MASK PATTERN INSPECTION APPARATUS WITH KOEHLER ILLUMINATION SYSTEM USING LIGHT SOURCE OF HIGH SPATIAL COHERENCY

摘要

A semiconductor device fabrication-use mask pattern inspection apparatus having an optical configuration adaptable for achievement of a Koehler illumination system using a light source high in spatial coherency is disclosed. This apparatus includes a laser light source, a beam expander which is disposed between the laser source and a mask for expanding laser light to form an optical path of collimated light rays, and a beam splitter placed in the collimated light ray optical path for splitting the optical path into two optical paths. In one of these paths, a transmissive illumination optics is placed which irradiates transmission light onto the mask; in the other path, a reflective illumination optics is placed for irradiation of reflected light onto the mask. A pattern image of this mask is detected by a photosensitive device to generate a detected pattern image, which is sent to a comparator for comparison with a fiducial image thereof.