PURPOSE: To make the whole surface flat by a method wherein, after end side walls of an opening of a resist mask installed on the surface of a semiconductor substrate have been formed to be inclined on the surface of the substrate, a dry etching operation is executed while the surface of the semiconductor substrate is irradiated from a direction identical to the angle of inclination of one of the side walls.

CONSTITUTION: An end face 14 of an opening of a resist mask installed on the surface of a semiconductor substrate 11 is inclined on the surface of the substrate 11; after that, the surface of the semiconductor substrate 11 is irradiated with an ion beam 13 obliquely; a dry etching operation is executed. In this way, an angle of inclination of the end face 14 of the opening of the resist mask to the surface of the substrate 11 is made nearly equal to a desired angle of inclination of an inclined face to be formed in the semiconductor substrate 11; accordingly, it is possible to form an inclined face 15 where an edge part of the resist mask does not retreat and where a flat mirror face is formed over the whole surface.