PURPOSE: To construct a resist film capable of high-precision patterning by a method wherein an organic silicon resin film attached as an intermediate layer is subjected to an oxygen-plasma treatment.

CONSTITUTION: An aluminum alloy film 13 is attached to a semiconductor substrate 11 that includes a step, a flattening resist film 14 (thickness: 1-3μm) is applied to the aluminum alloy film 13, and an SOG film 15 (thickness: several thousand ) is formed by application on the resist film 14. The SOG film 15 is exposed to oxygen plasma for the solidification of its surface, whereon a resist film 16 (thickness: 1μm) is provided by application, to be exposed and then developed for the formation of a pattern. Next, with the resist film 16 serving as a mask, etching is accomplished by using a fluorine-based gas for the patterning of the SOG film 15. The SOG film 15 serves as a mask in a process wherein the resist film 14 is exposed to an oxygen gas reactive ion etching treatment for the transfer of the pattern. The patterned resist film then serves as a mask in a process of patterning the aluminum alloy 13 that is accomplished by using a chlorine-based gas as an etching gas.