Non-volatile memory with intentional overprogramming to improve short term data retention issue
To remedy short term data retention issues, a non-volatile memory performs a multi-pass programming process to program data into a set of non-volatile memory cells and identifies non-volatile memory cells that experienced downward threshold voltage drift after a first pass of the multi-pass programming process and prior to a final pass of the multi-pass programming process. The final pass of the multi-pass programming process comprises programming non-volatile memory cells not identified to have experienced the downward threshold voltage drift to a set of final target threshold voltages and purposefully overprogramming non-volatile memory cells identified to have experienced the downward threshold voltage drift to threshold voltages greater than respective final target threshold voltages by one or more offsets.
1. A non-volatile storage apparatus, comprising:
a first set of non-volatile memory cells; and
one or more control circuits connected to the non-volatile memory cells, the one or more control circuits are configured to perform a multi-pass programming process to program data into the first set of non-volatile memory cells by performing a first pass of the multi-pass programming process including programming the first set of non-volatile memory cells using a set of intermediate verify voltages and performing a second pass of the multi-pass programming process including programming the first set of non-volatile memory cells using a set of final target verify voltages, the final target verify voltages are greater in voltage magnitude than respective intermediate verify voltages;
the one or more control circuits are further configured to:
identify non-volatile memory cells of the first set of non-volatile memory cells that experienced downward threshold voltage drift after successfully completing the first pass of the multi-pass programming process and before starting the second pass of the multi-pass programming process; and
perform the second pass of the multi-pass programming process by programming non-volatile memory cells not identified to have the experienced downward threshold voltage drift to the set of final target verify voltages and programming non-volatile memory cells identified to have the experienced downward threshold voltage drift to a set of offset verify voltages greater than respective final target verify voltages.
2. The non-volatile storage apparatus of claim 1 , further comprising:
a first word line connected to the one or more control circuits, the first set of non-volatile memory cells are connected to the first word;
a second word line connected to the one or more control circuits; and
a second set of non-volatile memory cells connected to the second word line;
the one or more control circuits are configured to perform the multi-pass programming process for the second set of non-volatile memory cells by performing the first pass of the multi-pass programming process including programming the second set of non-volatile memory cells using the set of intermediate verify voltages and performing the second pass of the multi-pass programming process for the second set of non-volatile memory cells using the set of final target verify voltages; and
the one or more control circuits are configured to identify the non-volatile memory cells of the first set of non-volatile memory cells that experienced downward threshold voltage drift after performing the first pass of the multi-pass programming process for the first set of non-volatile memory cells, after performing the first pass of the multi-pass programming process for the second set of non-volatile memory cells and prior to performing the second pass of the multi-pass programming process for the first set of non-volatile memory cells.
3. The non-volatile storage apparatus of claim 1 , wherein:
the multi-pass programming process is a foggy-fine programming process that includes a foggy pass and a fine pass;
the first pass of the multi-pass programming process is the foggy pass; and
the second pass of the multi-pass programming process is the fine pass.
4. The non-volatile storage apparatus of claim 1 , wherein:
the one or more control circuits are configured to complete the multi-pass programming process by overprogramming non-volatile memory cells identified to have the experienced downward threshold voltage drift to threshold voltages greater than respective final target verify voltages by an offset voltage.
5. The non-volatile storage apparatus of claim 1 , wherein:
the one or more control circuits are configured to perform the multi-pass programming process by programming the first set of non-volatile memory cells to a set of data states;
the set of data states include a lower subset of data states and a higher subset of data states, the data states of the lower subset of data states have lower threshold voltages than the data states of the higher subset of data states; and
the one or more control circuits are configured to identify non-volatile memory cells of the first set of non-volatile memory cells that experienced downward threshold voltage drift only for the higher subset of data states.
6. The non-volatile storage apparatus of claim 5 , wherein:
the one or more control circuits are configured to adjust which data states of the set of data states are in the higher subset of data states.
7. The non-volatile storage apparatus of claim 1 , wherein:
the one or more control circuits are configured to perform the multi-pass programming process by programming the first set of non-volatile memory cells to a set of data states; and
the one or more control circuits are configured to perform the second pass of the multi-pass programming process by verifying at two verify levels for at least a subset of the data states, the two verify levels include a respective final target verify voltage and an offset verify voltage that is greater than the respective final target verify voltage by an offset.
8. The non-volatile storage apparatus of claim 7 , wherein:
the one or more control circuits are configured to perform the verifying at two verify levels by sensing at two different sense times in response to a same word line voltage applied to the first set of non-volatile memory cells.
9. The non-volatile storage apparatus of claim 8 , wherein:
the one or more control circuits are configured to adjust the difference in the two different sense times.
10. The non-volatile storage apparatus of claim 7 , further comprising:
bit lines connected to the first set of non-volatile memory cells, the one or more control circuits are configured to perform the verifying at two verify levels by applying different bit line voltages when sensing.
11. The non-volatile storage apparatus of claim 10 , wherein:
the one or more control circuits are configured to adjust at least one of the different bit line voltages.
12. The non-volatile storage apparatus of claim 1 , wherein:
the first of non-volatile memory cells are positioned in NAND strings of a three dimensional memory array.
13. The non-volatile storage apparatus of claim 1 , wherein:
the first set of non-volatile memory cells are positioned in a memory die; and
the one or more control circuits are positioned in a control die that is bonded to the memory die, the one or more control circuits include a first interface to the memory die and a second interface to a memory controller that is separate from the control die.
14. A method of operating non-volatile storage, comprising:
performing a first pass of a multi-pass programming process including successfully programming a first set of non-volatile memory cells connected to a first word line using an intermediate verify voltage;
after performing the first pass of the multi-pass programming process including successfully programming the first set of non-volatile memory cells using the intermediate verify voltage, performing the first pass of the multi-pass programming process including programming a second set of non-volatile memory cells connected to a second word line using the intermediate verify voltage;
after performing the first pass of the multi-pass programming process including programming the second set of non-volatile memory cells using the intermediate verify voltage, sensing whether the first set of non-volatile memory cells have threshold voltages below the intermediate verify voltage;
after the sensing, performing a second pass of the multi-pass programming process for the first set of non-volatile memory cells including:
programming, using a final verify voltage, non-volatile memory cells of the first set of non-volatile memory cells that do not have threshold voltages below the intermediate verify voltage, and
programming, using an offset verify voltage that is greater than the final verify voltage by an offset, non-volatile memory cells of the first set of non-volatile memory cells that have threshold voltages below the intermediate verify voltage; and
after performing the second pass of the multi-pass programming process for the first set of non-volatile memory cells, performing a second pass of the multi-pass programming process for the second set of non-volatile memory cells.
15. The method of claim 14 , wherein:
the multi-pass programming process is a foggy-fine programming process;
the first pass of the multi-pass programming process is a foggy pass; and
the second pass of the multi-pass programming process is a fine pass.
16. The method of claim 14 , wherein:
the programming using the final verify voltage and the programming using the offset verify voltage are performed by verifying at two verify levels in response to a same gate voltage applied to the first set of non-volatile memory cells.
17. The method of claim 14 , further comprising:
adjusting the offset.
18. A non-volatile storage apparatus, comprising:
a set of non-volatile memory cells; and
means, connected to the set of non-volatile memory cells, for performing a foggy-fine programming process to program data into the set of non-volatile memory cells including identifying non-volatile memory cells of the set of non-volatile memory cells that experienced downward threshold voltage drift after successfully completing a foggy pass of the foggy-fine programming process and prior to a fine pass of the foggy-fine programming process, and performing the fine pass of the foggy-fine programming process by programming non-volatile memory cells not identified to have the experienced downward threshold voltage drift to a set of final target threshold voltages and purposefully overprogramming non-volatile memory cells identified to have the experienced downward threshold voltage drift to threshold voltages greater than respective final target threshold voltages of the set of final target threshold voltages by one or more offsets.