Patent ID: 7052960

Claim:
A method of manufacturing a flash memory device, the method comprising: providing a semiconductor substrate on which a pad oxide film is formed in a cell region, a low voltage gate oxide film is formed in a low voltage field, and a high voltage gate oxide film is formed in a high voltage field; forming a first polycrystalline silicon film in the low and high voltage fields; depositing a pad nitride film on the overall structure including the first polycrystalline silicon film; forming a first trench by partially patterning the pad nitride film, the pad oxide film, and the semiconductor substrate in the cell region; forming second and third trenches by partially patterning the pad nitride film, the pad oxide film, and the semiconductor substrate in the low and high voltage fields, respectively; forming a field isolation film to fill up the first through third trenches; removing the pad nitride film; forming a tunnel insulation film on the overall structure where the field isolation film is formed; and forming a floating gate by depositing and patterning a second polycrystalline silicon film on the tunnel insulation film.