Kt. Nishinohara et al., Surface channel metal gate complementary MOS with light counter doping andsingle work function gate electrode, JPN J A P 1, 40(4B), 2001, pp. 2603-2606
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 me
tal gate MOSFET, counter doping is useful, However, a buried channel with h
eavy counter doping has several disadvantages, such as the degradation of s
ubthreshold 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 imp
acts of the channel profile of such a device. It was found that using count
er doping with low concentration to an optimized depth results in better su
bthreshold characteristics than that using shallow counter doping with high
concentration. A lower counter dopant concentration also suppresses V-th d
eviations. The damascene gate process was used in the fabrication.