Patent Number: 
Section: claims

1. An extreme ultraviolet light source comprising:a production site producing extreme ultraviolet radiation;a collector optics (6) for collimating the extreme ultraviolet radiation produced at the production site;a vacuum applied at a center of the collector optics (6) that actively pumps out of the device; anda pressurized influx of gas that forms a gas curtain between the production site and the collector optics (6) to protect the collector optics (6) from debris (4) generated at the production site, wherein the gas influx is directed in a way that it follows the surface of the collector optics (6), wherein the gas is used simultaneously as a coolant for the collector optics (6) by conducting it along a back side of the collector optics (6) before it reaches an injection point (12) where it begins to protect the surface of the collector optics (6) from deposition and erosion by debris, and is injected at the injection point (12) with a maximum stagnation temperature of 700 K, andwherein internal cooling is tailored to match heat flux on the surface of the collector optics (6) by controlling the mass flow of the gas on the back side of the collector optics (6) with an arrangement of turbulators (18). 2. An extreme ultraviolet light source according to claim 1, further comprising a plurality of axis-symmetric injection nozzles (17) positioned around the outer border of the collector optics (6) to produce the gas influx. 3. An extreme ultraviolet light source according to claim 1, further comprising one axis-symmetric injection nozzle (17) covering the whole outer border of the collector optics (6) to produce the gas influx. 4. An extreme ultraviolet light source according to claim 1, wherein the gas comprises a noble gas selected from the group containing Hydrogen, Helium, Argon, Neon, Krypton, Xenon, Nitrogen, Chlorine, Fluorine, Bromine, and Iodine. 5. An extreme ultraviolet light source according to claim 1, wherein the gas influx speed is very high, and preferably significantly above the speed of the sound at an injection point (12). 6. An extreme ultraviolet light source comprising:a production site producing extreme ultraviolet radiation;a collector optics (6) for collimating the extreme ultraviolet radiation produced at the production site; anda pressurized influx of gas that forms a gas curtain between the production site and the collector optics (6) to protect the collector optics (6) from debris (4) generated at the production site, wherein the gas influx is directed in a way that it follows the surface of the collector optics (6), wherein the gas is used simultaneously as a coolant for the collector optics (6) by conducting it along a back side of the collector optics (6) before it reaches an injection point (12) where it begins to protect the surface of the collector optics (6) from deposition and erosion by debris, and is injected at the injection point (12) with a maximum stagnation temperature of 700 K, and further wherein internal cooling is tailored to match heat flux on the surface of the collector optics (6) by controlling the mass flow of the gas on the back side of the collector optics (6) and wherein matching of the heat flux is achieved by an arrangement of turbulators (18) on the backside of the collector optics (6). 7. An extreme ultraviolet light source according to claim 1, wherein the gas influx further comprises an additional component that is tangent to the border of the collector optics (6) so that a swirl is induced in the flow of the gas curtain. 8. An extreme ultraviolet light source according to claim 7, wherein a tangential angle at an injection point (12) relative to the radial line is between 0° and 45°. 9. An extreme ultraviolet light source according to claim 1, wherein matching of the heat flux is achieved by a geometric arrangement of holes (10) on the backside of the collector optics (6). 10. An extreme ultraviolet light source according to claim 1, wherein the gas is injected with an exit static pressure of at least the pressure in the extreme ultraviolet light production site. 11. An extreme ultraviolet light source according to claim 1, wherein the gas is further used to clean the surface of the collector optics (6). 12. An extreme ultraviolet light source according to claim 11, wherein the gas is ionized. 13. An extreme ultraviolet light source according to claim 1, wherein the collector optics (6) comprises a collector mirror containing a hole (7) in its center. 14. An extreme ultraviolet light source according to claim 1, wherein the gas influx is injected in parallel to the collector optics (6) such that it has a radial component with respect to the outer border of the collector optics (6). 15. An extreme ultraviolet light source according to claim 1, further comprising a separate (19), closed-loop, collector cooling system (8, 9, 10, 11). 16. An extreme ultraviolet light source according to claim 6, further comprising a vacuum applied at the center of the collector optics (6) that actively pumps out of the device.