Interface Stability of Ti(Si_1−yGe_y)₂ and Si_1−xGe_X Alloys

Abstract

The stability of C54 Ti(Si_1−yGe_y)₂ films in contact with Si_1−xGe_x substrates was investigated. The titanium germanosilicide films were formed from the Ti − Si_1−xGe_x solid phase metallization reaction. It was observed that Ti(Si_1−yGe_y)₂ initially forms with the same germanium content as the Si_1−xGe_x substrate (i.e., y = x). Following the initial formation of TiM₂ (M = Si_1−yGe_y), silicon and germanium from the substrate diffuse into the TiM₂ layer, the composition of the TiM₂changes, and Si_1−zGe_z precipitates form along the TiM₂ grain boundaries. The germanium content of the Ti(Si_1−yGe_y)₂ decreases, and the Si_1−zGe_z precipitates are germanium rich such that y < x < z. This instability of the TiM₂ film and the dynamics of the germanium segregation were examined using the Ti-Si-Ge ternary equilibrium diagram. The relevant region of the ternary diagram is the two phase domain limited by a Si-Ge solid solution and a TiSi₂–TiGe₂ solid solution. In this study first approximation Ti(Si_1−yGe_y)₂ -to- Si_1−xGe_x tie lines were calculated on the basis of classical thermodynamics. The tie line calculations indicate that for C54 Ti(Si_1−yGe_y)₂ to be stable in contact with Si_1−xGe_x, the compositions of the two phases in equilibrium must be such that y < x. The specific compositions of the two phases in equilibrium depend on the temperature and the relative quantities of the two phases. The dynamic processes by which the Ti(Si_1−yGe_y)₂/Si_1−xGe_xsystem progresses from the as-formed state (y = x) to the equilibrium state (y < x) can be predicted using the tie line calculations.