Barrier/glue layer on polysilicon layer

Abstract

A method for forming a barrier/glue layer above the polysilicon layer of a MOS transistor gate comprising the step of providing a semiconductor substrate, and then forming a gate oxide layer above the substrate. Next, a polysilicon layer is formed over the gate oxide layer. Thereafter, a titanium layer is deposited over the polysilicon layer first, and then a titanium nitride layer is deposited above the titanium layer. This titanium/titanium nitride bi-layer is capable of increasing the adhesive strength with a subsequently deposited tungsten silicide layer, and preventing the peeling of the tungsten silicide layer. Furthermore, the titanium nitride layer acts as a barrier for fluorine atoms preventing their diffusion to the gate oxide layer/polysilicon layer interface, and affecting the effective thickness of the gate oxide layer. In the subsequent step, a tungsten suicide layer is formed above the titanium nitride layer. Finally, after an annealing operation, the titanium layer will react with the silicon in the polysilicon layer and the tungsten silicide layer to form a titanium silicide layer. Hence, the resistance of the polycide layer in a MOS transistor gate can be reduced.