Automated visual inspection for LSI wafer patterns using a derivative-polarity comparison algorithm

Algorithms for visual inspection of LSI wafer multilayer patterns have been developed. These algorithms compare corresponding images of two dies on a wafer. In this paper, two algorithms are proposed. The derivative-polarity comparison algorithm compares the polarities of the first derivatives of two images, and recognizes the regions whose polarities are not matched as positional discrepancies (defects), in order to cope with gray-scale differences caused by pattern thickness errors. The multiple-displacement pattern matching algorithm executes the above polarity comparisons at several positions with images suitably aligned, and determines the common unmatched regions as defective, in order to handle the interlayer- registration errors encountered with multilayer patterns. These algorithms were evaluated experimentally, and it was verified that defects of 0.3 micrometers or more can be reliably detected in multilayer patterns by combining these algorithms.