Patent ID: 7408617

Claim:
A lithographic apparatus, comprising: an illumination system that conditions a radiation beam; an array of individually controllable elements that modulate the radiation beam; a substrate table that supports a substrate; a projection system that projects the modulated radiation beam onto a target portion of the substrate, thereby applying a pattern to the target portion of the substrate, the pattern comprising a first line and a second line, the first line being offset from the second line; a position encoder that determines a position of the substrate table, the position encoder comprising a position sensor and a scale, the scale comprising a plurality of lines intended to be straight and parallel to one another; an imaging device that obtains an image of the first line and the second line; and an image processing unit that measures separation between the first line and the second line in a plurality of locations thereby defining a plurality of separations and determines a non-uniformity of at least a part of the scale from the plurality of separations.