| 摘要 |
A method for forming a field oxide film includes the steps of: (i) laminating a gate insulating film, a polysilicon layer and a first silicon nitride film over the entire surface of a semiconductor substrate in this order; (ii) patterning the gate insulating film, the polysilicon layer and the first silicon nitride film to a desired shape; (iii) forming a sidewall spacer of a second silicon nitride film on a side wall of the gate insulating film, the polysilicon layer and the first silicon nitride film; (iv) selectively etching a portion of the semiconductor substrate with the first silicon nitride film and the sidewall spacer used as a mask; and (v) forming a field oxide film on the etched portion of the semiconductor substrate in a self-aligned manner relative to the polysilicon layer. According to the invention, lifting up of the polysilicon layer caused by the bird's beak of the field oxide film coming under the polysilicon layer can be reduced. Also, horizontal extension (in a direction parallel to the substrate surface) of the bird's beak can be controlled.
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