The formation of CoSi₂ from an amorphous Co₇₀Ti₃₀ alloy film on Si(100) has been studied by Auger depth profiling, Rutherford backscattering spectrometry, cross-section transmission electron spectroscopy and X-ray diffraction. The solid-state reaction starts around 400 degrees C with the diffusion of Co out of the alloy into the substrate, forming an interface layer consisting of CoSi and CoSi₂. The simultaneous diffusion of Si into the Co-depleted region of the film is limited for annealing temperatures below 600 degrees C. After removing the remaining top layer by selective etching, an extra heat treatment is performed to transform the mixed silicide layer completely into CoSi₂. The latter is found to be partially aligned with the substrate. The amount of epitaxial CoSi₂ increases with the use of higher post-anneal temperatures.