Patent ID: 7476583
Filing Date: 2009-01-13
Classification: H01L

Abstract:
1. A method of manufacturing a semiconductor device comprising: a semiconductor substrate having a main surface; an insulating film formed on the main surface of said semiconductor substrate; a floating gate electrode formed on the main surface of said semiconductor substrate via said insulating film; and an assist gate electrode provided on both sides of said floating gate electrode via a side wall to form an inversion layer in said semiconductor substrate, said insulating film having a first insulating film located at both end portions below said floating gate electrode and a second insulating film sandwiched between said first insulating films and located in a middle portion below said floating gate electrode, and said first insulating film being thicker than said second insulating film, comprising the steps of: forming said assist gate electrode at an appropriate position on the main surface of said semiconductor substrate; performing thermal oxidization on the surface of said semiconductor substrate sandwiched between said assist gate electrodes to form a thermal oxide film serving as said first insulating film; forming said side wall made of a silicon oxide film on a side of said assist gate electrode and removing a middle portion of said oxide film; and performing wet etching to reduce a surface of said side wall and an inner end portion of said oxide film simultaneously.