METHOD AND APPARATUS FOR DETECTING EXTRANEOUS SUBSTANCE

摘要

PURPOSE:To make it possible to eliminate an oversight of an extraneous substance by separating and detecting the extraneous substance from the background by a threshold curve determined on a two-dimensional plane which is formed of detection signal values obtained by first and second detecting means. CONSTITUTION:An extraneous substance emphatical detection output VL obtained from a photoelectric conversion element 6L which detects an extraneous substance on a wafer 1 with emphasis and a pattern emphatical detection output VH obtained from a photoelectric conversion element 6H which detects a pattern (background) on the wafer 1 with emphasis are converted into digital values by A/D converters 12. Then, a free curve threshold f(VL) determined primarily for the value of the extraneous substance emphatical detection output VL is outputted by a threshold memory 13, with the value of the VL used as an address, and the pattern emphatical detection output VH and the threshold f(VL) are compared with each other by a comparator circuit 14. In this way, the extraneous substance is recognized as existing when the pattern emphatical detection output VH is smaller than the threshold f(VL). According to this constitution, an oversight of the extraneous substance in proximity to a pattern existing area is prevented.