Stability of C54 titanium germanosilicide on a silicon-germanium alloy substrate

The stability of C54 Ti(Si_1-yGe_y)₂ films in contact with Si_1-xGe_x substrates was investigated. The C54 Ti(Si_1-yGe_y)₂ films were formed from the Ti-Si_1-xGe_x solid phase metallization reaction. It was determined that initially C54 Ti(Si_1-yGe_y)₂ forms with a Ge index y approximately the same as the Ge index x of the Si _1-xGe_x substrate (i.e., y≊x). After the formation of the C54 titanium germanosilicide, Si and Ge from the Si_1-xGe _x substrate continue to diffuse into the C54 layer, presumably via lattice and grain boundary diffusion. Some of the Si diffusing into the C54 lattice replaces Ge on the C54 lattice and the Ge index of the C54 Ti(Si _1-yGe_y)₂ decreases (i.e., y<x). We propose that this process is driven by a reduction in C54 crystal energy which accompanies the replacement of Ge with Si on the C54 lattice. The excess Ge diffuses to the C54 grain boundaries where it combines with Si _1-xGe_x from the substrate and precipitates as Si _1-zGe_z which is Ge-rich relative to the substrate (z≳x). This segregation and precipitation enhances the agglomeration of the C54 titanium germanosilicide film (i.e., lower agglomeration temperature). It was observed that rapid thermal annealing techniques could be used to reduce the annealing duration and resulted in a reduction of the Ge segregation.