Showing papers in "Journal of Vacuum Science and Technology in 1972"
TL;DR: The effect of grain growth on stresses in films is discussed in this paper, where grain growth generally leads to stress relaxation when the film is under a compressive stress and further grain growth can occur if plastic flow relieves some of the strain energy.
Abstract: The effect of grain growth on stresses in films is discussed. Grain growth generally leads to stress relaxation when the film is under a compressive stress. When the initial grain size is below a critical value, grain growth can occur by normal boundary migration and generates a tensile stress in the plane of the film. Grain growth proceeds until a particular grain size is reached, at which the sum of the strain energy and surface energy is minimized. Further grain growth can occur if plastic flow relieves some of the strain energy. When the initial grain size is above the critical size, there is no minimum in the energy vs grain size relationship, and grain growth to infinite size can occur by normal boundary migration. In the presence of impurities, apparently anomalous intrinsic stresses in films may be produced.
273 citations
TL;DR: In this article, the basic concepts in the theory of chemisorption of atoms on metals are reviewed, and the sharp atomic levels of the free atom are broadened into virtual levels by electron tunneling between the atom and the solid.
Abstract: The basic concepts in the theory of chemisorption of atoms on metals will be reviewed. The sharp atomic levels of the free atom are broadened into virtual levels by electron tunneling between the atom and the solid. For rapid tunneling, correlation effects on the adatom are weak and a self-consistent field molecular orbital approach is appropriate. The adatom density of states can vary from a Lorentzian level to states split above and below the valence band of the solid, corresponding to the bonding and antibonding orbitals of a surface complex formed between the adatom and its surroundings. The Anderson model treats only Coulomb interactions on the adatom, while the CNDO method of quantum chemistry has been recently employed to include Coulomb interactions in the solid. For strong intra-atomic Coulomb interaction on the adatom, correlation effects are important and the localized magnetic moment on the adatom as predicted by the unrestricted Hartree–Fock approximation is quenched. Correlations have been treated by extended valence bond methods, multiple scattering theory, and configuration mixing techniques. Semiquantitative agreement with experiment is obtained in a number of systems.
175 citations
TL;DR: Activated reactive evaporation as discussed by the authors is a new process developed for the high rate deposition of compounds, and it circumvents problems associated with direct evaporation of compounds. But it is not suitable for high rate compound synthesis, since the reaction has to be activated by ionization of the reacting species.
Abstract: Activated reactive evaporation is a new process developed for the high rate deposition of compounds. It circumvents problems associated with direct evaporation of compounds. Metal vapors from high rate evaporation sources are reacted with a gas in the vapor phase to form and deposit compounds. The vapor phase reaction has to be activated by ionization of the reacting species, i.e., metal vapor and gas in the reaction zone. The steps of compound synthesis and compound deposition are thus separated. Control of deposit stoichiometry, e.g., [C/M] ratio for TiC synthesis is readily achieved by controlling the relative amounts of reactants. Results on the synthesis of carbides, oxides, and nitrides are presented.
163 citations
TL;DR: In this paper, it was shown that continuous or intermittent ion bombardment during deposition can change the growth mode of thick deposits formed by sputtering or evaporation, and that this growth habit modification may also be obtained in sputter deposited nonmetallic materials and chemical vapor deposits by ion bombarding the deposit during growth.
Abstract: It is shown that continuous or intermittent ion bombardment during deposition can change the growth mode of thick deposits formed by sputtering or evaporation. The columnar morphology commonly found when deposits exceed 1 μ in thickness can be disrupted and the deposit densified by negatively biasing the deposit and subjecting it to ion bombardment during growth. This effect is found to occur in a number of metal systems and may be attributed to resputtering during growth. In the case of sputter deposited tantalum, the density of 6-μ thick films can be increased from 14 g/cm3 at 0 deposit bias to 16.3 g/cm3 at −500-V bias. The macroscopic stress in the deposited film is also shown to be a function of the deposit bias. It is proposed that this growth habit modification may also be obtained in sputter deposited nonmetallic materials and chemical vapor deposits by ion bombarding the deposit during growth.
150 citations
TL;DR: In this article, the interdiffusion and subsequent compound formation was investigated in thin film couples of Ti-Au, Ti-Pd, and Ti3Pt using transmission and glancing angle electron diffraction techniques.
Abstract: The interdiffusion and subsequent compound formation was investigated in thin film couples of Ti–Au, Ti–Pd, and Ti–Pt using transmission and glancing angle electron diffraction techniques. Aging temperatures up to 500°C and times up to 8 h were considered. For all three couples, intermetallic compound formation was observed in the as-deposited films indicating substantial diffusion during deposition (= 100–150°C). For the Ti–Au couples, the TiAu2, TiAu, and Ti3Au compounds formed during diffusion. For the Ti-Pd and Ti-Pt couples the isostructural compounds TiPd, TiPt and Ti3Pd, Ti3Pt were observed. After the formation of the Ti3Pd type compound diffusion ceased for temperatures <500°C indicating that this compound was acting as a diffusion barrier. In all cases Ti was found to be the fastest diffusing species, where it was observed that the diffusion occurred principally through the Au, Pd, or Pt grain boundaries. The effective diffusion coefficient was estimated to be about 105 times larger than expected...
140 citations
TL;DR: In this article, two types of switching phenomena that characterize thin films of covalent amorphous solids are described in detail and several mechanisms that can account for these phenomena are presented and analyzed in view of recent experimental data.
Abstract: The two types of switching phenomena that characterize thin films of covalent amorphous solids are described in detail. Several mechanisms that can account for these phenomena are presented and analyzed in view of recent experimental data. Two applications of bistable switching to computer memories are discussed—the electronically alterable Read-Mostly Memory (RMM) and the mass optical memory (MOM).
135 citations
TL;DR: In this paper, the catalytic reaction between CO and O2 on a Pt (110) surface is investigated by residual gas analysis for different partial pressures of CO and o2 and various temperatures.
Abstract: The catalytic reaction between CO and O2 on a Pt (110) surface is investigated by residual gas analysis for different partial pressures of CO and O2 and various temperatures. The surface cleanliness of the Pt crystal is monitored by Auger electron spectroscopy. The results of the reaction study are generally in agreement with previous studies for polycrystalline Pt catalysts. The temperature dependence of the formation rate of CO2 exhibits a maximum whose position depends on the composition of the gas phase. At T=215°C two different rate laws are valid. For PO2>PCO the rate of CO2 formation is proportional to PO21.1PCO−0.6, while for PO2>PCO it is proportional to PO20.25 PCO0.75. These observations support the idea that the reaction obeys an Eley-Rideal mechanism in the pressure and temperature range investigated, and the results are evaluated accordingly. The influence of segregated Si on the CO oxidation reaction is investigated and found to be small.
120 citations
TL;DR: In this article, total energy distributions of field emitted electrons from the tungsten (110) and (100) planes as a function of coverage by hydrogen and deuterium have been recorded utilizing a spherical deflection energy analyzer.
Abstract: Total energy distributions of field emitted electrons from the tungsten (110) and (100) planes as a function of coverage by hydrogen and deuterium have been recorded utilizing a spherical deflection energy analyzer. The elastic tunneling resonance spectrum gives a plot of the 'local density of states' in the adsorbate. The inelastic tunneling spectrum reveals those discrete excitation energies available in the adsorbate-substrate complex. These spectroscopic data have been used to infer the chemical nature of the binding states which have been observed in the flash desorption spectrum of hydrogen from tungsten.
119 citations
TL;DR: In this article, surface chemical analysis by Auger electron spectroscopy (AES) is carried out simultaneously with inert gas sputtering to obtain composition profiles normal to the solid-vacuum interface Chemical profiles are presented for as-evaporated and air-heated nichrome thin film resistors.
Abstract: An apparatus is described in which surface chemical analysis by Auger electron spectroscopy (AES) is carried out simultaneously with inert gas sputtering to obtain composition profiles normal to the solid–vacuum interface Chemical profiles are presented for as-evaporated and air-heated nichrome thin film resistors
116 citations
TL;DR: In this article, it was shown that grain boundary grooving can be restricted by inhibiting surface diffusion, as is shown in the case of silver stripes with a superimposed 100-A chromium film.
Abstract: Mechanisms proposed to describe electromigration damage in thin film stripes are based on the observations that mass transport in films is controlled mainly by grain boundary diffusion and that irregularities in the boundary network give rise to divergencies in the mass flux. Two such irregularities, for example, are the triple point configuration (three grain junction) and mixed grain size. Calculation of the vacancy supersaturation level at these sites gives a value of about unity, which can allow condensation into voids at heterogeneous nucleating surfaces, but not within pure boundaries. In lieu of void nucleation, vacancies diffuse to the surface where grain boundary grooving takes place, eventually resulting in a hole. Grooving can be restricted by inhibiting surface diffusion, as is shown in the case of silver stripes with a superimposed 100-A chromium film. Inhibition of boundary electromigration is achieved by either producing a textured film or by adding solute. In the textured film, the boundar...
112 citations
TL;DR: In this paper, an apparatus for the study of gas-solid reactions which produce gaseous reaction products is described, where the reactant gas contacts the solid as a molecular beam travelling in vacuum.
Abstract: An apparatus for the study of gas-solid reactions which produce gaseous reaction products is described. The reactant gas contacts the solid as a molecular beam travelling in vacuum. Gaseous reaction products are monitored by a mass spectrometer as they are emitted from the surface. The technique relies heavily upon modulation of the molecular beam to improve the signal-to-noise ratio. In addition, chopping of the reactant beam induces modulation at the same frequency in the reaction products and the phase differences between these two signals contains important kinetic information. Methods of comparing theoretical models of the surface processes with the phase and amplitude information provided by the experiment are presented.
TL;DR: In this article, surface potentials, diffraction patterns, and vibrational frequencies have been compared in relation to the chemisorption bond and the relationship between the surface potential and the vibrational frequency has been discussed.
Abstract: Although it is much less active than the transition metals copper does catalyse reactions of hydrogen and carbon monoxide. The nature of the weak adsorptions of these gases has been investigated by surface potentials, low energy electron diffraction, and infrared spectroscopy. Hydrogen is dissociatively adsorbed by copper but the adsorption is activated. Surface potential measurements have provided isotherms and isosteric heats of adsorption. Carbon monoxide is adsorbed in two distinct stages giving positive and negative surface potential changes. The positive stage is accompanied by a sharp infrared absorption band near 2100 cm−1 which is sufficiently strong to permit reflection spectroscopic studies on single crystal surfaces. Frequency shifts occur during the negative stage. Direct comparisons of surface potentials, diffraction patterns, and vibrational frequencies have been made and will be discussed in relation to the chemisorption bond.
TL;DR: In this paper, the authors investigated the sorption of oxygen on the (110) face of a nickel single crystal and obtained the spectra obtained by varying the angle of incidence relative to the surface and the crystal orientation, can be explained by the assumption that in the case of the (2×1) structure every second place in the top [110] rows of Ni is occupied by an oxygen atom.
Abstract: In an experiment which combines low energy noble gas ion backscattering with LEED the sorption of oxygen on the (110) face of a nickel single crystal is investigated. The energy of the backscattered He+ ions is governed by binary collisions whereas the intensity of the spectrum is given by the cross sections, the concentration of surface atoms, the neutralization probabilities and the geometry. The spectra obtained by varying the angle of incidence relative to the surface and the crystal orientation, can be explained by the assumption that in the case of the (2×1) structure every second place in the top [110] rows of Ni is occupied by an oxygen atom. From a shadow effect observed at small angles of incidence it can be estimated that the adsorbed oxygen protrudes beyond the plane of the Ni atoms by about 0.4–0.8 A.
TL;DR: A change in substrate temperature produces a marked change in the microstructure, preferred orientation, and microhardness of TiC deposits as discussed by the authors, and the high temperature deposits exhibit very high micro-hardness values (∼4500-5000 kg/mm2
Abstract: A change in substrate temperature produces a marked change in the microstructure, preferred orientation, and microhardness of TiC deposits. At low temperatures (∼500 °C) the structure consists of tapered crystallites and changes to a structure consisting of columnar grains at the higher temperatures (∼1000 °C). The high temperature deposits exhibit very high microhardness values (∼4500–5000 kg/mm2 KHN).
TL;DR: In this paper, a high resolution electron spectrometer (ΔE≈10 meV) was used to investigate surface vibrations with a high-resolution electron analyzer, where the electrons are scattered by the extended electric dipole field associated with certain types of surface vibrations.
Abstract: Surface vibrations are investigated with a high resolution electron spectrometer (ΔE≈10 meV). For sufficiently low electron energies the electrons are scattered mainly by the extended electric dipole field associated with certain types of surface vibrations. The excitation of Fuchs-Kliewer surface modes in infrared-active materials is illustrated in zinc oxide. On the cleaved (111) silicon surface a surface phonon of ℏω=56 meV is found. Furthermore, the localized modes of oxygen adsorbed on a (111) silicon surface are discussed. The sensitivity of electron spectroscopy is several orders of magnitude higher than light spectroscopy.
TL;DR: In this article, grain boundary sliding or oxide film voids (on the aluminum film) are shown to be possible nucleation sites of hillocks and depressions in annealing aluminum films.
Abstract: Vacuum deposited aluminum films are extensively used as inter- and intra-connects on silicon integrated circuits for their advantageous electrical and metallurgical properties. Hillock growth occurs after annealing of the films in the form of aluminum projections normal to the film surface. The growth of these hillocks (as well as depressions) takes place during the heating and cooling portions of the annealing cycle caused by differences in expansion coefficient between film and substrate. Diffusional creep (with grain boundary diffusion) or grain boundary sliding is believed to occur in these films to relieve the thermally induced stresses which result in annealing hillocks and depressions. Foreign impurities such as Cu in the aluminum film or the surface anodization of the aluminum inhibit hillock growth. Both approaches are being explored to achieve essentially hillock free deposits. These results support either grain boundary sliding or oxide film voids (on the aluminum film) as possible nucleation s...
TL;DR: In this article, a model is presented which attributes the increase in activation energy caused by copper to the dissolution of Al2Cu precipitates and to the adsorption of copper atoms on aluminum grain boundaries.
Abstract: The addition of copper to aluminum thin films has previously been shown to reduce the rate of electromigration failure considerably. The effective “activation energy” for failure time has been found to be a function of the concentration of copper. A model is presented which attributes the increase in activation energy (about 0.2–0.3 eV) caused by copper to the dissolution of Al2Cu precipitates and to the adsorption of copper atoms on aluminum grain boundaries.
TL;DR: In this paper, the temperature rise during film deposition by rf sputtering of Ta, Au, and Pd films was investigated, and it was found that by sputtering from water-cooled cathodes at power levels between 0.1 and 2 kW, the contribution due to radiation from the plasma and the cathode is negligible.
Abstract: The temperature rise during film deposition by rf sputtering of Ta, Au, and Pd films and dc sputtering of Ta films has been investigated. The film temperature was measured for various cathode to anode distances, as a function of applied power used for sputtering and sputtering time. It was found that by sputtering from water-cooled cathodes at power levels between 0.1 and 2 kW, the contribution due to radiation from the plasma and the cathode is negligible. To a first approximation, heating is caused in varying amounts by the kinetic energy of the sputtered atoms, the latent heat of condensation of the sputtered atoms, and electron bombardment. The film temperature also depends on the optical emissivity of the deposited materials causing the temperature of films with higher emissivities such as Pd to remain significantly lower for comparable sputter times and power. For dc sputtering from an uncooled cathode, it was estimated that radiation from the cathode contributes significantly to the heating of the sputtered films.
TL;DR: In this article, the effect of exposure to oxygen at pressures up to 1 Torr and temperatures up to 500 C was investigated using a crystal isolation valve, and the chemisorbed oxygen caused mainly a strong faceting of the (100) and (110) faces, and a 4×4 superstructure on the (111) face.
Abstract: The chemisorption of oxygen on the (100), (110), and (111) faces of silver single crystals was studied with LEED, secondary electron spectroscopy, and other auxiliary techniques. The effect of exposures to oxygen at pressures up to 1 Torr and temperatures up to 500 °C was investigated using a crystal isolation valve. The chemisorbed oxygen causes mainly a strong faceting of the (100) and (110) faces, and a 4×4 superstructure on the (111) face. The effect of the internally diffused oxygen on the surface behavior was also investigated.
TL;DR: In this paper, the transport properties of vacuum evaporated films of pure selenium and Selenium doped with small quantities of Cl (0−40 ppm) and As (∼12at.%) were examined using a time-resolved drift technique.
Abstract: The transport properties of vacuum evaporated films of “pure” selenium and selenium doped with small quantities of Cl (0–40 ppm) and As (∼12at.%) have been examined using a time-resolved drift technique. Addition of Cl alone acts as an electron trap, and addition of As alone acts as a hole trap while greatly increasing the electron free-carrier lifetime. When used in combination, controlled addition of these two impurities can be used to produce hole ranges greater than 7.5×10−6 cm2/V and electron ranges greater than 1.2×10−6 cm2/V in the same film. This hole range is approximately a factor of 3 greater and the electron range a factor of 5 greater than that observed in the best pure Se films.
TL;DR: In this paper, the adaption of Cs and O on W(112) has been studied with systematic variations of the composition and the sequence of deposition of the adsorbates.
Abstract: Adsorption of Cs and O on W(112) has been studied with systematic variations of the composition and the sequence of deposition of the adsorbates. The results suggest that Cs and O form a W-O-Cs double layer, regardless of the sequence of deposition. The differences in structure of Cs on clean W and O/W are compared. It is found that Cs and O affect the structures of each other. The change in work function of the surface at various Cs and O coverages are reported. Throughout the coverage range of the present study, there is no apparent evidence of cesium oxide formation.
TL;DR: In this paper, a retarding field analyzer consisting of four spherical grids was used to obtain the calibration curve between the chemical composition and the peak-to-peak height of the derivative Auger peak.
Abstract: The changes in surface composition of Cu–Ni alloys after various treatments have been observed by means of Auger electron spectroscopy. A retarding field analyzer consisting of four spherical grids was used. Samples of six different compositions were examined to obtain the calibration curve between the chemical composition and the peak-to-peak height of the derivative Auger peak. The sample surfaces were only polished with emery papers and rinsed in water and acetone. The apparatus was ion pumped to the mid 10−9-Torr range without baking so as not to affect the samples by heating. It was found that the Ni content on the sample surfaces for 80% Ni alloy decreases during the annealing process above 100 °C; and sputtering with argon ions of about 500 eV causes the nickel to become enriched in the surface layers. A slight increase of the nickel was observed on the surface of 38% Ni alloy after initial heating.
TL;DR: In this paper, the reactions of titanium and silicon with slags of the system alumina-calcium oxide-fluorspar were calculated and confirmed by melts in a laboratory induction furnace and also through statistical calculations of 320 heats of 500mm □ (3,6 ton) ingots for the Ti-Al2O3 reaction and of 100 ESR heats of the same ingot size for the Si-Al 2 O3 reaction.
Abstract: The reactions of titanium and silicon with slags of the system alumina-calcium oxide-fluorspar were calculated. The calculations were confirmed by melts in a laboratory induction furnace and also through statistical calculations of 320 heats of 500 mm □ (3,6 ton) ingots for the Ti–Al2O3 reaction and of 100 ESR heats of the same ingot size for the Si–Al2O3 reaction. By statistical evaluation of all heats the dependence of the aluminum and titanium or silicon contents for different TiO2 or SiO2 contents of the slags were determined. By application of these data the losses of Ti or Si by a reaction with alumina can be prevented.
TL;DR: In this article, a UHV system, containing a heatable (up to >2600°K) W ribbon target, a Finkelstein ion source (Ar+, 2'keV) with magnetic mass separator, an electron source (300'eV), a quadrupole secondary ion mass filter with a counting channel electron multiplier and a quad-rupole gas analyzer, is used for the study of the adsorption and desorption of H2, O2, and CO on W by simultaneous, i.e., fast interchanging
Abstract: A UHV system, containing a heatable (up to >2600 °K) W ribbon target, a Finkelstein ion source (Ar+, 2 keV) with magnetic mass separator, an electron source (300 eV), a quadrupole secondary ion mass filter with a counting channel electron multiplier and a quadrupole gas analyzer, is used for the study of the adsorption and desorption of H2, O2, and CO on W by simultaneous, i.e., fast interchanging “static” SIMS [secondary (ion induced) ion mass spectroscopy] and EID [electron induced (ion) desorption] and by flash-filament measurements. Different binding states can be distinguished. The emission cross sections of the adsorbate-specific ions by ion bombardment depend far less upon the gas exposure (and therefore upon the coverage) than those corresponding to electron bombardment.
TL;DR: The structure of massive deposits produced by high rate physical vapor deposition processes above 0.3 Tm substrate temperature consists of columnar grains, and the length and width of the columnar grain increases with substrate temperature as discussed by the authors.
Abstract: The structure of massive deposits produced by high rate physical vapor deposition processes above 0.3 Tm substrate temperature consists of columnar grains. The length and width of the columnar grains increases with substrate temperature. Ion bombardment of the deposit during deposition by biasing the substrate negatively to 5 kV produces a marked refinement in grain size. A possible mechanism is nucleation of new grains by localized temperature spikes at the vapor–solid interface due to ion bombardment.
TL;DR: In this article, the authors measured the speed distribution of the reflected atoms at suitably spaced scattering angles within the plane of incidence for the scattering of a nearly monoenergetic beam of thermal energy He atoms from a cleaved (001)LiF crystal surface, and identified elastic and one-phonon inelastic scattering processes.
Abstract: For the scattering of a nearly monoenergetic beam of thermal-energy He atoms from a cleaved (001)LiF crystal surface, speed distributions of the reflected atoms are measured at suitably spaced scattering angles within the plane of incidence. From the measurements, elastic and one-phonon inelastic scattering processes are identified. Elastically scattered atoms distribute themselves in a set of sharp diffraction peaks. One-phonon inelastically scattered atoms are dispersed about each diffraction peak. The most probable velocities of the inelastically scattered atoms exhibit a characteristic sawtooth variation with scattering angle which, to first approximation, corresponds to conservation of the component of atom momentum tangent to the surface.-
TL;DR: In this article, a surface composition analysis is obtained through monitoring the binary scattering of low energy noble gas ions from surface atoms, which is accomplished with simplified instrumentation and to be primarily sensitive to the first atomic surface layer.
Abstract: A sensitive method of surface composition analysis is obtained through monitoring the binary scattering of low energy noble gas ions from surface atoms. Such analyses have been shown to be accomplished with simplified instrumentation and to be primarily sensitive to the first atomic surface layer. The technique has been extended to include the direct examination of electrically insulating surfaces, and examples of surface compositions obtained from ceramic and glass will be presented. With the capability of examining surfaces irrespective of their electrical conductivity, multilayer thin film structures become a prime example of the dual utilization of the probe ion beam to both analyze and simultaneously controllably remove surface atoms. Such a depth composition profile will be shown for a TiO2 thin film sandwich in which interface contamination was found. Quantitative aspects of the technique will be shown in the SiOx system. Diverse applications of surface analyses will also be shown on metal, semicon...
TL;DR: The charged particle oscillator as discussed by the authors is a device by which particles of one sign are confined to a limited volume solely by means of a static electric field and can be used as a low pressure ion source.
Abstract: The charged particle oscillator is a device by means of which particles of one sign are confined to a limited volume solely by means of a static electric field. In one form it consists of a pair of positively charged wires surrounded by an earthed conducting cylinder. An electron released from rest within the cylinder follows a stable oscillatory path which always passes between the wires and which is up to 5 km in length. The properties of this device have been explored by experiment and by computation, and are discussed with particular reference to its use as a uhv gauge of high sensitivity and as a low pressure ion source.
TL;DR: In this article, the results of an LCAO-band structure calculation of graphite are presented, which is a crucial step for a balanced description of chemisorption is a band structure calculation applied to a properly defined molecular unit cell.
Abstract: The interaction of atomic species with simple surfaces has been effectively simulated previously by us, using molecular orbital treatments at two levels of approximation to the Hartree-Fock equations. These earlier efforts allowed examination of binding sites, bonding arrangements, and charge transfer in terms of orbital and spatial geometries of the systems simulated. However, these techniques do not describe the electronic structure of the solid substrate as well as they do for small molecules, for which they were initially designed. We present the results of an LCAO-band structure calculation of graphite that compares well with the results of an ab initio calculation. A crucial step for a balanced description of chemisorption is a band structure calculation applied to a properly defined molecular unit cell, which is described in detail. The advantages of this approach are discussed, and a brief, qualitative description of the results of preliminary calculations is presented.