Enhancement of the formation of theC54phase ofTiSi2through the introduction of an interposed layer of tantalum

When annealing a Ti/Mo bilayer deposited on Si substrate, a layer of ${\mathrm{}(\mathrm{M}\mathrm{o},\mathrm{T}\mathrm{i})\mathrm{Si}}_2$ forms first and then acts as a template for the growth of the $C54\mathrm{}$ phase of ${\mathrm{TiSi}}_2$ at 650 °C that is about 100° lower than what is usually needed for the $C49\mathrm{}–C54\mathrm{}$ phase transformation. We show in this paper that using Ta instead of Mo as the interposing layer between Ti and Si also leads to the formation of the $C54\mathrm{}$ phase apparently without going through the otherwise usual sequence for the formation of ${\mathrm{TiSi}}_2,$ i.e., the $C49\mathrm{}$ phase forms as a result of the Ti-Si interaction and the $C54\mathrm{}$ phase forms as the product of phase transformation. The choice of Ta here is based on simple crystallographic considerations; the in-plane lattice mismatch between the basal planes of the hexagonal ${\mathrm{TaSi}}_2$ phase and the 〈010〉 planes of the $C54\mathrm{}$ phase is within 0.3%, a factor of 10 times better than that between the basal planes of the hexagonal ${\mathrm{}(\mathrm{M}\mathrm{o},\mathrm{T}\mathrm{i})\mathrm{Si}}_2$ phase and the 〈010〉 planes of the $C54\mathrm{}$ phase. No ternary phase seems to form in the Ta-Ti-Si ternary system, and Si is the dominant diffusion species in both binary systems Ta-Si and Ti-Si. Hence, the formation of the hexagonal ${\mathrm{TaSi}}_2$ phase at the interface between Ti and Si is expected to be straightforward without complications. The template growth of the $C54\mathrm{}$ phase is found unaffected by varying the conditions used for the metal deposition. The present results with Ta as well as with Mo confirm that the template mechanism is responsible for the enhanced formation of the $C54\mathrm{}$ phase of ${\mathrm{TiSi}}_2.$