Dry etching method for w polycide using sulfur deposition

Abstract

A dry etching method for anisotropically etching a polycide film without using chlorofluorocarbon (CFC). For instance, in a W polycide gate electrode forming process, a W polycide film is etched by using sulfur fluorides, like S.sub.2 F.sub.2, with a high S/F ratio (i.e. the ratio of the number of sulfur atoms to that of fluorine atoms). In a first step, at least the upper WSi.sub.x layer of the W polycide film is etched with the wafer kept at temperatures between -20.degree. C. and room temperature or with non-depositional fluorine based compounds like SF.sub.6 added to etching gas, thus decreasing the S/F ratio of the etching system. This first step promotes elimination of WF.sub.x and reduces the quantity of free sulfur. Therefore, WF.sub.x is inhibited from reacting with sulfur to form WS.sub.x for deposition in excessive quantities on the sidewalls of the WSi.sub.x pattern, thus preventing occurrence of critical dimension losses between the resist mask and the W polycide gate electrode. In a second step, the lower polysilicon layer of the W polycide film is etched with the wafer cooled to lower temperatures or with H.sub.2 S, etc. added to etching gas, thus increasing the S/F ratio of the etching system. This second step promotes deposition of sulfur on the sidewalls of the polycide pattern and improves anisotropy.