Patent ID: 7618876

Claim:
A method of manufacturing a semiconductor device comprising: forming a first silicon oxide film on a semiconductor substrate; forming a polycrystalline silicon film on the first silicon oxide film; forming a silicon nitride film on the polycrystalline silicon film; etching the silicon nitride film, the polycrystalline silicon film, the first silicon oxide film, and the semiconductor substrate to form a trench; forming a first high-density plasma (HDP) film in the trench, the first HDP film being formed along side surfaces of the first silicon oxide film, the polycrystalline silicon film and the silicon nitride film, and being formed on an upper surface of the silicon nitride film so that a first recess is formed over the trench; forming a coating film so as to fill the first recess therewith; transforming the coating film into a second silicon oxide film; planarizing the first HDP film and the second silicon oxide film using the silicon nitride film as a stopper; removing the first HDP film formed along the side surfaces of the first silicon oxide film, polycrystalline silicon film and the silicon nitride film while removing the second silicon oxide film so that a second recess is formed over the trench, a width of an opening of the second recess is larger than a width of an opening of the first recess; forming a second HDP film in the second recess and on the silicon nitride film; planarizing the second HDP film using the silicon nitride film as a stopper; etching the second HDP film to expose the side surface of the polycrystalline silicon film; removing the silicon nitride film to expose an upper surface of the polycrystalline silicon film; forming an insulating film on the exposed polycrystalline silicon film; and forming a control gate on the insulating film.