Patent Number: 
Section: claims

1. An extreme ultra-violet lithographic apparatus for imaging a pattern onto a substrate, said apparatus comprising:a radiation system constructed and arranged to provide a beam of an extreme ultra-violet radiation;an absorber arranged in the beam and constructed and arranged to absorb at least a portion of the extreme ultra-violet radiation in the beam of the extreme ultra-violet radiation, said absorber comprising a structure defining an internal volume configured to accommodate a flow of an absorbing gas, the flow being directed in a transverse direction with respect to the beam, said structure having an extreme ultra-violet radiation-transmissive beam entry area and an extreme ultra-violet radiation-transmissive beam exit area; anda gas inlet actuator array configured to inject said gas into the internal volume of the absorber and a gas outlet actuator array arranged to evacuate the gas from the internal volume of the absorber,wherein said absorber further comprises a first pump unit and a second pump unit, the gas inlet actuator array and the gas outlet actuator array being located between said first pump unit and said second pump unit along the beam path, said first pump unit and said second pump unit being arranged to substantially prevent the absorbing gas from escaping into an atmosphere of the lithographic apparatus by providing, in use, a vacuum seal for the internal volume of the absorber. 2. The extreme ultra-violet lithographic apparatus according to claim 1, wherein an evacuation capacity of the gas outlet actuator array is at least equal to a supply capacity of the gas inlet actuator array. 3. The extreme ultra-violet lithographic apparatus according to claim 1, wherein the structure is arranged as an open structure with respect to the beam entry area and the beam exit area. 4. The extreme ultra-violet lithographic apparatus according to claim 1, further comprising:an illumination system configured to condition the radiation beam;a patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam,wherein the absorber is positioned in a beam path between the illumination system and the patterning device. 5. The extreme ultra-violet lithographic apparatus according to claim 1, wherein the gas inlet actuator array comprises a plurality of individually adjustable elements configured to selectively control gas concentration in a vicinity of the said elements. 6. The extreme ultra-violet lithographic apparatus according to claim 5, wherein the adjustable elements comprise piezo elements constructed and arranged to selectively obstruct a portion of an area of the gas inlet actuator array. 7. The extreme ultra-violet lithographic apparatus according to claim 1, wherein the gas is selected from a group consisting of krypton, xenon, argon neon, helium, hydrogen, oxygen, and nitrogen. 8. The extreme ultra-violet lithographic apparatus according to claim 1, wherein said gas inlet actuator array and/or said gas outlet actuator array is arranged to generate a non-uniform distribution of gas concentration in a cross-section of the absorber, the distribution extending in a direction substantially perpendicular to the beam path. 9. The extreme ultra-violet lithographic apparatus according to claim 1, further comprising:a sensor constructed and arranged to measure a gas concentration in at least one portion of the internal volume of the absorber; anda controller constructed and arranged to be responsive to said sensor, and to control the gas inlet actuator array or the gas outlet actuator array. 10. The extreme ultra-violet lithographic apparatus according to claim 1, wherein the gas inlet actuator array comprises supersonic jets. 11. The extreme ultra-violet lithographic apparatus according to claim 1, wherein said structure is a tubular structure. 12. The extreme ultra-violet lithographic apparatus according to claim 1, wherein the extreme ultra-violet radiation has a wavelength in the range of about 5-20 nm. 13. A device manufacturing method comprising:patterning an extreme ultra-violet radiation beam;projecting the patterned radiation beam onto a target portion of a substrate;controlling an intensity of the radiation beam with an absorber arranged in the beam by absorbing at least a portion of the extreme ultra-violet radiation in the extreme ultra-violet radiation beam as the radiation beam passes through the absorber, said absorber comprising a structure defining an internal volume accommodating a transverse flow of an absorbing gas with respect to the beam; andevacuating the absorbing gas from the internal volume of the absorber with a first pump unit and a second pump unit positioned downstream of the first pump unit with respect to the propagation of the radiation beam to substantially prevent the absorbing gas from escaping the absorber by creating a vacuum seal for the internal volume of the absorber. 14. The device manufacturing method according to claim 13, wherein the absorbing gas is evacuated from the internal volume of the absorber with a capacity at least equal to a capacity of injection of the gas into the internal volume of the absorber. 15. The device manufacturing method according to claim 13, wherein the absorber is positioned in the beam between a illumination module and a beam patterning device. 16. The device manufacturing method according to claim 13, further comprising:controlling a gas concentration in a vicinity of a plurality of individually adjustable elements. 17. The device manufacturing method according to claim 13, wherein the gas is selected from a group consisting of krypton, xenon, argon neon, helium, hydrogen, oxygen, and nitrogen. 18. The device manufacturing method according to claim 13, further comprising generating a non-uniform distribution of the gas concentration in a cross-section of the absorber transverse to the beam. 19. The device manufacturing method according to claim 13, wherein the method further comprises:measuring a gas concentration in at least one portion of the internal volume of the absorber; andcontrolling a gas inlet actuator array and/or a gas outlet actuator array in response to said measuring.