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Session Chairs: A. Zangwill, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332; S.A. Barnett, Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208
9:00 am INVITED
LOW-ENERGY ION AND HYPERTHERMAL NEUTRAL BEAMS FOR FILM GROWTH: EFFECTS ON NUCLEATION, MICROSTRUCTURE EVOLUTION, EPITAXIAL THICKNESS, ROUGHENING, AND STRAIN RELAXATION: Joe Greene, Materials Science Dept., Univ. of Illinois, Urbana, IL 61801
Low-energy (10-100 eV) ion and hyperthermal neutral irradiation during filmgrowth from the vapor phase are used to provide new chemical reaction pathways, modify film growth kinetics, and, hence, controllably alter film properties. During low-temperature epitaxial growth from hyperthermal Si beams, critical epitaxial thicknesses were increased by up to an order of magnitude over those obtained with MBE due to enhanced interlayer mass transport and more effective filling of interisland trenches. For heteroepitaxial Si1-xGex growth on Si(001), AFM and XTEM studies show that strain-induced roughening, which occurs at elevated growth temperatures, is strongly suppressed at Ts between 300 and 400°C, with no indication of low-temperature kinetic roughening. The use of low-energy primary- ion beam sources in which ion energy and ion/neutral flux ratios can be varied independently during the growth of Al, Cu, and TiN polycrystalline layers on SiO2 will be shown to provide dramatic differences in nucleation rates, mosaicity, preferred orientation, strain, and microstructure evolution.
9:40 am INVITED
GLANCING-ANGLE ION BOMBARDMENT FOR MODIFICATION AND MONITORING OF SEMICONDUCTOR SURFACES: J.G.C. Labanda, S.A. Barnett, Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208; Lars Hultman, IFM, Linköping University, S-581 83 Linköping, Sweden
Using glancing-angle ion bombardment for surface modification rather than conventional near-normal incidence ions has the advantages of reducing damage and implantation projected ranges, reducing channeling, reducing sputtering, and preferentially removing surface asperities leading to flat surfaces. The effect of bombardment conditions on the surface morphology and perfection of GaAs(001), InP(001) and Si(001) surfaces are reported. Air-exposed surfaces were cleaned and smoothened to near atomic flatness without damage for optimal conditions: for example, with GaAs this was observed for 1000 eV Ar ions incident at 15° from the surface plane at a dose of 2x1016 ions/cm2. For a given set of bombardment conditions, ion damage (observed as small dislocation loops in a 20-30 nm thick surface layer) decreased with decreasing ion incidence angle, and was eliminated below a critical angle. Sputtering yield, measured using film thicknesses and changes in reflection high-energy electron diffraction oscillations, decreased with decreasing incidence angle. The low sputtering yield and minimal damage make a glancing-angle geometry ideal for real-time characterization by ion scattering spectroscopy. Surface composition measurements on single monolayers of InAs on GaAs showed that the glancing-angle Ar beam did not did not measureably change the In coverage over relatively long times.
INFLUENCE OF PROCESSING PARAMETERS ON THE STABILITY OF MAGNETRON SPUTTERED DEPOSITED GROUP VI THIN FILMS: M.J. O'Keefe, Avionics Directorate, Wright Laboratory, WPAFB, OH 45433
Sputter deposition of metallic thin films is commonly used to fabricate electrically conducting contacts and interconnects on semiconductor devices. For military applications, the stability of the patterned metal under adverse environmental conditions, such as prolonged exposure to elevated temperatures, can significantly influence the reliability of the device. In this investigation the influence of magnetron sputter deposition processing parameters on the stress, adhesion, resistivity and crystal structure Group VI (i.e.. Cr, Mo, W) thin films was studied. The influence of elevated temperature on the stability of the films was evaluated, in part, using a Tencor Flexus-2900 thin film stress measurement system. Results from the study indicate that minor changes in processing conditions can significantly affect the as-deposited and elevated temperature properties of the films.
10:40 am BREAK
11:00 am INVITED
KINETIC ROUTES TO COHERENT ISLANDS: Andrew Zangwill, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332; Harvey T. Dobbs & Dimitri D. Vvedensky, Blackett Laboratory, Imperial College, London SW7 2BZ, UK
The Stranski-Krastanov growth morphology of heteroepitaxy consists of three dimensional islands that nucleate on top of a few strained layers of film material that wet the substrate. It is well understood on the basis of energetic considerations that such islands can be entirely free of misfit dislocations, i.e., coherent, until they grow rather large. But the kinetic processes that govern their formation are far less clear. Motivated by recent scanning tunnelling microscopy studies of this phenomenon for Ge/Si(111), InAs/GaAs(001), and InSb/GaAs(001), we present a combination of atomistic Monte Carlo simulations and mean-field rate theory designed to reveal the kinetic pathways to coherent islands. Particular emphasis is placed on the role of interface alloying and the dynamics of the wetting layers.
MORPHOLOGICAL INSTABILITIES AND EVOLUTION OF THIN FILMS: H. Wong, P.W. Voorhees, M.J. Miksis, S.H. Davis, Northwestern University, Evanston, IL 60208
The driving force for morphological evolution of thin films increases as the size of the films decreases. Thus, to further miniaturize microelectronic and optoelectronic devices, the morphological instability and evolution of thin films need to be understood. We study the linear instability of two film shapes commonly encountered in experiment: a strip on a substrate, and a hole in a uniform film on a substrate. We assume that the instability is driven by capillarity and the film evolves via surface diffusion. The contact angle is fixed at a value between 0 and 180 degree. We find that both film shapes are unstable to certain disturbances. We also simulate numerically the evolution of the film shapes triggered by an unstable disturbance to reveal new stable steady states. The implications of these results on the long term stability of solid-film devices will be discussed. *Supported by NSF and DOE.
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