Semiconductor device and process for producing the same

A process for producing a semiconductor device, comprising:

• forming a pad oxide film on a circuit forming side of a semiconductor substrate,
• forming an anti-oxidation film on the pad oxide film,
• forming a photoresist film on the anti-oxidation film,
• removing portions of the anti-oxidation film and the pad oxide film,
• trenching a groove at an angle of 95° to 110° of the inside wall of the groove to the surface of the semiconductor substrate in a portion of the semiconductor substrate from which the pad oxide film has been removed while masking an element region,
• removing a portion of the photoresist film,
• removing another portion of the photoresist film on the anti-oxidation film,
• forming a space to an extent of 5 to 40 nm on the semiconductor surface around the groove by etching the pad oxide film from the side wall of the groove,
• forming a second silicon oxide film by oxidation in the recessed space, wherein the oxidation is carried for a sufficient time until a lower surface of the recessed space and a surface in the groove are fully covered by the second oxide film, and wherein the oxidation is stopped at or before a time when the recessed space is completely filled by said second silicon oxide film,
• embedding an element isolation film in the groove having the second oxide film,
• removing the anti-oxidation film and the pad oxide film on the semiconductor substrate,
• forming a gate dielectric film on the surface of the semiconductor substrate in the element isolation region, and
• forming a gate electrode on the gate dielectric film.