Nanostructural Analysis of CMOS-MEMS-Based Digital Microphone for Performance Optimization

In this paper, systematic analysis on the digital microphone is performed using energy dispersive X-ray spectroscopy (EDS) and transmission Kikuchi diffraction (TKD) in the scanning electron microscopy (SEM). Digital microphone is an integrated chip composed of complementary metal-oxide semiconductor (CMOS) and micro-electro-mechanical systems (MEMS). Using EDS, quantitative chemical composition and elemental maps on the integrated CMOS-MEMS-based microchip were obtained. Microanalytical X-Ray technique along with TKD was applied to reveal the nanostructure of the MEMS region, i.e., diaphragm membrane and then the CMOS region, i.e., tungsten through-silicon via. Device performance and lifetime were correlated with chemical diffusions, metal interface boundaries, grain structures, and phases existing at CMOS and MEMS junctions. Our results demonstrated that SEM-based TKD with EDS is a powerful microstructural characterization tool and performs vital role in failure analysis for device optimization.