A Novel Faster-Than-at-Speed Transition-Delay Test Method Considering IR-Drop Effects

Interconnect defects such as weak resistive opens, shorts, and bridges increase the path delay affected by a pattern during manufacturing test but are not significant enough to cause a failure at functional frequency. In this paper, a new faster-than-at-speed method is presented for delay test pattern application to screen small delay defects. Given a test pattern set, the technique groups the patterns into multiple subsets with close path delay distribution and determines an optimal test frequency considering both positive slack and performance degradation due to IR-drop effects. Since, the technique does not increase the test frequency to an extent that any paths exercised at the rated functional frequency may fail, it avoids any scan flip-flop masking. As most semiconductor companies currently deploy compression technologies to reduce test costs, scan-cell masking is highly undesirable for pattern modification as it would imply pattern count increase and might result in pattern regeneration. Therefore, our solution is more practical as the test engineer can run the same pattern set without any changes to the test flow other than the at-speed test frequency.