| 摘要 |
A tunnel insulating film of a three-layer structure, wherein an oxide film is interposed between nitrided oxide films, is formed on the surface of a semiconductor substrate. A first polysilicon film serving as a low-concentration impurity region is formed on the tunnel insulating film. An oxide film is formed on that region of the first polysilicon film, which corresponds to the tunnel insulating film, the oxide film having such a thickness that the film can serve as a stopper for impurity diffusion and can allow electrons to pass through. A second polysilicon film, having an impurity concentration higher than that of the first polysilicon film, is formed on the oxide film. The first and second polysilicon films constitute a floating gate. A third polysilicon film serving as a control gate is formed above the second polysilicon film, with an insulating layer interposed therebetween.
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