Recently, RB SiC as a two-phase mirror material has taken particularly attraction because of its readily formable to near-net-shape. But it is difficult to obtain high quality optical surface due to the polish rate differences between SiC and Si components. Typical defects, such as polishing scratches, pores and surface irregularities which are mostly caused by the inhomogeneity of SiC and Si phase distributions are easily detected. The solution is the addition of a thick coating to cover these surface defects which may be polished to improve the quality of optical surface. Two thick coatings, PVD Si and PVD SiC, were applied by RF magnetron sputtering in this paper. After a series of sputtering parameters optimization, both the coatings' surfaces show fewer defects than that of RB SiC after polished. Results from this PVD progress, the surface morphologies' changes in optimization and the surface defects after polished are presented.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.