US Patent 7372742 Memory block erasing in a flash memory device

The erase and verify method performs an erase operation and an erase verify read operation. If the erase verify read operation fails because unerased memory cells have been found, a normal memory read operation is performed in order to determine which memory cells are still programmed. A selective erase operation is then performed on the memory cells such that only the rows that comprise unerased memory cells undergo additional erase operations.