Long-life laser chamber electrodes

Abstract

An apparatus and method for creating a protective layer on at least one electrode in a laser chamber is disclosed, wherein a layer-forming gas is added to the laser chamber and then the electrode is used to generate a plasma in the laser chamber, resulting in the formation of the protective layer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 62 / 845,926, filed on May 10, 2019, entitled “Long Life Laser Chamber Electrode,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The presently disclosed subject matter relates to light sources such as those produced by lasers used in integrated circuit lithography manufacturing processes. Background Art

[0004] In laser discharge chambers such as ArF power ring amplifier excimer discharge chambers ("PRA") or KrF excimer discharge chambers, electrode erosion severely limits the service life of chamber modules. One measure to extend the service life of KrF excimer discharge chamber modules includes using wear-resistant materials to make the anode. For example, information on materials suitable for use as anode materials can be found in U.S. Pat. No. 7,301,980, issued on November 27, 2007, and U.S. Pat. No. 6,690,706, issued on February 10, 2004, both of which are assigned to the assignee of the present application and both of which are incorporated herein by reference in their entirety.

[0005] Fluorine-containing plasmas are highly corrosive to metals and thus can lead to electrode corrosion and erosion during operation of the chamber. For example, nucleation and growth of localized areas of corrosion product accumulation may occur on the surface of the anode. This leads to uneven discharge between the electrodes and downstream arcing. Erosion leads to an increase in the discharge gap width and discharge extension. Both phenomena lead to a reduction in the energy density in the discharge, which in turn drives the need to increase the voltage difference across the electrodes necessary to maintain energy output. In addition, discharge extension reduces the clearance rate of the gas flow, leading to increased downstream arcing, resulting in energy losses and resulting dose errors. Once the dose error rate increases above a predetermined threshold, the chamber is considered to have reached the end of its service life and must be replaced.

[0006] One or more metal oxide layers or metal oxynitride layers can be used as protective layers on the electrode surface. For example, the formation of CuO or ZnO can protect electrode materials (e.g., brass) from fluoridation. The same is true for the formation of metal oxynitrides, which have excellent compressive strength, flexural strength, fracture toughness, Knoop hardness, and shear modulus, and are very resistant to fluoridation. Having such a layer can increase the life of the electrode. However, current techniques for making metal oxides on electrodes involve heating the electrode in a furnace in an oxygen bath. These techniques cause the electrode to warp, shrink, and deform. In addition, they typically result in the entire electrode being covered with a protective layer, which is not desirable because these methods are not in situ, and if the entire electrode is coated, it is difficult, if not impossible, to install the coated electrode in a chamber. Summary of the invention

[0007] A simplified overview of one or more embodiments is given below to provide a basic understanding of the present invention. This overview is not an extensive overview of all contemplated embodiments, is not intended to identify key elements or important elements of all embodiments, and is not intended to describe the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to a more detailed description that is presented later.

[0008] According to one aspect of the embodiments, a laser chamber having an electrode is disclosed, the laser chamber being configured to expose the electrode to a layer-forming gas while generating a plasma in the laser chamber to grow a protective metal oxide layer or a metal oxynitride layer on the electrode. Thus, during the plasma discharge, the layers grow in the chamber, i.e., in situ. This provides better spatial control of the layers and does not deform the electrode.

[0009] Further embodiments, features, and advantages of the present invention, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate embodiments of the methods and systems of the present invention by way of example and not limitation. Together with the detailed description, the accompanying drawings are also used to explain the principles of the methods and systems proposed herein and enable those skilled in the relevant art to make and use the methods and systems proposed herein. In the accompanying drawings, the same reference numerals indicate the same or functionally similar elements.

[0011] Figure 1 A schematic and not to scale view of an overall broad concept of a lithography system according to aspects of the disclosed subject matter is shown.

[0012] Figure 2A schematic and not to scale view of the overall broad concept of an illumination system according to one aspect of the disclosed subject matter is shown.

[0013] Figure 3 is a schematic and not-to-scale cross-sectional view of a discharge chamber for an excimer laser in accordance with aspects of the disclosed subject matter.

[0014] Figure 4 is a schematic and not-to-scale cross-sectional view of a discharge chamber for an excimer laser in accordance with aspects of the disclosed subject matter.

[0015] Figure 5 is a cross-sectional view of an electrode with a protective layer according to aspects of the disclosed subject matter.

[0016] Figure 6 is a flow chart illustrating a method according to aspects of the disclosed subject matter.

[0017] The further features and advantages of the present invention and the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Based on the teachings contained herein, additional embodiments will be apparent to those skilled in the relevant art. DETAILED DESCRIPTION

[0018] Now, various embodiments are described with reference to the accompanying drawings, wherein similar reference numerals are used to refer to similar elements throughout. In the following description, for the purpose of explanation, many specific details are set forth to facilitate a thorough understanding of one or more embodiments. However, in some or all instances, it is apparent that any embodiment described below can be put into practice without adopting the specific design details described below. In other instances, well-known structures and devices are shown in block diagram form to facilitate the description of one or more embodiments. In order to provide a basic understanding of the embodiments, a simplified overview of one or more embodiments is presented below. This overview is not a broad overview of all contemplated embodiments, is not intended to identify the key elements or important elements of all embodiments, and is not intended to describe the scope of any or all embodiments.

[0019] Figure 1A lithography system 100 is shown that includes an illumination system 105. As described more fully below, the illumination system 105 includes a light source that generates a pulsed light beam 110 and directs it to a lithography exposure device or scanner 115 that patterns microelectronic features on a wafer 120. The wafer 120 is placed on a wafer stage 125 that is constructed to hold the wafer 120 and is connected to a positioner that is configured to accurately position the wafer 120 according to certain parameters.

[0020] The photolithography system 100 uses a light beam 110 having a wavelength in the deep ultraviolet (DUV) range (e.g., having a wavelength of 248 nanometers (nm) or 193 nm). The minimum size of a microelectronic feature that can be patterned on a wafer 120 depends on the wavelength of the light beam 110, with shorter wavelengths resulting in smaller minimum feature sizes. For example, when the wavelength of the light beam 110 is 248 nm or 193 nm, the minimum size of the microelectronic feature can be 50 nm or less, but other wavelengths of light and other minimum feature sizes can be generated according to other embodiments. The bandwidth of the light beam 110 can be the actual instantaneous bandwidth of its spectrum (or emission spectrum), which contains information about how the light energy of the light beam 110 is distributed over different wavelengths. The photolithography exposure device or scanner 115 includes an optical arrangement having, for example, one or more focusing lenses, a mask, and an objective lens arrangement. The mask can be moved along one or more directions (such as along the optical axis of the light beam 110 or in a plane perpendicular to the optical axis). The objective arrangement includes a projection lens and enables image transfer from the mask to the photoresist on the wafer 120. The illumination system 105 adjusts the range of angles for the impingement of the light beam 110 on the mask. The illumination system 105 also homogenizes (evens out) the intensity distribution of the light beam 110 on the mask.

[0021] The scanner 115 may include, among other features, a lithography controller 130, air conditioning equipment, and power supplies for various electrical components. The lithography controller 130 controls how layers are printed on the wafer 120. The lithography controller 130 includes a memory that stores information such as a process recipe. The process program or recipe determines the length of the exposure on the wafer 120 based on, for example, the mask used and other factors that affect the exposure. During lithography, multiple pulses of the light beam 110 illuminate the same area of ​​the wafer 120 to constitute an exposure dose.

[0022] The lithography system 100 may also advantageously include a control system 135. Typically, the control system 135 includes one or more of digital electronic circuits, computer hardware, firmware, and software. The control system 135 also includes a memory, which may be a read-only memory and / or a random access memory. Storage devices suitable for tangibly recording computer program instructions and data include all forms of non-volatile memory, including, for example: semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks.

[0023] The control system 135 may also include one or more input devices (such as a keyboard, a touch screen, a microphone, a mouse, a handheld input device, etc.) and one or more output devices (such as a speaker or a monitor). The control system 135 also includes one or more programmable processors and one or more computer program products, which are tangibly recorded in a machine-readable storage device for execution by the one or more programmable processors. One or more programmable processors can each execute an instruction program to perform the desired function by operating on input data and generating appropriate outputs. Typically, the processor receives instructions and data from a memory. Any of the above contents can be supplemented or incorporated by a specially designed ASIC (application-specific integrated circuit). The control system 135 can be centralized, or can be partially or completely distributed throughout the lithography system 100.

[0024] refer to Figure 2 , the exemplary illumination system 105 is a pulsed laser source that generates a pulsed laser beam as the light beam 110 . Figure 2 A gas discharge laser system according to an embodiment of certain aspects of the disclosed subject matter is schematically illustrated in a block diagram. The gas discharge laser system can include, for example, a solid-state or gas discharge seed laser system 140, an amplification stage (e.g., a power ring amplifier ("PRA") stage 145), relay optics 150, and a laser system output subsystem 160. The seed system 140 can include, for example, a master oscillator ("MO") chamber 165.

[0025] The seed laser system 140 may also include a master oscillator output coupler ("MO OC") 175, which may include: a partially reflective mirror formed with a reflective grating (not shown) in a line-narrowing module ("LNM") 170; an oscillator cavity in which the seed laser 140 oscillates to form a seed laser output pulse, i.e., forming a master oscillator ("MO"). The system may also include a line-center analysis module ("LAM") 180. The LAM 180 may include an etalon spectrometer for fine wavelength measurement and a grating spectrometer for coarser resolution. A MO wavefront engineering box ("WEB") 185 may be used to redirect the output of the MO seed laser system 140 toward the amplifier stage 145, and may include, for example, beam expansion using, for example, a multi-prism beam expander (not shown) and coherence busting, for example, in the form of an optical delay path (not shown).

[0026] The amplification stage 145 may include, for example, a PRA lasing chamber 200, which may also be an oscillator formed, for example, by seed beam injection and output coupling optics (not shown), which may be incorporated into a PRA WEB 210 and may be redirected back through the gain medium in the chamber 200 by a beam reverser 220. The PRA WEB 210 may incorporate a partially reflecting input / output coupler (not shown) and a maximum reflector for a nominal operating wavelength (e.g., approximately 193 nm for an ArF system) and one or more prisms.

[0027] A bandwidth analysis module ("BAM") 230 at the output of the amplifier stage 145 can receive the output laser beam pulse from the amplifier stage and pick a portion of the beam for metrology purposes, for example, to measure the output bandwidth and pulse energy. The laser output beam pulse then passes through an optical pulse stretcher ("OPuS") 240 and an output combined automatic shutter metering module ("CASMM") 250, which can also be the location of a pulse energy meter. One purpose of the OPuS 240 can be, for example, to convert a single output laser pulse into a pulse train. The secondary pulses generated from the original single output pulse can be delayed relative to each other. By distributing the original laser pulse energy into a series of secondary pulses, the effective pulse length of the laser can be extended while reducing the peak pulse intensity. Thus, the OPuS 240 can receive the laser beam from the PRA WEB 210 via the BAM 230 and direct the output of the OPuS 240 to the CASMM 250.

[0028] The PRA lasing chamber 200 and MO 165 are configured as a chamber in which a discharge between electrodes can cause a lasing gas discharge in a lasing gas to create an inverted population of high energy molecules (including, for example, Ar, Kr and / or Xe) to produce relatively wide band radiation, which can be a line narrowed to a relatively very narrow bandwidth and a center wavelength selected in a line narrowing module (“LNM”) 170, as is known in the art.

[0029] Figure 3 A configuration for such a chamber 300 is shown, Figure 3 300 includes an upper electrode 310 that serves as a cathode and a lower electrode 320 that serves as an anode. One or both of the lower electrode 300 and the upper electrode 310 may be completely contained within the pressure envelope of the chamber 300 defined by the chamber wall 305, or one of the electrodes may not be so contained. A lasing gas discharge occurs between the two electrodes in the gap A. Figure 3 Also shown are an upper insulator 315 and a lower insulator 325. The lower electrode 320 is electrically connected to the wall 305 of the chamber 300. For safety reasons, it is desirable to maintain the chamber wall 305 and the lower electrode 320 at ground potential. Figure 3 In the illustrated embodiment, the upper electrode 310 is driven by a voltage source 340 at a voltage that is negative relative to the lower electrode 320 .

[0030] As mentioned, Figure 3 Also shown is a voltage source 340 that establishes a voltage gradient across the cathode 310 and the anode 320. Although a sign (-) is shown for the polarity of the output of the voltage source 340, it should be understood that this is a relative polarity rather than an absolute polarity, that is, relative to the polarity of the lower electrode 320, which is generally in electrical contact with the body of the chamber 300 and must be maintained at ground (0) potential. The upper electrode (cathode 310) is charged to a large (~20 kV) negative voltage.

[0031] The electrodes in chamber 300 are known to corrode. Depending on the embodiment where, for example, ArF or KrF is used, the corrosion may be the result of the fluorine reacting with the electrode material, or the corrosion may be due to any of a variety of other corrosion mechanisms. According to one aspect of the embodiment, a layer-forming gas is introduced into chamber 300 and then a plasma is struck in chamber 300 to promote the formation of a protective layer on the electrode. This Figure 4 In Figure 4In the embodiment, there is a gas inlet 400 for introducing a layer-forming gas into the chamber 300. The inlet 400 is in fluid communication with a valve 410, which is operated under the control of a control unit 430 to selectively connect the inlet 400 to at least one layer-forming gas source 420. Once the partial pressure of the layer-forming gas in the chamber 300 reaches a desired value, a plasma is triggered in the chamber 300 by establishing an appropriate voltage difference between the electrodes 310 and 320. After a predetermined interval, the voltage difference is removed and the layer-forming gas is evacuated, but the protective layer 510 has been formed on the electrodes 310 and 320, as shown in FIG. Figure 5 shown.

[0032] Plasma can be used to help grow metal oxides, metal nitrides and metal oxynitrides on the surface. The discharge chamber is essentially a plasma source, so under appropriate conditions, the protective layer can be grown in situ. As an example, a layer forming gas containing oxygen and / or nitrogen can be introduced into the chamber. The chamber will then operate in a manner similar to its normal operation to serve as a laser chamber. The plasma, together with the oxygen and / or nitrogen, creates the protective layer.

[0033] If the desired protective layer is a metal oxide, the layer forming gas may be, for example, an oxygen-containing gas. Examples of oxygen-containing gases include O2, H2O, H2O2, O3, nitrogen oxides (NO x ) and air. If the desired protective layer is a nitride, the layer forming gas may be, for example, a nitrogen-containing gas. Examples of nitrogen-containing gases include N2, NH3, nitrogen oxides (NO x ) and air. If the desired protective layer is a metal nitride oxide, the layer forming gas may be, for example, a gas containing nitrogen and oxygen or a mixture of nitrogen and oxygen. Examples of such gases include nitrogen oxides (NO x ), a mixture of the oxygen-containing gas and the nitrogen-containing gas mentioned above, and air. These are just examples, and it is obvious to those skilled in the art that other gases can be used.

[0034] The concentration / pressure of the layer-forming gas used to form the protective layer may advantageously be in the range of about a few parts per million level to about 38 kPa or in the range of about a few parts per million to about 4 kPa. Since the total filling pressure of the chamber is of the order of 380 kPa of laser gas, this corresponds to a concentration of the layer-forming gas of the order of a few parts per million to about 1%.

[0035] Under these conditions, plasma may be struck in chamber 300 by applying a voltage differential in a range of about 17 kV to about 28 kV, as an example, although other voltage differentials may also be used.

[0036] like Figure 5As shown, electrode 500 (which can be electrode 310 or electrode 320) is formed of a bulk material (such as brass, which is an alloy of copper and zinc). As a result of exposure to the plasma and layer forming gas, a protective layer 510 will be formed on the exposed surface of electrode 500. Generally, the composition of the protective layer 510 depends on the electrode material and layer forming gas being used. Oxygen-containing gas can be used to form a protective layer 510 made of a mixture of CuO or ZnO on the brass electrode. Nitrogen-containing gas can be used to create a protective layer 510 of copper nitride (Cu3N) or zinc nitride (Zn3N2) using a brass electrode. Nitrogen-containing and oxygen-containing gases can be used to create copper oxynitride (Cu x O y N z ) or zinc oxynitride (Zn x O y N z ) of the protective layer 510. It is obvious to those skilled in the art that other combinations are also possible. The thickness of the protective layer 510 is generally in the range of nanometers to 10 micrometers.

[0037] In general, the thickness of protective layer 510 is a function of the formation rate and formation time. The formation rate depends on the chemical composition of the layer formation and the characteristics of the plasma.

[0038] The protective layer formed on the electrode surface due to the in-situ layer reduces the corrosion of the electrode. In many embodiments, the protective layer formed on the electrode surface due to the in-situ layer formation plays an important role in reducing the reaction of fluorine with the bulk material of the electrode. The denser and more uniform the protective layer, the lower the corrosion rate.

[0039] Figure 6 1 is a flow chart describing an in-situ formation process of a protective layer on an electrode according to one aspect of an embodiment. In step S10, a layer-forming gas is introduced into a chamber containing an electrode to a desired partial pressure. In step S20, a plasma is triggered by applying a voltage to the electrode for a predetermined period of time so that the layer-forming gas can form a protective layer on the electrode surface. In step S30, the plasma is quenched by removing the voltage. In step S40, the layer-forming gas is evacuated from the chamber. Thus, a protective layer is formed on the electrode.

[0040] These steps may be repeated periodically to regrow the layer.Alternatively, the protective layer may be grown continuously by controlled introduction of a dilute mixture containing oxygen, nitrogen or both.

[0041] One advantage of the process just described is that the layer growth is confined to the discharge region of the electrode in which the plasma is present, so there is better spatial control over the layer growth. In addition, the heating of the electrode is no different from the heating that the electrode usually experiences during normal operation of the chamber, so there is less possibility of deformation of the electrode. The possibility that the growth cycle can be repeated at any time also helps to extend the overall life of the electrode.

[0042] The above description includes examples of multiple embodiments. Of course, for the purpose of describing the aforementioned embodiments, it is not possible to describe every conceivable combination of parts or methods, but those of ordinary skill in the art will recognize that many other combinations and arrangements of the various embodiments are possible. Thus, the described embodiments are intended to include all such changes, modifications and variations that fall within the spirit and scope of the appended claims. Further, with respect to the term "includes" used in the specific embodiments or claims, such terms are defined as inclusive in a manner similar to the term "comprising", as interpreted when the term "comprising" is adopted as a transition word in the claims. Further, although the elements of the described aspects and / or embodiments may be described or claimed in the singular, the plural form is also contemplated unless explicitly stated to be limited to the singular. In addition, unless otherwise stated, all or a portion of any aspect and / or embodiment may be used together with all or a portion of any other aspect and / or embodiment.

[0043] Further aspects of the invention are set out in the following numbered clauses.

[0044] 1. A device comprising:

[0045] Laser chamber;

[0046] an electrode at least partially located within the laser chamber;

[0047] a source of layer-forming gas connectable to the laser chamber; and

[0048] A voltage source is electrically connected to the electrode and configured to supply voltage to the electrode to generate plasma at a surface of the electrode in the presence of a layer-forming gas to form a protective layer on the electrode.

[0049] 2. An apparatus according to item 1, wherein the layer-forming gas comprises an oxygen-containing gas.

[0050] 3. An apparatus according to item 2, wherein the oxygen-containing gas comprises O2.

[0051] 4. An apparatus according to item 2, wherein the oxygen-containing gas comprises H2O.

[0052] 5. An apparatus according to item 2, wherein the oxygen-containing gas comprises H2O2.

[0053] 6. An apparatus according to item 2, wherein the oxygen-containing gas comprises O3.

[0054] 7. An apparatus according to clause 2, wherein the oxygen-containing gas comprises nitrogen oxides.

[0055] 8. An apparatus according to clause 2, wherein the oxygen-containing gas comprises air.

[0056] 9. The device of any one of clauses 1 to 8, wherein the protective layer comprises a metal oxide.

[0057] 10. The device of any of clauses 2 to 8, wherein the electrode comprises brass and the protective layer comprises copper oxide (CuO).

[0058] 11. A device according to any of clauses 2 to 8, wherein the electrode comprises brass and the protective layer comprises zinc oxide ZnO.

[0059] 12. The apparatus of clause 1, wherein the layer-forming gas comprises a nitrogen-containing gas.

[0060] 13. An apparatus according to clause 12, wherein the nitrogen-containing gas comprises N2.

[0061] 14. An apparatus according to clause 12, wherein the nitrogen-containing gas comprises NH3.

[0062] 15. The apparatus of clause 12, wherein the nitrogen-containing gas comprises nitrogen oxides.

[0063] 16. The apparatus of clause 12, wherein the nitrogen-containing gas comprises air.

[0064] 17. A device according to any of clauses 12 to 16, wherein the protective layer comprises a metal nitride.

[0065] 18. The device of any of clauses 12 to 16, wherein the electrode comprises brass and the protective layer comprises copper nitride.

[0066] 19. The device of any of clauses 12 to 16, wherein the electrode comprises brass and the protective layer comprises zinc nitride.

[0067] 20. The apparatus of clause 1, wherein the layer-forming gas comprises a nitrogen-containing and oxygen-containing gas.

[0068] 21. The apparatus of clause 20, wherein the nitrogen- and oxygen-containing gas comprises nitrogen oxides.

[0069] 22. The apparatus of clause 20, wherein the nitrogen- and oxygen-containing gas comprises air.

[0070] 23. A device according to any of clauses 20 to 22, wherein the protective layer comprises a metal oxynitride.

[0071] 24. The apparatus of any of clauses 20 to 22, wherein the electrode comprises brass and the protective layer comprises copper oxynitride.

[0072] 25. The apparatus of any of clauses 20 to 22, wherein the electrode comprises brass and the protective layer comprises zinc oxynitride.

[0073] 26. A method for forming a protective layer on an electrode in a laser discharge chamber, the method comprising:

[0074] adding a layer forming gas into the laser discharge chamber to achieve a predetermined partial pressure; and

[0075] Plasma is generated within the laser discharge chamber using electrodes for a predetermined amount of time.

[0076] 27. The method of clause 26, wherein the layer-forming gas comprises an oxygen-containing gas.

[0077] 28. A method according to item 27, wherein the oxygen-containing gas comprises O2.

[0078] 29. The method of clause 27, wherein the oxygen-containing gas comprises H2O.

[0079] 30. The method of clause 27, wherein the oxygen-containing gas comprises H2O2.

[0080] 31. The method of clause 27, wherein the oxygen-containing gas comprises O3.

[0081] 32. The method of clause 27, wherein the oxygen-containing gas comprises nitrogen oxides.

[0082] 33. The method of clause 27, wherein the oxygen-containing gas comprises air.

[0083] 34. The method of any one of clauses 26 to 33, wherein the protective layer comprises a metal oxide.

[0084] 35. A method according to any one of clauses 26 to 33, wherein the electrode comprises brass and the protective layer comprises copper oxide (CuO).

[0085] 36. A method according to any one of clauses 26 to 33, wherein the electrode comprises brass and the protective layer comprises zinc oxide ZnO.

[0086] 37. The method of clause 26, wherein the layer-forming gas comprises a nitrogen-containing gas.

[0087] 38. A method according to item 37, wherein the nitrogen-containing gas comprises N2.

[0088] 39. The method of clause 37, wherein the nitrogen-containing gas comprises NH3.

[0089] 40. The method of clause 37, wherein the nitrogen-containing gas comprises nitrogen oxides.

[0090] 41. The method of clause 37, wherein the nitrogen-containing gas comprises air.

[0091] 42. A method according to any one of clauses 37 to 41, wherein the protective layer comprises a metal nitride.

[0092] 43. A method according to any one of clauses 37 to 41, wherein the electrode comprises brass and the protective layer comprises copper nitride.

[0093] 44. A method according to any one of clauses 37 to 41, wherein the electrode comprises brass and the protective layer comprises zinc nitride.

[0094] 45. The method of clause 26, wherein the layer-forming gas comprises a nitrogen-containing and an oxygen-containing gas.

[0095] 46. ​​The method of clause 26, wherein the nitrogen- and oxygen-containing gas comprises nitrogen oxides.

[0096] 47. The method of clause 26, wherein the nitrogen-containing gas and the oxygen-containing gas comprise air.

[0097] 48. A method according to any one of clauses 45 to 47, wherein the protective layer comprises a metal oxynitride.

[0098] 49. A method according to any one of clauses 45 to 47, wherein the electrode comprises brass and the protective layer comprises copper oxynitride.

[0099] 50. The method of any one of clauses 45 to 47, wherein the electrode comprises brass and the protective layer comprises zinc oxynitride.

[0100] Further aspects of the invention are set out in the following claims.

Claims

1. A device, include: i. Laser chamber; ii. an electrode located at least partially within the laser chamber; iii. a source of layer-forming gas connectable to the laser chamber, wherein the layer-forming gas comprises an oxygen-containing gas and / or a nitrogen-containing gas; and iv. a voltage source electrically connected to the electrode and configured to supply a voltage to the electrode to generate a plasma at the surface of the electrode in the presence of the layer-forming gas to form a protective layer on the electrode, wherein the protective layer comprises a metal oxide, a metal nitride and / or a metal oxynitride.

2. The device according to claim 1, wherein the oxygen-containing gas comprises O 2 , H 2 O or H 2 O 2 .

3. The device according to claim 1, wherein the oxygen-containing gas comprises O 3 .

4. The apparatus according to claim 1, wherein the oxygen-containing gas comprises nitrogen oxides or air. The device according to claim 1 , wherein the protective layer is an anti-fluorination layer. 6 . The device of claim 1 , wherein the electrode comprises brass, and the protective layer comprises copper oxide (CuO) or zinc oxide (ZnO).

7. The apparatus according to claim 1, wherein the nitrogen-containing gas comprises N 2 or NH 3 .

8. The device of claim 1, wherein the electrode comprises brass and the metal nitride is copper nitride or zinc nitride.

9. The device of claim 1, wherein the protective layer comprises copper oxynitride or zinc oxynitride, and the electrode comprises brass.

10. A method for forming a protective layer on an electrode in a laser discharge chamber, the method include: i. adding a layer-forming gas to the laser discharge chamber to achieve a predetermined partial pressure; as well as ii. generating a plasma within the laser discharge chamber using the electrode for a predetermined amount of time so that the layer-forming gas forms the protective layer on the electrode, wherein the layer-forming gas comprises an oxygen-containing gas and / or a nitrogen-containing gas, and wherein the protective layer comprises a metal oxide, a metal nitride and / or a metal oxynitride.

11. The method according to claim 10, wherein the oxygen-containing gas comprises O 2 , H 2 O or H 2 O 2 .

12. The method according to claim 10, wherein the oxygen-containing gas comprises O 3 .

13. The method of claim 10, wherein the oxygen-containing gas comprises nitrogen oxides or air.

14. The method of claim 10, wherein the electrode comprises brass, and the protective layer comprises copper oxide (CuO) or zinc oxide (ZnO).

15. The method according to claim 10, wherein the nitrogen-containing gas comprises N 2 or NH 3 . The method according to claim 10 , wherein the protective layer is an anti-fluorination layer.

17. The method of claim 10, wherein the electrode comprises brass and the metal nitride comprises copper nitride or zinc nitride.

18. The method of claim 10, wherein the electrode comprises brass and the protective layer comprises copper oxynitride or zinc oxynitride.

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