Illuminator for a lithographic apparatus and method

1. An illuminator for a lithographic apparatus, the illuminator comprising an illumination mode defining element and a plurality of polarization modifiers, the polarization modifiers being moveable into or out of partial intersection with a radiation beam having an angular and spatial distribution as governed by the illumination mode defining element, wherein at least one of the plurality of polarization modifiers is moveable relative to at least one other of the plurality of polarization modifiers.

2. The illuminator of claim 1 , wherein the polarization modifiers are located between the illumination mode defining element and a pupil plane of the illuminator.

3. The illuminator of claim 1 , wherein the polarization modifiers are located in a pupil plane of the illuminator.

4. The illuminator of claim 1 , wherein the polarization modifiers are connected to actuators which are arranged to move the polarization modifiers into and out of intersection with the radiation beam.

5. The illuminator of claim 4 , wherein the actuators are controlled by an automated controller.

6. The illuminator of claim 1 , wherein the polarization modifiers are polarization rotators.

7. The illuminator of claim 1 , wherein the polarization modifiers are half-wave plates.

8. The illuminator of claim 1 , wherein the polarization modifiers are quarter-wave plates.

9. The illuminator of claim 1 , wherein the polarization modifiers comprise birefringent material configured to apply a polarization adjustment to the radiation beam.

10. The illuminator of claim 1 , wherein one or more sets of polarization modifiers are provided displaced from one another along the optical axis of the illuminator.

11. A lithographic apparatus comprising:

an illuminator configured to provide a radiation beam;

a support structure configured to support a patterning device, the patterning device serving to impart the radiation beam with a pattern in its cross-section;

a substrate table configured to hold a substrate; and

a projection system configured to project the patterned radiation beam onto a target portion of the substrate;

wherein the illuminator comprises an illumination mode defining element and a plurality of polarization modifiers, the polarization modifiers being moveable into or out of partial intersection with a radiation beam having an angular and spatial distribution governed by the illumination mode defining element, wherein the polarization modifiers are located between the illumination mode defining element and a pupil plane of the illuminator and at least one of the plurality of polarization modifiers is moveable relative to at least one other of the plurality of polarization modifiers.

12. A lithographic method comprising:

providing a substrate;

providing a radiation beam;

using an illumination mode defining element to modify an angular distribution of the radiation beam;

using a plurality of polarization modifiers to modify the polarization of one or more parts of the radiation beam, the polarization modifiers being moved into and out of intersection with parts of the radiation beam as desired, such that at least one of the plurality of polarization modifiers moves relative to at least one other of the plurality of polarization modifiers;

using a patterning device to impart the radiation beam with a pattern in its cross-section; and

projecting the patterned radiation beam onto a target portion of the substrate.

13. The method of claim 12 , wherein a different polarization modification is applied to different parts of the radiation beam.

14. The method of claim 12 , wherein a proportion of radiation having a given polarization in a given part of the radiation beam is adjusted, by adjusting the proportion of that part of the radiation beam which is intersected by one or more polarization modifiers.

15. The method of claim 14 , wherein the adjustment is achieved by moving one or more polarization modifiers transverse to an optical axis of the radiation beam.

16. The method of claim 12 , wherein a controller is used to move the polarization modifiers.

17. The method of claim 12 , wherein the polarization of only part of the radiation beam is modified.

18. The method of claim 12 , wherein the polarization modifiers are polarization rotators.

19. The method of claim 12 , wherein the polarization modifiers are half-wave plates.

20. The method of claim 12 , wherein the polarization modifiers are quarter-wave plates.

21. The method of claim 12 , wherein the polarization modifiers are moved into and out of intersection with parts of the radiation beam at a location between the location of modification of the angular distribution of the radiation beam using the illumination mode defining element and a pupil plane of an illuminator comprising the illumination mode defining element and the polarization modifiers.

22. A device manufacturing method comprising:

conditioning a radiation beam;

modifying an angular distribution of the radiation beam using an illumination mode defining element of an illuminator;

modifying polarization of one or more parts of the radiation beam using a plurality of polarization modifiers, the polarization modifiers moveable into and out of intersection with parts of the radiation beam at a location between the location of modification of the angular distribution of the radiation beam using the illumination mode defining element and a pupil plane of the illuminator and at least one of the plurality of polarization modifiers is moveable relative to at least one other of the plurality of polarization modifiers;

patterning the radiation beam with a pattern in its cross-section to form a patterned beam of radiation; and

projecting the patterned radiation beam onto a target portion of a substrate.

23. The method of claim 22 , wherein the modifying includes modifying different parts of the radiation beam with different polarizations.

24. The method of claim 22 , further comprising controlling movement of the polarization modifiers.