Dynamic MEMS measurement using a strobed interferometric system with combined coherence sensing and phase information

To assure proper MEMS performance, accurate metrology of the devices during actuation is required. Stiction, motion versus drive signal, radii of curvature changes, angular repeatability and resonant frequency are all of interest. By obtaining topographic information as these drive conditions are varied, MEMS devices can be fully characterized. Interference microscopes have long been used to obtain MEMS topography. Through the addition of a strobed-illuminator, the motion of a device can be effectively frozen. By varying the phase, frequency and drive signal of the strobe and MEMS device, a complete picture of the motion can be obtained. Topologies and motions of several millimeters may be measured with nanometer-level accuracy. This paper describes the design of the hardware and software for a strobed interference microscope for MEMS metrology. We present data on MEMS devices showing their motion under different conditions and relating that data to critical part parameters.