FIELD OXIDE FILM FORMATION OF SEMICONDUCTOR ELEMENT

PURPOSE: To provide a formation method for field oxide film in a semiconductor device which minimizes the generation of bird's beak by using a triple buffer (nitriding film/nitride film). CONSTITUTION: A pat oxide film 2 and a first buffer nitriding film 3 are formed one after another on a silicon substrate 1. A fist patterned mask 5 is arranged thereon where the exposed first buffer nitride film is etched. Then, the first patterned mask 5 is removed, thereby forming a buffer oxide film 6. A second buffer nitride film 7 is further formed thereon and a second patterned mask 8 is arranged thereon and the exposed second nitride film 7 is etched. Then, the second patterned mask 8 is removed and the buffer oxide film 6 is arranged to grow, thereby forming a field oxide film 9. Then, the second nitriding film 7 is removed. A bird's beak removal mask 10 is arranged on the field oxide film 9, thereby removing the bird's beak.