Abstract: When an Ir-based conductor film, particularly an IrO2 film, is patterned by dry etching using a resist mask, reaction products having a low vapor pressure are likely to be left on the side surface of a pattern. This invention is directed to prevent the reaction products from remaining on the side surface and moreover, to form a miniature pattern with high dimensional accuracy. When an IrO2 film 55 is patterned by dry etching using a resist mask 56, an etching gas comprising a chlorine gas as a main component and containing oxygen as an additional gas is used in order to lower a selection ratio of the IrO2 film 55 to the resist, and a side wall adhesion film 57 adhering to the side wall of the pattern is eliminated, by recessing the side wall of the resist mask 56.