Self-diffusion in intermetallic AlAu4: Molecular dynamics study down to temperatures relevant to wire bonding

We demonstrate the ability of long time (∼1 μs) molecular dynamics modeling to provide quantitative diffusion coefficients for the compound AlAu4 (β-Mn type), down to temperatures (∼200 °C) that are relevant to AlAu wire bonding. Concerning Au diffusion, our results agree quite well with DFT calculations of the vacancy-formation energy, the activation energy, and the diffusion mechanisms. Our model underestimates, however, the vacancy-formation energy of Al, whose diffusivity is found to be at least 10 orders of magnitude slower than Au one. The van Hove correlation-function analysis shows that Au diffusion takes place mainly on the Wyckoff b sublattice. Moreover, we shed light on the high-temperature region, as the stability limit T★ of AlAu4 is approached and unfavorable jumps contribute to the diffusivity. This concerns, for instance, jumps generating antisites defects. The latter lead to a massive disorder which ends up in a phase change to a distorted fcc structure at T★. Including the melting temperature in the potential-fitting procedure seems to be an effective way to gauge the temperature scale and properly capture the order of magnitude of diffusion.