Contributors: Zhihai Wang, D.B. Aldrich, Y.L. Chen, D.E. Sayers, and Robert J. Nemanich
ABSTRACT
The formation and stability of the products of Ti and Co reacting with Si1 − x Gex substrates were investigated. For the system, when a C54 Ti(Si1 − yGey)2 layer forms, the Ge index y is initially the same as the Ge index of the Si1−xGex substrate (i.e. y = x). Thereafter Si1 − xGex 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(Si1 − yGey)2 becomes silicon enriched (i.e. y < x). For the system, it was determined that a silicon-enriched Co(Si1 − yGey) 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 Si1 − zGe(z > x) islands were observed. It was found that for the reacted layer consisted of CoSi2 and Si1 − zGez, after high-temperature annealing (≈700 °C). We propose that these processes are driven by a reduction in the crystal energy of the C54 Ti(Si1 − yGey)2 phase in the system and the Co(Si1 − yGey) phase in the system which accompanies the replacement of Ge with Si.