Lithographic apparatus and method of manufacturing a device
There is disclosed a lithographic apparatus provided with a spectral purity filter which may be provided in one or more of the following locations: (a) in the illumination system, (b) adjacent the patterning device, either a static location in the radiation beam or fixed for movement with the patterning device, (c) in the projection system, and (d) adjacent the substrate table. The spectral purity filter is preferably a membrane formed of polysilicon, a multilayer material, a carbon nanotube material or graphene. The membrane may be provided with a protective capping layer, and/or a thin metal transparent layer.
1. A lithographic apparatus comprising:
an illumination system configured to condition a radiation beam;
a support structure configured to support a patterning device;
a substrate table configured to hold a substrate;
a projection system configured to project a pattern imparted to the radiation beam by the patterning device onto a target portion of the substrate; and
a filter adjacent the substrate table and configured to reduce or eliminate deep ultraviolet (DUV) radiation, wherein the filter at least partially closes an opening in the projection system, and wherein the filter comprises a membrane.
2. The lithographic apparatus as claimed in claim 1 , wherein the filter is movable between a first position in the path of the radiation beam and a second position in which the filter is not in the path of the radiation beam.
3. The lithographic apparatus as claimed in claim 2 , wherein the filter is mounted in a holder, the holder being movable between a first location wherein the filter is in the first position and a second location wherein the filter is in the second position.
4. The lithographic apparatus as claimed in claim 3 , wherein the projection system has a projection system wall, the projection system wall including the opening, and wherein the first location comprises a recessed portion of the projection system wall surrounding the opening.
5. The lithographic apparatus as claimed in claim 4 , wherein the holder includes an inner annular wall, and wherein the inner annular wall forms a part of the opening when the holder is in the first location.
6. The lithographic apparatus as claimed in claim 5 , wherein the holder includes conduits to permit a gas to be supplied to the opening.
7. The lithographic apparatus as claimed in claim 2 , further comprising a closure member adapted to close the opening when the filter is removed.
8. The lithographic apparatus as claimed in claim 7 , wherein the closure member includes a first conduit connecting an interior and an exterior of the projection system, and a second conduit for delivering gas to the first conduit.
9. The lithographic apparatus as claimed in claim 1 , further comprising at least one conduit configured to supply gas to the opening such that gas is supplied to both sides of the filter.
10. The lithographic apparatus as claimed in claim 1 , further comprising a gas supply configured to supply hydrogen gas to a surface of the filter, and wherein the gas supply includes a heating element configured to generate hydrogen radicals that are delivered to the surface of the filter.
11. The lithographic apparatus as claimed in claim 1 , further comprising a gas supply line configured to deliver gas to a location adjacent the filter, and wherein the gas supply line includes a branch configured to deliver gas to a location remote from the filter, the gas supply line and the branch including respective flow restriction elements configured such that, at a first gas flow rate, gas is delivered to the filter, and at a second gas flow rate greater than the first gas flow rate, the majority of gas is supplied to the remote location.
12. The lithographic apparatus as claimed in claim 1 , wherein the filter further comprises a layer of capping material.
13. The lithographic apparatus as claimed in claim 1 , wherein the filter comprises layers of niobium, molybdenum and silicon.
14. The lithographic apparatus as claimed in claim 1 , wherein the membrane is curved and configured to compensate for transmission variation.
15. The lithographic apparatus as claimed in claim 1 , wherein the membrane has a varying thickness and is configured to compensate for transmission variation.
16. The apparatus according to claim 1 , wherein the filter has at least one of the following characteristics: (a) a DUV transmission of less than 30%, and (b) is an extreme ultraviolet (EUV) transmission filter with an EUV transmission of at least 80%.
17. The apparatus according to claim 1 , wherein the membrane includes polysilicon, a multilayer material, a carbon nanotube material or graphene.
18. A method of manufacturing a device using a lithographic apparatus, comprising:
generating a beam of radiation including extreme ultraviolet (EUV) radiation and deep ultraviolet (DUV) radiation;
conditioning the radiation beam in an illumination system and directing the radiation beam onto a patterning device;
projecting a patterned radiation beam onto a substrate supported on a substrate table by means of a projection system;
filtering, using a filter, the DUV radiation from the radiation beam in a location adjacent the substrate table; and
at least partially closing an opening in the projection system using the filter, wherein the opening is in a wall of the projection system facing the substrate table, and wherein the filter comprises a membrane.
19. The method as claimed in claim 18 , further comprising removing wrinkles from the membrane by maintaining a pressure differential across the membrane.
20. The method according to claim 18 , wherein the membrane includes polysilicon, a multilayer material, a carbon nanotube material or graphene.
21. The method according to claim 18 , wherein the filtering the DUV radiation from the radiation beam comprises transmitting less than 30% of the DUV radiation in the radiation beam and at least 80% of the EUV radiation in the radiation beam.