Cost-effective IR-Drop Failure Identification and Yield Recovery through a Failure-adaptive Test Scheme

Ever-increasing test mode IR-drop results in a significant amount of defect-free chips failing at-speed testing. The lack of a systematic IR-drop failure identification technique engenders a highly increased failure analysis time/cost and significant yield loss. In this paper, we propose a failure-adaptive test scheme that enables a fast differentiation of the IR-drop induced failure from the actual defects of the chip. The proposed technique debugs the failing chips using low IR-drop vectors that are custom-generated from the observed faulty response. Since these special vectors are designed in such a way that all the actual defects captured by the original vectors are still manifestable, their application can clearly pinpoint whether the root cause of failure is IR-drop or not, thus eliminating reliance on an intrusive debugging process that incurs quite a high cost. Such a test scheme further enables effective yield recovery from failing chips by passing the ones validated by the debugging vectors whose IR-drop level matches the functional mode. Experimental results show that the proposed scheme delivers a significant IRdrop reduction in the second test (debugging) phase, thus enabling a highly effective IR-drop failure identification and yield recovery at a slightly increased test cost.