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

Issue 3 • Date May 1987

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Displaying Results 1 - 25 of 25
  • Si(111) cleavage and the (2×1) reconstruction process

    Page(s): 293 - 294
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    Using a computer simulation technique with a semiempirical potential, a Si crystal was cleaved along the (111) plane. The π‐bonded chain structural features of the Si(111) cleavage surface are observed and found to be a consequence of the dynamics of this cleavage process and seem not to be influenced by the final energetics. View full abstract»

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  • Application of glow discharge mass spectrometry and sputtered neutral mass spectrometry to materials characterization

    Page(s): 295 - 301
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    Postsputtering ionization using an inert gas plasma to decouple the sputtering and ionization processes minimizes matrix effects commonly associated with conventional secondary ion mass spectrometry. Glow discharge mass spectrometry (GDMS) utilizes ions generated in a dc inert gas plasma to sputter atoms into the ambient plasma from the surface of a cathode composed of the material to be studied. The sputtered atoms, predominantly neutral, are then ionized in the plasma by Penning and electron impact ionization. GDMS provides excellent sensitivity and signal stability, and has found wide uses for characterization of bulk materials such as metals and GaAs. The sensitivity and large sampling volume also make it ideal for determining nonuniform trace contaminants in materials, e.g., U and Th in metals. Sputtered neutral mass spectrometry uses either low‐energy plasma ions (direct bombardment mode or DBM) or an independent focused ion beam (separate bombardment mode or SBM) to sputter atoms into a low‐pressure high‐frequency plasma for electron impact ionization. DBM offers better depth resolution than conventional surface analytical techniques and is ideal for thin‐film studies. The plasma electrons compensate for sample charging in SBM and make this method ideal for the analysis of insulating material such as phosphosilicate glass. View full abstract»

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  • Calibration of oxygen Auger signal from single‐crystal ZnO surfaces

    Page(s): 302 - 304
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    The Auger spectra of the polar and prism surfaces of single‐crystal ZnO were measured. The sensitivity factors derived from the differentiated spectra are 0.26 and 0.25 for a beam energy of 3 and 5 keV, respectively. These values agree fairly well with the theoretical calculations of Mroczkowski and Lichtman. View full abstract»

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  • Estimation of C2 and C3 hydrocarbon production yields of graphite due to hydrogen ion bombardment

    Page(s): 305 - 307
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    A numerical method is proposed for estimating the production yields of C2 and C3 hydrocarbons, which are generated by bombarding graphite with hydrogen ions, from signal intensities of a quadrupole mass spectrometer (QMS). It is shown that the C2H2, C2H4, C2H6, C3H4, C3H6, and C3H8 production yields can be easily estimated by fitting the calculated intensities of QMS signals, by means of summing up the crackings of species, to the measured ones, whose masses range between 24 and 44. The derived formulas can uniquely determine the yields, using the measured data of the cracking coefficients and sensitivities of purified standard gases for the QMS as well as of the intensities of QMS signals. View full abstract»

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  • Measurements of the secondary ion mass spectrometry isotope effect

    Page(s): 308 - 312
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    The heavier isotopes of a given element are generally underrepresented in the secondary ion mass spectrometry mass spectrum since they emerge from the sample with lower average velocity and are therefore less likely to be emitted as ions. The relative deviation of an isotope ratio measurement from its expected value is represented in the literature by the parameter α. In this work we report measurements of α as a function of secondary ion energy in high‐purity Ge, Mo, Pd, Cd, Sn, and W samples; each of which offers several abundant isotopes for examination. A Cameca IMS‐3f magnetic sector instrument is operated in the high‐energy resolution mode for these measurements. The α values are determined from weighted least‐squares fits to the isotope ratio deviations. Appropriate precautions against beam instability, mass interference, and detector saturation effects are employed. Positive and negative ion emission, induced by O+2 and Cs+ bombardment, respectively, are examined. For monatomic positive ion (M+) emission, the magnitude of α correlates roughly with the secondary ion yields and generally increases with increasing emission energy. In contrast, α values for oxide species (MO+) display an inverse dependence on energy indicating surface emission. For negative ion (M-) emission, α changes sign at low energies indicating that, at low energy, ion emission is dominated by the survival probability of the negative ion while, at higher energies, emission depends on the probability of ion formation by electron attachment. Measured α values for diatomic (M+2, M-2) emission are examined with respect to current models of molecular ion formation. View full abstract»

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  • Secondary ion mass spectrometry profiling of shallow, implanted layers using quadrupole and magnetic sector instruments

    Page(s): 313 - 320
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    The analysis of shallow, steeply varying profiles, using secondary ion mass spectrometry with quadrupole and magnetic sector instruments, is described. The problems in generating a reliable profile, free of transient effects, and ion beam induced displacements and broadening effects, in both types of instruments are discussed. The most important conclusion is that one should be capable of varying the primary beam energy, primary mass, the angle of incidence, and the polarity of the secondary ions independently of each other. We also report the use of special experimental conditions which circumvent some of the problems posed in magnetic sector instruments; low‐energy Cs beams (down to 1 keV) are used in combination with sensitive detection of positive secondary ions. Finally, it is shown that for a 5‐kV As+ implanted Si specimen all the projected ranges and decay lengths of the profiles, measured with different primary masses, angles of incidence, and primary energies, can be correlated in a universal curve which has the penetration depth of the primary ion as the basic parameter. The effect of the ambient pressure on the results is also described. View full abstract»

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  • Anomalous sputtering of gallium–antimonide under cesium‐ion bombardment

    Page(s): 321 - 326
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    A large distortion in the secondary ion mass spectrometry depth profile in GaSb is found under cesium‐ion bombardment. The result is interpreted in terms of a nonuniform sputter removal near the initial surface. On the cesium‐ion‐bombarded GaSb surface, microcrystalline GaSb growth takes place to upheave the bombarded region up to 0.1 μm from the initial surface in the very early stage of cesium‐ion bombardment. Above a cesium‐ion dose of 1×1017 ions cm-2, the normal sputtering rate versus ion dose was obtained. This phenomenon is thought to be the cesium induced microcrystal growth specific to the stoichiometric GaSb surface. View full abstract»

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  • Surface differential reflectivity spectroscopy of semiconductor surfaces

    Page(s): 327 - 332
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    An overview of the method of surface differential reflectivity (SDR) for the study of semiconductor surfaces is presented. This includes the principles of the technique, the experimental apparatus, and some theoretical considerations concerning the connection of SDR data with the microscopic properties of the surface. Experimental results are also presented as an example of the application of this spectroscopy to the study of semiconductor surfaces. View full abstract»

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  • A comparison of three‐dimensional and two‐dimensional simulations of contact step coverage

    Page(s): 333 - 336
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    A model is presented for calculating the film profiles of sputtered metal into axially symmetric contacts. The model assumes an isotropic source of metal vapor and considers the dynamic shadowing of deposition flux into the contact. Simulations from this model predict substantially worse step coverage than simulations from a two‐dimensional model but experimentally produced profiles have step coverages in between the two models. View full abstract»

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  • Porosity in thin Ni/Au metallization layers

    Page(s): 337 - 342
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    Thin films of Ni covered with Au and supported on oxidized silicon wafers were deposited by thermal evaporation or electron beam evaporation. After heating in oxidizing environments from 250 to 400 °C, porosity was observed in the Au films. The pores were typically 2000 Å in diameter and ∼2 μm apart after heating for 1 h at 400 °C in oxygen. By considering models of grain boundary grooving, it has been shown that a porous, discontinuous thin Au film is thermodynamically stable. View full abstract»

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  • Thin‐film formation using single‐grid ion‐beam sputtering

    Page(s): 343 - 346
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    This paper discusses fundamental characteristics of a single‐grid ion‐beam sputtering system as well as indicating the optimum aperture dimensions and transparency of a grid. With an optimum thickness and aperture size, a high deposition rate of over 90 nm/min and a grid lifetime of over 10 h were obtained at an accelerator voltage of ≪600 V. The effect of the accelerator voltage or the beam current on the thin‐film properties were investigated and it was clarified that films prepared with a lower accelerator voltage or lower beam current are likely to become amorphous. View full abstract»

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  • Surface analysis of gold containing polyimide films

    Page(s): 347 - 353
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    Polyimide films with metallic surfaces were produced by thermal treatment of solutions containing HAuCl4∙3H2O, hydrogen tetrachloroaurate trihydrate, and either Ciba–Geigy XU 218, poly[5(6)‐amino‐1‐(4’ phenyl)‐1,3,3 trimethylindane‐3,3’,4,4’‐benzophenonetetracarboxylimide] or BTDA‐ODA, poly [ p, p’‐oxybis (phenylene)‐3,3’,4,4’‐benzophenonetetracarboxylimide]. Scanning electron microscopy indicated that 0.1‐μ particles covered a large portion of the air side surface; whereas, 10‐μ particles covered the glass side surface of these films. Auger electron spectroscopy and x‐ray photoelectron spectroscopy (XPS) indicated that the particles were gold in the metallic state. Model imide compounds were synthesized and used to evaluate the XPS spectra of both unmodified and gold containing films. Surface analysis data suggested that only a small amount of gold was located within the XPS sampling depth and that the observed gold particles resided underneath a polyimide overlayer. The discrete metal particles had an unexpected influence on the photoelectron spectra of the polyimide and the influence was dependent on particle size. A schematic model of the multilayered modified film surface was developed and the model further probed by electron flood gun and metal vapor deposition studies. View full abstract»

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  • Negative resist behavior of obliquely deposited Ge–Sb–Se thin films

    Page(s): 354 - 357
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    The photon and electron‐beam induced changes in the selective solubility of Ge–Se–Sb films have been investigated to show that these films can be used as a negative resist. The formation of Sb2Se3 on the top of the film surface after exposure, as confirmed by x‐ray diffraction and x‐ray photoelectron spectroscopy studies, gives rise to a negative tone behavior. The addition of 10 at. % of Sb in the GeSe3 films saturates the change in the chemical solubility after photo‐ and electron‐beam exposures. The chemical solubility difference can be increased by increasing the angle of deposition and is maximum at 80°. Contrast (γ) and sensitivity (s) values of 2.85 and ∼1020 photons/cm2, respectively, for photons, and 4.2 and 6×10-5 C/cm2 for electrons have been obtained. View full abstract»

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  • Friction and wear behavior of ion‐plated lead–tin coatings

    Page(s): 358 - 363
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    A systematic study of lead–tin alloys deposited by ion plating, vacuum deposition, and electrodeposition is carried out and reported in this paper. The effects of sliding distance and load on friction coefficient and wear are studied for lead–tin coatings having from 10 to 40 wt. %Sn. The lead–tin alloys were deposited on polished steel disk substrates. The coefficients of friction and wear were measured under lubricated conditions using ball‐on‐disk geometry. The tests were carried out under different loads from 15 to 145 N and for sliding distances from 250 to 1500–1800 m. The wear loss is evaluated by wear volume and maximum wear depth, and weight loss. View full abstract»

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  • Performance comparison of electrostatic lenses for field emission ion and electron sources

    Page(s): 364 - 371
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    Four electrostatic lenses are analyzed with respect to field emission ion and electron sources for beam energies of 5 to 50 keV. The ion sources considered are the hydrogen field ionization and gallium liquid metal ion sources, while the electron source considered is the thermal field emission source. The lenses analyzed are (1) the three‐element asymmetric lens of Orloff and Swanson, (2) the previous lens only reversed, (3) a symmetric version of the previous three‐element lenses, and (4) the four‐element condenser lens of Kurihara. For the extraction voltage (7.5 keV) and working distance (50 mm) used in this study, the asymmetric lens of Orloff–Swanson operating in the acceleration mode typically results in a smaller spot at low beam energies (5 keV), while the four‐element lens of Kurihara operating in the acceleration mode results in a smaller spot at higher beam energies (≫15 keV). View full abstract»

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  • Quantitative study of the thermal transpiration effect in vacuum gauges

    Page(s): 372 - 375
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    Pressure measurements in the range of low and medium vacuum are conveniently and accurately performed by mechanical instruments which detect pressure‐induced deformations. The stability of both calibration and zero setting are considerably improved by operating the transducers at a stabilized elevated temperature. Due to thermal transpiration the temperature difference between transducer and vacuum vessel may cause a pressure difference which depends on the pressure itself, the geometry and surface properties of the interconnection, and also the gas species. In order to determine the vessel pressure, the empirical correction formula of Takaishi and Sensui has proved to be successful. Our accurate measurements reveal for the first time a minor, but systematic failure of this correction procedure. This failure is attributed to an improper application of the formula, i.e., the disregard of the specific surface properties of the interconnection. To overcome this deficiency, we suggest using fitted values for the temperature and diameter which appear in the formula, instead of actual values. By this procedure the systematic deviations are removed, and the Takaishi and Sensui formula allows description of our vessel pressures better than 0.1%. View full abstract»

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  • Low‐range flowmeters for use with vacuum and leak standards

    Page(s): 376 - 381
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    Vacuum pressure standards of the orifice‐flow type require known gas flows of 10-6 mol/s (10-2 atm cm3/s at 0 °C) and less. Known gas flows can also be used to calibrate ‘‘standard’’ leaks by comparing the pressures generated when flows from the leak and the flowmeter are alternately passed through a constant conductance. Two constant‐pressure, piston displacement flowmeters developed at the National Bureau of Standards are described that can generate flows between 10-6 and 10-10 mol/s with an estimated uncertainty of 0.8% to 2%. Comparisons of the flowmeters with alternate calibration techniques, and repeated low‐range leak and vacuum gauge calibrations, have been used to confirm the estimated uncertainty and random errors of the flowmeter. View full abstract»

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  • Simple, inexpensive delay circuit for protection against vacuum loss from power interruptions

    Page(s): 386 - 387
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    We describe a simple, inexpensive electrical circuit which protects a turbomolecular pumped chamber against vacuum loss in the event of a power failure. The circuit is timed to ensure proper sequencing of events, and also to distinguish between a short and long power failure. View full abstract»

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  • Coaxial helium leak detection probe

    Page(s): 390 - 391
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    A coaxial device has been developed which makes it possible to pinpoint a leak in a piece of vacuum hardware or tubing within a space of one‐sixteenth of an inch. The device consists of a delivery tube which directs the helium to a precise spot and a coaxial outer tube which pumps away the excess helium. This arrangement prevents diffusion or drift to a real leak in close proximity of the test area. 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