Adjustable soft mounts in kinematic lens mounting system

• US 20030234918A1
• Filed: 05/27/2003
• Published: 12/25/2003
• Est. Priority Date: 06/20/2002
• Status: Abandoned Application

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Watson, Douglas C.
• Application Number:
  US10/446,882
• Publication Number:
  US 20030234918A1
• Time in Patent Office: Days
• US Class Current: 355/53
• CPC Class Codes: G02B 7/023 permitting adjustment
• CPC Class Codes: G02B 7/026 using retaining rings or springs G02B7/027 takes precedence
• CPC Class Codes: G03F 7/70833 Mounting of optical systems, e.g. mounting of illumination system, projection system or stage systems on base-plate or ground

Abstract

A mounting system for mounting an optical element such as a deformable lens for use in a lithographic exposure process employs a plurality of adjustable soft mounts to support it and apply vector and moment forces at its peripheral portions so as to correct its shape. These adjustable soft mounts each have an elastic member such as a coil spring, a cantilever plate spring or a torsion spring and a force-adjusting member such as an adjusting screw or bolt that varies the force applied by the elastic member to a peripheral portion of the optical element. The soft mounts are significantly less rigid than position defining mounts that support the optical element at a desired position.

Claims

1. A mounting system for kinematically mounting an optical element, said mounting system comprising a plurality of adjustable soft mounts, each of said adjustable soft mounts applying shape-adjusting forces selected from the group consisting of vector forces and moment forces on a portion of said optical element and thereby deformably adjusting shape of said optical element and having a position defining mount for defining a position of said peripheral portion, said soft mounts being significantly less rigid than said position defining mount.

2. The mounting system of claim 1 wherein said portion is a peripheral portion of said optical element.

3. The mounting system of claim 1 wherein said plurality of adjustable soft mounts include axially rigid structures and tangentially rigid structures, each of said axially rigid structures being rigid in an axial direction of said optical element and applying at least one force in a selected direction other than said axial direction, each of said tangentially rigid structures being rigid in a tangential direction of said optical element and applying at least one force in a selected direction other than said tangential direction, whereby unwanted forces imposed on said optical element are compensated by the forces applied by the axially rigid structures and the tangentially rigid structures.

4. The mounting system of claim 2 wherein said plurality of adjustable soft mounts include axially rigid structures and tangentially rigid structures, each of said axially rigid structures being rigid in an axial direction of said optical element and applying at least one force in a selected direction other than said axial direction, each of said tangentially rigid structures being rigid in a tangential direction of said optical element and applying at least one force in a selected direction other than said tangential direction, whereby unwanted forces imposed on said optical element are compensated by the forces applied by the axially rigid structures and the tangentially rigid structures.

5. The mounting system of claim 3 wherein three of said axially rigid structures and three of said tangentially rigid structures are disposed alternately and equidistantly around said optical element.

6. The mounting system of claim 4 wherein three of said axially rigid structures and three of said tangentially rigid structures are disposed alternately and equidistantly around said optical element.

7. The mounting system of claim 1 wherein each of said adjustable soft mounts comprises an elastic member that directly or indirectly contacts and applies a biasing force in a specified direction on a portion of said optical element and a force-adjusting member that contacts and controllably deforms said elastic member so as to adjustingly vary said biasing force.

8. An adjustable soft mount for adjustably supporting an optical element, said soft mount comprising an elastic member that directly or indirectly contacts and applies a biasing force in a specified direction on a portion of said optical element and a force-adjusting member that contacts and controllably deforms said elastic member so as to adjustingly vary said biasing force.

9. The soft mount of claim 8 wherein said specified direction is upward, said soft mount further comprising an additional elastic member that directly or indirectly contacts and applies a downward biasing force on said elastic member.

10. The soft mount of claim 8 wherein said elastic member is a coil spring and said force-adjusting member comprises an adjustment screw.

11. The soft mount of claim 8 wherein said elastic member is a torsion spring and said force-adjusting member comprises an adjustment screw.

12. The soft mount of claim 8 wherein said elastic member is a cantilever plate spring and said force-adjusting member comprises an adjustment screw.

13. An assembly comprising:

a deformable optical element;

three kinematic mounts each supporting said optical element at a peripheral position of said optical element; and

three moment-applying devices at each of said kinematic mounts, applying three different moments to said optical element.

14. The assembly of claim 13 wherein said three different moments are mutually orthogonal.

15. The assembly of claim 13 wherein one of said three moments is around a radial axis of said optical element and another is around a tangent to the perimeter of said optical element.

17. The assembly of claim 13 wherein said moments are applied passively.

18. The assembly of claim 13 wherein said moments are actively controlled.

19. A method of mounting an optical element, said method comprising the steps of:

providing a position defining mount for defining a position of said optical element;

providing a plurality of soft mounts, each of said soft mounts supporting and applying a shape-adjusting force on a peripheral portion of said optical element, said soft mounts being significantly less rigid than said position defining mount; and

adjusting said shape-adjusting force of each of said soft mounts.

20. The method of claim 19 wherein said shape-adjusting force is selected from the group consisting of vector forces and moment forces.

21. A metrology system comprising:

a reticle serving as a source of exposure light having an optical axis;

an optical system including optical elements for projecting said exposure light on a target object of exposure;

a metrology light source situated off said optical axis with respect to said reticle for emitting aberration-detecting light;

a metrology sensor for receiving said aberration-detecting light;

devices for altering shapes of said optical elements based on the aberration-detecting light received by said metrology sensor;

wherein at least one of said optical elements is mounted in a mounting system, said mounting system comprising a plurality of adjustable soft mounts, each of said adjustable soft mounts applying shape-adjusting forces selected from the group consisting of vector forces and moment forces on a peripheral portion of said optical element and thereby deformably adjusting shape of said optical element and having a position defining mount for defining a position of said peripheral portion, said soft mounts being significantly less rigid than said position defining mount.

22. The metrology system of claim 21 wherein said exposure light and said aberration-detecting light have different wavelengths.

23. A lithography system for projecting a pattern on a wafer by a projection beam by preliminarily determining a surface profile of the wafer on a stage and subsequently introducing the stage with the wafer into the projection beam, said lithographic system comprising:

an illumination source;

an optical system including a mounting system that mounts an optical element kinematically;

a reticle stage arranged to retain a reticle;

a working stage arranged to retain a workpiece; and

an enclosure that surrounds at least a portion of the working stage, the enclosure having a sealing surface;

wherein said mounting system comprises a plurality of adjustable soft mounts, each of said adjustable soft mounts applying shape-adjusting forces selected from the group consisting of vector forces and moment forces on a peripheral portion of said optical element and thereby deformably adjusting shape of said optical element and having a position defining mount for defining a position of said peripheral portion, said soft mounts being significantly less rigid than said position defining mount.

24. An object manufactured with the lithography system of claim 23.

25. A wafer on which an image has been formed by the lithography system of claim 23.

26. A method for making an object using a lithography process, wherein the lithography process utilizes a lithography system as recited in claim 23.

27. A method for patterning a wafer using a lithography process, wherein the lithography process utilizes a lithography system as recited in claim 23.