Through-Transmissive-Media (TTM) Interferometric Techniques Applied to Characterizing Packaged MEMS and MOEMS Devices

摘要

MEMS (Micro-Electro-Mechanical Systems) and MOEMS (Micro-Opto-Electro-Mechanical Systems) are devices comprised of integrated mechanical, electrical and optical components, manufactured using techniques similar to those of integrated circuits. As in semiconductor manufacturing, quality control is the key to successful products-so much so that 50-80% of the cost of a MEMS device is incurred in final packaging and test. Optical profiling (white light interferometry), which combines high speed, accuracy, resolution and flexibility, has proven successful for measuring surface features of unpackaged MEMS devices. With the further productization of MEMS technology, however, devices also need to be tested in their final, packaged state, typically beneath a protective, transparent cover. Objectives capable of imaging through transparent media at low magnifications have been available for several years. Increasingly, however, higher magnifications are required to resolve smaller critical features. At high magnifications, transmissive media can greatly degrade interferometric measurements due to dispersion and aberration effects. In this paper we describe an improved technique for measuring MEMS features through transmissive media, at magnifications as high as 40X. The technique enables improved dispersion compensation, reduced coherence effects, thickness variation insensitivity, and enhanced illumination. Measurement results are presented, as well as examples of MEMS applications.