Study on sensitive character of unexpected high impedance circuit in VLSI failure analysis

Microprobe analysis plays an important role in failure analysis as it could reveal the failed signal directly and help to isolate the final failed device. But when met unexpected high impedance circuit, the real signal couldn't be measured as high impedance site was sensitive to probe needle and strong light. One real Case and experiment was studied in this paper to show how high impedance circuit was sensitive and how to find the root cause of this unstable failure efficiently.