Automated photomask inspection apparatus and method

摘要

A transmissive substrate (14) is illuminated by a laser (30) through an optical system comprised of a laser scanning system (40,42), individual transmitted and reflected light collection optics (84,35) and detectors (34,36) collect and generate signals representative of the light transmitted and reflected by the substrate (14) as the substrate is scanned repeatedly in one axis in a serpentine pattern by a laser beam (13) which is focused on the patterned substrate surface. The defect identification of the substrate is performed using only those transmitted and reflected light signals (15,17), and other signals derived from them, such as the second derivative of each of them. The actual defect identification is then performed by comparing combinations of at least two of those measured and derived signals.