Effects of Cu on the electromigration behavior of Al interconnect by using first-principles method

Electromigration resistance of Al could be improved through adding a small amount of Cu elements. In this paper, Al31Cu supercell was constructed to calculate the effects of the solute elements on the properties of face central cubic (FCC) Al, including the diffusion activation energy, electronic structure etc, to explain why Cu can suppress the EM process occurred in pure Al interconnect, by employing the density functional theory based on the first-principles method. The calculated diffusion activation energy for pure Al with vacancy-mediated mechanism is -1.29 eV, which is comparable with the experimental result, -1.48 eV. The addition of Cu atom results in the increase of diffusion energy of Al atom near the solute atom, it is -1.57 eV. Since EM failure is greatly related with the diffusion activation energy, EM resistance of Al interconnect is expected to be enhanced by Cu solute. Likewise, the value of the density of states of the systems at the Fermi level (N(E_F)), as well as that of the Al atoms at the specific sites could also be reduced slightly by Cu. These two results indicate that the nearest neighbor Al atoms could be stabilized by the above elements. Our calculations are in good agreement with the previous calculations and experimental phenomenon at some extent.