still for the coordination of a microscopic worm monster with a microscopic halvledareskivmonster

摘要

In a semiconductor photolithographic mask alignment system, a unique bifocus element is included in the microscope for permitting simultaneous focusing on the mask and semiconductor wafer surface, even though the mask and wafer separation is greater than the microscope depth of field. The bifocus element is preferably located at the rear focal plane of the microscope objective and is designed to image, at the same location, light from the mask polarized in a first direction and light from the wafer polarized at right angles to the first direction.