Characterization of static and dynamic microstructures by microscopic interferometry based on a Fourier transform method

The surface profile and dynamic characteristics are some of the important specifications that influence the performance and stability of a MEMS device. Microscopic interferometry is, up to now, the most widely used technique for surface profiles of microstructures, and is also capable of measuring out-of-plane motion of microstructures with stroboscopic illumination. In this paper, a stroboscopic Mirau microscopic interferometer system was developed by integrating some commercially available components and instruments. In order to obtain a lower acquisition time and improve the measurement accuracy and stability of interference phases, an improved Fourier transform method (FTM) for fringe pattern analysis is described. It is necessary to process two interferograms with different phase shifting to achieve reliable phase demodulation in the measurement of surface profile. Out-of-plane motion can be calculated from one interferogram sequence, in which only one interferogram per motion phase is collected. Experimental studies of the measurement of a microcantilever surface profile and out-of-plane motion are described, and the measurement results are compared with that of a five-step phase-shifting method. It is demonstrated that stroboscopic microscopic interferometry based on a FTM can be used to determine the static and dynamic characteristics of microstructures.