Exploiting path delay test generation to develop better TDF tests for small delay defects

Abstract

Localized small delay defects, for example due to degraded transistor drive strength caused by a broken fin, are a growing concern in current FinFET and emerging gate all around (GAA) technologies. Such defects are currently targeted by timing-aware Transition Delay Fault (TDF) tests that aim to test the target nodes along the longest path. The resulting tests often require considerable test generation time, have high test data volume, and at times do not provide the desired coverage. In this paper, we show that Path Delay Fault (PDF) test generation can be exploited to not only generate the timing tests more efficiently, but the resulting TDF test sets are also more compact and perform better on commonly used delay test coverage metrics. This is because all TDF faults along a PDF targeted timing-critical path can be detected efficiently by generating a single PDF test. This efficiency is not explicitly exploited by node oriented TDF test generation even when the TDFs are targeted along the longest paths. We demonstrate the effectiveness of our methodology for a range of benchmark circuits by comparing the results from a commercial timing-aware ATPG (TA-ATPG) with our new approach that efficiently exploit PDF tests wherever possible. The proposed new approach results in approximately 12.5% reduction in pattern volume, 35% reduction in ATPG runtime and also a 5% improvement in delay test coverage (DTC) when compared to existing TA-ATPG approaches.