PURPOSE: To form a substratum film trench pattern finer than a resist trench pattern by a method wherein the sectional form of a resist is changed from a rectangle to a semicircle by heat treatment after the forming of resist pattern, and increasing the length of a base.

CONSTITUTION: A lower layer organic film 2 is formed on a substrate 17 an interlayer inorganic film 3 is formed on the lower layer organic film 2; resist is spread thereon and pre-baking is performed; an upper resist pattern 4 is formed by exposure and development. Then an upper resist pattern 4' after heat treatment is formed by baking; the interlayer inorganic film 3 and the lower organic layer 2 are sequentially etched by anisotropic etching. In this manner, the heat treatment is performed after the forming of resist pattern: the sectional form of the resist pattern 4' is changed to increase the length of the base. Thereby, a fine trench pattern exceeding the resolution limit of lithography is formed.