Method and apparatus for extending the life of electrodes in a laser chamber - Patents.com

Abstract

To extend a useful lifetime of a laser discharge chamber.SOLUTION: Disclosed are methods of and apparatus for extending a useful lifetime of a laser discharge chamber. In the laser discharge chamber, the polarity of an electrode positioned at a fixed position within the chamber is caused to be positive with respect to the polarity of a second electrode defining a discharge gap with the first electrode. The first electrode is made of a material that forms an erosion resistant surface when the first electrode is used and an anode. Also disclosed are an arrangement in which a first electrode is positionable with respect to a second electrode defining a discharge gap with the second electrode, and the position of the first electrode controlled to maintain the width of the gap within a predetermined range.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 62 / 576,371, filed October 24, 2017, which is incorporated by reference in its entirety herein.

[0002] The subject matter of this disclosure relates to laser-generated light sources such as those used in integrated circuit photolithography manufacturing processes. [Background technology]

[0003]

[0003] In laser discharge chambers, such as ArF power amplifier excimer discharge chambers ("PRA") or KrF excimer discharge chambers, electrode erosion imposes significant limitations on the useful life of the chamber modules. One method of extending the useful life of KrF excimer discharge chamber modules involves making the anode of a material that does not wear out. Information regarding materials suitable for use as anode materials can be found, for example, in U.S. Pat. No. 7,301,980, issued Nov. 27, 2007, and U.S. Pat. No. 6,690,706, issued Feb. 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. Some of these materials are not only corrosion resistant, but actually grow an erosion resistant coating ("reef") that maintains the anode surface in its original position, i.e., substantially the same position as when the electrode was new.

[0004]

[0004] The erosion resistant coating formed on the anode is not formed on the cathode, so if a material that forms an erosion resistant coating is used as the anode, the coating will not form if that material is used as the cathode material and will not protect the cathode from erosion when the laser is fired.

[0005]

[0005] In current chambers, erosion leads to both an increase in the width of the discharge gap and a broadening of the discharge. Both of these phenomena lead to a lower energy density discharge, which in turn creates a need to increase the voltage difference between the electrodes required to maintain the energy output. Furthermore, the broadening of the discharge reduces the clearing rate of the gas flow, leading to increased arcing downstream, resulting in energy dropout and resulting dose error. Once the dose error rate increases beyond a certain threshold, the chamber is considered to have reached the end of its useful life and must be replaced.

[0006]

[0006] Thus, while it has been found possible to provide an anode that can last indefinitely in certain discharge chamber designs, it has not been found possible to provide a cathode that can last indefinitely, so that the cathode life remains a limiting factor for the overall chamber life. Thus, there is a need for an arrangement that significantly extends the cathode life and / or compensates for cathode erosion. Summary of the Invention

[0007]

[0007] The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of the invention. This summary is not an exhaustive overview of all contemplated embodiments, and is not intended to identify key or critical elements of all embodiments or to delineate 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 the more detailed description that is presented later.

[0008]

[0008] According to one aspect, the subject matter of the present disclosure extends the life of the chamber by reversing the polarity of the discharge. Thus, the upper electrode becomes the anode and is made of a material that forms a protective layer that prevents erosion. The advantages of this configuration are enhanced by using a mechanism attached to the lower electrode (here the cathode) that can raise the lower electrode, which is more susceptible to erosion, to compensate for its erosion gradually throughout the life of the chamber.

[0009] According to one aspect, a laser is disclosed that includes a discharge chamber, a first electrode disposed at least partially within the discharge chamber, a second electrode disposed at least partially within the discharge chamber, the first electrode having a first discharge surface and the second electrode having a second discharge surface, the first discharge surface and the second discharge surface being disposed opposite each other across a gap, and a motor mechanically coupled to the second electrode for positioning the second discharge surface to control a width of the gap, the polarity of the first electrode being positive with respect to the polarity of the second electrode such that the first electrode functions as an anode during discharge in the discharge chamber. The position of the first electrode may be fixed with respect to the discharge chamber. The first electrode may include a material that forms an erosion resistant coating when the first electrode functions as an anode during discharge in the discharge chamber. Additionally or alternatively, the first electrode may include an applied erosion resistant coating. The laser may also include a controller connected to the motor, the controller providing a control signal to control the motor, thereby controlling the width of the gap. The controller may control the motor to maintain the width of the gap within a predetermined range. The controller may generate the control signal based at least in part on a magnitude of a voltage difference between the first and second electrodes required to maintain a substantially constant output power during discharge or based at least in part on a cap width measured or inferred by the detector. The laser may include a power supply electrically connected to the first and second electrodes to provide a plurality of pulses to at least one of the first and second electrodes, the power supply including a commutator module and a compression head module, the commutator module and the compression head module being adjusted such that a polarity of the first electrode is positive with respect to a polarity of the second electrode such that the first electrode functions as an anode during a pulse.

[0010] According to another aspect, a laser is disclosed that includes a discharge chamber, a first electrode at least partially disposed within the discharge chamber and fixed relative to the discharge chamber, and a second electrode at least partially disposed within the discharge chamber, the first electrode having a first discharge surface and the second electrode having a second discharge surface, the first discharge surface and the second discharge surface facing each other across a gap, the polarity of the first electrode being positive with respect to the polarity of the second electrode such that the first electrode functions as an anode during discharge in the discharge chamber, and the first electrode includes a material that forms an erosion resistant coating when the first electrode functions as an anode during discharge in the discharge chamber. The laser may further include a motor mechanically coupled to the second electrode for positioning the second discharge surface to control a width of the gap, and a controller connected to the motor, the controller providing a control signal for controlling the motor to control the width of the gap. The controller may control the motor to maintain the width of the gap within a predetermined range. The controller may generate the control signal based at least in part on a magnitude of a voltage difference between the first electrode and the second electrode during the discharge. The laser may further include a detector connected to the controller for measuring a width of the gap and providing a signal indicative of the gap width, the controller generating the control signal based at least in part on the gap width measured by the detector.

[0011] According to another aspect, a method of controlling operation of a laser is disclosed, the laser including a discharge chamber and a first electrode and a second electrode spaced apart by a gap, the second electrode positionable to define a width of the gap, the method including the steps of operating the laser by generating a discharge in the discharge chamber between the first electrode and the second electrode, the polarity of the first electrode being positive relative to the polarity of the second electrode such that the first electrode functions as an anode in the discharge chamber, and controlling the position of the second electrode to maintain the width of the gap within a predetermined range. The position of the second electrode may be based at least in part on a magnitude of a voltage difference between the first and second electrodes required to maintain a substantially constant output power during the discharge, or at least in part on a gap width measured in the measuring step, or at least in part on a number of discharges generated in the discharge chamber. [Brief description of the drawings]

[0012] [Figure 1] 1 shows a schematic diagram, not to scale, of the overall broad concept of a photolithography system according to one aspect of the disclosed subject matter. [Diagram 2]

[0013] 1 shows a schematic diagram, not to scale, of the overall broad concept of a lighting system according to one aspect of the disclosed subject matter. [Diagram 3]

[0014] 1 is a schematic cross-sectional view, not to scale, of a discharge chamber for an excimer laser in accordance with an aspect of the disclosed subject matter. [Figure 4]

[0015] 1 is a schematic cross-sectional view, not to scale, of a discharge chamber for an excimer laser in accordance with an aspect of the disclosed subject matter. [Diagram 5]

[0016] 1 is a schematic cross-sectional view, not to scale, of a discharge chamber for an excimer laser in accordance with an aspect of the disclosed subject matter. [Figure 6]

[0017] 1 is a flow chart of a method for controlling the effects of electrode erosion in accordance with an aspect of the disclosed subject matter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013]

[0018] Various embodiments will now be described with reference to the drawings. In the drawings, like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to facilitate a thorough understanding of one or more embodiments. However, it may be apparent that in some or all cases, any of the embodiments described below can be practiced without the specific design details described below. In other cases, well-known structures and devices are shown in block diagram form to facilitate the description of one or more embodiments. A simplified summary of one or more embodiments is presented below to provide a basic understanding of the embodiments. This summary is not an exhaustive overview of all contemplated embodiments, nor is it intended to identify key or critical elements of all embodiments or to delineate the scope of any or all embodiments.

[0014]

[0019] 1, there is shown a photolithography system 100 that includes an illumination system 105. As described more fully below, illumination system 105 includes a light source that generates a pulsed light beam 110 and directs the beam to a photolithography exposure tool or scanner 115 that patterns microelectronic features on a wafer 120. Wafer 120 rests on a wafer table 125 that is constructed to hold wafer 120 and connected to a positioner configured to precisely position wafer 120 according to certain parameters.

[0015]

[0020] The photolithography system 100 uses a light beam 110 having a wavelength in the deep ultraviolet (DUV) range, for example with a wavelength of 248 nanometers (nm) or 193 nm. The minimum dimension of the ultra-fine electronic features that can be patterned on the wafer 120 depends on the wavelength of the light beam 110, with shorter wavelengths resulting in smaller minimum feature sizes. For a wavelength of the light beam 110 of 248 nm or 193 nm, the minimum dimension of the ultra-fine electronic features can be, for example, 50 nm or less. The bandwidth of the light beam 110 can be the actual instantaneous bandwidth of the light spectrum (or radiation spectrum), which contains information on how the light energy of the light beam 110 is distributed across various wavelengths. The scanner 115 includes an optical arrangement, for example having one or more focusing lenses, a mask, and an objective arrangement. The mask can be moved along one or more directions, for example 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 of the light beam 110 that strikes the mask. The illumination system 105 also homogenizes the intensity distribution of the light beam 110 across the mask.

[0016]

[0021] The scanner 115 may include, among other things, a lithography controller 130, an air conditioner, 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 memory that stores information such as a process recipe. The process program or recipe determines the length of exposure on the wafer 120 based on, for example, the mask used, as well as 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.

[0017]

[0022] Photolithography system 100 also preferably includes a control system 135. Generally, control system 135 includes one or more of digital electronic circuitry, computer hardware, firmware, and software. Control system 135 also includes memory, which may be read-only memory and / or random access memory. Suitable storage devices for specifically incorporating computer program instructions and data include, by way of example, all forms of non-volatile memory, including 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.

[0018]

[0023] The control system 135 may also include one or more input devices (e.g., a keyboard, a touch screen, a microphone, a mouse, a handheld input device, etc.) and one or more output devices (e.g., a speaker or a monitor, etc.). The control system 135 also includes one or more programmable processors and one or more computer programs tangibly embodied in a machine-readable storage device for execution by the one or more programmable processors. Each of the one or more programmable processors can execute a program of instructions to perform a desired function by manipulating input data and generating appropriate output. Typically, a processor receives instructions and data from a memory. Any of the foregoing may be supplemented by, or incorporated in, specially designed ASICs (application-specific integrated circuits). The control system 135 may be centralized or partially or fully distributed throughout the photolithography system 100.

[0019]

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

[0020]

[0025] The seed laser system 140 may also include a master oscillator output coupler ("MO OC") 175, which may include a partially reflective mirror that, together with a reflective grating (not shown) in the line narrowing module ("LNM") 170, forms an oscillator cavity in which the seed laser 140 oscillates to form the seed laser output pulse, i.e., forms the 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 measurements and a grating spectrometer for coarse resolution. The MO wavefront engineering box ("WEB") 185 may act to redirect the output of the MO seed laser system 140 to the amplification stage 145 and may include beam expansion, for example, using a multi-prism beam expander (not shown), and coherence destruction, for example, in the form of an optical delay path (not shown).

[0021]

[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 the 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 reflective input / output coupler (not shown), a maximally reflective mirror for the nominal operating wavelength (e.g., about 193 nm for an ArF system), and one or more prisms.

[0022]

[0027] A bandwidth analysis module ("BAM") 230 at the output of the amplification stage 145 may receive the pulses of the laser light beam output from the amplification stage and take a portion of the light beam for metrology purposes, for example, to measure the output bandwidth and pulse energy. The pulses of the laser output light beam then pass through an optical pulse stretcher ("OPuS") 240 and an output coupling automatic shutter metrology module ("CASMM") 250, which may also be where the pulse energy meter is located. One purpose of the OPuS 240 may be, for example, to convert a single output laser pulse into a pulse train. Secondary pulses generated from the original single output pulse may be delayed relative to each other. By distributing the energy of the original laser pulse to the secondary pulse train, the effective pulse length of the laser may be expanded and at the same time the peak pulse intensity may be reduced. Thus, the OPuS 240 may 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.

[0023]

[0028] The PRA lasing chamber 200 and MO 165 are configured as chambers in which an electrical discharge between electrodes creates a lasing gas discharge in the lasing gas to produce a population inversion of energetic molecules, including, for example, Ar, Kr, and / or Xe, generating a relatively broadband radiation that may be line narrowed to a relatively very narrow bandwidth and center wavelength selected in a line narrowing module ("LNM") 170, as known in the art. Such a chamber 300 configuration is shown in FIG. 3, which is a highly stylized cross-sectional view of a discharge chamber. The chamber 300 includes an upper electrode 310 that functions as a cathode and a lower electrode 320 that functions as an anode. One or both of the lower electrode 320 and the upper electrode 310 may be completely contained within the pressure envelope of the chamber 300 defined by the chamber walls 305, or one of these electrodes may not be so contained. A lasing gas discharge occurs between these two electrodes in a gap having a width A. Also shown in Figure 3 are upper insulator 315 and lower insulator 325. Lower electrode 320 is electrically connected to walls 305 of chamber 300. For safety reasons, it is desirable to maintain chamber walls 300, and therefore lower electrode 320, at ground potential. In the embodiment shown in Figure 3, upper electrode 310 is driven by voltage source 340 at a voltage that is negative with respect to lower electrode 320.

[0024]

[0029] When functioning as an anode, as shown in FIG. 3, the lower electrode 320 is advantageously made from a material that does not exhibit wear, but actually grows an erosion coating 330 (also called a "leaf") that maintains the surface of the lower electrode 320 in substantially the same position as when the lower electrode 320 was new. Alternatively, the electrode may be coated with an erosion-resistant coating. The dimensions of the coating 330 are exaggerated in FIG. 3 for illustrative purposes. The growth of the coating 330 does not form on the upper electrode 310 when the upper electrode 310 functions as a cathode, and as a result, the upper electrode 310 is eroded when the laser is fired. In the current chamber, this erosion results in both an increase in the dimension A of the discharge gap and a spreading of the discharge. Note also that the upper electrode is provided with a small bump 312.

[0025]

[0030] 3 also shows a voltage source 340 that establishes a voltage gradient between the cathode 310 and the anode 320. Although a (-) notation is shown for the polarity of the output of the voltage source 340, it should be understood that this is a relative, rather than an absolute, polarity, i.e., with respect to the polarity of the lower electrode 320, which is generally in electrical contact with the body of the chamber 300 and should remain at ground (0) potential. The upper electrode (cathode 310) is charged to a large (approximately 20 kV) negative voltage.

[0026]

[0031] According to one aspect of the disclosed subject matter, for "reefing anode" chambers such as KrF MO and PRA, the polarity of the discharge is reversed and the upper electrode 310 becomes the anode, forming a protective corrosion layer 330 and preventing erosion. This is shown in FIG. 4. In configurations where the lower electrode 320 is in electrical contact with the chamber body and must remain held at ground, this means that the upper electrode 310 is charged to a large (approximately 20 kV) positive voltage. This can be achieved by modifying the voltage source 340. The voltage source 340 can be split into three modules: a high voltage power supply, a commutator, and a compression head. The commutator module may include a step-up transformer. Modifying the voltage source 340 may include changing the polarity of the commutator module. This also includes changing the magnetics of the voltage source compression head. The compression head uses magnetic pulse compression to compress the pulses from the commutator. The compression head magnetics may also need to be modified to accommodate the change in polarity.

[0027]

[0032] While the system just described addresses wear of the upper electrode 310, the lower electrode 320 becomes a cathode, and therefore an electrode susceptible to erosion. Also, there are discharge chambers, e.g., ArF MO, where the choice of anode material that forms a protective erosion layer results in unacceptable degradation of laser performance, especially at high repetition rates. To address these issues, the lower electrode anode 320 is preferably connected to a mechanism that can be used to gradually lift its surface throughout the chamber life, thereby maintaining the surface in its original (new) position. In chambers where a lower, movable electrode is maintained as the anode, erosion of the fixed upper cathode will still occur, but at a much slower rate than the erosion rate of the anode. Anodes whose positions are mechanically adjustable are described, for example, in U.S. Pat. No. 9,246,298, issued Jan. 26, 2016, and assigned to the assignee of the present application, the contents of which are incorporated herein in their entirety. However, the advantages of using adjustable electrodes are particularly evident when applied to electrodes that are more susceptible to wear, such as the lower electrode, which functions as the cathode and, as a result, no corrosion resistant layer is expected to form on the lower electrode.

[0028]

[0033] It is generally preferred to have the lower electrode moveable rather than the upper electrode, since it is preferred that the upper electrode form part of the pressure envelope of the discharge chamber, and there are strong constraints on the shape and volume requirements of this electrode in order to maintain low head inductance (which is important for good efficiency).

[0029]

[0034] Specifically, in FIG. 5, a motor 360 is mechanically coupled to the lower electrode 320 in a manner that controls the position of the upper surface of the lower electrode 320 and thus the width A of the gap between the lower electrode 320 and the upper electrode 310. Here and elsewhere in this specification, "motor" is used broadly to mean any device or combination of devices capable of producing motion. For example, the motor 360 can be a screw drive, a friction drive, or a rack and pinion drive coupled to a linear electric motor or a piezoelectric device. The motor 360 is adapted to receive a control signal from a controller 370. The controller 370 may provide a control signal to the motor 360 to raise the upper surface of the lower electrode 320 based on the elapsed time of operation or the number of pulses generated in the chamber. The controller 370 may also provide a control signal based on some operating parameter, such as the variation or magnitude of the drive voltage. For example, the control signal may be based at least in part on the voltage required to achieve a fixed target output energy. The controller 370 may also provide a control signal based on the size A of the gap between the electrodes, as measured by a metrology unit 380 or inferred by some other means.

[0030]

[0035] 5 is beneficial for chamber designs in which the upper electrode 310 is necessarily part of the pressure envelope of the chamber 300, and as a result, providing a mechanism to move the upper electrode 310 to compensate for erosion is not feasible. In chamber designs in which only the lower electrode 320 is fixed, the upper electrode 310 can be configured to be positionable. In chamber designs in which neither electrode is fixed and neither is entirely within the pressure envelope of the chamber 300, one or both electrodes can be configured to be positionable.

[0031]

[0036] FIG. 6 is a flow chart illustrating an example of a method of operating an arrangement as shown in FIG. 5. In step S10, a laser is provided having at least two electrodes separated by a gap. It will be appreciated that one of the electrodes, electrically connected to function as a cathode, is movable under the control of a control signal, such that the width of the gap between the electrodes can be automatically controlled. In step S20, the laser is operated, and in step S30, at least one operating parameter of the laser is measured. The operating parameter may be any of the parameters mentioned above, such as the magnitude of the elapsed operating time of the chamber, the number of pulses generated in the chamber, the variation or magnitude of the drive voltage required to achieve a fixed target output energy, or the size of the gap between the electrodes, measured by the metrology unit 380 or inferred by some other means. In step S40, the width of the gap is controlled based on the measured operating parameter. For example, the movable electrode may be moved in a manner to make the width of the gap substantially equal to a predetermined value, such as the original gap width. It will be appreciated that the process of FIG. 6 can be performed essentially continuously or at predetermined intervals.

[0032]

[0037] The above description includes examples of several embodiments. Of course, for purposes of describing the foregoing embodiments, it is not possible to describe every conceivable combination of components or methods, but one skilled in the art can appreciate that numerous further combinations and permutations of the various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such changes, modifications, and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term "includes" is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term "comprising," as "comprising" is interpreted when used as a transitional term in the claims. Furthermore, although elements of the described aspects and / or embodiments may be described or claimed in the singular, the plural is also contemplated, unless limitation to the singular is expressly stated. Furthermore, unless otherwise specified, all or a portion of any aspect and / or embodiment may be utilized with all or a portion of any other aspect and / or embodiment.

[0033]

[0038] The embodiments may be further described using the following clauses. Clause 1. A laser, A discharge chamber; a first electrode disposed at least partially within the discharge chamber; a second electrode disposed at least partially within the discharge chamber, the first electrode having a first discharge surface and the second electrode having a second discharge surface, the first discharge surface and the second discharge surface disposed opposite each other across a gap; a motor mechanically coupled to the second electrode for positioning the second discharge surface to control the width of the gap; The polarity of the first electrode is positive with respect to the polarity of the second electrode such that the first electrode functions as an anode during discharge in the discharge chamber of the laser.

[0034] Clause 2. The laser of clause 1, wherein the position of the first electrode is fixed relative to the discharge chamber.

[0035] Clause 3. The laser of clause 1, wherein the first electrode comprises a material that forms an erosion resistant coating when the first electrode functions as an anode during discharge in the discharge chamber.

[0036] Clause 4. The laser of clause 1, further comprising an erosion resistant coating applied to the first electrode.

[0037] Clause 5. The laser of clause 1, further comprising a controller connected to the motor, the controller providing a control signal to the motor to control the width of the gap.

[0038] Clause 6. The laser of clause 5, wherein the controller controls the motor to maintain the gap width within a predetermined range.

[0039] Clause 7. The laser of clause 5, wherein the controller generates the control signal based at least in part on a magnitude of a voltage difference between the first electrode and the second electrode during the discharge required to maintain a substantially constant output power.

[0040] Clause 8. The laser of clause 5, further comprising a detector connected to the controller for measuring the width of the gap and providing a signal indicative of the width, the controller generating a control signal based at least in part on the width measured by the detector.

[0041] Clause 9. The laser of clause 1, further comprising a power supply electrically connected to the first electrode and the second electrode to supply a plurality of pulses to at least one of the first electrode and the second electrode, the power supply including a commutator module and a compression head module, the commutator module and the compression head module being adjusted such that the polarity of the first electrode is positive with respect to the polarity of the second electrode so that the first electrode functions as an anode during the pulse.

[0042] Clause 10. The laser of clause 5, wherein the controller generates the control signal based at least in part on the number of discharges generated within the discharge chamber.

[0043] Clause 11. A laser, A discharge chamber; a first electrode disposed at least partially within the discharge chamber and fixed relative to the discharge chamber; a second electrode disposed at least partially within the discharge chamber, the first electrode having a first discharge surface and the second electrode having a second discharge surface, the first discharge surface and the second discharge surface facing each other across a gap, the polarity of the first electrode being positive with respect to the polarity of the second electrode such that the first electrode functions as an anode during discharge in the discharge chamber, and the first electrode including a material that forms a corrosion resistant coating when the first electrode functions as an anode during discharge in the discharge chamber; a motor mechanically coupled to the second electrode for positioning the second discharge surface to control the width of the gap; a controller connected to the motor, the controller providing a control signal to the motor to maintain the gap width within a predetermined range.

[0044] Clause 12. The laser of clause 11, wherein the controller generates the control signal based at least in part on the number of discharges generated within the discharge chamber.

[0045] Clause 13. A laser, A discharge chamber; a first electrode disposed at least partially within the discharge chamber and fixed relative to the discharge chamber; a second electrode disposed at least partially within the discharge chamber, the first electrode having a first discharge surface and the second electrode having a second discharge surface, the first discharge surface and the second discharge surface disposed opposite each other across a gap; The polarity of the first electrode is positive relative to the polarity of the second electrode such that the first electrode functions as an anode during discharge in the discharge chamber, and the first electrode includes a material that forms an erosion resistant coating when the first electrode functions as an anode during discharge in the discharge chamber, the laser.

[0046] Clause 14. The laser of clause 13, further comprising a motor mechanically coupled to the second electrode for positioning the second discharge surface to control the width of the gap.

[0047] Clause 15. The laser of clause 14, further comprising a controller connected to the motor, the controller providing a control signal to the motor to control the width of the gap.

[0048] Clause 16. The laser of clause 15, wherein the controller controls the motor to maintain the gap width within a predetermined range.

[0049] Clause 17. The laser of clause 15, wherein the controller generates the control signal based at least in part on a magnitude of a voltage difference between the first electrode and the second electrode during discharge.

[0050] Clause 18. The laser of clause 15, further comprising a detector connected to the controller for measuring a width of the gap and providing a signal indicative of the width, the controller generating a control signal based at least in part on the width measured by the detector.

[0051] Clause 19. The laser of clause 13, wherein the controller generates the control signal based at least in part on the number of discharges generated within the discharge chamber.

[0052] Clause 20. A method of controlling operation of a laser, the laser including a discharge chamber and a first electrode and a second electrode spaced apart by a gap, the second electrode positionable to define a width of the gap, the method comprising: operating the laser by generating a discharge in a discharge chamber between a first electrode and a second electrode, the polarity of the first electrode being positive with respect to the polarity of the second electrode such that the first electrode functions as an anode during discharge in the discharge chamber; measuring an operating parameter of the laser; and automatically controlling a position of the second electrode based at least in part on the measured operating parameter.

[0053] Clause 21. The method of clause 20, wherein the operating parameter measured is the magnitude of the voltage difference between the first electrode and the second electrode during discharge required to achieve or maintain a predetermined output energy.

[0054] Clause 22. The method of clause 20, wherein the operating parameter measured is a dimension of the width of the gap between the first electrode and the second electrode.

[0055] Clause 23. The method of clause 20, wherein the operating parameter measured is the number of discharges generated within the discharge chamber.

[0056]

[0039] Other embodiments are within the scope of the claims.

Claims

1. A discharge chamber; a first electrode disposed at least partially within the discharge chamber; a second electrode disposed at least partially within the discharge chamber; a motor mechanically coupled to the second electrode for positioning the second discharge surface to control the width of the gap; a controller in signal communication with the motor adapted to provide a control signal and to control the motor to cause the width of the gap to be substantially equal to an original gap width; Equipped with the first electrode has a first discharge surface, the second electrode has the second discharge surface, and the first discharge surface and the second discharge surface are arranged to face each other across the gap; the polarity of the first electrode is positive with respect to the polarity of the second electrode such that the first electrode functions as an anode during discharge in the discharge chamber; The controller generates the control signal based at least in part on a magnitude of a voltage difference between the first electrode and the second electrode during the discharge required to maintain a substantially constant output power of the laser.

2. 10. The laser of claim 1 wherein the position of said first electrode is fixed relative to said discharge chamber.

3. 10. The laser of claim 1 wherein said first electrode comprises a material that forms an erosion resistant coating when said first electrode functions as an anode during said discharge in said discharge chamber.

4. 10. The laser of claim 1 further comprising an erosion resistant coating applied to said first electrode.

5. 10. The laser of claim 1 further comprising a detector connected to said controller for measuring the width of said gap and providing a signal indicative of said width, said controller generating said control signal based at least in part on the width measured by said detector.

6. 10. The laser of claim 1 further comprising a power supply electrically connected to said first electrode and said second electrode to supply a plurality of pulses to at least one of said first electrode and said second electrode, said power supply comprising a commutator module and a compression head module, said commutator module and said compression head module adjusted such that said polarity of said first electrode is positive with respect to a polarity of said second electrode such that said first electrode functions as an anode during said pulses.

7. 10. The laser of claim 1 wherein said controller generates said control signals based at least in part on a number of discharges generated in said discharge chamber.

8. A discharge chamber; a first electrode disposed at least partially within the discharge chamber and fixed relative to the discharge chamber; an erosion resistant coating on the first electrode; a second electrode disposed at least partially within the discharge chamber and spaced from the first electrode to define a gap; a motor mechanically coupled to the second electrode for positioning a second discharge surface to control a width of the gap; a controller connected to the motor, the controller providing a control signal to the motor to control the width of the gap within a predetermined width; Equipped with The light source, wherein the controller generates the control signal based at least in part on a magnitude of a voltage difference between the first electrode and the second electrode during a discharge required to maintain a substantially constant output power.

9. 9. The light source of claim 8, wherein the polarity of the first electrode is positive with respect to the polarity of the second electrode such that the first electrode functions as an anode during operation in the discharge chamber.

10. The light source of claim 8 , wherein the control signal is based on an elapsed time of operation occurring within the discharge chamber.

11. 10. The light source of claim 8, wherein the control signal is based on a voltage required to achieve a fixed target output energy.

12. The light source of claim 8 , wherein the second electrode is free of the erosion resistant coating.

13. A discharge chamber; a first electrode disposed at least partially within the discharge chamber and fixed relative to the discharge chamber; a second electrode disposed at least partially within the discharge chamber and positioned below the first electrode; a vertical separation between the first electrode and the second electrode; a motor mechanically coupled to the second electrode configured to move the second electrode vertically to maintain the vertical separation within a predetermined range; a controller coupled to the motor, the controller providing a control signal based on a size of the vertical separation; Equipped with A lighting system, wherein the controller generates the control signal based at least in part on a magnitude of a voltage difference between the first electrode and the second electrode during a discharge required to maintain a substantially constant output power.

14. 14. The lighting system of claim 13, further comprising a measurement unit configured to measure the size of the vertical separation.

15. 14. The lighting system of claim 13, wherein the second electrode is at ground potential.

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