PURPOSE: To improve the etching rate of a polycrystalline silicon film and the etching selection ratio of the polycrystalline silicon film to a foundation oxide film and, further, avoid an undercut by a method wherein the polycrystalline silicon film is selectively etched with etching gas composed of bromine system reactive gas and oxygen or the like added to it while a substrate temperature is controlled.

CONSTITUTION: A resist film 14 having a required pattern is formed on a polycrystalline silicon film 13 built up on a substrate 11. Then the polycrystalline silicon film 13 is selectively etched with etching gas composed of bromine system reactive gas such as bromine and hydrogen bromine which does not contain carbon and oxygen or gas containing oxygen which does not contain carbon and is added to the bromine system gas while the temperature of the substrate 11 is controlled. For instance, while the temperature of a sample 7 is controlled within a range of 50-150°C, the etching gas composed of Br2 and O2 added to it is introduced into a reaction chamber 1 through a gas introducing tube 2 and discharged through a gas exhaust tube 3 and a pressure in the reaction chamber 1 is maintained at 0.1Torr and a radio frequency voltage is applied to the sample 7 by a radio frequency source 6 to subject the sample 7 to dry etching.