Molecular dynamics simulation of the direct bonding of (111)-oriented nanotwinned Cu and its related mechanical behavior

Abstract

The effects of the bonding temperature and interference amount (extent of contact between two Cu microbumps during the bonding process) on the bonding mechanism and mechanical behavior of Cu-to-Cu direct bonding using (111)-oriented nanotwinned Cu (NT-Cu) have been studied using molecular dynamics simulations. The simulation results show that two NT-Cu microbumps gradually bond and the interface voids eliminated via atomic diffusion during the bonding and holding processes. NT-Cu bonded at higher temperature has more randomly distributed disordered atoms and fewer remaining grain boundaries. Few cracks directly nucleate at the bonding interface of bonded NT-Cu during stretching for various bonding temperatures and interference amounts, indicating the good bonding quality. Bonding at temperatures in the range of 300–623 K with an interference value of 0 nm generally lead to higher yield strength and lower yield strain and ultimate strength and strain than those of raw NT-Cu. In addition, bonding at higher temperature leads to better ductility at room temperature. The yield strain and ultimate strength and strain for bonded NT-Cu obtained at 423 K with an interference value of 0 nm can be significantly improved upon increasing the interference value.