By using two sets of Raman systems with excitation lines of 514.5 and 632.8 nm, the influence of annealing ambience was investigated on the formation of cobalt silicides. The results show that a more uniform, compact and thermal stable cobalt silicide film can be formed in the hydrogen annealing ambience than that in the Ar annealing ambience. Two characteristic bands located at 305 and 325 cm(-1), which may be assigned to the CoSi. and COSi2, respectively, were found during the phase transition processes. The strong band which appeared at 325 cm(-1) that can only be detected with the excitation line of 632.8 nm was found to be due to the resonant Raman effect. (C) 2003 Elsevier Science B.V. All rights reserved.