Published online by Cambridge University Press: 25 February 2011
The reactions in sputter deposited Si-Ti-Si diffusion couples were investigated with X-ray diffraction, Auger electron spectroscopy and cross-section transmission electron microscopy. Anneals at a temperature of 400°C resulted in the growth of an amorphous phase at the Si-Ti interfaces. Crystalline silicides were only found after an anneal at temperatures of 500°C or higher.
It was demonstrated that an amorphous layer of approximately 8 nm thickness sustained a concentration gradient from about 73% Si at the Si side to about 28% Si at the Ti side of the diffusion couple. The measured width of the phase field agreed with the width predicted from a calculated free energy versus composition diagram. Actually the observed phase field was found to be so wide, that it contains the stoichiometry of all equilibrium silicides. The consequences of our results for the explanation of silicide first phase nucleation were discussed.