Projection exposure method and apparatus to determine optical performance of reticle

A projection exposure apparatus to be used with a reticle wherein a semi-transparent material effective to partially transmit exposure light and also effective to change a phase of the exposure light is used to form a circuit pattern and a light blocking zone adjacent to the circuit pattern, upon a transparent substrate to provide the reticle, the light blocking zone being constituted by a pattern not resolved by a projection optical system, and wherein the reticle is illuminated with the exposure light and is projected on a member to be exposed, through the projection optical system, said apparatus comprising:

• a movable stage for carrying thereon the member and being movable;
• a photodetector fixedly mounted on said movable stage;
• and
• control means for causing said movable stage to move said photodetector to a position where an image of the light blocking zone is formed through the projection optical system, to detect light quantity of the image with said photodetector, and for comparing the result of detection with a predetermined value to discriminate appropriateness of performing an exposure process with the reticle.