Patent Number: 
Section: claims

1. A lithographic projection apparatus comprising:a radiation system for providing a beam of radiation;a support structure for supporting a patterning structure, the patterning structure serving to pattern the beam of radiation according to a desired pattern;a substrate table for holding a substrate; anda projection system for projecting the patterned beam onto a target portion of the substrate,wherein at least one of the radiation system and the projection system comprises at least one optical member and a piezoelectric actuator for positioning said optical member such that the piezoelectric actuator is constructed and arranged to position the optical member in two substantially orthogonal directions. 2. An apparatus according to claim 1, wherein said piezoelectric actuator is an inch-worm actuator. 3. An apparatus according to claim 1, wherein said piezoelectric actuator comprisestwo outer plates;an inner plate positioned between said two outer plates; andat least two piezoelectric stacks positioned on at least one side of said inner plate between said inner plate and one of said two outer plates;wherein said outer and inner plates are substantially parallel and said outer plates are biased towards each other by a compression structure. 4. An apparatus according to claim 3, wherein said piezoelectric stacks are secured to said one of said inner or outer plates. 5. An apparatus according to claim 3, wherein said piezoelectric stacks comprise a first layer of piezoelectric material capable of expanding/contracting in a first direction and, a second layer of piezoelectric material capable of expanding/contracting in a second direction, said first and second directions being substantially orthogonal to one another and at least one of said directions having a component in a direction perpendicular to the plane of said inner and outer plates. 6. An apparatus according to claim 5, further comprising a third layer of piezoelectric material capable of expanding/contracting in a third direction, said first, second and third directions all being substantially orthogonal to one another. 7. An apparatus according to claim 3, wherein said one of said two outer plates has a central cut-out through which a central pin attached to said inner plate at one end extends, and a connection between said central pin and said inner plate comprises a membrane-like portion located in a cut-out area of said inner plate and held by said inner plate at its outer circumference, wherein the central pin is connected to a central area of the membrane-like portion. 8. An apparatus according to claim 7, wherein said membrane-like portion comprises a plurality of spokes which extend from the central area to the outer circumference of the central pin. 9. An apparatus according to claim 8, wherein said membrane-like portion comprises a plurality of spokes which extend from the inner plate to a periphery edge of the central cut-out. 10. An apparatus according to claim 3, further comprising a further inner plate, said further inner plate having a central cut-out in which said inner plate is attached by a membrane-like portion. 11. An apparatus according to claim 1, wherein said optical member is supported by a mounting frame, the frame extending in a plane transverse to a path of radiation to or from the optical member and the frame thereby enclosing the optical member, wherein the optical member is connected to the frame and the frame is connected to at least one piezoelectric actuator. 12. An apparatus according to claim 11, wherein said frame comprises a plurality of struts which are connected at corners of the frame so as to form a frame structure with at least three corners and one of said at least one piezoelectric actuators is connected with each of said at least three corners.