Determination of word line to word line shorts between adjacent blocks
A number of techniques for determining defects in non-volatile memory arrays are presented, which are particularly applicable to 3D NAND memory, such as that of the BiCS type. Word line to word shorts within a memory block are determined by application of an AC stress mode, followed by a defect detection operation. An inter-block stress and detection operation can be used determine word line to word line leaks between different blocks. Select gate leak line leakage, both the word lines and other select lines, is consider, as are shorts from word lines and select lines to local source lines. In addition to word line and select line defects, techniques for determining shorts between bit lines and low voltage circuitry, as in the sense amplifiers, are presented.
1. A method comprising:
performing a select gate to select gate stress operation on a first select gate line and a second select gate line of a non-volatile memory circuit comprising a memory array that includes a plurality of memory cells coupled in series between one or more drain select gates and one or more source select gates, the first select gate line coupled to a first one of the one or more drain select gates and the one or more source select gates, and the second select gate line coupled to a second one of the one or more drain select gates and the one or more source select gates, the select gate to select gate stress operation including applying a set of stress voltage levels to the first and second select gate lines to thereby introduce a voltage differential therebetween; and
subsequently performing a defect determination operation on the first and second select gate lines to determine leakage therebetween.
2. The method of claim 1 , wherein the first and second select gate lines are coupled to corresponding source select gates.
3. The method of claim 1 , wherein the first and second select gate lines are coupled to corresponding drain select gates.
4. The method of claim 1 , wherein the set of stress voltage levels comprise a DC stress.
5. The method of claim 1 , wherein the set of stress voltage levels comprise an AC stress.
6. The method of claim 1 , wherein the first and second select gate lines comprise a common set of NAND strings.
7. The method of claim 1 , wherein the memory array comprises a plurality of blocks and the first and second select gate lines comprise differing adjacent blocks.
8. The method of claim 1 , wherein the memory array comprises a plurality of blocks each having a plurality of independently selectable sub-blocks, and the first and second select gate lines comprise differing adjacent sub-blocks of the same block.
9. The method of claim 1 , wherein the first one of the one or more drain select gates and the one or more source select gates, and the second one of the one or more drain select gates and the one or more source select gates each have programmable threshold levels, and wherein the defect determination operation comprises:
performing a programming operation on the first one of the one or more drain select gates and the one or more source select gates, and the second one of the one or more drain select gates and the one or more source select gates; and
determining whether the programming operation was successful.
10. The method of claim 1 , wherein:
the memory circuit comprises a monolithic three-dimensional semiconductor memory device where the memory cells are arranged in multiple physical levels above a silicon substrate and comprise a charge storage medium; and
the memory array comprises NAND strings that run in a vertical direction relative to the substrate.
11. A method comprising:
performing a word line to select gate stress operation on a word line and a select gate line of a non-volatile memory circuit comprising a memory array that includes a plurality of memory cells coupled in series between a drain select gate and a source select gate, the word line coupled to one of the memory cells, the select gate line coupled to the drain select gate or the source select gate, the word line to select gate stress operation including applying a set of stress voltage levels to the word line and select gate line to introduce a voltage differential therebetween; and
subsequently performing a defect determination operation on the word line and select gate line to determine leakage therebetween.
12. The method of claim 11 , wherein the select gate line is coupled to the source select gate.
13. The method of claim 11 , wherein the select gate line is coupled to the drain select gate.
14. The method of claim 11 , wherein the set of stress voltage levels comprise a DC stress.
15. The method of claim 11 , wherein the set of stress voltage levels comprise an AC stress.
16. The method of claim 11 , wherein the memory circuit is a monolithic three-dimensional semiconductor memory device where the memory cells are arranged in multiple physical levels above a silicon substrate and comprise a charge storage medium, and wherein the memory array comprises a NAND type architecture in which NAND strings run in a vertical direction relative to the silicon substrate.