The irradiation effects of 2 MeV He+ and Ar+ ions on the film structure of the C-Si system were investigated with RHEED and XPS. The formation of SiC phase and/or the growth of epitaxial SIC were possible by He+ irradiation for the carbon films up to 0.7 nm in thickness, which was thinner than that by Ar+ irradiation. The He+ irradiation could not grow the turbostratic graphite which could be grown by Ar+ irradiation. The mechanism of the formation and the epitaxial growth of SiC by ion irradiation was discussed from the view point of the energy transfer from the irradiated ions.