IC Diagnosis Using Multiple Supply Pad IDDQs

screen for shorting defects in digital integrated circuits. Unfortunately, single-threshold IDDQ methods applied to devices fabricated in deep-submicron technologies result in unacceptably high levels of yield loss. The significant increase in subthreshold leakage currents in these technologies makes it difficult to set an absolute pass/fail threshold to fail only defective devices.1 There have been proposed solutions to the subthreshold leakage current problem and, more recently, to process variation issues. Current signatures, delta-IDDQ and ratio IDDQ are based on a self-relative analysis, in which the average IDDQ of each device is factored into the pass/fail threshold value.2–4 We refer to the technology dependency of subthreshold leakage current as a technology-related variation effect to contrast it with the chip-to-chip variation effects caused by changes in process parameters (process variation). We base our approach on a previous VDDTbased method called transient signal analysis (TSA).5 TSA uses regression analysis to calibrate for process and technology-related variation effects by cross-correlating multiple supply pin transient signals measured under each test sequence. The IDDQ signal analysis, or QSA, method proposed uses a set of IDDQ measurements instead, each obtained from the individual supply pins of the device under test (DUT). The process and technology calibration procedure used in QSA is based on a regression analysis procedure similar to TSA. In TSA, we referred to signal variation resulting from defects as regional variation, to contrast it with the global variations introduced by process and technology-related effects. For transient signals, the supply rail’s resistancecapacitance (RC) network modifies signal characteristics, such as phase and magnitude, at different supply pin test points. In QSA, only the resistive component of the supply rail network introduces variation in the IDDQ values at different supply pins. In either case, the position of the defect in the layout with respect to any given power supply pin is related to the amount of regional defect variation observed at that pin. For QSA, the variation is directly related to the resistance between the defect site and the pin. For example, a larger value of IDDQ is expected on supply pins closer to the defect site because of the smaller resistance. Therefore, the multiple IDDQ measurements can be used to detect the defect as well as triangulate the physical position of the defect in the layout. Defect detection experiments are on going and will be addressed in a future work. In this work, we develop a diagnostic method for QSA and present a set of simulation results are to demonstrate its defect localization accuracy. A IC Diagnosis Using Multiple Supply Pad IDDQs IC Diagnosis