bluuebunny/crossref_metadata_2025 huggingface dataset:
Photointeraction between Oxygen and Nonporous Particles of Anatase
Authors: Formenti M. , Courbon H. , Juillet F. , Lissatchenko A. , Martin J. R. , Meriaudeau P. , Teichner S. J.
Published: July 2002

Small particles (diam 150 Å) of anatase (TiO2) may be reduced on surface by uv irradiation at room temperature in vacuo. Irradiation in oxygen creates O2− species which are active in the oxidation of hydrocarbons at room temperature in ultraviolet.
Time-of-Flight Analysis of Ions and Excited Neutrals Released by ESD of CO on (100) W
Authors: Newsham Ivor G. , Sandstrom Donald R.
Published: July 2002

The release of ions and excited neutrals by the interaction of low energy electrons with CO on (100) W is studied by a time-of-flight technique. The flight time distributions, approximate threshold energies, adsorption kinetics, and dependence behavior of the desorbed particle currents upon heating and heavy electron bombardment are presented for the excited neutrals, CO+ and O+ ions in the temperature range 110–600 K. The fact that the binding state producing the excited neutrals is identical with the state releasing CO+ ions suggests that the excited neutrals are CO molecules.
Angular dependence of SiO2 etching in a fluorocarbon plasma
Authors: Cho Byeong-Ok , Hwang Sung-Wook , Lee Gyeo-Re , Moon Sang Heup
Published: July 2002

SiO 2 etch rates in a CF4 plasma were obtained at various surface angles using a Faraday cage with pinholes on the upper plane through which ions are incident on the substrate fixed at various angles inside the cage. The reactive ion etching experiments were performed at 5 mTorr in a wide bias-voltage range from −100 to −800 V. The normalized etch-yield curves showed virtually the same angular dependence regardless of the ion incident energy. The curve shape was similar to that of physical sputtering except that the ratio of the maximum yield to that at 0° was as low as about 1.3. This is the deviation from the cosine dependence characteristic of chemical sputtering, which is the main mechanism of SiO2 etching in a fluorocarbon plasma. This deviation is partly attributed to the fluorocarbon polymer film, which existed as a few monolayers-thick film on the substrate surface at low angles near 0° but as a submonolayer at high angles between 45° and 75°. The effect of the film-coverage difference on the deviation is explained in terms of reactant chemisorption, product desorption, energy deposited by ions causing the collision cascade, and incorporation of projectiles and recoils leading to the mixing effect. The deviation is also attributed to physical sputtering, which became comparable to chemical sputtering as the ion energy increased. Both factors, i.e., the formation of the thin fluorocarbon polymer film and physical sputtering, are supposed to contribute to the curve deviation, although their relative importance changed with the ion incident energy.
Electron Beam Testing of Circuit Interconnections using Collector Stabilized Conductor Charging
Authors: Sebeson J. M.
Published: July 2002

A noncontact procedure for sensing continuity and isolation faults in large, dense interconnection patterns by means of selective deposition of charge by an electron beam is proposed and discussed. When the accelerating potential is properly chosen, a marked variation in the secondary electron signal occurs during the charging of an electrically floating element to an equilibrium potential. This phenomenon forms the basis of the method. A laboratory system has been constructed to demonstrate the procedure. Results obtained indicate agreement with the basic theory and demonstrate the application of the technique to continuity and isolation testing of conductor films. Electron-beam testing has a clear advantage over mechanical-probe testing in terms of speed and flexibility. The less attractive features include the need for a vacuum system and the inability to detect continuity faults when the fault resistance is less than about one megohm.
Thick deposits of ultrahigh-purity aluminum
Authors: Love R. B. , Bower W. K.
Published: July 2002

Films of ultrahigh-purity aluminum 150-μ thick were vacuum deposited on nickel ribbon as a technique for fabricating strip conductors. These films were deposited from an electron-beam gun which was mounted in an oil diffusion pumped vacuum system. Sources of film contamination were isolated analytically and the techniques used to eliminate them are described and verified analytically.
Surface and line-edge roughness in solution and plasma developed negative tone resists: Experiment and simulation
Authors: Patsis G. P. , Tserepi A. , Raptis I. , Glezos N. , Gogolides E. , Valamontes E. S.
Published: July 2002

A methodology is described for the experimental and theoretical study of surface roughness (SR) and line-edge roughness (LER) and their relation for solution and plasma developed resist schemes. Experimental results for a negative-tone nonchemically amplified siloxane bilayer resist scheme are shown. In addition, a molecular-type simulation of SR and LER is presented. The simulator can follow the appearance of SR and LER after each process step and predict the roughness dependence on material properties and process conditions. The simulation results are compared with SR experimental data for a negative-tone chemically amplified epoxy resist.
Study of chromium oxide film growth by chemical vapor deposition using infrared reflection absorption spectroscopy
Authors: Bermudez V. M. , DeSisto W. J.
Published: July 2002

Polarization-modulated infrared reflection absorption spectroscopy (aided by numerical modeling) is demonstrated as a potentially useful tool for the study of the chemistry of materials growth and processing under steady-state conditions. This approach is applied to a preliminary investigation of the growth of Cr oxide films at low-temperature (⩽270 °C) on Al2O3 using Cr(CO)6 and O2. The use of a buried metal layer and of polarization modulation enables detection of surface species with good sensitivity in the presence of strong absorption by gas-phase molecules. Cr(CO)6 weakly interacting with Al2O3 and Cr oxide surfaces has been observed under equilibrium conditions, and a desorption energy of ∼11 kcal/mol has been deduced from the temperature-dependent intensity of the v6(t1u) carbonyl stretching mode. The 735 cm−1 longitudinal optic mode of Cr2O3 is observed during steady-state growth and simulated using the multilayer Fresnel relations for polarized reflectance. The growth is found to be first order in the Cr(CO)6 pressure under the present conditions.
Field emission characteristics of carbon nanotube emitters synthesized by arc discharge
Authors: Kwo J. L. , Tsou C. C. , Yokoyama Meiso , Lin I. N. , Lee C. C. , Wang W. C. , Chuang F. Y.
Published: July 2002

The fabrication of carbon nanotube emitters with excellent emission properties is described. The nanotubes synthesized by arc discharge are used as electron emitters. The fibrous bundles containing nanotubes were crushed, mixed with conductive pastes, and slurries and then screen printed. The scanning electron microscopy images showed that the nanotubes were disordered and the average diameter was about several tens of nanometers. In a diode structure, the electron field emission can be turned on at a field as low as 2 V/μm and attains current density as large as 7.2 mA/cm2. No significant degradation of these performance is observed for thus made electron emitters, operated under 3 V/μm (J=2.8 mA/cm2) for tens of hours. The influence of the growth condition and post-treatment process on the emission characteristics of carbon nanotubes emitters will also be discussed in this article.
Adsorption of TiCl4 and initial stages of Ti growth on Si(001)
Authors: Mitsui Toshiyuki , Hill Eric , Curtis Robert , Ganz Eric
Published: July 2002

Adsorption of TiCl4 and Ti growth on Si(001) were investigated over a range of temperatures by scanning tunneling microscopy. At 300 K, intact TiCl4, Ti and Cl, and mobile TiCl2, are identified on the Si surface. At higher temperatures, deposition initially produces two-dimensional Ti islands, and continued deposition produces three-dimensional clusters. Above 630 K, both Si and Ti islands and Si/Ti clusters are formed. However, cluster growth is limited by Cl passivation of Si and Ti surfaces below 950 K. Above 950 K, the tops of partially submerged titanium silicide crystals are observed.
Nano- and microchannel fabrication using column/void network deposited silicon
Authors: Nam Wook Jun , Bae Sanghoon , Kaan Kalkan A. , Fonash Stephen J.
Published: July 2002

Nano- and microchannels are fabricated using a novel deposited column/void network silicon film as a sacrificial material. This nanostructured silicon consists of nanometer-sized columns defined normal to the substrate in a void matrix, where the voids are continuously connected with each other, forming a network. The void network structure results in a high sacrificial layer etch rate due to the void network-enhanced transport of reactant and reaction products during the etching process, and high effective surface area. The use of our unique deposited column/void network material coupled with lift-off processing results in a manufacturable process for nano- and microchannel and nano- and microcavity fabrication. The approach provides extremely flat surfaces without a chemical–mechanical polishing process, and allows for multiple layers of channel or cavity structures with crossovers.
Dependence of compositions and crystallization behaviors of dc-sputtered TiNi thin films on the deposition conditions
Authors: Ting Jyh-Ming , Chen Peter
Published: July 2002

TiNi alloy thin films, whose properties are very sensitive to the composition, were prepared using a dc sputter deposition technique. Effects of major deposition parameters on the resulting thin film properties were investigated. The atomic percent of Ti was found to increase with increasing working distance or pressure. The deposition rate was found to increase with the dc power but decrease with the working distance and pressure. The activation energy was also determined and compared to that of bulk TiNi alloys.
Angular dependence of the surface excitation probability for medium energy electrons backscattered from Al and Si surfaces
Authors: Werner Wolfgang S. M. , Smekal Werner , Störi Herbert , Eisenmenger-Sittner Christopher
Published: July 2002

Reflection electron energy loss spectra have been measured for medium energy electrons backscattered from Al and Si surfaces. Angular distributions were obtained for emission angles between 15° and 90° with respect to the surface normal as well as for incidence angles in the same range. The surface excitation parameter (SEP), i.e., the average number of surface excitations an electron experiences when it crosses a surface once, was extracted from each spectrum by fitting the raw data to theory and determining the ratio of the surface loss peak to the elastic peak intensity. No difference in the SEP for incoming and outgoing electrons could be detected in the data. The SEP was found to depend linearly on the time an electron spends in the vicinity of the surface. Both the energy and angular dependence of the SEP can be accurately described by free-electron theory when the electron momentum is rescaled by a material-dependent parameter. The value of the scaling parameter is given for Al and Si so that the SEP in these materials can accurately be predicted for medium energies and arbitrary experimental configurations.
Notch formation by stress enhanced spontaneous etching of polysilicon
Authors: Chang Jane P. , Sawin Herbert H.
Published: July 2002

Notch formation during overetching of polysilicon is shown to be caused by stress enhanced spontaneous etching in part, and is not solely a result of feature charging. Notch formation in plasma etching is the lateral etching at the polysilicon–oxide interface that occurs during overetching. In the literature, notching has been attributed to solely charging within the feature. In this work, it is shown that the fields necessary for ion bombardment deflection alone to form a notch are too large to be sustained by an oxide surface. Stress at the polysilicon–oxide interface can induce spontaneous etching of the polysilicon, contributing to the formation of a notch. The effect of stress on spontaneous etching was demonstrated by applying mechanical stress to patterned polysilicon samples taken from the same wafer and observing the changes in notch formation.
Run to run control in tungsten chemical vapor deposition using H2/WF6 at low pressures
Authors: Sreenivasan Ramaswamy , Gougousi Theodosia , Xu Yiheng , Kidder John , Zafiriou Evanghelos , Rubloff Gary W.
Published: July 2002

Run to run control with an Internal Model Control (IMC) approach has been used for wafer state (thickness) control in the tungsten chemical vapor deposition (CVD) process. The control implementation was preceded by establishing a stable wafer state thickness metrology using in situ mass spectrometry. Direct reactor sampling was achieved from an Ulvac ERA-1000 cluster tool module during the H2/WF6 W CVD process at 0.5 Torr for temperatures 350–400 °C using a 300 amu closed ion source Inficon Transpector system. Signals from HF product generation were used for in-process thickness metrology and compared to ex situ, postprocess thickness measurements obtained by microbalance mass measurements, providing a metrology accuracy of about 7% (limited primarily by the very low conversion efficiency of the process used, ∼2%–3%). A deliberate systematic process drift was introduced as a −5 °C temperature change for each successive wafer, which would have led to a major (∼50%) thickness decrease over ten wafers in an open loop system. A robust run to run (RtR) control algorithm was used to alter the process time in order to maintain constant HF sensing signal obtained from the mass spectrometer, resulting in thickness control comparable to the metrology accuracy. The efficacy of the control algorithm was also corroborated by additional experiments that utilized direct film weight measurements through the use of the microbalance. A set of simulations in Matlab® preceded the control implementation and helped in tuning the controller parameters. These results suggest that in situ chemical sensing, and particularly mass spectrometry, provide the basis for wafer state metrology as needed to achieve RtR control. Furthermore, since the control was consistent with the metrology accuracy, we anticipate significant improvements for processes used in manufacturing, where conversion rates are much higher (40%–50%) and corresponding signals for metrology will be much larger.
Impurity-free intermixing of GaAs/AlGaAs quantum wells using SiOx capping: Effect of nitrous oxide flow rate
Authors: Deenapanray Prakash N. K. , Jagadish C.
Published: July 2002

In this work, impurity-free interdiffusion of GaAs/AlGaAs quantum wells was investigated as a function of the quality of SiOx capping layers grown by plasma-enhanced chemical vapor deposition. The quality of dielectric layers was varied by changing the nitrous oxide flow rate N (30 sccm⩽N⩽710 sccm), while maintaining a fixed silane flow rate. The pressure, substrate temperature, and rf power were also kept constant during depositions. Deposited films were characterized by Rutherford backscattering spectroscopy, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy. Following rapid thermal annealing, we have observed an increase in the energy shift of quantum wells with increasing N with a maximum in the range 100 sccm<N<200 sccm. Any further increase in N resulted in a lowering in blueshift, and reached an almost constant value for N>350 sccm. The variation of energy shift with N cannot be explained by considering only the oxygen content of the SiOx layer. It is shown that the deposition rate of the capping layer plays an important role in determining the extent of quantum well intermixing. Effects related to the stress imposed by the capping layer on the GaAs/AlGaAs heterostructure and the presence of hydrogen in the capping layer are also discussed.
Proximity effect correction using pattern shape modification and area density map for electron-beam projection lithography
Authors: Osawa Morimi , Takahashi Kimitoshi , Sato Masami , Arimoto Hiroshi , Ogino Kozo , Hoshino Hiromi , Machida Yasuhide
Published: July 2002

A novel proximity effect correction algorithm using pattern shape modification and the area density map method for electron-beam projection lithography is proposed. This algorithm enables fast, accurate and self-consistent calculation of modified pattern sizes. The correctable minimum feature sizes for shape modification were investigated from two viewpoints, mask fabrication restriction and dose margin. The correctable minimum sizes are mostly determined by the dose margin requirement in the case of isolated and dense repeated patterns, implying that the tool resolution determines correctable minimum sizes. A special technique is required for isolated space patterns where the backscattering energy cannot be reduced by simple sizing. We have implemented an algorithm in which pattern densities at middle parts of large patterns are reduced by using a lines and spaces (L/S) pattern or mesh patterns for that case. Successful correction results down to 60 nm from the simulation and 100 nm from the experiment have been obtained.
Field emission emitter array with a self-aligned volcano-type gate: Fabrication and characterization
Authors: Ivanov Tz. , Rangelow I. W. , Biehl St. , Chakarov I. R.
Published: July 2002

Field electron emitters with self-aligned volcano-type gate arrays were fabricated in order to generate an electron beam and their characteristics were measured. These devices were fabricated by reactive ion etching followed by successive forming of an insulating layer and deposition of a gate electrode. The self-aligned gate is achieved by reactive ion etching a planarizing resist film in 1:2 O2/Ar plasma and high dc bias (200 V). The device presented here has a 0.4 μm gate opening. The fabrication technology and structural and electrical characteristics of a self-aligned volcano-type gate field emission triode emitter array are reported.
Lateral force on fluoroalkylsilane self-assembled monolayers dependent on molecular ordering
Authors: Sugimura Hiroyuki , Ushiyama Kazuya , Hozumi Atsushi , Takai Osamu
Published: July 2002

Fluoroalkylsilane (FAS) self-assembled monolayers were prepared on silicon oxide surfaces by exposing the oxide surfaces to vapor of an FAS precursor, that is, [CF3(CF2)n(CH2)2Si(OCH3)3, n=5 or 7, referred to as FAS13 or FAS17, respectively] and were studied by lateral force microscopy (LFM). The water-contact angles of these FAS13 and FAS17 monolayers were ∼106° and 112°, respectively. LFM values for the FAS13 monolayer were found to be slightly greater than that on the FAS17 monolayer. CF3/CF2 ratios of the monolayers measured by x-ray photoelectron spectroscopy suggest that a surface CF3 density of the FAS17 monolayer was greater than that of the FAS13 monolayer. These results indicates that the FAS13 monolayer has a molecular assembled structure more disordered than that of the FAS17.
High precision measurements of arsenic and phosphorous implantation dose in silicon by secondary ion mass spectrometry
Authors: Chi P. H. , Simons D. S. , McKinley J. M. , Stevie F. A. , Granger C. N.
Published: July 2002

The metrology section of the 1999 International Technology Roadmap for Semiconductors specifies in-line dopant profile concentration precision requirements ranging from a value of 5% in 1999 to a value of 2% in 2008. These values are to be accomplished with “low systematic error.” Secondary ion mass spectrometry (SIMS) has demonstrated the capability to meet these requirements for B, As, and P. However, the detailed analytical protocols required to achieve these goals have not been completely specified. This article reports the parameters that must be controlled to make highly repeatable dose measurements of As and P implants in Si with magnetic sector SIMS instruments. Instrument conditions that were investigated include analytical species, matrix ion species, energy bandpass, and sample holder design. With optimized settings, we demonstrate the ability to distinguish As or P implant doses differing by 5%.
Morphology and electronic transport of polycrystalline silicon films deposited by SiF4/H2 at a substrate temperature of 200 °C
Authors: Hazra Sukti , Mukhopadhyay Sumita , Ray Swati
Published: July 2002

Undoped and phosphorous doped polycrystalline silicon (poly-Si) films were deposited using a SiF4/H2 gas mixture at a substrate temperature of 200 °C by radio frequency plasma enhanced chemical vapor deposition (rf-PECVD). Fourier transform infrared (FTIR) spectroscopy and x-ray diffraction (XRD) experiments reveal that the present poly-Si films are equivalent to the poly-Si films deposited at high temperature (>600 °C). XRD and scanning electron microscope observations show that the crystalline quality of slightly P-doped film is better compared to that of undoped poly-Si films. Phosphorus atom concentration in the slightly P-doped poly-Si film is 5.0×1016 atoms/cm3. Association of a few phosphorous atoms in the silicon matrix enhances crystallization as eutectic-forming metals do. Dark conductivity of slightly P-doped film is 4 orders of magnitude higher, although mobility–lifetime product (ημτ) is 2 orders of magnitude lower than that of undoped film. The presence of higher density of strained Si–Si bonds in the amorphous regions of slightly P-doped films revealed by FTIR spectroscopy reduces the value of ημτ.
Microstructural characterization of radio frequency magnetron sputter-deposited Ga2O3:Mn phosphor thin films
Authors: Kim Joo Han , Holloway Paul H.
Published: July 2002

Ga 2 O 3 : Mn phosphor thin films have been prepared by radio frequency (rf) magnetron sputtering of a 2 mol % Mn-doped Ga2O3 target in an oxygen–argon mixture atmosphere. The deposition rate of the films decreased from 14 to 12 Å/min when the working gas pressure decreased from 30 to 2 mTorr, while the O/Ga ratio of ∼1.5 did not systematically depend on the pressure. Films deposited at higher working gas pressure had a porous columnar structure containing a large void, typical of zone 1 growth, while films produced at lower pressure had relatively smooth surfaces with a dense structure, typical of zone T growth. The results obtained are consistent with energetic particle bombardment of the depositing films promoting surface adatom mobility at lower working gas pressure. Films deposited at working gas pressures⩾15 mTorr showed a random orientation after a postdeposition anneal at 1000 °C. Below 15 mTorr, annealed films were strongly textured with the (111) and (020) planes parallel to the surface.
Photodesorption of Carbon Monoxide
Authors: Lange W. J.
Published: July 2002

The desorption of carbon monoxide from surfaces in a vacuum under photon irradiation has been studied. As the coverage on tungsten approaches completion, thermal desorption from a very weakly bound phase dominates. Negligible photodesorption from quartz is found. Desorption from borosilicate glass is found to be dependent upon the CO pressure and history.
Mass Spectrometer Ion Source for Ionization Cross-Section Measurement
Authors: Crawford C. K.
Published: July 2002

A new electrode geometry for a crossed-beam mass-spectrometer ion source has been developed. The geometry is particularly suited to the measurement of electron ionization cross sections for low vapor pressure materials and for materials which would normally contaminate source surfaces. Ions are generated at the intersection of an electron beam and an atomic beam in the center of a six-sided ionization chamber; each side of which is formed out of fine wire grids. By applying different electrical potentials to the grids and by passing trickle currents directly through the grid wires (resulting in small voltage drops), a variety of calculable field configurations may be set up. Passing higher currents through the grids allows the structure to be flashed clean. No insulators are exposed to any beam. The ions are extracted perpendicularly to both the electron and atomic beams; extraction in one direction shoots them into a large quadrupole mass spectrometer, extraction in the opposition direction shoots them into a total ion collector. The chamber may be run with a uniform electric extraction field, with conventional nonuniform fields, as a field-free region, in a saddle potential mode, or in a variety of pulsed modes. The source has been used in the uniform field mode to measure the absolute electron-ionization cross sections for several metals.
Electrical Characterization of Radio-Frequency Sputtering Gas Discharge
Authors: Logan J. S. , Mazza N. M. , Davidse P. D.
Published: July 2002

In the design of rf sputtering systems, the electrical equivalent of the gas discharge must be known. For this purpose, an experiment was conducted in which the electrical impedance (capacitance and conductance) of an rf sputtering gas discharge was determined as a function of pressure, magnetic field strength, and rf power input. The method of measurement involved the use of a matching network, an incident and reflected power meter, and a Boonton radio-frequency admittance meter. Values of conductance and capacitance for the discharge were deduced from measurements on the matching network after termination of the discharge. Results show that both capacitance and conductance increase strongly with increasing magnetic field. Capacitance changed from 0.97×10−13 F/cm2 to 2.5×10−13 F/cm2 between zero and 156 G. Conductance changed from 1.6×10−6 mho/cm2 to 3.9×10−6 mho/cm2 in the same interval. Pressure dependence was strongest at zero magnetic field, changing both capacitance and conductance approximately 30% between 7.5 and 30 mTorr (argon). At high magnetic field, there was very little effect. No appreciable change was observed between 1.1 and 6.5 W/cm2 power application. Design equations are given for a simple matching network, and a design example is presented to demonstrate application.
Kinetics of Electron Impact Desorption of Ions and Neutrals from Polycrystalline Tungsten
Authors: Nishijima Mitsuaki , Propst Franklin M.
Published: July 2002

A cylindrical magnetic spectrometer has been constructed to study electron impact desorption of ions and neutrals from solid surfaces. The apparatus has been applied to the study of polycrystalline tungsten with O2, CO, CO2, N2, H2, and H2O adsorbed. This paper reports the results of the measurements of the kinetics of the adsorption and desorption processes, the states of adsorption which are observed, the total desorption cross sections for these states, and electronic and thermal conversion between states.
Swelling studies of vanadium and a vanadium−1 wt.% titanium alloy using ion simulation techniques
Authors: Santhanam A. T. , Taylor A. , Kestel B. J. , Steves C.
Published: July 2002

The void swelling of HPV and V−1 Ti has been investigated by irradiating the samples side by side with 3−MeV 51V+ ions to damage doses between 2.4 and 54 dpa at a temperature of 700°C. Examination of the irradiated samples by transmission electron microscopy revealed that voids and dislocation networks had formed at 2.4 dpa in HPV and that swelling increased less than linearly with dose. In contrast, V−1 Ti showed negligible swelling even at 54 dpa. The swelling resistance of V−1 Ti to large doses is believed to be, at least in part, due to irradiation−induced precipitation.
Plasma stream transport method (1) Fundamental concept and experiment
Authors: Tsuchimoto Takashi
Published: July 2002

The principle of the plasma stream transport method is discussed and the transport characteristics are estimated. Using a simplified experimental machine based on this principle, transport experiments with silicon, silicon nitride, oxygen, and flurocarbon plasma stream were carried out. The deposition of silicon and silicon nitride films on silicon wafers was observed, and reactive etching of photoresist by oxygen and of silicon and silicon dioxide by fluorocarbon were observed.
Controlled vapor growth of small particles of Pd and Fe on thin Al2O3 substrates
Authors: Poppa Helmut , Lee Eal H. , Moorhead R. Dale
Published: July 2002

An exploratory study, dealing with the preparation of well-defined particulate metal deposits that can be used in model studies of catalytic reactions, was performed. Small metal particles of Fe and Pd were grown in situ in an electron microscope by vapor deposition onto different phases of electron transparent alumina substrates. The results show that characteristic properties of the deposits, such as particle density, size distribution, habit, and orientation, are strongly dependent on the cleanliness, phase, and crystallographic orientation of the alumina substrate; also, the deposition conditions can be chosen in such a way as to reproducibly manipulate the overall deposit structure.
Deposition of aluminum on Kapton laminates by electron-beam evaporation
Authors: Sherman Dudley M.
Published: July 2002

Aluminum films 10 μm thick have been deposited on the Kapton surface of a laminated substrate consisting of Kapton–Kapton–aluminum foil bonded with a thermosetting adhesive. The processing of the substrates before deposition necessary to obtain reasonably short deposition cycle times and a minimal amount of deposition system contamination was developed. The laminated substrates required bakeouts both at atmosphere and in high vacuum prior to deposition to permit evaporation at a pressure of 0.1 mPa (1×10−6 Torr). The deposited films exhibited a high specular reflectance, resistivity within 5% of that of bulk aluminum, and a strong (111) fiber texture.
Electronic states of impurities located at or near semiconductor–insulator interfaces
Authors: Lipari Nunzio O.
Published: July 2002

We solve the effective mass equations describing donor impurities localized at semiconductor–insulator interfaces using a method which involves an expansion of the impurity wavefunction in terms of spherical harmonics. We also investigate the behavior of the impurity energies as a function of the donor distance from the interface both in the insulator and in the semiconductor. This allows, for the first time, the connection between surface and bulk donor properties. Results for the Si–SiO2 case are presented.
Photoemission studies of intrinsic surface states on Si(100)
Authors: Himpsel F. J. , Eastman D. E.
Published: July 2002

We have determined the energy vs. k∥ dispersion of intrinsic surface states on Si(100) (2×1) by means of angle-resolved photoemission with synchrotron radiation. For k∥=0, there is a very pronounced surface state 0.7 eV below EF(i.e.,∠0.4 eV below the top of the valence band) which disperses downwards with increasing k∥. At J′ on the boundary of the surface Brillouin zone, we find two states with binding energies of 0.7 and 1.2 eV with respect to EF. A number of geometrical models and their corresponding theoretical surface state bands have recently been published for Si(100) (2×1). Our results disagree qualitatively with all surface state dispersions calculated up to date, i.e., the ideal surface, the vacancy model, the pairing model, and the zig-zag-chain model. Namely, we observed semiconducting surface state bands with a low state density at EF while all models calculated to date yield metallic surface states with a large state density at EF.
Strain effects in surface segregation—The Au/Ni system
Authors: Kelley Michael J. , Gilmour Phyllis W. , Swartzfager Dennis G.
Published: July 2002

Previous studies have reported segregation of the minority element to the surface at both ends of the gold–nickel phase diagram. These results, which contradict the predictions of bond-breaking arguments, were attributed to strain effects arising from the large atomic size difference between gold and nickel. Such effects for this and other alloy systems have been calculated by an elastic continuum model which suffers from several limitations. A pair-potential model is proposed here which overcomes these difficulties. Dilute alloys of gold and nickel were studied by ion-scattering spectroscopy to test these predictions. The calculations predict and the measurements show that the surface of either gold-rich or nickel-rich alloys becomes enriched in gold.
Theoretical studies of the reconstruction of the (110) surface of III–V and II–VI semiconductor compounds
Authors: Swarts C. A. , Goddard III W. A. , McGill T. C.
Published: July 2002

We have studied the reconstruction of the (110) surface of various III–V semiconductor compounds (GaAs, GaP, GaN, AlAs, AlP, AlN, BAs, BP, BN) by applying quantum chemical methods to small clusters representative of these surfaces. Application of these techniques to GaAs (110) leads to a surface shear (0.67 Å) in excellent agreement with experimental values (0.65–0.70 Å). The results lead to trends in the surface distortions and reconstruction consistent with those predicted from local valence considerations. Possibilities for the electronic structure of II–VI semiconductor compounds are also considered.
XPS study of chemically etched GaAs and InP
Authors: Bertrand P. A.
Published: July 2002

The surface composition of p-type GaAs etched in HCl or Br2 in methanol, and n-type InP etched in HCl, H2SO4, HNO3, or Br2 in methanol has been studied by means of x-ray photoelectron spectroscopy (XPS). The surface compositions of GaAs and the binding energy of the surface As atoms vary with the etching solution and with the extent of oxidation of the surface. The full width at half-maximum of the Ga(3p) photoelectron peak increases upon exposure of etched GaAs to air. The XPS results are compared with Schottky barrier heights previously measured for similarly prepared surfaces with Pb contacts. The amount of oxidized P on InP surfaces is higher after an HNO3 etch than after HCl, H2SO4, or Br2/methanol treatments. An HCl etch leaves an unoxidized slightly In-rich surface.
Scanning Auger microprobe study of gold–nickel–copper diffusion in thin films
Authors: Brady T. E. , Hovland C. T.
Published: July 2002

The gold–nickel–copper system, with nickel the intended diffusion barrier, has been used extensively in the electronics industry for wire spring connectors, thin films on ceramic, and connectors on printed circuit boards. Although no visible contamination can be seen on the surface of the gold, poor bonding or high contact resistance frequently occurs. It has been assumed that some grain boundary diffusion of nickel has been occurring through the 2 μm gold film. A scanning Auger microanalysis was conducted on the surface and in depth on the thin film structure before and after heating at 300 °C for 4 h. Two-dimensional Auger analysis, after heating, showed the nickel to be distributed along the grain boundaries on the surface of the gold film. Subsequent Auger depth profiling showed the nickel layer to be oxidized and approximately 50 Å in depth. This characterization has led to improved understanding of the bonding problems and variation of contact resistance with this metallization system.
Auger lineshapes of solid surfaces—Atomic, bandlike, or something else?
Authors: Dunlap B. I. , Hutson F. L. , Ramaker D. E.
Published: July 2002

A simple model is presented to predict the level of localization (i.e., localization onto an atomic, bonding lobe, molecular, or band orbital) of the two- and three-hole final states in Auger lineshapes. In the spirit of the Hubbard model, the extent of localization is predicted from the one- and two-center Coulomb interaction potentials and the relevant valence bandwidths. Results from the model are compared with experiment for the N KVV lineshape from NaNO3, and the S and Si L23VV lineshapes from Li2SO4 and SiO2. These lineshapes exhibit a wide range of localization consistent with the model.
Analysis of glass shell blowing gases from metal-organic gels
Authors: Downs R. L. , Ebner M. A. , Homyk B. D. , Nolen R. L.
Published: July 2002

To develop better control of size, wall thickness, and shell quality, we have studied the physical and chemical transformations of metal-organic gels during heating, employing a number of thermal analytical techniques, such as pyrolysis-gas chromatography (PGC), pyrolysis-mass spectrometry (PMS), TGA, DTA, and hot stage microscopy. This work will be the basis for mathematical modeling of the shell blowing process. The residual blowing gases in the glass spheres and the volatile gas content of the metal-organic gels were analyzed. The effect of gel aging on these was also studied. The primary component of the residual gases in the spheres is 70%–80% carbon dioxide, with the balance oxygen and nitrogen; water has also been found in some cases. The potential volatiles in metal-organic gels depend on the aging history of the gel, and consist primarily of water, carbon dioxide, and a variety of organic species.
Origin of U-shaped background density of interface states at nonlattice matched semiconductor interfaces
Authors: Singh J. , Madhukar A.
Published: July 2002

Recent experiments on the behavior of the density of interface states (DOIS) in the semiconductor band gap for Si/SiO2 as well as for III–V compound semiconductor/dielectric systems reveal the presence of a U-shaped background with specific structure riding on top. Among several suggestions for the origin of such states, the idea that strain/ disorder present at the interface may play a significant role has also been put forward. However, the nature of the states contributing to the background, and especially their energy distribution, has remained unexplained. In this paper we show that a thin disordered layer on the semiconductor side near the interface can produce such a U-shaped background in the DOIS arising from the Anderson localized states. Employing a simple model of a disordered system we provide the first derivation of their energy distribution valid over essentially the whole band tail region away from valence and conduction band edges. We have re-examined the existing data on Si/SiO2 interfaces in light of the above proposition and the new theoretical results. The exponential decay rates of the DOIS from the valence and conduction band edges, calculated on the basis of expected and realistic disorder, are found to provide a quantitative and consistent understanding of the behavior of the U-shaped curve throughout the gap region. It is thus suggested that lattice matched semiconductor-dielectric systems should be sought for applications requiring very low levels of interface state density.
Composition and thermal stability of thin native oxides on InP
Authors: Wager J. F. , Ellsworth D. L. , Goodnick S. M. , Wilmsen C. W.
Published: July 2002

The chemical composition of surface films formed on air exposed bromine/methanol etched InP were investigated in both the ’’as etched’’ condition and after in situ heat treatment. Both UPS and XPS spectra were obtained in order to probe at two different depths into the surface (≊5 and 15 Å, respectively). The as etched surface appears to be composed primarily of In2O3 with a small concentration of a phosphate compound, presumably either InPO4 or H3PO4. Prolonged exposure to water or water vapor causes additional film growth. The new growth increases the phosphate concentration and an In compound which, by the location the In3d5/2 peak at 445.6 eV, indicates either InPO4 or In(OH)3. Heating the as etched surface in situ also causes film growth. The phosphate is found to evaporate from the outer surface of the film but to grow underneath the In2O3 skin as the substrate is heated. It is suspected that excessive H2O on CO background in the vacuum chamber caused a rapid oxidation of the surface as the sample was heated.
Atomic geometry of Al−GaAs interfaces: GaAs (110)–p(1 × 1)–Al(ϑ), 0?ϑ?8.5 monolayers
Authors: Kahn A. , Carelli J. , Kanani D. , Duke C. B. , Paton A. , Brillson L.
Published: July 2002

The atomic structure of Al on GaAs(110) is studied by soft x-ray photoemission spectroscopy (SXPS) and elastic low energy electron diffraction (ELEED) for coverages ranging from 0.5 to 8.5 monolayers (ML). The core level measurements show a heat-induced chemical shift of Al–2p to higher binding energy consistent with an Al–Ga replacement reaction and the formation of AlAs, and a decrease in emission from Al–2p and Ga–3d, indicating a penetration of Al in the lattice and thermal desorption or formation of islands of Ga freed by the replacement reaction. The ELEED multiple scattering analysis yields a correspondence between the initial experimental coverage and the structure of the interface. The low coverage (0.5–1.0 ML) data are best described by a replacement of Ga in the second layer, the medium coverage (1.5–2.5 ML) data by a replacement in the second and third layers and the high coverage (5.5–8.5 ML) data by replacing Ga in all layers (pure AlAs).
Interference enhanced Raman scattering study of the interfacial reaction of Pd on a-Si:H
Authors: Nemanich R. J. , Tsai C. C. , Thompson M. J. , Sigmon T. W.
Published: July 2002

The application of interference enhanced Raman scattering to probe the structure of metal/semiconductor interfaces is described. This technique is used to study the interface structures of Pd on hydrogenated amorphous Si (a-Si:H) with particular attention to the effects of a native oxide layer on the a-Si:H. It is found that for deposition on lightly oxidized a-Si:H, ∠20 Å of Pd is consumed to form a crystalline silicide interfacial structure with composition near Pd2Si. Annealing causes growth of this phase and further consumption of Pd until a second phase of Pd2Si is observed. If the deposition is repeated on more heavily oxidized a-Si:H, no silicide formation is observed even at annealing temperatures of 400 °C.
Cluster adsorption on amorphous and crystalline surfaces: A molecular dynamics study of model Pt on Cu and model Pd on Pt
Authors: Garofalini S. H. , Halicioglu T. , Pound G. M.
Published: July 2002

Molecular dynamics was used to study the structure, dispersion and short-time behavior of ten-atom clusters adsorbed onto amorphous and crystalline substrates, in which the cluster atoms differed from the substrate atoms. Two adatom–substrate model systems were chosen; one, in which the interaction energy between adatom pairs was greater than that between substrate pairs, and the other, in which the reverse was true. At relatively low temperature ranges, increased dispersion of cluster atoms occurred: (a) on the amorphous substrate as compared to the FCC(100) surface, (b) with increasing reduced temperature, and (c) with adatom–substrate interaction energy stronger than adatom–adatom interaction. Two dimensional clusters (rafts) on the FCC(100) surface displayed migration of edge atoms only, indicating a mechanism for the cluster rotation and shape changes found in experimental studies.
Pressure and angle of incidence effects in reactive planar magnetron sputtered ZnO layers
Authors: Maniv S. , Westwood W. D. , Colombini E.
Published: July 2002

ZnO films have been prepared by rf sputtering a Zn target in a planar magnetron system with controlled Ar/O2 gas mixtures. The films were deposited on unheated glass substrates which were either stationary in front of the target or in constant motion. Both the system pressure and plasma impedance changed when an oxide layer formed on the target surface. This occurred at an oxygen flow rate which increased almost linearly with rf power; at 500 W, the required flow rate was 9 ml/min and the pressure increased from 0.1 to 1.2 Pa due to the reduced oxygen gettering. High resistance ZnO films were deposited at oxygen flow rates above this threshold value. The target self-bias voltage increased by 30 V at this value; it is affected by both the system pressure and the power. The deposition rate increased linearly with power at approximately 0.03 (μm/min)/(W/cm2) which appears to be typical of sputtering from a ZnO layer or target. For continuous substrate motion, the average rate was approximately 7% of this value. All the films were polycrystalline ZnO with a preferred orientation, the c axis of the hexagonal structure being within a small angle of the substrate normal; this orientation was improved by motion of the substrate past the target. Films deposited at pressures of approximately 0.4 Pa had a large internal stress, as revealed both by substrate bending and x-ray measurements. Increasing the pressure to 4.7 Pa decreased the stress by an order of magnitude. SEM analysis showed that this was associated with the development of a columnar structure. The refractive indices obtained from guided wave measurements were 1.940±0.006 and 1.962±0.003, which correspond to 97% of the single crystal values. The resistivity measured normal to the film plane was greater than 107Ω cm. The changes in film stress and structure are similar to effects in metal films. The electromechanical coupling coefficients obtained from SAW measurements are approximately half the best reported value.
Effect of low-intensity laser radiation during oxidation of the GaAs(110) surface
Authors: Petro W. G. , Hino I. , Eglash S. , Lindau I. , Su C. Y. , Spicer W. E.
Published: July 2002

Considerable interest in the use of laser irradiation as a means of processing (annealing, cleaning, alloying, etc.) semiconductor materials, as well as the importance of the oxygen surface chemistry on III-V semiconductors, has led us to study the effect of low-intensity (?3 W/cm2) laser radiation on the oxidation behavior of (110) surfaces of GaAs cleaved in UHV (<10−10 Torr). The oxygen sticking probability in the submonolayer coverage range has been increased by a factor of 103 (from a probability of ∠10−9 to ∠10−6) by uniform irradiation of the GaAs surface with a continuous wave Ar+ laser (λ = 5145 Å) during the oxygen exposure. We find the data cannot be explained in terms of either heating of the surface or excitation of the oxygen by the laser radiation; it appears that the most likely explanation of the phenomena is an increase in the density of electrons and/or holes at the surface. A limiting step in the oxygen uptake process is the breakup of the oxygen molecule; this dissociation would be increased by increasing the number of electrons at or near the surface. In chemical terms, the reconstructed GaAs surface has no orbitals suitable for binding oxygen—such orbitals can be provided by changing the charge state of a surface atom via optical excitation.
Theory of the electronic and atomic structure of Si(111): Surface spin-polarization effects
Authors: Chadi D. J. , Del Sole R.
Published: July 2002

The electronic structure 1×1 and 2×1 reconstructed Si(111) surfaces are examined using a simple theoretical model which incorporates intra-atomic correlation effects. Electron spin polarization is shown to lead to a low-energy nonmetallic ground state for the nonbuckled Si(111) surface which is energetically more favorable than the metallic, half-filled band state. Spin- polarization and spin-ordering effects are shown to be important for the buckled surface. The incorporation of electronic correlations and spin in the calculations yields results consistent with photoemission, optical, and low energy electron diffraction data. The calculated oscillator strength for optical transitions between dangling-bond bands and its anisotropy are found to be in satisfactory agreement with experimental data. The buckling is estimated to be 0.3 Å.