Patent ID: 7524729

Claim:
A method of manufacturing a semiconductor integrated circuit device comprising steps of: (a) forming a first silicon oxide film over a surface of a semiconductor substrate by thermally oxidizing said substrate and then forming an oxidation resistant film over said first silicon oxide film, and selectively exposing said surface of said substrate for an element isolation region by removing said oxidation resistant film and said first silicon oxide film; (b) after said step (a), recessing an end of said first silicon oxide film inward more than an end of said oxidation resistant film; (c) forming a second silicon oxide film, having a thickness larger than that of said first silicon oxide film, on said surface of said substrate which is exposed after said step (b) by thermally oxidizing said exposed substrate surface including a silicon surface extending from an edge of said first silicon oxide film and under said oxidation resistant film, said second silicon oxide film including a bird's beak that extends inwardly from the end of said oxidation resistant film; (d) exposing said surface of said semiconductor substrate in said element isolation region by etching said second silicon oxide film, including said bird's beak, to form an inclined surface of said substrate at an edge of said element isolation region, wherein said edge of said element isolation region extends inwardly from the end of said oxidation resistant film; (e) forming a trench in said substrate of said element isolation region by etching said substrate exposed in said step (d) to form a concave surface at said edge of said element isolation region, using said oxidation resistant film as a mask; (f) after said step (e), cleaning said substrate; (g) after said step (f), rounding said edge of said element isolation region by thermal oxidation; and (h) after said step (g), burying said trench with an insulating film by polishing an insulating film formed over said oxidation resistant film and said trench.