Accurate Identification of the Evolution of MEMS Resonant Accelerometer Residual Stresses at the Wafer-Die-Chip Level

Abstract

In this work, the processing error including the overetching error and residual stresses in the manufacturing process of a microelectromechanical system (MEMS) resonant accelerometer is identified. The performance of the accelerometer is affected by the processing error, especially the residual stress due to the multiple temperature loads in the manufacturing process. Thus, it is essential to identify the processing error for a high-precision MEMS resonant accelerometer. The overetching error is assessed using the sensitivity of the accelerometer resonator. With the multi-step measurement of the resonator frequency variation in the packaging process, the residual stresses of the MEMS accelerometer at different stages are decomposed and identified, combined with surface morphology measurement and finite element analysis simulations. The results of the analysis demonstrate that: 1) The processing error distribution of the accelerometer at the wafer level is related to the morphology of the wafer, which is decided by the low-order main vibrating modes. 2) The residual stress is distributed from high to low from the center to the edge in the wafer. 3) The residual stress at the wafer level is the main part of the MEMS accelerometer when low-stress packaging technology is adopted at the chip level. 4) The variation of the residual stresses in the manufacturing process is a non-monotonic process. The accurate identification of the processing error provides an effective foundation for the improvement and optimization of the MEMS resonant accelerometer. [2022-0041]