CPC G11C 16/3463 (2013.01) [G11C 16/102 (2013.01); G11C 16/26 (2013.01); G11C 16/3404 (2013.01)] | 15 Claims |
1. A method of operating a memory system including memory cells, the method comprising:
preprogramming and erasing the memory cells to set a first threshold voltage distribution for the memory cells;
detecting fast cells among the memory cells set in the first threshold voltage distribution, wherein normal cells among the memory cells each have a threshold voltage equal to or greater than a first threshold voltage, and the fast cells each have a threshold voltage less than or equal to a second threshold voltage which is less than the first threshold voltage; and
programming the memory cells set in the first threshold voltage distribution to a second threshold voltage distribution greater than the first threshold voltage distribution, said programming comprising,
normal programming the normal cells to the second threshold voltage distribution by applying a sequence of incremental step pulse program (ISPP) voltage pulses to the normal cells, and
over-programming the fast cells to the second threshold voltage distribution by applying the sequence of ISPP voltage pulses to the fast cells,
wherein a voltage of an ISPP voltage pulse applied during over-programming is greater than a voltage of a corresponding ISPP voltage pulse applied during normal programming, and
wherein a level of a verification voltage applied during the over-programming is greater than a level of a corresponding verification voltage applied during the normal programming.
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