We have used cross-section and through-foil TEM, RBS, and x-ray diffraction to investigate reactions upon rapid thermal annealing of sputtered Ti-Si multilayers of various compositions and bilayer spacings. This study addresses the behavior of the Ti-Si interface at low annealing temperatures (T< 600δC) to determine the extent to which interdiffusion occurs prior to suicide formation, and to detect the formation of the first suicide at an early stage. Whereas most previous work studied a single Ti-Si interface, we have used multilayer films because a reaction occurs at many interfaces, allowing detection of a phase even if it is formed to a very limited extent.
The silicon layers in the as-deposited films are amorphous; the titanium layers are polycrystalline hep. The compositions of the samples are 40 at.% Ti, 60 at.% Si and 60 at.% Ti, 40 aL% Si, and the bilayer periodicity is about 10 nm. After a 30 second anneal at 455°C, significant interdiffusion occurs and we observed the formation of an amorphous Ti-Si alloy by interfacial reaction. The metastable disilicide, C49 TiSi2, nucleated along with a small amount of TiSi in the sample with higher silicon content (60%) upon annealing at 550°C for 10 seconds, but the amorphous alloy remained as the only product of reaction in the 40 at. % Si sample. Cross-section TEM of a sample fabricated at 60°C suggests that interdiffusion had begun during deposition of the films.