Failure analysis on non-visible front-end defects in deep NWELL implantation related process

In this paper, a low yield case with a specific failing pattern in the wafers and related to a systematic front-end defect in DNWELL from a specific location and structure in the device was discussed. This paper also illustrates and put emphasis on the importance of different Electrical and Physical FA techniques are critical to identify the culprit. These FA techniques include engaging TIVA analysis with DUT board, AFP current Imaging and nano-probing, Camelot layout path tracing, FIB circuit edit and junction staining. The systematic defect was due to DNWELL shorted to NWELL and resulted in IDD_off leakage. A detailed root cause analysis and failure mechanism of why this particular site always failed will be discussed in this paper. It would serve as a good reference to wafer Fab that encountered such issue.