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This paper presents a analysis of depth of focus (DOF) based on optics or detector pixel size inoptical microscopes with electronic cameras. We first generally analyze DOF based on optics indifferent cases related to the spatial coherence of illumination and the object, and then use adesign example of infinity correction system for review system to show DOF depended on illumi- nation numerical aperture. Finally, we discuss DOF increase based on detector pixel size, and thenuse a design example of infinity correction system for inspection system. Both designs are verified with simulation using CODEY, a optical design software. Both designs are used in KLA STAR-1ight' Multi-surface Inspection (backside glass and pellicles).Keywords: depth of focus, spatial partial coherence, illumination numerical aperture, infinity cor-rection, diffraction encircled energy1. INTRODUCTIONThe performance of optical microscopes is assessed primarily by the resolution (R) and the depthof focus (DOF). These microscopes are used in the inspection and review systems of flat paneldisplays, wafers and photomasks (including backside glass and pellicles). In describing in opticsand optical engineering, it is common to use the following:DOF = |
