Tungsten gate technology for quarter-micron application

The feasibility of pure tungsten as a gate electrode of quarter-micron MOSFETs (metal-oxide-semiconductor field effect transistors) was investigated experimentally. Issues investigated are 1) tungsten gate dry etching, 2) gate oxide dielectric for the tungsten gate, and 3) threshold voltage control of tungsten gate MOSFET. A 0.1-mu m tungsten gate electrode on a 5-nm-thick gate oxide was fabricated successfully for the first time, using microwave plasma etching and chlorine as the reaction gas. It was confirmed that the dielectric characteristics of the gate oxide for the tungsten gate are acceptable when its thickness exceeds 6 nm. It was demonstrated that the threshold voltage of tungsten gate MOSFETs was successfully controlled by counter-doping without degradation of the short-channel characteristics.