| 摘要 |
PROBLEM TO BE SOLVED: To substantially improve data retention characteristics of a second cell (a reference cell, a redundancy memory cell, an OTP region, etc.), comprising substantially the same steps and same structure as those of a first cell (memory cell), without increasing the number of steps needlessly. SOLUTION: By utilizing the property that a threshold returns to initial value, namely an initial threshold by the fact that a second cell is damaged by baking, the initial threshold of the second cell is shifted to approach a setting threshold demanded for the second cell as closely as possible. Specifically, when threshold control ions are implanted in a channel region, impurities having concentration different from a memory cell or impurities having different conductivity types are ion implanted.
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