Patent ID: 7256871

Claim:
A lithographic apparatus comprising: a substrate table configured to hold a substrate; an illuminator configured to condition a beam of radiation; a support structure configured to support a patterning device that imparts a desired pattern to the beam of radiation; a projection system configured to project the patterned beam onto a target portion of the substrate; and a motion control system configured to control a movement of the substrate table, the motion control system comprising a plurality of position detectors that detect a position of the substrate table, at least three of the position detectors each including a single or multi-dimensional optical encoder to provide at least six position values, the optical encoders being coupled to the substrate table at different locations within a three dimensional coordinate system, wherein at least one position value is provided for each dimension of the three dimensional coordinate system, wherein the motion control system is configured to calculate the position of the substrate table within the three dimensional coordinate system from a subset of at least three of the six position values and to calculate an orientation of the substrate table with respect to the three dimensional coordinate system from another subset of at least three of the six position values, wherein the position detectors comprise: a first two-dimensional encoder configured to measure a position of the substrate table in a first and a third dimension of the three dimensional coordinate system, the first encoder being mechanically coupled to a first side of the substrate table where the first side is substantially parallel to the first dimension, a second one-dimensional encoder configured to measure a position in the third dimension of the three dimensional coordinate system, the second encoder being mechanically coupled to the first side of the substrate table, wherein the first and second encoder are coupled to opposite parts of the first side with respect to a middle of the first side, and wherein the motion control system determines a position in the first dimension from a position value of the first encoder and determines a rotation of the substrate table around the second dimension from position values of the first and second encoders.