Microscopic interferometry for dimensional characterization of MEMS devices

Abstract

Microscopic interferometry for dimensional characterization and device inspection is described in this paper. This method is characteristic of fast speed, non-destructive, non-contact, and easy to be carried out at wafer scale with submicrometer lateral resolution and nanoscale vertical resolution. The measurement system is based on a Mirau microscopic interferometric objective with a piezo objective nano-positioner to realize accurate phase shifting and scanning in vertical direction in the range of one hundred micrometers. The method consists of phase shifting interferometry (PSI) and vertical scanning interferometry (VSI), the former can measure smooth surface with high accuracy and the latter can measure samples with large step variations. The measurement accuracy of the system is calibrated by a step height standard certificated by NIST. Two MEMS devices are employed to illustrate the capability of the system which is regarded as as a measurement and process characterization tool.