Self-diusion of silicon in TiSi 2 competing phases by tight- binding molecular dynamics Marcella Iannuzzi a,b , Paolo Raiteri a,b , Leo Miglio a,b, * a Istituto Nazionale di Fisica della Materia (INFM), Italy b Dipartimento di Scienza dei Materiali, Universit  a di Milano-Bicocca, via Cozzi 53, I-20125, Milano, Italy Received 15 February 2000 Abstract Tight-binding (TB) potentials allow for a straightforward separation of the binding and repulsive contributions in the total energy. This issue can be used in molecular dynamics runs to correlate the local atomic structure to the diusion paths and the activation energies of silicon mobility in TiSi 2 , which is the most common material for me- tallisations and local interconnects in microelectronic devices. In this work we focus on the self-diusion process at high temperature and a relation between the crystal structures and the diusion paths for the two competing phases is drawn. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction Titanium disilicide is commonly applied in in- tegrated circuits, for local interconnects, gate me- tallisations and Schottky barriers due to its high thermal and electrical conductivity, strong adhe- sion with silicon substrate and high corrosion re- sistance. The growth of TiSi 2 is usually obtained by solid state reaction: a Ti layer is in fact de- posited on top of the silicon substrate and the silicide formation at the interface is then activated by a thermal treatment [1±6]. TiSi 2 has two competing crystalline structures. The stable phase, which is the only one existing as monocrystal, is the C54 phase. The other one, the C49 phase, appears during the formation of the polycrystalline ®lm by solid-phase reaction or by epitaxial growth. It is the ®rst phase which is formed around 450±600°C [4±6] and for this rea- son the C49 is said to be kinetically favoured. Still, the thermal and electrical conductivity are far be- low the ones of the C54 phase and a further heating at higher temperatures (650±800°C) is then necessary to achieve the latter, through a poly- morphic transformation which occurs by means of nucleation and growth [7]. Since the growth of the silicide at the Ti/Si in- terface is supported by atomic diusion along the grain boundaries, we are interested in verifying which is the mobile species in TiSi 2 . The growth should be sustained by Si upward diusion through the growing layer, but no direct evidence that silicon is the mobile species has been given (e.g., in other transition metal disilicides, such as CoSi 2 , the diusive species is the metal). Since two competing phases are present in TiSi 2 , it is inter- esting to check if this is true for both structures, at www.elsevier.com/locate/commatsci Computational Materials Science 20 (2001) 394±400 * Corresponding author. Tel.: +39-2-6448-5217; fax: +39-2- 6448-5403. E-mail address: leo.miglio@mater.unimib.it (L. Miglio). 0927-0256/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 0 2 5 6 ( 0 0 ) 0 0 1 9 9 - 3