Formation mechanism of ultrathin WSiN barrier W/WN,/Si system

A W/WN,/poly-Si composite structure (poly-metal) has been proposed as a low resistivity gate material. It has been found that an ultrathin WSiN layer forms at the W/Si interface after annealing, and as a result, the W/WSiN/poly-Si structure is very stable up to 950°C. In this paper, the formation mechanism of the ultrathin WSiN layer was studied. It was found that a 1 nm WSiN layer forms by solid state reaction between the WN, and poly-Si during annealing. A part of nitrogen atoms originally incorporated in the WN, film react with Si to form a 1 nm WSiN layer during annealing. Chemical bonds in the ultrathin WSiN layer consists of Si-N bonds and metallic W bonds. Metallic W bonds are attributed to W-W or W-Si bonds. There is no W-N bonds. Therefore, it is speculated that the WSiN consists of Si,N, and W or WSi, and stabilizes the W/poly-Si interface. Since the WSiN layer acts as an excellent barrier metal for W and Si diffusion, the sheet resistivity of the poly-metal structure (where W thickness is 100 nm) can be maintained to be lower than 1.5 a/sq.