| 摘要 |
A method for erasing a flash memory is provided to enhance reliability after an initial operation and repeated cycles by designing a narrow threshold voltage distribution of an erasing cell, as a verification reference level is set to the left/right side during an erase operation. All cells are programmed in advance by responding to an erase command(102). The preprogrammed cells are erased and verified(104). The cells are soft programmed by using an ISPP(Incremental Step Pulse Program) mode(105). The cells are verified by using a first level of the threshold voltage distribution of the erasing cell as a standard and the cell failed in verification is soft programmed again(106). The cells passing a first verification process are verified by using a second level higher than the first level(107). An erasure verification line verifies all word lines with 0-1 volt during the erase operation. The cells are programmed by applying a word line distribution of 10-15 volts during a soft program operation.
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