Effect of Residual Gradient Stress of Cantilever Plate Structure Deposited Metal Layers with Different Constraints on Deformation

Abstract

Cantilever plate structure deposited metal layer is widely used MEMS. Due to mismatch of thermal expansion coefficients between structure and metal layers, residual gradient stress would be induced and deform structure as devices cooling down from process high temperature to room temperature. In this work, constraints effect is investigated. There are three constraints discussed and could be fabricated by back etching, isotropic wet etching, and anisotropic dry etching. For detail analysis, finite element method is used to analyze. Different width and length of structure sizes are used to discuss constraint effect. From the results, it is found different constraint would affect deformation. Under the same structure sizes, flat surface constraint has the largest deformation. And ICP etching constraint has the smallest deformation. Due to mechanics behavior of plate being much different comparing to beam, deformation of plate is no long parabolic shape in length direction. There are complex deformations in width direction. It is also found the deformation is determined by mechanics behavior on constraints. Width and constraint types have no significant on deformation when length is large at free end and middle section. And length has no significant effect on deformation for ICP and backside etching at clamped end. Temperature would induce increasing deformation linearly at free end and middle section.