Abstract
With the increase in size and capacity of flash memory, long test times on complicated automatic test equipment (ATE) are now commonly seen. The test-consuming diagnosis process for ATEs results in high test cost and slow time-to-volume; thus, efficient diagnosis of flash memory has recently become a critical issue. Based on our previous work, which developed a set of disturb fault models using a systematic approach and improved March-like algorithms for both bit-oriented and word-oriented flash memory, in this work we propose cost-effective diagnostics for flash memory. The diagnosis methodology efficiently distinguishes the fault types of faulty cell from the fail bit-maps by comparing the fault signature with the fault dictionary and the fault bit-maps provide detailed diagnosis information for yield and reliability improvement. We also propose a built-in self-diagnosis (BISD) scheme that collects useful test information for off-chip diagnosis analysis and contains a unique test mode control that reduces test time and diagnostic data shift-out cycles by using a parallel shift-out mechanism. Additionally, test time is also greatly reduced by accessing the engineering test mode to do parallel programming and parallel erasing. Finally, we show a configurable diagnostics system for low-cost test and diagnosis environment. Experiments were done using industrial flash products to justify the effectiveness of our low-cost configurable diagnostics system and the efficiency using March-like test algorithm in the test flow. Furthermore, a systematic approach to minimize themass production test time by analyzing and rearranging the test items in the test flow is also presented in this work. We propose three test time reduction (TTR) techniques and implement an automatic TTR tool based on these techniques to identify redundant test items, suggest proper tests, and provide correlation between the test items. Experimental results show the TTR tool effectively reduces the test time of industrial memory mass production test flow; the results are on top of the original test flow that has been compacted by conventional way based on statistics.