Barrier capability of TaN_x films deposited by different nitrogen flow rate against Cu diffusion in Cu/TaN_x/n⁺-p junction diodes

This paper investigates the barrier capability of tantalum nitride (TaN_x) layers against Cu diffusion. The TaN_x layers were reactively sputtered in contact holes to a thickness of 50 nm by using a different nitrogen flow rate. Results indicate that the TaN_x layers fail to be a diffusion barrier due to a relative high resistivity for nitrogen flow ratios exceeding 10%. In addition, we found that the phase of α-Ta(-N) functions as an effective barrier against Cu diffusion and that Cu/TaN(3-5%)/n⁺-p junction diodes are able to sustain a 30 min furnace anneal up to 500 °C without causing degradation of the electrical characteristics. The high-temperature failure of barrier capability for the TaN_x layers is due to interdiffusion of Cu and Si across the TaN_x film structure to form Cu₃Si. The surface roughness and the film structure of TaN_x layers determine the ability of Cu and Si interdiffusion.