Importance

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Abstract

In a nonvolatile semiconductor memory device with a two-layer gate structure, an interlayer insulating film is formed on a floating gate electrode of, e.g., polycrystalline silicon. The interlayer insulating film has a four-layer structure in which a first silicon nitride film, a first silicon oxide film, a second silicon nitride film and a second silicon oxide film are laminated in this order on the floating gate electrode, or a two-layer structure in which a first silicon nitride film and a first silicon oxide film are laminated in this order on the floating gate electrode. With the above structure, the threshold voltage of the semiconductor device is stabilized even after data-erase operation. Since, moreover, the first silicon oxide film can be formed by oxidizing the first silicon nitride film, then the quality of the first silicon oxide film can be enhanced, and accordingly the charge retaining properties of the device can be increased.

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First Claim