Experimental study on roughness and flatness of micromirror fabricated by different anisotropic silicon etching processes

Fabrication of flat, free-standing silicon diaphragms as micromirrors using etching processes is the key in the development of optical Micro-Elecro- Mechanical System(MEMS) devices, such as tunable F-P(Fabry-Perot) filters. It is very important for etching process to get smooth surface and uniform depth because they greatly affect the performance of the final device. In this paper, we report the experimental results about roughness and flatness of silicon micromirror fabricated by wet and dry etching processes. The investigated process involved wet-etching process in self-prepared KOH solution, and dry etching process with such machines as ALCATEL 601E DRIE(Deep Reactive Ion Etching) and STS ICP (Inductivity Coupling Plasma). It was found that wet etching process could supply more uniform etching depth, whereas the better surface roughness was gotten by dry etching. For a 30μm target depth, surface roughness less than 3-nm and maximal depth difference less than 0.3-μm were obtained by STSICP and KOH respectively.