Method of fabricating semiconductor device

摘要

After P+ ions are implanted into a polysilicon film in an nMOSFET region, a heat treatment is performed to diffuse phosphorus down to the lower part of the polysilicon film. The diffusion reduces the concentration of phosphorus in an upper end portion of the polysilicon film and inhibits the upper end edges of a gate electrode from being increased in size during patterning. Then, B+ ions are implanted into the polysilicon film in a pMOSFET region and the polysilicon film is etched into a gate configuration. Since a heat treatment for simultaneously diffusing phosphorus and boron in the polysilicon film is not performed, the entrance of boron from the gate electrode into a semiconductor substrate is inhibited, while the occurrence of side etching during the formation of an n-type polysilicon gate is suppressed.