bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of adsorbed gas on the interior-surface of the GAMMA 10 tandem mirror by the electron-impact desorption technique
Authors: Nakashima Y. , Peranich L. S. , Tsuchiya K. , Yamaguchi N. , Yatsu K. , Inutake M. , Ichimura M. , Leikind B. , Miyoshi S.
Published: July 2002

An analysis for adsorbed gas on wall surfaces using an electron-impact desorption (EID) technique was developed and applied to the evaluation of wall conditioning in the GAMMA 10 tandem mirror. The partial pressure rise due to EID (ΔPEID) was measured with a quadrupole mass analyzer installed near an electron emitting filament inserted in the central cell of GAMMA 10. The analysis using this method was performed during the wall-conditioning period and the ΔPEID related to light impurities (M=15, 28, 44) was observed to decrease by an order of magnitude with the progress of the wall conditioning. It was also observed that a good correlation exists between the ΔPEID and the partial pressure rise induced by the plasma discharge (ΔPPID). The desorption efficiency of typically adsorbed gas molecules ξ was estimated by a simple balance equation for the partial pressures. A significant reduction of ξ due to the wall conditioning was observed.
The structure of CdTe–InSb multilayers grown on (001) InSb using molecular beam epitaxy
Authors: Williams G. M. , Cullis A. G. , Barnett S. J. , Whitehouse C. R. , Golding T. D. , Dinan J. H.
Published: July 2002

Molecular beam epitaxy has been used to prepare multilayer structures of CdTe/InSb on (001) InSb at a growth temperature of 300 °C. Transmission electron microscopy and double crystal x-ray diffraction were employed to analyze the multilayer specimens and also a series of single CdTe layers grown on (001) InSb at substrate temperatures ranging from 180 to 300 °C. The detrimental effect on the CdTe layers of increasing the substrate temperature is clearly demonstrated and modification of the Cd:Te flux ratio during growth is shown to reestablish high structural quality material. Both x-ray and transmission electron microscopy studies confirm the high structural quality that can be achieved when multilayers are grown at 300 °C using the modified Cd:Te flux ratio conditions. These analytical techniques also reveal the presence of strain at each CdTe/InSb interface possibly associated with the formation of a thin (≤2 nm) layer of an indium telluride (e.g., In2Te3 ). The growth of high structural quality multilayers with individual layer thicknesses ≤22.5 nm is seen to break down rapidly as growth proceeds and a possible explanation for this observation is discussed.
Laser induced photodesorption of SiCl from Si(100) monitored by time of flight and time resolved reflectivity
Authors: Boulmer J. , Bourguignon B. , Budin J.-P. , Débarre D. , Desmur A.
Published: July 2002

The excimer laser induced desorption rate of SiCl molecules from a chlorinated silicon surface is measured in real time together with the transient change of the surface reflectivity at 632.8 nm. It is demonstrated that, under conditions where gas-phase chlorine is not photoexcited and does not collide with the surface during the laser pulse, laser induced desorption occurs only when the surface melts, at the laser wavelengths 308 and 248 nm.
Resonance frequency shifts of a photothermal vibration in vacuum
Authors: Inaba S. , Hane K.
Published: July 2002

The resonance frequency shifts of a glass thin plate vibrated by a photothermal effect have been measured in the pressure region from 10−4 to 760 Torr for He, Ne, Ar, Kr, and Xe gas. The frequency shift in the pressure region above 100 Torr is caused by the viscous drag of the gas and that below 1 Torr is due to the thermal conduction of the gas.
The effect of limiter conditioning on the Tokamak Fusion Test Reactor edge plasma
Authors: Kilpatrick S. J. , Pitcher C. S. , Dylla H. F. , Manos D. M. , Nyberg I. , Ramsey A. T. , Stratton B. C. , Timberlake J. , Ulrickson M. J.
Published: July 2002

Measurements by moveable Langmuir probes and edge spectroscopy diagnostics have documented the conditioning effect of low-density helium-initiated discharge sequences on the Tokamak Fusion Test Reactor edge plasma. Langmuir probe measurements shown in general that the edge electron density ne decreases by less than a factor of 2 while the edge electron temperature Te doubles. Radial profiles to the plasma boundary show that the density scrape-off length increases somewhat while the temperature scrape-off length decreases substantially. The particle flux density is unaffected. The spectral emission of C II decreases by a factor of 2, a much smaller change than that exhibited by the Dα signal. These results complement previous accounts of the conditioning technique. Comparisons of these He conditioning measurements are made to edge measurements during a deuterium density scan experiment, showing many similarities, and to an existing edge model of the conditioning process, showing qualitative agreement.
Plasma diagnostic studies of the influence of process variable upon the atomic and molecular species ejected from (1−x)Li4SiO4:xLi3PO4 targets during radio frequency magnetron sputtering
Authors: Wachs A. L. , Bates J. B. , Dudney N. J. , Luck C. F.
Published: July 2002

The deposition of thin-film electrolytes is a critical step in the development of lithium microbatteries with the potential for circuit integration. We have performed a preliminary study of the rf-magnetron sputtering of (1−x)Li4SiO4:xLi3PO4 targets used to deposit amorphous thin-film electrolytes formed of the three-component system Li2O–SiO2–P2O5. Mass and optical emission spectroscopies have been used to investigate the effects of target composition and the deposition conditions upon the atomic and molecular species ejected from the targets. The data provide important information for understanding the mechanism of film formation and for monitoring the Li atomic flux onto the substrates during film growth.
Etching of thin metal films using a ballistic model
Authors: Tait R. N. , Dew S. K. , Smy T. , Brett M. J.
Published: July 2002

A two-dimensional model for plasma etching has been developed based on simulation by ballistic deposition (SIMBAD), a two-dimensional model for film growth over topography. By incorporating the effects of shadowing, adatom mobility, and incident flux distributions, SIMBAD is able to predict microstructure and density of films deposited by physical vapor deposition methods such as evaporation and sputtering. The plasma etch has been similarly modeled using an appropriate incident angular distribution for reactive species and a fixed probability of reaction. Simulation predictions are shown to agree well with experimental results for etching of tungsten films sputtered over trenches. For a 0.9-μm-thick tungsten film on a 1.8-μm-wide 0.6 aspect ratio trench with 80° sidewalls, the etch rate on the sidewalls was found to be about twice the rate on the horizontal sections of film for a CF4/O2 plasma etch. This is in agreement with the computed results.
Test structures for secondary ion mass spectrometry analysis of patterned silicon wafers
Authors: Stevie F. A. , Cochran G. W. , Kahora P. M. , Russell W. A. , Linde N. , Wroge D. M. , Garcia A. M. , Geva M.
Published: July 2002

Secondary ion mass spectrometry (SIMS) analysis of patterned silicon wafers is complicated by the small areas available for study, the difficulty in finding the analysis location, the existence of thick insulating layers that cause charging, quantification of multilayer structures, and the presence of a high concentration of the element of interest adjacent to the area of study. Special SIMS test structures have been implemented to provide large, easily identifiable, analysis areas that have proved to be an asset in both process characterization and failure analysis of product wafers. Descriptions are provided for test structures ranging from a 400×600-μm pattern in a test chip design to a 100×125-μm pattern on a product wafer. Applications are shown for test sites generated by projection and step and repeat printing. The grid region between devices provides a practical location for SIMS test areas on current product wafers. The amount of grid space available may be insufficient to accommodate the full complement of structures needed to characterize a particular process technology, but space requirements can be reduced by the use of smaller patterns for certain applications. Analysis of patterned wafers using grid test patterns can still be affected by charging, and often requires the removal of insulating layers by etching and the use of primary beams that are well focused and do not impact on the sample outside of the test pattern.
Understanding surface activity of oxides from oxide–metal interface formation
Authors: Mukhopadhyay S. M. , Chen C. S.
Published: July 2002

We propose a technique to estimate the concentration of reactive oxidation sites on an otherwise nonreacting oxide surface; it involves evaporating submonolayer amounts of a nonreacting metal on the oxide and carefully analyzing the fraction that undergoes chemical bonding, using x-ray photoelectron spectroscopy. In this report, Ni has been evaporated on alumina, magnesia, and silica surfaces, and the growing Ni 2p photoelectron peak carefully monitored. It was observed that during the initial stages of bonding, a fraction of the first monolayer of Ni undergoes oxidation to form NiO. This oxidized component grows initially and then saturates to a certain level. This saturation level, expressed as a fraction (Θ) of the first monolayer, can be used as a measure of oxygen-active sites such as unattached oxygen bonds. We found that on epitaxially polished sapphire, Θ was as high as 20% of a monolayer. It was considerably reduced when the surface was sputtered with Ar+ ions in vacuum, a process which is known to create an oxygen-deficient Al2O3 surface. In MgO crystals (which do not tend to lose oxygen on ion sputtering), Θ remained practically unchanged. Such observations confirm the feasibility of using this technique as a probe for surface oxygen activity. It was found that increased level of dissolved magnesia in the sapphire lattice reduced the fraction of oxidized component. On the other hand, excessive doping with MgO (which leads to second phase spinel precipitates) seems to increase it considerably. The former observation is attributed to defect chemistry of the corrundum lattice and the latter has been discussed in light of earlier mass transport measurements. Silica surfaces were found to offer negligible oxidation sites, irrespective of sample history. Using this technique, one can systematically study how the concentration of reactive sites (which determines the amount of interfacial bonding) will be influenced by surface modifications.
Study of the performance of a group of quadrupole mass spectrometers
Authors: Austin W. E. , Leck J. H. , Batey J. H.
Published: July 2002

Results are presented from a series of experiments that were designed to characterise quadrupole analyzers. Three different analyzers have been studied. The first, typical of the small quadrupoles often used for residual gas analysis, has rods 50 mm long and 6.25 mm in diameter. The second uses rods of similar diameter, but 125 mm long. The third uses rods of diameter 12 mm and length 230 mm. Simple ion sources were used. All had cylindrical ionization regions with external filaments, in a configuration similar to an extractor ion gauge. All were operated under similar conditions. The sensitivity and linearity of the instrument is found to depend in a complex way on the operating conditions of the ion source. The observed behavior is explained qualitatively by the presence of both electronic and ionic space charge in the ion source.
Cluster formation in the vapor produced by laser pulsing of the Y1Ba2Cu3O7 superconducting solid
Authors: Moalem M. , Olander D. R. , Balooch M. , Fluss M. J.
Published: July 2002

Formation of neutral clusters in the vapor plume generated by laser-pulse heating of YBa2Cu3O7−x in vacuum was investigated. A Nd-glass laser of 1060 nm wavelength and 1.75 ms pulse width was used to generate peak power densities in the range of 104–105 W/cm2 over an area of 3–28 mm2. Time-of-flight mass spectrometry was used to identify neutral species contained in the plume and quadrupole mass spectrometry provided the time variation of the signal of several low-mass species. In both cases a transient optical pyrometer was used to monitor the surface temperature of the target during the laser pulse. At power densities generating peak surface temperatures less than 2300 K, the vapor consisted primarily of monomer species O, O2, Cu, Ba, BaO, and the dimer (BaO)2. At higher-power densities the major part of the vapor was made up of clusters of mass up to and beyond 3500 amu. These observations were complemented by microscopic examination of deposited plumes. Thin films of the target material were deposited on silicon and graphite substrates and examined by atomic force microscopy and scanning tunneling microscopy. Clusters 3 nm in diameter were observed in submonolayer films. Films of ≳∼100 nm were made up of stacks of such clusters. Very few liquid droplets from direct ejection from the target surface were observed. In-flight illumination of the plume by light from the laser did not significantly affect the mass distribution in the plumes; however, cluster formation at high-laser-power density (∼1012 W/cm2) was much lower than at 105 W/cm2.
X-ray photoemission spectroscopy studies of cesium and oxygen on GaAs(100)
Authors: Balasubramanian T. , Cao Jianming , Gao Y.
Published: July 2002

We have studied the interface formation of Cs on an As rich GaAs(100) surface and the subsequent oxidation of the cesiated surface using x-ray photoemission spectroscopy at room temperature. Several aspects of this interface are in sharp contrast to the nonreacting Cs/GaAs(110) interface. We found that Cs disrupted the GaAs(100) surface and caused As to segregate. Unlike the one monolayer (ML) saturation coverage for Cs/GaAs(110) at room temperature, no saturation coverage for Cs/GaAs(100) could be found. Further exposure to oxygen seemed to resurface the Cs atoms originally buried under the segregated As. The work function reduction was found to be 3.1 eV at Cs coverage of 3.0 ML, and the work function increased by 0.45 eV after 100 L oxygen, unlike the work function decrease found on cesiated GaAs(110). A feature of the conduction band electronic states of GaAs, which is below the vacuum level for a clean surface, was observed to appear in the secondary electron spectrum during the process of cesiation.
Heat transport in cold-wall single-wafer low pressure chemical-vapor-deposition reactors
Authors: Hasper A. , Schmitz J. E. J. , Holleman J. , Verwey J. F.
Published: July 2002

A model is formulated to understand and predict wafer temperatures in a tungsten low pressure chemical-vapor-deposition (LPCVD) single-wafer cold-wall reactor equipped with hot plate heating. The temperature control is usually carried out on the hot plate temperature. Large differences can occur between the susceptor and the wafer temperature, especially at the typically low pressures for LPCVD systems. Verification of the model was done by measurements of the true wafer temperatures as a function of total pressure, gas composition, gas flow, and coatings of wafer and susceptor. A good agreement between model and measurements was found by considering the heat transport by radiation and gas conduction.
Etching of silicon in low-pressure plasmas containing fluorine and oxygen: A comparison of real-time and postplasma surface studies
Authors: Oehrlein Gottlieb S. , Kroesen Gerrit M. W. , Lindström J. Lennart
Published: July 2002

The issue, to what extent the state of a surface after an etching plasma has been extinguished represents the state of the surface under actual plasma conditions, has been addressed for reactive ion etching (RIE) of silicon in CF4/O2 using ellipsometry during and after RIE, and x-ray photoemission spectroscopy (XPS) after transferring the sample in vacuum. In XPS, a≂1–2-nm-thick reaction layer consisting of silicon bound to fluorine and oxygen is observed. An increase in the oxygen content of the feed gas mixture produces a thicker SiFxOy layer which contains more oxygen. Qualitatively similar reaction layer trends as a function of the process parameters were seen in the ellipsometry raw data taken during the plasma process. Upon extinguishing the plasma, the ellipsometric variables changed in a systematic fashion, which is shown to be primarily due to substrate cooling effects. In addition, a rapid change of the optical parameters of the substrate upon termination of the discharge is observed which cannot be explained by sample cooling. This change of the ellipsometric variables appears to be due to the adsorption of ≂1 monolayer of material upon extinguishing the plasma. The reaction layer thicknesses determined by ellipsometry before and after extinction of the plasma agree with each other and the XPS thickness estimates reasonably well (to within a few percent for the 25% O2 to 50% O2 range, where a simple model of a transparent overlayer can be used to describe the data), if substrate cooling is taken into account. This result validates postplasma surface reaction layer studies.
Characterization of Cu–In–Se–Te system in thin films grown by thermal evaporation
Authors: Díaz R. , León M. , Rueda F.
Published: July 2002

The growth conditions of thin films of Cu–In–Se–Te system fabricated by thermal evaporation and their composition, structural, optical, and electrical properties have been studied. When analyzing the optical absorption coefficient of the films, several energy gap discrete values appear: 0.86±0.04, 0.95±0.05, 1.26±0.06, 1.51±0.02, and 1.71±0.03 eV. Resistivities and mobilities varying in the ranges of 10−3 to 8 Ω cm and 0.2 to 28.6 cm2 V−1 s−1, respectively were found depending on growing conditions. The ‘‘as grown’’ samples were p type. The thermal treatments may change the type of conduction from p to n.
Growth of Al films by gas-temperature-controlled chemical vapor deposition
Authors: Kobayashi Tsukasa , Sekiguchi Atsushi , Akiyama Naoto , Hosokawa Naokichi , Asamaki Tatsuo
Published: July 2002

Epitaxial single-crystal aluminum (Al) films were deposited on 4-in.-diam silicon (Si) substrates by gas-temperature-controlled chemical vapor deposition using tri-isobutyl aluminum (TIBA). The TIBA was preheated just prior to the deposition by a gas-temperature controller (GTC). The crystallographic orientation of Al films was determined by the gas flow rate and the degree of thermal decomposition of TIBA. The GTC was thought to work in such a manner as to efficiently generate a desirable intermediate of unknown composition. Four kinds of Al single-crystalline epitaxial films on Si substrates were obtained: Al(001)/Si(001), Al(001)/Si(111), Al(111)/Si(111), and Al(110)/Si(115). The common epitaxial relationship in these films was Al[11̄0]∥Si[11̄0] in the interfacial plane. Along this direction, four lattice spacings of Al matched three lattice spacings of Si at the interface.
Characterization of a novel microwave stripper
Authors: Pasierb F. , Ghanbari A. , Ameen M. S. , Heinrich R. S.
Published: July 2002

A microwave downstream reactor has been designed and constructed for use as a photoresist stripper. The reactor incorporates a cylindrical resonant cavity with a 19 mm wide quartz tube along its axis. The geometry of the cavity is designed to excite the TE112 cavity mode. An oxygen plasma is generated in the quartz tube and the afterglow of the plasma is used to strip the wafer. We have measured removal rates up to 3.5 μm/min on a 150 mm wafer. The removal rates were measured as a function of flow in the range of 0.5–5 slm, wafer temperature in the range of 75–345 °C, and power in the range of 350–700 W. Analysis of the data resulted in an activation energy of 7 kcal/mol.
Electron cycloton resonance etching of aluminum alloys with BCl3–Cl2–N2
Authors: Marx William F. , Ma Diana X. , Chen Ching-Hwa
Published: July 2002

Etching of submicron aluminum features is required in the manufacture of advanced integrated circuits. In this study the etching of aluminum-1% silicon-0.5% copper alloys with BCl3–Cl2–N2 chemistry has been characterized using a remote electron cyclotron resonance (ECR) plasma source. Mirror magnetic fields were used to modify the extracted plasma. The dependence of etch rate, uniformity, and selectivity has been measured as a function of gas flow rates, pressure, distance from the plasma source to the wafer, microwave power, and radio-frequency (rf) power applied to the wafer holder. Pressures in the range of 0.75 to 6.4 mTorr, microwave powers in the range of 600 to 1200 W, and rf powers in the range of 125 to 375 W were used. Optimal processes demonstrate etch rates above 1.0 μ/min, uniformities less than ±4%, and selectivity to photoresist of 2.0 to 3.8. Etched feature profiles are vertical for submicron lines and spaces.
Geometric and electronic structure of epitaxial iron silicides
Authors: Alvarez J. , Vázquez de Parga A. L. , Hinarejos J. J. , de la Figuera J. , Michel E. G. , Ocal C. , Miranda R.
Published: July 2002

The geometric and electronic structure of several iron silicide phases epitaxially grown on Si(111)7×7 have been characterized by means of surface sensitive techniques including scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy, ion scattering spectroscopy (ISS), and ultraviolet photoelectron spectroscopy. The silicides were grown by solid-phase and reactive-deposition epitaxy, and their stability range was determined in situ as a function of iron coverage and annealing temperature. In particular, we have studied the phases appearing in the low-coverage low-temperature region. Additionally, the crystallites of the most important FeSi2 phases (γ-FeSi2 and β-FeSi2) have been characterized at atomic level with STM, while the surface termination was analyzed with ISS.
In situ, real-time diffuse optical reflectivity measurements during GaAs cleaning and subsequent ZnSe/GaAs heteroepitaxy
Authors: Rouleau C. M. , Park R. M.
Published: July 2002

Real-time diffuse optical reflectivity measurements were performed during conventional in situ thermal cleaning and while employing a combined thermal/H-atom treatment of GaAs substrates, the H-atom flux being derived from a rf plasma discharge, hydrogen free-radical source. The diffuse optical reflectivity technique was subsequently employed to monitor heterointerface roughening during molecular-beam epitaxial growth of ZnSe on GaAs substrates which were cleaned in situ using the combined thermal/H-atom treatment. Atomically clean GaAs surfaces were found to be specular when prepared in situ using the combined thermal/H-atom treatment in contrast to conventional thermally treated GaAs surfaces which are considerably rough on the atomic level, surface roughening in this case being associated with the oxide desorption process. A further benefit associated with the specular nature of the thermal/H-atom treated GaAs surfaces is that heterointerface roughening occurring as a consequence of plastic deformation could be detected upon attainment of the critical thickness in the case of the ZnSe/GaAs heteroepitaxial system by monitoring diffuse optical scattering as a function of deposition time. In addition to providing critical thickness data, this real-time monitoring technique also revealed that the degree of heterointerface roughening mirrors the strain relaxation process as a function of increasing film thickness, being complete at a ZnSe film thickness around 0.5 μm.
Photoellipsometry determination of surface Fermi level in GaAs (100)
Authors: Xiong Yi-Ming , Snyder Paul G. , Woollam John A.
Published: July 2002

Photoellipsometry, a new contactless optical method, is presented. Related to photoreflectance, this method utilizes spectroscopic ellipsometry with the addition of a laser pump beam directed at nearly normal incidence onto the sample surface, where photoexcited electron-hole pairs modify the built-in electric field as a result of the photovoltaic effect. The field-induced changes in the real and imaginary parts of the complex pseudodielectric function can be directly measured, and analyzed in terms of the pump beam power density or the probe beam photon energy to determine parameters, such as surface Fermi level, built-in field strength, depletion depth, broadening, critical point energies, etc., of a semiconductor under study. Demonstration of this method was made with two n-type GaAs (100) substrates, where the measurements were taken in room air near the band-gap E0 region, for determination of surface Fermi level.
X-ray photoelectron spectroscopy study of low energy CF+ ion interactions with silicon
Authors: Chang W. H. , Bello I. , Lau W. M.
Published: July 2002

Surface modifications of silicon by exposure to a mass-separated, reactive ion beam of CF+ were studied by x-ray photoelectron spectroscopy. The effects of ion kinetic energy were characterized in terms of the various surface chemical states induced by the bombardment. The results showed that with an ion kinetic energy of 2 eV, which was much lower than the C–F bond energy of about 5 eV, molecular adsorption took place. At a bombardment energy of 10 eV, dissociative chemisorption was observed but the reaction was confined to the top surface with disproportionation of CF as the main route and little fluorination of silicon. With an ion energy of 100 eV, the atomic fragments generated by the CF dissociation possessed enough energy to penetrate below the silicon surface. It was found that silicon carbide and fluorosilyl species comprised the modified surface region and that fluorine atoms were situated closer to the surface than the carbon atoms of the carbide. Fluorocarbon species were minor surface reaction products. This work shows that distinct surface reactions may be chemically switched between the CF+ ion and the silicon surface as a function of the ion kinetic energy.
Structure and tribology of hard carbon films synthesized by ion beam deposition
Authors: He Xiaoming , Li Wenzhi , Li Hengde
Published: July 2002

Hard carbon films were formed on Si(111) wafer and AISI 52100 steel by CHn+ ion beam deposition with energies varied from 200 eV to 15 keV. The effects of bombarding energy of CHn+ on the bonding structure and hardness of carbon films were investigated. The films were revealed to consist of amorphous carbon with the structure of mixed sp3+sp2 bonding. However, it was showed that carbon films prepared under bombarding energy of 200–550 eV were much similar to diamond in the valence band structure and had more sp3 bonds. The friction and wear properties of films deposited on AISI 52100 steel were also detected and the experimental results indicated that as wear load was less or equal to 15 N, the normal wear process can steadily last with a friction coefficient of 0.1–0.15. In addition, hard carbon films were suggested to possess the self-lubricating function and good impact-resistance to enhance their antiwearing ability.
Comparison of mechanical and microstructural properties of hydrogen and silane reduced low pressure chemical vapor deposited tungsten films
Authors: Sivaram S. , Dass M. L. A. , Wei C. S. , Tracy B. , Shukla R.
Published: July 2002

We have compared the physical, mechanical, microstructural, and structural properties of tungsten thin films produced by reducing tungsten hexaflouride by silane and hydrogen. We show that despite similarities in chemical composition and film density, the films exhibit differing film hardness and elastic compliances. The origin of the differences is shown to arise from the differences in film growth rate and the incorporation of impurities during film growth. Hydrogen reduction results in the formation of second phase W20O58 particles in the tungsten bulk, which leads to film hardening. Silane reduced films show strong texture in the [110] direction, which decays with increasing film thickness. Silane films also show a larger tensile stress and faulted microstructure. Extensive transmission electron microscopy analysis has been carried out and the results have been correlated to x-ray diffraction studies. We also have studied the surface morphology of the films and show clustering of grains which results in a larger surface feature, compared to the average grain size of the film. As a result of this study, we show the need to complete film characterization prior to changing chemistries to meet specific macroscopic film properties such as film step coverage.
Direct numerical method to analyze thermal desorption spectra
Authors: Froitzheim H. , Schenk P. , Wedler G.
Published: July 2002

Using a general formulation, which describes the development of pressure during a thermal desorption experiment, a numerical approach has been derived to allow for an exact determination of the desorption rate, the effective binding energies and the preexponential factors from measured spectra independently of the heating rate. With the resulting parameters as input into assumed model rate equations the simultaneous integration of the pressure equation and these rate equations yield a theoretical temperature programmed desorption spectrum, which can be compared with the experiment.
In situ infrared measurements of film and gas properties during the plasma deposition of amorphous hydrogenated silicon
Authors: Morrison Philip W. , Haigis John R.
Published: July 2002

This research has performed preliminary in situ Fourier transform infrared (FTIR) measurements during the plasma deposition of amorphous silicon (a-Si:H). Experiments demonstrate both gas phase and film measurements within a simple SiH4 plasma reactor using a specially modified FTIR spectrometer. Films are deposited on substrates of either gold (mirror finish) or stainless steel (matte finish). In particular, in situ emission/reflection FTIR of the film yields information about surface temperature, film thickness, and film composition. We have measured surface temperature to ±5 K and detected the onset of poor film growth at a thickness of 500–1000 Å using the 2080 cm−1 absorption feature. A simple model for the reflectance of a film on a metal is employed to determine the thickness of the films. In situ emission/transmission FTIR of the plasma determines the gas composition and average gas temperature. Measurements show that the silane conversion is ∼11% within the plasma region for a typical deposition at 250 °C and roughly doubles for a deposition at room temperature. The FTIR spectra show that most of this converted silane reappears as disilane (Si2H6). Before starting the plasma, the silane gas is ∼30 K cooler than the nominal substrate temperature of 250 °C; starting the plasma raises the average temperature another 20 °C.
Steady-state hydrogen transport in a metal membrane exposed to hydrogen gas and/or a hydrogen ion beam: Reexamination of transport regime and synergistic effects
Authors: Nagasaki Takanori , Ohno Hideo
Published: July 2002

We reexamined the formalism to describe the steady-state hydrogen transport in a metal membrane exposed to hydrogen gas or a hydrogen ion beam. On the basis of the formalism, we derived the relation between the material/injection parameters and the transport regimes, which were characterized by specific profiles of the hydrogen concentration in the membrane or specific rate-limiting processes. The obtained relation was inconsistent with the previous one of Doyle and Brice (DB). Our derivation is directly based on the concentration profiles, and should therefore be correct as far as the concentration profile is concerned. We then extended the formalism to the ion-driven transport in the presence of the simultaneous gas-driven transport. Our formalism is different from DB’s in that the former treats the increment in the concentration and the flux density due to the ion injection whereas the latter treats the total concentration and flux density. As far as the total quantities are concerned, DB’s formalism will be preferable. However, our formalism may be more illuminating when the transport of the ion-originating hydrogen is important.
Preparation of Sb/GaSb{111}-oriented multilayer structures using molecular-beam epitaxy and migration enhanced epitaxy
Authors: Wang W. C. , Dura J. A. , Zborowski J. T. , Vigliante A. , Chen H. C. , Golding T. D. , Meyer J. R.
Published: July 2002

We have performed an investigation into the synthesis of Sb/GaSb heterojunctions and multilayers using the technique of molecular-beam epitaxy. The GaSb/Sb system has a number of unique features relevant to synthesis of an epitaxial semimetal/semiconductor system. On the (111) plane of the rhombohedral crystal structure of Sb, both the hexagonal symmetry and in plane lattice parameter allow near perfect registry to the Sb atoms on the (111) plane of the zinc blende structure of GaSb. This study shows that Sb can be grown epitaxially on GaSb{111} oriented epilayers and that GaSb can be subsequently grown on the Sb epilayers at temperatures ≤300 °C by migration enhanced epitaxy. Growth and resultant film properties have been characterized by reflection high-energy electron diffraction, x-ray diffraction, x-ray photoelectron spectroscopy, and Hall.
Study of the time dependence of differentially sputtered currents from multiphase powder targets
Authors: Cohen Y. , Riess I.
Published: July 2002

The time dependence of differentially sputtered currents from a multiphase powder target is studied both theoretically and experimentally. A model for the powder particle distribution is presented which allows an analytic solution for a mixture containing two or more phases. The calculated time dependence of the currents is exponential. This is in agreement with experimental data obtained using sputtering from a three phase target.
Planar magnetron glow discharge on copper: Empirical and semiempirical relations
Authors: Escrivão M. L. , Moutinho A. M. C. , Maneira M. J. P.
Published: July 2002

Empirical and semiempirical relations linking parameters in magnetron-assisted abnormal glow discharges can provide insight into the physical phenomena occurring and lead to better control of processes utilizing such discharges. The deposition rate dependence upon pressure (at constant power) for planar magnetron sputtering of copper in argon has been studied. The results fit the empirical equation, R=KRe−βp, where R is the deposition rate (nm/s), and p is the pressure (Pa). KR increases linearly with the input power (KR=a+bw); the constants a and b were found to be 0.5 nm/s and 6.9×10−3 nm/(s W), respectively. The parameter β decreases with power. From this empirical equation and some physical considerations, near-cathode gas temperature and mean-free path of sputtered atoms for a given pressure, as a function of power, were obtained.
Comparison of argon electron-cyclotron-resonance plasmas in three magnetic field configurations. II. Energy distribution of argon ions
Authors: Junck Kevin L. , Getty Ward D.
Published: July 2002

A gridded energy analyzer (GEA) has been implemented on a 2.45 GHz magnetic-mirror electron-cyclotron-resonance plasma tool to characterize the energy distribution function of Ar ions downstream from the cyclotron-resonance region. The microwave power is applied through an alumina window located near one mirror peak, and the GEA is located 14 cm beyond the second mirror peak at the substrate location. The mirror peak-to-peak separation is 50 cm. The dependence of the ion distribution function and current density upon pressure, microwave power, and magnetic field configuration were determined. Three magnetic field configurations were studied: symmetric mirror with a mirror ratio of 2; asymmetric mirror (i.e., divergent field), and minimum-B mirror. The operating pressure was found to have a small effect on the average ion energy until the pressure dropped below 0.05 mTorr. For pressures from 0.05 to 1.0 mTorr the energy distribution function usually exhibited a large low-energy peak with a high-energy tail or peak. The upper edge of this high-energy ion group corresponded to the midplane plasma potential measured by a Langmuir probe and ranged from 15 to 25 eV. As pressure increased, the position of the low-energy peak dropped from 10 to 5 eV. At the GEA position downstream from the mirror midplane, the maximum current density was found to be 4.5 mA/cm2 for a symmetric mirror magnetic field profile. For an asymmetric mirror configuration the current density was found to be only 1 mA/cm2, increasing to 3.5 mA/cm2 as the downstream mirror coil current was increased. The minimum-B field gave a current density similar to that of the asymmetric case.
Plasma-enhanced chemical vapor deposition of a-SiC:H films from organosilicon precursors
Authors: Loboda M. J. , Seifferly J. A. , Dall F. C.
Published: July 2002

A study of the growth of a-SiC:H films by plasma-enhanced chemical vapor deposition (PECVD) from two organosilicon precursors, silacyclobutane (H2CH2SiCH2CH2 or SCB) and methylsilane (CH3SiH3), is described. A capacitively coupled, parallel plate PECVD system was used to grow films at 250 °C and deposition pressure of 2.0 Torr. Standard (13.56 MHz) and low frequency (0.125 MHz) rf sources were used to generate the deposition plasma. Depositions were performed with and without argon dilution (neat) of the precursor. We report some of the first process/property relationships for organosilicon based a-SiC:H films grown using a fixed, controlled set of deposition conditions. Included are data on film composition, structure, dielectric constant and stress. Films deposited from silacyclobutane had much higher carbon concentrations than those deposited from methylsilane, but in both cases the carbon fraction in the film was lower than that in the precursor. It is found that the plasma drive frequency has a stronger influence on film composition than argon dilution of the precursor during deposition. The low frequency plasma significantly increases the film growth rate for the neat precursor process. Depending on the growth process, the relative dielectric constants of the a-SiC:H films ranged from 3.6 to 8.7. The variation of the dielectric constant over the frequency range 0.1–1000 kHz was negligible. All measured film stress was compressive and ranged from 0.1 to 1.0 GPa depending on precursor and plasma frequency. Films deposited from a 10% organosilicon/90% argon mixture showed higher dielectric constants, higher refractive indices and less bound hydrogen when compared to neat organosilicon precursor depositions. The films exhibited excellent oxidation resistance and could not be etched in 6:1 buffered HF solutions. The properties of the a-SiC:H films are compared to PECVD hydrogenated silicon nitride and discussed in the context of applications requiring low temperature deposited protective dielectric coatings.
Nonlinearities in sensitivity of quadrupole partial pressure analyzers operating at higher gas pressures
Authors: Cowen M. C. , Allison W. , Batey J. H.
Published: July 2002

We show, by direct numerical simulation, how space charge effects in an ion source give rise to nonlinearities in quadrupole gas analyzers operating at high pressures. Numerical simulations were performed on a model for a generic electron impact ionizer and the calculations included the effects of both the electron and the ion space charge. By comparing the results of the simulations with previous experimental work we conclude that the most important effects arise in the ion source itself rather than at later stages in the mass analysis process. It was not necessary to invoke ion–molecule scattering mechanisms to reproduce the trends in the experimental data. The results show how competition between the negative and positive space charges can lead to either an increase or a decrease in relative sensitivity as the pressure of gas in the source is raised. Our conclusions are extended to a discussion of nonlinearities in other types of partial pressure analyzer and to extractor gauges measuring total pressure.
Protein interaction with surfaces: Separation distance-dependent interaction energies
Authors: Lee Samuel J. , Park Kinam
Published: July 2002

A computational method was used to calculate the distance-dependent adsorption energies of three proteins, immunoglobulin Fab, trypsin, and lysozyme, on polyethylene, polypropylene, and poly(vinyl alcohol) surfaces. Two different protein orientations for each protein were used to calculate the interaction energy as a function of the separation distance. The programs developed in our laboratory considered van der Waals, electrostatic, and solvation interaction energies. Our computer simulation study suggests that the protein adsorption energy on three polymer surfaces is determined mainly by the relative importance of the attractive van der Waals interaction. The minimum and maximum total adsorption energies calculated in our study were −15.65 kJ/mol for lysozyme on polypropylene and −181.66 kJ/mol for trypsin on polypropylene. The total energy was dependent on the orientation of a protein even on the same polymer surface as expected. The smallest difference between the adsorption energies of the two orientations was 2.03 kJ/mol for trypsin on poly(vinyl alcohol) and the largest difference was 137.93 kJ/mol for lysozyme on poly(vinyl alcohol). Electrostatic and solvation interaction energies showed both attractive and repulsive interaction energies depending on the protein orientation. The simulation study shows that the protein–surface interaction becomes negligible, when the distance between them exceeds 20–30 Å. The distance at which the total interaction energy becomes −2 kJ/mol varied between 9.37 and 24.70 Å for lysozyme on polyethylene and trypsin on poly(vinyl alcohol), respectively. Our results indicate that the grafting of short hydrophilic polymer chains may be enough to prevent protein adsorption.
Fourier-transform infrared absorption spectrometry measurements of a CF4 discharge in an electron cyclotron resonance reactor
Authors: Goeckner M. J. , Henderson M. A. , Meyer J. A. , Breun R. A.
Published: July 2002

Knowledge of the neutral gas composition in a discharge is important for understanding the chemical processes involved in both etching and deposition environments. We have performed Fourier-transform infrared absorption spectrometry measurements of a CF4 plasma in an electron cyclotron etching tool. Spectral bands from both CF4 and CF3 were observed. The densities of these species were calculated from the strength of the measured absorption. It was found for typical discharge powers that the CF4 density was approximately 20% of the total density and depended only on the plasma density. This data is used to show that recycling of the daughter species (C, CFx, Fx, etc.) on the chamber walls is the major source of the CF4 observed. Thus one finds that wall conditions play a very important role in determining the plasma chemistry in this high density, ≳1011 cm−3, and low neutral pressure, <10 mTorr, discharge. Additionally, it was found that the CF3 density was approximately 20% of the total density and depended on the product of the plasma density and the CF4 density. This implies that the CF3 is produced primarily through an e−+CF4→e−+CF3+F type of reaction. Finally, it was found that the upper limit of CF2 density was 1.6×1013 cm−3 over the entire parameter range explored.
Studies on thermionic cathode anodic vacuum arcs
Authors: Musa G. , Ehrich H. , Mausbach M.
Published: July 2002

Vacuum arc discharges with evaporating anodes employing directly as well as indirectly heated thermionic cathodes are investigated. The observed volt-ampere characteristics of these discharges depend strongly on the temperature of the thermionic cathode, the evaporated anode material, and the relative position of the electrodes. A simple model describing the observed discharge characteristics is proposed. With respect to a possible coating application, the plasma of this arc discharge is investigated at a distance of 250 mm from the evaporating anode. For arc currents between 2 and 4 A and Cu as evaporating anode material, the deposition rate is between 3.5 and 5.1 nm/s, the degree of ionization ranges from 0.6% to 6.2%, and electron temperatures are between 5.8 and 15 eV. The observed directed energy of the ions exceeds 100 eV. An examination of the deposited Cu films reveals as main results: Purity≳99.5%, compact structure, and smoothening of the film surfaces with increasing degree of ionization.
Intramolecular structures of C60 adsorbed on the Cu(111)1×1 surface studied by the field ion-scanning tunneling microscopy
Authors: Hashizume T. , Motai K. , Wang X. D. , Shinohara H. , Pickering H. W. , Sakurai T.
Published: July 2002

The adsorption of C60 molecules on the Cu(111)1×1 surface has been investigated by field ion- scanning tunneling microscopy (FI-STM). At the initial stage adsorption, C60 molecules are mobile on the terrace at room temperature and segregate to the steps to form linear chains. With increasing coverage, two-dimensional islands form with a close-packed configuration. Upon monolayer adsorption, a highly ordered Cu(111)-(4×4)-C60 overlayer forms. Bias voltage-dependent scanning tunneling microscope images of the individual C60 molecules show unique intramolecular structures. The adsorption geometry of C60 is determined by analyzing the scanning tunneling microscope images and the intramolecular structures are interpreted as the local density of the states of C60 interacting with the substrate.
Properties of titanium layers deposited by collimation sputtering
Authors: Hara Tohru , Nomura Tomo , Mosley R. C. , Suzuki Hajime , Sone Kazuho
Published: July 2002

Thin Ti films are deposited by collimation sputtering. Resistivity is around 80 μΩ cm in the as-deposited collimation film. This value does not decrease with the increase of sputtering power and of deposition rate, and is higher than that of 60–65 μΩ cm in film by conventional sputtering. Strongly (002) oriented Ti film is deposited in conventional sputtering. However, weak (002) and (101) peaks appear in films by collimation sputtering. X-ray intensity ratio, I(002)/[I(002)+I(101)], indicating the grain growth of preferential Ti(002), does not increase to 0.93 attained in the conventional sputtering with increasing power.
Chemical evaluation of Cu–polyimide interfaces
Authors: Davis G. D. , Rees B. J. , Whisnant P. L.
Published: July 2002

The interactions of copper overlayers with four different polyimides [pyromellitic dianhydride–oxydianiline (PMDA–ODA), benzophenonetetracarboxylic dianhydride–diaminobenzophenone (BTDA–DABP); oxydiphthalic anhydride–oxydianiline (ODPA–ODA); and pyromellitic dianhydride–phenylene diamine (PMDA–PDA)] have been studied by x-ray photoelectron spectroscopy. Emergent etherlike functionalities on polyimides without innate ether groups suggest a copper-induced partial reduction of carbonyl groups. A surface behavior diagram of the carbon chemistry confirms this reaction by indicating a partial conversion of carbonyl moieties to etherlike moieties.
Thermal outgassing behavior and photoemission studies of Haynes Alloy 214
Authors: Sharma Pramod K. , Hickey Gregory S.
Published: July 2002

Processing of many materials at high temperatures requires a high purity environment. The outgassing from hot surfaces of the processing chamber or the heating elements is a potential problem. The total amount of outgassing as well as the time- and temperature- dependent outgassing rates are important. The outgassing from Haynes Alloy 214 has been studied experimentally under a vacuum in the temperature range from room temperature to 600 °C. In addition to the outgassing rates, the composition of the outgassed species was determined through mass spectrometric analysis. Alloy surface composition was determined by x-ray photoelectron spectroscopy. Changes in surface composition before and after heating can be accounted for by the outgassed species.