Static fault localization on Memory failures using Photon Emission Microscopy

Conventionally, Static Random Access Memory (SRAM) failures rely on memory bitmap for failure analysis. Static fault localization approach is ineffective except if the defect is large enough to cause a resistive short between the VDD and VSS nodes. However, it was observed that subtle defects that fall in the wordline (WL) of the pass gate transistor results in a partially turned-on NMOS with electroluminescence that can be effectively localized by Photon Emission Microscopy (PEM). In this paper, we leverage on this phenomenon to showcase 4 cases where static fault localization using PEM has helped the foundry to resolve memory BIST yield loss on advanced technology node devices without bitmap capability.