Method of forming metal gate structure and method of forming metal gate transistor

Abstract

A method of forming metal gate transistor includes providing a substrate; forming a gate dielectric layer, a work function metal layer and a polysilicon layer stacked on the substrate; forming a hard mask and a patterned photoresist on the polysilicon layer; removing the patterned photoresist, and next utilizing the hard mask as an etching mask to remove parts of the polysilicon layer and parts of the work function metal layer. Thus, a gate stack is formed. Since the patterned photoresist is removed before forming the gate stack, the gate stack is protected from damages of the photoresist-removing process. The photoresist-removing process does not attack the sidewalls of the gate stack, so a bird's beak effect of the gate dielectric layer is prevent.