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

CD Wu and CF Liao, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 187, 111872 (2024).

DOI: 10.1016/j.jpcs.2024.111872

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.

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