Patent ID: 8634062

Claim:
A lithographic apparatus comprising: a radiation beam conditioning system configured to condition a beam of radiation, wherein the radiation beam conditioning system comprises an optical element and an actuator system arranged to control a position of the optical element, the actuator system comprising: first and second actuating elements, each having a first end connected to a base of the actuator system and a second end connected to the optical element, the first actuating element comprising first and second sections of material that are joined to each other with both sections extending from the first end to the second end of the first actuating element, and the second actuating element comprising third and fourth sections of material that are joined to each other with both sections extending from the first end to the second end of the second actuating element, and at least one power supply, configured to provide heat to the first and second actuating elements, the at least one power supply controlling the heat provided to the first actuating element independently from the heat provided to the second actuating element, wherein: the optical element is set apart from the base in a first direction, the coefficient of thermal expansion of the first section of material is different from that of the second section of material, the coefficient of thermal expansion of the third section of material is different from that of the fourth section of material, and the first and second actuating elements are each configured such that, when the temperature of the actuating element increases from a nominal working temperature, the actuating element applies a force to the optical element to be actuated that is parallel to a second direction, perpendicular to the first direction, such that the force applied by the first actuating element when its temperature increases is in an opposite direction to the force applied by the second actuating element when its temperature increases; a patterning device configured to pattern the conditioned beam of radiation; and a projection system configured to project the patterned beam of radiation onto a substrate.