Analyzing the effectiveness of multiple-detect test sets

Abstract

Multiple-detect test sets have been shown to be effective in lowering defect level. Other researchers have noted that observing the effects of a defect can be controlled by sensitizing affected sites to circuit outputs but defect excitation is inherently probabilistic given a defect’s inherent, unknown nature. As a result, test sets that sensitize every signal line multiple times with varying circuit state has a greater probability of detecting a defect. In past work, the entire circuit is considered when varying circuit state from one vector to another for a given signal line. However, it may be possible to improve defect excitation by exploiting the localized nature of many defect types. Spec$cally, by varying circuit state in the physical region or neighborhood surrounding a line affected by a defect, the defect excitation and therefore detection can be improved. In this paper, we present a method for extracting a physical region surrounding a signal line but more importantly, techniques for analyzing the excitation characteristics of the region. Analysis of 4-detect test sets reveals that 30% to 60% of signal line regions do not achieve at least four unique states, indicating opportunity to further reduce defect level.