Optical imaging apparatus

摘要: An imaging apparatus, for instance a wafer stepper, has an optical system forming image of object such as reticle and it focusing device. The device detector means determining deviations between the actual surface second (surface semiconductor wafer) on which is to be formed. includes two sets means, each said set having fast with constructed focus spot monochromatic light under large angle incidence onto collecting reflected by differential so located that centered when surfaces coincide summing signals supplied detectors both sets, being arranged path in substantially reverse from other.