High temperature CVD dichlorosilane (DC) tungsten silicide (WSix) and in-situ doped CVD polysilicon (poly) have been widely used as gate materials in VLSI metal oxide semiconductors (MOS). However, low temperature ( greater than 600xc2x0 C.) oxidation of WSix makes the WSix process control very critical on tungsten (W) ratio and makes later process integration more difficult.
U.S. Pat. No. 6,100,193 to Suehiro et al. describes an in-situ tungsten deposition and an SiN CVD step for a tungsten gate.
U.S. Pat. No. 5,981,380 to Trivedi et al., U.S. Pat. No. 5,924,000 to Linliu, and U.S. Pat. No. 5,888,588 to Nagabushnam et al. describe various WSix, processes.
Accordingly, it is an object of the present invention to provide a method of forming tungsten polycide gate electrodes without tungsten silicide oxidation.
Other objects will appear hereinafter.
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a semiconductor wafer having a silicon substrate is provided. A WSix layer is formed over the silicon substrate. An SiN layer is formed upon the WSix layer in the absence of O2; whereby the WSix layer is non-oxidized.