Finite element analysis of deflection and residual stress on machined ultra-thin silicon wafers

Abstract

The demand for ultra-thin silicon wafers has escalated in recent years with the rapid development of miniaturized electronic devices. Residual stress generated in the thinning process has a great influence on the machining quality of ultra-thin wafers. This work has developed a 2D axisymmetric finite element (FE) model to predict the deflection and full-field residual stress of ground ultra-thin wafers. The FE model consists of two-layer structures, i.e. a damage layer induced by the thinning process and a bulk silicon crystal layer without defects. A series of uniform in-plane strains is applied to the damage layer to simulate machining-generated initial stress. A full-field residual stress distribution in a machined ultra-thin wafer is predicted with the developed FE model after the initial stress is released. Based on the FE model, effects of wafer geometrical dimensions and loaded initial strain (or stress) on the maximum compressive/tensile residual stress and the maximum wafer deflection are revealed. The model is finally verified by comparing the simulated wafer deflection with the measured value. Based on this work, the deflection and residual stress of a machined ultra-thin wafer can be conveniently predicted.