bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray photoelectron spectroscopy and Auger spectroscopy studies of thin silicon nitride films thermally grown on silicon
Authors: Sobolewski M. A. , Helms C. R.
Published: July 2002

The composition of silicon nitride films obtained by rapid thermal nitridation of silicon in NH3 at 1000–1250 °C for 10–20 s was analyzed using x-ray photoelectron spectroscopy (XPS) and Auger spectroscopy. The films were 10–25 Å thick. The depth resolution of Auger sputter profiling was not sufficient to analyze these films. Instead, depth profiles were obtained by chemical etching techniques. XPS peak intensity profiles and analysis of XPS peak shapes indicated that oxygen contamination was incorporated within the film in a silicon oxynitride state. The concentration of oxygen was peaked at both the surface of the film and the substrate–film interface. Observed XPS peak shifts within the film are explained by the variation in oxygen content. A 10%–20% decrease in Dλ (product of density and electron escape depth) was detected near the interface. Despite the extreme thinness of these films, they were found to be resistant to room-temperature oxidation and to degradation from chemical cleaning techniques.
Study of the background sources in the trace analysis of carbon using secondary ion mass spectrometry
Authors: Kobayashi Junji , Nakajima Masato , Ishida Koichi
Published: July 2002

The background sources have been studied in the trace analysis of carbon (and oxygen) using secondary ion mass spectrometry. In particular, the physical mechanism limiting the detection limit of carbon (and oxygen) in GaAs was investigated. It was speculated that the three kinds of background sources could be discriminated using the simple method that we called the background source analysis (BGA) method. It was found that memory effect was the most harmful barrier to lowering the detection limit of carbon impurity in GaAs at the conventional pressure (10−9 Torr). On the basis of the quantitative BGA method, the best condition of the measurement in the trace analysis of carbon in GaAs was estimated to be 50 nA for the primary beam current at the raster-scanned area of 30×30 μm2.
Etching of thin SiO2 layers using wet HF gas
Authors: van der Heide P. A. M. , Baan Hofman M. J. , Ronde H. J.
Published: July 2002

The etching of SiO2 layers on silicon with HF/H2O vapor mixtures using a N2 gas flow as a carrier was studied. The differences between the etching process of SiO2 on silicon using HF in water solutions and the gaseous etching process were investigated using x-ray photoelectron spectroscopy analysis. The experiments focused on the removal of thin (native) oxide layers. It is shown that HF gas etching yields a good and reproducible removal of the suboxide (SiOx) interface layer. Various parameters influencing the etching process are discussed. In our experiments the HF-gas etch proved to be superior to the liquid-HF etch with respect to the removal of the SiOx layer. After the HF gas etching process a logarithmic regrowth of an oxide layer in air occurs at a rate of 0.2 to 0.3 nm/decade (time in hours). Flashing HF gas etched samples to 700 °C for 2–3 min under ultrahigh vacuum conditions results in complete removal of oxygen.
Low-level extrinsic doping for p- and n-type (100) HgCdTe grown by molecular-beam epitaxy
Authors: Temofonte T. A. , Noreika A. J. , Bevan M. J. , Emtage P. R. , Seiler C. F. , Mitra P.
Published: July 2002

Doping control of (100)-oriented Hg1−xCdxTe layers grown by molecular-beam epitaxy has been achieved in situ by stoichiometric adjustment and by extrinsic acceptor and donor incorporation. Silver and indium were found to be relatively efficient acceptor and donor dopants, respectively, at concentrations lower than previously reported for HgCdTe. Modeling results show that these levels are required for high-performance wide-band-gap p-type on narrow-band-gap n-type heterojunction detectors. Classic variable-temperature Hall behavior is typically observed. However, low temperatures (<77 K) and high fields (to 50 kG) have been used to characterize HgCdTe films, especially p-type ones, which can exhibit anomalous behavior particularly for low doping levels.
A kinematic model of surface evolution during growth and erosion: Numerical analysis
Authors: Katardjiev I. V.
Published: July 2002

A concise and critical review of the basic ideas of the kinematic model of surface evolution during growth and erosion is presented. Further generalization of a recent development based on the Huygens principle of wave-front propagation is briefly discussed. Numerical analysis and consequent numerical procedures based on the generalized kinematic model are also presented. A number of simulation examples of surface evolution are given to illustrate the advantages and capabilities of the numerical method.
X-ray reflectivity study of SiO2 on Si
Authors: Heald S. M. , Jayanetti J. K. D. , Bright A. A. , Rubloff G. W.
Published: July 2002

X-ray reflectivity is a powerful probe of thin film morphology. It can be used to nondestructively determine the interface and surface roughness, thickness, and density of the layers. This paper presents the application of the technique to the case of SiO2 on Si. Experimental reflectivity results with a dynamic range of 106 have been obtained on a number of oxide layers prepared using processing conditions. The reflectivity oscillations caused by oxide layers could be easily observed over this entire range, and significant differences were observed between samples. In particular, a plasma enhanced chemical vapor deposition grown oxide is found to have an interfacial layer of lower density.
Spatial structure of a planar magnetron discharge
Authors: Wendt A. E. , Lieberman M. A.
Published: July 2002

In planar magnetron sputter deposition, metal atoms are sputtered from a cathode target by a magnetically confined plasma. The spatial structure of the planar magnetron discharge and the resultant etch track in the cathode depend on gas pressure, discharge voltage V, current I, and magnetic field strength B. We investigate the distribution of discharge current at a cylindrically symmetric cathode. The radial distribution of current at the cathode has been measured for a range of values of the above parameters using a radially staggered array of 1-mm diameter current probes embedded in the cathode plate. The distribution is peaked at the radius at which the magnetic field is tangent to the cathode, and the width of the distribution w̄, is a function of the discharge parameters. We compare this width to two models of the motion of secondary electrons emitted from the cathode. When the cathode sheath is thin compared to the axial range of the secondary electrons, the scaling is w̄∝V1/4/B1/2. We develop a new model of the magnetron discharge when the cathode sheath is thick compared to the energetic electron gyroradius and obtain w̄∝V1/10I1/5/B4/5. We find that the thick sheath model yields the best agreement to the experiment.
Chemical doping of HgCdTe by molecular-beam epitaxy
Authors: Wu Owen K. , Kamath G. S. , Radford W. A. , Bratt P. R. , Patten E. A.
Published: July 2002

Chemical doping of HgCdTe is an important issue in II–VI compound semiconductors. In this paper, we will report on the molecular-beam epitaxy (MBE) growth and characterization of n- and p-type HgCdTe. We have grown n- and p-type layers of HgCdTe with indium and arsenic as the dopants using MBE at 170 °C–180° C without photo or ion excitation. The doped layers, which range from 1015 cm−3 to 1018 cm−3 have been characterized by a variety of techniques including infrared IR transmission, Hall measurement, scanning electron microscopy, minority carrier lifetime, and secondary ion mass spectroscopy. The results indicate that n-type alloy layers are easier to form than p type because of the efficient incorporation of indium in the mercury (or cadmium) sublattice. Memory effects of indium were not observed. We have also demonstrated that our p-type layers remain p type after mercury anneal indicating that they are extrinsically doped. The breakthrough in chemical doping of HgCdTe has enabled us to grow several double layer heterojunction structures. Several diodes have been fabricated and their electrical and optical characteristics are discussed.
‘‘Pinning’’ and Fermi level movement at GaAs surfaces and interfaces
Authors: Spicer W. E. , Newman N. , Spindt C. J. , Liliental-Weber Z. , Weber E. R.
Published: July 2002

Band bending at GaAs interfaces with either metals or insulators is of considerable importance. Recently a literature has developed, which shows for both metals and insulators, that this band bending can be modified, i.e., the Fermi level position Efi at the interface changes. Of the five metals studied in detail, Ag, Au, Al, Ti, and Cr, three (Au, Al, and Ti) have been shown to produce Fermi level changes on the order of 0.1 eV (i.e., change in the Schottky barrier height φ) on thermal annealing. For n-type GaAs φ decreases for Au, and increases for Al and Ti. These changes of Efi can be explained in terms of the generation of excess As or Ga at the interface due to chemical reactions between the metal and the GaAs. The Fermi levels move toward the conduction-band minimum (CBM) when the As/Ga ratio is increased and toward the valence-band maximum (VBM) when it decreases. The changes in As/Ga ratio have been confirmed independently. No movement is seen for Ag, which is unique in having little reaction with GaAs, or for Cr, which bonds to both As and Ga. The Fermi level position can also be changed at the GaAs insulator interface. Na2S⋅H2O and (NH4)2S treatments of the GaAs surface reduce surface recombination. Recent studies show that such treatments increase rather than decrease the band bending on n-GaAs. All of these results agree with a model in which AsGa and GaAs antisites dominate the interface and Fermi level changes are explained in terms of changes in the relative numbers of these defects.
Improved thickness uniformity in molecular beam epitaxial growth of GaAs using a tilted conical insert crucible
Authors: SpringThorpe A. J. , Majeed A. , Miner C. J. , Wasilewski Z. R. , Aers G. C.
Published: July 2002

Significant improvements in the uniformity of epitaxial layers of GaAs, deposited using a V80-H molecular beam epitaxy system, can be obtained by modifying the crucible so that the flux is directed towards the center of rotation of the substrate. This has been obtained with a dual crucible system, consisting of a tilted conical insert inside a large capacity straight sided crucible. With this combination the layer uniformity can be improved to better than ±1.5% over the useable area of a 76 mm diam substrate and to ±0.7% for 50 mm diam substrates. These results are in excellent agreement with the predictions of recent flux modeling calculations.
Measurements of catalytic efficiency of surfaces for the removal of atomic oxygen using NO*2 continuum
Authors: Wickramanayaka Sunil , Meikle S. , Kobayashi T. , Hosokawa N. , Hatanaka Y.
Published: July 2002

The wall recombination coefficient (γ) of several materials for atomic oxygen was measured introducing a new method based on the NO*2 continuum in a discharge-flow system. This method has many advantages, such as the ability of measuring γ under different pressures, nonessentiality of measuring absolute atom concentrations, simplicity of experimental technique, etc. over the previous methods. Investigated materials in this work were selected specially considering the feasibility of industrial applications of plasmas. Although a few metals show slight differences, most of the calculated values of γ are in agreement with the literature values. Observed γ for Al and Al based materials were in the order of 10−3. The highest and lowest γ measured were of Cu and teflon, as 2.6×10−2 and 7.3×10−5 , respectively.
(1̄1̄1̄) CdTe surface structure: A study by reflection high energy electron diffraction, x-ray photoelectron spectroscopy, and x-ray photoelectron diffraction
Authors: Duszak R. , Tatarenko S. , Cibert J. , Saminadayar K. , Deshayes C.
Published: July 2002

The (1̄1̄1̄) CdTe surface is studied by reflection high energy electron diffraction, x-ray photoelectron spectroscopy, and x-ray photoelectron diffraction (XRD). Several surface reconstructions are described. Shifts in the Cd (3d) binding energy levels allow separation of contribution of surface Cd atoms from that of the bulk. While bulk atoms exhibit XPD effects along the standard crystallographic directions, for surface atoms the diffraction effects occur along distinct directions which correspond to an outwards relaxation of the topmost Te layer. These findings are consistent with a recently proposed model of the CdTe (1̄1̄1̄) surface.
Influence of pressure and radio frequency power on deposition rate and structural properties of hydrogenated amorphous silicon thin films prepared by plasma deposition
Authors: Andújar J. L. , Bertran E. , Canillas A. , Roch C. , Morenza J. L.
Published: July 2002

The influence of radio frequency (rf) power and pressure on deposition rate and structural properties of hydrogenated amorphous silicon (a-Si:H) thin films, prepared by rf glow discharge decomposition of silane, have been studied by phase modulated ellipsometry and Fourier transform infrared spectroscopy. It has been found two pressure regions separated by a threshold value around 20 Pa where the deposition rate increases suddenly. This behavior is more marked as rf power rises and reflects the transition between two rf discharges regimes (α and γ). The best quality films have been obtained at low pressure and at low rf power but with deposition rates below 0.2 nm/s. In the high pressure region, the enhancement of deposition rate as rf power increases first gives rise to a reduction of film density and an increase of content of hydrogen bonded in polyhydride form because of plasma polymerization reactions. Further rise of rf power leads to a decrease of polyhydride bonding and the material density remains unchanged, thus allowing the growth of a-Si:H films at deposition rates above 1 nm/s without any important detriment of material quality. This overcoming of deposition rate limitation has been ascribed to the beneficial effects of ion bombardment on the a-Si:H growing surface by enhancing the surface mobility of adsorbed reactive species and by eliminating hydrogen bonded in polyhydride configurations.
Molecular flow transmission probabilities of rectangular tubes
Authors: Santeler D. J. , Boeckmann M. D.
Published: July 2002

New data are presented on the molecular-flow transmission probability of short rectangular tubes having long-side to short-side ratios from 1:1 to 24:1 and length to short-side ratios from 0.01 to 100. A caution is provided regarding the improper use of transmission probabilities as well as the component conductances derived from them. The view-factor technique was used for the present analysis and is discussed in the report. A cross check of the data using a Monte Carlo analysis was made and yielded extremely good agreement. A short-tube and a long-tube approximation are also presented and compared to the computer analysis. A composite set of short rectangular tube equations for all gas flow regimes, viscous through molecular, is still in process.
The effects of substrate potentials on electron cyclotron resonance plasmas
Authors: Rossnagel S. M. , Schatz K. , Whitehair S. J. , Guarnieri R. C. , Ruzic D. N. , Cuomo J. J.
Published: July 2002

In a conventional, axial electron cyclotron resonance (ECR) plasma source, the substrate is typically in the diverging magnetic field region immediately downstream from the ECR region. Due to the high electron mobility along magnetic field lines, the substrate potential may influence the properties of the plasma. A substrate electrode consisting of seven, individually biasable, concentric rings was positioned below the ECR source, such that the potential at the termination of the field lines could be controlled. The ECR source used was a commercial, 1.5-kW device operating at 2.45 gHz and utilized two large electromagnets to provide magnetic fields in the range of 200–1000 G. The plasmas were diagnosed by means of a microwave interferometer in the source region, an automated Langmuir probe, and an array of ground potential metal rings in both the source and sample regions of the chamber. The results suggest that ions in this source are poorly confined (by the magnetic field) while electrons are well confined. The electron density could be increased slightly by electron reflection from the substrate region, or could be depleted strongly by substrate potentials exceeding the floating potential. The net efficiency of these sources is low: only about 14% of the ion flux from the plasma is incident on the sample position. The rest of the ions are lost at the source walls.
Effect of Ge overlayers on the electrical resistance of thin Cr films
Authors: Schröder K. , Walsh L.
Published: July 2002

Cr films were prepared by evaporation on Corning glass plates. The base pressure of the vacuum system was in the 10−9 to 10−8 Torr range. The resistance R of the Cr films was measured at room temperature. The deposition of NaCl on a Cr film lead to practically no change in the resistance. However, Ge overlayers reduce R by about 10% for films about 10-nm thick. The maximum resistance decrease was found for a Cr film with a thickness of about 3 nm. There the Ge overlayer reduced R by nearly 40%. The resistance decrease due to Ge overlayers cannot be explained with conduction in the Ge overlayer. It seems also unlikely that one can contribute it to the formation of a compound at the interface between the Cr film and the Ge overlayer. It is suggested that the change in R may be associated with the exciton mechanism, but more work is required before we can understand the effect.
Chemical nature of the barrier in Pb/YBa2Cu3O7−x tunneling structures
Authors: Vasquez R. P. , Foote M. C. , Hunt B. D. , Bajuk L.
Published: July 2002

Several reports of reproducible tunneling measurements on YBa2Cu3O7−x thin films or single crystals with a Pb counterelectrode have recently appeared. The nature of the tunnel barrier, formed by air exposure, in these structures has been unknown. In the present work, the chemical nature of the tunnel barrier is studied with x-ray photoelectron spectroscopy (XPS). Laser-ablated films grown on LaAlO3 which have been chemically etched and heated in air are found to form nonsuperconducting surface Ba species, evident in an increase of the high binding energy Ba 3d and O 1s signals. A deposited Pb film ∼10 Å thick is found to be oxidized, and Cu+2 is partially reduced to Cu+1. The tunneling barrier thus appears to consist of species resulting from a combination of the air exposure and a reaction between the superconductor and the deposited Pb counterelectrode.
Scanning tunneling microscopy study of supported Pt and Pd catalysts: Microstructure and morphology
Authors: Yeung King Lun , Wolf E. E.
Published: July 2002

Supported Pt crystallites were prepared by two different methods, physical deposition by vacuum evaporation of Pt metal, and chemical impregnation from a precursor solution. Physically deposited Pt forms large elongated crystallites of approximately pillbox or inverted boat shape with an irregular, highly striated surface, while Pt crystallites from impregnated catalysts are small and have regular boxlike morphology. H2 treatment of the physically deposited Pt results in fragmentation of the Pt crystallites into smaller but irregularly shaped particles. Pd crystallites prepared from a tetraammine precursor are large and ellipsoidal in shape, while the crystallites prepared from a tetrapyridine precursor are small and have emeraldlike morphology. The shape distribution of the supported particles for Pt and Pd impregnated catalysts shows that only 30% to 40% of the crystallites have an equilibrium aspect ratio of 1.0 and 60%–70% have an aspect ratio ≳1.0 characteristic of metastable morphology.
Moisture-induced interfacial oxidation of chromium on polyimide
Authors: Furman B. K. , Childs K. D. , Clearfield H. , Davis R. , Purushothaman S.
Published: July 2002

Interfacial strength of Cr/polyimide thin film structures and its durability to thermal exposure as a function of process variables was determined by 90° peel testing. Results were correlated with surface and interfacial characterization of thin film structures and peel failure surfaces using Auger, x-ray photoelectron spectroscopy, and secondary ion mass spectroscopy techniques. Initial adhesion in as-deposited Cr/polyimide structures exhibits a mild dependence on radio-frequency Ar plasma surface modifications and deposition process conditions. However, the durability of these structures under thermal process cycles depends strongly on these process parameters, greater doses of energetic ion bombardment were seen to yield greater durability. Characterization of peel failure surfaces revealed that fracture in the as-deposited and peeled samples occurs cohesively in the near surface region within the polyimide. Cohesive fracture was also seen in some samples after thermal process exposures, with peel strengths that were acceptable but somewhat less than the corresponding unannealed samples. Failure at an oxidized Cr to polyimide interface was observed in other thermally annealed samples whose peel strengths were very low. It is proposed that both types of degradation are caused by the water absorbed in the polyimide. The slight adhesion degradation appears to be due to water reaction and hydrothermal weakening of the modified near surface polymer region during thermal processing. The more catastrophic degradation is due to the oxidation of the Cr by the absorbed water during the anneal cycles. Results of critical experiments that verify these hypotheses are presented.
Diagnostics of dual source reactive magnetron sputter deposition of aluminum nitride and zirconium nitride thin films
Authors: Sell Jeffrey A. , Meng W. J. , Perry Thomas A.
Published: July 2002

The process of reactive sputtering of elemental Al and Zr in an Ar/N2 mixture has been examined by atomic absorption spectroscopy. Results have been presented further supporting the existence of a chemical competition effect during dual source reactive sputtering. The growth of epitaxial AlN film on Si(111) by laser beam interference is monitored in real time, which yielded a measurement of the true growth rate. By correlating the two measurements, a linear proportionality between the true growth rate of AlN and the gas phase Al density has been demonstrated.
Copper deposition onto polyetherimide: Interface composition and adhesion
Authors: Burrell Michael C. , Porta G. M. , Karas B. R. , Foust D. F. , Chera J. J.
Published: July 2002

The chemical composition and adhesion of the interface between copper (applied via an electroless bath or by vacuum evaporation) and polyetherimide substrates are investigated. Electroless copper deposition requires a chemical pretreatment to ensure final adhesion values of 180–220 g/mm, whereas comparable adhesion is obtained for evaporated copper without pretreatment. Both metallization methods require a postdeposition heat treatment to maximize the copper/polyetherimide adhesion. The interface side of the metal deposits are exposed by a substrate dissolution technique and analyzed using x-ray photoelectron spectroscopy. A thin (∼30 Å) insoluble polymer layer remains which is believed to chemically interact with the metal. In addition, interfacial oxidation of the metal deposit increases with the application of the heat treatment. The role of this interfacial chemistry on copper/polyetherimide adhesion is discussed.
Room temperature oxidation of ultrathin deposits of tin on the Au(111) surface
Authors: Zhang Y. , Slavin A. J.
Published: July 2002

The growth of oxide on bulk tin has been modeled in a layer-by-layer fashion by using successively greater deposits of Sn on a Au(111) surface. The Au does not oxidize and merely acts as a support. Auger electron spectroscopy, electron energy-loss spectroscopy, and work function measurements have been made. The initial fast-growth stage of the oxide is complete by about 3×104 L. SnO2 forms either for oxygen exposures up to 1900 L or with oxide films limited to about 1 monolayer in thickness. For films up to nine atomic layers thick, a thin layer of SnO, probably one monolayer in thickness, forms on the surface with SnO2 underneath. It appears that for a Sn deposit up to the equivalent of one atomic layer in thickness, the oxygen bonds above the surface, while for larger deposits the oxygen moves below the surface. A comparison is made with earlier results for lead and bismuth.
Preparation of strontium titanate thin film on Si substrate by radio frequency magnetron sputtering
Authors: Cho Neung-Ho , Nam Seung-Hee , Kim Ho-Gi
Published: July 2002

Strontium titanate (SrTiO3) thin films on silicon wafers were grown by radio frequency (rf) magnetron sputtering at various growth conditions. The films were characterized using x-ray diffraction (XRD), infrared (IR) spectroscopy, and scanning electron microscopy (SEM). The films deposited below 200 °C were amorphous state and above 300 °C were crystalline state according to XRD and IR spectroscopy. The surface of strontium titanate film deposited at room temperature was smooth and those deposited at higher substrate temperatures showed discernible grains of which size were increased with increasing substrate temperature. By annealing at 600 °C in oxygen atmosphere, the amorphous strontium titanate were crystallized and the grain size of the films were increased. The deposition rate of the films were investigated by the growth parameters such as substrate temperature, Ar–O2 gas composition, and rf power.
Process effects on structural properties of TiO2 thin films by reactive sputtering
Authors: Wicaksana Dwi , Kobayashi Akihiko , Kinbara Akira
Published: July 2002

We have been investigating the growth of crystalline titanium dioxide films at deposition temperature between room temperature and about 400 °C. The films were prepared by a dc magnetron reactive sputtering on glass and Si(100) substrates. The structural properties of the films were analyzed by x-ray diffractometry. The influence of total pressure, oxygen mole fraction in the mixture of Ar–O2, discharge current, and substrate temperature on the structural properties were studied. In addition to higher substrate temperature, low total pressure, high discharge current, and small oxygen mole fraction were shown to be preferable for growing anatase–rutile mixture films. Annealing of the films in air at 850 °C showed that anatase–rutile transformation strongly depends on the deposition temperature; the films deposited at temperature below 400 °C were converted to the anatase–rutile mixture films, and the films deposited at 400 °C to complete rutile films.
Temperature-dependent x-ray photoelectron diffraction of Pb(100): Experimental results and the single-scattering cluster model
Authors: Murphy E. A. , Elsayed-Ali H. E. , Park Ken T. , Gao Y.
Published: July 2002

An angle-resolved x-ray photoelectron diffraction study of the temperature-dependent surface structure of Pb(100) is performed. Below 550±11 K, the decrease in forward-scattered intensity attenuation is exponential with temperature. The intensity attenuation of the forward-scattered peaks is much larger than predicted by both single-scattering and multiple-scattering x-ray photoelectron diffraction models for a bulklike lattice. Corrections for surface relaxation and thermal expansion in the single-scattering cluster model result in an increase in the predicted intensity attenuation; however, sufficient agreement between experiment and calculation is not achieved.
Temperature-dependent composition, ordering, and band bending at GaP(100) surfaces
Authors: Vitomirov I. M. , Raisanen A. , Brillson L. J. , Lin C. L. , McInturff D. T. , Kirchner P. D. , Woodall J. M.
Published: July 2002

We have used soft x-ray photoemission spectroscopy (SXPS), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED) to investigate thermally induced changes in atomic composition, bonding, and geometric ordering at GaP(100) surfaces prepared by molecular-beam epitaxy. Following growth, GaP(100) surfaces were coated with several monolayers of P, after which an ∼2000 Å-thick As cap was applied to seal the structure for transfer to analytical chambers. Surface-sensitive SXPS core-level spectra and more bulk-sensitive AES spectra collected at in situ annealed surfaces indicate complex changes in P, As, and Ga atomic ratios throughout the 350–650  °C desorption temperature range. Core-level photoemission intensity ratios reveal rapid loss of both P and As for surface annealing temperatures below 450 °C, a dramatic increase (decrease) in the P (As) concentration in the 450–550 °C range, and a relatively stable, stoichiometric GaP(100) surface composition for temperatures between ∼550 and 640 °C, above which thermally driven surface decomposition becomes noticeable. Existence of clear LEED patterns, (1×2) for desorption temperatures below ∼450 °C and (4×2)-c(8×2) above this temperature, indicates little sensitivity of GaP(100) surface reconstructions to details of surface stoichiometry and bonding. We propose that both this insensitivity and the abrupt changes in the P to As atomic ratios indicate strong competition between the two anions to form bonds with Ga surface atoms. In this context, compositional and structural details of decapped GaP(100) depend sensitively on the interplay of surface desorption, atomic diffusion from the substrate to the free surface, and the anion-cation chemical bonding at the surface. Overall, our work demonstrates the success of As and P capping combined with subsequent thermal desorption in producing stable GaP(100) surfaces with desired chemical and electronic properties.
Calculation of the Schottky barrier height at the Al/GaAs(001) heterojunction: Effect of interfacial atomic relaxations
Authors: Dandrea R. G. , Duke C. B.
Published: July 2002

First-principle local density functional calculations are used to determine the equilibrium atomic geometry and associated Schottky barrier height at the ideal Al/GaAs(001) interface. The 1.3% lattice mismatch (after 45° rotation of the Al into an epitaxial position) causes a 3% tetragonal distortion of fcc Al grown on a GaAs(001) substrate. There are also substantial interface-localized atomic relaxations from this tetragonal geometry: the Ga–As layer spacing nearest the interface lengthens, while the Al layers near the interface are found to strongly buckle. The interface considered here is composed of an As–Al bond, and the equilibrium As–Al bond length is found to be about 10% larger than that of zincblende AlAs. Calculation of the Schottky barrier heights for the cubic, tetragonal, and buckled-tetragonal geometries shows strong Fermi level pinning: the barrier heights vary by less than 0.1 eV for the various geometries considered. Only interfacial relaxations which change the As–Al interfacial bond length are found to alter the Schottky barrier height.
Thermal stability of encapsulated tungsten/carbon multilayer thin films
Authors: Chao B. S. , Gonzalez-Hernandez J. , Chan A. R. , Gavulic J. M. , Ovshinsky S. R. , Wood J. L.
Published: July 2002

Tungsten/carbon (W/C) multilayer thin films prepared by sputtering on unheated Si (100) substrates were encapsulated with two types of layers having low x-ray absorption. The encapsulating layers are SiNx and carbon prepared by plasma enhanced chemical vapor deposition and sputtering techniques, respectively. Isochronal annealings for 1 h in the temperature range from 300 to 600 °C and isothermal annealings at 300 and 400 °C were carried out under ambient conditions (in air) on coated and uncoated multilayers. Previous studies have shown that unprotected W/C multilayers annealed in air exhibit oxidation at relatively low temperatures (∼300 °C). In the present study, we have used Raman scattering, Auger depth profiling, and scanning electron microscopy to investigate the effects of thermal treatments on the encapsulated W/C multilayers. The results indicate that oxidation of both W and C layers takes place during annealing at temperatures as high as 600 °C on the SiNx coated multilayer.
Adsorption and decomposition of Ge2H6 on Si(100)
Authors: Klug Debra-Ann , Du Wei , Greenlief C. Michael
Published: July 2002

The adsorption and decomposition of digermane, Ge2H6, on the Si(100)-(2×1) surface has been investigated with the intent of elucidating the surface processes leading to the deposition of epitaxial Ge thin films from gaseous Ge-containing sources. Exposure of Ge2H6 to Si(100) at 110 K results in molecular adsorption. Upon heating to 150 K, Ge–Ge bond scission occurs and a surface covered with germyl groups is observed. Warming the surface to higher temperatures decomposes the germyl surface groups. The final reaction products are H2 and atomic Ge. The hydrogen thermal desorption that results from the decomposition of Ge2H6 contains features from a distribution of surface sites. Some of the desorption sites are strongly influenced by Ge, lowering the desorption temperature of H2 by over 150 K when compared to the clean silicon surface.
Epitaxial bilayer growth of CaF2(111)/Pd(111) on CaF2(111) substrates
Authors: Jo B. H. , Vook R. W.
Published: July 2002

Epitaxial Pd(111) films were grown in UHV on air-cleaved CaF2(111) substrates. Subsequently, epitaxial CaF2(111) films were grown on top of the Pd layer. All films were grown by vacuum evaporation techniques. The growth conditions, structure, and surface morphology of the evaporated epitaxial bilayers of Pd and CaF2 were studied with reflection high energy electron diffraction, x-ray diffraction, and scanning electron microscopy. This epitaxial dielectric film/metal film/insulator substrate structure has possible important applications for monolithic microwave integrated circuit devices.
Plasma passivation of gallium arsenide*
Authors: Herman J. S. , Terry F. L.
Published: July 2002

Improved electrical properties of the SiO2–GaAs interface have been obtained using in situ plasma surface treatments prior to film deposition. We present a comparison of several hydrogen based plasma passivation schemes: H2, H2/N2, and H2S. Hydrogen plasmas remove native oxides, while nitrogen or sulfur form passivating surface layers. Samples were characterized using metal–insulator–semiconductor C–V analysis, x-ray photoemission spectroscopy (XPS) and spectroscopic ellipsometry. The H2/N2 and H2S treated samples display improved C–V characteristics. XPS indicates the presence of nitrogen and sulfur respectively on the uncapped samples, although little evidence remains after SiO2 deposition. H2S plasmas offer the best results, providing a self-terminating process that prevents roughening of the GaAs surface by hydrogen plasma etching. However, surfaec doping effects were observed after exposure to high temperatures.
Trapping and behavior of particulates in a radio frequency magnetron plasma etching tool
Authors: Selwyn Gary S. , Haller Kurt L. , Patterson Edward F.
Published: July 2002

Particle contamination has been studied in a commercial, magnetron reactive ion etching tool using rastered laser light scattering. Particles present in the plasma were imaged in real time, showing their spatial position and motion. The effect of the rotating magnetic field was also studied. In the absence of the magnetic field, particles were trapped near the inside circumference of the wafer clamp ring directly over the edge of the wafer, near the protruding ‘‘fingers’’ contacting the wafer. With the rotating magnetic field, particles moved in a wave like motion within the confines of the clamp ring and near the interior tool walls. Magnetron operation also resulted in a decrease of the sheath thickness, suspending particles closer to the wafer. Several process changes were shown to promote particle removal from the plasma.
CO adsorption on Pd(111) and Pd(100): Low and high pressure correlations
Authors: Szanyi János , Kuhn W. Kevin , Goodman D. Wayne
Published: July 2002

The adsorption of CO on Pd(111) and Pd(100) have been studied using infrared reflection–absorption spectroscopy over a wide range of CO pressures and temperatures. A strong dependence of CO adsorption on the initial conditions was found for Pd(111) while CO adsorption on Pd(100) was essentially independent of the conditions of adsorption. Initial isosteric heats of adsorption of 30 and 38 kcal/mol were determined for Pd(111) and Pd(100), respectively. For Pd(111) and equilibrium phase diagram was constructed on the basis of the infrared (IR) data. The excellent correspondence among IR data for the single crystal Pd surfaces and a supported Pd catalyst suggests that the Pd particles in the supported catalyst consist primarily of low index [(111) and (100)] crystal faces.
Reactive ion etching induced damage to SiO2 and SiO2–Si interfaces in polycrystalline Si overetch
Authors: Gu Tieer , Ditizio R. A. , Awadelkarim O. O. , Fonash S. J. , Rembetski J. F. , Aum P. , Reinhardt K. A. , Chan Y. D.
Published: July 2002

The effects of reactive ion etching on the properties of SiO2 and SiO2–Si interfaces have been examined for the case of polycrystalline Si overetch exposures. HBr/Cl2-based polycrystalline Si etch chemistry was used and damage effects for thermally grown oxides with various thicknesses were determined as a function of the overetch exposure times. A large amount of charge was found from capacitance–voltage measurements to be created in the plasma exposed oxides. This charge density increased with increasing overetch time and decreasing initial oxide thickness. Ramp voltage and constant current stress tests were both used to determine the dielectric strength and long-term reliability of these same plasma exposed oxides. A very significant degradation of charge to breakdown was found for the plasma exposed oxides as compared to unexposed control oxides.
Creation of deep gap states in Si during Cl2 or HBr plasma etch exposures
Authors: Awadelkarim O. O. , Gu T. , Ditizio R. A. , Mikulan P. I. , Fonash S. J. , Rembetski J. F. , Chan Y. D.
Published: July 2002

We explore the effects of polycrystalline Si overetches on the Si substrate in the SiO2/Si materials system. Conventional reactive ion etching (RIE) and magnetically enhanced RIE (MERIE) with Cl2 or HBr-based chemistries are used. The introduction of electrically active gap states, four hole traps, and an electron trap in the Si substrate during these overetches is revealed by deep level transient spectroscopy. The production rates of these observed defects are found to be unaffected by the magnetic field; however, due to a defect–hydrogen interaction, these rates are observed to become slower in long-duration overetching using hydrogen-rich plasmas in the MERIE mode. Based on their annealing and electronic properties, these traps are tentatively assigned to multivacancy defect structures, and the formation and interaction mechanisms for the suggested defects are discussed in terms of a phenomenological model in which the single vacancy is proposed to play a key role.
Radio-frequency reactive sputter etching in magnetron fields
Authors: Davies K. E. , Gross M. , Horwitz C. M.
Published: July 2002

The etch rates of materials in rf discharges can be enhanced at low target voltages and low discharge pressures by the application of magnetic fields. In a previous article magnetic enhancement in diode and hollow cathode systems was experimentally studied using an axial magnetic field, applied perpendicular to the target. The field in the present article is applied parallel to the target surface, in a magnetron configuration. Experimental results are given here for etch rate, uniformity, and power input. Etch rates of SiO2 were studied as a function of CF4 pressure, magnetron field, and mechanical discharge confinement. Various electrode shapes were used to confine the discharge and hence increase discharge ionization. Etch rate uniformity at low pressure was measured as a function of electrode confinement and magnetic field, and is discussed in terms of both the motion of glow electrons and the measured sheath (or dark space) heights. Etch rates increase with increasing gas pressure, electrode confinement, or magnetron field. At 2 Pa CF4 pressure and 975 Vpp at 13.56 MHz in a diode machine, etch rates increased by a factor of 10 using either electrode confinement or a 208 G magnetron field. Both methods improve electron trapping, thereby increasing ionization and etch rates. With applied voltage and gas pressure held constant, magnetron fields increase etch rate by a factor of 9 for a diode, 5 for an unconfined hollow cathode, and 1.7 for a target confined hollow cathode. Magnetron fields result in very poor etch rate uniformity, which can however be improved by adding electrode confinement to improve electron trapping. Etch power efficiency varied by only 33% over the magnetic field range studied here, indicating little magnetic field-induced depletion of chemically reactive species even in our most intense discharges. However, compared to the diode, power efficiency was up to two times greater in the electrode-confined hollow cathodes due to their more efficient utilization of these chemically reactive species.
Study of the effect of a probe on the plasma in the source region of an electron cyclotron resonance discharge
Authors: Bowden M. D. , Kimura F. , Muta H. , Uchino K. , Muraoka K. , Maeda M.
Published: July 2002

Langmuir probes are commonly used to measure electron density and temperature in the low temperature and low density plasmas used in plasma processing, although the plasma conditions are sometimes not ideal for such measurements. We report measurements of the perturbing effect of such probes in the high magnetic field region of an electron cyclotron resonance discharge by making Thomson scattering measurements of electron temperature and density under normal operating conditions and also in the presence of a probe. The results revealed that the probe clearly qualitatively changed the plasma. An attempt to quantify this change appeared to indicate that the effect of the probe was to decrease the electron density and increase the electron temperature in the vicinity of the probe.
Nuclear magnetic resonance probe for low level hydrogen detection
Authors: Levy D. H. , Gleason K. K.
Published: July 2002

The design for a nuclear magnetic resonance (NMR) probe capable of detecting hydrogen signals at levels of <5×1016 H/sample is presented. In order to reduce background signals, the design eliminates polymeric materials from the probe head area and allows for a dry nitrogen purge during experimental runs to avoid signals due to ambient moisture. In addition, a metal cleaning process is employed that removes 1H NMR detectable contaminants from copper components. Use of this NMR probe for thin solid films and other low hydrogen content materials is demonstrated. The probe holds these samples without a NMR sample tube, further eliminating background hydrogen signals. In addition, a calibration curve for low hydrogen content standards demonstrates that NMR signal response is indeed linear at low hydrogen concentrations, leading to accurate quantification of hydrogen.
Simple source of atomic hydrogen for ultrahigh vacuum applications
Authors: Bischler U. , Bertel E.
Published: July 2002

A simple doser for atomic hydrogen is described. It basically consists of a tungsten capillary which on the outlet is heated by electron bombardment to 1800–2000 K. This temperature is sufficient to achieve nearly total H2 dissociation under relevant working pressures. The performance of the atomic hydrogen source was tested by H adsorption studies on Cu(110). The saturation coverage on this surface could be achieved with a nominal exposure which was smaller by a factor of ∼10−3 as compared to conventional methods of dissociation on a hot filament. The higher efficiency of the present H source greatly reduces the risk of sample contamination.
Comparing reactive ion etching of III–V compounds in Cl2/BCl3/Ar and CCl2F2/BCl3/Ar discharges
Authors: Juang Y. Z. , Su Y. K. , Shei S. C. , Fang B. C.
Published: July 2002

The reactive ion etching (RIE) of GaAs, AlGaAs, InP, InGaAs, InGaAsP in Cl2/BCl3/Ar or CCl2F2/BCl3/Ar discharges is investigated as a function of the plasma parameters: power, pressure, and relative composition as well as etching time. For the reason of In-based fluoride with high boiling point, the etching rates of all of these materials are faster in Cl2/BCl3/Ar in comparison to CCl2F2/BCl3/Ar. The In-based compounds show a similar dependence on power density and discharge composition, but it is quite different from GaAs. When discharges containing CCl2F2 are used, the surface morphologies are quite rough after the treatment of RIE with either type of discharge, although smooth etching surfaces can be obtained under appropriate conditions. Using BCl3 containing gas discharges will enhance smooth surface and maintain high etching rate. For selective etching of GaAs on AlGaAs, gas mixtures containing CCl2F2 are used. High performance and high selective etching can be obtained by using CCl2F2/BCl3/Ar gases mixtures. Photoresist or SiO2 were used as etching masks. Silicon dioxide is better than the photoresist mask for its low etching rate and sputtering to III–V compounds, and it could be in situ removed by CF4 plasma. The photoluminescence measurements show high performance of etched results when the power density was maintained at less than 0.6 W/cm2.
Growth and characterization of Si1−xGex/Si multilayers on patterned Si(001) substrates using gas source molecular beam epitaxy
Authors: Zhang J. , Marinopoulou A. , Hartung J. , Lightowlers E. C. , Anwar N. , Parry G. , Xie M. H. , Mokler S. M. , Wu X. D. , Joyce B. A.
Published: July 2002

Ridges developing during growth of a Si buffer layer on a Si(001) substrate patterned with V grooves, are utilized as an alternative approach to quantum wire fabrication by gas source molecular beam epitaxy. Secondary electron microscopy indicates the advantages in quality and definition of those microstructures over quantum wells grown in the vertex of V grooves. Photoluminescence results of multiple quantum well (MQW) structures grown on patterned substrates, show the existence of a more spatially confined structure and that the MQWs are almost free of dislocations.
New technique for coprecipitation of organic dye with polymer under high vacuum
Authors: Hiraga T. , Tanaka N. , Takarada S. , Hayamizu K. , Kikuchi N. , Moriya T.
Published: July 2002

A new technique for coprecipitation of organic dye with polymer using high vacuum (HV) conditions has been developed. Rapid evaporation of solvents from a solution of dye dissolved polymer under HV is essential for controlling the association of dye molecules in the solidified polymer matrices in contrast to a slow evaporation method under atmospheric conditions. Varied sizes of the association in densely dissolved dye/polymer systems have been experimentally observed.
Oxygen-plasma-enhanced crystallization of a-Si:H films on glass
Authors: Yin Aiguo , Fonash S. J.
Published: July 2002

An oxygen plasma exposure has been used successfully to develop a new unique low thermal-budget crystallization process for a-Si:H films on glass. In this study, 1500 Å a-Si:H films deposited by plasma-enhanced chemical vapor deposition were first exposed to an electron cyclotron resonance oxygen plasma. These exposed films were then crystallized by either furnace thermal annealing or rapid thermal annealing. Compared to control samples without the plasma treatment, the crystallization time was found to be reduced from 14 to 5 h in 600 °C furnace annealing, and the crystallization temperature was reduced from 680 to 650 °C for 5 min rapid thermal annealing. X-ray photoelectron spectroscopy demonstrates that a thin layer of SiO2 was grown on the a-Si films during the oxygen plasma exposure. Our model proposes that oxygen plasma exposure produces a supersaturation of silicon atoms below the Si/SiO2 interface and these serve to enhance poly-Si grain growth during crystallization.