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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 1 • Date Jan 1989

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Displaying Results 1 - 25 of 25
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Photoyield spectromicroscopy of silicon surfaces using monochromatic synchrotron radiation

    Page(s): 1 - 4
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    A photoemission electron microscope has been used to generate spatial maps of silicon surfaces, along with chemical spectroscopy of the silicon core levels at micron‐scale spatial resolution. The electron optics permits scanned photon energy imaging of the sample surface, with image capture at video rates in a 512×512 pixel buffer memory. The image is generated primarily by low‐energy secondary electrons produced by photoabsorption. Near‐edge structure in the image photoyield as a function of photon energy is used to determine the oxidation state of microscopic regions of the surface of a single‐crystal Si(111) sample. These measurements show that spectroscopic imaging with 100‐nm resolution will be possible using undulator generated synchrotron radiation. View full abstract»

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  • Diffusion of Si into Ge studied by core level photoemission

    Page(s): 5 - 8
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    Ge(3d) and Si(2p) core level photoemission intensities were measured to monitor the coverage of Ge(001) and Ge(111) surfaces during the interrupted deposition of a thin Si film at room temperature and upon annealing. Annealing treatments were performed at temperatures up to a maximum of 880 K and interrupted a few times to allow for core level measurements. The Ge(3d) core level intensity was found to almost recover to its initial value upon annealing while the Si(2p) intensity decreased ∼60%. Intensity changes were observed at temperatures from 680 K upwards. It is concluded that above 680 K a significant diffusion of Si into Ge occurs, although at higher temperatures island formation or surface roughening also takes place. View full abstract»

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  • Quantitative Auger electron spectroscopy of TiSiy: Peak height, line‐shape, and sputtering yield analyses

    Page(s): 9 - 16
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    The Auger electron spectroscopy (AES) peak heights, sputtering yields, and line shapes of well‐characterized TiSiy films were examined. Analysis of AES peak‐to‐peak heights showed that the total correction factor (KT) used for quantification varied linearly by a factor of 10 as the mole fraction of Si (XSi) changes from 0 to 1. The KT variation was attributed primarily to preferential sputtering although line‐shape variations also had some effect. The line shapes of the derivative SiLVV and TiLVV spectra were examined as a function of XSi. The TiLVV line shape did not change significantly with composition. However, the characteristic features (peak height, peak width, skewdness, etc.) of the SiLVV line shape were shown to vary linearly with silicide composition. The average sputtering rates and yields of the titanium silicides were shown to vary by a factor of 2 as XSi varies from 0 to 1. The average sputtering yields of the silicides varied linearly with composition while the sputtering rates did not. The use of peak height, line‐shape, and sputtering yield calibration lines for quantitative concentration and depth determinations is discussed. View full abstract»

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  • High‐sensitivity plasma‐based sputtered neutral mass spectrometry depth profiling of zinc‐implanted GaAs

    Page(s): 17 - 20
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    A commercial sputtered neutral mass spectrometer, using a rf‐generated plasma for both sputtering and postionization of sputtered particles, has been modified to improve sensitivity for trace analysis. The modified instrument has been used to depth profile zinc‐implanted gallium arsenide. A detection limit of 20 ppma was attained for zinc under conditions of maximum depth resolution from an analyzed sample area of 0.2 cm2 with a useful yield of 5 to 7×10-10 . The results have been compared with those of secondary ion mass spectrometry. Sputtered neutral mass spectrometry (SNMS) depth profiles revealed zinc redistribution in one heavily implanted sample, leading to the discovery of unusual structural damage through transmission electron microscopy. This investigation is discussed as an example of the usefulness of the SNMS technique in practical applications. View full abstract»

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  • An in situ spectroscopic erosion yield measurement with applications to sputtering and surface morphology alterations

    Page(s): 21 - 26
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    An in situ spectroscopic erosion yield measurement is developed and used to monitor material surface erosion during bombardment by a plasma. The experiments are performed in a plasma that has the characteristics of a fusion tokamak boundary plasma but the technique is applicable to many processes where plasma erosion is important. Erosion yield of materials bombarded in a high flux (up to 1018 ion/cm2 s) plasma environment has been previously studied using weight loss measurements. In the present study, the sputtered flux from a material is monitored by the line emission intensities of atoms eroded from the surface. The line intensities can be used to infer erosion yields after proper calibration. The method agrees well with results from weight loss measurements. Earlier work established that the material surface structure can substantially influence the erosion yield. When a change of surface morphology (e.g., cone formation) occurs, weight loss methods cannot be used to determine the erosion yield. However, the in situ erosion measurement is suitable and is used to investigate the relation between the onset of morphology changes and alternations in erosion yield during plasma bombardment. Experiments are reported for copper, as an example of a pure material, and stainless steel, as an example of an alloy system. The formation of surface cones is observed only when both the sample temperature is above a critical value and surface impurities exist. If the source of impurities is removed, or the sample temperature is lowered below the critical value, a surface rough with cones will be returned to a smooth state. View full abstract»

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  • Evaporating and sputtering: Substrate heating dependence on deposition rate

    Page(s): 27 - 30
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    The deposition of copper into the through holes and vias of printed wiring boards (PWB’s) has been done using vacuum processing techniques such as evaporation and sputtering. One of the most important limiting factors for any deposition process is the substrate heating. The temperature of epoxy‐glass PWB’s should not exceed 180 °C (350 °F). For evaporation, there are two major contributions, the heat of condensation and radiant heating, with the heat of condensation dominating at deposition rates ≫2 μm/min. The radiant heating is very dependent on α ϵ, the product of the substrate absorptivity and the source emissivity. Sputter deposition has two main sources of substrate heating: the heat of condensation and the kinetic energy of the incident atoms and ions. The experimental apparatus used to measure the power absorbed by a PWB substrate is described. Data are presented for the power absorbed by the substrate as a function of deposition rate for sputtered copper. These data are compared with the results obtained by other investigators for evaporated aluminum and sputtered aluminum and copper. The various contributions to substrate heating are theoretically determined for both evaporation and sputtering systems. The absorbed power per unit area is calculated as a function of deposition rate and agrees very well with experimental results. It is discovered that the heating rate of a substrate is very similar for evaporation or sputtering of copper for deposition rates ≲3 μm/min. Sputtering heats the substrate more than evaporation at higher deposition rates, primarily because of heating by energetic atoms and ions. View full abstract»

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  • The deposition rate and properties of the deposit in plasma enhanced chemical vapor deposition of TiN

    Page(s): 31 - 35
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    Titanium nitride (TiN) films were deposited onto tool steels and cemented carbide cutting tools by plasma enhanced chemical vapor deposition (PECVD) using a gaseous mixture of TiCl4, N2, H2, and Ar in order to find out the effects of the deposition temperature and rf power density on the deposition rate and properties of deposited TiN. The deposition rate and crystallinity of the deposited TiN was affected by the deposition temperature as well as the plasma power density. The deposition rate was decreased with an increase in deposition temperature between 270 and 430 °C. The crystallinity of deposited TiN was improved by an increase in deposition temperature as well as rf power density. Crystalline TiN was obtained above 300 °C and showed a strong crystallographic preferred orientation of 〈200〉. TiN layers deposited by PECVD using TiCl4 as a reactant contained chlorine, the content of which was increased with a decrease in deposition temperature. Oxygen at the interface between the TiN deposited layer and the substrate excluded nitrogen and chlorine. The surface morphology of the deposited TiN is a dome‐shaped cluster composed of many fine grains. View full abstract»

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  • Large grain size thin films of carbon with diamond structure

    Page(s): 36 - 39
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    Diamond thin films were formed by deflecting the flow of CH+4 using a magnetic field. The possibility of involvement of neutral particles and their effects on film formation were examined. The results show (i) the estimated amount of the neutral particle involved during the ionized deposition was nearly 30%, (ii) the surface morphology of the film prepared by the deposition of the deflecting ion was very smooth when it was examined by scanning electron microscopy, and (iii) transmission electron diffraction and transmission electron microscopy indicated relatively large grain polycrystalline diamond films. View full abstract»

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  • Ruthenium impregnation of plasma grown alumina films

    Page(s): 40 - 48
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    This investigation centers around the impregnation of plasma grown alumina films using the incipient wetness technique for introduction of ruthenium chloride to the surface. The modeling of bulk alumina catalysts by use of planar alumina films necessitates investigation of the impregnation of these films. It has been found that very different products are formed by slight changes in the process used for impregnation. The impregnation was found to yield a product ranging from a highly dispersed ruthenium species to the dispersion of relatively large metal islands on the surface of the alumina. Characterization by x‐ray photoelectron spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy indicates that the products containing highly dispersed metal are suitable for further investigation in the modeling of bulk ruthenium catalysts. View full abstract»

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  • Thermal oxidation of gallium arsenide

    Page(s): 49 - 54
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    Here we present some results of transmission electron microscopy and secondary ion mass spectroscopy of thermally oxidized gallium arsenide with different types of dopants. At temperatures below 400 °C an amorphous oxide is formed. Oxidation at temperatures between 500 and 600 °C initially produces an epitaxial film of γ‐Ga2O3. As the reaction proceeds, this film becomes polycrystalline and then transforms to β‐Ga2O3. This film contains small crystallites of As2O5 and As2O3 in the case of the chromium doped samples, whereas only the former was detected in the case of silicon and tellurium doped samples. Elemental arsenic was always found at the interface between the oxide and GaAs. Chromium doped gallium also exhibited a slower oxidation kinetics than the other materials. View full abstract»

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  • Interfacial reactions at copper surfaces coated with polyimide films prepared from poly(amide–acid) precursors

    Page(s): 55 - 58
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    Thin films of polyimide were prepared by spin coating the poly(amide–acid) precursor onto copper and aluminum substrates, followed by the usual heat treatment to promote imidization (curing) of the film. Films prepared on aluminum substrates were completely cured during the heat treatment, as shown by x‐ray photoelectron spectroscopy and infrared measurements. On copper substrates, the thinnest films (2000 Å or less) showed considerable intermixing of copper ions in the polymer layer. This prevented the films from curing completely during heat treatment. The formation of a copper carboxylate at the acid site in the polyimide precursor is postulated. View full abstract»

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  • Photodesorption from copper‐plated stainless steel at liquid‐helium temperature and at room temperature

    Page(s): 59 - 63
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    Photodesorption yields have been measured from copper‐plated stainless steel at liquid‐helium temperature and at room temperature using synchrotron radiation. The copper‐plated surface is a proposed inner surface for the liquid‐helium temperature beam pipe of the Superconducting Super Collider (SSC). The inner surface of the SSC beam pipe will be illuminated by synchrotron radiation from 20‐TeV protons. The number of H2 molecules desorbed per incident photon (ηH2) from the liquid‐helium temperature surface has been measured as ∼0.018 for an accumulated photon dose of 1016 photons/cm2 and as ∼0.004 for an accumulated dose of 1018 photons/cm2. The ratio of ηH2 for the liquid‐helium temperature surface to ηH2 for the room‐temperature surface is ∼1.1 for an accumulated dose of 1016 photons/cm2 and is ∼2.0 for an accumulated dose of 1018 photons/cm2. Estimates of η for H2O, CO, and CO2 are also given. View full abstract»

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  • Electrohydrodynamic ion emission from molten lithium nitrate

    Page(s): 64 - 68
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    Positive ions have been generated at the surface of molten lithium nitrate by applying a high electrostatic field to a thin layer of the molten salt on the apex of a field emitter tip. The ion emission process is characteristic of electrohydrodynamic ion formation, usually observed when a high electric field is applied to the surface of a liquid metal or alloy. With molten lithium nitrate, a single emission site appears at threshold. The divergence of the ion beam is several degrees. At higher field strengths multiple emission sites are observed. An ion species at m/e=76 amu dominates the mass spectrum at all field strengths. This species is identified as a cluster ion (LiNO3 )Li+ . At low source temperatures, (LiNO3 )2 Li+ is also observed. Despite the low ionization potential of lithium (5.4 eV), Li+ accounts for ≪8% of the total ion current generated by the source under all operating conditions. Multiply charged lithium is not detected in the mass spectra, suggesting the electric field at the Taylor cone apex is not sufficient to field‐ionize singly charged species by a postionization process. View full abstract»

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  • Kinetic and structural aspects of trapping and recycling of hydrogen on metallic surfaces exposed to low‐pressure hydrogen plasma

    Page(s): 69 - 76
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    Studies of hydrogen trapping and recycling were performed on cleaned and on contaminated metallic surfaces exposed to a hydrogen discharge with parameters typical of the scrape‐off layer in devices for controlled nuclear fusion research. Detailed analysis of the time‐ and temperature‐ dependent trapping and release of hydrogen upon start and termination of the discharge, respectively, allows one to draw conclusions regarding the nature of the trapping sites. These data were complemented by transmission electron microscopic investigation of the structural damage in the near‐surface region and by the measurement of the amount of hydrogen trapped in the damaged area. Formation of dislocation loops at small doses and their agglomeration into an extended dislocation network at a fluence of ≤1017 cm-2 were found. The data indicate that the defects are located within a depth significantly larger than the projected range of the impinging ions. The concentration of hydrogen within this area reaches up to several tens of at . %, and its stability with respect to thermal release suggests that hydrogen is strongly trapped at the defect sites. Only a small fraction (10%–30%) of the implanted hydrogen takes part in the recycling during a 10–30 s long discharge pulse at a wall temperature of ≤300 °C. Implications of these results for the current models of hydrogen recycling are discussed. View full abstract»

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  • Comparison of chemical cleaning methods of aluminum alloy vacuum chambers for electron storage rings

    Page(s): 77 - 82
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    Three chemical precleaning methods suitable for aluminum alloy vacuum chambers for electron storage rings have been compared. The methods ranged from vapor degreasing with no chemical attack to light alkaline etching and strong alkaline etching in NaOH. The techniques used to evaluate and compare the three treatments included Auger analysis, thermal outgassing, electron and x‐ray induced neutral gas desorption, argon glow discharge cleaning, and scanning electron microscope examination of the surface. In general, the NaOH treatment was best followed closely by the light alkaline etch and then the vapor degreasing. A variant of the light alkaline etch method was used to clean the 2000 Al vacuum chambers of the CERN large electron positron storage ring project. Two chambers cleaned by this method were exposed to synchrotron radiation in a dedicated beam line of a synchrotron radiation source. Compared to a reference chamber cleaned by NaOH these two chambers were initially worse, but after 1 A h of machine operation the difference practically vanished. View full abstract»

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  • Gas utilization in the Tokamak Fusion Test Reactor neutral beam injectors

    Page(s): 83 - 89
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    Measurements of gas utilization were performed using hydrogen and deuterium beams in the Tokamak Fusion Test Reactor (TFTR) neutral beam test beamline to study the feasibility of operating tritium beams with existing ion sources under conditions of minimal tritium consumption. (i) It was found that the fraction of gas molecules introduced into the TFTR long‐pulse ion sources that are converted to extracted ions (i.e., the ion source gas efficiency) was higher than with previous short‐pulse sources. Gas efficiencies were studied over the range 33%–55%, and its effect on neutralization of the extracted ions was studied. At the high end of the gas efficiency range, the neutral fraction of the beam fell below that predicted from room‐temperature molecular gas flow (similar to observations at the Joint European Torus). (ii) Beam isotope change studies were performed. No extracted hydrogen ions were observed in the first deuterium beam following a working gas change from H2 to D2. There was no arc conditioning or gas injection preceding the first beam extraction attempt. (iii) Experiments were also performed to determine the reliability of ion source operation during the long waiting periods between pulses that are anticipated during tritium operation. It was found that an ion source conditioned to 120 kV could produce a clean beam pulse after a waiting period of 14 h by preceding the beam extraction with several acceleration voltage/filament warm‐up pulses. It can be concluded that the operation of up to six ion sources on tritium gas should be compatible with on‐site inventory restrictions established for D–T, Q=1 experiments on TFTR. View full abstract»

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  • Prospects for a contamination‐free ultravacuum facility in low‐Earth orbit

    Page(s): 90 - 99
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    The old concept of using the wake of a spacecraft to obtain an ultrahigh vacuum is revisited. A wakeshield can be configured so that a surface of interest does not subtend any walls that could become contaminated, thus it should be possible to achieve a contamination‐free, ultrahigh vacuum capability with infinite pumping speed even in the presence of high heat loads and moderate gas loads. This paper analyzes the conceptual design for a Space Ultravacuum Research Facility (SURF), both in a shuttle‐attached mode and as a free flyer. It is shown that even in the shuttle‐attached mode, it should be possible to obtain vacuum levels equivalent to 10-9 to 10-10 Torr with O and N2 as the primary constituents. As a free flyer the SURF will be limited primarily by the gas load from the process being performed. For chemical beam epitaxy it is shown that equivalent vacuum levels of 10-14 Torr should be possible at 300 km. View full abstract»

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  • Wavelength‐dependent studies of optical second‐harmonic generation from Fe–18Cr–3Mo(110) in ultrahigh vacuum

    Page(s): 100 - 102
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    This paper describes second harmonic generation which is a promising surface diagnostic that will alloys surface studies under ambient pressure and studies of liquid-solid and solid-solid interfaces. The structure and composition of the interface can be determined by this method. This metho d is demonstrated for Fe-18Cr-3Mo (100) in ultrahigh vacuum. (AIP) View full abstract»

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  • Effect of noble gases on the properties of ion beam sputtered niobium films

    Page(s): 102 - 104
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    We present result to support our hypothesis that the reflection of the primary beam during ion-beam sputtering of niobium films plays a significant role in determining final film properties, especially in the case of ion-beam sputtering. The film properties are afected by both the noble gas incorporation in and noble-gas bombardment of the growing film. (AIP) View full abstract»

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  • Experimental and theoretical investigation of hydrogen diffusion on a metal surface

    Page(s): 104 - 107
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    We describe experimental and theoretical studies of hydrogen diffusion on metal surfaces. The experimental system is H/Pd(111) and we describe the utilization of low‐energy electron diffraction in combination with electron stimulation of the surface by the incident beam to investigate surface diffusion. Electron stimulated desorption, as well as disordering are discussed with regard to the interpretation of the experiments. To study surface diffusion theoretically, variational transition state theory is employed. The system studied by this technique is H/Ni(111) and comparison to experiment is given. View full abstract»

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  • Cryogenic sample manipulator for multipurpose sample analysis

    Page(s): 108 - 109
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    A cryogenic sample manipulator for ultrahigh vacuum studies of surfaces by Raman spectroscopy of physisorbed gasses is described. The development of a cryogenic off-axis sample manipulator that can be cooled to 15 K and allows the sample to be placed at any distance desired from the rotational axis is reported in this paper. (AIP) View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

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Editor
G. Lucovsky
North Carolina State University