PURPOSE: To form a field oxide film having sufficient film thickness even when the space where the film will be formed is small by a method wherein the end part of the first nitride film pattern is extended from the edge of the second nitride film pattern to outside using the laminated film pattern having a buffer film interposed between the lower layer of the first thin nitride film pattern and the upper layer of the second thick nitride film pattern.
CONSTITUTION: A patterning is performed on the first CVD-SiO 2 film 17 and the second silicon nitride film 16, and after the second CVD-SiO 2 film 18 has been deposited on the whole surface, the film 18 is left on the respective side walls by performing an etching back with an RIE. Then, after a patterning has been perforated on the first silicon nitride film 14 and the second polycrystalline silicon layer 15, the first and the second CVD-SiO 2 films 17 and 18 are removed, and the ion-implantation for a channel stopper is performed. Then, a selective oxidization is performed using the first and the second nitride film patterns 12 and 14 as an oxidation resistant mask, and a field oxide film 19 is formed. Subsequently, the nitride film 16, the silicon layer 15, the nitride film 14 and the silicon layer 12 are removed successively.