Epitaxial Growth and Stability of C 49 TiSi 2 on Si(111).
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EPITAXIAL GROWTH AND STABILITY OF C49 TiSi2 ON Si(111). Hyeongtag Jeon, J. W. Honeycutt, C. A. Sukow, T. P. Humphreys, R. J. Nemanich, and G. A. Rozgonyi Department of Physics and Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-8202 Abstract Epitaxial TiSi 2 films have been grown by molecular beam epitaxy (MBE) on atomically clean Si(l 1I1)-orientated substrates. The growth procedure involves the ambient temperature deposition of Ti films of 50A thickness and annealing to 800'C. In situ low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) techniques have been used to monitor the TiSi 2 formation process. The epitaxial films have been identified as the C49 metastable phase by both Raman spectroscopy and electron diffraction. Plan view transmission electron microscopy shows three different connected island morphologies. The individual island structures are single crystal and are grown epitaxially with different crystallographic orientations. The orientational relationship of the largest islands is given by [3 1 11 C49 TiSi2//[112]Si and (130) C49 TiSi2//(l 1 )Si. High resolution transmission electron microscopy (HRTEM) cross-section shows a coherent interface extending over several hundred angstroms.
Introduction Epitaxial silicides are considered for use as low resistivity contacts and in novel high speed devices structures such as metal based transistors. To date, the growth of epitaxial silicides such as CoSi2 and NiSi 2 which have a cubic crystal structure have been widely reported. TiSi 2 among the silicides is one of the best candidates for VLSI application because it exhibits low resistivity and a high temperature stability. Thin film reaction of Ti on Si results in the formation of two different forms of TiSi 2 which have been identified as the C49 and C54 crystal structures [1]. Both structures are orthorhombic. The C49 phase is metastable (ie. it is not represented in the binary phase diagram), and forms at temperatures from 450 to 600'C. The stable C54 phase forms after higher temperature annealing to > 650'C. While the TiSi2 films formed by reaction are already important for VLSI applications, there are only a few reports which have demonstrated TiSi 2 epitaxy for the corresponding C49 and C54 TiSi 2 phases [2,3,41. It has recently been shown that for Ti thicknesses < 100,A, the metastable C49 phase is stable to temperatures > 800'C. This temperature is higher than the 650'C temperature where the transition to C54 TiSi 2 occurs for thicker films. In this paper we present results pertaining to the nucleation, morphology and epitaxial growth of thin film C49 TiSi 2 on Si( 11l)-oriented substrates. Previous studies have related the nucleation and island formation aspects of TiSi 2 /Si to the surface and interface energies of the materials. In this study different island morphologies are identified. In all cases the islands are epitaxial, and the corresponding crystallographic orientational relationships are determined from selected
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