Abstract
A method is proposed to support fast product-specific threshold setting in case of inspection by comparison of gray-scale images. With the proposed method, emphasis is laid on false alarms (false recognition of normal parts as defects), and the optimal threshold is set as the minimum value to keep the false alarm rate within acceptable limits. The proposed procedure of threshold setting consists of three stages, namely, calculation of initial threshold, preliminary inspection/review, and threshold correction. In initial threshold calculation and threshold correction, fast threshold renewal is obtained by numerical analysis, specifically, by successive approximations. The proposed method was applied to an actual device for visual inspection of LSI wafer patterns and proved to offer fast and efficient threshold setting. Thus, the threshold now can be set efficiently for specific products in an LSI production line, ensuring adequate feedback at a low false alarm rate. This implies flexible inspection in multi-item production with prompt adjustment to new products. © 1998 Scripta Technica, Syst Comp Jpn, 29(14): 81–91, 1998
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