Visual defect inspection of masks

摘要

An optical system and method for direct human eye visual inspection of specimens of photoresist coated masks for defects as small as 2 mu m. The specimens are uniformly illuminated with a partially coherent sodium light that has very high illuminance and constrast levels. The system consists of a high pressure (1-1.5 atmosphere) sodium lamp source projected onto the specimen by a Kohler-type illumination system.