Computational Simulation on Thermal Aspect of Micro-Fabrication Process for MEMS Device

Abstract

The inherent residual stresses and strains from micro fabrication process can have profound effects on the functionality and reliability of MEMS devices. Surface micromachining fabrication involves a series of sequential steps of addition and subtraction of materials through deposition and etching techniques. For instance, when a typical micro cantilever beam is fabricated, layers of silicon dioxide and polysilicon structures are deposited on top of silicon substrate. Part of the silicon dioxide layer is chemically etched out before the deposition of polysilicon layer. Due to mismatch of coefficients of thermal expansion (CTE) in layered structure, thermal cycle loading during micromachining fabrication can induce significant residual stress within a part from thermal aspect alone. Computational method is used to simulate the micromachining fabrication process for MEMS and to predict the residual stresses/strains in a selected MEMS device. The focus of the study is on the thermal aspect of deposition and etching processes during micromachining. Particular attention is placed on the effects of deposition temperature and polysilicon film thickness on resulting residual stresses.