Film thickness effects in the Ti-Si_1-xGe_x solid phase reaction

The effects of film thickness on the Ti-Si_1-xGe_x solid phase reaction were investigated. Thin C49 TiM₂ (M=Si _1-yGe_y) films were formed from the solid phase reaction of 400 Å Ti or 100 Å Ti with Si_1-xGe_x alloys. It was determined that for films formed from 400 Å Ti, the nucleation barrier of the C49-to-C54 transformation decreases with increasing germanium content, for alloy compositions with up to ≊40 at. % germanium (i.e., x≤0.40). It was also observed that germanium segregates out of the TiM ₂ lattice, for both the C49 and C54 phases, and is replaced on the TiM₂ lattice with Si from the substrate. The germanium segregation changes the Ge index y of the Ti(Si_1-yGe_y)₂. For films formed from a 100 Å Ti layer it was observed that the C54 TiSi₂ nucleation temperature was increased by ≥125°C. The addition of germanium to the silicon increased the agglomeration of the C49 phase and caused the C54 TiM₂ nucleation barrier to increase further. The results also indicate that the increased temperature required for the transition to the C54 phase, for the 100 Å films, leads to an increased rate of germanium segregation.