NANOOCS

Overlay optical metrology systems comprised of measurement optics, wafer handling mechanisms and system control hardware and software for measuring the difference between two nearly coincident patterns on a sample, such as a semiconductor wafer, which patterns are formed by a process such as photolithography, and which patterns are overlaid, one on top of the other and the overlay difference or error may be fed back to the exposure system that created the patterns so that this difference may be corrected on future exposures