Methodology of Generating Timing-Slack-Based Cell-Aware Tests

In order to reduce defect parts per million, cell-aware (CA) methodology was proposed to cover various types of intracell defects. In this article, we present a novel methodology for generating 2-time-frame (2tf) CA tests based on timing slack analysis. The proposed 2tf CA fault model, aware of timing slack and named TS, defines a fault: 1) on a cell instance basis and 2) based on per-instance timing criticality (according to timing slack). By comparing the derived extra delay against the timing slack of the cell instance, a delay fault can be defined, and according to its severity, the fault can be further classified into small-delay fault or gross-delay fault. In contrast to prior 2tf CA methodology that is on a cell (rather than cell instance) basis and unaware of timing criticality/slack, our methodology can identify 'more realistic' faults which really need to be considered, and potentially the cost/effort for testing those 2tf CA faults can be reduced. We also propose a test quality metric, timing slack defect coverage (TSDC), to measure the effectiveness of automatic test pattern generation (ATPG) tests in terms of the ability to detect small-delay TS defects along long paths. Experimental results on a set of 22-nm industrial designs demonstrate that, due to more realistic fault identification, the number of identified small-delay faults can be reduced by 56.8%. With the slack-based ATPG for testing small-delay faults along long paths, TS can reduce the number of test patterns by 33.1% while achieving 0.49% higher TSDC, compared with the results of prior 2tf CA methodology.