Systems and methods for electrode position sensing and adjustment

Abstract

A light source includes a chamber configured to house a gas discharge medium, a first electrode, a second electrode, an actuator coupled to the second electrode, and a controller coupled to the actuator. The first and second electrodes are configured to excite the gas discharge medium and generate a light beam. The second electrode is spaced apart from the first electrode by a discharge gap. The actuator is configured to adjust a position of the second electrode to maintain the discharge gap. The controller is configured to adjust the actuator based on one or more measured parameters of the light source. Advantageously the system can maintain the discharge gap over time, provide feedback to adjust the actuator based on the measured parameters (e.g., chamber operating pressure, blower current signal, capacitor voltage waveform), reduce errors in the light beam, and increase a lifetime of the light source.

Description

SYSTEMS AND METHODS FOR ELECTRODE POSITION SENSING AND ADJUSTMENTCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to U.S. Provisional Application No. 63 / 571,241, filed March 28, 2024, and U.S. Provisional application No. 63 / 659,921, filed June 14, 2024, which are hereby incorporated by reference in their entirety.FIELD

[0002] The present disclosure relates to light source apparatuses, systems, and methods, for example, light source apparatuses, systems, and methods to maintain or adjust a discharge gap over time.BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern of a patterning device (e.g., a mask, a reticle) onto a layer of radiation-sensitive material (photoresist or, simply, “resist”) provided on a substrate.

[0004] To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses deep ultraviolet (DUV) radiation, having a wavelength within the range 20-400 nm, for example 193 nm or 248 nm, may be used to form features on a substrate.

[0005] Since errors and contamination occur during processing of the substrate, a metrology / inspection apparatus is used to detect the manufacturing errors, identify contaminants, and / or measure critical dimensions. In some instances, a light source that generates DUV radiation is employed in the metrology / inspection apparatus.

[0006] A master oscillator power amplifier (MOPA), a master oscillator power oscillator (MOPO), or a master oscillator power ring amplifier (MOPRA) is a two-stage optical resonator arrangement that produces a highly coherent amplified light beam. The performance of the MOPA, MOPO or the MOPRA can depend critically on the master oscillator (MO), the power amplifier (PA), the power oscillator (PO), and / or the power ring amplifier (PRA). Electrodes of the MO, the PA, the PO, and / or the PRA surrounding a gas discharge medium and / or optical components of the MOPA, MOPO or the MOPRA can degrade overtime, leading to reduced laser performance and required laser maintenance.

[0007] A discharge gap between electrodes of a gas discharge chamber can be held constant and maintained over time for optimal laser performance. Electrode erosion can impose significant limits on the useful lifetime of the gas discharge chamber and laser performance, and can lead to both an increase in the discharge gap and broadening of the generated discharge. Over time, the electrodes can erode due to fast ions and electrons from the generated discharge during lasing. As the electrodes erode, thedischarge gap can increase to the point where operational characteristics of the laser are so severely affected that laser operation must be stopped.

[0008] Movable electrodes can be used to compensate for electrode erosion overtime and can maintain the discharge gap. However, some gas discharge chambers have slower or faster electrode erosion rates than others, and an average erosion rate may not be reliable. Further, current systems may not actively measure an anode position over time and, thus, may not maintain an accurate discharge gap over time.SUMMARY

[0009] Accordingly, there is a need to develop a system and a method that can accurately measure a discharge gap of a light source over time (e.g., periodically, in real-time, in near real-time), actively maintain the discharge gap over time, and provide feedback to a controller (e.g., via a feedback loop) to adjust a dimension of the discharge gap over time based on one or more measured parameters of the light source (e.g., chamber operating pressure, blower current signal, change in blower current signal over time, capacitor voltage waveform, change in peak voltage over time, change in zero-crossing time over time). This approach can reduce errors in the generated light beam, reduce errors in a lithographic process, perform diagnostics of the light source, identify optimal maintenance planning or adjustment of the light source, enhancing the accuracy of process monitoring, stabilizing inspections, ensuring the quality of measurement, and / or increase a lifetime of the light source.

[0010] In some aspects, a light source can include a chamber, an electrode assembly, an actuator, and a controller. In some aspects, the chamber can be configured to house a gas discharge medium. In some aspects, the electrode assembly can include a first electrode and a second electrode. In some aspects, the first electrode can have a first discharge surface. In some aspects, the second electrode can have a second discharge surface. In some aspects, the second electrode can be opposite the first electrode. In some aspects, the second discharge surface can be spaced apart from the first discharge surface by a discharge gap. In some aspects, the actuator can be coupled to the second electrode. In some aspects, the actuator can be configured to adjust a position of the second discharge surface to maintain the discharge gap. In some aspects, the controller can be coupled to the actuator. In some aspects, the controller can be configured to adjust the actuator to maintain the discharge gap based at least in part on one or more measured parameters of the light source. In some aspects, the first and second electrodes can be configured to excite the gas discharge medium and generate a light beam.

[0011] In some aspects, the one or more measured parameters can include an operating pressure of the chamber. In some aspects, the operating pressure of the chamber can include an accumulative average operating pressure of the chamber.

[0012] In some aspects, the controller can be configured to adjust the actuator to maintain the discharge gap based at least in part on a function correlating the operating pressure of the chamber to an erosion rate of the second electrode. In some aspects, the operating pressure of the chamber can be inversely proportional to the erosion rate of the second electrode. In some aspects, the function can include alinear regression between the operating pressure of the chamber and the erosion rate of the second electrode. In some aspects, the function can include a polynomial regression between the operating pressure of the chamber and the erosion rate of the second electrode. In some aspects, the controller can be configured to adjust the actuator to maintain the discharge gap based on the erosion rate exceeding a predetermined threshold.

[0013] In some aspects, the chamber can include a power ring amplifier (PRA). In some aspects, the chamber can include a master oscillator (MO).

[0014] In some aspects, the light source can further include a blower assembly configured to circulate the gas discharge medium within the chamber. In some aspects, the one or more measured parameters can include a blower current signal of a motor coupled to the blower assembly. In some aspects, the controller can be configured to adjust the actuator to maintain the discharge gap based at least in part on a function correlating the blower current signal of the motor to an erosion rate of the second electrode.

[0015] In some aspects, the one or more measured parameters can include a capacitor voltage waveform of a capacitor coupled to the electrode assembly. In some aspects, the capacitor voltage waveform can include a peak voltage, a zero-crossing time, a voltage overshoot, or a combination thereof. In some aspects, the controller can be configured to adjust the actuator to maintain the discharge gap based at least in part on a function correlating the capacitor voltage waveform of the capacitor to an erosion rate of the second electrode.

[0016] In some aspects, a method of controlling operation of a light source can include measuring one or more parameters of the light source. In some aspects, the light source can be configured to generate a light beam. In some aspects, the light source can include a chamber, a blower assembly, and an electrode assembly. In some aspects, the method can further include adjusting a discharge gap between a first electrode and a second electrode of the electrode assembly based at least in part on the one or more parameters to reduce errors in the light beam.

[0017] In some aspects, the measuring the one or more parameters can include measuring an operating pressure of the chamber, a blower current signal of a motor coupled to the blower assembly, a capacitor voltage waveform of a capacitor coupled to the first electrode, or a combination thereof. In some aspects, the adjusting the discharge gap is based at least in part on one or more functions correlating the operating pressure of the chamber, the blower current signal of the motor, the capacitor voltage waveform of the capacitor, or a combination thereof to an erosion rate of the second electrode.

[0018] In some aspects, a computer-readable storage medium storing instructions which, when executed by one or more processors, cause the one or more processors to perform operations including measuring one or more parameters of a light source. In some aspects, the light source can be configured to generate a light beam and can include a chamber, a blower assembly, and an electrode assembly. In some aspects, the operations can further include adjusting a discharge gap between a first electrode and a second electrode of the electrode assembly based at least in part on the one or more parameters toreduce errors in the light beam. In some aspects, the one or more parameters can include an operating pressure of the chamber, a blower current signal of a motor coupled to the blower assembly, a capacitor voltage waveform of a capacitor coupled to the first electrode, or a combination thereof.

[0019] Implementations of any of the techniques described above may include a DUV light source, a system, a method, a process, a device, and / or an apparatus. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

[0020] Further features and exemplary aspects of the present disclosure, as well as the structure and operation of various aspects, are described in detail below with reference to the accompanying drawings. It is noted that the aspects are not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0021] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the aspects and, together with the description, further serve to explain the principles of the aspects and to enable a person skilled in the relevant art(s) to make and use the aspects.

[0022] FIG. 1 is a schematic illustration of a photolithography system, according to an exemplary aspect.

[0023] FIG. 2 is a schematic illustration of an illumination system, according to an exemplary aspect.

[0024] FIG. 3 is a cross-sectional schematic illustration of a gas discharge chamber, according to an exemplary aspect.

[0025] FIG. 4 shows a plot of electrode erosion rates as a function of chamber operating pressures, according to an exemplary aspect.

[0026] FIG. 5 shows a plot of blower current signals from motors of a blower assembly as a function of anode protrusion, according to an exemplary aspect.

[0027] FIG. 6 shows a plot of capacitor voltage waveforms from a capacitor of an electrode assembly for different discharge gaps, according to an exemplary aspect.

[0028] FIG. 7 shows a magnified plot of the capacitor voltage waveforms shown in FIG. 6 at a peak voltage (negative) region, according to an exemplary aspect.

[0029] FIG. 8 shows a magnified plot of the capacitor voltage waveforms shown in FIG. 6 at a zerocrossing time region, according to an exemplary aspect.

[0030] FIG. 9 illustrates a flow diagram for a light source, according to an exemplary aspect.

[0031] FIG. 10 is a schematic illustration of a computing system, according to an exemplary aspect.

[0032] The features and exemplary aspects of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like referencenumbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0033] Provided herein are system, apparatus, device, method, process, and / or computer program product aspects, and / or combinations and sub -combinations thereof, for adjusting or maintaining a discharge gap of a light source overtime.

[0034] A system as described below can include a chamber configured to house a gas discharge medium, an electrode assembly having first and second electrodes spaced apart by a discharge gap and configured to excite the gas discharge medium to generate a light beam, an actuator coupled to the second electrode, and a controller coupled to the actuator and configured to adjust the actuator to maintain the discharge gap based on one or more parameters of the system (e.g., chamber operating pressure, blower current signal, capacitor voltage waveform).

[0035] This specification discloses one or more aspects that incorporate the features of this present invention.

[0036] The aspect(s) described, and references in the specification to “one aspect,” “an aspect,” “an example aspect,” “an exemplary aspect,” etc., indicate that the aspect(s) described may include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0037] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0038] The term “about” or “substantially” or “approximately” as used herein indicates the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the term “about” or “substantially” or “approximately” can indicate a value of a given quantity that varies within, for example, 1-15% of the value (e.g., ±1%, ±2%, ±5%, ±10%, or ±15% of the value).

[0039] Numerical values, including endpoints of ranges, can be expressed herein as approximations preceded by the term “about,” “substantially,” “approximately,” or the like. In such cases, other aspects include the particular numerical value. Regardless of whether a numerical value is expressed as anapproximation, two aspects are included in this disclosure: one expressed as an approximation, and another not expressed as an approximation. It will be further understood that an endpoint of each range is significant both in relation to another endpoint, and independently of another endpoint.

[0040] Aspects of the disclosure may be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure may also be implemented as instructions stored on a machine-readable medium (e.g., memory), which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine -readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[0041] The term “real-time” or “real time” as used herein indicates one or more operations or other processes that guarantee response times within a specified time with no delay. In some aspects, realtime can include a timescale or response within one second (s). In some aspects, real-time can include a timescale or response within one millisecond (ms). In some aspects, real-time can include a timescale or response within a reaction time or capability of one or more actuators of the light source (e.g., linear motor, servo motor, piezoelectric, stepper, etc.).

[0042] The term “near real-time” or “near real time” as used herein indicates one or more operations or other processes that guarantee response times within a specified time minus a processing time (e.g., electronic communication, automatic data processing) with no significant delays. Near real-time is slightly slower or delayed compared to real-time. In some aspects, near real-time can include a timescale or response within a range of 100 ms to 1 s. In some aspects, near real-time can include a timescale or response within a range of 1 s to 10 s.

[0043] The term “maintenance planning” as used herein indicates a planned or scheduled maintenance of one or more components of the light source, for example, including but not limited to, adjustment, recalibration, repair, replacement, and / or batch replacement of one or more components of the light source.

[0044] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure may be implemented.

[0045] Exemplary Photolithography System

[0046] Systems such as those described herein may render benefits in a wide range of applications and implementations. For the sake of having a specific non-limiting example to facilitate description, one such application is in semiconductor photolithography. FIG. 1 shows a photolithography system 100that includes an illumination system 105. As described more fully below, the illumination system 105 includes a light source that produces a pulsed light beam 110 and directs it to a photolithography exposure apparatus or scanner 115 that patterns microelectronic features on a wafer 120. The wafer 120 is placed on a wafer table 125 constructed to hold wafer 120 and connected to a positioner 127 configured to accurately position the wafer 120 in accordance with certain parameters.

[0047] The pulsed light beam 110 may have a wavelength in the DUV range, for example, with a wavelength of 248 nanometers (nm) or 193 nm. The scanner 115 includes an optical arrangement 117 having, for example, one or more condenser lenses, a mask, and an objective arrangement. The mask is movable along one or more directions, such as along an optical axis of the pulsed light beam 110 or in a plane that is perpendicular to the optical axis. The objective arrangement includes a projection lens and enables an image transfer to occur from the mask to photoresist on the wafer 120. The illumination system 105 adjusts the range of angles for the pulsed light beam 110 impinging on the mask. The illumination system 105 also homogenizes (makes uniform) the intensity distribution of the pulsed light beam 110 across the mask.

[0048] The scanner 115 can include, among other features, a lithography controller 130 that controls how layers are printed on the wafer 120. The lithography controller 130 may include a memory that stores information such as process recipes that determine the parameters including a length of the exposure on the wafer 120 based on, for example, the mask used, as well as other factors that affect exposure. During lithography, a burst of pulses of the pulsed light beam 110 illuminates the same area of the wafer 120 to constitute an illumination dose.

[0049] The photolithography system 100 also preferably includes a control system 135. In general, the control system 135 includes one or more of digital electronic circuitry, computer hardware, firmware, and software. The control system 135 can be centralized or be partially or wholly distributed throughout the photolithography system 100. In some embodiments, the pulsed light beam 110 is implemented in a metrology / inspection system for semiconductor manufacturing process.

[0050] Exemplary Illumination System

[0051] FIG. 2 shows a pulsed laser source that produces a pulsed laser beam as the pulsed light beam 110 as an example of an illumination system 105. FIG. 2 shows a two-chamber laser system as a nonlimiting example but it will be understood that the principles explained herein are equally applicable to a single chamber laser system or a laser system having more than two chambers. The gas discharge laser system may include a seed laser generation stage, e.g., a solid state or gas discharge master oscillator (“MO”) seed laser system 140, an energy amplification stage, e.g., a power oscillator (“PO”), a power amplifier (“PA”), or a power ring amplifier (“PRA”) system 145, relay optics 150, and laser system output subsystem 160. The MO seed laser system 140 may include, e.g., an MO chamber 165 which includes a pair of electrodes 167 and 168.

[0052] The MO seed laser system 140 may also include a master oscillator output coupler (“MO OC”) 175, which may comprise a partially reflective mirror, forming an MO chamber 165 with an oscillatorcavity defined by a reflective grating (not shown) in a line narrowing module (“LNM”) 170 that oscillates to form the seed laser output pulse. The MO seed laser system 140 may also include a linecenter analysis module (“LAM”) 180. A MO wavefront engineering box (“WEB”) 185 may serve to redirect the output of the MO seed laser system 140 toward the amplification stage 145, and may include, e.g., a multi prism beam expander (not shown) and an optical delay path (not shown).

[0053] The amplification stage 145 may include, e.g., a PRA lasing chamber 200, which also may be an oscillator, e.g., formed by seed beam injection and output coupling optics (not shown) that may be incorporated into a PRA WEB 210. The beam may be redirected back through the gain medium in the PRA lasing chamber 200 by a beam reverser (“BR”) 220. The PRA WEB 210 may incorporate a partially reflective input / output coupler (not shown) and a maximally reflective mirror for the nominal operating wavelength (e.g., at around 193 nm for an ArF system) and one or more prisms. The PRA lasing chamber 200 may also include a pair of electrodes 207 and 208.

[0054] A bandwidth analysis module (“BAM”) 230 may receive the output laser light beam of pulses from PRA lasing chamber 200 and pick off a portion of the light beam for metrology purposes, e.g., to measure the output bandwidth and pulse energy. The laser output light beam of pulses then passes through the PRA WEB 210 to an optical pulse stretcher (“OPuS”) 240 and an autoshutter, in this case a combined autoshutter metrology module (“CASMM”) 250, which may also be the location of a pulse energy meter. One purpose of the OPuS 240 may be, e.g., to convert a single output laser pulse into a pulse train. Secondary pulses created from the original single output pulse may be delayed with respect to each other. By distributing the original laser pulse energy into a train of secondary pulses, the effective pulse length of the laser can be expanded and at the same time the peak pulse intensity reduced. The OPuS 240 may accordingly be arranged to receive the laser beam from the PRA WEB 210 and direct its output to the CASMM 250.

[0055] The PRA lasing chamber 200 and the MO chamber 165 are configured as chambers in which electrical discharges between the electrodes cause lasing gas discharges in a lasing gas to create an inverted population of high energy molecules, including, e.g., Ar, Kr, F2, and / or Xe, to produce relatively broad band radiation that may be line narrowed to a relatively very narrow bandwidth and center wavelength selected in the LNM 170.

[0056] Alignment is the process of adjusting the position, orientation, etc. of these optical components so that the laser beam propagates along a desired beam path. Alignment of modules with respect to the laser beam and the other components may entail adjusting the components making up the module. For example, the alignment of the amplification stage may be determined with respect to a PRA alignment path 260 shown by the broken line in FIG. 2. The PRA alignment path 260 as shown includes the BR 220, the PRA lasing chamber 200, the BAM, 230, the PRA WEB 210, the OPuS 240, and the CASMM 250. The PRA alignment path 260 in the example shown also includes the path of the seed laser beam from the MO WEB 185.

[0057] Alignment and other laser beam characteristics are determined by obtaining information about the laser beam at alignment ports at various positions in the PRA alignment path 260, referred to herein as imaging the laser beam. For example, the laser beam may be imaged at a first position 270 at the BR 220. The laser beam may also be imaged at a second position 272 at the PRA WEB 210 and at a third position 274 at the CASMM 250. These images may be near field images or far field images. Laser beam imaging may include obtaining information about the laser beam, laser beam edge detection, aperture edge detection, laser beam contours, laser beam cross sectional structure, positions of relay optics fixtures, and the like.

[0058] Exemplary Gas Discharge Chamber

[0059] FIG. 3 illustrates gas discharge chamber 300, according to various exemplary aspects. Gas discharge chamber 300 can be configured to excite gas discharge medium 301 between discharge gap 340 of electrode assembly 360 (e.g., between cathode assembly 320 and anode assembly 330) and generate a light beam. Gas discharge chamber 300 can be further configured to measure (e.g., via a controller) one or more parameters of gas discharge chamber 300 (e.g., operating pressure, position of cathode, position of anode, or a combination thereof) overtime.

[0060] Although gas discharge chamber 300 is shown in FIG. 3 as a stand-alone apparatus and / or system, the aspects of this disclosure can be used with other apparatuses, systems, and / or methods, such as, but not limited to, elements in FIGS. 1, 2, and 4-10, e.g., photolithography system 100, illumination system 105, chamber operating pressure correlation 420, blower current signals 510, 520, capacitor voltage waveforms 610, 620, 630, 640, flow diagram 900, computing system 1000, and / or any suitable metrology / inspection systems.

[0061] As shown in FIG. 3, gas discharge chamber 300 can include gas discharge medium 301, chamber base 302, interior surface 304, cavity 308, blower assembly 310, and electrode assembly 360. Chamber base 302 can include interior surface 304 forming cavity 308 to house gas discharge medium 301 (e.g., halogens, noble gases, and / or chemical compounds thereof), blower assembly 310, and electrode assembly 360. In some aspects, chamber base 302 can include one or more rigid materials (e.g., metals, ceramics, etc.) to seal gas discharge medium 301 within cavity 308 of gas discharge chamber 300. In some aspects, interior surface 304 can include one or more filters (e.g., screens, traps, etc.) configured to collect particles (e.g., metal fluoride dust) generated by electrode assembly 360. In some aspects, gas discharge chamber 300 can be part of an illumination system, for example, a MO chamber and / or PA / PO / PRA lasing chamber.

[0062] In some aspects, gas discharge chamber 300 can include one or more pressure sensors or pressure detectors to measure an operating pressure of gas discharge medium 301. In some aspects, for example, the one or more pressure sensors can detect an accumulative average operating pressure of gas discharge chamber 300. In some aspects, the one or more pressure sensors can be coupled to a controller (e.g., control system 135, computing system 1000) to monitor the operating pressure over time (e.g., in real-time).

[0063] In some aspects, gas discharge chamber 300 can provide a feedback signal to a controller (e.g., via a feedback loop) to adjust a dimension (e.g., width) of discharge gap 340 overtime (e.g., via actuator 338) based on one or more measured parameters of gas discharge chamber 300. For example, gas discharge chamber 300 can measure an operating pressure of gas discharge medium 301 via one or more pressure sensors and provide the feedback signal to the controller. In some aspects, gas discharge chamber 300 can provide a plurality of chamber operating pressures of gas discharge medium 301 over time to a controller coupled to gas discharge chamber 300 to determine a chamber operating pressure correlation (e.g., trendline) to an electrode erosion rate (e.g., anode erosion rate) for that gas discharge chamber 300.

[0064] For example, as shown in FIG. 4 and described below, chamber operating pressures 410 can be measured over time by a controller (e.g., control system 135, computing system 1000) to determine (e.g., correlate) a rate of electrode erosion (e.g., change in discharge gap 340) based on a chamber operating pressure correlation 420 (e.g., linear regression).

[0065] In some aspects, with reference to FIGS. 3 and 4, a controller can be configured to measure a chamber operating pressure (e.g., accumulative average operating pressure) of gas discharge medium 301 in gas discharge chamber 300. For example, as shown in FIG. 4, the controller can measure chamber operating pressures 410 of gas discharge chamber 300 over time and determine (e.g., calculate) a chamber operating pressure correlation 420 (e.g., linear fit or polynomial fit of chamber operating pressures 410) to correlate the chamber pressure 404 to an electrode erosion rate 402 (e.g., anode erosion rate).

[0066] With reference back to FIG. 3, blower assembly 310 can be configured to circulate gas discharge medium 301 within cavity 308. Blower assembly 310 can be further configured to flow gas discharge medium 301 (e.g., via gas flow 314) through discharge gap 340. As shown in FIG. 3, blower assembly 310 can include blower 312. Blower 312 can be configured to circulate gas discharge medium 301 (e.g., gas flow 314). In some aspects, blower 312 can include a fan, a blower, an impeller, a rotor, a turbine, or any other rotary device that can circulate gas discharge medium 301. Blower 312 can be coupled (e.g., electrically) to a motor to control rotation of blower 312.

[0067] In some aspects, blower assembly 310 can provide a feedback signal to a controller (e.g., via a feedback loop) to adjust a dimension (e.g., width) of discharge gap 340 over time (e.g., via actuator 338) based on one or more measured parameters of blower assembly 310. For example, blower assembly 310 can measure a blower current signal of a motor coupled to blower 312 and provide the feedback signal to the controller. In some aspects, blower assembly 310 can provide a plurality of blower current signals of a motor coupled to blower 312 over time to a controller coupled to blower assembly 310 to determine a blower current signal correlation (e.g., trend) to an electrode erosion rate (e.g., anode erosion rate) forthat gas discharge chamber 300.

[0068] For example, as shown in FIG. 5 and described below, blower current signals 510, 520 can be measured over time by a controller (e.g., control system 135, computing system 1000) to determine(e.g., correlate) a rate of electrode erosion (e.g., change in discharge gap 340) based on a change in blower current signals over time (e.g., change in blower current signal over time, change in average or trend of a plurality of blower current signals over time, or a combination thereof).

[0069] In some aspects, with reference to FIGS. 3 and 5, a controller can be configured to measure a blower current signal (e.g., motor current) of a motor coupled to blower assembly 310. For example, as shown in FIG. 5, the controller can measure blower current signals 510, 520 (e.g., motor currents) of blower assembly 310 over time and determine (e.g., calculate) an average or trend to correlate the blower current 502 to an anode protrusion 504.

[0070] With reference back to FIG. 3, electrode assembly 360 can be configured to excite gas discharge medium 301 between discharge gap 340 of cathode assembly 320 and anode assembly 330 to generate a light beam. Electrode assembly 360 can be further configured to provide feedback to a controller (e.g., via a feedback loop) to adjust a dimension (e.g., width) of discharge gap 340 overtime (e.g., via actuator 338) based on one or more measured parameters of electrode assembly 360. Electrode assembly 360 can be further configured to adjust one or more electrode positions (e.g., position of first electrode 322 and / or position of second electrode 332) over time (e.g., periodically) via adjustment of one or more actuators (e.g., actuator 338) to attain or maintain a desired discharge gap 340 (e.g., via a controller). As shown in FIG. 3, electrode assembly 360 can include cathode assembly 320 and anode assembly 330.

[0071] Cathode assembly 320 can be configured to act as a cathode (e.g., negative charge) and excite gas discharge medium 301 between discharge gap 340. As shown in FIG. 3, cathode assembly 320 can include first electrode 322 (e.g., cathode (-)), one or a first plurality of capacitors 324, and one or a second plurality of capacitors 326. First electrode 322 can include first discharge surface 344 configured to generate a discharge plasma and form a first endpoint of discharge gap 340. First electrode 322 can be coupled (e.g., electrically) to one or first plurality of capacitors 324 and one or second plurality of capacitors 326. First and second capacitors 324, 326 can be configured to supply a charge (e.g., high negative charge) to first electrode 322 and second electrode 332.

[0072] In some aspects, electrode assembly 360 includes a resistor, inductor, and capacitor (RLC) circuit. In some aspects, first and second capacitors 324, 326 can be peaking capacitors (Cp) configured to generate high-frequency pulses (e.g., nanosecond pulses). In some aspects, first and second capacitors 324, 326 can be a single capacitor (e.g., a peaking capacitor) coupled to first electrode 322 and / or second electrode 332. In some aspects, cathode assembly 320 can include a peaking circuit (e.g., power supply, peaking capacitor, electrode) to generate high-frequency peak currents. In some aspects, cathode assembly 320 can include a pulsed power supply coupled to first electrode 322, first capacitor 324, and second capacitor 326.

[0073] In some aspects, cathode assembly 320 can be stationary. In some aspects, cathode assembly 320 can be adjustable such that a position of first electrode 322 (e.g., first discharge surface 344) relative to second electrode 332 (e.g., second discharge surface 346) can be changed, thereby adjustingdischarge gap 340. For example, cathode assembly 320 can include one or more actuators (e.g., similar to actuator 338) coupled to first electrode 322 to adjust a position of first discharge surface 344 to attain or maintain a desired discharge gap 340. In some aspects, cathode assembly 320 is opposite anode assembly 330, for example, perpendicular to anode assembly 330 such that first and second discharge surfaces 344, 346 are facing one another.

[0074] Anode assembly 330 can be configured to act as an anode. As shown in FIG. 3, anode assembly 330 can include second electrode 332 (e.g., anode (+)) and one or more actuators 338 (e.g., linear motor, spring). Second electrode 332 can include second discharge surface 346 configured to generate a discharge plasma and form a second endpoint of discharge gap 340. In some aspects, current return tines can be coupled (e.g., electrically) to second electrode 332 and can be configured to establish an electrical path from second electrode 332 to cathode assembly 320 (e.g., an RCL circuit, peaking capacitors, and / or a pulsed power supply). Actuator 338 can be configured to adjust a position (e.g., vertical) of second discharge surface 346 to maintain discharge gap 340. In some aspects, actuator 338 can include one or more actuators (e.g., linear motor, servo motor, piezoelectric, stepper, cam, spring, etc.).

[0075] In some aspects, anode assembly 330 can be adjustable such that a position of second electrode 332 (e.g., second discharge surface 346) relative to first electrode 322 (e.g., first discharge surface 344) can be changed, thereby adjusting discharge gap 340. For example, anode assembly 330 can include one or more actuators (e.g., actuator 338) coupled to second electrode 332 to adjust a position of second discharge surface 346 to attain or maintain a desired discharge gap 340. In some aspects, electrode assembly 360 can include a movable anode assembly (e.g., anode assembly 330) controlled by one or more actuators (e.g., actuator 338). For example, certain movable anode assemblies have been previously described in U.S. Patent No. 8,526,481, issued September 3, 2013, and U.S. Patent No. 11,777,271, issued October 3, 2023, which are hereby incorporated by reference herein in their entireties.

[0076] In some aspects, electrode assembly 360 can provide a feedback signal to a controller (e.g., via a feedback loop) to adjust a dimension (e.g., width) of discharge gap 340 over time (e.g., via actuator 338) based on one or more measured parameters of electrode assembly 360. For example, electrode assembly 360 can measure a capacitor voltage waveform of first capacitors 324 and / or second capacitors 326 and provide the feedback signal to the controller. In some aspects, cathode assembly 320 can provide a capacitor voltage waveform (e.g., voltage on capacitor) of first capacitors 324 and / or second capacitors 326 coupled to first electrode 322 to a controller coupled to cathode assembly 320 to determine a capacitor voltage waveform correlation (e.g., signature or shift) to an electrode erosion rate (e.g., anode erosion rate) forthat gas discharge chamber 300.

[0077] For example, as shown in FIG. 6 and described below, capacitor voltage waveforms 610, 620, 630, 640 can be measured overtime by a controller (e.g., control system 135, computing system 1000) to determine (e.g., correlate) a rate of electrode erosion (e.g., change in discharge gap 340) based on achange in capacitor voltage waveforms overtime (e.g., a change in peak voltage overtime, a change in zero-crossing time over time, a change in voltage overshoot over time, or a combination thereof).

[0078] In some aspects, with reference to FIGS. 3 and 6, a controller can be configured to measure a capacitor voltage waveform (e.g., voltage on capacitor) of at least one of first capacitors 324 and / or second capacitors 326 coupled to first electrode 322. For example, as shown in FIG. 6, the controller can measure capacitor voltage waveforms 610, 620, 630, 640 (e.g., voltage on capacitor) of cathode assembly 320 over time and determine (e.g., calculate) one or more changes in capacitor voltage waveforms 610, 620, 630, 640 (e.g., change in peak voltage charging region 606, change in zerocrossing time region 607, change in voltage overshoot region 608, etc.) to correlate the one or more changes in capacitor voltage waveforms 610, 620, 630, 640 to an electrode erosion rate (e.g., anode erosion rate). In some aspects, region 606 is defined as a region close to the end of charging cycle and / or the beginning of the discharging cycle.

[0079] Exemplary Chamber Operating Pressure Correlation

[0080] As discussed above, FIG. 4 illustrates exemplary chamber operating pressures 410 of gas discharge chamber 300 measured by a controller to determine a chamber operating pressure correlation 420 to an electrode erosion rate (e.g., anode erosion rate), according to various exemplary aspects. FIG. 4 shows plot 400 of chamber operating pressures 410 of gas discharge chamber 300 shown in FIG. 3 for different discharge gaps 340 (e.g., electrode erosion rates), according to an exemplary aspect. Although chamber operating pressure correlation 420 is shown in FIG. 4 as a stand-alone apparatus and / or system, the aspects of this disclosure can be used with other apparatuses, systems, and / or methods, such as, but not limited to, elements in FIGS. 1-3 and 5-10, e.g., photolithography system 100, illumination system 105, gas discharge chamber 300, blower current signals 510, 520, capacitor voltage waveforms 610, 620, 630, 640, flow diagram 900, computing system 1000, and / or any suitable metrology / inspection systems.

[0081] As shown in FIG. 4, plot 400 shows electrode erosion rate (pm / billion pulses (Bp)) 402 (e.g., anode erosion rate) as a function of chamber pressure (kPa) 404 for chamber operating pressures 410 over time to determine chamber operating pressure correlation 420, corresponding to different electrode erosion rates (e.g., anode erosion rates) and discharge gaps. Plot 400 includes chamber operating pressures 410 of gas discharge chamber 300, chamber operating pressure correlation 420, and constant electrode erosion rate 430 (e.g., constant anode erosion rate). In some aspects, chamber operating pressure correlation 420 can be based on a fit of chamber operating pressures 410 to correlate chamber pressure 404 to electrode erosion rate 402 (e.g., anode erosion rate). In some aspects, chamber operating pressures 410 can include an accumulative average chamber operating pressure. In some aspects, gas discharge chamber 300 (FIG. 3) can include a PA chamber, a PO chamber or a PRA chamber. In some aspects, gas discharge chamber 300 can include a MO chamber. In some aspects, electrode erosion rate 402 can be an anode erosion rate. In some aspects, electrode erosion rate 402 can be a cathode erosion rate.

[0082] In some aspects, chamber operating pressure correlation 420 (e.g., variable anode protrusion rate based on chamber operating pressure) can reduce a standard deviation (e.g., spread or variation) of the anode protrusion rate relative to a target (optimal) anode protrusion rate, compared to constant electrode erosion rate 430 (e.g., constant anode protrusion rate). For example, chamber operating pressure correlation 420 can reduce the standard deviation of the anode protrusion rate compared to constant electrode erosion rate 430 (e.g., constant anode erosion rate) by at least 50 percent, thereby increasing a lifetime of gas discharge chamber 300 (FIG. 3).

[0083] In some aspects, with reference to FIGS. 3 and 4, a controller can be configured to adjust actuator 338 to maintain discharge gap 340 based on chamber operating pressure correlation 420. For example, the controller can be configured to adjust actuator 338 (e.g., via closed-loop feedback algorithm) to maintain discharge gap 340 based on chamber operating pressure correlation 420, which correlates chamber pressure 404 to a target (optimal) anode protrusion rate to compensate for the corresponding electrode erosion rate 402 (e.g., anode erosion rate) for that gas discharge chamber 300. In some aspects, for example, chamber operating pressures 410 can be inversely proportional to electrode erosion rate 402 (e.g., anode erosion rate). For example, as shown in FIG. 4, chamber operating pressure correlation 420 shows that electrode erosion rate 402 (e.g., anode erosion rate) decreases as chamber pressure 404 increases, and vice versa.

[0084] In some aspects, a controller can be configured to adjust actuator 338 to maintain discharge gap 340 based at least in part on a function correlating chamber operating pressures 410 of gas discharge chamber 300 to an electrode erosion rate 402. In some aspects, the function can include a linear regression between chamber operating pressures 410 and electrode erosion rate 402. For example, as shown in FIG. 4, chamber operating pressure correlation 420 is based on a linear regression (e.g., linear fit) of chamber operating pressures 410 to determine a current electrode erosion rate (e.g., anode erosion rate) based on the current chamber operating pressure. In some aspects, the function can include a polynomial regression between chamber operating pressures 410 and electrode erosion rate 402.

[0085] In some aspects, a controller can be configured to adjust actuator 338 to maintain discharge gap 340 (e.g., adjust anode protrusion rate) based on the electrode erosion rate 402 exceeding a predetermined threshold. For example, based on chamber operating pressure correlation 420, if the current electrode erosion rate 402 (e.g., as determined by current chamber operating pressure) deviates from a target (predicted) electrode erosion rate (e.g., 60 pm / Bp) by the predetermined threshold (e.g., anode erosion rate increase of 15%, etc.), the controller can adjust the anode protrusion rate accordingly to account for the deviation in electrode erosion rate 402.

[0086] Exemplary Blower Current Signals

[0087] As discussed above, FIG. 5 illustrates exemplary blower current signals 510, 520 of blower assembly 310 measured by a controller to determine a blower current correlation to an electrode erosion rate (e.g., anode erosion rate), according to various exemplary aspects. FIG. 5 shows plot 500 of blower current signals 510, 520 from a motor of blower assembly 310 shown in FIG. 3 for different dischargegaps 340 (e.g., anode protrusions), according to an exemplary aspect. Although blower current signals 510, 520 are shown in FIG. 5 as a stand-alone apparatus and / or system, the aspects of this disclosure can be used with other apparatuses, systems, and / or methods, such as, but not limited to, elements in FIGS. 1-4 and 6-10, e.g., photolithography system 100, illumination system 105, gas discharge chamber 300, chamber operating pressure correlation 420, capacitor voltage waveforms 610, 620, 630, 640, flow diagram 900, computing system 1000, and / or any suitable metrology / inspection systems.

[0088] As shown in FIG. 5, plot 500 shows blower current (A) 502 as a function of anode protrusion (pm) 504 for blower current signals 510, 520, corresponding to different anode protrusions and discharge gaps. Plot 500 includes first blower current signal 510 and second blower current signal 520 from a motor coupled to blower 312 (FIG. 3). In some aspects, second blower current signal 520 can be measured from another motor coupled to another blower (e.g., similar to blower 312) of blower assembly 310 (FIG. 3). In some aspects, peaks of first and second blower current signals 510, 520 can be normalized to a default (e.g., “zero”) relative position of anode at a constant erosion rate (e.g., about 1 pm / Bp to about 100 pm / Bp). In some aspects, blower current signals 510, 520 can correspond to different anode protrusions of second discharge surface 346 (FIG. 3) of second electrode 332 (FIG. 3) relative to first discharge surface 344 (FIG. 3) (e.g., corresponding to discharge gap 340).

[0089] In some aspects, a change in blower current signals 510, 520 can be determined by comparing one or more aspects (e.g., change in current) of blower current signals 510, 520. For example, a change in blower current signal Al over time can be determined based on a current comparison between a final value and an initial value, for example, an initial current value at “zero” position (e.g., 0 mm) and a final current value at a second anode protrusion (e.g., -0.6 mm), for example, Al = about -0.1 mA to about -0.5 mA (e.g., indicating a decrease in current signal from anode deviation from “zero” position). In some aspects, a blower current erosion rate can be determined by comparing blower current signals I of first blower current signal 510 and / or second blower current signal 520. For example, as shown in FIG. 5, blower current erosion rate (e.g., about 0.1 mA / mm to about 0.5 mA / mm) can be determined based on a change in blower current signal Al of first blower current signal 510 and corresponding anode protrusions (e.g., discharge gap Ad) between a “zero” position and a second anode position, for example, Al / Ad = about 0.1 mA / mm to about 0.5 mA / mm. These parameters are all exemplary for illustration purposes, and non-limiting.

[0090] In some aspects, with reference back to FIG. 3, a controller can be configured to adjust actuator 338 to maintain discharge gap 340 based on one or more measured parameters of blower assembly 310 (e.g., blower current signal, change in blower current signal over time, change in average or trend of a plurality of blower current signals over time, or a combination thereof). For example, the controller can be configured to adjust actuator 338 (e.g., via closed-loop feedback algorithm) to maintain discharge gap 340 based on a change in blower current signal Al, a change in blower current signal AIzero from a default (e.g., “zero”) relative position of anode at a constant erosion rate, or a combination thereof.

[0091] In some aspects, with reference to FIGS. 3 and 5, a controller can be configured to adjust actuator 338 to maintain discharge gap 340 based at least in part on a function correlating blower current signals 510, 520 of blower assembly 310 to an electrode erosion rate (e.g., via anode protrusion 504). In some aspects, the function can include a linear regression between blower current signals 510, 520 and the electrode erosion rate. For example, as shown in FIG. 5, blower current signals 510, 520 can each be based on a linear regression (e.g., linear fit) to determine a current electrode erosion rate (e.g., anode erosion rate) based on the current blower current signal. In some aspects, the function can include a polynomial regression between blower current signals 510, 520 and the electrode erosion rate (e.g., anode erosion rate).

[0092] Exemplary Capacitor Voltage Waveforms

[0093] As discussed above, FIGS. 6-8 illustrate exemplary capacitor voltage waveforms 610, 620, 630, 640 of cathode assembly 320 measured by a controller to determine a capacitor voltage waveform correlation to an electrode erosion rate (e.g., anode erosion rate), according to various exemplary aspects. FIG. 6 shows plot 600 of capacitor voltage waveforms 610, 620, 630, 640 from one or first plurality of capacitors 324 of cathode assembly 320 shown in FIG. 3 for different discharge gaps 340 (e.g., anode protrusions), according to an exemplary aspect.

[0094] FIG. 7 shows magnified plot 700 of capacitor voltage waveforms 710, 720, 730, 740 at peak voltage charging region 606 shown in FIG. 6, according to an exemplary aspect.

[0095] FIG. 8 shows magnified plot 800 of capacitor voltage waveforms 810, 820, 830, 840 at zerocrossing time region 607 shown in FIG. 6, according to an exemplary aspect.

[0096] Although capacitor voltage waveforms 610, 620, 630, 640 are shown in FIGS. 6-8 as a standalone apparatus and / or system, the aspects of this disclosure can be used with other apparatuses, systems, and / or methods, such as, but not limited to, elements in FIGS. 1-5, 9, and 10, e.g., photolithography system 100, illumination system 105, gas discharge chamber 300, chamber operating pressure correlation 420, blower current signals 510, 520, flow diagram 900, computing system 1000, and / or any suitable metrology / inspection systems.

[0097] As shown in FIG. 6, plot 600 shows capacitor voltage (V) 602 as a function of time (ps) 604 for capacitor voltage waveforms 610, 620, 630, 640, corresponding to different anode protrusions (e.g., position of second discharge surface 346) and discharge gaps. Plot 600 includes preionization event 605 (e.g., discharging of a preionization capacitor — start of avalanche effect to negatively charge capacitor), peak voltage charging region 606 (e.g., peak avalanche effect — maximum negative voltage on capacitor, magnified plot 700 shown in FIG. 7), zero-crossing time region 607 (e.g., zero-crossing during breakdown effect — negative-to-positive voltage (0 V) on capacitor, magnified plot 800 shown in FIG. 8), and voltage overshoot region 608 (e.g., peak breakdown effect — maximum positive voltage on capacitor).

[0098] In some aspects, with additional reference to FIG. 3, capacitor voltage waveforms 610, 620, 630, 640 can correspond to different anode protrusions of second discharge surface 346 of secondelectrode 332 relative to first discharge surface 344 (e.g., corresponding to discharge gap 340). For example, as shown in FIG. 6, first capacitor voltage waveform 610 can represent a first position of second discharge surface 346 (e.g., about 0 mm), second capacitor voltage waveform 620 can represent a second position of second discharge surface 346 (e.g., about 0.5 mm), third capacitor voltage waveform 630 can represent a third position of second discharge surface 346 (e.g., about 1.0 mm), and fourth capacitor voltage waveform 640 can represent a fourth position of second discharge surface 346 (e.g., about 1.5 mm). These parameters are all exemplary for illustration purposes, and non-limiting.

[0099] In some aspects, a change in capacitor voltage waveforms 610, 620, 630, 640 can be determined by comparing one or more aspects (e.g., change in voltage) of capacitor voltage waveforms 610, 620, 630, 640 to each other. For example, a change in peak voltage AVmax over time can be determined based on a voltage comparison, for example, between first capacitor voltage waveform 610 and fourth capacitor voltage waveform 640, for example, AVmax = about 25 mV to about 125 mV. In some aspects, a peak voltage erosion rate can be determined by comparing peak voltages VmaXof capacitor voltage waveforms 610, 620, 630, 640 to each other. For example, as shown in FIG. 7, peak voltage erosion rate 706 (e.g., about 25 mV / mm to about 75 mV / mm) can be determined based on a change in peak voltage AVmax and corresponding anode protrusions (e.g., discharge gap Ad), for example, between first capacitor voltage waveform 710 and fourth capacitor voltage waveform 740, for example, AVmax / Ad = about 25 mV / mm to about 75 mV / mm. These parameters are all exemplary for illustration purposes, and non-limiting.

[0100] In some aspects, a change in capacitor voltage waveforms 610, 620, 630, 640 can be determined by comparing one or more aspects (e.g., change in breakdown time) of capacitor voltage waveforms 610, 620, 630, 640 to each other. For example, a change in breakdown time Atbreak over time can be determined based on a breakdown time comparison, for example, between first capacitor voltage waveform 610 and fourth capacitor voltage waveform 640, for example, Atbreak = about -1 ns to about - 5 ns (e.g., indicating an earlier breakdown time as anode protrusion increases). In some aspects, a breakdown time erosion rate can be determined by comparing breakdown times tbreak (e.g., starting point of breakdown or voltage inversion from peak voltage Vmax) of capacitor voltage waveforms 610, 620, 630, 640 to each other. For example, as shown in FIG. 7, breakdown time erosion rate 708 (e.g., about -0.5 ns / mm to about -3.5 ns / mm) can be determined based on a change in breakdown time Atbreak and corresponding anode protrusions (e.g., discharge gap Ad), for example, between first capacitor voltage waveform 710 and fourth capacitor voltage waveform 740, for example, Atbreak / Ad = about -1 ns / mm to about -5 ns / mm. These parameters are all exemplary for illustration purposes, and non -limiting.

[0101] In some aspects, a change in capacitor voltage waveforms 610, 620, 630, 640 can be determined by comparing one or more aspects (e.g., change in zero-crossing breakdown time) of capacitor voltage waveforms 610, 620, 630, 640 to each other. For example, a change in zero-crossing breakdown time Atze ro -cross over time can be determined based on a zero-crossing breakdown time comparison, forexample, between first capacitor voltage waveform 610 and fourth capacitor voltage waveform 640, for example, Atzero-cross = about -1 ns to about -5 ns (e.g., indicating an earlier zero-crossing breakdown time as anode protrusion increases). In some aspects, a zero-crossing breakdown time erosion rate can be determined by comparing zero-crossing breakdown times tzero-cross (e.g., zero-crossing point of breakdown or negative-to-positive voltage (0 V) on capacitor) of capacitor voltage waveforms 610, 620, 630, 640 to each other. For example, as shown in FIG. 8, zero-crossing breakdown time erosion rate 806 (e.g., about -1 ns / mm to about -5 ns / mm) can be determined based on a change in zero-crossing breakdown time Atzero-cross and corresponding anode protrusions (e.g., discharge gap Ad), for example, between first capacitor voltage waveform 810 and fourth capacitor voltage waveform 840, for example, Atzero-cross / Ad = about -1 ns / mm to about -5 ns / mm. These parameters are all exemplary for illustration purposes, and non-limiting.

[0102] In some aspects, a change in capacitor voltage waveforms 610, 620, 630, 640 can be determined by comparing one or more aspects (e.g., change in voltage overshoot) of capacitor voltage waveforms 610, 620, 630, 640 to each other. For example, a change in voltage overshoot (e.g., deviation from steady-state voltage after discharge) over time can be determined based on a voltage overshoot comparison, for example, between first capacitor voltage waveform 610 and fourth capacitor voltage waveform 640. In some aspects, a voltage overshoot erosion rate can be determined by comparing voltage overshoots (e.g., peak positive voltage on capacitor or decay time to steady-state voltage) of capacitor voltage waveforms 610, 620, 630, 640 to each other.

[0103] In some aspects, with additional reference to FIG. 3, a controller can be configured to adjust actuator 338 to maintain discharge gap 340 based on one or more measured parameters of electrode assembly 360 (e.g., capacitor voltage waveform, change in peak voltage over time, change in breakdown time over time, change in zero-crossing time over time, change in voltage overshoot over time, or a combination thereof). For example, the controller can be configured to adjust actuator 338 (e.g., via closed-loop feedback algorithm) to maintain discharge gap 340 based on a change in peak voltage AV max, a change in breakdown time Atbreak, a change in zero-crossing breakdown time Atzero-cross, a change in voltage overshoot, or a combination thereof.

[0104] In some aspects, a controller can be configured to adjust actuator 338 to maintain discharge gap 340 based at least in part on a function correlating capacitor voltage waveforms 610, 620, 630, 640 of electrode assembly 360 to an electrode erosion rate (e.g., anode erosion rate). In some aspects, the function can include a linear regression between capacitor voltage waveforms 610, 620, 630, 640 and the electrode erosion rate (e.g., anode erosion rate). In some aspects, the function can include a polynomial regression between capacitor voltage waveforms 610, 620, 630, 640 and the electrode erosion rate (e.g., anode erosion rate).

[0105] As shown in FIG. 7, magnified plot 700 of peak voltage charging region 606 shown in FIG. 6 shows capacitor voltage (V) 702 as a function of time (ps) 704 for capacitor voltage waveforms 710,720, 730, 740, corresponding to different anode protrusions and discharge gaps. Magnified plot 700 shows peak voltage charging (e.g., peak avalanche effect (electron avalanche) — maximum negative voltage on capacitor) of capacitor voltage waveforms 710, 720, 730, 740, and includes peak voltage erosion rate 706 and breakdown time erosion rate 708.

[0106] In some aspects, peak voltage erosion rate 706 can be determined by comparing peak voltages Vmax of capacitor voltage waveforms 710, 720, 730, 740 to each other. In some aspects, peak voltage erosion rate 706 can represent a change in peak voltage AVmax over a change in anode protrusion (e.g., discharge gap Ad), for example, AVmax / Ad = about 25 mV / mm to about 75 mV / mm. In some aspects, breakdown time erosion rate 708 can be determined by comparing breakdown times t break of capacitor voltage waveforms 710, 720, 730, 740 to each other. In some aspects, breakdown time erosion rate 708 can represent a change in breakdown time Atbreak over a change in anode protrusion (e.g., discharge gap Ad), for example, Atbreak / Ad = about -0.5 ns / mm to about -3.5 ns / mm. These parameters are all exemplary for illustration purposes, and non-limiting.

[0107] As shown in FIG. 8, magnified plot 800 of zero-crossing time region 607 shown in FIG. 6 shows capacitor voltage (V) 802 as a function of time (ps) 804 for capacitor voltage waveforms 810, 820, 830, 840, corresponding to different anode protrusions and discharge gaps. Magnified plot 800 shows zero-crossing breakdown times (e.g., zero-crossing during breakdown effect — negative-to- positive voltage (0 V) on capacitor) of capacitor voltage waveforms 810, 820, 830, 840 and includes zero-crossing breakdown time erosion rate 806. In some aspects, zero-crossing breakdown time erosion rate 806 can be determined by comparing zero-crossing breakdown times tzero-cross of capacitor voltage waveforms 810, 820, 830, 840 to each other. In some aspects, zero-crossing breakdown time erosion rate 806 can represent a change in zero-crossing breakdown time Atzero-cross and a change in anode protrusion (e.g., discharge gap Ad), for example, Atzero-cross / Ad = about -1 ns / mm to about -5 ns / mm. These parameters are all exemplary for illustration purposes, and non-limiting.

[0108] Exemplary Flow Diagram

[0109] FIG. 9 illustrates flow diagram 900, according to an exemplary aspect. For example, flow diagram 900 can be for illumination system 105 shown in FIG. 2. For example, flow diagram 900 can be for gas discharge chamber 300 shown in FIG. 3. Flow diagram 900 can be configured to measure one or more parameters of a light source (e.g., chamber operating pressure, blower current signal, change in blower current signal over time, change in average or trend of a plurality of blower current signals over time, capacitor voltage waveform, change in peak voltage over time, change in breakdown time over time, change in zero-crossing time over time, change in voltage overshoot over time, or a combination thereof). Flow diagram 900 can be further configured to adjust a discharge gap of electrode assembly 360 based on the one or more measured parameters. Flow diagram 900 can be further configured to maintain a discharge gap with one or more control signals from a controller based on the one or more measured parameters. Flow diagram 900 can be further configured to reduce errors in agenerated light beam, reduce errors in a lithographic process, perform diagnostics of a light source, enhancing the accuracy of process monitoring, stabilizing inspections, ensuring the quality of measurement, identify optimal maintenance planning or adjustment of the light source (e.g., illumination system 105), and increase a lifetime of the light source (e.g., illumination system 105).

[0110] It is to be appreciated that not all steps in FIG. 9 are needed to perform the disclosure provided herein. Further, some of the steps may be performed simultaneously, sequentially, and / or in a different order than shown in FIG. 9. Flow diagram 900 shall be described with reference to FIGS. 1-8 and 10. However, flow diagram 900 is not limited to those example aspects. Although flow diagram 900 is shown in FIG. 9 as a stand-alone method, the aspects of this disclosure can be used with other apparatuses, systems, and / or methods, such as, but not limited to, elements in FIGS. 1-8 and 10, e.g., photolithography system 100, illumination system 105, gas discharge chamber 300, chamber operating pressure correlation 420, blower current signals 510, 520, capacitor voltage waveforms 610, 620, 630, 640, computing system 1000, and / or any suitable metrology / inspection systems. In some aspects, flow diagram 900 can be implemented by illumination system 105 shown in FIG. 2 (e.g., via a controller or control system 135). In some aspects, flow diagram 900 can be implemented by gas discharge chamber 300 shown in FIG. 3 (e.g., via a controller or control system 135).[oni] In operation 902, as shown in the example of FIGS. 1-8 and 10, one or more parameters of a light source can be measured. In some aspects, the parameter(s) can be measured periodically (e.g., capacitor voltage waveform, change in peak voltage over time, change in zero-crossing time over time, or a combination thereof). In some aspects, the parameter(s) can be measured in real-time or near realtime (e.g., chamber operating pressure, blower current signal, change in blower current signal over time, change in average or trend of a plurality of blower current signals over time, or a combination thereof) .

[0112] In some aspects, the measured parameter(s) can include a chamber operating pressure of gas discharge chamber 300. For example, as shown in FIG. 4, chamber operating pressures 410 can be measured overtime (e.g., via one or more pressure sensors). In some aspects, the measured parameter(s) can include a chamber operating pressure correlation to an electrode erosion rate (e.g., anode erosion rate). For example, as shown in FIG. 4, chamber operating pressure correlation 420 can be determined for that gas discharge chamber 300 (e.g., linear fit or polynomial fit of chamber operating pressures 410) to correlate the chamber pressure 404 to an electrode erosion rate 402 (e.g., anode erosion rate).

[0113] In some aspects, the measured parameter(s) can include a blower current signal of a motor coupled to blower assembly 310. For example, as shown in FIG. 5, blower current signals 510, 520 can be measured over time (e.g., via a controller). In some aspects, the measured parameter(s) can include a change in the blower current signal over time. For example, as shown in FIG. 5, a blower current erosion rate (e.g., about 0.1 mA / mm to about 0.5 mA / mm) can be determined based on a change in blower current signal Al of first blower current signal 510 and corresponding anode protrusions (e.g., discharge gap Ad) between a “zero” position and a second anode position, for example, Al / Ad = about0.1 mA / mm to about 0.5 mA / mm. These parameters are all exemplary for illustration purposes, and non-limiting.

[0114] In some aspects, the measured parameter(s) can include a capacitor voltage waveform of one or first plurality of capacitors 324 and / or one or second plurality of capacitors 326 coupled to first electrode 322. For example, as shown in FIG. 6, capacitor voltage waveforms 610, 620, 630, 640 can be measured over time (e.g., via a controller).

[0115] In some aspects, the measured parameter(s) can include a change in a peak voltage of the capacitor voltage waveform over time. For example, as shown in FIG. 7, peak voltage erosion rate 706 (e.g., about 25 mV / mm to about 75 mV / mm) can be determined based on a change in peak voltage AVmax and corresponding anode protrusions (e.g., discharge gap Ad), for example, between first capacitor voltage waveform 710 and fourth capacitor voltage waveform 740, for example, AVmax / d = about 25 mV / mm to about 75 mV / mm. These parameters are all exemplary for illustration purposes, and non-limiting.

[0116] In some aspects, the measured parameter(s) can include a change in a zero-crossing time of the capacitor voltage waveform overtime. For example, as shown in FIG. 8, zero-crossing breakdowntime erosion rate 806 (e.g., about -1 ns / mm to about -5 ns / mm) can be determined based on a change in zerocrossing breakdown time Atzero-cross and corresponding anode protrusions (e.g., discharge gap Ad), for example, between first capacitor voltage waveform 810 and fourth capacitor voltage waveform 840, for example, Atzero-cross / Ad = about -1 ns / mm to about -5 ns / mm. These parameters are all exemplary for illustration purposes, and non-limiting.

[0117] In operation 904, as shown in the example of FIGS. 1-8 and 10, discharge gap 340 between first and second electrodes 322, 332 can be adjusted (e.g., via actuator 338 to adjust a position of second discharge surface 346) based on the one or more measured parameter(s) (e.g., chamber operating pressure, blower current signal, change in blower current signal over time, change in average or trend of a plurality of blower current signals over time, capacitor voltage waveform, change in peak voltage overtime, change in zero-crossing time overtime, or a combination thereof). In some aspects, discharge gap 340 can be adjusted by adjusting a position of second discharge surface 346 with actuator 338 coupled to second electrode 332 based on the measured parameter(s). In some aspects, discharge gap 340 can be adjusted by adjusting a position of first discharge surface 344 with an actuator (e.g., similar to actuator 338) coupled to first electrode 322 based on the measured parameter(s).

[0118] In operation 906, as shown in the example of FIGS. 1-8 and 10, discharge gap 340 can be maintained by one or more control signals from a controller (e.g., in a closed-loop feedback algorithm) based on the one or more measured parameter(s) (e.g., chamber operating pressure, blower current signal, change in blower current signal over time, change in average or trend of a plurality of blower current signals over time, capacitor voltage waveform, change in peak voltage over time, change in zero-crossing time over time, or a combination thereof).

[0119] In operation 908, optionally, as shown in the example of FIGS. 1-8 and 10, a chamber operating pressure (e.g., chamber operating pressures 410, chamber operating pressure correlation 420 shown in FIG. 4) of gas discharge medium 301 of gas discharge chamber 300 can be measured (e.g., via one or more pressure sensors coupled to a controller).

[0120] In operation 910, optionally, as shown in the example of FIGS. 1-8 and 10, a blower current signal (e.g., blower current signals 510, 520 shown in FIG. 5) of a motor coupled to blower assembly 310 of gas discharge chamber 300 can be measured (e.g., via a controller).

[0121] In operation 912, optionally, as shown in the example of FIGS. 1-8 and 10, a capacitor voltage waveform (e.g., capacitor voltage waveforms 610, 620, 630, 640 shown in FIG. 6) of one or first plurality of capacitors 324 and / or one or second plurality of capacitors 326 coupled to first electrode 322 of electrode assembly 360 can be measured (e.g., via a controller).

[0122] In some aspects, a sequence of operation 908, operation 910, and operation 912 can be performed in an opposite or alternative order, depending on processing efficiency. For example, the blower current signal and / or the capacitor voltage waveform can be used to perform a coarse adjustment, and the chamber operating pressure can be used to provide fine-tuning of the discharge gap. As another example, operations 908, 910 and 912 are performed in parallel, and the controller adaptively adjust the actuator to move the electrode in response to at least one of the measured results from operations 908, 910 and 912.

[0123] Exemplary Computing System

[0124] FIG. 10 illustrates computing system 1000, according to an exemplary aspect. Computing system 1000 can be configured to implement one or more of the above described aspects, or portions thereof, as computer-readable code. For example, the methods, processes, flow diagrams, and / or systems described herein can be implemented by computing system 1000. Although computing system 1000 is shown in FIG. 10 as a stand-alone apparatus and / or system, aspects of this disclosure can be used with other apparatuses, systems, and / or methods, for example, elements in FIGS. 1-9, e.g., photolithography system 100, illumination system 105, gas discharge chamber 300, chamber operating pressure correlation 420, blower current signals 510, 520, capacitor voltage waveforms 610, 620, 630, 640, flow diagram 900, and / or any suitable metrology / inspection systems.

[0125] Various aspects of the disclosure can be implemented using one or more computing devices, such as computing system 1000 shown in FIG. 10, by software, firmware, hardware, or a combination thereof. Various aspects are described herein in terms of exemplary computing system 1000. One or more computing systems 1000 can be used, for example, to implement any of the aspects described herein, as well as combinations and sub -combinations thereof. Cloud implementations can include one or more of exemplary computing system 1000 operating locally or distributed across one or more server sites.

[0126] As shown in FIG. 10, computing system 1000 can include processor 1002, controller 1004, main memory 1006, communication infrastructure 1008 (e.g., a bus), user input / output (I / O) interface(s)1010, user I / O device(s) 1012, secondary memory 1020, communications interface 1034, and remote device(s) 1038. Computing system 1000 can include one or more processors (also called central processing units, or CPUs), such as processor 1002. Processor 1002 can be a special purpose processor or a general purpose processor. Processor 1002 can be connected to communication infrastructure 1008 (e.g., a bus, a network). Processor 1002 can include a CPU, a graphics processing unit (GPU), an accelerated processing unit (APU), an application-specific integrated circuit (ASIC), a field- programmable gate array (FPGA), a digital signal processor (DSP), a microprocessor, other similar general purpose or specialized processing units, or a combination thereof. In some aspects, processor 1002 can include a GPU that is a specialized electronic circuit designed to process mathematically intensive applications. For example, the GPU can have a parallel structure that is efficient for parallel processing of large blocks of data, such as mathematically intensive data common to computer graphics applications, images, videos, etc.

[0127] Computing system 1000 can also include a controller 1004. Controller 1004 can include functionalities to control data access to main memory 1006 and secondary memory 1020. In some aspects, controller 1004 can be external to processor 1002, for example, as shown in FIG. 10. In some aspects, controller 1004 can be directly part of processor 1002. Controller 1004 can include a microcontroller or microcontroller unit (MCU).

[0128] Computing system 1000 can also include a main memory 1006. Mainmemory 1006 can include volatile memory (e.g., random-access memory (RAM)) and / or non-volatile memory (e.g., read-only memory (ROM), non-volatile RAM (NVRAM), flash). Main memory 1006 can include one or more levels of cache and be divided into channels. Main memory 1006 can have stored therein control logic (e.g., computer software) and / or data.

[0129] Computing system 1000 can also include user I / O interface(s) 1010 coupled to user I / O device(s) 1012. Computing system 1000 can also include user I / O device(s) 1012, such as monitors, keyboards, pointing devices, etc., which can communicate with communication infrastructure 1008 through user I / O interface(s) 1010.

[0130] Computing system 1000 can also include one or more secondary storage devices or memory 1020. Secondary memory 1020 can include, for example, a hard disk drive 1022 and / or a removable storage device or drive 1024. Removable storage drive 1024 can include a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, a tape backup device, a flash memory, and / or any other storage device / drive.

[0131] Removable storage drive 1024 can interact with a first removable storage unit 1026. First removable storage unit 1026 can include a computer usable or readable storage device having stored thereon control logic (e.g., computer software) and / or data. First removable storage unit 1026 can be a floppy disk, a magnetic tape drive, a compact disk drive, a DVD, an optical storage device, a tape backup device, a flash memory, and / or any other computer data storage device. Removable storage drive 1024 can read from and / or write to first removable storage unit 1026.

[0132] Secondary memory 1020 can include other means, devices, components, instrumentalities, or other approaches for allowing computer programs, other instructions, and / or data to be accessed by computing system 1000. Such means, devices, components, instrumentalities, or other approaches can include, for example, a second removable storage unit 1032 and an interface 1030. Examples of the second removable storage unit 1032 and the interface 1030 can include a program cartridge and cartridge interface (e.g., such as that found in video game devices), a removable memory chip (e.g., such as an EPROM or PROM) and associated socket, a memory stick and USB port, a memory card and associated memory card slot, and / or any other removable storage unit and associated interface that allow software and / or data to be transferred from the second removable storage unit 1032 to computing system 1000.

[0133] Computing system 1000 can further include a communications or network interface 1034. Communications interface 1034 can enable computing system 1000 to communicate and interact with any combination of external devices, external networks, external entities, etc. (referenced individually and collectively by reference number 1038). For example, communications interface 1034 can allow computing system 1000 to communicate with external or remote devices 1038 over communications path 1036, which can be wired, wireless, or a combination thereof, and which can include any combination of LANs, WANs, the Internet, etc. Control logic and / or data can be transmitted to and from computing system 1000 via communications path 1036. Communications interface 1034 can include a modem, a communication port, a PCMCIA slot and card, or the like. Software and / or data can be transferred via communications interface 1034 in the form of signals, which can be electronic, electromagnetic, optical, or other signals capable of being transmitted and received by communications interface 1034. The signals can be provided to communications interface 1034 via communications path 1036 (e.g., wired, wireless, etc.).

[0134] Computing system 1000 can also include any computing device, for example, a laptop or notebook computer, a desktop workstation, a netbook, a tablet, a smart phone, a smart watch or other wearable device, a personal digital assistant (PDA), an Intemet-of-Things (loT) device, an embedded system, or any combination thereof.

[0135] Computing system 1000 can include a user device or server, accessing or hosting any applications and / or data through any delivery paradigm, including, but not limited to, remote or distributed cloud computing solutions; local or on-premises software (“on-premise” cloud-based solutions); “as a service” models (e.g., content as a service (CaaS), digital content as a service (DCaaS), software as a service (SaaS), managed software as a service (MSaaS), platform as a service (PaaS), desktop as a service (DaaS), framework as a service (FaaS), backend as a service (BaaS), mobile backend as a service (MBaaS), infrastructure as a service (laaS), etc.); and / or a hybrid model including any combination of the foregoing examples or other services or delivery paradigms.

[0136] Any applicable data structures, file formats, and schemas in computing system 1000 can be derived from standard programming languages, including, but not limited to, C, C++, Python, Perl,JavaScript Object Notation (JSON), Extensible Markup Language (XML), Yet Another Markup Language (Y AML), Extensible Hypertext Markup Language (XHTML), Wireless Markup Language (WML), MessagePack, XML Customer Interface Language (XUL), or any other functionally similar representations alone or in combination. Alternatively, proprietary data structures, formats or schemas can be used, either exclusively or in combination with known or open standards.

[0137] In some aspects, a tangible, non-transitory apparatus or article of manufacture comprising a tangible, non-transitory computer useable or readable medium having control logic (software) stored thereon can also be referred to herein as a computer program product or program storage device. This can include, but is not limited to, computing system 1000, main memory 1006, secondary memory 1020, first removable storage unit 1026, and second removable storage unit 1032, as well as tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (e.g., such as computing system 1000), can cause such data processing devices to operate as described herein.

[0138] Based on the teachings contained in this disclosure, it will be apparent to persons skilled in the relevant art(s) how to make and use aspects of this disclosure using data processing devices, computing systems, and / or computing architectures other than those described herein (e.g., shown in PIG. 10). In particular, aspects can operate with software, hardware, and / or operating system implementations other than those described herein.

[0139] Although specific reference may be made in this text to the use of the apparatus, system, and / or lithographic apparatus in the manufacture of ICs, it should be explicitly understood that such an apparatus, system, lithographic apparatus, and / or metrology / inspection apparatus described herein may have other possible applications, for example, it can be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCD panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle,” “wafer,” or “die” herein may be considered as synonymous with the more general terms “mask,” “substrate,” and “target portion,” respectively.

[0140] Although specific reference may have been made above to the use of aspects in the context of optical lithography, it will be appreciated that aspects may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0141] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0142] The term “substrate” as used herein describes a material onto which material layers are added. In some aspects, the substrate itself may be patterned and materials added on top of it may also be patterned, or may remain without patterning. The substrate referred to herein may be processed, before or after exposure, for example, in a track unit (e.g., a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology unit, and / or an inspection unit. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example, to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0143] The following examples are illustrative, but not limiting, of the aspects of this disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which would be apparent to those skilled in the relevant art(s), are within the spirit and scope of the disclosure.

[0144] While specific aspects have been described above, it will be appreciated that the aspects may be practiced otherwise than as described. The description is not intended to limit the scope of the claims.

[0145] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary aspects as contemplated by the inventor(s), and thus, are not intended to limit the aspects and the appended claims in any way.

[0146] The aspects have been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

[0147] The foregoing description of the specific aspects will so fully reveal the general nature of the aspects that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation, without departing from the general concept of the aspects. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein.

[0148] Aspects and implementations of the present disclosure can be further described using the following numbered clauses:1. A light source comprising: a chamber configured to house a gas discharge medium; an electrode assembly including a first electrode having a first discharge surface and a second electrode opposite the first electrode having a second discharge surface, wherein the second discharge surface is spaced apart from the first discharge surface by a discharge gap;an actuator coupled to the second electrode and configured to adjust a position of the second discharge surface to maintain the discharge gap; and a controller coupled to the actuator and configured to adjust the actuator to maintain the discharge gap based at least in part on one or more measured parameters of the light source, wherein the first and second electrodes are configured to excite the gas discharge medium and generate a light beam.2. The light source of clause 1, wherein the one or more measured parameters comprises an operating pressure of the chamber.3. The light source of clause 2, wherein the operating pressure of the chamber comprises an accumulative average operating pressure of the chamber.4. The light source of clause 2, wherein the controller is configured to adjust the actuator to maintain the discharge gap based at least in part on a function correlating the operating pressure of the chamber to an erosion rate of the second electrode.5. The light source of clause 4, wherein the operating pressure of the chamber is inversely proportional to the erosion rate of the second electrode.6. The light source of clause 4, wherein the function comprises a linear regression between the operating pressure of the chamber and the erosion rate of the second electrode.7. The light source of clause 4, wherein the function comprises a polynomial regression between the operating pressure of the chamber and the erosion rate of the second electrode.8. The light source of clause 4, wherein the controller is configured to adjust the actuator to maintain the discharge gap based on the erosion rate exceeding a predetermined threshold.9. The light source of clause 2, wherein the chamber comprises a power ring amplifier (PRA).10. The light source of clause 2, wherein the chamber comprises a master oscillator (MO).11. The light source of clause 1, further comprising a blower assembly configured to circulate the gas discharge medium within the chamber.12. The light source of clause 11, wherein the one or more measured parameters comprises a blower current signal of a motor coupled to the blower assembly.13. The light source of clause 12, wherein the controller is configured to adjust the actuator to maintain the discharge gap based at least in part on a function correlating the blower current signal of the motor to an erosion rate of the second electrode.14. The light source of clause 1, wherein the one or more measured parameters comprises a capacitor voltage waveform of a capacitor coupled to the electrode assembly.15. The light source of clause 14, wherein the capacitor voltage waveform comprises a peak voltage, a zero-crossing time, a voltage overshoot, or a combination thereof.16. The light source of clause 14, wherein the controller is configured to adjust the actuator to maintain the discharge gap based at least in part on a function correlating the capacitor voltage waveform of the capacitor to an erosion rate of the second electrode.17. A method of controlling operation of a light source, the light source configured to generate a light beam and comprising a chamber, a blower assembly, and an electrode assembly, the method comprising: measuring one or more parameters of the light source; and adjusting a discharge gap between a first electrode and a second electrode of the electrode assembly based at least in part on the one or more parameters to reduce errors in the light beam.18. The method of clause 17, wherein the measuring the one or more parameters comprises measuring an operating pressure of the chamber, a blower current signal of a motor coupled to the blower assembly, a capacitor voltage waveform of a capacitor coupled to the first electrode, or a combination thereof.19. The method of clause 18, wherein the adjusting the discharge gap is based at least in part on one or more functions correlating the operating pressure of the chamber, the blower current signal of the motor, the capacitor voltage waveform of the capacitor, or a combination thereof to an erosion rate of the second electrode.20. A computer-readable storage medium storing instructions which, when executed by one or more processors, cause the one or more processors to perform operations comprising: measuring one or more parameters of a light source, the light source configured to generate a light beam and comprising a chamber, a blower assembly, and an electrode assembly; and adjusting a discharge gap between a first electrode and a second electrode of the electrode assembly based at least in part on the one or more parameters to reduce errors in the light beam, wherein the one or more parameters comprises an operating pressure of the chamber, a blower current signal of a motor coupled to the blower assembly, a capacitor voltage waveform of a capacitor coupled to the first electrode, or a combination thereof.

[0149] The breadth and scope of the aspects should not be limited by any of the above -described exemplary aspects, but should be defined only in accordance with the following clauses and their equivalents.

Claims

CLAIMS1. A light source comprising: a chamber configured to house a gas discharge medium; an electrode assembly including a first electrode having a first discharge surface and a second electrode having a second discharge surface, wherein the second discharge surface is spaced apart from the first discharge surface by a discharge gap; an actuator coupled to the second electrode and configured to adjust a position of the second discharge surface to maintain the discharge gap; and a controller coupled to the actuator and configured to adjust the actuator to maintain the discharge gap based at least in part on one or more measured parameters of the light source, wherein the first and second electrodes are configured to excite the gas discharge medium and generate a light beam.

2. The light source of claim 1, wherein the one or more measured parameters comprises an operating pressure of the chamber.

3. The light source of claim 2, wherein the operating pressure of the chamber comprises an accumulative average operating pressure of the chamber.

4. The light source of claim 2, wherein the controller is configured to adjust the actuator to maintain the discharge gap based at least in part on a function correlating the operating pressure of the chamber to an erosion rate of the second electrode.

5. The light source of claim 4, wherein the operating pressure of the chamber is inversely proportional to the erosion rate of the second electrode.

6. The light source of claim 4, wherein the function comprises a linear regression between the operating pressure of the chamber and the erosion rate of the second electrode.

7. The light source of claim 4, wherein the function comprises a polynomial regression between the operating pressure of the chamber and the erosion rate of the second electrode.

8. The light source of claim 4, wherein the controller is configured to adjust the actuator to maintain the discharge gap based on the erosion rate exceeding a predetermined threshold.

9. The light source of claim 2, wherein the chamber comprises a power ring amplifier (PRA).

10. The light source of claim 2, wherein the chamber comprises a master oscillator (MO).

11. The light source of claim 1, further comprising a blower assembly configured to circulate the gas discharge medium within the chamber.

12. The light source of claim 11, wherein the one or more measured parameters comprises a blower current signal of a motor coupled to the blower assembly.

13. The light source of claim 12, wherein the controller is configured to adjust the actuator to maintain the discharge gap based at least in part on a function correlating the blower current signal of the motor to an erosion rate of the second electrode.

14. The light source of claim 1, wherein the one or more measured parameters comprises a capacitor voltage waveform of a capacitor coupled to the electrode assembly.

15. The light source of claim 14, wherein the capacitor voltage waveform comprises a peak voltage, a zero-crossing time, a voltage overshoot, or a combination thereof.

16. The light source of claim 14, wherein the controller is configured to adjust the actuator to maintain the discharge gap based at least in part on a function correlating the capacitor voltage waveform of the capacitor to an erosion rate of the second electrode.

17. A method of controlling operation of a light source, the light source configured to generate a light beam and comprising a chamber, a blower assembly, and an electrode assembly, the method comprising: measuring one or more parameters of the light source; and adjusting a discharge gap between a first electrode and a second electrode of the electrode assembly based at least in part on the one or more parameters to reduce errors in the light beam.

18. The method of claim 17, wherein the measuring the one or more parameters comprises measuring an operating pressure of the chamber, a blower current signal of a motor coupled to the blower assembly, a capacitor voltage waveform of a capacitor coupled to the first electrode, or a combination thereof.

19. The method of claim 18, wherein the adjusting the discharge gap is based at least in part on one or more functions correlating the operating pressure of the chamber, the blower current signal ofthe motor, the capacitor voltage waveform of the capacitor, or a combination thereof to an erosion rate of the second electrode.

20. A computer-readable storage medium storing instructions which, when executed by one or more processors, cause the one or more processors to perform operations comprising: measuring one or more parameters of a light source, the light source configured to generate a light beam and comprising a chamber, a blower assembly, and an electrode assembly; and adjusting a discharge gap between a first electrode and a second electrode of the electrode assembly based at least in part on the one or more parameters to reduce errors in the light beam, wherein the one or more parameters comprises an operating pressure of the chamber, a blower current signal of a motor coupled to the blower assembly, a capacitor voltage waveform of a capacitor coupled to the first electrode, or a combination thereof.

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