Silicide formation and stability of Ti SiGe and Co SiGe

The formation and stability of the products of Ti and Co reacting with Si_{1 - x} Ge_x substrates were investigated. For the Ti SiGe system, when a C54 Ti(Si_{1 - y}Ge_y)₂ layer forms, the Ge index y is initially the same as the Ge index of the Si_1-xGe_x substrate (i.e. y = x). Thereafter Si_{1 - x}Ge_x from the substrate continues to diffuse into the C54 layer via lattice and grain-boundary diffusion. Some of the Si which diffuses into the C54 lattice replaces Ge in the lattice, and the C54 Ti(Si_{1 - y}Ge_y)₂ becomes silicon enriched (i.e. y < x). For the Co SiGe system, it was determined that a silicon-enriched Co(Si_{1 - y}Ge_y) layer was formed at ~ 400 °C. As the annealing temperature was increased, the reacted layer became even more Si enriched. For both materials systems, Ge-enriched Si_{1 - z}Ge(z > x) islands were observed. It was found that for Co Si₁ - xe_x the reacted layer consisted of CoSi₂ and Si_{1 - z}Ge_z, after high-temperature annealing (≈700 °C). We propose that these processes are driven by a reduction in the crystal energy of the C54 Ti(Si_{1 - y}Ge_y)₂ phase in the Ti SiGe system and the Co(Si_{1 - y}Ge_y) phase in the Co SiGe system which accompanies the replacement of Ge with Si.