Patent Number: 
Section: claims

1. A beam splitting apparatus for use within a lithographic system, comprising:a plurality of static mirrors each configured to receive a different part of a first radiation beam from a radiation source and reflect a respective portion of radiation along one of a plurality of directions to form a plurality of branch radiation beams for provision to two or more lithographic apparatuses,wherein each lithographic apparatus is configured to receive a respective one of the plurality of branch radiation beams, direct the respective branch radiation beam onto a patterning device, and project a respective patterned beam onto a substrate,wherein each lithographic apparatus is associated with a respective patterning device and a respective substrate such that patterning of plural substrates can be performed by the two or more lithographic apparatuses in parallel,wherein the radiation source comprises a first free electron laser and a second free electron laser, andwherein the first radiation beam is a composite radiation beam comprising radiation from at least one of the first and second free electron lasers. 2. The beam splitting apparatus of claim 1, wherein each of the plurality of directions provides a respective branch optical path, each branch optical path being associated with a respective one of the lithographic apparatuses. 3. The beam splitting apparatus of claim 2, wherein at least one branch optical path is associated with two or more of the plurality of the static mirrors such that at least one of the plurality of branch radiation beams comprises a plurality of said reflected portions of radiation. 4. The beam splitting apparatus of claim 2, wherein each of the branch optical paths is associated with a respective plurality of the static mirrors such that each branch radiation beam comprises a plurality of said reflected portions. 5. The beam splitting apparatus of claim 1, wherein each static mirror is arranged to extend partially across a path of the first radiation beam. 6. The beam splitting apparatus claim 1, wherein at least some of the plurality of static mirrors are configured to reflect a solid area of the first radiation beam. 7. The beam splitting apparatus of claim 2, wherein at least two or more of the plurality of static mirrors comprise a reflective grating, wherein the reflective grating comprises a plurality of faces. 8. The beam splitting apparatus of claim 7, wherein each face of the reflective grating that is associated with a same one of the plurality of directions extends substantially parallel to a single silicon crystal plane of the reflective grating. 9. The beam splitting apparatus of claim 7, wherein the reflective grating is a macro-scale grating. 10. The beam splitting apparatus of claim 9, wherein the faces are arranged such that expansion of each reflected portion causes partial overlap of at least two reflected portions associated with one branch optical path at the one of the lithographic apparatuses associated with that one branch optical path. 11. The beam splitting apparatus of claim 10, wherein the faces are arranged such that the overlapping reflected portions provide a branch radiation beam having an intensity profile substantially the same as an intensity profile of the first radiation beam. 12. The beam splitting apparatus of claim 7, wherein the reflective grating comprises a first plurality of faces associated with a first branch optical path to provide a first branch radiation beam;wherein each one of the first plurality of faces is arranged to reflect a respective part of the first radiation beam to form a respective sub-beam of the first branch radiation beam; andwherein the first plurality of faces is arranged such that if a position of the first radiation beam changes in a plane perpendicular to a propagation direction of the first radiation beam, a power received by at least one of the first plurality of faces increases and a power received by at least one of the first plurality of faces decreases. 13. The beam splitting apparatus of claim 7, wherein the reflective grating is a micro-scale grating. 14. The beam splitting apparatus of claim 13, wherein the faces of the reflective grating are arranged such that portions of radiation reflected from the grating diffract to provide said plurality of branch radiation beams. 15. The beam splitting apparatus of claim 14, wherein the faces of the reflective grating are arranged such that each branch radiation beam has an intensity profile substantially similar to an intensity profile of the first radiation beam. 16. The beam splitting apparatus of claim 7, wherein the faces of the reflective grating have translational symmetry in at least one direction perpendicular to a direction of propagation of the first radiation beam. 17. The beam splitting apparatus of claim 7, wherein the beam splitting apparatus comprises expansion and/or flat-top forming optics, and wherein the reflective grating is disposed upstream of said expansion and/or flat-top forming optics. 18. The beam splitting apparatus of claim 7, wherein the reflective grating is arranged to receive the radiation beam from a flat mirror disposed between the radiation source and the reflective grating. 19. The beam splitting apparatus of claim 7, wherein the reflective grating is formed from etched silicon. 20. The beam splitting apparatus of claim 19, wherein the reflective grating comprises a reflective coating, the reflective coating comprising a material or composition selected for grazing incidence reflectivity of a desired wavelength. 21. The beam splitting apparatus of claim 7, further comprising a second reflective grating arranged to further split at least one of the branch radiation beams provided by the reflective grating. 22. The beam splitting apparatus of claim 1, wherein at least one of the static mirrors is provided with one or more apertures arranged to permit a portion of the first radiation beam not reflected by the at least one static mirror through the aperture towards a further one of the plurality of static mirrors. 23. The beam splitting apparatus of claim 1, wherein at least one of said static mirrors comprises a ring-shaped reflective surface arranged to reflect a portion of radiation along an associated branch optical path and to permit a portion of the first radiation beam through an aperture defined by the ring toward a further one of the plurality of static mirrors. 24. The beam splitting apparatus of claim 23, wherein said ring-shaped reflective surface is arranged such that if a position of the first radiation beam changes in a plane perpendicular to a propagation direction of the first radiation beam, a power received by at least one part of the ring-based reflective surface increases and a power received by at least a further part of the ring-based reflective surface decreases. 25. The beam splitting apparatus of claim 1, wherein at least one of the static mirrors comprises a first reflective surface and a second reflective surface joined along an edge, wherein the edge is arranged for placement within a radiation beam. 26. The beam splitting apparatus of claim 1, wherein at least one of the static mirrors is provided with active cooling. 27. The beam splitting apparatus of claim 1, further comprising: at least one diverging optical element arranged to increase the divergence of a radiation beam. 28. The beam splitting apparatus of claim 27, further comprising: a plurality of diverging optical elements, each arranged to increase the divergence of a respective one of the branch radiation beams. 29. A system comprising:a radiation source configured to produce a main radiation beam, the radiation source comprising:a first free electron laser; anda second free electron laser;a plurality of optical elements configured to:receive at least one of a first radiation beam from the first free electron laser and a second radiation beam from the second free electron laser; andoutput the main radiation beam;a beam splitting apparatus configured to split the main radiation beam into a plurality of branch radiation beams, comprising:a plurality of static mirrors each configured to:receive a different part of the main radiation beam; andreflect a respective portion of radiation along one of a plurality of directions to form the branch radiation beams; andtwo or more lithographic apparatuses, wherein each lithographic apparatus is configured to receive a respective one of the plurality of branch radiation beams, direct the respective branch radiation beam onto a patterning device, and project a respective patterned beam onto a substrate,wherein each lithographic apparatus is associated with a respective patterning device and a respective substrate such that patterning of plural substrates can be performed by the two or more lithographic apparatuses in parallel. 30. The system of claim 29, further comprising: a respective diverging optical element for each of the lithographic apparatuses. 31. The system of claim 30, wherein the beam splitting apparatus is configured such that at least two or more of the plurality of static mirrors comprise a reflective grating comprising a plurality of faces, and wherein each respective diverging optical element is downstream of the reflective grating. 32. The system of claim 30, wherein the diverging optical element comprises a convex, concave, and/or saddle shaped grazing incidence mirror. 33. The system of claim 29, further comprising: optics configured to modify a cross-sectional shape of a branch radiation beam. 34. The system of claim 33, wherein the optics comprise an array of mirrors arranged to split the branch radiation beam into a plurality of sub-beams and to combine the sub-beams together. 35. The system of claim 29, wherein the main radiation beam comprises EUV radiation. 36. The system of claim 29, further comprising: a mask inspection apparatus arranged to receive one of the branch radiation beams from the beam splitting apparatus. 37. A method comprising:producing a main radiation beam using a radiation source wherein the radiation source comprises a first free electron laser and a second free electron laser, wherein the main radiation beam is a composite radiation beam comprising radiation from at least one of the first and second free electron lasers; anddirecting the main radiation beam to a beam splitting apparatus,wherein the beam splitting apparatus comprises a plurality of static mirrors each arranged to receive a different part of the main radiation beam and reflect a respective portion of radiation along one of a plurality of directions to form a plurality of branch radiation beams for provision to a first lithographic apparatus and a second lithographic apparatus,wherein the first and second lithographic apparatuses are each configured to receive a respective one of the plurality of branch radiation beams, direct the respective branch radiation beam onto a patterning device, and project a respective patterned branch onto a substrate, andwherein each lithographic apparatus is associated with a respective patterning device and a respective substrate such that patterning of plural substrates can be performed by the two or more lithographic apparatuses in parallel. 38. The method of claim 37, further comprising: directing each branch radiation beam to a respective lithographic apparatus.