Rapid pattern inspection of shadow masks by machine vision integrated with Fourier optics

Abstract

We present a machine vision inspection method that is specially devised to detect defects on shadow masks. This method incorporates Fourier optics to capture only irregular defects in real time by blocking out the periodically repetitive pattern of normal mask holes using a pinhole type spatial filter under coherent illumination. In addition, a fast defect-detection image processing algorithm efficiently suppresses undesirable background noisy images. Experimental results prove that this method provides a detection capability of 500 mu m(2) for the least defect size. (C) 1997 Society of Photo-Optical Instrumentation Engineers.