Layout-Oriented Defect Set Reduction for Fast Circuit Simulation in Cell-Aware Test

Abstract

The cell-aware test (CAT) methodology was previously proposed to target cell-internal faults that cannot be easily detected by gate-level stuck-at fault (SAF) patterns generated by conventional ATPG. It was shown to reduce the defect level on CMOS-based designs, with the help of detailed defect injected transistor-level circuit simulation and defect-enhanced SAF ATPG. The detailed transistor-level circuit simulation has been considered an issue in CAT, as it is very time consuming. The problem mainly lies in that all parasitic capacitors and resistors extracted from cell layout are considered as defect targets, so the defect set is large. To reduce the defect set, and therefore the circuit simulation time, we take layout into consideration when we construct the defect set for each cell, effectively removing the redundant or unnecessary defects and therefore reducing the circuit simulation time dramatically. We propose a generalized approach that can be used to build the fault models based on the cell layout, where the generated faults are closer to the realistic physical defects on the layout, so the number of faults is significantly reduced. The proposed method is verified by commercial 180nm and 350nm CMOS standard cell library, and the circuit simulation time is reduced to only 19% or even lower as compared with the original CAT methodology.