A print bias target is imaged in a single layer of light-sensitive material. The print bias target is made up of a pair of concentric geometric shapes in which a plurality of target regions forms a plurality of isolated edges. Each target region is of a different image structure than each...http://www.google.com.hk/patents/US5776645?utm_source=gb-gplus-share專利 US5776645 - Lithographic print bias/overlay target and applied metrology
