Patent ID: 8394695

Claim:
A semiconductor device production method comprising the steps of: forming a trench adjacent to a channel region in a semiconductor substrate; filling an oxide film in the trench; forming an oxidation resistant mask film which covers the channel region as protruding by a predetermined distance on the trench and uncovers a portion of the oxide film in the trench adjacent to a boundary between the channel region and the trench; performing a selective thermal oxidation process by using the oxidation resistant mask film as a mask to cause a bird's beak to grow as extending from the trench to the channel region; and forming a gate oxide film on the channel region after the selective thermal oxidation step, wherein the oxidation resistant mask film forming step comprises the step of forming the oxidation resistant mask film into a pattern which uncovers a pair of regions on opposite sides of the channel region, and the selective thermal oxidation step comprises the step of growing LOCOS oxide films in the pair of regions.