Advanced Method to Locate The Defect on Zener Diode to Avoid Cutting The Circuit in Failure Analysis

Due to metal layers coverage, many signals couldn’t be measured by mechanical probe test to perform electrical isolation. And usually EMMI^[1] (Emission Microscope) or OBIRCH^[2] (Optical Beam Induced Resistor Change) analysis can’t directly highlight the real defect for function failure. It’s difficult to isolate Zener diode failure because the current path which through others device. We can’t test the Zener diode leakage directly unless to cut the circuit to isolate the Zener diode alone. In the paper we proposed one novel and effective method for locating Zener diode defect on device level to avoid the irreversible destructive test. The main idea was that if there is a defect on Zener diode in spite we can’t find a leakage effected by others circuit but we can find the voltage is abnormal. Then we can use the function EMMI^[3] to location the defect instead of cut the circuit to isolate the Zener diode alone. After PFA (Physical Failure Analysis), the defect was found. Thus, we believe the advantage measurement method is novel, effective and save cycle time. It was beneficial to our FA for Zener diode on device level in electrical failure isolation.