Smooth and highly conductive(18${mu}{Omega}$ㆍcm) CoS$i_2$filme were obtained by means of rapid thermal annealing(RTA) process from the deposited Co layers on Si by e-beam evaporation. Crystal phase transition, film morphologies and atomic species distribution of silicides were studied by XRD, SEM, TEM, and SIMS. The sheet resistances of cobalt silicides were affected by the base pressure during Co metal evaporation and the annealing temperature. It was found that sheet resistances of the films annealed below 75$0^{circ}C$ fpr 20s were lowered greatly with the decreasing of the base pressures form 4${ imes}{10^{-6}}$ to 6${ imes}{10^{-7}}$Torr during Co evaporation. For the Co films with 260$AA$thickness, the CoS$i_2$ phase with the (110) preferred orientation was formed after annealing at 50$0^{circ}C$ for 20s in $N_2$ ambinet. From the TEM micrographs, the formed CoS$i_2$/Si layer annealed at 85$0^{circ}C$ for 20s showed smooth seftional surface with a relatively large grains(about 0.15${mu}{ extrm}{m}$). According to SIMS analysis, oxygen was detected in the as-deposited film and Co penetrates into Si region to form CoS$i_2$.