Low pressure anisotropic etch process for tantalum silicide or titanium silicide layer formed over polysilicon layer deposited on silicon oxide layer on semiconductor wafer

A low pressure process is described for the anisotropic etching of a titanium or tantalum silicide layer formed over a polysilicon layer on a gate oxide layer, and then masked. The etch process is carried out at a low pressure of about 10 milliTorr to about 30 milliTorr using Cl2 and HBr etching gases, preferably only Cl2 at the etching gas, to etch the silicide without undercutting the mask layer. In a preferred embodiment, etch residues are also eliminated by the use of only Cl2 as the etching gas in the low pressure etch step. In the most prefferred embodiment, any bulges which might otherwise remain in the sidewalls of the underlying polysilicon layer, are also eliminated by using only HBr as the etching gas in the over-etch step, which is highly selective to oxide to protect the underlying gate oxide layer; resulting in an anisotropic etch of both the titanium/tantalum silicide and polysilicon layers, without leaving etch residues on the wafer surface.