Deformation of varifocal mirror with narrow frame by SOI wafer residual stress

Silicon-on-insulator (SOI) wafers are used for many micro-electro- mechanical systems (MEMS). The influences of residual stress of SOI wafer on the fabricated structures are important especially for micro-mirror because the optical performances are often affected by them. In this study, we propose an analytical calculation for the deformation of mirror and frame of a varifocal mirror. The deformations of the fabricated structures were measured using a white light interferometer. The frame was tilted at 2.8 mrad which was explained by the calculated value of 3.9 mrad. The mirror was deflected by 100 nm with the top-flat shape, which also agreed well with the proposed analysis.