VORRICHTUNG ZUM ERMITTELN VON FEHLERN IN FLAECHENHAFTEN MUSTERN, INSBESONDERE IN PHOTOMASKEN

摘要

An apparatus for detecting defects in patterns, particularly defects in chip patterns of photomasks used for manufacturing semi-conductor integrated circuits comprises means such as a flying spot scanner for producing a scanning light spot, an optical system for projecting said scanning light spot simultaneously on to identical portions of two patterns to be compared with each other, said patterns being placed on a carrier stage, first and second photoelectric converters, each converter receiving the light spot passing through or reflected from a respective pattern to produce an output electrical signal; and an electric circuit for receiving the output signals from said first and second photoelectric converters and subtracting one of them from the other to produce a difference signal which represents detected defects in the patterns. The electric circuit means further comprise a delay circuit for delaying before subtraction one of the signals from the photoelectric converters or delaying said difference signal by a predetermined time period so as to delete pseudo-defects in the patterns.