Flatness maintenance and roughness reduction of silicon mirror in chemical mechanical polishing process

As an important optical component in laser system, silicon mirror surface is required to have micron-level flatness and subnanometer-level roughness. The research concentrates on how to improve roughness as far as possible while maintaining flatness of silicon mirror surface during chemical mechanical polishing (CMP) process. A polishing edge effect model is established to explain the reason of flatness deterioration, and a roughness theoretical model is set up to get the limit of perfect surface roughness. Based on the models above, a polishing device is designed to maintain the surface flatness, and the optimized polishing process parameters are obtained by orthogonal tests to get a near-perfect surface roughness. Finally the maintenance of flatness and the improvement of roughness can be achieved at the same time in one step of CMP process. This work can be a guide for silicon mirror manufacture to improve optical reflection performance significantly.