Patent ID: 6449030
Filing Date: 2002-09-10
Classification: G03F

Abstract:
A lithographic projection apparatus comprising:a radiation system which supplies a projection beam of radiation; a first object table for holding a mask; a second object table for holding a substrate; an imaging projection system which images irradiated portions of the mask onto target portions of the substrate; a balanced object table positioning system which positions at least one of said object tables; first and second balance masses; a bearing, supporting said first and second balance masses so as to be substantially free to translate in at least a first direction; a linear actuator which directly acts between said at least one of said object tables and said first and second balance masses to rotate said at least one of said object tables about an axis perpendicular to said first direction, said actuator being arranged to exert linear forces on said first and second balance masses in opposite directions to effect said rotation of said at least one of said object tables; and a drift control which limits drift of said balance masses, said drift control comprising a servo control system and an actuator which applies forces to said balance masses biasing the combined center of mass of said balance masses, the object table positioning system and the at least one of said object tables to a desired position.