Effects of anodic dissolution on diffusion in Cu/Ag thin film couples

Thin, 100-nm films of first silver and then copper were deposited consecutively onto pure single-crystal silicon substrates by magnetron sputter deposition. Controlled anodic current densities were applied at room temperature to dissolve the outer copper film to varying depths approaching the copper/silver interface. Profiles of copper and silver concentration vs. depth below the anodically dissolved surfaces were subsequently obtained by argon ion sputtering and simultaneous Auger Electron Spectroscopy. Despite some intrinsic mixing during the profile analysis, there is clear evidence that diffusion of copper and silver into one another was enhanced by anodic currents at the outer copper surface. We believe that the effect is caused by surface formation of vacancies during anodic dissolution. The anodically generated vacancies subsequently migrate as divacancies to che copper/silver interface where they enhance diffusion by the usual vacancy exchange mechanism.