Patent Number: 
Section: claims

1. A radiation source configured to generate radiation, the radiation source comprising:a fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site;a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site;a controller configured to control the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets; anda collector constructed and arranged to collect radiation generated by a plasma formed at the plasma formation site when the beam of radiation and a droplet collide, the collector being configured to reflect the radiation substantially along an optical axis of the radiation source,wherein the laser beam is directed to the plasma generation site through an aperture provided in the collector. 2. The radiation source of claim 1, wherein the stream of droplets are directed such that the stream of droplets has a component of movement along the optical axis of the radiation source pointing away from the collector. 3. The radiation source of claim 1, wherein the laser beam and the stream of droplets are directed such that the laser beam and the stream of droplets have a component of movement along the optical axis of the radiation source pointing away from the collector. 4. The radiation. source of claim 1, wherein the angle between the direction of movement of the stream of droplets and the direction of the laser beam is less than 85 °. 5. The radiation source of claim 1, wherein the angle between the direction of movement of the stream of droplets and the direction of the laser beam is less than 45 °. 6. The radiation source of claim 1, wherein the stream of droplets are directed to the plasma generation site through an aperture provided in the collector. 7. The radiation source of claim 1, wherein the radiation source is configured to generate EUV radiation. 8. The radiation source of claim 1, wherein the angle between the direction of movement of the stream of droplets and the direction of the laser beam is less than 90°. 9. A method of generating radiation, comprising:directing a stream of droplets of fuel from a fuel droplet generator to a plasma generation site;directing a laser beam generated by a single laser to the plasma generation site;controlling the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets;collecting radiation generated by a plasma formed at the plasma formation site when the beam of radiation and a droplet collide with a collector; andreflecting the radiation substantially along an optical axis of the radiation source,wherein the laser beam and/or the stream of droplets are directed to the plasma generation site through an aperture provided in the collector. 10. A radiation source configured to generate radiation, the radiation source comprising:a fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site;a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site; anda controller configured to control the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets. 11. The radiation source of claim 10, wherein the direction of the laser beam and/or the stream of droplets is controlled to control the time taken for a droplet of the stream of droplets to pass through at least a part of the laser beam. 12. The radiation source of claim 10, wherein an angle between the stream of droplets and the direction of the laser beam is less than 90°. 13. The radiation source of claim 10, wherein the stream of droplets are directed to the plasma generation site through an aperture provided in the collector. 14. A method of generating radiation, the method comprising:directing a stream of droplets of fuel from a fuel droplet generator to a plasma generation site;directing a laser beam generated by a single laser to the plasma generation site; andcontrolling the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets. 15. A fuel droplet-laser beam collision time increasing apparatus arranged to generate radiation, the apparatus comprising:a fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site;a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site, an angle between the direction of movement of the stream of droplets and the direction of the laser beam being less than about 90°; anda controller constructed and arranged to control the position or orientation of the fuel droplet generator and/or the laser to control the angle between the direction of movement of the stream of droplets and the direction of the laser beam. 16. A method of increasing the collision time between a droplet of fuel and at least a part of a laser beam, the collision resulting in the generation of radiation, the method comprising:directing a stream of droplets of fuel from a fuel droplet generator to a plasma generation site;directing a laser beam generated by a single laser to the plasma generation site, an angle between the stream of droplets and the direction of the laser beam being less than about 90°; andcontrolling the position or orientation of the fuel droplet generator and/or the laser to control the angle between the direction of movement of the stream of droplets and the direction of the laser beam. 17. A lithographic apparatus comprising:a radiation source configured to generate radiation, the radiation source comprisinga fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site,a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site,a controller configured to control the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets, anda collector constructed and arranged to collect radiation generated by a plasma formed at the plasma formation site when the beam of radiation and a droplet collide, the collector being configured to reflect the radiation substantially along an optical axis of the radiation source to an intermediate focus,wherein the laser beam is directed to the plasma generation site through an aperture provided in the collector;a support constructed and arranged to support a patterning device, the patterning device being configured to pattern radiation that passes through the intermediate focus; anda projection system constructed and arranged to project the patterned radiation onto a substrate. 18. A lithographic apparatus comprising:a radiation source configured to generate radiation, the radiation source comprising:a fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site;a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site; anda controller configured to control the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control the angle between the laser beam and the stream'of droplets;a support constructed and arranged to support a patterning device, the patterning device being configured to pattern radiation that passes from the radiation source and through an intermediate focus; anda projection system constructed and arranged to project the patterned radiation onto a substrate. 19. A lithographic apparatus comprising:a fuel droplet-laser beam collision time increasing apparatus arranged to generate radiation, the fuel droplet-laser beam collision time increasing apparatus comprisinga fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site,a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site, an angle between the direction of movement of the stream of droplets and the direction of the laser beam being less than about 90°, anda controller constructed and arranged to control the position or orientation of the fuel droplet generator and/or the laser to control the angle between the direction of movement of the stream of droplets and the direction of the laser beam;a support constructed and arranged to support a patterning device, the patterning device being configured to pattern radiation that passes from the fuel droplet-laser beam collision time increasing apparatus and through an intermediate focus; anda projection system constructed and arranged to project the patterned radiation onto a substrate. 20. A device manufacturing method comprising:generating radiation, said generating radiation comprisingdirecting a stream of droplets of fuel from a fuel droplet generator to a plasma generation site,directing a laser beam generated by a single laser to the plasma generation site,controlling the position or orientation of the fuel droplet generator and/or the laser to control the angle between the direction of movement of the stream of droplets and the direction of the laser beam,collecting radiation generated by a plasma formed at the plasma formation site when the beam of radiation and a droplet collide with a collector, andreflecting the radiation substantially along an optical axis of the radiation source,wherein the laser beam and/or the stream of droplets are directed to the plasma generation site through an aperture provided in the collector;patterning the radiation with a pattering device; andprojecting the patterned radiation onto a substrate. 21. A device manufacturing method comprising:generating radiation, said generating radiation comprisingdirecting a stream of droplets of fuel from a fuel droplet generator to a plasma generation site,directing a laser beam generated by a single laser to the plasma generation site, andcontrolling the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets;patterning the radiation with a pattering device; andprojecting the patterned radiation onto a substrate. 22. A device manufacturing method comprising:generating radiation by increasing the collision time between a droplet of fuel and at least a part of a laser beam, said increasing the collision time comprisingdirecting a stream of droplets of fuel from a fuel droplet generator to a plasma generation site,directing a laser beam generated by a single laser to the plasma generation site, an angle between the stream of droplets and the direction of the laser beam being less than about 90°, andcontrolling the position or orientation of the fuel droplet generator and/or the laser to control the angle, between the direction of movement of the stream of droplets and the direction of the laser beam;patterning the radiation with a patterning device; andprojecting the patterned radiation onto a substrate.