反应烧结碳化硅(RB-SiC)是一种性能良好的反射镜镜胚材料，但其固有的一些缺陷导致未经特殊处理无法获得光滑的光学表面。使用X 射线衍射(XRD)测试了反应烧结碳化硅试片的晶体结构，结果表明其主要成分为多晶态碳化硅和多晶态硅。扫描电子显微镜和原子力显微镜的测试结果指出镜胚表面残留的孔洞及抛光形成的台阶是造成散射降低光学性能的原因。通过等离子辅助沉积技术在反应烧结碳化硅表面镀制了一层硅改性层，消除了缺陷，再精细抛光硅改性层，获得了质量良好的光学表面。自行搭建的总积分散射仪对镀制硅改性层前后的反应烧结碳化硅表面进行了测量，总积分散射分别为9.37%和1.84%，改性后数值降低到改性前的1/5。反应烧结碳化硅反射镜光学性能得到了明显提高，接近抛光良好的K9 玻璃。

Reaction bonded silicon carbide (RB-SiC) is a kind of mirror substrate material with good performance, however, it′s difficult to obtain fine surface without special treatment for the intrinsic defects. Xray diffraction (XRD) is used to measure the crystal structure of the RB-SiC substrate, polycrystalline silicon carbide and polycrystalline silicon are the main composition. The residual pin holes and steps on the surface observed by scanning electron microscope (SEM) and atomic force microscope (AFM) cause the scattering and decrease the optical performance directly. A silicon surface modification coating is deposited on the RB-SiC surface by the plasma ion assisted deposition (PIAD), and the defects are eliminated, a fine optical surface is achieved after polishing the silicon surface modification coating. Total integrated scattering of bare RB-SiC and the surface after surface modification is measured by a self-made scatterometer, the results are 9.37% and 1.84% , respectively, the value after modification is only 1/5 compared to that of the bare RB-SiC. Great optical performance improvement of the RB-SiC mirror is achieved, and it′s almost close to the performance of the fine polished K9 glass.