Patent attributes
In a method of manufacturing a nonvolatile semiconductor storage device, an element isolation region is formed in a semiconductor substrate, a tunnel oxide film and a polysilicon layer are successively formed on the semiconductor substrate, and nitrogen ions are thereafter implanted into the front surface of the polysilicon layer so as to stay in the front surface only. The polysilicon layer is patterned to form a floating gate, which is then thermally oxidized to form an inter-gate insulating film. Since thermal oxidation is suppressed by nitrogen ions, the inter-gate insulating film is thicker at the side surfaces of the floating gate than at the front surface. The inter-gate insulating film at the edge of the floating gate can be formed as designed, so that the storage device is free from bad influence during electrical programming and erasing, and can retain charge longer.
