Method and apparatus for producing extreme ultraviolet radiation or soft X-ray radiation

1. A method of producing extreme ultraviolet radiation (EUV) or soft X-ray radiation by means of an electrical operated discharge, in particular for EUV lithography or for metrology, in which a plasma ( 22 ) is ignited in a gaseous medium between at least two electrodes ( 14 , 16 ) in a discharge space ( 12 ), said plasma emitting said radiation that is to be produced,

wherein said gaseous medium is produced from a metal melt ( 24 ), which is applied to a surface in said discharge space ( 12 ) and at least partially evaporated by an energy beam, in particular by a laser beam ( 20 ).

2. A method as claimed in claim 1 , wherein said metal melt ( 24 ) is applied to a surface of said two electrodes ( 14 , 16 ) and/or to a surface of a metal screen ( 36 ) arranged between said two electrodes ( 14 , 16 ).

3. A method as claimed in claim 2 , wherein said electrodes ( 14 , 16 ) and/or said metal screen ( 36 ) are placed in rotation during operation.

4. A method as claimed in claim 3 , wherein said electrodes ( 14 , 16 ) are placed in rotation around rotation axes, which are inclined to each other.

5. A method as claimed in claim 3 , wherein said electrodes ( 14 , 16 ) and/or said metal screen ( 36 ) dip, while rotating, into containers ( 26 , 56 ) containing the metal melt ( 24 ) in order to receive the metal melt ( 24 ).

6. A method as claimed in claim 5 , wherein said electrodes ( 14 , 16 ) are supplied with power via the metal melt ( 24 ).

7. A method as claimed in claim 2 , wherein said metal melt ( 24 ) is evaporated on at least one of the surfaces of said two electrodes ( 14 , 16 ) by said energy beam ( 20 ).

8. A method as claimed in claim 2 , wherein said metal melt ( 24 ) is evaporated on the surface of said metal screen ( 36 ) by said energy beam ( 20 ).

9. A method as claimed in claim 1 , wherein the energy beam ( 20 ) is a laser beam ( 20 ) which is transmitted by a glass fiber.

10. A method as claimed in claim 1 , wherein the energy beam ( 20 ) is distributed over a number of points or a circular ring on said surface for evaporation of said metal melt ( 24 ).

11. A method as claimed in claim 1 , wherein the radiation produced is detected by means of a detector, the output value of which controls or switches off the production of said radiation.

12. An apparatus ( 10 ) for producing extreme ultraviolet radiation (EUV) or soft X-ray radiation by means of an electrically operated discharge, in particular for EUV lithography or for metrology, comprising at least two electrodes ( 14 , 16 ) arranged in a discharge space ( 12 ) at a distance from one another which allows ignition of a plasma in a gaseous medium between said electrodes,

wherein said apparatus further comprises a device ( 26 , 56 ) for applying a metal melt ( 24 ) to a surface in said discharge space ( 12 ) and an energy beam device adapted to direct onto said surface an energy beam ( 20 ) evaporating said applied metal melt ( 24 ) at least partially thereby producing said gaseous medium.

13. An apparatus as claimed in claim 12 , wherein said device ( 26 , 56 ) is adapted for applying the metal melt ( 24 ) to a surface of said electrodes ( 14 , 16 ) and/or to a surface of a metal screen ( 36 ) arranged between said two electrodes ( 14 , 16 ).

14. An apparatus as claimed in claim 13 , wherein said electrodes ( 14 , 16 ) and/or said metal screen ( 24 ) can be placed in rotation during operation.

15. An apparatus as claimed in claim 14 , wherein said electrodes ( 14 , 16 ) can be placed in rotation around rotation axes, which are inclined to each other.

16. An apparatus as claimed in claim 14 , wherein said electrodes ( 14 , 16 ) and/or said metal screen ( 36 ) dip, while rotating, into containers ( 26 , 56 ) containing the metal melt ( 24 ) in order to receive the metal melt ( 24 ).

17. An apparatus as claimed in claim 16 , wherein the electrodes ( 14 , 16 ) are electrically connected to a power supply via the metal melt ( 24 ).

18. An apparatus as claimed in claim 16 , further comprising a device ( 28 ) for setting a layer thickness of the metal melt ( 24 ) applied to the two electrodes ( 14 , 16 ) and/or the metal screen ( 36 ).

19. An apparatus as claimed in claim 18 , wherein said device for setting a layer thickness is a stripper ( 28 ) that reaches up to an outer edge of the respective electrodes ( 14 , 16 ) and/or the metal screen ( 36 ).

20. An apparatus as claimed in claim 12 , wherein the electrodes ( 14 , 16 ) have at least one core of highly heat-conductive material.

21. An apparatus as claimed in claim 12 , wherein the electrodes ( 14 , 16 ) have at least one copper core which is provided with a high-temperature-resistant sheath.

22. An apparatus as claimed in claim 12 , further comprising means ( 38 ; 42 ) which prevent metal vapor from escaping.

23. An apparatus as claimed in claim 22 , wherein said means are formed by a thin-walled honeycomb structure ( 38 ) and/or thin metal sheets ( 42 ) having electric potentials and/or wire gauzes having electric potentials.

24. An apparatus as claimed in claim 12 , wherein the energy beam device is a laser beam device comprising a glass fiber for transmitting said laser beam ( 20 ).

25. An apparatus as claimed in claim 12 , wherein means for distributing the energy beam ( 20 ) over a number of points or over a circular ring on said surface for evaporating said applied metal melt ( 24 ) are provided.

26. An apparatus as claimed in claim 12 , wherein a metal screen ( 36 ) is arranged between the electrodes ( 14 , 16 ).