Dynamic out-of-plane profilometry for nano-scale full field characterization of MEMS with automatic detection of vibratory modes and MHz-scale measurement bandwidth

Abstract

A dynamic 3-D nano-scale surface profilometer using stroboscopic white light interferometry with novel image deconvolution and automatic identification of structure resonant modes was successfully developed. As micro electromechanical systems (MEMS) increase rapidly towards industrial application, the needs of accurate dynamic characterization are extremely important to optimal design and fabrication. To meet the demands, an optical microscopy based on stroboscopic interferometry was developed to achieve full-field vibratory out-of-plane surface profilometry and system characterization. A novel deconvolution strategy with correction of the light response function was established to remove the potential image blurs caused by the unavoidable vibration of the tested parts. With this technical advance, the bandwidth of dynamic measurement can be significantly increased up to 10 MHz without sacrificing measurement accuracy. Meanwhile, an innovative detection algorithm based on image contrast measure was developed for automatic identification of accurate resonant modes. The detection method provides the simplest and most economic way to detect accurate resonant peaks without adding any significant hardware in a stroboscopic interferometric framework. To verify the effectiveness of the developed methodology, AFM cantilever beams were measured to analyze the full-field resonant vibratory modes and dynamic characteristics. The experimental results confirm that the resonant vibration behavior of the tested microcantilever beams can be accurately characterized and 5 nm of vertical measurement accuracy as well as tens micrometers of vertical measurement range can be achieved. The measured results were satisfactorily consistent with the theoretical simulation outcomes from ANSYS.