Phase transition and dopant redistribution during silicidation of $CoSi_2$ thin films were characterized depending on their preparation methods. Our results indicated that cleanness of the substrate surface played an important role in the formation of the final phase. This effect was found to be reduced by addition of W resulting in the formation of $CoSi_2$. However, even in this case, the formation of the final phase was achieved at the cost of extra thermal energy, which induced rough interface between the substrate and the silicide film. As for the dopant redistribution, the deposition sequence of Co and Si on SiGe was observed to induce significant differences in the dopant profiles. It was found that co-deposition of Co and Si resulted in the least redistribution of dopants thus maintaining the original dopant profile.