METROLOGY METHOD AND APPARATUS LITHOGRAPHIC APPARATUS LITHOGRAPHIC PROCESSING CELL AND SUBSTRATE COMPRISING METROLOGY TARGETS

摘要

The metrology apparatus is arranged to illuminate a plurality of targets in an off-axis illumination mode. The images of the targets are obtained using only a first order diffracted beam. If the target is a composite grating, the overlay measurements may be obtained from the intensities of the images of the different gratings. The overlay measurements may be corrected for errors caused by position changes of the gratings in the image field.