Design of a long range bidirectional MEMS scanner for a tunable 3D integrated Mirau interferometer

Abstract

Mirau interferometers are two beam interferometers with coaxial optical beams that are widely used in full-field optical surface profilers. An integrated Mirau interferometer with a MEMS mirror scanner is proposed in this paper. The novelty of the scanner design is the use of self-aligned vertical electrostatic combs made in double SOI wafer technology which allows a large range, bidirectional, and symmetric vertical translation of the reference mirror. Electrostatic and mechanical analytical calculations and Finite Element Modeling simulations were carried out to design and optimize the MEMS scanner. A large bidirectional range (+/-20 μm) motion under 60V applied voltage is achievable. Good flatness of the reference mirror is preserved during motion, what is essential for interferometrie measurements. A fabrication process which minimizes the number of mask levels is proposed. It is based on front and back side Deep Reactive Ion Etching and dry film photoresist lithographic steps.