| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a nonvolatile semiconductor memory device capable of preventing excessive data erasure while suppressing the increase of an erasing time. <P>SOLUTION: After memory cell data are erased en bloc by a predetermined block unit (step S2), a threshold voltage Vth is compared with a first repair verify voltage RV0 to determine whether each memory cell of the block is in an excessively erased state or not (step S3). If not in the excessively erased state, the threshold voltage Vth is compared with an erasure verify voltage EV to determine whether it is in a desired erased state or not (step S6). If in the excessively erased state, the threshold voltage Vth is compared with a second repair verify voltage RV1 higher than the first repair verify voltage RV0 (step S5) to check the removal of the excessively erased state, and then the threshold voltage Vth is compared with the erasure verify voltage EV to determine whether it is in a desired erased state or not. <P>COPYRIGHT: (C)2005,JPO&NCIPI</p> |
