Diffusion barrier properties of very thin TaN with high nitrogen concentration

TaN deposited by magnetron sputtering has application in semiconductor interconnect structures as a diffusion barrier and adhesion layer. TaN used in these applications has a hexagonal or cubic structure consistent with roughly 1:1 Ta:N levels, with a bulk resistivity of 300–500 μΩ cm and a diffusion barrier failure temperature for 5 nm films of around 650 °C (Ref. 1). The diffusion barrier failure temperature (for Si/TaN-barrier/Cu samples) is a strong function of nitrogen concentration in the TaN; at the highest N levels (equivalent to nearly Ta3N5), the failure temperature exceeded 900 °C. At intermediate compositions, the failure temperature was found to exceed 700 °C even for films as thin as 0.4 nm. This suggests an interfacial contribution to diffusion barrier effectiveness, in addition to conventional grain boundary or bulk interdiffusion resistance, which may dominate conventional grain boundary diffusion.