Abstract: Leakage current increase is a main failure pattern for integrated circuit(IC). By combining photon emission microscopy (PEM) with optical beam induced current change (OBIRCH) complementarily, PN junction leakage, isolation reduction of dielectric layer, consequential leakage current failure and backside analysis cases were studied, and localization techniques were analyzed in these electrical overstress, metal bridge and ESD failures. It can be concluded that the shape and location of a photon emission spot can be used to judge whether the failure is induced by an original leakage current or a consequential one. The result combined with circuit analysis can explain the cause of photon emission. OBIRCH can work as a more precise localization method for original defect, and backside OBIRCH analysis has an advantage in multilayer structure.