Lattice Distortion Formations by Low-Energy Ar + Bombardment of Thin Silicon Films Grown on Silicon (100)
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stal growth techniques such as molecular beam epitaxy (MBE), sputter deposition, and chemical vapor deposition have made possible the growth of silicon thin films, which are important for the fabrication of solid-state devices. It has become clear that low-energy ion beams play an important role in influencing the processing of silicon thin films. Lowenergy ion beams are used to sputter surfaces as well as clean and etch them, enhance dopant incorporation during the growth modes of the films, and shorten the kinetic formations of silicides.[1–4] The development of strain (stress) in thin silicon layers evolves during epitaxial growth as a result of the migration and interaction of defects on the surface. During MBE, adatom defects are added to the surface constantly. The resulting silicon levels of strain and surface morphology are determined by the incorporation of these defects into the surface, which in turn, are influenced by the presence of other adatoms, terrace ledges, clusters, and dislocations formed during higher aging temperatures. Similarly, during ion bombardment, ion-induced defects (surface vacancies and, to a lesser extent, adatoms) are created, which must be incorporated into the surface. Distortion in crystals caused by impurity atoms point defects can result in diffuse scattering. Essentially, the peculiarities of the diffuse scattering intensity distribution (isodiffuse surface shape) in the reciprocal lattice space depend on the defect type, its position in crystal lattice, and the interaction between defects with matrix PAUL ROZENAK, Director, is with the Hydrogen Energy Batteries LTD, Omer 84965, Israel. Contact e-mail: [email protected] Manuscript submitted February 9, 2010. Article published online June 12, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
atoms. By means of diffuse X-ray and transmission electron microscopy (TEM) data, it is possible to analyze defect types and their characteristics during aging treatments in epitaxial silicon growth. The study of low-energy beam–surface interactions is motivated by the need for more sophisticated understanding and lattice control of film growth processes. To produce precise lattice-controlled structures with atomically abrupt interfaces at the nanometer scale, processes need be developed that occur near thermodynamic equilibrium to those cases limited by surface kinetic phenomena.
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EXPERIMENTAL
The silicon films were grown in an MBE system with two beam sources and a Kaufman-type ion source capable of Ar+ ion beam at energies of 50 eV to 1200 eV. The base pressure of the system was between 1 9 1010 torrs and 1 9 1011 torrs. During operation of the ion gun, the system was back-filled with Ar gas to a pressure of 8 9 105 torr. Distorted silicon films 1000 A˚ thick were grown at a constant rate between 0.08 9 109 m/s and 0.2 9 109 m/s on a (001) silicon wafer in the direction of [001] after the growth of a 500A˚ buffer layer of pure silicon by conventional MBE. Ion-assisted beam/atom films grown by beam flux rations were in the range of 1:10 thro
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