Patent ID: 7283249

Claim:
A lithographic apparatus comprising: (a) an object support configured to support an object; (b) an interferometer measurement system including an X interferometer measurement system configured to measure a position of said object support in an X direction of an XYZ coordinate system, a Y interferometer measurement system configured to measure a position of said object support in a Y direction of the XYZ coordinate system, and a Z interferometer measurement system configured to measure a position of said object support in a Z direction of the XYZ coordinate system; (c) an object support positioning system configured to position the object support in a number of degrees of freedom based on measurements of the interferometer measurement system; and (d) a calibration device configured to: (i) measure a rotation Ry of the object support about the Y direction with the X interferometer measurement system in at least two different Z positions; (ii) measure a rotation Ry of the object support about the Y direction with the Z interferometer measurement system in at least two different Z positions; (iii) calibrate a linear Z dependency of Ry on the basis of measurement of the rotation Ry with the X interferometer measurement system and measurement of the rotation Ry with the Z interferometer measurement system; and (iv) calibrate a linear X dependency of Z on the basis of calibration of the linear Z dependency of Ry.