1. Field
Some example embodiments of the present inventive concepts relate to a method of fabricating a semiconductor device.
2. Description of the Related Art
A semiconductor device has a trend of demanding lower power consumption and higher operating speed as well as higher integration. A CMOS device requires lower threshold voltage for transistors so as to meet the trend. The CMOS device includes an NMOS transistor and a PMOS transistor. The NMOS transistor used N-type polysilicon as a gate electrode, and the PMOS transistor used P-type polysilicon as a gate electrode. However, degradation of drive current due to depletion of polysilicon has been a problem with the advanced fineness of transistors. Accordingly, there are limitations to improve or optimize threshold voltages of NMOS and PMOS transistors.