bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron stimulated carbon adsorption in ultrahigh vacuum monitored by Auger electron spectroscopy
Authors: Scheuerlein C. , Taborelli M.
Published: July 2002

Electron stimulated carbon adsorption at room temperature has been studied in the context of radiation induced surface modifications in the vacuum system of particle accelerators. The stimulated carbon adsorption was monitored by Auger electron spectroscopy (AES) during continuous irradiation by 2.5 keV electrons and simultaneous exposure of the sample surface to CO, CO2, or CH4. The amount of adsorbed carbon was estimated by measuring the carbon Auger peak intensity as a function of the electron irradiation time. Investigated substrate materials are technical oxygen-free electrolytic copper and TiZrV nonevaporable getter thin film coatings, which are saturated either in air or by CO exposure inside the Auger electron spectrometer. On the copper substrate electron induced carbon adsorption from gas phase CO and CO2 is below the detection limit of AES. During electron irradiation of the nonactivated TiZrV getter thin films, electron stimulated carbon adsorption from gas phase molecules is detected when either CO or CO2 is injected, whereas the CH4 partial pressure has no influence on the carbon Auger peak intensity evolution.
Ultraviolet-assisted pulsed laser deposition of La0.7Ca0.3MnO3 thin films with improved oxygen content, crystallinity and magnetoresistive properties
Authors: Kumar D. , Pietambaram Srinivas V. , Craciun V. , Singh Rajiv K. , Perriere J. , Sankar J.
Published: July 2002

Colossal magnetoresistive La0.7Ca0.3MnO3 (LCMO) films with improved magnetoresistance properties have been grown at relatively low temperatures using an ultraviolet-assisted pulsed laser deposition technique. In this technique, a low pressure Hg lamp having a fused silica envelope, which allows more than 85% of the emitted 184.9 nm radiation to be transmitted, is added inside the growth chamber during pulsed laser deposition of LCMO films. Magnetoresistance (MR) measurements carried out on LCMO films grown under identical conditions barring the presence/absence of UV radiation during thin film formation have shown that the MR ratio of UV-assisted grown LCMO films is nearly two orders of magnitude higher than that of LCMO films grown without UV. The improvement in magnetoresistive properties of LCMO film deposited in the presence of UV is assumed to be related with improvement in oxygen content, oxygen homogeneity, and crystallinity. Evidences supporting this assumption are obtained from analysis of spectra recorded using x-ray photoelectron spectroscopy and Rutherford backscattering measurements.
Optical transitions in piezoelectrically polarized GaInN/GaN quantum wells
Authors: Wetzel C. , Nelson J. , Kamiyama S. , Amano H. , Akasaki I.
Published: July 2002

The electronic band structure in polarized GaInN/GaN heterostructures is studied in photoluminescence excitation spectroscopy. Within multiple quantum well samples optimized for homogeneity, sets of narrow excitation maxima with full width at half maximum values of 10 and 25 meV (T≈12 K) are identified and attributed to interband transitions involving excited quantized states of the quantum wells. A selective attenuation is achieved by variation of the detection energy. Those values are significantly smaller than the linewidth of the emission paths. Together with higher emission energies emphasized by higher excitation energies, this supports concepts where absorption and emission paths do not share the same broadening nor the same interband transition. The result of such well-resolved transition levels provides a basis for future detailed band-structure models.
Spectroscopic characterization of acid generation and concentration and free volume evolution in chemically amplified resists
Authors: Jessop J. L. P. , Goldie S. N. , Scranton A. B. , Blanchard G. J.
Published: July 2002

We report on the measurement of proton concentration and local viscosity in a polymeric chemically amplified photoresist material. We interrogate these properties using crystal violet, a cationic triphenylmethane dye molecule. To determine the quantity of acid generated by the chemically amplified photoresist material on exposure to UV light, we characterize the pH-dependent linear optical response of crystal violet. To establish a frame of reference for these data, we determine the acid dissociation constants of crystal violet in aqueous solution. The viscosity of the resist material is related to the transient optical response of crystal violet. The data on the photoresist material demonstrate a rapid and persistent pH change in the polymer matrix upon UV irradiation, with the viscosity of the matrix changing by a relatively small amount, going from ∼150 cP prior to processing to ∼190 cP after UV exposure and heating.
Effects of photowashing treatment on electrical properties of a GaAs metal–semiconductor field-effect transistor
Authors: Choi Kyoung Jin , Lee Jong-Lam , Mun Jae Kyoung , Kim Heacheon
Published: July 2002

Effects of photowashing treatment on electrical properties of GaAs metal–semiconductor field-effect transistors (MESFETs) were investigated using x-ray photoemission spectroscopy. The binding energy of the Ga–As bond shifted toward lower binding energies and the ratio of Ga/As was increased, namely the formation of the Ga-rich surface. This suggests that acceptor-type defects GaAs− were produced by the photowashing treatment and the level for Fermi energy pinning at the surface moved to acceptor states. The Fermi energy pinning caused by GaAs− results in an increase of the depletion layer width at the ungated region of the MESFET via the increase of band bending from the surface. Therefore the drain current density at a positive gate bias and the leakage current at gate-to-drain were simultaneously reduced.
Effects of deposition temperature on the conduction mechanisms and reliability of radio frequency sputtered TiO2 thin films
Authors: Chen Shih-Fang , Wang Ching-Wu
Published: July 2002

The electrical conduction mechanisms and reliability characteristics of rf-sputtered TiO2 thin films deposited at different temperatures have been systematically investigated. Analytical results revealed that adequate sputtering temperature not only provided a superior polycrystallized TiO2 film as well as a less leakage current, but also reduced the oxygen vacancy, resulting in the Frenkel–Poole (FP) conduction mechanism of low-temperature (400–500 °C) sputtered samples transiting to the Schottky emission (SE) process of medium-temperature (600–700 °C) sputtered samples. However, for samples sputtered by higher temperature (750–800 °C), the evident oxygen deficiency due to the deteriorated crystallinity and significant Si diffusion contamination in the TiO2 films were asserted to be the two main causes leading to the SE conduction process in medium-temperature (600–700 °C) sputtered samples transiting to the FP conduction mechanism in high-temperature (750–800 °C) sputtered samples again. Besides, the excellent agreement between the E model and the time-dependent-dielectric-breakdown data suggested strongly that the exhibited best long-term reliability of metal–oxide–semiconductor capacitors with TiO2 gate oxide sputtered at 700 °C was due to the possession of superior crystallinity and less interface hole trap density at the junction of TiO2/Si, resulting in a higher thermal activation energy Ea of 0.709 eV at 5 MV/cm, reducing the breakdown occurrence.
Influence of the cap layer on the Gibbs free energy above a layer of buried InGaAs islands
Authors: Jogai B.
Published: July 2002

The Gibbs free energy above a layer of buried InxGa1−xAs islands embedded in a GaAs cap layer is calculated as a function of the cap thickness and mole fraction of the dots. The model is based on a three-dimensional calculation of the elastic strain within the continuum elastic theory. A surface map of the Gibbs free energy due to strain variations is a useful guide in understanding the vertical ordering of dots as well as cooperative nucleation in the lateral direction. The calculated results have implications for determining how thick a cap layer can be before preferential nucleation above a layer of buried stressors ceases. Additionally, the Gibbs potential depth is estimated for varying In composition of the buried pyramidal stressors. It is found that even a slight change in the shape of the island can influence the degree of screening that the GaAs cap exerts on the Gibbs potential.
Trench-type InGaAs quantum-wire field effect transistor with negative differential conductance fabricated by hydrogen-assisted molecular beam epitaxy
Authors: Sugaya Takeyoshi , Bird Jonathan P. , Ferry David K. , Jang Kee Youn , Ogura Mutsuo , Sugiyama Yoshinobu
Published: July 2002

Trench-type narrow InGaAs quantum wires (QWRs) with a cross-sectional depth of 8 nm and a width of 25 nm have been successfully fabricated by hydrogen-assisted molecular beam epitaxy. Optical properties of the QWRs are improved by atomic-hydrogen irradiation as observed by photoluminescence measurement. The trench-type QWR-FET has a pronounced negative differential conductance with a low onset voltage and a high peak-to-valley current ratio. We also study the quantum-interference characteristics of the trench-type QWR-FET, and find very different behavior to that typically exhibited by disordered wires. This Aharonov–Bohm effect points to an interference process in which the one-dimensional subbands of the wire themselves constitute well-resolved paths for electron interference.
In-situ measurement of magnetostrictive coefficient and elastic properties for thin films during growth
Authors: Jin Xuesong , Kim C. O. , Lee Y. P. , Zhou Y.
Published: July 2002

A method to determine simultaneously the magnetostrictive coefficient and the elastic properties (Young’s modulus and Poisson ratio) of a thin film during the growth was developed based on minimization of the total elastic energy of a cantilever film-substrate system. Compared to other published measurement methods, an inaccuracy in the magnetostrictive coefficient, caused by assuming the elastic properties of the film as those of the bulk material, could be avoided. Only one elastic isotropic substrate is employed in the present method. The experimental data of an Fe-based amorphous thin film was analyzed using the model. The calculated dependence of the magnetostrictive coefficient on the external magnetic field was compared with the experiment, and the discrepancy between both results is explained. Furthermore, the elastic properties of the film were also obtained.
Optimum B+ implantation conditions for the edge termination of the Au/n-Si Schottky diodes
Authors: Choi C. S. , Choi W. Y. , Joo M. H. , Song J. H. , Im S.
Published: July 2002

Boron ion implantation for edge termination was performed as a simple technique to improve the breakdown characteristics in Au/n-Si Schottky diodes. Four doses of 1×1013, 1×1014, 1×1015, and 1×1016 B cm−2 were implanted at the ion energy of 30 keV. The Schottky diode implanted with the dose of 1×1013 B cm−2 shows the best edge termination characteristics. In addition, 20, 40, and 50 keV ion energies were also adopted to investigate the influences of implantation energies on edge termination in the Schottky diodes. The current–voltage measurement results show that the diode implanted with 1×1013 B cm−2 at 30 keV has the highest breakdown voltage of 386 V while the diode treated at 20 keV has the abrupt breakdown at only 150 V. Leakage currents at the reverse bias are attributed to the deep level defects introduced by ion implantation. Using two-dimensional simulation, it is verified that the anomalous breakdown phenomena in the diode implanted at 20 keV result from the high electric field near the Au contact edge.
Deep in situ dry-etch monitoring of III-V multilayer structures using laser reflectometry and reflectivity modeling
Authors: Moussa H. , Daneau R. , Mériadec C. , Manin L. , Sagnes I. , Raj R.
Published: July 2002

Deep reactive ion etching of III-V multilayer structures is an important issue for long wavelength vertical cavity surface emitting laser (VCSELs) where full laser structures are usually very thick. Test etchings were performed on GaAs/AlxGa1−xAs Bragg mirror structures and monitored using laser reflectometry at 651.4 nm. In order to perform very deep etching, up to 9 μm, we designed and fabricated a special two-level mask made up of a thick nitride layer and a thin nickel layer. The etching rate is a complex function of many parameters and may change from run to run for similar structures. Therefore, it is important to have a method to control accurately the process in situ by continuously matching, experimental curves with the results of the reflectivity modeling. Here, we present a model, based on the Abelès matrix method, of the normal incidence reflectivity of a multilayer stack as a function of etch depth. Comparison between the model and the observed reflectivity variation during etching makes it possible to distinguish individual layers with very high precision.
The optical properties and applications of AlN thin films prepared by a helicon sputtering system
Authors: Chiu W. Y. , Wu C. H. , Kao H. L. , Jeng Erik S. , Chen Jyh Shin , Jaing C. C.
Published: July 2002

AlN thin films were grown on SiO2/Si and quartz substrates using a helicon sputtering system. The dependence of film quality on growth parameters, such as total sputtering pressure, substrate temperature, and nitrogen concentration has been studied. There is a good correlation of thin film crystallinity addressed by x-ray diffraction (XRD) and spectroscopic ellipsometer. The optimized films exhibit highly oriented, with only (002) peak shown in a θ–2θ scan XRD pattern, and extremely smooth surface with rms roughness of 2 Å. The extinction coefficient of the film was 4×10−4, which is lower than that of AlN films grown by conventional sputtering. Double-layer antireflection (DLAR) coating using AlN and Al3O3 grown on quartz has been demonstrated. The transmittance of DLAR was high as 96% compared to 93% of bare substrates with the measurement error less than 0.2%. AlN films prepared by Helicon sputtering thus are potential for optical application.
Electron-beam double resist process to enhance bright field pattern resolution
Authors: Chan Victor W. C. , Chan Philip C. H.
Published: July 2002

Electron-beam direct write is a promising technique for deep submicron lithography. One of the common methods to define a bright field pattern for the gate electrode masking uses negative resist. However, the resolution of many popular negative resists is low compared to that of positive resists. A technique is demonstrated that takes advantage of positive resist, such as polymethylmethacrylate and converts it to a bright field masking step. The technique involves (1) using a negative resist coating on a positive resist pattern, (2) plasma etching the negative resist down to the top of the positive resist, (3) exposing large area with electrons or deep ultraviolet photons, and (4) developing the result with a ratio of methyl isobutyl ketone and isopropanol. The resulting bright field masking provides high-resolution dense line patterns, which are difficult to achieve using the common negative resists alone.
On the mechanism of self-deceleration of the thin oxide film growth
Authors: Mukhambetov D. G. , Chalaya O. V.
Published: July 2002

The objective of this work was to investigate the kinetics of the two-phase oxide film growth on the α-Fe surface at temperatures of 650–750 K. We experimentally determined that the film thickness (h)–time oxidation (τ) relationship in the range denoted above is a logarithmic function, whereas Cabrera and Mott’s theory gives a square law of film growth. In our work, analytical treatment of experimental data was made based on this theory, but we propose that self-deceleration of the film growth is caused not by attenuation of the electric intensity in the film because of an increase of h but by the shielding influence of the space charge of diffusing ions and electrons in that oxide film. With that purpose in view, the Debye shielding distance for plasma substance state in the oxide film was taken into consideration. The logarithmic law of oxide film growth was derived. Estimated calculations of this law’s parameters were made that quantitatively correspond with literature data. The results obtained were used in developing the surface oxidation technology of electric steel.
Photon-stimulated desorption from an aluminum surface after water vapor exposure
Authors: Chen J. R. , Yang K. Y. , Yang J. Y. , Hsiung G. Y.
Published: July 2002

Photon-stimulated desorptions from aluminum surfaces was studied. Aluminum samples, following exposure to water vapor, were irradiated by synchrotron light with a critical photon energy of 2.1 keV. The signal corresponding to H2O gas exponentially decreased during irradiation. Experiments were performed under various conditions of target bias, sample temperature, photon flux, and photon dose to clarify the H2O PSD behavior. The experimental system, results, and discussions are described.
Impact of residual by-products from tungsten film deposition on process integration due to nonuniformity of the tungsten film
Authors: Sidhwa Ardy , Spinner Chuck , Gandy Todd , Melosky Steve , Brown William , Ang Simon , Naseem Hameed , Ulrich Richard
Published: July 2002

The effects of residual by products from a tungsten film deposition process and their impact on process integration due to the nonuniformity of the tungsten film were investigated in this work. The tungsten film deposition process involves three steps: nucleation, stabilization, and tungsten bulk fill. Six experiments were conducted in search for a solution to the problem. The resulting data suggest that excess nitrogen left in the chamber following the tungsten nucleation step, along with residual by products, causes a shift in the tungsten film uniformity during the tungsten bulk fill process. Data reveal that, due to the residual by products, an abnormal grain growth occurs causing a variation in the tungsten thickness across the wafer during the bulk fill step. Although several possible solutions were revealed by the experiments, potential integration problems limited the acceptable solutions to one. The solution chosen was the introduction of a 10 s pumpdown immediately following the nucleation step. This choice did not create any integration problems as confirmed by subsequent studies.
Optical properties of bias-induced CH4–H2 plasma for diamond film deposition
Authors: Zhu X. D. , Zhan R. J. , Zhou H. Y. , Wen X. H. , Li D.
Published: July 2002

Methane (CH4) and hydrogen (H2) reactive gas mixture has been in situ investigated in a hot filament diamond chemical vapor deposition reactor with a negatively variable biasing voltage applied to the hot filament with respect to the substrate using infrared absorption spectroscopy and optical emission spectroscopy. It is found that CH4 converts increasingly to C2H2 upon raising the filament temperature in a pure thermal activation state, no optical emission of species is observed. Upon bias application, both CH4 and C2H2 in infrared (IR) absorption intensity decrease with increasing bias current, even the IR absorption intensity of C2H2 decreases more rapidly than that of CH4. Meanwhile, the clear emission lines indexed to H, CH, and CH+ appear in the optical emission spectrum obtained, showing that a large amount of excited radicals are produced in the gas phase after applying bias. It is believed that the further generation of activated radicals induced by electron impact may be responsible for the increase of the growth rate of diamond films due to bias application.
Quadrupole Mass Filter: Circular Rods and Peak Shapes
Authors: Dawson P. H. , Whetten N. R.
Published: July 2002

A frequently observed characteristic of quadrupole mass filters is the appearance, at high resolution, of a separate “precursor” peak on the low mass side of each mass peak. The present report shows that such false precursor peaks can result from the use of round rods (rather than hyperbolic rods) that are common in all commercial instruments. Round rods introdnce sixth- and tenth-order terms to the ideal quadrupole field. We have computed the amount of sixth-order distortion introduced by the use of circular rods. The equipotential line produced at the surface of a round rod can be represented quite well by a quadrupole field with a large amount of sixth-order distortion. This distortion introduces a resonance line in the Mathieu stability diagram that at high resolution is near the edge of the peak on the low mass side. The resonance line can distort the peak to produce an apparent precursor peak.
Structure of Ni-rich Ni–Cr–B–Si coating alloys
Authors: Knotek O. , Lugscheider E. , Reimann H.
Published: July 2002

The structures of quaternary, nickel-rich Ni–Cr–B–Si alloys were analyzed at a constant boron content of 10 at.% and a temperature of 850 °C. The composition range for silicide formation was determined. In these quaternary alloys, known binary nickel silicides, nickel and chromium borides, and the ternary silico-boride Ni6Si2B were confirmed. A new composition for the W5Si3-type phase in the Ni–B–Si system was proposed.
The atomic geometry of c (2×2) overlayers of sulfur on Ni(100)
Authors: Duke C. B. , Lipari N. O. , Laramore G. E.
Published: July 2002

Our earlier determination of the structure of Ni(100)−c (2×2)−S overlayers via the analysis of elastic low−energy electron diffraction (ELEED) intensities is reexamined following a −2.5−eV contact−potential correction to the energies of the ELEED intensities measured by Theeten. While this correction does not alter our conclusions that the surface is unreconstructed and that the S atoms occupy sites of four−fold coordination, it does render dS = 1.3 Å a slightly better choice for the vertical height of the sulfur overlayer than the value of 1.7 Å previously reported. A discussion is given of the influence of the model of the electron−ion−core potential on the ELEED lineshapes and the empirical optical potential parameters. For our overlapping atomic potentials, the use of about ten phase−shifts is required for complete convergence of the single−atom scattering factors over the energy range 100 eV?E?200 eV. Estimation of the optical potential for clean Ni suggests that calculations based on a 10−phase−shift model would exhibit empirical real inner potentials 2−5 eV smaller in magnitude than those obtained in our present 4−phase−shift analysis.
Thin film compositional analysis—a comparison of techniques
Authors: Evans Charles A.
Published: July 2002

The increasing demands for surface and thin film compositional analyses have fostered the development of a variety of analytical techniques. Three of these techniques, secondary ion mass spectrometry, Auger electron spectrometry, and MeV ion backscattering spectrometry, have become the most widely used for thin film compositional analysis. This paper discusses the relative merits of these three techniques with respect to a variety of analytical features such as sensitivity, matrix effects, and spatial resolution.
Influence of mask materials on ion-etched structures
Authors: Dimigen H. , Lüthje H. , Hübsch H. , Convertini U.
Published: July 2002

We have investigated how the sputter yield and the shrinkage of masking structures depend on the angle of incidence of the bombarding ions. In numerous cases, suitable mask materials can be used in the preparation of deep structures with high lateral resolution by adjusting the angle of incidence of the ion beam to maximize the difference between the sputter yield of the masking material and of the etched structure.
Limitations of kinetic studies of catalytic reactions on a single-crystal surface at low pressures in a UHV system
Authors: Steinbrüchel Ch. , Somorjai G. A.
Published: July 2002

We present an analysis of the kinetics of catalytic reactions occuring on a small area (∠1 cm2), single-crystal surface in an UHV system at low pressures (10−8–10−4 Torr). We find that one can measure reaction probabilities as low as 10−4 under flow conditions and 10−7 under batch conditions. For the purpose of illustration we give two practical examples: hydrogenolysis of isobutane and dehydrogenation of cyclohexane on platinum surfaces.
Adhesion study of silver films deposited from a hot hollow-cathode source
Authors: Naimon E. R. , Vigil D. , Villegas J. P. , Williams L.
Published: July 2002

A study of the adhesion of silver films deposited from a hot hollow cathode source was undertaken. The coating process consisted of two stages: an ’’ion-bombardment’’ cleaning phase followed (continuously) by a vapor deposition phase. Effects of four process parameters were investigated: chamber pressure; substrate bias during ion bombardment; substrate current during ion bombardment; and duration of the ion bombardment. Substrate materials investigated were beryllium and aluminum tensile coupons. Pairs of coated coupons were subsequently solid-state bonded and then tensile tested. Tensile strength data provided a measure of the silver film adhesion, as well as a measure of the integrity of a solid-state joint. ’’Thresholds’’ of total ion bombardment energy have been established for ensuring minimum adhesion strengths of approximately 0.28 GPa (40 000 psi) for silver on beryllium and aluminum.
Auger spectroscopic study of nickel films on Pyrex
Authors: Sexton B. A. , Baker B. G. , Armstrong R. A.
Published: July 2002

The surface compositions of vacuum-evaporated nickel films are analyzed by Auger electron spectroscopy. The Auger tube was constructed principally of Pyrex glass and the film deposition conditions are typical of those in Pyrex UHV systems. It is shown that clean nickel surfaces can be produced at temperature 78–450 K provided the following precautions are taken: (i) the evaporation filament is subjected to a preliminary slow-evaporation in a separate vacuum system; (ii) the vacuum is maintained at less than 10−9 Torr (10−7 Pa); (iii) the film substrate is freshly flamed and washed, and glassblowing is not subsequently done near the film substrate. Failure to meet condition (i) results in contamination by carbon and possibly sulphur; failure of (ii) results in contamination by carbon and possibly oxygen; and failure of (iii) results in contamination by boron and carbon. The impurities carbon and boron are found to have high mobility above ambient temperature. They migrate to the surface of any fresh nickel film deposited over a contaminated substrate.
Evaluation of ’’barrier’’ metals for sintered platinum–GaAs contacts
Authors: Berenz J. J. , Scilla G. J. , Wrick V. L. , Eastman L. F. , Morrison G. H.
Published: July 2002

Tungsten, titanium, molybdenum, and hafnium are evaluated as ’’barrier’’ metals for preventing gallium (Ga) and arsenic (As) out-diffusion from sintered Pt–GaAs contacts. Secondary ion mass spectrometry (SIMS) and x-ray diffraction are employed to qualitatively assess the extent of interdiffusion and intermetallic compound formation which occur in these contacts as a result of heat treatment. In spite of the complex nature of the metallurgical reactions and despite inherent limitations in the analysis, tungsten and hafnium are clearly shown to be effective in preventing Ga and As out-diffusion from sintered Pt–GaAs contacts.
Reduction of niobium pentoxide in a hydrogen discharge
Authors: Wertheimer M.R. , Bailon J.-P.
Published: July 2002

When exposed to ’’active hydrogen’’ from a microwave discharge, white α-niobium pentoxide becomes gray-black. This reduction product has been examined by several techniques, including Auger electron spectroscopy. It is found that the material within a few tenths of a micrometer from the surface is reduced to niobium dioxide, and that the remaining Nb2O5 remains unchanged.
Geometry and properties of the plasma in a quadrupole ion pump
Authors: Schwarz Helmut
Published: July 2002

The diameter of the plasma in a quadrupole ionization gauge and quadrupole ion pump has been measured as a function of pressure. The radio-frequency quadrupole systems are tuned in such a way that electrons remain on stable trajectories in the center of the tube. Being emitted at one end, the electrons encounter an inverted field at the other end so that they travel on spiral paths back and forth until they collide with the rest gas molecules, producing ions which are collected as an ion current i+ at a cylinder surrounding the four hyperbolically shaped quadrupole electrodes. The inverse pressure relationship pi+4/3=const can be explained with the experimental result showing the plasma diameter d being inversely proportional to the square root of the pressure p: d=a0p−1/2.
Some investigations on deposition and etching profiles in masked rf sputtering
Authors: Sopori B. L. , Chang W. S. C.
Published: July 2002

Profiles of sputter-deposited films using a mask were measured and compared to theoretical profiles. A discontinuity in the slope of the film profile is shown to be due to the finite thickness of the mask. Backscattering in rf sputter etching is shown to cause two effects: an apparent enhanced etching rate near the mask edge and nonvertical edges of the etched groove. Significant improvement in the etching profile was obtained by using slow-etching electrodes and low gas pressures.
On temperature measurements of metallic substrates during evaporation
Authors: Amith A.
Published: July 2002

The problem of knowing the exact temperature of a radiatively heated substrate has been recognized for some time. The present paper reports direct measurements which quantify the types of errors introduced into thermocouple readings (due to the radiation field); it also demonstrates the extent of temperature variations when the substrate and radiant heater are large and of comparable size, and not in intimate and uniform contact. Thermocouples can be used only if their contact to the substrate is intimate (e.g., welded), if they traverse minimum distance in the radiation field (through the heater to the substrate), and if they are protected by their own radiation shield.
Thin-film deposition using low-energy ion beams (2) Bb+ ion-beam deposition and analysis of deposits
Authors: Amano J. , Lawson R. P. W.
Published: July 2002

Thin films of Pb were grown on C and NaCl substrates by retarding a 4-keV, mass-analyzed Pb+ ion beam to a low energy before deposition. The films were examined using Rutherford backscattering analysis, scanning electron microscopy, and transmission electrn microscopy. Adhesion was found to be independent of deposition energy for all deposits grown between 24 and 200 eV. The thickness, degree of surface coverage, and crystalline orientation are dependent n incident Pb+ ion energy. 50 eV is an optimum energy of deposition when parameters such as space-charge expansion, self-sputtering, film thickness, and surface coverage are considered. As the deposition energy is increased above 50 eV, the crystalline structures of deposits grown on single-crystal NaCl substrates becomes more ordered with a strongly preferred [100] orientation. High purity and homogeneity of the deposits were attributed to the use of a mass-analyzed beam and the maintenance of ultra-high-vacuum conditions in the substrate chambers.
Adhesion of films of MoS2 to oxidized metal surfaces
Authors: Stupian G. W. , Chase A. B.
Published: July 2002

The adhesion of MoS2 (a layer-lattice compound used as a solid lubricant), burnished by a standard procedure onto various metal substrates, has been investigated. The degree of adhesion, as determined by microscopic examination of the burnished surfaces, has been related to differences in states of surface oxygen observed by x-ray photoelectron spectroscopy and Auger electron spectroscopy. Experimental data confirm our previously reported conclusion that the substrate metal–sulfur bond strength is of primary importance in MoS2 adhesion. However, the substrate metal atoms must be accessible to sulfur in order for these bonds to form. On some metals, e.g., copper, it was found that surface oxygen is not present as an oxide but exists in a precursor state less tightly bound than an oxide. The formation of substrate metal–sulfur bonds by displacement of oxygen is facilitated by the existence of this precursor state. On metals with more stable surface oxides, e.g., titanium, oxygen lattice vacancies are present that again expose surface metal atoms to sulfur. Experiments in which MoS2 films were burnished onto both oxidized metals and metal–oxide single crystals are reported here. All results are consistently interpreted in terms of the nature of the oxygen initially present on the metal surface.
Simulation of a monopole mass spectrometer with a view to determining operating parameter tolerances
Authors: Musumeci R. A. , Richards J. A.
Published: July 2002

Results from a computer model of the operation of a monopole mass spectrometer are presented and used to illustrate the dependence of peak shape, transmission, and resolution upon various waveform and geometric parameters. In addition, the parameter tolerances necessary for highly stable operation are derived and shown to be within the capabilities of present electronic techniques. In particular, for a duty cycle (rectangular waveform operation) or dc–rf ratio (sinusoidal excitation) tolerance of the order of 10 ppm, peak height stability of about 0.1% is seen to be attainable at high resolution and high transmission. This is an order of magnitude better than is possible with a quadrupole mass filter.
Apparatus for the detection of small numbers of desorbing inert gas atoms
Authors: Kornelsen E. V. , Blair D. L.
Published: July 2002

An ultrahigh vacuum apparatus is described which is suitable for the detection of inert gases thermally desorbing from a solid following ion implantation. Using a sensitive mass spectrometer as a detector and a desorption volume of 2.27 l, it was found possible to detect the desorption of 1–2×107 helium atoms over a period of a few seconds. This is in good agreement with a theoretical expression derived for the minimum number of desorbed atoms detectable in terms of the system parameters and the shot noise on the detector ion current. Some experimental desorption spectra are given to demonstrate the capabilities of the apparatus.
Interaction of scandium dideuteride with reactive gases
Authors: Holloway D. M. , Swartz W. E.
Published: July 2002

Thin films of scandium dideuteride have been thermally cycled in vacuum to determine the specific reactions that occur with the residual gases of the vacuum. The thickness of the films, expressed as areal density, was nominally at 1.5 mg/cm2. The data indicate the film activates at 648 K as evidenced by rapid oxygen depletion from the surface. Upon activation of the film, reactions with carbon monoxide and water vapor occur. The data also indicate that extensive hydrogen isotopic exchange reactions occur at the surface. These reactions are important considerations in hydrogen isotopic storage applications and in thin-film hydrides used for neutron generator targets.
Regulated particle-delivery system for vacuum furnances
Authors: Schwab M. , Rossow T. L. , Mattson G. E. , Parrish W. H.
Published: July 2002

A system for delivering a stream of particles into a vacuum furnance has been developed. Its chief features are: (1) closed-loop feedback to regulate the feed rate, (2) jam-free particle flow through the elimination of close tolerances in the mechanical design, and (3) an external reloading system that allows uninterrupted particle delivery without affecting vacuum operation. Feed rate is determined and controlled by measuring light scattered from a laser beam as it passes through the particle stream.
Silicon monoxide antireflection coatings for InP/CdS solar cells
Authors: Olson D. H.
Published: July 2002

A hard and durable antireflection coating that bonds well to cadmium sulfide has been developed. Silicon monoxide films evaporated at 140°C substrate temperature produce homogeneous films with high adhesion and solvent resistance. These films raise the Air Mass 2 short circuit currents of single-crystal InP/CdS solar cells by 18.5% and of polycrystalline InP/CdS cells by 15.5%.
Schottky barriers on ordered and disordered surfaces of GaAs(110)
Authors: Amith A. , Mark P.
Published: July 2002

The properties of gold Schottky barriers on the GaAs(110) surface were measured to determine the influence of atomic order, cleanliness and surface processing. Clean and ordered surfaces were prepared by ion bombardment and thermal annealing. Their chemical condition was monitored by AES and their atomic order by LEED. Some surfaces were subsequently disordered by further ion bombardment or by exposure to oxygen; others were not subjected to any further processing. Gold dots were evaporated on all surfaces without breaking the UHV. No significant differences among barrier height values measured by internal photoemission were observed, suggesting Fermi-level pinning for all junctions. Major and consistent differences in capacitance–voltage and in current–voltage measurements were found between clean and ordered surfaces, and disordered surfaces. The experimental results indicate that transport across the barriers is very sensitive to inhomogeneities in the layers adjacent to the metallurgical junction introduced during the various steps employed in cleaning and ordering the surface. Chemical polishing, sputter etching and annealing all affect the stoichiometry at the surface. Annealing by itself appears to produce an intrinsic layer and while it results in ordering of the surface, it does not eradicate defects and other spatial inhomogeneities, nor the drastic changes in the electronic properties which are introduced in the surface by sputtering. Surfaces may have the same structure and ordering, yet differ widely in their electronic properties. Seeming inconsistencies among results of different measurement methods are ascribed to the fact that each method probes a different region and is sensitive to different conditions.
Influence of sample inclination and rotation during ion-beam etching on ion-etched structures
Authors: Hosaka Sumio , Hashimoto Seiya
Published: July 2002

Influences of inclination angle and rotation on etching characteristics are investigated. Inclination and rotation are two of the advantages of the ion-beam etching method, therefore their influence is studied with particular interest. Experiments are carried out to examine the relation of sample inclination angle to the sputtering yield, etching rate, and etching factor of an etched cross section. The influence of the sample inclination angle on the etching factor is also studied. In addition, it is found that in the case of the ion-beam etching method, the desired etched cross section can be obtained by controlling the sample inclination angle. This etching characteristic is due mainly to the ion-restriction effect of the mask material and the horizontal etching rate characteristic to the substrate.
Effect of substrate temperature on the thickness of evaporated Se-36.7 at. % As alloy films
Authors: Abowitz Gerald , Leder Lewis B.
Published: July 2002

The condensation of thermally evaporated Se-36.7 at. % As alloys on glass, sapphire, and aluminum surfaces was measured as a function of substrate temperature between ambient and 250°C. The ’’sticking fraction’’ τ/τ0, defined as the film thickness deposited at the temperature of interest divided by the thickness deposited at room temperature, was found to decrease rapidly with increasing substrate temperature. τ/τ0 was independent of flux density in the range between 1015 and 1017 cm−2 s−1. A difference in sticking fraction was observed between the glass substrate on the one hand and the sapphire and aluminum surfaces on the other hand with no differences observed between the latter two substrates. At the higher temperatures, where τ/τ0 <0.4, the film morphology became discontinuous, leading to a well-developed island structure. Desorption energies of 0.33 eV on Al and sapphire and 0.40 eV on glass were obtained from the temperature dependence of the sticking fraction.
Resistance stabilization of Ni–Cr films by surface oxide formation
Authors: Nocerino G. , Singer K. E.
Published: July 2002

An investigation has been made of the resistivity and temperature coefficient of resistivity of Ni–Cr thin films deposited under carefully controlled conditions in ultrahigh vacuum. Auger depth profiling has been used to monitor the films, quantification of the Auger data being achieved both by the use of bulk alloy standards and by Rutherford backscattering. This paper deals specifically with the effects of residual gas on the resistance of the film and describes how this may be stabilized by the formation of a surface oxide. After stabilization the films have resistivities and temperature coefficients of resistivity which are indistinguishable from bulk samples of the same composition. Auger data has shown that the skin is predominately chromium oxide with a thickness in the region of two monolayers, this figure being supported by the percentage change of resistance on oxidation.
Effects of oxygen ion implantation on the structure and properties of aluminum thin films
Authors: Gangulee A. , d’Heurle F. M. , Ranieri V. A. , Fiorio R. A.
Published: July 2002

Aluminum thin films having a nominal thickness of 350 nm were implanted with oxygen ions to integrated dosage of 1017–1018 atom/cm2. Structural investigations by x-ray diffraction techniques indicated that ion implanation substantially decreased the particle size, increased the magnitude of microstrains and introduced significant amount of stacking faults. Implantation also tended to introduce macroscopic compressive stresses. Both structural and electrical resistivity measurements showed that the ion implanted structure has exceptional thermal stability. Cross-stripe experiments gave direct evidence that oxygen ion implantation decreases the grain boundary diffusivity in aluminum.
Raman scattering from carbon monoxide adsorbed on evaporated silver films
Authors: Wood Thomas H. , Klein Miles V.
Published: July 2002

We present an ultrahigh vacuum study of the carbon monoxide–silver system using Raman scattering. Silver films deposited in UHV on a room-temperature substrate cooled close to 78 K and exposed to saturation doses of CO show Raman lines at 1995 and 2070 cm−1. These disappear upon warming to room temperture. Films freshly deposited on a cooled substrate show a line at 2010 cm−1 which appears at 10 L and grows in intensity through 105 L. A second line, thought to be due to residual CO, is visible on the fresh film at 2124 cm−1 and shows only minor changes with CO exposure. Further study of surfaces prepared in this manner shows at least 16 lines in the region 40–2600 cm−1 after exposure to 105 L of CO. Analysis of the data shows the utility of Raman scattering as a surface probe.
Chemisorption studies of chlorine and fluorine on the silicon (111) surface
Authors: Chen M. , Batra Inder P.
Published: July 2002

Electronic energy structure calculations were performed for a 12-layer slab of Si (111) with and without monolayer of adsorbates. Overlapping Gaussian-fitted atomic potential with Slater’s Xα-exchange approximation was employed to approximate the crystal potential. Using α=0.9 we obtained non-self-consistent band structure and density of states for relaxed Si(111) and Si(111) –Cl which are in good agreement with the results of experiment and other theoretical calculations. Having established the reliability of our approach on these well-known systems, we applied our method to the more reactive and technologically important Si/F system. We investigated both onefold and threefold sites for F chemisorption and found a net charge transfer of −0.8e to F on both of these sites. More importantly, we found marked differences in the location of F(2p) -related levels for the two sites.
GaAs surface states observed by x-ray photoemission
Authors: Ludeke R. , Ley L.
Published: July 2002

X-ray photoemission spectra taken at glancing angles from GaAs(110) cleaved surfaces indicate structure at 1.1, 1.9, 3.7, 6.5, 11.0, and 12.0 eV which can be directly related to peaks in the surface density of states. Nearly identical structure was observed for (100) surfaces. Strong fluctuations in the emission intensities of the Ga and As(3d) core levels were observed with the emission angle. Their origins and implications are discussed.
Schottky barrier formation on (Pb,Sn)Te
Authors: Buchner S. , Sun T. S. , Beck W. A. , Byer N. E. , Chen J. M.
Published: July 2002

It is shown by using Auger depth profiling and I–V measurements that Schottky barriers of Pb on Pb0.8Sn0.2Te form only when the semiconductor surface is exposed to oxygen prior to the deposition of the Pb. In those cases where the Pb is deposited on a clean semiconductor surface the Sn migrates through the interface and no Schottky barrier is formed. The presence of oxygen at the interface acts as a barrier to the migration of Sn and so plays an important role in barrier formation.
Low energy electron diffraction (LEED) study of the adsorption of acetic acid and propanoic acid on Ag(111) and Pt(111)
Authors: Firment L. E. , Somorjai G. A.
Published: July 2002

The adsorption of acetic acid and of propanoic acid on Ag(111) and Pt(111) single crystal surfaces has been studied with LEED. Both acetic acid and propanoic acid formed two-dimensional structures in two different types of orientation on Ag(111) and propanoic acid apparently formed the same structure on graphite covered Pt(111). Neither acid formed ordered monolayers when adsorbed on clean Pt(111). The similar LEED data and physical properties of the acid molecules suggested similar structures for both acids consisting of closely packed arrays of hydrogen-bonded dimers.
Radio-frequency sputtered NiFe films on Au
Authors: Ahn K. Y.
Published: July 2002

The coercivity of rf-sputtered thick NiFe films (≳0.3 μm) on thick gold (≳0.3 μm) is generally lower than in films deposited by thermal evaportion. Especially low values of coercivity (Hc?0.7 Oe) are obtained in NiFe films on gold conductors which are deposited onto thin adhesive layers of refractory metals having lattice parameters around 3 Å. For a given NiFe film thickness, the coercivity is found to decrease with increasing gold thickness up to 1 μm in sharp contrast to evaporated films.
A new method for the investigation of stress in MIS devices using SEM electron channeling patterns
Authors: Davis G. E. , Taylor M. E.
Published: July 2002

A proposed new method to measure the elastic stress in silicon induced by the presence of a thin amorphous layer is presented. The method is based on measuring the difference in the selected area channeling patterns generated by a stress-free region of the substrate and a stressed region located under an insulating layer. The maximum thickness of the amorphous insulating layer which can be used before the backscattered signal is totally absorbed was found to be approximately 600 Å for silicon dioxide and 400 Å for silicon nitride. The strain in SiO2 and Si3N4 was found to be thickness dependent. For silicon dioxide, the stress varied between 109 to 1010 dynes/cm2. For silicon nitride, the stress was on the order of 1010 dynes/cm2.