Interface stability of Ti(Si1-yGey)2 and Si1-xGex alloys

Contributors:   D.B. Aldrich, F.M. D'Heurle, D.E. Sayers, and Robert J. Nemanich

ABSTRACT

The stability of C54 Ti(Si1-yGey)2 films in contact with Si1-xGex substrates was investigated. The titanium germanosilicide films were formed from the Ti - Si1-xGex solid phase metallization reaction. It was observed that Ti(Si1-yGey)2 initially forms with the same germanium content as the Si1-xGex substrate (i.e., y = x). Following the initial formation of TiM2 (M = Si1-yGey), silicon and germanium from the substrate diffuse into the TiM2 layer, the composition of the TiM2 changes, and Si1-zGez precipitates form along the TiM2 grain boundaries. The germanium content of the Ti(Si1-yGey)2 decreases, and the Si1-zGez 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(Si1-yGey)2 -to- Si1-xGex tie lines were calculated on the basis of classical thermodynamics. The tie line calculations indicate that for C54 Ti(Si1-yGey)2 to be stable in contact with Si1-xGex, 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(Si1-yGey)2/Si1-xGex system progresses from the as-formed state (y - x) to the equilibrium state (y < x) can be predicted using the tie line calculations.

Publisher: Materials Research Society Symposium Proceedings,   Volume: 402,   21-26 ||  Published: 1996-01 ||   Read more...