Systematic methods to identify and verify non-visible defects in silicon substrate

For failure analysis, most of defects are visible to imaging tools, such as OM, SEM, FIB, TEM etc. However, there are still lots of non-visible defects which cannot be caught by these tools. As complexity for such non-visible defect failure analysis is much high, FA engineers were often puzzled where to begin from. Two such cases were presented in this paper with solutions. The systematic methods for these cases include electrical data mining, brainstorming or fish-bone diagram method to list all failure possibilities, and then proper characterization tools or methods were used to identify and verify the hypotheses. Finally DOE (design of experiments) was used to verify the root cause. As a result, phosphorus contamination was found for embedded Flash products' MOS threshold voltage shift issue, and higher substrate oxygen concentration for Power MOS products source to drain low breakdown voltage issue.