Failure analysis of off-state leakage in high-voltage word-line decoder circuit of memory device

After 500-hour HTOL reliability test on memory device, off-state leakage was found in nMOSFETs of word-line decoder. According to electrical and physical failure analysis on IC and device level, we found that holes were trapped in SiN of STI edge, which lowered threshold voltage of nMOSFETs and lead to off-state leakage from drain to source. The hole-traps came from anode gate low current flow and were trapped in SiN layer. The hole-traps could be annihilated by electron beams from SEM, and this phenomenon might mislead judgment during failure analysis. Detailed failure analysis, failure mechanism and corresponding improvement of circuit and process are presented in this paper.