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

Issue 2 • Date Mar 1994

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Displaying Results 1 - 25 of 57
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • ‘‘Oriented film growth,’’ not ‘‘epitaxy’’ in HTSC film growth

    Page(s): 269 - 273
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    A survey of the literature reveals that the following materials have been used as the substrates for ‘‘epitaxial’’ deposition of YBCO high Tc superconducting (HTSC) thin films: SrTiO3, ZrO2 (or YSZ), MgO, LaAlO3, Si and Al2O3 (with or without buffer layers), SiO2, Pt, MgAl2O4, even noncrystalline substrates. An analysis of the structural relations between the substrate and HTSC phase is presented. It is obvious that the term ‘‘epitaxy’’ is misapplied in many of these cases. We analyze the evidence for actual crystal structural control from the substrate influencing the oriented growth of the desired phase and find it nonexistent in many cases, very weak in others, and persuasive in a few cases. For the superconductor quality what matters is the quality of the HTSC film, not what it is sitting on. This quality can be quantified in four steps, the first three describing the degree of orientation in none (random‐orientation), one (growth direction), or two (in film plane) crystallographic directions. The fourth is the degree of continuity of the film or absence of grain boundaries (i.e., a 100% perfectly oriented set of separated islands with grain boundaries will clearly be considerably poorer than a continuous (single) phase). We propose that instead of the term epitaxial one should focus only on the degree of orientation and continuity of the ‘‘oriented film.’’ The phase immediately contiguous to the film (including many so‐called buffer layers) should be designated substrate. Any phase below such a substrate is structurally and chemically insignificant (to the YBCO growth), although it may be necessary to obtain the oriented ‘‘buffer layer.’’ Such phases should be designated as carriers, not substrates. View full abstract»

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  • Improved substrate temperature control for growth of twin‐free cadmium mercury telluride by molecular beam epitaxy

    Page(s): 274 - 277
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    The growth of cadmium mercury telluride (CMT) by molecular beam epitaxy requires control of the substrate temperature within a narrow window of a few degrees for growth of twin‐free layers on the (111)B and (211)B orientations. It is shown that a thermocouple in contact with the substrate holder does not necessarily provide a sufficient temperature stability and reproducibility. Improving the thermal contact between the substrate holder and the thermocouple by wetting the interface between them with gallium results in a drastic improvement of the substrate temperature control. Reproducible twin‐free growth of CMT on (211)B, as well as on misoriented (111)B CdZnTe surfaces have been demonstrated without any change of set points for the substrate or cell temperatures during the growth run. This demonstrates that the growth of twin‐free layers does not require a change in the growth conditions with time. View full abstract»

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  • Low temperature growth of ZnTe by synchroton radiation using metalorganic sources

    Page(s): 278 - 281
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    The use of synchrotron radiation to convert diethylzinc and diethyltelluride molecules into ZnTe has been employed for ZnTe growth. The formation of ZnTe epitaxial layer on (100) oriented GaAs substrate at room temperature is experimentally demonstrated. It is shown by x‐ray photoelectron spectroscopy that no carbon is included in the film.   View full abstract»

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  • Magnesium cluster‐beam deposition on glass and Si(111)

    Page(s): 282 - 288
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    Magnesium cluster beams have been obtained from supersonic nozzle expansions. The low boiling point of Mg (1363 K) allows conditions for clustering to be reached with and without argon as a carrier gas. This article reports on cluster size and intensity as a function of expansion conditions, and discusses the characteristics of magnesium films obtained by cluster‐beam deposition. The source parameters were temperature T0≤1600 K, total pressure p0≤5000 hPa, magnesium partial pressure pMg≤2600 hPa, supersonic conical nozzle: diameter d=0.25 mm, cone angle 2α=10°, and cone length l=27 mm. For the Ar/Mg mixture the cluster‐beam intensity corresponded to deposition rates of up to 83 nm/s at a 0.3 m distance from the nozzle. This exceeds the ‘‘ideal’’ intensity from a sonic nozzle operated with the same magnesium mass flow by about a factor of 3.5. For the neat Mg vapor the deposition rates extended up to 190 nm/s, but at a higher Mg mass flow compared to the Ar/Mg mixture. The cluster beams were deposited on room‐temperature glass and Si(111) substrates. Films about 1000 nm thick were examined by x‐ray diffraction. Compared to films produced by atomic beam deposition with a typical polycrystalline structure the cluster films are distinguished by a preferential orientation of (002) planes parallel to the substrate. This feature was observed for both types of cluster beams, with and without argon as a carrier gas, and for both glass and Si substrates. The highly specular film surfaces turned usually into a golden‐yellow color after exposure to air, with the notable exception of the film formed with the highest intensity (510 nm/s). The surface structure studied with an atomic force microscope showed an increase in grain size with increasing deposition rate. View full abstract»

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  • Ion beam assisted growth of β‐FeSi2*

    Page(s): 289 - 294
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    This article reports the structural and morphological characterization of β‐FeSi2 films, about 120 nm thick, grown by ion beam assisted deposition (IBAD). The silicide layers were obtained by Fe evaporations onto (001) Si substrates maintained at T=600 °C, while an Ar+ beam bombarded the sample surface at an energy ranging between 100 and 650 eV. Beta‐FeSi2 films were even grown at several ion current densities and, in one case, the beam bombardment was limited to the early stage of the silicide formation. We have found that IBAD process reduces the crystalline grain size and improves the film morphology. Moreover, the relationship between ion beam process and grain nucleation at the silicide/silicon interface shows that when the number of Ar+ reaching the silicide/Si interface is about 1/3 of the Si substrate surface atomic density, the nucleation mechanism tends to saturate. View full abstract»

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  • Photoresponse probe of the space charge distribution in ferroelectric lead zirconate titanate thin film memory capacitors

    Page(s): 295 - 299
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    A photoresponse study of sol‐gel derived polycrystalline thin films of lead zirconate titanate (PZT) is described. Thin film ferroelectric capacitors were fabricated in a sandwich geometry with a transparent top electrode, and illuminated with ≊365 nm wavelength (PZT band gap ∼3.5 eV) light pulses. The observed photocurrent has two components: first, a transient spike coincident with the onset of the illumination pulse, and second, a steady dc photocurrent which prevails as long as the light is ‘‘ON.’’ The steady current response exhibits a weak dependence on the polarization, whereas the transient response exhibits a distinct polarization dependence. To understand the nature of this photoresponse we have studied the variation of the photoresponse as a function of the duration of the ‘‘write’’ pulse used to program the ferroelectric capacitor. The peak value of the polarization dependent transient component of the photoresponse relates to the injected space charge and the distribution of deep traps within the ferroelectric thin film. This, in turn, is modulated by the duration of the write pulse used to program the capacitor. We provide a space charge model that offers a framework for interpreting the photoresponse. The transient photoresponse thus serves as a qualitative measure of the space charge in the ferroelectric film, and to a limited extent, an indirect measure of the remanent polarization. We propose that these photoresponse effects can be applied as diagnostic probes of the space charge distribution in the ferroelectric thin film. View full abstract»

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  • Electron cyclotron resonance plasma source for metalorganic chemical vapor deposition of silicon oxide films

    Page(s): 300 - 307
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    An electron cyclotron resonance (ECR) plasma source was employed for low‐temperature (50–300 °C) metalorganic plasma‐enhanced chemical vapor deposition of silicon oxide films. The plasma was excited in mixtures of oxygen and tetraethylorthosilicate vapor, and oxygen and tris(trimethylsiloxy)boron (TTMSB) vapor. The operation pressure range was 1–50 mTorr; oxygen and metalorganic vapor flow rates varied from 10 to 100 sccm. Microwave power (f=2.45 GHz, P=100–1500 W) was introduced into a 15‐cm‐diam ECR chamber via a microwave quartz introduction window. A static magnetic field in the plasma chamber was generated by two Helmholtz coils. It had intensity near the microwave window, Bvw=875–935 G in a narrow plasma mode, and Bvw=1000–1100 G in a uniform plasma mode. Silicon dioxide films were deposited onto a 10‐cm‐diam silicon wafer located at 16 cm from the source output. A line‐averaged plasma density N¯e was measured with a microwave interferometer (35 MHz) at 11 cm from the source output. In the mixture of TTMSB vapor and oxygen (20 mTorr), N¯e was 1.5–1.7×1011 cm-3 and then decreased as pressure grew. The film deposition rate increased with TTMSB flow rate; it had a maximum value of 1200 Å/min at total pressure of 15–20 mTorr. View full abstract»

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  • Fluorinated diamondlike carbon films deposited from radio‐frequency glow discharge in a triode reactor

    Page(s): 308 - 313
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    Diamondlike carbon thin films have been deposited by H2–C2F6 fed rf‐glow discharges in a triode reactor. Raman spectroscopy and electron spectroscopy for chemical analysis have been utilized as diagnostic tools to investigate structural properties and chemical composition of deposited films. Transitions in film properties have been observed, from those typical of hydrogenated polymers to those of diamondlike and fluorinated polymers, by changing feed composition, substrate bias, and substrate temperature. In particular, it has been shown that the energy of the ions bombarding the growing films, as well as the fluorine contents in the films is the most critical parameter to obtain materials with diamondlike structure. View full abstract»

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  • Influence of an external axial magnetic field on the plasma characteristics and deposition conditions during direct current planar magnetron sputtering

    Page(s): 314 - 320
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    The magnetic field distribution between substrate and target in a dc magnetron sputtering system was altered by superimposing an axially symmetric external magnetic field Bext to the original field of the magnetron source. The magnetron was operated with a Mo target and Ne, Ar, and Kr discharges were investigated. The plasma parameters in the substrate vicinity were measured as a function of Bext using both cylindrical and flat Langmuir probes. It was found that the variation of the magnetic field strength caused large changes in the plasma parameters, such as charge carrier density, plasma and floating potentials, electron temperature, and electron energy distribution function while the cathode discharge processes remained unchanged. The Mo deposition flux was found to be independent of Bext, but the ion saturation current to the negatively biased substrate holder could be changed by a factor of ∼50 by varying Bext. In addition to the ion flux, the two other sources of energetic species arriving at the substrate—the sputtered Mo atoms and the reflected Ne, Ar, and Kr neutrals from the target were calculated using a trim computer code and taking into account gas phase scattering en route between target and the substrate. View full abstract»

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  • Deposition of aluminum oxide films with high refractive index

    Page(s): 321 - 322
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    Aluminum oxide (Al2O3) films are used in a variety of applications including optics and microelectronics. We have deposited aluminum oxide films on 5 in.2 polished fused quartz substrates by the rf sputtering method. It was found that properties of these films such as refractive index and density varied significantly while the deposition conditions were held constant. Films with a high refractive index (n≳1.7) were denser and were not attacked by the chemical solution, while the films with a low refractive index (n≪1.6) were less dense and readily attacked. Films with a high refractive index can be reproducibly obtained when a surface layer of the fused quartz substrates was removed by sputter etch before the film deposition. The amount of sputter etch required depended upon the deposition rate to be employed subsequently. The results are consistent with a model in which a hydrated surface layer on the fused quartz substrates provided a source of water molecules that may migrate into the growing Al2O3 films. View full abstract»

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  • Fluorocarbon high‐density plasmas. I. Fluorocarbon film deposition and etching using CF4 and CHF3

    Page(s): 323 - 332
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    Fluorocarbon film deposition in discharges used for oxide etching plays a key role in determining the profile shape of contact holes and the etch selectivity with respect to the mask and the underlayer. For low‐density capacitatively coupled rf discharges this deposition is due to neutral radicals. We report a study of fluorocarbon film deposition and etching phenomena in electron cyclotron resonance (ECR) discharges of CF4 and CHF3. Plasma operation without rf sample bias in the pressure range below 10 mTorr results in the deposition of fluorocarbon films for both gases, with the highest deposition rate in each case at 2 mTorr (≂120 nm/min for a 1000 W CF4 plasma and ≂180 nm/min for CHF3 using the same conditions). For CF4 this behavior differs dramatically from that seen for conventional rf diode plasmas where no deposition occurs. The deposition is due to the more efficient breakdown and ionization of CF4 and CHF3 in the ECR discharge and the lack of energetic ion bombardment of the substrate as compared to capacitatively coupled rf diode plasmas. We have used a double grid ion energy analyzer in front of a silicon wafer being ellipsometrically sampled to unambiguously demonstrate that in these high‐density discharges, fluorocarbon deposition is primarily due to bombardment with low energy ions. The fluorocarbon growth rate dropped by a factor of 5 if positive biasing of the grid prevented ions from reaching the fluorocarbon film surface in a CHF3 plasma at 2 mTorr. The energy distribution of the ions which may be obtained from these data is in good agreement with measurements of the plasma potential. The ion fluxes for CF4 are ≂4–5 times greater than the fluorine and carbon atom fluxes required to explain the deposition rates (assuming a sticking coefficient of 1). Film‐growth due to direct ion incorporation r- - ather than ion enhancement can explain the experimental results. For CHF3 plasmas the deposition rates are ≂100 nm/min greater than for CF4 for all conditions. This suggests that neutrals contribute strongly to fluorocarbon film growth for CHF3 since the ion currents are nearly the same as for CF4. The ion enhancement effect of film growth rate decreases at higher pressure and lower microwave powers and mirrors the behavior of the ion current. This finding has important implications for etch selectivity, etching profiles, and the slow‐down of the SiO2 etch rates in high‐aspect ratio contact holes. Biasing the substrate reduces the net fluorocarbon deposition rate for low rf bias values. At higher rf bias values, etching of the initially deposited film takes place. These threshold voltages for etching are higher for CHF3 than CF4, e.g., 55 versus 35 V for 1 mTorr operation. Oxide etching can only take place for rf bias values equal or greater than these threshold voltages. View full abstract»

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  • Fluorocarbon high‐density plasmas. II. Silicon dioxide and silicon etching using CF4 and CHF3

    Page(s): 333 - 344
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    We report a study of the application of CF4 and CHF3 electron cyclotron resonance (ECR) discharges to selective etching of SiO2 over Si. Due to significant fluorocarbon film deposition for plasma operation without rf sample bias in the pressure range below 10 mTorr, rf biasing is required for etching of SiO2 and Si. The rf threshold voltage for etching is 55 V for CHF3 and 35 V for CF4 at a pressure of 1 mTorr. At 100 V rf bias, silicon dioxide etch rates were greater than ≂600 nm/min in CF4 and 450 nm/min for 1000 W plasmas at 1 mTorr pressure. A plot of the oxide etch rate vs rf bias exhibits a fluorocarbon film suppression regime at low rf voltages and an oxide sputtering regime at higher rf voltages. In the fluorocarbon suppression regime, the etch rate is primarily determined by fluorocarbon deposition which results in a thin fluorocarbon film being present on the SiO2 surface during steady‐state etching. In the oxide sputtering regime, the oxide etch rate increases linearly with the ion current to the wafer and the square root of the ion energy. The etch yields decrease with increasing microwave power and decreasing pressure and are in the range 0.5–2 atoms per incoming ion. The silicon etch rate is much lower in CHF3 than in CF4, which translates into better SiO2‐to‐Si etch selectivity in CHF3 (≂15) than in CF4 (≂5). The lower Si etch rate in CHF3 is due to a greater thickness of the fluorocarbon film present on the silicon surface during steady‐state etching. The fluorocarbon film thickness is ≂5.5 nm in CHF3 as compared to ≂2.5 nm in a CF4 discharge (at a rf bias of 100 V). The oxide surface is free of fluorocarbon film for the same conditions. The etch depth of ≂2.5 μm deep contact holes et- - ched using 1 mTorr CHF3 plasmas into photoresist patterned SiO2 was measured by scanning electron microscopy as a function of the feature width. The etch depth decreased by ≂10% as the feature size was reduced from 1.3 to 0.6 μm. View full abstract»

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  • Study on electromagnetron for plasma polymerization. II. Magnetic field enhanced radio frequency plasma deposition of organogermanium films from tetraethylgermanium

    Page(s): 345 - 353
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    Construction of a reactive magnetron rf plasma deposition system with cylindrical electrodes is presented. Design of an individual electrode equipped with integrated multiple electromagnet system together with the characteristics of its magnetic field is described. Properties of magnetron discharge and plasma geometry are also presented. Deposition of organogermanium films from tetraethylgermanium in magnetically enhanced rf plasma is discussed in terms of deposition rates and general properties of the films with the particular attention paid to their density. Both, elemental composition of these films by electron spectroscopy for chemical analysis and their chemical functionality by Fourier transform infrared spectroscopy are also given. The main advantage of magnetic field enhancement is local increase of plasma density restricting the discharge, and consequently deposition, to the desired volume. Additionally, the application of a system of integrated electromagnets enables the use of magnetic field intensity as an independent process optimization parameter. View full abstract»

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  • Redeposition kinetics in fluorocarbon plasma etching

    Page(s): 354 - 364
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    The redeposition kinetics of plasma etching products have been measured as a function of ion and free‐radical fluxes which are representative of the fluorocarbon etching environment. Silicon and SiO2 surfaces were exposed in a multibeam etching tool to energetic ions (Ar+), etchant radicals (F), and depositing carbonaceous species (CF2), the relative fractions of which were independently varied to alter the etching product distributions. The rate of product redeposition (i.e., the deposition rate on nonbombarded surfaces such as trench or via sidewalls) was measured using a quartz crystal microbalance (QCM) which could be rotated around the etching sample face. While redeposition rates of Ar+ sputtering products from Si and SiO2 were characteristically high, the addition of F suppressed redeposition by nearly an order of magnitude. The mechanisms for this reduction involve the passivation of the nonbombarded QCM surface by atomic F, the chemical etching of the redeposited material, and the production of volatile products which do not readily stick to sidewall surfaces. Redeposition rates during ion‐enhanced F etching of Si and SiO2 surfaces are largely determined by the fraction of physical sputtering, which emits unsaturated ‘‘sticky’’ products. Accordingly, redeposition rates are observed to increase with decreasing F/Ar+ ratio and increasing ion energy. Addition of CF2 radicals during ion bombardment was observed to suppress redeposition rates measured during pure physical sputtering, but had no significant effect on redeposition in the presence of atomic F. View full abstract»

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  • Plasma fluorination of graphite

    Page(s): 365 - 368
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    Fluorinated graphites are low surface energy, thermally stable solids that have applications as moisture resistant lubricants, water repellents, release agents, and lithium battery cathodes. Conventional methods of synthesizing fluorinated graphite, however, make inefficient use of fluorine feed stocks, are time consuming and limited by safety considerations. In this article, we demonstrate that plasma processing techniques can be used to fluorinate graphite surfaces and thereby reduce the surface free energy from an untreated value of 50 mJ/m2 to as low as 7 mJ/m2. Pressed graphite pellets and graphite foils are exposed to nitrogen trifluoride and sulfur hexafluoride plasmas. Fluorination is monitored with x‐ray photoelectron spectroscopy (XPS), while liquid contact angle measurements are used to assess the free energy of the treated surfaces. Results indicate that significant surface fluorination can be achieved in exposure times of 10–15 min and with only modest plasma energies of 0.2 W/cm2. X‐ray photoelectron spectroscopy (XPS) confirms the formation of CF2 and CF covalent bonds. Fluorine depth profiles show that CF2 species predominate on the fluorinated graphite surface, while CF species are found in the subsurface at depths less than 100 Å. View full abstract»

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  • Cleaning of metal parts in oxygen radio frequency plasma: Process study

    Page(s): 369 - 378
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    The removal of different lubricants (oils and greases) from metal surfaces by use of a capacitively coupled 13.56 MHz low‐pressure oxygen discharge has been examined. Stainless steel, tool steel, brass, aluminum, and copper were used as a substrate materials. The ion bombardment and chemical reactions occurring at the metal surfaces in such a discharge allow for high cleaning speed. A hollow‐cathode discharge has been used to increase the plasma density in contrast to a plane cathode discharge configuration. The cleaning process was characterized by use of emission spectroscopy and mass spectroscopy. Influence of rf power (up to 1 kW), pressure (from 0.01 to 1 mbar), and magnetic field (up to 20 mT) on the process duration and surface cleanliness has been investigated. The criteria for detection of the process end point are formulated and checked. The spectral information is useful for end point detection only in restricted regions of the process conditions. Results indicate a strong influence of the lubricant temperature on the process duration. The removal rate of N62 oil at 140 °C is twice as high as that at 50 °C. For temperatures higher than 140 °C the creation of a hardly removable solid residue occurs. The influence of the initial lubricant area and lubricant thickness on the process duration has been investigated. The increase of the lubricant area results in an increase of the process time (loading effect for cleaning process). The increase of the lubricant film thickness results in a proportional increase of the process time. View full abstract»

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  • Synchrotron radiation excited etching of SiC film using reactive species generated by a microwave discharge

    Page(s): 379 - 383
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    Synchrotron radiation (SR) excited etching of SiC film was studied using a mixture of SF6 and Ar. It was found that only the region irradiated by SR was etched. By introducing a 2.45 GHz microwave discharge as a generator of reactive species, the etch rate of the irradiated region was increased by one order of magnitude while retaining the area selectivity. It was determined that the etching reaction occurred due to a surface photochemical reaction and was promoted by the increase in the number of reactive species affected by means of microwave discharge. From the dependence of the etch rate on the photon energy using monochromatic soft x rays, it was found that the photoabsorption of the sample took part in the etching reaction. View full abstract»

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  • Elimination of serious artifacts in temperature programmed desorption spectroscopy

    Page(s): 384 - 387
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    Regurgitation and wall displacement processes are often encountered in temperature programmed desorption measurements. Such effects can lead to misleading interpretations of the surface reaction and desorption products. A simple and useful pumping scheme is described which overcomes this problem by using a cryogenically cooled titanium sublimation pump (TSP) for differential pumping of the mass spectrometer. It is demonstrated that minor wall displacement effects (mainly CO, H2O, and H2) are present in temperature programmed desorption spectroscopy and are insensitive to the mode of differential pumping. In comparison to ion pumping, however, serious methane (CH4) regurgitation and displacement effects can be completely eliminated when the TSP is employed.   View full abstract»

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  • Effects of processing on electrical properties of YBa2Cu3O7 films. II. In situ deposition processes

    Page(s): 388 - 392
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    The effects of several patterning process steps on the critical current Jc and surface resistance Rs of YBa2Cu3O7 films are described. Included are two off‐axis sputtering processes and a metalorganic chemical‐vapor deposition (MOCVD) process, all producing in situ superconducting films with c‐axis epitaxial orientation. Jc and Rs parameters were measured by mutual inductance and parallel plate resonator techniques, respectively, so that the films did not require patterning for the measurement. Applying a polymer film and stripping, either with acetone or with an O2 plasma, resulted in no change in Rs. Brief ion milling, as well as baking at 185 °C with polymer film present, caused moderate degradation (∼25 μΩ) for films deposited on MgO (both sputtered and MOCVD). The damage caused by ion milling sputtered films on LaAlO3 was considerably greater (∼100 μΩ); photoresist developer also had a significant effect. The degree of degradation in Rs for these films suggests that the surface damage results in secondary effects that penetrate well into the film. This damage was not removed by annealing in O2; in fact it was made substantially worse. Jc was increased slightly by all processes, by an amount ranging from 5% to 50%. View full abstract»

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  • Thermally induced changes in TeOx thin layers

    Page(s): 393 - 398
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    TeOx layers with controlled Te/O ratio and thickness are prepared by thermal coevaporation of TeO2 and Te. Using various transmission and scanning electron microscopy techniques it is shown that the as‐deposited layers represent a composite system, consisting of finely dispersed, partly agglomerated crystalline Te particles embedded in an amorphous TeO2 matrix with columnar structure and fine‐grained substructure. The effect of annealing and laser exposure on the layers is investigated. A strong correlation of the change in transmission and the Te redistribution is found. It is shown that the variations in the optical properties of the TeOx layers are caused by aggregation of the crystalline Te particles and migration of Te to the upper free surface of the layer. View full abstract»

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  • Acceleration of high current heavy ions using a variable energy radio‐frequency quadrupole linac and measurement of the input beam emittance

    Page(s): 399 - 404
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    A high current ion beam injection system and a variable energy radio‐frequency quadrupole (RFQ) accelerator with an external LC resonance circuit are tested. A four‐rod RFQ electrode of 2.3 m length is newly designed to obtain a milliampere class MeV ion beam. To increase accelerated beam current, injected beam emittance into the RFQ is measured and compared with the designed RFQ acceptance. Injected beam emittance tends to increase with the beam current increase. The beam acceleration tests are carried out with a cw rf power supply of 100 kW (10–30 MHz, continuously variable). Results show that the time‐averaged beam currents of N+ and Ar2+ are 1.1 mA (0.4 MeV) and 1.03 mA (1.0 MeV), respectively, and that the peak current of these beams is about 5 mA. As representative ion species for fabricating semiconductor devices, P+ and P2+ are accelerated, and the time‐averaged beam current of 0.48 mA (0.56 MeV) and 0.28 mA (0.81 MeV) are obtained, respectively. This high current MeV ion implanter has great potential for application to high‐dose implantation and high throughput production of semiconductor devices and material surface modifications. View full abstract»

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  • Correction of dead time effects in time‐of‐flight mass spectrometry

    Page(s): 405 - 410
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    This is a report on the feasibility of dead time correction of single‐ion‐counting data in time‐of‐flight mass spectrometry. Here signals vary on a time scale similar to the dead time of the detector. The correction of dead time effects based on the Poisson distribution is practicable for single peak integrals. This leads to a sufficient correction for most applications like the measurement of isotope, element, and molecule ratios or ion imaging. Even the exact dead time correction of total mass spectra is possible but requires the precise knowledge of the dead time. This is, in general, not a fixed time interval but has to be described by a probability function. View full abstract»

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  • Study of the structure of the Rh/Ag surface using positron annihilation induced Auger electron spectroscopy

    Page(s): 411 - 417
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    Positron annihilation induced Auger electron spectroscopy (PAES), electron induced Auger electron spectroscopy (EAES), and low‐energy electron diffraction have been used to study the temperature dependent composition of vapor‐deposited of Rh on Ag(100). Earlier work using AES, ion scattering spectroscopy, and TDS has shown that a Ag layer diffuses to the Rh surface upon annealing to form a structure in which Rh is sandwiched between a Ag cap layer and the Ag substrate. In this work, the top layer selectivity of PAES was utilized to study the diffusion of Ag to the surface as Rh films deposited at 173 K were heated to 573 K. Analysis of the PAES spectra indicates that Rh remains in the top layer during the ∼3 h required to take PAES data when the sample is maintained at the 173 K temperature of deposition. There is a clear indication that significant migration of Ag to the surface takes place by 373 K. The Ag content of the top layer increases to approximately 100% above 473 K. View full abstract»

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  • Photoemission study of the growth of the LaF3/Si (111) interface

    Page(s): 418 - 422
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    Photoemission spectroscopy with synchrotron radiation was used to study the LaF3/Si (111) interface as a function of annealing temperature for LaF3 films. These films range in thickness from 0.7–11 monolayers and have been deposited at room temperature. The La/Si photoemission intensity ratio at surface sensitive and bulk sensitive experimental conditions shows that island formation occurs at 420 °C. The stoichiometry of the LaF3 films is conserved until desorption begins at approximately 580 °C, where fluorine desorbs from the surface completely and lanthanum remains on the silicon substrate. From a line shape analysis of the Si 2p and La 4d core levels it is apparent that the interface is dominated by La–Si bonds. Changes in the surface Fermi level are induced by the penetration of lanthanum into the surface layers of the silicon substrate upon annealing. 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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Meet Our Editors

G. Lucovsky
North Carolina State University