US Patent 7751047 Alignment and alignment marks

A lithographic substrate provided with an alignment mark, the alignment mark having a plurality of features spaced apart from one another, each feature being spaced apart from adjacent features by a different distance is disclosed. Further, there is disclosed a method of aligning a lithographic substrate provided with an alignment mark which has a plurality of features spaced apart from one another, each feature being spaced apart from adjacent features by a different distance, the method including measuring a distance between two of the features on the substrate, comparing the distance with a recorded set of distances, and determining from the comparison the position of the substrate.