Multiple pass programming for memory with different program pulse widths

摘要

Techniques are provided for programming memory cells while reducing the effects of detrapping which cause a downshift in the threshold voltage distribution. Detrapping is particularly problematic for charge-trapping memory cells such as in a 3D stacked non-volatile memory device. After completion of a full programming pass, a verify test is performed to identify cells for which reprogramming is warranted. The reprogramming can include multiple program-verify iterations which use longer program pulses than in the full programming pass. Moreover, the number of program-verify iterations is limited to reduce the reprogramming time. In one approach, cells of all target data states are programmed together. In another approach, cells of different target data states are programmed separately.

主权项

1. A method for programming in a memory device, comprising:
performing a plurality of program-verify iterations in one programming pass for a set of memory cells until a completion criterion is met for the one programming pass, wherein the set of memory cells comprises respective subsets of memory cells, each respective subset of memory cells has a respective target data state defined by a respective verify voltage and the completion criterion is met when at least a specified percentage of memory cells of each set of memory cells has a threshold voltage which is above the respective verify voltage; after the completion criterion is met for the one programming pass, identifying memory cells of each respective target data state for which reprogramming is warranted by performing a verify test to identify memory cells of each respective target data state having a threshold voltage which exceeded and then fell below a respective verify voltage; and performing a plurality of program-verify iterations in a reprogramming pass for the memory cells of each respective target data state for which reprogramming is warranted, wherein for each respective target data state, a width of a program pulse applied to the set of memory cells during the program-verify iterations in the reprogramming pass is longer than a width of a program pulse applied to the set of memory cells during the program-verify iterations in the one programming pass.