A New Pulse Plasma Enhanced Atomic Layer Deposition of Tungsten Nitride Diffusion Barrier for Copper Interconnect

Abstract

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 200–400°C. 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 ∼1.3 monolayer/cycle at 350°C. 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 600°C for 30 min.