PURPOSE: To simply and quickly form a microscopic pattern, having a high aspect ratio and also having no etching residue and no etching irregularity, in a highly precise manner by a method wherein a dry etching, in which a reactive ion etching process and an oxidizing process for etching part are alternately repeated, is conducted on a metal thin film.

CONSTITUTION: A dry etching treatment is conducted on the high melting point metal layer 2, consisting of Ta, W, Mo, Ti and the like, on which a mask pattern layer 3 is formed. First, said etching is stopped at the point of time when the etching is progressed to a specific depth of the high melting point metal layer 2. The method of etching in this case is the reactive ion etching in which CBrF3 is used as etching gas. An oxide layer 4 is formed on the recessed surface of the etching part of the etched high melting point metal layer 2. This oxide layer 4 is formed by exposing the high melting point metal layer to the oxidizing atmosphere such as O2 plasma and the like. Then, a reactive ion etching treatment is conducted continuously on the high melting point metal layer 2 on which the oxide layer 4 is formed. Accordingly, the bottom face of the recessed part formed on the layer 2 can be etched more deeply by the above- mentioned etching.