bluuebunny/crossref_metadata_2025 huggingface dataset:
Photon desorption measurements of copper and copper plated beam tubes for the SSCL 20 TeV proton collider
Authors: Foerster C. L. , Lanni C. , Maslennikov I. , Turner W.
Published: July 2002

Relativistic protons circulating in the SSCL 20 TeV collider emit synchrotron radiation (1016 photons/m/s, Ecrit=284 eV). This radiation will photodesorb gases from the walls of the beam tube. The 4.2 K superconducting magnet bore tubes will act as very long distributed pumps. Build up of cryosorbed gases could severely limit collider operation and may require a bore tube liner to hide cryosorbed molecules from the photon flux and to increase the H2 pumping capacity. To predict collider vacuum performance, photon stimulated desorption experiments have been running at the National Synchrotron Light Source (NSLS) at BNL and on the VEPP2M storage ring at BINP, Novosibirsk, Russia. At the U10B beamline of the VUV ring at NSLS, beam tube samples were exposed to over 1023 photons/m with Ecrit=486 eV and incident angle=12 mrad. Unbaked copper and copper plated stainless steel have been tested. In addition, results have been obtained with a 1100 G dipole magnetic field and with a 350 °C vacuum bake. Results are presented and compared with other measurements at the NSLS and at other laboratories.
Comparison of photodesorption yields using synchrotron radiation of low critical energies for stainless steel, copper, and electrodeposited copper surfaces
Authors: Gómez-Goñi J. , Gröbner O. , Mathewson A. G.
Published: July 2002

Photon-stimulated gas desorption yields from metal surfaces, typically used in large vacuum systems, such as stainless steel, copper, and electrodeposited copper, have been measured using synchrotron radiation with critical energies from 12.4 to 284 eV, thus allowing to obtain initial yields applicable to future large hadron colliders. The main gases desorbed from all surfaces are: H2, CO2, CO, and CH4. Water is also desorbed and greatly increases with exposure until a saturation value is reached. In situ bakeout reduces the amount of water desorbed, but only slightly reduces the yield of the other gases. The dependance of the yields on critical energy is almost linear, except for H2O. Photoelectron yields have also been measured, showing a good linear relation with the pressure increase, thus suggesting a process where a photon produces an electron that subsequently desorbs a gas molecule.
III–V on dissimilar substrates: Epitaxy and alternatives
Authors: De Boeck J. , Demeester P. , Borghs G.
Published: July 2002

The technological processes that share the goal of combining dissimilar (III–V and Si) semiconductor materials on a single substrate in order to achieve enhanced performance and functionality of devices and circuits is reviewed. In particular, these techniques that enable monolithic solutions based on the fabrication of thin crystalline III–V films on a dissimilar substrate are addressed. This fabrication process can be completed by heteroepitaxial growth or thin-film transfer and the present state of these techniques is discussed. Here, III–V on Si is used as a generic example of heteroepitaxy and it is found that research is still largely focusing on the materials quality. However, creative materials engineering is displayed to assure a steady progress toward applicability. Thin-film transfer technology is currently tackling more processing related issues. It will be shown that heteroepitaxy is competing for some (large area) applications and that for other, often very appealing applications thin-film transfer is the only solution, offering high flexibility and exciting combinations of materials and functions. Besides these thin-film-based technologies, hybrid flip–chip is also a mature candidate for integration of optical and electronic functions.
Interaction of Al with oxidized Ge/Si(001): A synchrotron radiation photoelectron spectroscopy study
Authors: Prabhakaran K. , Ogino T. , Scimeca T. , Oshima M.
Published: July 2002

Interaction of aluminum with an oxidized sample of ultrathin layer Ge (7 Å) deposited on Si(001) at room temperature [Ge (7 Å)/Si(001) RT] is studied employing synchrotron radiation photoelectron spectroscopy. Ge (7 Å)/Si(001) RT, on exposure to air, forms Ge suboxides, GeO2 and Si suboxides on the surface. GeO2 is selectively removed completely by rinsing the sample in warm water, and during this process a small amount of Si oxides is also formed. Upon depositing Al on this surface, it reacts with oxides of Si and Ge and forms an overlayer of Al2O3 on the surface, thereby reducing the oxides to elemental Si and Ge. Further, the reaction is activated by an increase in surface temperature. In the early stages of the reaction, reduction of suboxides take place in preference to SiO2.
Compositional change of (0001) WS2 surfaces induced by ion beam bombardment with energies between 100 and 1500 eV
Authors: Rumaner L. E. , Tazawa T. , Ohuchi F. S.
Published: July 2002

Ion beam bombardment at low ion energies is of interest in both surface analysis and thin film deposition, however, concerns exist regarding preferential sputtering and chemical reduction at the surface. In this study, the rate of reduction and extent of alteration of (0001) WS2 was examined with respect to type of ion beam (Ne+, Ar+, and Kr+), incident ion energy and ion beam dosage using x-ray photoelectron spectroscopy. At saturation, the surface stoichiometry was reduced to approximately WS0.4, in general agreement with preferential sputtering models. By decreasing the atomic mass of the ion or the energy of the ion beam, the resolution of the surface species formed was enhanced. With ion bombardment, the W(4f) spectrum shows the formation of a reduced W species representing metallic W. In addition, the enhanced W concentration at the surface causes an increased density of states up to the Fermi level as well as a 0.5 eV band bending due to pinning at surface defects. The corresponding S(2p) spectrum shows the formation of a reduced S species. This reduced S species is associated with S surrounded by metallic W, which causes a final state polarization effect, decreasing the binding energy.
Quantification of the composition of alloy and oxide surfaces using low-energy ion scattering
Authors: Jacobs J.-P. , Reijne S. , Elfrink R. J. M. , Mikhailov S. N. , Brongersma H. H. , Wuttig M.
Published: July 2002

The influence of the chemical environment on the low-energy ion scattering (LEIS) intensities from aluminum and nickel is investigated by studying a number of different alloys (Ag80Al20, Ni80Pt20, NiAl{110}) and oxides (γ-Al2O3, α-Al2O3, α-Al2O3 sapphire {11̄02}, NiO, 14 wt % Ni/γ-Al2O3). The neutralization behavior of the He ions scattered from Al and Ni in alloys was found to be the same as for the metals. Even for the oxides, where the chemical environment of Al and Ni is radically different from that of the pure metals, the scattered ion fractions are unaffected. For NiAl{110}, however, He ions scattered from Al in the alloy show a significant lower neutralization probability in comparison to the pure Al. This was attributed to the difference in chemical environment. It will be shown that the influence of surface roughness on the LEIS-signal intensity can be quantified. Furthermore, this influence can be neglected when comparing pressed powders having different surface morphologies.
Angular distributions of Auger electrons from surfaces: Conclusions from full multiple-scattering simulations
Authors: Chen X. , Harp G. R. , Saldin D. K.
Published: July 2002

We address some of the recent controversies regarding the interpretation of Auger electron diffraction patterns by simulating those from the 64 eV M2,3VV and the 914 eV L3VV lines from a Cu(001) surface. The lower-energy diffraction pattern, in particular, is found to be strongly dependent on the angular momentum l of the emitted Auger electrons, in line with the observations of some other authors. However, we find that both peaks and dips are observed on the same diffraction pattern at the projections of different atomic rows, indicating that the angular momentum of the source wave cannot be the only determinant of these features. We find that the distance of the scatterer from the source, as well as overlap and interference effects from scatterers in other atomic rows to be an equally important determining factor. On comparing our simulations with experimental diffraction patterns, we find that, for an l=3 source wave, our simulations agree remarkably well with the data from both Auger lines.
Pumping of helium and hydrogen by sputter-ion pumps. II. Hydrogen pumping
Authors: Welch K. M. , Pate D. J. , Todd R. J.
Published: July 2002

The pumping of helium by various forms of sputter-ion pumps (i.e., SIPs) is given in part I [K. M. Welch, D. J. Pate, and R. J. Todd, J. Vac. Sci. Technol. A 11, 1607 (1993)]. The pumping of hydrogen in diode and triode SIPs is herein discussed. The type of cathode material used in these pumps is shown to have a significant impact on the effectiveness with which hydrogen is pumped. Examples of this include data for pumps with aluminum, titanium, and titanium-alloy cathodes. Diode pumps with aluminum cathodes are shown to be no more effective in the pumping of hydrogen than in the pumping of helium. The use of titanium anodes and titanium shielding of a pump body is also shown to impact measurably the speed of a pump at very low pressures. This stems from the fact that hydrogen is ×106 more soluble in titanium than in stainless steel. Hydrogen becomes resident in the anodes because of fast neutral burial. Ions and fast neutrals of hydrogen are also buried in the walls of pump bodies. Outgassing of this hydrogen from the anodes and pump bodies results in a gradual increase in pump base pressure and consequential decrease in hydrogen pump speed at very low base pressures.
Low-Knudsen-number transport and deposition
Authors: Liao Hung , Cale Timothy S.
Published: July 2002

We present our model for transport and deposition in features for situations in which intermolecular collisions dominate the species transport. Species transport in this ‘‘low’’-Knudsen-number regime is modeled using continuum diffusion. Our model allows both homogeneous reactions and heterogeneous (surface) reactions. We use the Galerkin finite element method to estimate reactant species concentration profiles for infinite trenches with arbitrary cross section, for which two-dimensional profile evolution is appropriate. We simulate deposition processes using a solution domain which includes the trench as well as a specified region above the surface of the wafer. As an example application, we present results for the deposition of tungsten using the hydrogen reduction of tungsten hexafluoride in trenches of rectangular cross section with initial aspect ratio 4. The model predicts that step coverage increases with decreasing temperature and increasing tungsten hexafluoride partial pressure, while keeping hydrogen partial pressure and the height of the solution domain constant. These trends are in agreement with experimental observations for tungsten deposition processes. Trends in film conformality with deposition conditions are explained in terms of the ‘‘step coverage modulus’’ and reactant concentration ratios for given initial trench dimensions. The step coverage modulus is the ratio of a characteristic deposition rate to a characteristic transport rate.
Thermal reactions of fluorocarbon and hydrofluorocarbon species on Si(100)-(2×1)–CF3I, CF3CH2I, and C2F4
Authors: Lin Jong-Liang , Yates John T.
Published: July 2002

The thermal reactions of CF3I, CF3CH2I, and C2F4 are studied by temperature-programmed reaction/desorption (TPR/D) on a Si(100) surface. CF3I, CF3CH2I dissociate on the surface, whereas C2F4 adsorbs reversibly, without dissociation. Dissociation of the iodine-containing molecules is probably initiated by the cleavage of the relatively weak C–I bonds. In the case of CF3I, the C–I bond dissociation generates I(a) and CF3(a). I(a) desorbs as atomic I. CF3(a) dissociates in sequence, producing gas phase SiF2 and SiF4 and a carbon deposit on the surface. In the case of CF3CH2I, the C–I bond dissociation generates I(a) and CF3CH2(a). CF3CH2(a) undergoes β–F elimination to form gas phase CF2CH2 as well as further decomposition on the surface. At higher temperatures H2, I, HI, and SiF2 desorb and carbon deposits on the surface.
Obtaining extremely high vacuum using sintered fine copper powder as a cryosorbent
Authors: Xu Minsheng , Matsui Yutaka
Published: July 2002

Fine copper powder (FCP), sintered to the cryopanels of cryopumps, was evaluated as a cryosorbent for H2. A Gifford–McMahon refrigerator cooled the tested cryopanel of a two-stage cryopump. The third stage of a three-stage cryopump that was tested was cooled by Joule–Thomson expansion of He. 30 g of FCP were sintered to the second stage panel (20 K) of the two-stage bakeable cryopump, whereas 10 g of FCP were sintered to the third stage panel (4.3 K) of the three-stage bakeable cryopump. Hydrogen pumping speed, capacity, and base pressure measurements are given as a function of temperature. Cryopanel preparation and system bakeout procedures, reliably leading to pressures <10−9 Pa, are given. Hydrogen thermal desorption peaks for the FCP sintered cryopanel are also reported.
Studies of Ag films deposited using partially ionized beam deposition
Authors: Ren Zhong-Min , Du Yuan-Cheng , He Mao-Qi , Ying Zhi-Feng , Xiong Xia-Xing , Li Fu-Ming , Su Yi , Chen Liang-Yao , Brown W. L.
Published: July 2002

Partially ionized beam deposition, in which the starting material Ag is evaporated form a crucible with a restricted nozzle, partially ionized by electron bombardment, and the ions accelerated to the deposition substrate, has been used to deposit Ag films on both Si(111) and Si(100) substrates. Characterization of the deposited films has been carried out by x-ray diffraction, scanning electron microscopy, α-step roughness, Auger electron spectroscopy, and ellipsometry. As a comparison, Ag films deposited without ion acceleration and by evaporated conventionally from an open crucible were also investigated. Highly textured Ag films with strong (111) orientation on Si(111) have been obtained at high accelerating voltage Va=4 kV. The surface flatness improves and the resistance of the films to impurity diffusion from the surface increases as the accelerating voltage increases.
Counterion and dopant induced effects on the structure of electropolymerized polyaniline thin films
Authors: Porter T. L. , Minore D. , Sykes A. G.
Published: July 2002

We have used the technique of scanning probe microscopy in the noncontact mode to investigate the nanometer-scale domain structure of electropolymerized polyaniline thin films. While undoped polyaniline films are structurally amorphous, doped, conductive polyaniline films exhibit a structure consisting of close-packed nanometer-scale domains. Using modified effective medium theory, it is possible to accurately predict the conductivity of these films using a model based on the size distribution of individual conducting domains within the material. Dipole–dipole interactions between conducting domains as well as size-induced metal insulator transition effects must be included in this model in order to fully account for the observed macroscopic conductivity.
Nanosphere lithography: A materials general fabrication process for periodic particle array surfaces
Authors: Hulteen John C. , Van Duyne Richard P.
Published: July 2002

In this article nanosphere lithography (NSL) is demonstrated to be a materials general fabrication process for the production of periodic particle array (PPA) surfaces having nanometer scale features. A variety of PPA surfaces have been prepared using identical single-layer (SL) and double-layer (DL) NSL masks made by self-assembly of polymer nanospheres with diameter, D=264 nm, and varying both the substrate material S and the particle material M. In the examples shown here, S was an insulator, semiconductor, or metal and M was a metal, inorganic ionic insulator, or an organic π-electron semiconductor. PPA structural characterization and determination of nanoparticle metrics was accomplished with atomic force microscopy. This is the first demonstration of nanometer scale PPA surfaces formed from molecular materials.
Photon stimulated desorption measurements of extruded copper and of welded copper beam chambers for the PEP-II asymmetric B factory
Authors: Foerster C. L. , Lanni C. , Perkins C. , Calderon M. , Barletta W.
Published: July 2002

PEP II is being built as a higher luminosity electron–positron collider with asymmetric beams of 9 and 3.1 GeV, having maximum currents of 3.0 A. Based on our previous work on the National Synchrotron Light Source (NSLS) vacuum ultraviolet beamline U10B, a copper was selected for construction of ultrahigh vacuum beam chambers and absorbers to minimize the pressure rise from synchrotron radiation during operation. An extruded beam chamber and a welded beam chamber were fabricated from the selected copper for photon stimulated desorption measurements on the NSLS x-ray beamline X28A. The chambers were exposed to white light with a critical energy of 5 keV, both directly and through a 0.010-in.-thick beryllium filter. Each chamber was exposed to a dose of approximately 1023 photons per meter at an incidence angle of 25 mrad, after argon glow preconditioning and a 150 °C vacuum bake. Desorption yields for H2 CO, CO2, and CH4 are reported as a function of accumulated photon flux, critical energy, and chamber preparation. The results are compared with the previous work on the beamline U10B and with those of other published work on copper.
Photon stimulated desorption measurement of an extruded aluminum beam chamber for the Advanced Photon Source
Authors: Foerster C. L. , Lanni C. , Noonan J. R. , Rosenberg R. A.
Published: July 2002

The Advanced Photon Source (APS), presently being commissioned, will produce x rays of unprecedented brightness. The high energy ring of the APS is a 7 GeV positron storage ring, 1104 m in circumference designed to operate at less than 10−9 Torr with 300 mA of beam and a greater than 10 h lifetime. The storage ring vacuum chamber is constructed from an extruded 6063 aluminum alloy. During the construction phase, a 2.34-m-long section of the APS extruded aluminum chamber was set up on National Synchrotron Light Source (NSLS) X-ray Beamline X28A and photon stimulated desorption (PSD) was measured. Cleaning and preparation of the chamber was identical to that of the APS construction. In addition to the chamber, small samples of Al, Be, and Cu were also exposed to white light having a critical energy of 5 keV. In addition to PSD, measurements were made of the specular and diffuse scattering of photons. The chamber and samples were each exposed to a dose greater than 1023 photons per m. Desorption yields for H2, CO, CO2, CH4, and H2O are reported as a function of accumulated flux, critical energy, incidence angle, and preparation. These results are compared with previous results for aluminum on NSLS Beamline U10B and PSD results of other laboratories published for aluminum.
Synchrotron radiation induced gas desorption from a Prototype Large Hadron Collider beam screen at cryogenic temperatures
Authors: Calder R. , Gröbner O. , Mathewson A. G. , Anashin V. V. , Dranichnikov A. , Malyshev O. B.
Published: July 2002

The performance of the vacuum system of the Large Hadron Collider will depend critically on the synchrotron radiation induced gas desorption and on the readsorption of molecules on the cold surfaces. The present design of the system is based on a so-called beam screen inserted in the 1.9 K cold bore of the magnets. Gas molecules desorbed will therefore readsorb on the beam screen which is held at a temperature between 5 and 20 K. Pumping slots in the beam screen enable some of the desorbed gas to be pumped onto the 1.9 K surface of the cold bore.
Plasma-enhanced chemical vapor deposition of thick silicon nitride films with low stress on InP
Authors: Shi L. , Steenbergen C. A. M. , de Vreede A. H. , Smit M. K. , Scholtes T. L. M. , Groen F. H. , Pedersen J. W.
Published: July 2002

We have developed a low-temperature plasma-enhanced chemical vapor deposition process that facilitates the deposition of silicon nitride films with controlled stress by using periodically alternating high- and low-frequency power sources. Very thick films of 3 μm with low stress were deposited on InP substrates. Suitable sidewall profiles for metallization are obtained at 250 °C deposition temperature. A 3-μm-thick low-stress nitride film was successfully applied to reduce the capacitance of bond pad for an array of four InP based photodetectors, that were integrated with a four channel phased-array wavelength demultiplexer. The capacitance of the detectors was below 0.5 pF at −5 V bias.
Influence of transition metal impurities on oxygen precipitation in Czochralski-grown silicon
Authors: Shen B. , Zhang R. , Shi Y. , Zheng Y. D. , Sekiguchi T. , Sumino K.
Published: July 2002

Oxygen precipitation in Czochralski-grown silicon intentionally contaminated with Cu or Fe is investigated by means of Fourier-transform infrared spectroscopy, transmission electron microscopy, and the electron-beam-induced-current technique. It is found that oxygen precipitation is not influenced by Cu impurities, but is enhanced significantly by Fe impurities even if the concentration of Fe is much lower than that of Cu in Si. Cu forms precipitate colonies of a low density and a large size, and does not react with minute oxygen precipitates existing in as-grown specimens. On the contrary, Fe precipitates on them and forms Fe decorated silica particles of a very high density, which serve as the efficient sites for the nucleation of oxygen precipitates.
Effects of hydrogenation of hydrogen termination of p+-silicon (100) surfaces by hydrofluoric acid
Authors: Kosugi Toshihiko , Ishii Hiromu , Arita Yoshinobu
Published: July 2002

We have investigated the hydrogen termination of p+-Si(100) surfaces treated with a dilute hydrofluoric acid solution after hydrogen plasma is used to deactivate the dopant. The carrier concentration of hydrogenated p+-Si is reduced by an order of magnitude by this hydrogen passivation but it can be largely restored simply by thermal annealing at moderate temperatures. Contact angle measurement and thermal desorption spectroscopy revealed that the hydrogenated p+-Si surface is efficiently terminated by hydrogen in HF solutions and that the H-terminated surface is more stable in water than the original p+-Si surface is. The hydrogenated p+-Si surface reacts with HF solutions in ways quite similar to these in which a p−-Si surface does. On the other hand, the hydrogenation does not affect the HF treatment properties of n+-Si. This hydrogen–plasma passivation enables us to obtain a clean H-terminated p+-Si surface by using the conventional dilute HF treatments.
Safety interlock and remote computer monitoring for a diffusion-pumped vacuum system
Authors: Chu Liang T.
Published: July 2002

A safety interlock system for a diffusion-pumped ultra-high vacuum chamber is presented. It controls and monitors vacuum system valves, diffusion pumps, liquid nitrogen filling, chilled water flow, and pressures in the chamber. The interlock system is interfaced with a phone dialer and a personal computer to provide remote monitoring and diagnostics of the vacuum system. This interlock prevents many operational errors and problems due to the power and liquid nitrogen failure.
Heterogeneous hydride pyrolysis in a chemical beam epitaxy cracker cell and growth of high quality InP
Authors: Rongen R. T. H. , Leys M. R. , van Hall P. J. , Vonk H. , Wolter J. H.
Published: July 2002

The decomposition of phosphine and arsine in a chemical beam epitaxy cracker cell was investigated with a quadrupole mass spectrometer. We have determined the kinetical parameters for a unimolecular reaction of the first order, i.e. the activation energy and frequency factor, from the decomposition efficiency as a function of temperature. These results are compared with data from literature. We find the lowest activation energies ever reported for the hydride pyrolysis, namely 72 and 48 kJ/mol for phosphine and arsine, respectively. This is due to the heterogeneous decomposition on catalytic molybdenum baffles inside the cracker cell. Additionally, we have studied the impurity incorporation in epitaxially grown bulk InP layers in relation to the efficiency of this particular molybdenum containing cracker cell. Impurity levels were determined by fitting calculated Hall values to experimental data. The best quality is achieved for the cracker temperature at which the efficiency starts to saturate. At this cracker temperature, optimized mass flow rates resulted in InP layers with a maximum mobility of 186 000 cm2/V s and impurity concentrations in the low 1014 cm−3 range.
Characterization of the low-pressure chemical vapor deposition grown rugged polysilicon surface using atomic force microscopy
Authors: Strausser Yale E. , Schroth Michael , Sweeney III John J.
Published: July 2002

In this work, rugged polysilicon films are deposited in a state-of-the-art low-pressure chemical vapor deposition reactor to produce the plates of dynamic random access memory charge storage capacitors with higher capacitance per unit area. The films are deposited at temperatures in the vicinity of 575 °C. The 〈311〉 textured, in situ crystallized films have high surface roughness as compared to the usual rather smooth, 〈110〉 textured, as deposited polysilicon. Atomic force microscopy measurement of the roughness of these films posed a challenge since the rugged polysilicon films are made up of a very hard material with a large amplitude of high spatial frequency roughness. A solution was found which involves using probes on which a carbon film has been applied to the standard Si probes. Combining these probes with carefully selected measurement parameters and proper data reduction techniques has produced good results. Using this solution has allowed us to measure the roughness of the rugged polysilicon films as a function of the critically controlled growth temperature and pressure. Substantial differences were found with small changes in temperature, with less difference coming from pressure variations. 570 °C and 200 mTorr produced the best results for large batch processing.
Improved current–voltage characteristics of downstream plasma enhanced chemical vapor deposition SiNx deposited at low temperature by using He as a dilution gas
Authors: Arps M. , Markwitz A.
Published: July 2002

We have compared the current–voltage characteristics of silicon nitrides prepared from the two gas combinations N2/NH3/SiH4 (N2–SiNx) and He/NH3/SiH4 (He–SiNx) at temperatures between 100 and 350 °C. A downstream plasma enhanced chemical vapor deposition reactor with a non-ECR microwave plasma source has been used. While N2–SiNx with reasonable electrical properties requires deposition temperatures of about 350 °C, the characteristics of He–SiNx even improve at decreasing process temperatures. Almost identical current–voltage characteristics are found for both N2–SiNx and He–SiNx prepared at 350 °C exhibiting an Ohmic behavior at low fields and a Poole–Frenkel (PF) conduction at high fields. At a deposition temperature of 100 °C the He–SiNx with a dielectric strength of 1.13×107 V/cm and an onset field strength of the PF conduction of 6.9×106 V/cm is in contrast to the N2–SiNx with a dielectric strength of 4.3×106 V/cm and a PF onset field strength of as low as 2×105 V/cm resulting in many orders of magnitude higher current flow. In order to find a correlation between the dielectric and the structural properties of the silicon nitrides several analyses are performed. The He–SiNx proves to be superior to the N2–SiNx concerning refractive index, mass density and buffered HF etch rate at every deposition temperature and the deterioration with decreasing deposition temperature is weaker. All SiNx films are found to be nitrogen-rich at a N:Si ratio of 5:3. As expected, the hydrogen content increases with decreasing deposition temperature, being lower for the He–SiNx than for the N2–SiNx. In all layers most of the hydrogen is bonded to the nitrogen atoms. A simple model is proposed that explains the difference between the two kinds of low-temperature SiNx by the microscopic void structure of the material.
Direct simulation Monte Carlo computation of reactor-feature scale flows
Authors: Hudson Mary L. , Bartel Timothy J.
Published: July 2002

The direct simulation Monte Carlo (DSMC) technique was used to model the flow around multiple features on a wafer. Since the DSMC technique is valid in both the continuum and rarefied flow regimes, the near-surface reactor flow was directly coupled with the features into a single reactor-feature scale model. This model was then used to determine the effects of operating conditions, feature geometry, and surface chemistry on the concentrations and fluxes to a flat and featured surface. The surface chemistry addressed both chlorine etching of aluminum and SiO2 deposition from a silane/oxygen/argon gas mixture. For both the etch and deposition cases, the concentration of products was higher near the featured surface than the flat surface. This was partially due to multiple molecular reflections between the horizontal and vertical surfaces of the features. While the reacting area of the features was greater than the flat surface with no features, the fluxes to the features were less due to the direction of the incoming flow. Thus, topography models using fluxes to flat surfaces, which are assumed in full reactor scale models, will overpredict deposition or etch rates. A simplified adjustment to the flat surface flux was made to obtain more accurate boundary conditions for topography models and thus, better predictions of deposition and etch rates.
Structural characterization of a Mo/Si multilayer reflector by means of x-ray diffraction measurements
Authors: Kim Dong-Eon , Cha Dong-Ho , Lee Sang-Won
Published: July 2002

The physical and optical characteristics of a multilayered synthetic microstructure (MLSM) have a significant structural dependence. Knowledge of the structure and its correlation to physical properties is needed in order to control the fabrication of MLSMs to obtain desired properties. Important parameters for the description of the structure are the thickness of a repeating unit, the thickness ratio of composite materials within the repeating unit and the degree of interdiffusion and roughness at interfaces. The effects of these various structural parameters on the small-angle x-ray diffraction (XRD) pattern are investigated for a molybdenum-silicon MLSM. The angular positions of the Bragg peaks are sensitive to the thickness of the repeating unit (Mo/Si bilayer in this study), and the pattern of the subsidiary peaks in the low-order Bragg region has a strong dependence on the thickness ratio. The major effect of interfacial diffusion is the overall reduction of the intensities of high-order Bragg peaks. However, the atomic concentration profile correlates with their relative intensities. The uncorrelated roughness is responsible for the increased linewidths of the Bragg peaks and the increase of the relative intensities of the subsidiary peaks to those of the Bragg peaks. Based on the above results, we present an analysis of the experimental XRD data in order to deduce the structural parameters of a molybdenum-silicon MLSM.
Factors causing deterioration of depth resolution in Auger electron spectroscopy depth profiling of multilayered systems
Authors: Satori K. , Haga Y. , Minatoya R. , Aoki M. , Kajiwara K.
Published: July 2002

We have investigated the effects of the sputter-induced roughness on the depth resolution Δz and on the interface position zc obtained by Auger electron spectroscopy (AES) depth profiling of a Ni/Cr multilayer and of an AlAs/GaAs superlattice. We also correlated the escape depth λ with Δz and zc. First, the sputter-induced roughness was evaluated by atomic force microscopy (AFM). Second, both Δz and zc were evaluated quantitatively using an error function fitting method of AES, depth profiles. The AFM observation shows that the height distribution of sputter-induced roughness is approximated to first order by a Gaussian distribution and is correlated with the resolution function which depends strongly on the sputter-induced roughness. The precise measured height distribution is, however, somewhat different from the Gaussian distribution. The computational simulation using the error function approximation fitting is in good agreement with experimental results. We also estimated the escape depth λ using the same computational simulation results. The results indicate that the error function approximation fitting is useful to evaluate Δz and zc as a practical method, but anomalies of Δz and zc are discernable at the specific interface. These anomalies are assumed to come from preferential sputtering.
Kinetics of adsorption and photodesorption of hydrogen on copper surfaces
Authors: Bailey W. H. , Rahman T. S. , Strongin M. , Davenport J. W.
Published: July 2002

The kinetics of adsorption and photodesorption of hydrogen on a Cu surface is discussed for the next generation of high energy proton colliders. The equilibrium solution of a rate equation describing the surface kinetics leads to an expression for the gas pressure, which we estimate to be about 10−8 Torr for proton beam colliders like the now defunct 20-TeV superconducting super collider. Using classical molecular dynamics simulations with reliable interatomic potentials we find the fractional energy loss of hydrogen on Cu(100), for incident energies ranging from 0.1–1.0 eV, to be between 1%–6%. This leads to an estimate of 10−4 s for the average lifetime of the hydrogen molecule in the beam tube.
Growth of polycrystalline hexagonal-close-packed Co films on glass substrates from low kinetic energy vapor
Authors: Ishii K. , Kawazu M. , Ohba T.
Published: July 2002

For the first time it has been demonstrated that polycrystalline Co films (10–300 nm) of hcp single phase can be produced on SiO2 glass substrates by a gas-flow-sputtering technique. The hcp Co films are obtained at substrate temperatures below 620 K and fcc Co films are obtained above 720 K. A mixture of hcp and fcc phases is formed between these temperatures. Gas-flow-sputtering allows the sputter deposition at high pressure in the range of 1 Torr, where sputtered particles are thermalized to the temperature of the sputtering gas; the deposition of such low kinetic energy vapor can be attributable to the formation of hcp phase for Co films.
Formation of periodic step and terrace structure on Si(100) surface during annealing in hydrogen diluted with inert gas
Authors: Kumagai Y. , Namba K. , Komeda T. , Nishioka Y.
Published: July 2002

Annealing of a Czochralski Si(100) substrate in a gas flow in which H2 is diluted to a concentration of 3% in He was investigated. The surfaces annealed at 900 °C or above showed well-developed terraces with mono-atomic steps that alternate between the straight A-step and the zigzag B-step configurations, whereas no morphological improvement occurred in the surfaces annealed at temperatures below 900 °C, as confirmed by atomic force microscopy. Reflection high-energy electron diffraction observations and Fourier-transform infrared attenuated total reflection spectra of the flat surfaces clarified that the surface Si atoms make dimers with their dangling bonds terminated by H atoms, i.e., the surface reconstruction is Si(100)2×1/1×2-H. We show that the depth of the etching was not sufficient to account for the observed smoothening of the surface during the annealing at high temperatures, and conclude that the main mechanism of surface flattening is surface migration of the Si atoms.
Effects of substrate temperature on the laser damage threshold of sputtered SiO2 films
Authors: Alvisi M. , De Nunzio G. , Ferrara M. C. , Perrone M. R. , Rizzo A. , Scaglione S. , Vasanelli L.
Published: July 2002

SiO 2 films have been deposited by ion-beam sputtering techniques either without assistance or with Ar-ion assistance and the role of the substrate temperature during the deposition process on the film damage threshold by laser light at the wavelength of 308 nm (XeCl) has been investigated. The photoacoustic probe beam deflection technique has been used to determine damage thresholds and it is shown that this technique provides valuable information on the mechanisms leading to laser damage. It has been found that the samples deposited by the Ar-ion beam sputtering technique are characterized by higher damage thresholds at lower temperatures of the substrate than the SiO2 films deposited without ion assistance.
Characterization of a novel lambda balanced inductive plasma source
Authors: Vinogradov G. K. , Menagarishvili V. M. , Yoneyama S.
Published: July 2002

A preliminary study on the 1–4.5 kW power industrial scale 27.12 MHz rf lambda-resonator oxygen asher is presented. Contact probes of several types, including single Langmuir and flat wall probes, thermocouples, and optical emission spectroscopy, are mainly used to diagnose plasma in the inductive source area, downstream chamber and in the vicinity of wafers. Electron density in a 200 mm wafer asher at 2 kW rf power varies from 2×1011 in the plasma source to 5×107 cm−3 in a downstream chamber 5–10 mm from a wafer. The ion density exceeds the electron density 10–60 times. The plasma space potential varies in a range of 14–22 V, while the floating potential of the bulk plasma and wall surface varies from +9 to −17 V. The minimum surface floating potential of −17 V exists at the maximum of the rf voltage standing wave distributed along the full lambda inductor. The wafer surface floating potential is in the range of 3–5 V depending on the reactor configuration and is constant within ±1 V on the 200 mm wafer. Positive ion current density on the wafer and downstream chamber surface is less than 1 μA/cm−2. The typical resist ashing nonuniformity is ⩽2%–5% (range, not sigma) for both 200 and 300 mm ashers at about a 6–8 μ/min ashing rate.
Homoepitaxial growth of CdTe on vicinal CdTe(100) surfaces: Reaction kinetics and mechanism
Authors: Yong Kijung , Martinez Herve , Gellman Andrew J. , Sides Paul J.
Published: July 2002

Homoepitaxial films of CdTe were grown on vicinal CdTe(100) surfaces using Cd(CH3)2 and Te(C3H7)2 precursors in an atmosphere of H2. The vicinal CdTe(100) substrates were misoriented by 0°, 2°, 4°, 6°, and 8° from the (100) direction towards the (111)Te direction and thus had systematically increasing step densities. The CdTe films grown on these surfaces were single crystalline and epitaxial but had gross surface morphologies that depended on the misorientation of the substrate. Films grown on the CdTe(100)-0° and CdTe(100)-8° substrates were rough while those grown on the CdTe(100)-4° substrate were smooth. The kinetics of film growth were studied through measurements of the overall film growth rates and measurements of precursor adsorption/desorption kinetics. Film growth rates were weakly dependent on the degree of substrate misorientation, increasing slightly with increasing step density. Although the step density determines film morphology, the steps are not active sites for decomposition of precursors and do not participate in the rate determining steps of the growth mechanism. Studies of the surface chemistry of the Cd(CH3)2 and Te(C3H7)2 precursors show that they are reversibly adsorbed on the vicinal CdTe(100) surfaces, which is quite different from precursor surface chemistry on III–V semiconductors where adsorption tends to be irreversible.
Low energy ion beam etching of CuInSe2 surfaces
Authors: Otte K. , Lippold G. , Frost F. , Schindler A. , Bigl F. , Yakushev M. V. , Tomlinson R. D.
Published: July 2002

A nitrogen ion beam was used to etch the surface of CuInSe2 single crystals. This technique, applied to CuInSe2 for the first time, was studied with respect to surface damage production at various ion energies and was compared to commonly used argon ion sputtering. Raman scattering and atomic force microscopy were applied as characterization methods. We observed a stress induced redshift of the Raman mode for the argon etched samples which could be explained by tensile stress in the damaged layer. Nitrogen ion beam etching at an energy of 1000 eV causes a blue shift due to the increased lattice damage. Nitrogen ion beam etching at energies below 500 eV was found to produce the lowest degree of damage and the lowest surface roughness, as compared with mechanical polish or argon ion sputtering. Therefore, this method is suitable for dry etching and smoothing of CuInSe2.
Spectroscopic analysis of photochromic films
Authors: Mo Yeon-Gon , Dillon R. O. , Snyder P. G.
Published: July 2002

Sol-gel processing was used to dope photochromic dyes into three matrices: metal alkoxide, metal alkoxide-polymer, and pure polymeric materials. The films on silicon and quartz substrates were examined, with and without ultraviolet (UV) irradiation, by ellipsometry, UV-visible transmission spectroscopy, and Fourier transform infrared (FTIR) transmission spectroscopy. Variable angle spectroscopic ellipsometry (VASE) data were analyzed for film thickness and optical constants, and in some cases thickness nonuniformity. A modified Cauchy and a combined Cauchy–Lorentz model were used to fit the unirradiated and irradiated film optical constants, respectively. The optical constants of the films showed significant changes upon irradiation. This means that the absorption coefficient and hence the emissivity of the films is being modulated with UV irradiation. The VASE-fitted thicknesses of the films were in the range of 1–6 μm. In the FTIR spectra, the spiropyran doped samples have shown IR transmission changes in the two spectral regions (6–7 and 7.5–8.5 μm) where changes are expected due to bond opening. The transmission ratio for UV irradiated and unirradiated samples decreased by as much as about 24% at a particular IR wavelength.
Effects of helium dilution of TEOS–O2–C2F6 gas mixture on plasma-enhanced chemical vapor deposition of fluorine-doped silicon oxide film
Authors: Yoshimaru Masaki , Koizumi Satoshi , Shimokawa Kimiaki , Mori Y. , Fukuda H. , Matsuki N.
Published: July 2002

It was found that helium dilution in reactant gas on plasma-enhanced chemical vapor deposition of fluorine-doped silicon oxide film increases the film deposition rate while decreasing hygroscopicity and dielectric constant. He dilution has also been found to decrease the intensity of the infrared absorption band at 980 and 923 cm−1, but affected band intensity only negligibly at about 948 cm−1. Absorption bands at 980 and 923 cm−1 are due to silicon difluoride sites, while that at 948 cm−1 is due to silicon monofluoride sites. He presumably plays an active role in chemical vapor deposition, not acting only as a dilution gas, increasing film deposition rate and reducing fluorine at silicon difluoride sites. The selective reduction of fluorine at silicon difluoride sites is also assumed to decrease the film hygroscopicity and dielectric constant.
Ultrahigh vacuum dual fluid line rotatable connector
Authors: Kaczer B. , Jones D. E. , Im H.-J. , Pelz J. P.
Published: July 2002

A compact connector allowing for ultrahigh vacuum sealed flow and simultaneous connection of two fluid lines has been designed and tested.
Electron beam dissociation of CO and CO2 on ZnS thin films
Authors: Darici Y. , Holloway P. H. , Sebastian J. , Trottier T. , Jones S. , Rodriquez J.
Published: July 2002

The effects of electron bombardment in 10−6 Torr CO or CO2 upon the surface composition of ZnS thin films was determined with Auger electron spectroscopy. The ZnS surface composition was stable in 1×10−9 Torr residual vacuum or for CO and CO2 exposures without electron bombardment. With electron bombardment and CO both present, C was deposited and S decreased, but no O accumulated on the surface. This was interpreted as an electron beam stimulated surface reaction in which CO was dissociated by the electron beam CO2 was reformed leaving C on the surface. For CO2, both C and O were increased on the surface while S was reduced. This was interpreted as a surface reaction involving dissociation of CO2 with reformation of COx leaving both C and O on the surface. The data suggest that the surface dissociation of CO2 did not occur when the sample temperature was increased from 30 °C to 150–200 °C. At 300 °C, S diffused from the ZnS substrate to the surface. The consequences of these reactions on ZnS cathodoluminescent phosphors are discussed.
Structural and electrical properties of SrTiO3 thin films prepared by plasma enhanced metalorganic chemical vapor deposition
Authors: Hahn Y. B. , Kim D. O.
Published: July 2002

The structural and electrical properties of SrTiO3 thin films (30–75 nm in thickness) prepared by plasma enhanced metalorganic chemical vapor deposition on Pt/Si and Ir/Si substrates were studied in terms of their crystallinity, microstructure, current density, and dielectric constant. Deposition at higher rf powers (>180 W) resulted in a poor crystalline structure mainly due to the sputtering effect. The surface morphology showed a quite smooth surface, but was independent of the substrate. The current density decreased as the deposition temperature increased up to 550 °C, and increased somewhat at 580 °C. The I-V characteristics showed that the conduction mechanism of the SrTiO3 film capacitor was controlled by the Schottky emission for thick films (>30 nm), but by the tunneling effect for the films thinner than 30 nm. The potential barrier height and the electron affinity of the SrTiO3 films were 1.2 and 4.0–4.3 eV, respectively.
Increase of etch resistance of deep ultraviolet photoresist by implantation
Authors: Ong K. K. , Liang M. H. , Chan L. H. , Soo C. P.
Published: July 2002

Ion implantation causes damage to photoresist and brings about the formation of a carbonized layer on the surface of the resist. The relationship between the extent of damage and the etch resistance of the resist was investigated. Four ion species, namely, Si, P, As, and BF2 were used. Heavier ions and higher implant energies generally increase the extent of damage and the density of the carbonized layer. Compared to a fresh resist, the formation of a dense carbonized layer increases the etch resistance whereas the formation of a porous carbonized layer decreases the etch resistance.
Metal overlayers on organic functional groups of self-assembled monolayers: VIII. X-ray photoelectron spectroscopy of the Ni/COOH interface
Authors: Herdt G. C. , Czanderna A. W.
Published: July 2002

The interaction of vacuum deposited Ni with the COOH organic functional groups of mercaptoundecanoic acid [HS(CH2)10COOH] self-assembled monolayers formed on an Au substrate has been characterized with in situ x-ray photoelectron spectroscopy. Steady loss and complete disappearance of the hydroxyl component of O 1s peak at 532.8 eV provides evidence for the formation of a Ni–O bond at the Ni/COOH interface. Further evidence for interfacial compound formation is provided by a binding energy shift in the high binding energy component of the Ni 2p3/2 peak from 854.8 to 854.4 eV for Ni coverages below ∼0.2 nm. These results are consistent with the donation of electrons from the deposited Ni to the COOH oxygens at low Ni coverages. The absence of the characteristic satellite feature in the Ni 2p peak excludes the possibility that a full electron charge is donated to each COOH organic functional group as a bidentate complex. However, the data are consistent with a two step reaction mechanism in which Ni initially reacts weakly with the oxygens in COOH below one monolayer coverage and then forms a complex above this coverage.