A junction leakage mechanism induced by structure enhanced defects multiplication at bird's beak of field oxide (FOX) is reported for the first time. For the junction structure with poly-Si on FOX, the mask-edge-defects (MED) resulted from high dose implantation will lead to the formation of dislocations during back-end processing. The position of dislocations may be as deep as 1-2 μm from Si surface. The stress induced by interlayer dielectric film is believed to be the driving force for the multiplication of dislocations. Process modifications, including implantation dosage reduction, screen oxide removal after implantation, post-implantation annealing, and implantation without screen oxide, are shown to be able to suppress the leakage current slightly. Thus, prevention of MED formation is believed to be a fundamental solution of this problem.