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 of determining one or more defective word lines, the method comprising:
performing an inter-block stress operation on a pair of physically adjacent blocks of non-volatile memory cells of an array formed along word lines in a memory circuit, including applying a set of stress voltage levels to word lines of the pair of blocks to introduce a voltage differential between the pair of physically adjacent blocks; and
subsequently performing a defect determination operation, including:
performing an erase operation on the pair of physically adjacent blocks;
determining whether the erase operation was successfully completed;
subsequently performing a write operation on the pair of physically adjacent blocks: and
determining whether the write-operation was successful.
2. The method of claim 1 , wherein the set of stress voltage levels applied to the word lines of the pair of blocks is a set of voltages associated with a DC stress.
3. The method of claim 1 , wherein the set of stress voltage levels applied to the word lines of the pair of blocks is a set of voltages associated with an AC stress.
4. The method of claim 1 , wherein the applying the set of stress voltage levels includes applying a high voltage level to word lines of a first block of the pair of physically adjacent blocks while concurrently setting word lines of a second block of the pair of physically adjacent blocks at a low voltage level.
5. The method of claim 4 , wherein the high voltage level is within the range of a programming voltage used during the write operation.
6. The method of claim 4 , wherein the low voltage level is ground.
7. The method of claim 1 , wherein the applying the set of stress voltage levels includes applying a high voltage level to even word lines of a first block of the pair of physically adjacent blocks and odd word lines of a second block of the pair physically adjacent blocks while concurrently setting odd word lines of the first block and even word lines of the second block at a low voltage level.
8. The method of claim 7 , wherein the high voltage level is within the range of a programming voltage used during the write operation.
9. The method of claim 7 , wherein the low voltage level is ground.
10. The method of claim 1 , further comprising:
in response to determining that the erase operation was not successfully completed, marking the pair of physically adjacent blocks as defective.
11. The method of claim 1 , wherein the determining whether the write operation was successful comprises:
reading written data from the pair of physically adjacent blocks; and
comparing the written data as read from the pair of physically adjacent blocks to original data used for the write operation.
12. The method of claim 1 , wherein the determining whether the write operation was successful comprises determining that the write operation failed based on a number of programming loops exceeding a limit.
13. The method of claim 1 , further comprising:
in response to determining that the write operation was not successfully completed, marking the pair of physically adjacent blocks as defective.
14. The method of claim 1 , wherein the defect determination operation further includes:
subsequently performing an erase operation on a first block of the pair of physically adjacent blocks; and
subsequently determining whether data stored in a second block of the pair of physically adjacent blocks was subject to an erase disturb in response to the erase operation on the first block of the pair of physically adjacent blocks.
15. The method of claim 14 . further comprising:
in response to determining that the second block of the pair of physically adjacent blocks was subject to an erase disturb in response to the erase operation on the first block of the pair of physically adjacent blocks, marking the pair of physically adjacent blocks as defective.
16. The method of claim 1 , wherein the array is formed according to a NAND type architecture.
17. The method of claim 1 , wherein the array is formed in a memory circuit, wherein the memory circuit includes a monolithic three-dimensional semiconductor memory device with the non-volatile memory cells arranged in multiple physical levels above a silicon substrate and wherein each of the non-volatile memory cells comprises a charge storage medium.
18. The method of claim 17 , wherein the array is formed according to a NAND type architecture having NAND strings that run in a vertical direction relative to the substrate, and wherein NAND strings of the pair of physically adjacent blocks are connected along a common set of bit lines running in a horizontal direction relative to the substrate.
19. The method of claim 1 , wherein the intra-block stress operation and subsequent defect determination operation are performed as a built in self-test process.
20. The method of claim 1 , wherein the inter-block stress operation further includes applying a set of stress voltage levels to select gate lines of the pair of blocks to introduce a voltage differential between the pair of physically adjacent blocks.