Pattern alignment method based on consistency among local registration candidates for LSI wafer pattern inspection

This paper reports an image-processing algorithm for robust inspection of LSI wafer patterns using SEM. In order to detect defects in a regular LSI pattern, a pair of long patterns are compared, blocked images are aligned, and defects are judged using the aligned images. The LSI wafer pattern is defined to consist of blank space, fine repetitive patterns, and unique patterns. Distortion of the SEM image is larger than the repetitive pattern pitch, requiring the system to keep track of the alignment in areas without pattern information or in blank space and mitigate the indeterminacy of repetitive patterns. To satisfy these requirements, a two-layer algorithm is proposed. The lower layer calculates registration candidates in each block, and the upper layer determines the correct registration route, i.e. the chain of the correct registration, using candidate information in all the related blocks. Experimental evaluations confirm that most pattern cases can be inspected correctly using the proposed SEM inspection system.