Method to enhance atomic-layer deposition of tungsten–nitride diffusion barrier for Cu interconnect

We have suggested an atomic layer deposition (ALD) method for preparing W–N films on Si and non-Si surfaces by using WF6 and NH3. It is very difficult to deposit W–N films with sequential exposures of WF6 and NH3 because WF6 either reacts with Si quickly due to the catalytic reaction of Si, forming a thick W layer instead of the W–N, or does not adhere to the non-Si surface at 200–400 °C. In this method, during the ALD cycle we have introduced NH3 gas with pulse rf power, resulting in a NH3 pulse plasma that modified Si and SiO2 surfaces to become Si–N and Si–O–N surfaces. With this method, we can obtain a uniformly distributed N concentration in the W–N films deposited on the Si and non-Si surfaces with the deposition rate of ∼2.2 Å/cycle at 350 °C. As a diffusion barrier for the Cu interconnect, high-resolution transmission electronic microscopy reveals that after annealing at 700 °C for 30 min, 22 nm thick W–N successfully prevents Cu diffusion.