The formation of thin (<15 nm) cobalt silicide layers on amorphous silicon (a-Si) has been investigated as a part of a program involving the fabrication of poly-Si-based single electron transistors. Rapid thermal annealing was used to promote the reaction between the a-Si and cobalt metal films. The effects of three most important factors on silicide formation during annealing (temperature, temperature ramp rate, and anneal time) were studied using both electrical (sheet resistance) and surface analysis (Auger electron spectroscopy) techniques. In particular, the impact of temperature ramp rate on silicide formation has been addressed. The optimization of the thin silicide process has been achieved by a statistical analysis. Transmission electron microscopy cross-sectional analysis has been performed to determine the thickness of the film.