Advanced scan chain failure analysis using laser modulation mapping and continuous wave probing

Scan chain failures are a significant fraction of yield loss. The complexity of modern design-for-test (DFT) implementation techniques and more subtle failure mechanisms of sub-40nm technologies make defect identification more challenging. Software chain diagnosis and a variety of EFA techniques have been deployed to improve scan chain failure isolation. However, we have found in practice that each of these techniques has significant limitations. In earlier papers we presented a new image-based laser technique (Modulation Mapping) to identify the first failing flop in the broken scan chain of stuck-at failures. Here we present three case studies of scan chains with more subtle resistive failure mechanisms, including transition, bridge, and slow-to-rise/fall failures, using a combination of modulation mapping (MM) and continuous-wave (CW) laser probing.