Columnar Epitaxy of Hexagonal and Orthorhombic Silicides on Si(111)
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COLUMNAR EPITAXY OF HEXAGONAL AND ORTHORHOMBIC SILICIDES ON Si(111) R.W. FATHAUER*, C.W. NIEH**, Q.F. XIAO,*** AND SHIN HASHIMOTO*** *Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109 **Keck Laboratory of Engineering, California Institute of Technology, Pasadena, CA 91125 (Present address: Hughes Research Laboratories, 3011 Malibu Canyon Road, Malibu, CA 90265) ***Physics Department and Institute for Particle-Solid Interactions, State University of New York at Albany, 1400 Washington Ave., Albany, NY 12222 ABSTRACT Columnar grains of PtSi and CrSi2 surrounded by high-quality epitaxial silicon are obtained by ultra-high vacuum codeposition of Si and metal in an approximately 10:1 ratio on Si(111) substrates heated to 610-840"C. This result is similar to that found previously for CoSi2 (a nearly-lattice-matched cubic-fluorite crystal) on Si(111), in spite of the respective orthorhombic and hexagonal structures of PtSi and CrSi 2 . The PtSi grains are epitaxial and have one of three variants of the relation defined by PtSi(010)//Si(111), with PtSi[001Y/Si. INTRODUCTION Metal silicides are technologically important materials, finding application in such technologies as integrated circuits and infrared-sensor focal-plane arrays [1,2]. PtSi has Schottky-barrier heights of 0.87 eV and 0.2-0.25 eV to ntype and p-type silicon, respectively, and a room-temperature resistivity of 28-35 1•1-cm L1,2]. The monosilicide has an orthorhombic structure with a=5.93 A, b=5.59 A, and c=3.60 A [2]. Partial epitaxial growth of PtSi on Si (111) has been reported [3,4], but single-crystal films have not been demonstrated. Instead, epitaxial grains related by 1200 rotations are observed [3]. CrSi 2 is a semiconductor with an indirect bandgap of approximately 0.35 eV [5]. It has a hexagonal structure, with a=0.443 nm and c=0.636 nm [6]. While there is a nearly lattice-matched orientation of CrSi2 on Si(111), the epitaxial unit cell is relatively large [6]. As a result, attempts at growing single-crystal CrSi 2 layers on Si(111) by molecular beam epitaxy (MBE) techniques have produced films containing multiple epitaxial orientations [6]. Buried films of CrSi 2 formed by Cr+ implantation and annealing have been reported with Rutherford backscattering (RBS) channeling minimum yields of 7% [7]. Recently, a unique epitaxial structure was demonstrated in the CoSi2/Si system consisting of epitaxial columns of CoSi 2 surrounded by epitaxial silicon [8]. This structure was obtained by MBE coevaporation of Co and Si on a heated Si substrate in a ratio highly silicon rich relative to the stoichiometric ratio, a technique referred to as "columnar epitaxy". Note that, in contrast to PtSi and CrSi2, CoSi2 has a similar crystal structure (cubic fluorite) to that of Si, and lattice matches Si to 1.2%. Not only have high-quality CoSi2 layers been grown, but multiple-layer epitaxial CoSi2/Si structures have been demonstrated [9]. We have found that the columnar epitaxy technique also works for the PtSi/Si an
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