Non-volatile storage system that reclaims bad blocks
View Patent ↗A non-volatile storage system is configured to reclaim bad blocks. One embodiment includes determining that a block of non-volatile memory cells is a bad block, leaving the block idle for a period of time to allow for self-curing of the block, verifying success of the self-curing, refreshing the block, verifying that the refresh was successful and subsequently using the block to store host data.
1. A non-volatile storage apparatus, comprising:
a plurality of non-volatile memory cells arranged as groups of non-volatile memory cells; and
one or more control circuits connected to the non-volatile memory cells and configured to determine that a particular group of non-volatile memory cells is a bad group and leave the particular group idle for a period of time such that no programming or erasing is performed for the particular group during the period of time and programming is performed for other groups of non-volatile memory cells during the period of time, the one or more control circuits are configured to determine that the particular group is no longer a bad group subsequent to the period of time and use the particular group to store host data in response to determining that the group is no longer a bad group.
2. The non-volatile storage apparatus of claim 1 , wherein:
the one or more control circuits are configured to leave the particular group idle for the period of time to allow for passive self-curing of the particular group.
3. The non-volatile storage apparatus of claim 1 , wherein:
the one or more control circuits are configured to leave the particular group idle for the period of time to allow the block to self-cure without applying additional heat.
4. The non-volatile storage apparatus of claim 1 , wherein:
the one or more control circuits are configured to leave the particular group idle for the period of time to allow for self-curing of the particular group; and
the one or more control circuits are configured to determine that the particular group has successfully completed the self-curing, the determining that the particular group is no longer a bad group is performed subsequent to determining that the particular group has successfully completed the self-curing.
5. The non-volatile storage apparatus of claim 4 , wherein:
the one or more control circuits are configured to refresh the particular group in response to determining that the particular group has successfully completed the self-curing;
the one or more control circuits are configured to verify that the particular group was successfully refreshed; and
the verifying that the particular group was successfully refreshed comprises the determining that the particular group is no longer a bad group.
6. The non-volatile storage apparatus of claim 5 , wherein:
the one or more control circuits are configured to refresh the particular group by performing an erase operation on the particular group; and
the one or more control circuits are configured to verifying that the particular group was successfully refreshed by performing an erase verification.
7. The non-volatile storage apparatus of claim 4 , wherein:
the one or more control circuits are configured to determine that the particular group has not successfully completed the self-curing and, in response thereto, provide for the particular group to remain idle for an additional period of time to allow for additional self-curing.
8. The non-volatile storage apparatus of claim 4 , wherein:
the one or more control circuits are configured to determine that the particular group has successfully completed the self-curing by performing partial re-programming of known data already stored in the particular group of non-volatile memory cells, determining a bit error rate for the known data in the particular group of non-volatile memory cells after the partial re-programming and comparing the bit error rate to a reference.
9. The non-volatile storage apparatus of claim 4 , wherein:
the one or more control circuits are configured to determine that the particular group has successfully completed the self-curing by reading data already stored in the particular group of non-volatile memory cells, performing partial re-programming of the data in the particular group of non-volatile memory cells based on the reading, determining a bit error rate for the known data in the particular group of non-volatile memory cells after the partial re-programming and comparing the bit error rate to a reference.
10. The non-volatile storage apparatus of claim 1 , wherein:
the one or more control circuits are configured to use a same standard for determining whether the particular group of non-volatile memory cells is a good group or a bad group before and after the period of time.
11. The non-volatile storage apparatus of claim 1 , wherein:
the groups of non-volatile memory cells are organized into subsets of groups; and
the one or more control circuits configured to operate over time using a repeating cycle of phases, during each phase the one or more control circuits are configured to perform multiple times more memory operations on only one of the subsets of groups as compared to other sub sets.
12. The non-volatile storage apparatus of claim 1 , wherein:
the groups of non-volatile memory cells are blocks and the particular group is a particular block;
the plurality of non-volatile memory cells comprise two dimensional flash memory cells with floating gates and tunnel dielectric regions; and
the one or more control circuits are configured to determine that the particular block of non-volatile memory cells is a bad block because the particular block of non-volatile memory cells includes charge trapped in the tunnel dielectric regions.
13. The non-volatile storage apparatus of claim 1 , wherein:
the groups of non-volatile memory cells are blocks and the particular group is a particular block; and
the plurality of non-volatile memory cells comprise a monolithic three dimensional flash memory that includes vertical NAND strings having charge trapping layers.