Detailed first-principles simulations were made of the Cu/TaN system. Various

interfacial structures between Cu- and Ta-based compounds were examined by

considering different surface orientations, in-plane arrangements, surface

terminations and chemical compositions. The coexistence of strong Cu-N ionic

bonding and Ta-Cu covalent/metallic bonding governed the stable interfacial

structures. Using the nudged elastic band method, the diffusion energy barriers of

Cu to pre-existing vacancies across Cu/TaN interfaces, and in bulk TaN

compounds, were calculated. As a comparison, Cu diffusion in Si was also studied.

It was found that Cu could easily diffuse into Si either spontaneously or with small

energy barriers. It was found that fcc TaN was an excellent candidate for diffusion

barrier material due to its extremely high interfacial diffusion energy barrier. The

bulk diffusion barrier of Cu in fcc TaN was also very high.

First-Principles Simulations of Copper Diffusion in Tantalum and Tantalum

Nitride. Y.Zhao, G.Lu: Physical Review B, 2009, 79[21], 214104