Diagnosis, modeling and tolerance of scan chain hold-time violations

Errors in timing closure process during the physical design stage may result in systematic silicon failures, such as scan chain hold time violations, which prohibit the test of manufactured chips. In this paper, we propose a set of techniques that enable the accurate pinpointing of hold time violating scan cells, their modeling and tolerance, paving the way for the generation of valid test data that can be used to test chips with such systematic failures. The process yield is thus restored, as chips that are functional in mission mode can still be identified and shipped out, despite the existence of scan chain hold time failures. The techniques that we propose are non-intrusive, as they utilize only basic scan capabilities, and thus impose no design changes. Scan cells with hold time violations can be identified with maximal possible resolution, enabling the incorporation of the associated impact during the ATPG process and thus the generation of valid test data for the chips with such systematic failures.