Massive Ta diffusion observed in Cu thin films but not in Ag counterparts

This letter presents an extensive investigation by means of microscopic and chemical analyses finding Ta diffusion in Cu films but not in Ag films. This difference in Ta diffusion persists in all samples containing either Cu/Ta or Ag/Ta interfaces, wherein both a driving force for diffusion and point defects for mediation of atomic movement are present. By referring to atomistic simulation results in the literature, it is plausible that the subtle difference between the Cu/Ta and Ag/Ta interfaces plays a crucial role in differentiating them in making Ta available for diffusion. The energetically favored binding between Cu and Ta assists in liberating Ta atoms from being strongly bound by surrounding Ta atoms, as the bond strength of Cu-Ta is about one third that of Ta-Ta. Hence, the formation of the much weaker Cu-Ta bonds acts as an important intermediate step. Such a mechanism does not exist for the Ag/Ta interface. (C) 2016 American Vacuum Society.