Patent ID: 7883967

Claim:
A manufacturing method of a nonvolatile semiconductor memory device, comprising: forming a tunnel insulating film including a three-layered structure in which a silicon nitride film is sandwiched between a first silicon oxide film and a second silicon oxide film, the forming of the tunnel insulating film including: oxidizing a surface of a silicon layer to form the first silicon oxide film, depositing an amorphous silicon film on the first silicon oxide film, nitriding the amorphous silicon film to form the silicon nitride film, and forming the second silicon oxide film on the silicon nitride film; forming a floating gate electrode on the tunnel insulating film; forming an inter-poly insulating film on the floating gate electrode; forming a control gate electrode on the inter-poly insulating film; and forming a gate portion by etching a laminated film of the floating gate electrode, the control gate electrode, the tunnel insulating film, and the inter-poly insulating film into a gate pattern, wherein the surface of the silicon nitride film is oxidized to form the second silicon oxide film on the silicon nitride film, the silicon nitride film is subjected to heat treatment before the second silicon oxide film is formed, and the heat treatment to which the silicon nitride film is subjected before the second silicon oxide film is formed is performed at temperatures not lower than the nitride film formation temperature.