PURPOSE: To achieve that a rounding treatment whose CD loss is small is executed to the corner of a trench, to reduce a dimensional error and to realize the uniformity of the performance of an element by a method wherein the trench is formed in a semiconductor substrate, amorphous silicon is then deposited on the semiconductor substrate and a thermal oxidation treatment is executed.

CONSTITUTION: The pattern of a photoresist 2 is formed on a silicon substrate 1; an anisotropic etching operation is performed; a trench (groove) as a capacitor formation region or an element isolation region is formed. Then, an amorphous silicon film 3 is formed on the silicon surface by a chemical vapor growth method; after that, the surface is oxidized in an oxidizing atmosphere. When the amorphous silicon film is formed in this manner, the corner of the silicon surface provided with uneven parts is changed to a shape which has been rounded in a pseudo manner, and a thermal oxidation operation is then performed. Thereby, the rounded shape is transferred and the corner of the uneven parts in the silicon substrate is rounded regarding the interface between an oxide film and silicon. After that, the oxide film 4 is removed, and the corner of the trench is rounded and a treatment is finished.