METROLOGY METHOD AND APPARATUS, LITHOGRAPHIC APPARATUS, LITHOGRAPHIC PROCESSING CELL AND SUBSTRATE COMPRISING METROLOGY TARGETS
摘要
<p>A metrology apparatus is arranged to illuminate a plurality of targets with an off-axis illumination mode. Images of the targets are obtained using only one first order diffracted beam. Where the target is a composite grating, overlay measurements can be obtained from the intensities of the images of the different gratings. Overlay measurements can be corrected for errors caused by variations in the position of the gratings in an image field.</p>
