Chemical bonding and Cu diffusion at the Cu/Ta2N interface: a DFT study

Abstract

Ta₂N is an effective diffusion barrier material to prevent undesired Cu diffusion in ultra-large scale integration circuits. Previous theoretical work has reported the interesting result that at the Cu/Ta₂N interface the Cu layer preferentially bonded with the Ta layer but not the N layer of Ta₂N. However, this result was calculated from largely lattice mismatched interface models. To confirm this theoretical result and unravel the cause of strong Cu–Ta bonding at the Cu/Ta₂N interface, in this study density functional theory calculations, on the basis of super-cell models, were performed to investigate the Cu(111)/Ta₂N(001) interface. We firstly calculated interface cohesive energies and confirmed that the Cu layer preferentially bonded with the Ta layer of Ta₂N. Then, electronic structure calculations revealed that the chemical bonding of the Cu–Ta bond at the Cu(111)/Ta₂N(001) interface was primarily covalent in character, providing a proper explanation for the close integration of the Cu layer and Ta layer. Lastly, Cu diffusion investigations revealed that Ta₂N was able to effectively prevent Cu diffusion. Furthermore, we found that the N layer of Ta₂N played the critical role in preventing Cu diffusion.