Silicide formation in thin cobalt/poly-Si layers capped with Ti during annealing in the temperature range between 420 and 510 C was investigated by time-resolved sheet resistance measurements. We found that Formula nucleation is a fast process while Co diffusion through Formula grain boundaries is a slow process. Simulations of the resistance curves vs. time have shown that the pre-exponential factor of cobalt diffusivity is reduced by the presence of Ti contamination at the Formula grain boundaries, as it was shown by energy-filtered transmission electron microscopy analyses, whilst the activation energy does not change with respect to a reference.© 2004 The Electrochemical Society. All rights reserved.