| 摘要 |
PURPOSE: To reduce the number of tail bits by providing small and uniform particles within a boundary area between a floating gate and tunnel oxide. CONSTITUTION: P<31> is injected into a strip 38a up to a level of about (1 to 8)×10<14> /cm<2> . A thin polysilicon layer 45 is lightly doped, making polysilicon particles in the thin polysilicon layer to be smaller in size. Therefore, a part formed of the thin polysilicon layer 45 of the strip 38a, that is, the particle size of a part closest to a tunnel oxide 39 becomes small because the layer 45 is thin and it is lightly doped. As a result, the change in threshold voltage between the gates after deletion is reduced greatly and the distribution of deleted voltage becomes dense. Therefore the number of tail bits having a lower threshold voltage than the desired value or the number of tail bits which intend to fail after cycling can be reduced to the most extent.
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