Effect of thinning a WSiN/WSix barrier layer on its barrier capability

We investigated the effects of tungsten silicon nitride/tungsten silicide (WSiN/WSix) barrier layer thickness on its barrier capability. WSiN was obtained by nitridizing the WSix surface with electron cyclotron resonance nitrogen plasma. The total thickness of the WSiN/WSix barrier layer was reduced by thinning the initial WSix layer. When 5-nm-thick WSix was nitridized, the N and Si contents in the WSiN/WSix layer became smaller than when WSix initial thickness was 20 nm. This barrier layer diffused into the copper (Cu) layer when annealed, and did not act as a barrier layer. On the contrary, a WSiN/WSix barrier layer formed by nitridizing 10-nm-thick WSix showed good barrier capability against Cu diffusion. We evaluated the leakage current between Cu damascene interconnections with this barrier layer and found that this barrier layer formed on the trench side wall prevents Cu diffusion when the thickness on the side wall is over 10 nm.