This invention relates generally to the fabrication of integrated circuits.
When making a complementary metal oxide semiconductor (CMOS) device that includes metal gate electrodes, it may be necessary to make the NMOS and PMOS gate electrodes from different materials. A replacement gate process may be used to form gate electrodes from different metals. In that process, a first polysilicon layer, bracketed by a pair of spacers, is removed to create a trench between the spacers. The trench is filled with a first metal. The second polysilicon layer is then removed, and replaced with a second metal that differs from the first metal.
To increase performance of NMOS and PMOS deep sub-micron transistors in CMOS technology, current state-of-the-art technology uses compressive stress in the channel of the PMOS transistors, and tensile stress in the case of NMOS transistors. This is usually achieved by substrate induced strain which is a very expensive technology option and also difficult to implement using a single substrate approach.
Thus, there is a need for a way to improve the performance of metal gate field effect transistors.
Features shown in these Figures are not intended to be drawn to scale.