Vibration isolation system and lithographic apparatus

1. A vibration isolation system, comprising

a piston arranged to carry a payload;

a connecting member;

a gas spring arranged to support the piston along a direction with a positive stiffness; and

a flexible member arranged to apply a force to the piston along the direction via the connecting member with a negative stiffness,

wherein the flexible member comprises a leaf spring buckled in a third buckling mode.

2. The vibration isolation system of claim 1 , wherein the connecting member is connected to the leaf spring in a center part of the leaf spring.

3. The vibration isolation system of claim 2 , further comprising:

a force frame arranged to support the leaf spring,

wherein the force frame comprises a plurality of clamping members, and

wherein a clamping member closer to the center part of the leaf spring is more flexible than a clamping member farther from the center part of the leaf spring.

4. The vibration isolation system of claim 1 , wherein the leaf spring has a main surface perpendicular to the direction.

5. The vibration isolation system of claim 1 , wherein the force is directed along the direction away from a nominal position in which the force is zero.

6. The vibration isolation system of claim 5 , wherein the leaf spring is compressed in the nominal position.

7. The vibration isolation system of claim 5 , wherein:

the piston, the nominal position and the center part are arranged along the direction, and

the nominal position is maintained in between the piston and the center part during operational use of the vibration isolation system.

8. The vibration isolation system of claim 7 , wherein the connecting member is a strut.

9. The vibration isolation system of claim 1 , wherein the connecting member is provided with elastic hinges.

10. The vibration isolation system of claim 1 , further comprising a damping material provided on the leaf spring.

11. The vibration isolation system of claim 1 , further comprising:

a second leaf spring, and a second connecting member,

wherein the second leaf spring is arranged parallel to the leaf spring at an offset along the direction, and

wherein the second connecting member connects the center part of the leaf spring with a center part of the second leaf spring.

12. The vibration isolation system of claim 11 , wherein the leaf spring and the second leaf spring are buckled in a same buckling mode mirrored relative to each other.

13. The vibration isolation system of claim 11 , wherein the second connecting member comprises an adjustment device arranged to adjust a rotation of at least one of the center part of the leaf spring and the center part of the second leaf spring,

wherein the rotation is along an axis perpendicular to the direction, wherein the adjustment device comprises a first part, a second part, a hinge and an adjustment arrangement,

wherein the first part is connected to the center part of the leaf spring,

wherein the second part is connected to the center part of the second leaf spring,

wherein the first part and the second part are rotatably connected to each other via the hinge, and

wherein the adjustment arrangement is arranged to set the rotation.

14. The vibration isolation system of claim 1 , wherein the connecting member is substantially rigid in the direction and is flexible in another direction other than the direction.

15. A lithographic apparatus, comprising:

a mask support to support a patterning device having a pattern;

a substrate support to support a substrate;

a projection system arranged to project the pattern on the substrate;

a metrology frame arranged to support at least part of a position measurement system arranged to determine a position of one of the mask support and the substrate support; and

a vibration isolation system comprising:

a piston arranged to carry a payload;

a connecting member;

a gas spring arranged to support the piston along a direction with a positive stiffness; and

a flexible member arranged to apply a force to the piston along the direction via the connecting member with a negative stiffness,

wherein the flexible member comprises a leaf spring buckled in a third buckling mode, and

wherein the payload comprises at least one of the projection system and the metrology frame.

16. The lithographic apparatus of claim 15 , wherein the connecting member is connected to the leaf spring in a center part of the leaf spring.

17. The lithographic apparatus of claim 16 , comprising a force frame arranged to support the leaf spring, wherein the force frame comprises a plurality of clamping members, and wherein a clamping member closer to the center part of the leaf spring is more flexible than a clamping member farther from the center part of the leaf spring.

18. The lithographic apparatus of claim 15 , wherein the connecting member is provided with elastic hinges.

19. The lithographic apparatus of claim 15 , further comprising a damping material provided on the leaf spring.

20. The lithographic apparatus of claim 15 , further comprising:

a second leaf spring, and a second connecting member,

wherein the second leaf spring is arranged parallel to the leaf spring at an offset along the direction, and

wherein the second connecting member connects the center part of the leaf spring with a center part of the second leaf spring.