| 摘要 |
PURPOSE:To manufacture a nonvolatile semiconductor memory device with excellent writing characteristics and very little leakage of stored charge by making the thickness of a silicon oxide film at the edge of a floating gate thicker than the thickness of the other part. CONSTITUTION:Thick 1st silicon oxide film 6 is formed on the surface of patterned 1st polycrystalline silicon film 4. Further, thin 2nd silicon oxide film 8 is formed on the exposed 1st polycrystalline silicon film 4. The 2nd silicon oxide film 8 is also formed by a thermal oxidation to have a thickness of about 1000 Angstrom and can be so formed as to be sufficiently thin to improve the writing characteristics. By adding the forming process of the 2nd silicon oxide film 8 to the forming process of the 1st silicon oxide film 6, the thick 1st silicon oxide film 6 and the thin 2nd silicon oxide film 8 can be selectively formed on the 1st polycrystalline silicon film 4 which is to be a floating gate easily and an advantage that the leakage of stored charge at the edge of the floating gate can be reduced to be less than a half of the leakage of a conventional EP.ROM can be achieved.
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