A new pulse plasma enhanced atomic layer deposition of tungsten nitride diffusion barrier for copper interconnect

We have deposited W-N thin films with a pulse plasma enhanced atomic layer deposition (PPALD) method by using WF6 and NH3. It has been very difficult to deposit W-N film on the SiO2 surface with ALD method by using WF6 and NH3 because WF6 does not adsorb on the SiO2 surface and not react with NH3 at 200-400degreesC. However, in this work introducing NH3 pulse plasma, which is synchronized with ALD cycles, we can deposit the W-N film on the SiO2 surface with the rate of similar to1.3 monolayer/cycle at 350degreesC. N concentration is also uniformly distributed in the W-N film. This is due to the surface nitridation to enhance the adsorption of WF6 at the SiO2 surface. As a diffusion barrier for the Cu interconnect, electrical measurement reveals that 22 nm thick W-N successfully prevents Cu diffusion after the annealing at 600degreesC for 30 min.