US Patent 10074440 Erase for partially programmed blocks in non-volatile memory

An erase operation includes one or more erase depth checks to detect the occurrence of shallow erased memory cells at the end of an erase process. Memory cells are subjected to erase and erase verification until erase verification success is achieved. At the end of successful erase verification, a subset of memory cells is read to detect an erase depth or level of the memory cells. If the erase depth check indicates that the subset memory cells are in a shallow erased condition, additional erasing and verification is performed.