S. B. , Sayer M.
Published: July 2002

Lead zirconate titanate, a multicomponent ferroelectric oxide has been sputtered using a planar rf magnetron technique. The characteristics of the discharge were monitored through the cathode self-bias voltage and were correlated with rf power, sputtering gas partial and total pressures, and the rate of film deposition. The physical properties of the films were affected by deposition rate, substrate temperature, and sputtering pressure. Good transparent ferroelectric PZT films exhibited a dielectric constant of 950 and conductivity as low as 10−10 Ω−1 cm−1. These films were sputtered in 100% oxygen at 40 mTorr at an optimum deposition rate of 0.6–0.7 μ/h.
Planar magnetron sputtering of a-Si:H and a-Ge:H thin films
Authors: Rudder R. A. , Cook J. W. , Schetzina J. F. , Lucovsky G.
Published: July 2002

We have designed and constructed a dual magnetron sputtering system for deposition of amorphous hydrogenated films of silicon (a-Si:H), germanium (a-Ge:H), and alloys of Si and Ge. The system was designed to optimize control of the deposition parameters which may affect film quality. Infrared and Auger electron spectroscopy of films grown in the system show no evidence of contamination by oxygen or carbon within the detection limit of these techniques (∼0.2 at. %). Photoconductivities of the a-Si:H films are comparable to those grown by other techniques. In contrast, the best a-Ge:H films have mobility-lifetime products which are at least an order of magnitude greater than those deposited by other techniques.
Fracto-emission: The role of charge separation
Authors: Dickinson J. T. , Jensen L. C. , Jahan-Latibari A.
Published: July 2002

Fracto-emission is the emission of particles (e.g., electrons, ions, ground state and excited neutrals, and photons) during and following fracture. We have found that during fracture in vacuum of adhesive bonds and crystalline materials involving large amounts of charge separation on the surface the emission of charged particles, excited neutrals, light, and radio waves occurs with unique and revealing time dependencies. In this paper we report simultaneous fracto-emission measurements on several systems. We interpret the results in terms of a conceptual model involving the following steps: (1) charge separation due to fracture, (2) desorption of gases from the material into the crack tip, (3) a gas discharge in the crack, (4) energetic bombardment of the freshly created crack walls, and (5) thermally stimulated electron emission, accompanied by electron stimulated desorption of ions and excited neutrals. In addition to evidence from fracture experiments, we present results from studies of electron bombardment of a polymer surface.
An acceleration method for measuring the adherence of plasma-sprayed coatings at elevated temperatures
Authors: Brown S. D. , Ferber M. K.
Published: July 2002

Presently, no satisfactory method for measuring the coating–substrate adherence in plasma-sprayed ceramic–metal systems exists. Conventional pull-off methods must rely upon adhesives or other means of attachment that become unreliable at elevated temperatures. Nevertheless, an accurate method for determining the adherence of plasma-sprayed coatings to their substrates at elevated temperatures would be useful. Many applications of such coatings are in high-temperature environments. An acceleration method reported in 1957 by May, Smith, and Snow for organic coatings has been analyzed and found promising, in modified form, for the determination of coating–substrate adherence of plasma-sprayed coatings. Calculations indicate that adherences as high as 103 MPa (15 000 psi) should be measurable. Moreover, the modified scheme appears easily adaptable to the making of adherence measurements at elevated temperatures. Unlike pull-off tests, the method is not dependent upon the thermal stability or properties of any adhesive or braze alloy. The relevant literature is reviewed. Our analysis is presented along with a schematic representation of the apparatus now under construction.
Glow discharge mass spectrometry for sputtering discharge diagnostics
Authors: Aita Carolyn Rubin
Published: July 2002

Glow discharge mass spectrometry (GDMS) is an in situ method used to determine the mass and energy of positive ions incident on the substrate during sputter deposition. In the first part of this review, we describe the sputtering glow discharge, creation of positive ions in the glow, determination of their mass and energy by GDMS, and the relationship between ionic flux and the flux of corresponding neutral species incident on the substrate. In the last section, several examples of the use of GDMS during reactive sputter deposition are presented, illustrating the strengths and limitations of this technique.
Two-dimensional overlayer growth: Island size and island separation distributions
Authors: Saloner D. , Wu P. K. , Lagally M. G.
Published: July 2002

The distributions in sizes and separations of ordered islands growing at submonolayer coverages on a surface are investigated in terms of the information available in a diffraction experiment. The effective distributions measured from an array of two-dimensional islands are examined in the limit of a slit detector (i.e., one that integrates the intensity in one direction of the diffracted-intensity distribution). The effective size and separation distributions measured by this slit detector are evaluated for different distributions of the overlayer island size and for different island shapes. For systems ordering with a superlattice the intensity distribution in the superlattice beams is shown to be sensitive to the overlayer size distribution only, whereas that in the fundamental beams always depends on both the size and separation distributions, independent of the existence of a superlattice.
Atomic rippling of a metallic ordered alloy surface–NiAl(110)
Authors: Davis H. L. , Noonan J. R.
Published: July 2002

Results from a low-energy electron diffraction (LEED) analysis of the NiAl(110) surface are presented and discussed. Ordered NiAl has a truncated bulk (110) surface consisting of composite layers of Ni and Al sites which are exactly coplanar. However, the present LEED results demonstrate that the actual NiAl(110) surface has a large rippled relaxation, with the Al sites of the outermost composite layer being 0.22 Å above the Ni sites. The agreement achieved between the calculated and experimental I–V profiles, total R factor of 0.053, is of the same quality as that obtained in better LEED analyses of monatomic metallic surfaces, which indicates the evidence for the rippling is quite strong. Also, a qualitative plausibility argument is given to indicate that such rippling is to be expected in surfaces of ordered alloys.
Characterization of anisotype and isotype Hg0.8Cd0.2Te/CdTe heterojunctions
Authors: LoVecchio P. , Reine M. B. , Grimbergen M. N.
Published: July 2002

The metallurgical heterojunction located between liquid phase epitaxial Hg0.8Cd0.2Te films and CdTe substrates is characterized electrically and electro-optically for the first time. This compositionally graded heterojunction is found to have zero bias resistance-area R0A products ranging from 102 to 105 Ω cm2 at 300 K, and from 106 to 109 Ω cm2 at 100 K. Between these two temperatures thermal activation energies of approximately 0.4 eV and 0.1 eV are measured. Measurements of capacitance, photoresponse position, and spectral sensitivity lead to the conclusion that a charge-separating depletion region and valence band barrier are located within the transition region, and are associated with the high R0A products. These conclusions are supported by numerically calculated band diagrams.
Hg loss rate limitation in HgCdTe thermal processing
Authors: Opyd W. G. , Dimiduk K. C. , Sigmon T. W. , Gibbons J. F.
Published: July 2002

The problem of Hg loss from HgCdTe is investigated for rapid thermal processing of device quality material. Outdiffusion of Hg from HgCdTe is characterized by fitting calculated diffusion profiles to measurements by Rutherford backscattering spectrometry (RBS). Fitting parameters used are diffusion length 2(Dt)1/2, and ratio of surface transfer rate to diffusion rate ht/(Dt)1/2. The results of these calculations include an estimation of diffusion coefficient D, surface transfer rate h, Hg concentration profile C(x,t), Hg flux F(t), and total Hg lost Q(t). Measurements were taken over a temperature range of 300 to 400 °C and for Cd compositions of 0.23 and 0.4. Surface transfer rate is found to have a strong dependence on surface preparation and diffusion coefficient is observed to change significantly under large Hg loss conditions. A vacancy pair diffusion mechanism is suggested. This work is intended to aid in establishing guidelines for device fabrication processes.
A stable optical photometer for vacuum coating
Authors: Bruce P. J. , Hodgkinson I. J.
Published: July 2002

A spatial filter is used instead of the conventional arrangement of a beam chopper and filter to reduce the effects of background light from the evaporation source. Without moving parts and with very simple electronics, the monitor is inherently stable and has a fast response.
Supply and recovery of hydrogen isotopes in high vacuum systems using ZrNi hydride getter pumps
Authors: Nakamura K. , Hoshi T.
Published: July 2002

In order to supply and recover hydrogen isotopes in small high vacuum systems, reversible pumps using ZrNi hydride as a getter material have been developed. Since the PC isotherms for the ZrNi–hydrogen system have two different plateau pressures corresponding to the existence of mono- and trihydrides, it is possible for the getter pumps to have two different equilibrium pressures. Because of the rapid decomposition kinetics of ZrNi hydride, these getter pumps are fast and consume little electric energy to supply hydrogen isotopes to high vacuum (HV) systems, e.g., it requires only 3.8 Wh and 150 s from onset of heating to supply 240 Torr liter (200 Torr×1.2 liter) D2 gas. One of the significant features of this getter pump is that, once activated, the gettering action proceeds at room temperature. Using a combination of two ZrNi hydride getter pumps having two different equilibrium pressures, it is possible to recover hydrogen isotopes completely from HV systems, e.g., 10 Torr D2 gas in a 1.2 liter glass HV system, can be pumped to 1×10−4 Torr within 200 s.
XPS studies of water and oxygen on iron-sputtered natural ilmenite
Authors: Schulze P. D. , Neil T. E. , Shaffer S. L. , Smith R. W. , McKay D. S.
Published: July 2002

The adsorption of D2O and O2 on polycrystalline FeTiO3 (natural ilmenite) has been studied by x-ray photoelectron spectroscopy. Oxygen was found to absorb reactively with Fe0 on Ar+-sputtered surfaces at and above 150 K while D2O was found to adsorb molecularly or in ice layers below 170 K on both Ar+ and O+2 ion-bombarded ilmenite. The D2O desorbs at 170 K with either the formation of an OD complex or a strongly bound molecular layer of water.
The etching of W(111) with XeF2
Authors: Winters Harold F.
Published: July 2002

Modulated beam mass spectrometry has been used to investigate the etch products, surface chemistry, and product desorption mechanisms for the interaction of XeF2 with W(111). Spontaneous etching was found to be very slow at room temperature but was enhanced substantially by bombardment with argon ions. It will be shown that ion bombardment causes the reaction probability (sticking probability) of XeF2 to increase from quite small values to almost unity. The desorbed etch product is primarily WF6 (gas). It will be shown that three factors influence ion enhanced chemistry for the W(111)–XeF2 system. First, ion bombardment causes tungsten and fluorine, which coexist in a stable form on the surface, to react chemically with each other to form WF6 (gas). WF6 physically trapped in the lattice may also be desorbed by ion bombardment. Secondly, ion bombardment produces lattice damage which enhances the spontaneous reaction between XeF2 and W(111). Finally, ion bombardment also tends to suppress the etch rate under some conditions. The first mechanisms seem to dominate the etching reaction except at low XeF2 fluxes. This paper will emphasize the interpretation of these observations.
Properties and microelectronic applications of thin films of refractory metal nitrides
Authors: Wittmer Marc
Published: July 2002

Refractory metal nitride coatings find numerous applications in cutting tools, wear resistant parts, and the jewelry industry. Recent investigations have disclosed interesting applications of thin films of refractory metal nitrides in microelectronics. This review discusses the preparation of such films by reactive evaporation and reactive sputtering and describes various applications in silicon-integrated circuit technology.
Effect of surface treatments on near surface composition of 316 nuclear grade stainless steel
Authors: Rao T. V. , Vook R. W. , Meyer W. , Joshi A.
Published: July 2002

The chemical composition of the surface and near surface region plays a significant role in determining the corrosion behavior of stainless steels. During industrial processing, stainless steels are often subjected to sandblasting, acid pickling, or electropolishing either for the removal of oxide scales or for generating a smooth surface. The effect of such pretreatments on the topography and surface composition has been investigated for 316 nuclear grade stainless steel using scanning electron microscopy and Auger electron spectroscopy. Sandblasted specimens have a rough textured surface whereas acid-pickled and electropolished specimens are relatively smooth. Sandblasted surfaces contain as much as ∼25 at. % Si and exhibit a low concentration of Ni (∼5 at. %). Surfaces which were acid pickled in HF+HNO3 solution have a chromium oxide outer layer similar to that observed in cold rolled sheet. Acid pickled surfaces and sandblasted surfaces, when subsequently electropolished (in a mixture of chromic and phosphoric acids) revealed (i) enrichment of chromium in the outer ∼200 Å and (ii) a sharp oxide–bulk interface. These results are utilized to explain the corrosion susceptibility and radioactive buildup of nuclear grade stainless steels with different surface treatments.
Recent developments concerning segregation and fracture at grain boundaries
Authors: White Calvin L.
Published: July 2002

Certain trace impurities have long been known to embrittle grain boundaries in polycrystalline metals and alloys. In recent years a large body of evidence, directly connecting impurity segregation to intergranular failure, has become available. Indeed, it was conventional wisdom for a time that all intergranular failure could be attributed to segregation of embrittling impurities, and that all segregation degrades grain boundary cohesion. There have been several interesting experimental and theoretical developments during the last 5–10 yr that run counter to this conventional wisdom, the study of which may significantly advance our understanding of the mechanism by which impurities affect grain boundary cohesion. Several examples of beneficial grain boundary segregants will be presented, and the relationship between segregation behavior and grain boundary cohesion will be discussed.
Metal–organic chemical vapor deposition of mercury cadmium telluride epitaxial films
Authors: Hyliands M. J. , Thompson J. , Bevan M. J. , Woodhouse K. T. , Vincent V.
Published: July 2002

The interdiffused multilayer process (IMP) has been implemented on a computer controlled metal–organic chemical vapor deposition (MOCVD) system to improve the compositional uniformity of epitaxial films grown by this technique. Currently, this process is giving compositional uniformity of ≂3% over 1 cm2 on CdTe substrates. Full temperature Hall measurements have been performed to show that as-grown mercury cadmium telluride (MCT) (x∼0.2 and 0.3 epilayers have consistent p-type conductivity with carrier levels in the range of 2.5×1016 cm−3 to 1.7×1017 cm−3 at 77 K. For MCT with composition in the range x=0.2 to 0.3, the acceptor levels increased as an alkyl source was exhausted, but improved when a new source was introduced. The as-grown MCT layers have mobilities typically of 350 cm2 V−1 s−1 at 77 K, consistent with p-type material, and the mobility shows a high degree of reproducibility. Preliminary mercury annealing experiments to identify residual impurity levels were performed. A 15 μm MOCVD layer of composition x=0.19 on a CdTe substrate was isothermally annealed at 250 °C and gave an extrinsic carrier density of 2.2×1014 cm−3 and a mobility of 4.9×105 cm2 V−1 s−1 measured at 9 K. As a consequence of the layer’s composition and low extrinsic properties, the extrinsic level was not reached at 77 K and a donor level of 6.0×1014 cm−3 and a mobility of 3.2×105 cm2 V−1 s−1 were found.
A comparison of CdTe grown on GaAs by molecular beam and organometallic vapor phase epitaxy
Authors: Feldman R. D. , Kisker D. W. , Austin R. F. , Jeffers K. S. , Bridenbaugh P. M.
Published: July 2002

CdTe has been grown on (100)GaAs by molecular beam epitaxy (MBE), organometallic vapor phase epitaxy (OMVPE), and photoassisted OMVPE (POMVPE). Optimum conditions for OMVPE are governed by the thermodynamics of the Cd–Te system. The conditions for growing (100) or (111) material for each technique are presented. (111) growth is shown to proceed via the formation of a relatively Te-poor Ga–As–Te surface phase. Surface treatments which result in different surface structures and yield (100) growth are presented.
Evolution of protrusions during sputtering from composite Ag–Si targets
Authors: Ashida Sumio , Yoshida Toyonobu , Akashi Kazuo
Published: July 2002

In this paper we describe studies on the effects of the sputtering pressure and power on shape and size of microscopic protrusions formed on a target consisting of a small Ag plate placed on a Si wafer. The influence of the target topography change during sputtering on the composition of the sputter-deposited film was investigated. It was found that the Ag concentration of the deposited films was considerably reduced with the growth of the target surface protrusion on Ag plates. This is considered to be attributable to the prevention of sputtered atoms from escaping from the target by surface protrusions.
Thermal stability of metal films on polyimide
Authors: Shanker Kartik , MacDonald Jack R.
Published: July 2002

Metal films of Ag, Cu, Ni, and Mo were deposited on Kapton H and spun deposited Pyralin 2540 polyimides. They were thermally treated for 0.25 to 4 h in vacuum, nitrogen (with about 1% O2), or air in the temperature range of 375 to 648 K. Their diffusion behavior was determined by Rutherford backscattering spectrometry. Ni and Mo showed excellent thermal stability, irrespective of the ambient atmosphere. Cu and Ag were, however, strongly influenced by the atmosphere during thermal treatment. Diffusion coefficient D values were calculated using the complementary error function that showed good correlation with the experimental data. The D values for Cu and Ag remained in the 10−15 cm2/s range when heated in vacuum. In the N2/O2 and air atmospheres, Ag and Cu exhibited higher diffusion at temperatures in excess of about 548 K. Ag D values showed a marked transition at 540–560 K, while Cu D values gradually increased with temperature. Cu D values increased into the 10−14 cm2/s range while that of Ag increased more rapidly to 9×10−13 cm2/s at 613 K. The behavior of all the films was independent of the polyimide (Kapton H or Pyralin 2540) or the film thickness.
A theoretical study of CO on NiAl(110) and (111) surfaces using cluster models
Authors: Tatar R. C. , Messmer R. P.
Published: July 2002

A variety of small molecules adsorb strongly on NiAl surfaces. Although small molecules are not readily chemisorbed on Al surfaces, the activity of NiAl could be rationalized on the basis of the strong affinity of small molecules for surfaces of Ni. Using generalized valence-bond calculations for simple cluster models of the (110) and (111) surfaces, we present evidence for the possibility that on NiAl, Al atoms may be active sites for adsorption of CO and other small molecules. Our results suggest that this can be understood in terms of a reduced electronic population and ‘‘activation’’ of Al in the presence of Ni. This has implications for understanding the chemistry of other bimetallic surfaces. Our model calculations qualitatively account for the differences between the (110) and (111) surfaces of NiAl for several experiments.
Sticking coefficient of molecular and atomic hydrogen on palladium
Authors: Dean B. , Haasz A. A. , Stangeby P. C.
Published: July 2002

Hydrogen recycle and inventory in first-wall materials of fusion reactors are strongly affected by surface and bulk properties—such as coefficients for hydrogen adsorption on the surface, and diffusion in the bulk. Here we present results for the sticking coefficients of molecular and atomic hydrogen on palladium, obtained from measurements of retained hydrogen subsequent to exposure to H2 and sub-eV H0 fluxes. Characteristic curves of the retained hydrogen versus incident fluence were used to determine the sticking coefficients αm and αa for H2 molecules and H0 atoms, respectively.
Growth and structure of chemical vapor deposited silicon carbide from methyltrichlorosilane and hydrogen in the temperature range of 1100 to 1400 °C
Authors: So Myoung Gi , Chun John S.
Published: July 2002

Silicon carbide has been grown at 1100 to 1400 °C by chemical vapor deposition using CH3SiCl3 and H2 gaseous mixture onto a graphite substrate. The effect of deposition temperature, total system pressure, and the CH3SiCl3 input fraction on growth characteristics and structure of deposits has been studied. The experimental results show that the SiC deposition reaction is a thermally activated process with the deposition rate limited by surface reactions. The apparent activation energy is about 26 kcal/mol at a system pressure of 200 Torr and decreases with the increasing total system pressure. In this experiment, polycrystalline β-SiC always has been deposited. The preferred orientation of the deposited SiC films changes from 〈111〉 to 〈220〉 with increasing deposition temperature. The size of the polycrystalline β-SiC grains becomes coarser as the deposition temperature and the CH3SiCl3 input fraction are increased.
On the existence of point defects in physical vapor deposited films of TiN, ZrN, and HfN
Authors: Perry A. J.
Published: July 2002

Sets of experimental data from a number of different techniques are summarized in the present work. They indicate that lattice defects in the form of vacancies and interstitials are very often present in films of the group-IVB nitrides as prepared by plasma enhanced physical vapor deposition methods. Lattice parameters, even allowing for the presence of residual stresses, density and positron annihilation data and the effect of deposition conditions on the reflectance and color of films, together with the effects of tempering, indicate that the fraction of interstitials increases with the energy input into the growing film. Vacancies always appear to be present. Interstitials can be retained after tempering, possibly as extrinsic dislocation loops, and vacancy clusters are formed. X-ray photoelectron spectroscopy spectra appear to be affected by such lattice defects but the understanding of the spectral effects is not sufficiently advanced to allow even a qualitative interpretation.
The properties of aluminum thin films sputter deposited at elevated temperatures
Authors: Inoue M. , Hashizume K. , Tsuchikawa H.
Published: July 2002

We have developed a new planarization technique by sputter deposition of Al–Si thin films at elevated temperatures, and have also studied their properties. The films were deposited by conventional dc magnetron sputtering apparatus without any substrate bias voltage, and during the depositions the substrates were heated on a gas-assisted stage. The step coverage was gradually improved at higher substrate temperatures. However, when the substrate temperature was above 500 °C, the surface topography was very smooth and planarized. In this temperature region, the structure of Al–Si thin films seemed to be different from that of films deposited at the lower temperatures. In addition, the effect of the underlying layer on the step coverage was investigated, and the presence of the TiN undercoat was shown to be effective to the enhancement of the surface migration of Al atoms. Furthermore, significant improvement was obtained in electromigration lifetimes with the TiN undercoat.
Investigation of cosputtered W–C thin films as diffusion barriers
Authors: Yang H. Y. , Zhao X.-A.
Published: July 2002

Polycrystalline thin films of W–C were deposited on single-crystal 〈111〉Si or SiO2 substrates by rf planar magnetron cosputtering of graphite (C) and W targets. The performance of cosputtered W75C25 thin films as diffusion barriers between a 〈111〉Si substrate and metallic overlayers of Ag, Au, or Al was investigated. Backscattering spectrometry and x-ray diffraction are used to detect metallurgical interactions. Four-point probe measurement of resistance is employed to monitor the electrical stability of the metallization schemes upon thermal annealing in a vacuum for 30 min in temperature ranges from 500 to 700 °C. The electrical resistivity of W75C25 films is 140 μΩ cm. A W75C25 layer 1100 Å thick prevents metallurgical interdiffusion and reaction between Au or Ag overlayers and the 〈111〉Si substrates up to 700 °C, and between an Al overlayer and the 〈111〉Si substrate up to 450 °C.
Investigation of silicon in air with a fast scanning tunneling microscope
Authors: Besocke K. H. , Teske M. , Frohn J.
Published: July 2002

Crystalline Si surfaces have been investigated in air with a fast operating scanning tunneling microscope. Pronounced atomic terrace and step structures have been observed on freshly prepared Si(100) surfaces. Displacements and changes in these structures during the scanning procedure have been recorded. The observed structures are attributed to water films on the surface.
Theory of scanning tunneling spectroscopy
Authors: Chen C. Julian
Published: July 2002

A new three-dimensional tunneling theory is introduced for interpreting scanning tunneling spectroscopy (STS) images. By expanding the asymptotic wave function of the acting atom in terms of complete sets of eigenfunctions in spherical coordinates and parabolic coordinates, a derivative rule is derived, which can be applied to interpret scanning tunneling microscopy and STS images immediately. The relation between the observed dynamic conductance and the density of states of the sample is shown in conjunction with a linear bias-distortion correction.
Effect of noble gases on the properties of ion beam sputtered niobium films
Authors: Lichtenwalner D. J. , Anderson A. C. , Rudman D. A.
Published: July 2002

We present result to support our hypothesis that the reflection of the primary beam during ion−beam sputtering of niobium films plays a significant role in determining final film properties, especially in the case of ion−beam sputtering. The film properties are afected by both the noble gas incorporation in and noble−gas bombardment of the growing film. (AIP)
Large grain size thin films of carbon with diamond structure
Authors: Namba Yoshikatsu , Wei Jin , Mohri Toshio , Heidarpour E. A.
Published: July 2002

Diamond thin films were formed by deflecting the flow of CH+4 using a magnetic field. The possibility of involvement of neutral particles and their effects on film formation were examined. The results show (i) the estimated amount of the neutral particle involved during the ionized deposition was nearly 30%, (ii) the surface morphology of the film prepared by the deposition of the deflecting ion was very smooth when it was examined by scanning electron microscopy, and (iii) transmission electron diffraction and transmission electron microscopy indicated relatively large grain polycrystalline diamond films.
A comparison between aluminum and copper interactions with high-temperature oxide and nitride diffusion barriers
Authors: Charai A. , Hörnström S. E. , Thomas O. , Fryer P. M. , Harper J. M. E.
Published: July 2002

A comparative study between the high-temperature diffusion barriers against either Al or Cu has been made. Several conducting oxides (RuO2, Mo–O) and nitrides (W–N) were examined using cross-sectional transmission electron microscopy, Auger electron spectroscopy and x-ray diffraction. Copper was chosen as a less reactive metal than aluminum, and it is widely used in Al–Cu interconnections. Al was found to reduce both oxides to form a thin self-limiting layer of Al2O3, which hinders interdiffusion between Al and Si. In addition, a localized and nonuniform reaction occurs at the RuO2/SiO2 interface giving rise to the metal-rich silicide Ru2Si. Cu was fully oxidized by reduction of RuO2 to form Cu2O but did not reduce Mo–O. For Cu on W–N, no reactions occur. However, we observe a significant modification of the Al/W–N interface. A nonuniform reaction giving WAl12 and a continuous thin amorphous layer which appears to be N-rich aluminum are present. When the W–N is exposed to air before Al deposition, an aluminum oxide is formed at Al/W–N interface and prevents the formation of WAl12. These results indicate that the formation of interfacial Al2O3 is a key ingredient in the success of high-temperature diffusion barriers for Al on Si. However, it may increase the contact resistance.
Tribological phenomena at the head–disk interface of thin-film rigid disks
Authors: Tsai Hsiao-chu , Mehmandoust Yassin , Samani Hamid , Eltoukhy Atef
Published: July 2002

The stiction/friction and contact start/stop tests of thin-film rigid disks were studied. The frictional phenomena observed in a variety of tests are correlated with the surface texturization, lubricant characteristics, and overcoat material. Among other issues, replenishment of lubricant, characterization of lubricant adhesion to surface of the disk, and the compatibility of lubricant with carbon overcoat are addressed. These experimental results showed clearly the highly interacting nature of the head–disk interface phenomena.
Ammonia adsorption and decomposition on several faces of platinum
Authors: Gohndrone J. M. , Olsen C. W. , Backman A. L. , Gow T. R. , Yagasaki E. , Masel R. I.
Published: July 2002

This paper is part of an ongoing study of the structure sensitivity of ammonia adsorption on platinum. In the work here, the adsorption of ammonia on Pt(111) and Pt(210) are compared using temperature programmed desorption (TPD), single-reflection infrared (IR), electron energy-loss spectroscopy (EELS), and molecular-beam techniques. In addition, the adsorption of ammonia on Pt(111), (5×20)Pt(100), (2×1)Pt(110), Pt(210), and Pt(211) are compared with TPD. It is found that the TPD spectrum of ammonia is similar on Pt(111), Pt(100), Pt(110), Pt(210), and Pt(211). There was always a molecular peak between 310 and 370 K, another peak at 170 K, and a multilayer peak at 120 K. The sticking probability was found to vary by a factor of 10 from Pt(210) to Pt(111). However, the infrared spectrum of ammonia adsorbed on Pt(111) is virtually identical to the EELS of ammonia on Pt(210) after accounting for a difference in the sensitivity of IR and EELS. Analysis of the TPD data indicates that the surface concentration of ammonia is a factor of 100–200 higher on Pt(210) than on Pt(111) at 670 K. By comparison, Pt(210) was found to be at least a factor of 100 more active than Pt(111) for ammonia dissociation at 670 K. There is more work to be done. However, the results so far indicate that the vaariations in sticking probability and residence time play an important role in the variations in rate.
Improved quantification and detection limits for oxygen analysis in AlxGa1−x As/GaAs multilayers with secondary ion mass spectroscopy
Authors: Meuris M. , Vandervorst W. , Borghs G.
Published: July 2002

The different contributions to the oxygen background signal in secondary ion mass spectroscopy measurements on AlGaAs and GaAs are investigated. The instrumental parameters for obtaining the lowest detection limits are established. The advantage of a heated sample holder, which reduces the oxygen background quickly after sample introduction in combination with the liquid-nitrogen cryoshield is demonstrated. A complete quantification procedure for oxygen in AlGaAs/GaAs multilayer structure is presented. Even at a conventional vacuum pressure 1×10−9 Torr and a primary current density allowing good depth resolution, a detection limit of oxygen in GaAs of 5×1015 cm−3 could be achieved, increasing with Al content to 1×1017 cm−3 in AlAs.