Method for forming field oxide film

Claim 1

A method for forming a field oxide film for a floating gate memory device, comprising the steps of: (i) laminating a gate insulating film, a polysilicon layer and a first silicon nitride film, in that order, over the entire surface of a semiconductor substrate; (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 patterned gate insulating film, polysilicon layer and 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; (v) forming a field oxide film on the etched portion of the semiconductor substrate in a self-aligned manner relative to the polysilicon layer, where the mask is formed by the first silicon nitride film and the sidewall spacer; (vi) removing the first silicon nitride film and the sidewall spacer of the mask; (vii) forming an insulating layer over the entire surface of the semiconductor substrate, including the polysilicon layer, (viii) laminating a second polysilicon layer on the insulating layer, and (ix) successively etching the second polysilicon layer, the insulating layer, the gate insulating film and the polysilicon layer to form a control gate and a floating gate of the floating gate memory device.

Claim 2

A method for forming a field oxide film for a floating gate memory device, comprising the steps of: (i) laminating a gate insulating film, a polysilicon layer and a first silicon nitride film, in that order, over the entire surface of a semiconductor substrate; (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 patterned gate insulating film, polysilicon layer and 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; (v) forming a field oxide film on the etched portion of the semiconductor substrate in a self-aligned manner relative to the polysilicon layer, where the mask is formed by the first silicon nitride film and the sidewall spacer; (vi) removing the first silicon nitride film and the sidewall spacer of the mask; (vii) forming an insulating layer over the entire surface of the semiconductor substrate, including the polysilicon layer, (viii) laminating a second polysilicon layer on the insulating layer, and (ix) successively etching the second polysilicon layer, the insulating layer, the gate insulating film and the polysilicon layer to form a control gate and a floating gate of the floating gate memory device.