Method and apparatus for generating high output power gas discharge based source of extreme ultraviolet radiation and/or soft x-rays Number:6,804,327 from the United States Patent and Trademark Office (PTO) owispatent

Title: Method and apparatus for generating high output power gas discharge based source of extreme ultraviolet radiation and/or soft x-rays

Abstract: The method and system herein pertain to an EUV photon source which includes a plasma chamber filled with a gas mixture, multiple electrodes within the plasma chamber defining a plasma region and a central axis, a power supply circuit connected to the electrodes for delivering a main pulse to the electrodes for energizing the plasma around the central axis to produce an EUV beam. The system can also include a preionizer for ionizing the gas mixture in preparing to form a dense plasma around the central axis upon application of the main pulse from the power supply circuit to the electrodes. A set of baffles may be disposed along the beam path outside of the pinch region to diffuse gaseous and contaminant particulate flow emanating from the pinch region and to absorb or reflect acoustic waves emanating from the pinch region away from the pinch region.

Patent Number: 6,804,327 Issued on 10/12/2004 to Schriever,   et al.

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Inventors:	Schriever; Guido (Gottingen, DE); Rebhan; Ulrich (Gottingen, DE)
Assignee:	Lambda Physik AG (Goettingen, DE)
Appl. No.:	10/109,581
Filed:	March 27, 2002

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Current U.S. Class:	378/119 ; 250/493.1; 250/505.1; 378/145
Field of Search:	378/119,121,122,145,34,84 250/493.1,504R,505.1

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Primary Examiner: Bruce; David V.
Assistant Examiner: Thomas; Courtney
Attorney, Agent or Firm: Stallman & Pollock LLP

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Parent Case Text

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PRIORITY

This application claims the benefit of priority to U.S. provisional patent application No. 60/281,446, filed Apr. 3, 2001.

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Claims

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What is claimed is:

1. An EUV photon source, comprising: a plasma chamber filled with a gas mixture; multiple electrodes within the plasma chamber defining a pinch region and a central axis; a power supply circuit connected to the electrodes for delivering a main pulse to the electrodes for energizing the plasma around the central axis to produce an EUV beam output; a preionizer for ionizing the gas mixture in preparing to form a dense plasma around the central axis upon application of the main pulse from the power supply circuit to the electrodes; an ionization unit positioned along a beam path of the EUV beam outside of the plasma region for ionizing contaminant particulates along the beam path; and an electrostatic particle filter for collecting the ionized particulates.

2. The EUV source of claim 1, wherein said ionizing unit generates a corona discharge.

3. The EUV source of claim 1, further comprising one or more baffles along the beam path outside of the pinch region.

4. The EUV source of claim 3, the one or more baffles for diffusing gaseous and contaminant particulate flow emanating from the pinch region.

5. The EUV source of claim 4, the one or more baffles further for absorbing or reflecting acoustic waves emanating from the pinch region away from the pinch region.

6. The EUV source of claim 3, further comprising a clipping aperture along the beam path outside of the pinch region for at least partially defining an acceptance angle of the EUV beam.

7. The EUV source of claim 6, wherein said aperture comprises ceramic.

8. The EUV source of claim 6, wherein said aperture comprises Al.sub.2 O.sub.3.

9. The EUV source of claim 6, wherein said power supply circuit generates the main pulse and a relatively low energy prepulse before said main pulse for homogenizing the preionized plasma prior to the main pulse.

10. The EUV source of claim 9, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

11. The EUV source of claim 10, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

12. The EUV source of claim 10, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

13. The EUV source of claim 6, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

14. The EUV source of claim 13, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

15. The EUV source of claim 13, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

16. The EUV source of claim 3, wherein said power supply circuit generates the main pulse and a relatively low energy prepulse before said main pulse for homogenizing the preionized plasma prior to the main pulse.

17. The EUV source of claim 16, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

18. The EUV source of claim 17, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

19. The EUV source of claim 17, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

20. The EUV source of claim 3, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

21. The EUV source of claim 20, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

22. The EUV source of claim 20, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

23. The EUV source of claim 1, further comprising a clipping aperture along the beam path outside of the pinch region for at least partially defining an acceptance angle of the EUV beam.

24. The EUV source of claim 23, wherein said aperture comprises ceramic.

25. The EUV source of claim 23, wherein said aperture comprises Al.sub.2 O.sub.3.

26. The EUV source of claim 23, wherein said power supply circuit generates the main pulse and a relatively low energy prepulse before said main pulse for homogenizing the preionized plasma prior to the main pulse.

27. The EUV source of claim 26, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

28. The EUV source of claim 27, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

29. The EUV source of claim 27, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

30. The EUV source of claim 23, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

31. The EUV source of claim 30, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

32. The EUV source of claim 30, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

33. The EUV source of claim 1, wherein said power supply circuit generates the main pulse and a relatively low energy prepulse before said main pulse for homogenizing the preionized plasma prior to the main pulse.

34. The EUV source of claim 33, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

35. The EUV source of claim 34, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

36. The EUV source of claim 34, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

37. The EUV source of claim 1, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

38. The EUV source of claim 37, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

39. The EUV source of claim 37, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

40. An EUV photon source, comprising: a plasma chamber filled with a gas mixture; multiple electrodes within the plasma chamber defining a pinch region and a central axis; a power supply circuit connected to the electrodes for delivering a main pulse to the electrodes for energizing the plasma around the central axis to produce an EUV beam output; a preionizer for ionizing the gas mixture in preparing to form a dense plasma around the central axis upon application of the main pulse from the power supply circuit to the electrodes; and one or more baffles along a beam path outside of the pinch region.

41. The EUV source of claim 40, the one or more baffles for diffusing gaseous and contaminant particulate flow emanating from the pinch region.

42. The EUV source of claim 41, the one or more baffles further for absorbing or reflecting acoustic waves emanating from the pinch region away from the pinch region.

43. The EUV source of claim 40, further comprising a clipping aperture along the beam path outside of the pinch region for at least partially defining an acceptance angle of the EUV beam.

44. The EUV source of claim 43, wherein said aperture comprises ceramic.

45. The EUV source of claim 43, wherein said aperture comprises Al.sub.2 O.sub.3.

46. The EUV source of claim 43, wherein said power supply circuit generates the main pulse and a relatively low energy prepulse before said main pulse for homogenizing the preionized plasma prior to the main pulse.

47. The EUV source of claim 46, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

48. The EUV source of claim 47, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

49. The EUV source of claim 47, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

50. The EUV source of claim 43, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

51. The EUV source of claim 50, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

52. The EUV source of claim 50, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

53. The EUV source of claim 40, wherein said power supply circuit generates the main pulse and a relatively low energy prepulse before said main pulse for homogenizing the preionized plasma prior to the main pulse.

54. The EUV source of claim 53, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

55. The EUV source of claim 54, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

56. The EUV source of claim 54, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

57. The EUV source of claim 40, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

58. The EUV source of claim 57, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

59. The EUV source of claim 57, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

60. An EUV photon source, comprising: a plasma chamber filled with a gas mixture; multiple electrodes within the plasma chamber defining a pinch region and a central axis; a power supply circuit connected to the electrodes for delivering a main pulse to the electrodes for energizing the plasma around the central axis to produce an EUV beam output; a preionizer for ionizing the gas mixture in preparing to form a dense plasma around the central axis upon application of the main pulse from the power supply circuit to the electrodes; and a clipping aperture along a beam path outside of the pinch region for at least partially defining an acceptance angle of the EUV beam.

61. The EUV source of claim 60, wherein said aperture comprises ceramic.

62. The EUV source of claim 60, wherein said aperture comprises Al.sub.2 O.sub.3.

63. The EUV source of claim 60, wherein said power supply circuit generates the main pulse and a relatively low energy prepulse before said main pulse for homogenizing the preionized plasma prior to the main pulse.

64. The EUV source of claim 63, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

65. The EUV source of claim 64, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

66. The EUV source of claim 64, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

67. The EUV source of claim 60, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam.

68. The EUV source of claim 67, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

69. The EUV source of claim 67, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

70. An EUV photon source, comprising: a plasma chamber filled with a gas mixture; multiple electrodes within the plasma chamber defining a pinch region and a central axis; a power supply circuit connected to the electrodes for delivering a main pulse to the electrodes for energizing the plasma around the central axis to produce an EUV beam output; a preionizer for ionizing the gas mixture in preparing to form a dense plasma around the central axis upon application of the main pulse from the power supply circuit to the electrodes, and wherein said power supply circuit generates the main pulse and a relatively low energy prepulse before said main pulse for homogenizing the preionized plasma prior to the main pulse.

71. The EUV source of claim 70, further comprising a multi-layer EUV mirror disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along a beam path of the EUV beam.

72. The EUV source of claim 71, wherein the EUV mirror has a curved contour for substantially collimating the reflected radiation.

73. The EUV source of claim 71, wherein the EUV mirror has a curved contour for substantially focusing the reflected radiation.

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Description

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to extreme ultraviolet (EUV) lithography, and particularly to an EUV radiation source configured for transmitting an improved EUV beam.

2. Discussion of the Related Art

Semiconductor manufacturers are currently using deep ultraviolet (DUV) lithography tools based on KrF-excimer laser systems operating around 248 nm, as well as the following generation of ArF-excimer laser systems operating around 193 nm. Industrial applications in the Vacuum UV (VUV) range involve the use of the F.sub.2 -laser operating around 157 nm. EUV radiation sources for EUV lithography emitting 11-15 nm photon beams are currently being developed.

EUV radiation sources have an advantageous output emission beam including 11-15 nm wavelength photons having photon energies greater than 90 eV. This short wavelength is advantageous for industrial applications, such as particularly photolithography, mask writing and mask and wafer inspection applications, because the critical dimension (CD), which represents the smallest resolvable feature size producible using photolithography, is proportional to the wavelength. This permits smaller and faster microprocessors and larger capacity DRAMs in a smaller package.

A promising technique for producing EUV lithography beams use a pair of plasma pinch electrodes for driving a preionized azimuthally symmetrical plasma shell to collapse to a central axis. A power supply circuit supplies a high energy, short duration pulse to the electrodes, wherein several kilovolts and up to 100 kiloAmps are applied over a pulse duration of less than a microsecond. A Z-pinch electrode arrangement generates a current through the plasma shell in an axial direction producing an azimuthal magnetic field that provides the radial force on the charged particles of the plasma responsible for the rapid collapse.

The excimer and molecular fluorine lithography lasers, mentioned above, emit laser beams using a gas discharge for creating a population inversion to a metastable state in the laser active gas, and a resonator for facilitating stimulated emission. It is not yet clear what radiative mechanism is responsible for the axial, high energy photon emission in plasma pinch EUV sources. The collapsing shell of charged particles of the plasma have a high kinetic energy due to their velocities in the radial direction. The rapid collapse of the shell results in collisions between all portions of the incoming shell at the central axis with radially opposed portions of the incoming shell.

The high kinetic energies of the particles are abruptly transformed into a hot, dense plasma which emits x-rays. A high recombination rate concentrated in the azimuthal direction due to the plasma being particularly optically dense in the azimuthal direction has been proposed (see, Malcolm McGeoch, Radio Frequency Preionized Xenon Z-Pinch Source for Extreme Ultraviolet Lithography, Applied Optics, Vol. 37, No. 9 (20 Mar. 1998), which is hereby incorporated by reference), and population inversion resulting in spontaneous emission and predominantly axial stimulated emission, and bremsstrahlung resulting from the rapid radially deceleration of the charged particles of the collapsing plasma, are other mechanisms of high energy photon emission.

It is desired to have an improved EUV photon source, particularly having output emission characteristics more suitable for industrial applications such as photolithography.

SUMMARY OF THE INVENTION

In view of the above, an EUV photon source is provided including a plasma chamber filled with a gas mixture, multiple electrodes within the plasma chamber defining a plasma region and a central axis, a power supply circuit connected to the electrodes for delivering a main pulse to the electrodes for energizing the plasma around the central axis to produce an EUV beam output, and a preionizer for ionizing the gas mixture in preparing to form a dense plasma around the central axis upon application of the main pulse from the power supply circuit to the electrodes.

According to a first embodiment, an ionization unit is positioned along a beam path of the EUV beam outside of the plasma region for ionizing contaminant particulates along the beam path. An electrostatic particle filter is further provided for collecting the ionized particulates. The ionizing device may be preferably of corona-type.

According to a second embodiment, one or more, and preferably a set of, baffles is disposed along a beam path outside of the pinch region. The baffle(s) may function to diffuse gaseous and contaminant particulate flow emanating from the pinch region. The baffle(s) may also function to absorb or reflect acoustic waves emanating from the pinch region away from the pinch region.

According to a third embodiment, a clipping aperture is disposed along a beam path outside of the pinch region for at least partially defining an acceptance angle of the EUV beam. The aperture may be formed of ceramic and may particularly be formed of Al.sub.2 O.sub.3.

According to a fourth embodiment, the power supply circuit generates the main pulse and a relatively low energy prepulse before the main pulse for homogenizing the preionized plasma prior to the main pulse.

According to a fifth embodiment, a multi-layer EUV mirror is disposed opposite a beam output side of the pinch region for reflecting radiation in a direction of the beam output side for output along the beam path of the EUV beam. The EUV mirror preferably has a curved contour for substantially collimating or focusing the reflected radiation. In particular, the EUV mirror may preferably have a hyperbolic contour.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an EUV generating source in accord with a preferred embodiment.

FIG. 2 schematically illustrates an EUV generating source including a reflecting surface opposite a beam output side of the central axis according to a first embodiment.

FIG. 3 schematically illustrates an EUV generating source including a reflecting surface opposite a beam output side of the central axis according to a second embodiment.

FIG. 4 schematically illustrates an EUV generating source including a reflecting surface opposite a beam output side of the central axis according to a third embodiment.

FIG. 5 schematically illustrates an EUV generating source including a reflecting surface opposite a beam output side of the central axis according to a fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of an EUV photon generating source are described below. The system generally includes a preionizer for generating a pinch plasma symmetrically defined around a central axis, a power supply circuit connected to electrodes for creating an azimuthal magnetic field for rapidly collapsing the plasma to the central axis to produce an EUV beam output along the central axis.

In a first embodiment, the system preferably further includes an ionizing unit preferably of corona type generating UV light for ionizing dust particles that tend to travel along with the beam. An electrostatic particle filter is provided for collecting the charged dust particles resulting in a cleaner beam path having many advantages.

In a second embodiment, the system preferably further includes one or more, and preferably a set of, baffles for diffusing the effect of acoustic waves emanating from the pinch region such as the flow of gases and contaminant particulates traveling with the acoustic waves, as well as to prevent reflections back into the pinch region.

In a third embodiment, the system preferably further includes a clipping aperture spaced a proximate distance from the pinch region to match the divergence of the beam and reduce the influence of reflections and acoustic waves along the beam path away from the pinch region beyond the aperture location. The aperture comprises a thermally stable material with relatively high thermal conductivity and relatively low coefficient of thermal expansion, and is positioned to maintain that thermal stability. The aperture preferably comprises Al.sub.2 O.sub.3.

In a fourth embodiment, the system generates a low energy prepulse which is applied to the electrodes just before the main electrical pulse. The prepulse creates more homogeneous conditions in the already preionized plasma preventing electrode burnout at hotspots from arcing due to the high voltage, fast rise time of the main pulse.

In a fifth embodiment, the system includes a reflecting surface opposite a beam output side of the central axis for reflecting radiation in a direction of the beam output side and preferably configured for focusing or collimating the beam. The reflecting surface is preferably of EUV multilayer type. The reflecting surface may be flat or hyperbolically-shaped or otherwise curved to focus the reflected radiation.

Referring now to FIG. 1, an EUV generating source is schematically illustrated in cross section in accord with a preferred embodiment. Many preferred components of the EUV source are described at U.S. Pat. No. 5,504,795 which is hereby incorporated by reference. The EUV source includes a pinch chamber 10 having a pinch region 12 defining a central axis 14 at the end of which is an EUV photon transmitting window 18. A dielectric liner 24 surrounds the pinch region 12.

A gas supply inlet 20 and an outlet 22 controllably supply active and diluent gases to the pinch region 12. The outlet 22 is connected to a vacuum pump 23. Other gas supply systems are possible such as may be borrowed and/or modified from excimer laser technology (see U.S. Pat. Nos. 4,977,573 and 6,212,214, and U.S. patent applications Ser. Nos. 09/447,882 (now issued U.S. Pat. No. 6,490,307), Ser. No. 09/734,459 (now issued U.S. Pat. No. 6,389,052), Ser. No. 09/780,120 (abandoned) and Ser. No. 09/453,670 (now issued U.S. Pat. No. 6,466,599), which are each assigned to the same assignee as the present application, and U.S. Pat. Nos. 5,978,406 and 5,377,215, all of which are hereby incorporated by reference). The gas may be circulated and electrostatic and or cryogenic purification filters may be inserted into the gas loop (see U.S. Pat. Nos. 4,534,034, 5,136,605 and 5,430,752, which are hereby incorporated by reference). A heat exchanger may also be provided in the gas loop (see the '670 application, mentioned above, and U.S. Pat. No. 5,763,930, which is hereby incorporated by reference).

The gas mixture includes an x-ray emitting gas such as xenon, krypton, argon, neon, oxygen or lithium. The gas mixture also preferably includes a low atomic number diluent gas such as helium, hydrogen, deuterium, and possibly nitrogen. Preferably xenon and helium are used.

A preionization electrode 26 is connected to a preionization unit 27 for preionizing the gas in the pinch region 12. Many preionization unit types are possible such as e-beam, conical pinch discharge and RF preionization (see the '795 patent and C. Stallings, et al., Imploding Argon Plasma Experiments, Appl. Phys. Lett. 35 (7), Oct. 1, 1979, which is hereby incorporated by reference). Some known laser preionization systems may be modified to provide preionization for the EUV source, as well (see U.S. Pat. Nos. 5,247,535, 5,347,532 and U.S. patent applications Ser. Nos. 09/247,887 (issued U.S. Pat. No. 6,650,679), Ser. No. 09/692,265 ([pending]) and Ser. No. 09/532,276 (issued U.S. Pat. No. 6,456,643), which are assigned to the same assignee as the present application and are hereby incorporated by reference). The preionization unit 27 and electrode 26 preionizes the pinch plasma in a symmetrical shell around the central axis 14, as shown, prior to the application of the main pulse to the main electrodes 30 and 32.

The preferred main electrodes 30, 32 are as shown in FIG. 1. The anode 30 and the cathode 32 are shown located at opposite ends of the pinch region 12. Many other anode-cathode configurations are possible (see U.S. Pat. Nos. 3,961,197, 5,763,930, 4,504,964 and 4,635,282, which are hereby incorporated by reference). A power supply circuit 36 including a voltage source 37, a switch 38 and capacitor 39 connected to electrodes 30, 32 generates electrical pulses that produce high electric fields in the pinch region which in turn create azimuthal magnetic fields causing the preionized plasma to rapidly collapse to the central axis 14 to produce an EUV beam output along the central axis 14. Many power supply circuits are possible (see U.S. Pat. No. 5,142,166 which is hereby incorporated by reference). The anode 30 and cathode 32 are separated by an insulator 40.

A prepulse is preferably generated in accord with a preferred embodiment. The prepulse occurs just prior to the main pulse and after the plasma is substantially preionized by the preionization unit 27 and electrode 26. The prepulse is a relatively low energy discharge provided by the main electrodes 30, 32. The prepulse creates more homogeneous conditions in the already preionized plasma preventing electrode burnout at hotspots from arcing due to the high voltage, fast rise time of the main pulse. A prepulse circuit is described at Giordano et al., referred to and incorporated by reference, below, and may be modified to suit the EUV source of the preferred embodiment.

In summary with respect to the first through fifth embodiments, an EUV photon source, e.g., a Z-pinch, HCT-pinch, capillary discharge, plasma focus, and/or laser produced plasma device, may include one or more advantageous features according to preferred embodiments herein. The EUV source may include a preionizer and multiple electrodes for generating a plasma symmetrically defined around a central axis, a power supply circuit connected to electrodes for generally creating an azimuthal magnetic field or an electric filed and/or discharge for energizing a plasma formed around the central axis which emits EUV radiation, to produce an EUV beam output. Among the advantageous features according to preferred embodiments are an ionizing unit preferably of corona type generating UV light ionizes contaminant particulates along the beam path and an electrostatic particle filter collects the charged particulates. Also, one or more, and preferably a set of, baffles may be used to diffuse the effect of acoustic waves emanating from the pinch region such as the flow of gases and contaminant particulates traveling with the acoustic waves, and to prevent reflections back into the plasma region. A clipping aperture may also be included formed of a thermally stable material such as a ceramic such as sapphire or alumina and spaced a proximate distance from the pinch region to match the divergence of the beam and reduce the influence of reflections of particulates and acoustic waves along the beam path. A low energy prepulse may also be applied to the electrodes just before the main electrical pulse creating more homogeneous conditions in the preionized plasma shell preventing electrode burnout at hotspots from arcing due to the high voltage, fast rise time of the main pulse.

Many other configurations of the above (and below) elements of the preferred embodiments are possible. For this reason, in addition to that which is described and/or incorporated by reference above and below herein, the following are hereby incorporated by reference:

Weinberg et al., A Small Scale Z-Pinch Device as an Intense Soft X-ray Source, Nuclear Instruments and Methods in Physics Research A242 (1986) 535-538;

Hartmann, et al., Homogeneous Cylindrical Plasma Source for Short-Wavelength laser, Appl. Phys. Lett. 58 (23), 10 Jun. 1991;

Shiloh et al., Z Pinch of a Gas Jet, Phys. Rev. Lett. 40 (8), 20 Feb. 1978;

Edita Tejnil, et al., Options for at-wavelength inspection of patterned extreme ultraviolet lithography masks, SPIE Vol. 3873, Part of the 19.sup.th Annual Symposium on Photomask Technology (September 1993)

Choi et al., Temporal Development of Hard and Soft X-ray Emission from a Gas-Puff Z Pinch, 2162 Rev. Sci. Instrum. 57 (8) August 1986;

McGeoch, Appl. Optics, see above;

Pearlman, et al., X-ray Lithography Using a Pulsed Plasma Source, 1190 J. Vac. Sci. Technol. 19 (4) November/December 1981;

Matthews et al.