Surface channel metal gate complementary MOS with light counter doping and single work function gate electrode

We propose a channel engineering guideline for the low threshold voltage (V-th) metal oxide silicon field effect transistor (MOSFET) with metal gate, which is promising for highly miniaturized MOSFETs. For lowering V-th of metal gate MOSFET, counter doping is useful, However, a buried channel with heavy counter doping has several disadvantages, such as the degradation of subthreshold swing. In this work, using a design with light counter doping, a surface channel complementary metal oxide silicon (CMOS) of low V-th with a single work function gate electrode was successfully fabricated showing superior characteristics. Device simulation was used to investigate the impacts of the channel profile of such a device. It was found that using counter doping with low concentration to an optimized depth results in better subthreshold characteristics than that using shallow counter doping with high concentration. A lower counter dopant concentration also suppresses V-th deviations. The damascene gate process was used in the fabrication.