A semiconductor device includes an interlayer insulating film formed on a substrate and including a trench, a gate insulating film formed in the trench, a work function adjusting film formed on the gate insulating film in the trench along sidewalls and a bottom surface of the trench, and including an inclined surface having an acute angle with respect to the sidewalls of the trench, and a metal gate pattern formed on the work function adjusting film in the trench to fill up the trench.

A method for manufacturing an injection-enhanced insulated-gate bipolar transistor, comprising the following steps: an n-type substrate (12) is provided; a p-type doped layer (14) is formed on the n-type substrate (12); a hard layer (20) is formed on the p-type doped layer (14); a groove (40) extending to the n-type substrate (12) is formed by etching on the p-type doped layer (14); an n-type doped layer (50) is formed on the sidewalls and bottom of the groove (40); the hard layer (20) is removed; p-type impurities of the p-type doped layer (14) and n-type impurities of the n-type doped layer (50) are driven in together, where the p-type impurities are diffused to form a p-type base region (60), and the n-type impurities are diffused to form an n-type buffer layer (70); a gated oxide dielectric layer (80) is formed on the surface of the groove (40); and, a polysilicon layer (90) is deposited in the groove having formed therein the gate oxide dielectric layer (80). In the method for manufacturing the injection-enhanced insulated-gate bipolar transistor, the p-type doped layer (14) and the n-type doped layer (50) are driven in together to form the p-type base region (60) and the n-type buffer layer (70), as only one drive-in process is required, production cycle is shortened in comparison with a conventional method for manufacturing the injection-enhanced insulated-gate bipolar transistor.