Selective anisotropic reactive ion etching process for polysilicide

Abstract

A reactive ion etching technique is disclosed for etching a gate electrode out of layers of tungsten silicide and polycrystalline silicon without etching the underlying layer of silicon dioxide which serves as the gate dielectric and which covers the source and drain regions. The key feature of the invention, wherein the gate, which has been partially etched out of the tungsten silicide and polycrystalline silicon layers, is coated with poly tetra-fluoroethylene (teflon) to protect the sidewalls of the gate from being excessively etched in the lateral direction while the etching continues at the bottom on either side of the gate. The process is especially suitable for formation of tungsten silicide structures since no subsequent thermal steps are required which would otherwise cause a delamination of the tungsten silicide. In addition to eliminating undercutting, the process does not disturb the gate oxide over the source and drain areas, which would otherwise create a leaky device unsuitable for applications such as dynamic RAMs. The entire process can be carried out in a single pump down and therefore contamination levels can be minimized.