Patent ID: 8338257

Claim:
A method for manufacturing a nonvolatile semiconductor storage device, comprising: forming a first semiconductor film and a second semiconductor film, over a substrate having an insulating surface; forming a first insulating film on a surface of the first semiconductor film and a surface of the second semiconductor film, comprising: an oxide film formed by performing first high-density plasma treatment under an oxygen atmosphere; and a film including oxygen and nitrogen formed on the oxide film, formed by performing second high-density plasma treatment under a nitrogen atmosphere; forming a charge accumulating layer comprising a material with a smaller energy gap than the first semiconductor film and the second semiconductor film over the first insulating film; forming a second insulating film over the charge accumulating layer; removing selectively the first insulating film, the charge accumulating layer, and the second insulating film which are formed over the second semiconductor film so as to expose the surface of the second semiconductor film; oxidizing a surface of the second insulating film by performing third high-density plasma treatment under an oxygen atmosphere; forming a conductive film over the oxidized surface of the second insulating film; removing selectively the first insulating film, the charge accumulating layer, the second insulating film, and the conductive film, thereby leaving parts of the first insulating film, the charge accumulating layer, the second insulating film, and the conductive film so as to overlap with at least a part of the first semiconductor film; and forming an impurity region in the first semiconductor film and the second semiconductor film, by introducing an impurity element, with the parts of the conductive film, formed over the first semiconductor film and the second semiconductor film, used as a mask, respectively.