AVS1996 Session VM-TuM: Advances in Deposition Technology

Tuesday, October 15, 1996 8:20 AM in Room 104A/B

Tuesday Morning

Start	Invited?	Item
8:20 AM		VM-TuM-1 The Origin of Plumes from Laser Irradiation of Wide Bandgap Insulators at Low Fluences D. Ermer, J. Shin, S. Langford, J. Dickinson (Washington State University) An important aspect of thin film growth by pulsed laser deposition methods is the mixture of atomic and molecular neutral species accompanied by high densities of electrons and ions. These species are incident upon substrates with varied kinetic energy as well as temporal and density distributions. After a brief introduction into the characterization of these features on laser irradiated dielectrics, we examine plume generation from laser interactions with surfaces under conditions where inverse bremstrahlung (normally invoked to explain plasma formation) is not possible due to insufficient photon and electron densities. We present new measurements addressing the interaction between the emitted particles in the near surface region from exposure to pulsed laser irradiation of surfaces of ionic crystals. These emissions include photoelectrons, energetic positive ions, and neutral atoms. We first establish experimentally that there is overlap in space and time of portions of the distributions in the near surface region. We then present a new model for the collected motion of these particles. We show that as laser fluence is increased, sufficient densities, overlap, and kinetic energies are available to explain the onset of plume formation. The features examined include excitation of neutral atoms to generate plume fluorescence and ionization of neutral species at fluences far below breakdown. These studies aid our understanding and possible control of energetic and reactive species desired for efficient and directed thin film growth.
8:40 AM	Invited	VM-TuM-2 Advances in Pulsed Laser Deposition Technology and Diagnostics D. Geohegan (Oak Ridge National Laboratory); A. Puretzky (Russian Academy of Sciences) Over the past nine years, the energetic nature of laser ablation has proven advantageous for film growth of a wide variety of simple or complex materials by pulsed laser deposition (PLD). Oxides, compound semiconductors, artificially-layered superconductors, metals, ferroelectrics, and ultrahard metastable phases are examples of materials easily formed by ablation in vacuum or background gases. Laser ablation into background gases is now being utilized to form nanocrystalline and composite materials via cluster formation and aggregation in the gas phase. Recent investigations employing fast diagnostics such as spectroscopic imaging have revealed fundamental collisional phenomena relevant to film growth by PLD and optimized cluster growth via laser vaporization. Spatially- and temporally-resolved (~0.1 mm, ~5 ns) plasma diagnostic investigations of the ablation of pyrolytic graphite will be presented to illustrate how the laser wavelength and intensity determine the species and kinetic energies responsible for optimized ultrahard amorphous diamond thin films. Optical emission spectroscopy, optical absorption spectroscopy, fast Langmuir probe analysis, and species-resolved gated-ICCD fast photography are combined to permit an understanding of the importance of gas dynamic effects on the time-of-flight distributions of species arriving during the deposition of thin films in both vacuum and background gases. Fundamental gas dynamic effects will be presented with applications to minimizing cluster formation for optimized amorphous diamond films, and maximizing cluster formation for fullerene and nanoparticle synthesis.
9:20 AM		VM-TuM-4 Heteroepitaxial Growth of Conductive SrRuO\sub 3\ Thin Films by Pulsed Laser Deposition Q. Jia, S. Foltyn, M. Hawley (Los Alamos National Laboratory); X. Wu (Symyx) Conductive SrRuO\sub 3\ thin films were heteroepitaxially grown on (100) LaAlO\sub 3\ substrates by pulsed laser deposition over a temperature range from 650 C to 825 C. The degree of crystallinity of the films improved with increasing deposition temperature as confirmed by x-ray diffraction. The increase of grain size with increasing deposition temperature was evident from scanning tunneling microscopy and scanning electron microscopy. Scanning electron microscopy also revealed no particulates on the film surface. The resistivity of the SrRuO\sub 3\ thin films was found to be a strong function of the crystallinity of the films and hence the substrate temperature during film deposition. The SrRuO\sub 3\ thin film deposited at 775 C has a room-temperature resistivity of 280 micro-Ohm-cm which is comparable to that of the bulk single crystalline SrRuO\sub 3\. A residual resistivity ratio (defined as the ratio of room-temperature resistivity and resistivity at 4.2 K of the film) of more than 8 was obtained for the SrRuO\sub 3\ thin films deposited under optimized processing conditions. The enhanced conductivity of the films deposited at optimized conditions can be explained by the reduced grain boundary scattering of the epi-films. The optimized pulse laser deposition conditions to grow smooth, particulate free, and high conductivity SrRuO\sub 3\ thin films will be presented. Applications of SrRuO\sub 3\ thin films as bottom electrodes for high capacity integrated thin film capacitors will be also discussed.
9:40 AM		VM-TuM-5 Preparation of Crystalline TiC/ Amorphous DLC Composite Films using Magnetron Assisted Pulsed Laser Deposition A. Voevodin, S. Prasad, J. Zabinski (Wright Laboratory) Composite materials consisting of crystalline and amorphous phases offer a number of unique properties. One of them is a combination of high hardness and toughness. Another is low friction and wear rates, when one of the phases has lubricious properties. Recent advances in vacuum deposition opened a possibility to grow nano-phase composite films, where the crystalline phase is embedded into an amorphous matrix. Such a matrix is a barrier to dislocations, forcing them to move along borders of a crystalline phase. This increases the hardness of the material and prevents brittle failure under deformation by deflection and braking macro-cracks. In the current study, we report the deposition of composite films consisting of a crystalline f.c.c. TiC and an amorphous diamond-like carbon (DLC) phases. Both of them are hard materials, and DLC has low friction coefficient. Films were grown at 100 C by a novel technique combining 248 nm pulsed laser ablation of C atoms and magnetron sputtering of Ti atoms, energetic fluxes of which were intersected on the steel substrate surface. Control of the film composition was achieved using the laser output parameters, which allowed pre-programmed variation from pure TiC phase to DLC phase through a two-phase region and enabled preparation of a range of composite TiC/DLC films. The phase transitions were investigated by XPS, XRD and high resolution SEM analyses. A hardness and elastic modulus maxima were found in a region, where TiC phase was embedded into DLC matrix. The correlation of deposition parameters, composition, morphology and mechanical properties of the films is discussed. The potential of the new technique for producing composite films with multifunctional mechanical characteristics is outlined.
10:00 AM		VM-TuM-6 Crystalline Alumina Deposited at Low Temperature by Reactive Ionized Magnetron Sputtering W. Sproul, J. Schneider (Northwestern University); A. Voevodin (Wright Laboratory); A. Matthews (University of Hull)
10:20 AM	Invited	VM-TuM-7 Intense Ion Beam Treatment of Materials D. Rej, H. Davis (Los Alamos National Laboratory); G. Remnev (Tomsk Polytechnic University); R. Stinnett (Quantum Manufacturing Technologies, Inc.); K. Yatsui (Nagaoka University of Technology, Japan) Over the past decade, researchers in Japan, Russia and the U.S. have been investigating the application of intense-pulsed-ion beams (IPIBs) for the surface treatment and coating of materials. The short range (0.1-10 \mu\m) and high-energy density (1-50 J/cm\super 2\) of these short-pulsed (t \<=\ 1 \mu\s) beams (with ion currents I = 5 - 50 kA, and energies E = 100 - 1000 keV) make them ideal flash-heat sources to rapidly vaporize or melt the near surface layer of targets, similar to the more familiar pulsed laser deposition or laser surface treatment. IPIB surface treatment is a thermal process that rapidly heats the surface to melt using only 10\super 13\ - 10\super 14\ ions/cm\super 2\/pulse, corresponding to an implanted species fraction of order 10\super -5\ at. in the treated surface region. Typical cooling rates of this process (10\super 9\ K/s) are sufficient to cause amorphous layer formation and the production of non-equilibrium microstructures (nano-crystalline and metastable phases). Treatment of O1 tool steel at 10\+-\3 J/cm\super 2\ results in the dissolving of C precipitates into the Fe matrix and a 3x increase in microhardness. Service lifetimes of treated steel drills, taps, and cutting tools are improved by 1.7 to 3.5 times. At higher beam power densities the target surface is vaporized, and the ablated vapor is condensed as coatings onto adjacent substrates or as nanophase powders. A variety of films have been prepared including diamond-like carbon, BN, metals (W, Te, Mo, Nb, Au, Al, Cu, Zn), YBa\sub 2\Cu\sub 3\O\sub 7-x\ superconductors, ZnS:Mn electroluminescent devices, BaTiO\sub 3\ dielectrics, and oxides such as ZrO\sub 2\. Ultra-fine powders of Al, Al\sub 2\O\sub 3\, TiO\sub 2\ and TiN with nanoscale grain (5 - 25 nm) have also been synthesized by evaporation of metallic targets in a background gas.
11:00 AM		VM-TuM-9 Morphology/Microstructure of Cu Films Fabricated via Directed Vapor Deposition P. Ratnaparkhi, H. Wadley (University of Virginia) A novel physical vapor deposition technique was recently developed that uses a differentially pumped e-beam gun for high rate evaporation and a supersonic inert gas jet to transport and deposit the vapor at high energies on the substrate. This results in unique deposition conditions as the growing film is bombarded with high energy metal and gas atoms. The operational principle of this directed vapor deposition (DVD) system is described and important process variables identified. Transmission electron microscopy and x-ray diffraction were used to characterize the temperature dependence of microstructure in Cu films fabricated using this system and the role of surface and bulk diffusion , granular epitaxy, surface energy and grain boundary mobility in controlling grain size and shape, porosity and film texture was explained. The results indicated that while some of the structural features such as column size and shape, porosity within a column, and grain structure could be interpreted using the widely studied structure zone models (SZM), significant discrepancies such as propagation of intercolumnar porosity (a zone I feature) and formation of large facets (a zone II feature) in the zone III temperature regime were also observed. Lastly, application of this process for metallization is discussed.
11:20 AM		VM-TuM-10 Aluminum-Silicon Carbide Interfaces: Effects of Ion Bombardment on Electronic Structure and Chemical Interactions F. Ohuchi, H. Beck (University of Washington) A detailed investigation into the SiC surface and its interaction with Al, in particular, focusing on the effect of ion bombardment, is described. This study has been motivated by the desire to further explore the phenomena of Surface Activated Bonding, a room temperature bonding technique developed by Suga. The fundamental process revolves around ion or fast atom bombardment, thus, the effect of surface activation and roughness, as well as possible surface stoichiometry changes, are explored. To this end, treatment of the SiC surface, aimed at producing clean, reconstructed or roughened, stoichiometric and/or carbon/silicon rich surfaces, have been investigated. A stoichiometric ion bombarded, a carbon rich reconstructed, and a carbon rich ion bombarded surface were all produced and analyzed, and the activity of these surfaces was compared with oxygen and aluminum adsorption. Cubic SiC has shown a preferential sputtering. While stoichiometrically sputtered surface showed vastly increased oxygen affinity, carbon rich sputtered surfaces did not. Aluminum deposition has caused significant Al-C interaction for the stoichiometric ion bombarded surface. Carbon rich surfaces have no significant interactions with as deposited Al, but may form aluminum carbide upon further ion bombardment, indicating the C surface layer is capable of interaction but requires an initial energy influx to disrupt strong surface C-C bonds.
11:40 AM		VM-TuM-11 Measurements and Modeling of the Angular-Resolved Sputtering Yield of Ar - Sputtered Al by 100 to 1000 eV Ar\super +\ P. Smith, R. Turkot, D. Ruzic (University of Illinois, Urbana-Champaign) The angular-resolved sputtering yield of Al by Ar+ was predicted and then measured. A 100 to 1000 eV ion beam from a Colutron was focused on to magnetron sputtering target Al samples. The Al samples were supplied by TOSOH SMD from a variety of manufacturig processes and with varying crystalographic orientations. The samples are exposed to an in situ dc Ar plasma to remove oxide, texturize the surface and more-nearly simulate steady state operating conditions in a magnetron. The angular distribution of the sputtered atoms was measured by collection on a highly ordered pyrolytics graphite witness plate. The areal density of Al and Al2O3 after exposure to air) was then measured using a Scanning Auger Spectrometer. Total yield is also measured by deposition onto a quartz crystal oscillator mounted alon side the witness plate. A three dimensional version of vectorized fractal TRIM (VFTRIM3D), a Monte-Carlo computer code which includes surface roughness characterized by fractal geometry, was used to predict the angular distribution of the sputtered particles and a global sputtering coefficient. Over 106 trajectories were simulated for each incident angle to determine the azimuthal and polar angle distributions of the sputtered atoms. A fractal dimension of 2.05, and a surface binding energy of 3.36 eV, both standard values for Al, were used.