Simulation of Cu bulge-out by cyclic Cu surface diffusion FEM in Cu/SiCN hybrid bonding

Elastic strain energy density (ESED) driven surface self-diffusion was previously identified as the mechanism underlying the Cu bulge-out phenomenon in wafer-to-wafer (W2W) hybrid bonding structures with unequal sized pads. Being able to predict the Cu bulge-out allows widening the CMP process window and increasing the yield. In this paper, an iterative finite element method (FEM) model is developed to track the evolution of ESED on the Cu pad surface and the corresponding Cu surface diffusion flow to predict the Cu bulge-out.