Molecular dynamics study of Co/Co interfacial diffusion for low-temperature hybrid bonding: Effects of orientation and surface roughness

Classical molecular dynamics simulations were used to examine how crystallographic orientation, temperature, normal loading, and deterministic nanoscale roughness affect short-time atomic rearrangement at Co/Co contacts relevant to low-temperature hybrid bonding. Six FCC-Co orientation relationships were screened at 623 K. Co(111)/Co(111) developed the largest structural overlap, whereas Co(100)/Co(110) showed the strongest lower-side z-direction mobility. Because the confined interface does not necessarily reach a long-time Fickian regime, the MSD-derived quantity is reported as an apparent coefficient, D z a p p , and is interpreted together with three-seed statistics, bulk-like reference regions, and 0 K-quenched configurations. Parallel HCP-Co/Co controls remained HCP-dominant over 4 ns. Independent validation of the Zhou04 EAM potential reproduced the small HCP-FCC energy difference and the negative intrinsic stacking-fault energy, while also revealing a limitation in the relative (100)/(111) surface-energy ordering. Normal loading promoted contact closure but did not produce a monotonic increase in structural overlap or bilateral mobility. For Co(100)/Co(110), an expanded roughness sweep at λ = 20 Å identified A = 1 Å as the strongest bilateral response among the sampled amplitudes; additional λ = 10, 17.5, and 35 Å controls showed that this enhancement is strongly wavelength-dependent. These results provide a cautious atomistic structure–kinetics framework for low-temperature Co/Co bonding.