Patent ID: 8368902

Claim:
A lithographic apparatus comprising: a patterning device support configured to hold a patterning device, the patterning device configured to pattern a beam of radiation to provide a patterned beam of radiation; a substrate support configured to hold a substrate; a projection system configured to project the patterned beam of radiation onto the substrate; and a positioning system configured to position one of the patterning device support or the substrate support, the positioning system comprising a first encoder configured to measure a position of said one of the patterning device support or the substrate support along a first direction, a second encoder configured to measure a position of said one of the patterning device support or the substrate support along a second direction, a grating configured to cooperate with said first and second encoders to measure the position of said one of the patterning device support or the substrate support along the first and second directions, said grating extending along the first and second directions, wherein a dimension of said grating along the first direction is greater than a dimension of said grating along said second direction, wherein each of said first and second encoders have a nominal calibration accuracy and wherein only said first encoder is further calibrated to enhance the nominal calibration accuracy.