Gas laser with reduced water consumption through smart temperature adjust and monitor algorithm

Abstract

A system and method for adjusting a target temperature of a gas chamber in a laser apparatus comprises monitoring performance parameters of the laser and updating the target temperature based on the results of such monitoring. The target temperature may be incrementally increased or decreased to optimize the laser gas temperature. Such optimization may improve performance, reduce errors, and reduce water consumption of resources in a cooling system.

Description

REDUCED WATER CONSUMPTION THROUGH SMART TEMPERATURE ADJUST AND MONITOR ALGORITHMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 720,499 which was filed on November 14, 2024 which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] The subject matter disclosed herein relates to maintenance of light sources such as those used for integrated circuit photolithographic manufacturing processes.BACKGROUND

[0003] Laser radiation for semiconductor photolithography is typically supplied by a system referred to as a light source. These light sources may produce radiation as a series of pulses at specified repetition rates, for example, in the range of about 500 Hz to about 6 kHz. They conventionally have expected useful lifetimes measured in terms of the number of pulses they are projected to be able to produce before requiring repair or replacement, typically expressed as billions of pulses.

[0004] Some systems for generating laser radiation at frequencies useful for semiconductor photolithography (deep-ultraviolet (DUV) wavelengths) utilize one or more gas-filled chambers. For example, an Argon Fluoride (ArF) laser may use a master oscillator power amplifier (MOP A) dual-gas-discharge-chamber configuration. This configuration has two chambers, a master oscillator chamber (MO chamber) and a power amplifier chamber (PA chamber). Other systems, such as Krypton Fluoride (KrF) lasers may utilize a single chamber. The temperatures in each chamber must be precisely controlled to ensure that the light source functions properly. This may be achieved by controlling a temperature of gas inside the chamber.SUMMARY

[0005] The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of the present invention. This summary is not an extensive overview of all contemplated embodiments and is not intended to identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

[0006] Some embodiments of the present disclosure provide a laser apparatus. The laser apparatus may comprise: a laser chamber comprising a gas; a temperature control system configured to control a temperature of the gas based on a target temperature of the gas; and a controller comprising one or more processors. The controller may be configured to cause the laser apparatus to perform operationscomprising: performing a monitoring of a performance parameter of the laser apparatus; and updating the target temperature based on a value of the performance parameter.

[0007] Some embodiments of the present disclosure provide a method. The method may comprise: operating a laser apparatus, operating a temperature control system to control a temperature of a gas in a laser chamber of the laser apparatus based on a target temperature of the gas; performing a monitoring of a performance parameter of the laser apparatus; and updating the target temperature based on a value of the performance parameter.

[0008] Some embodiments of the present disclosure provide a non-transitory computer-readable medium. The non-transitory computer-readable medium may store a set of instructions that is executable by at least one processor of an apparatus to cause the apparatus to perform operations comprising: operating a laser apparatus, operating a temperature control system to control a temperature of a gas in a laser chamber of the laser apparatus based on a target temperature of the gas; performing a monitoring of a performance parameter of the laser apparatus; and updating the target temperature based on a value of the performance parameter .

[0009] Further features and advantages of the disclosed technology, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. It is noted that the disclosed embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein and their understanding of the underlying technology.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. 1 is a diagrammatic representation of an example photolithography system, consistent with embodiments of the present disclosure.

[0011] Fig. 2 is a diagrammatic representation of an example laser system, consistent with embodiments of the present disclosure.

[0012] Fig. 3 is a diagrammatic representation of an example temperature control system for a laser system, consistent with embodiments of the present disclosure.

[0013] Fig. 4 illustrates an example flow chart of a process for maintaining a temperature at a fixed target in a laser system, consistent with embodiments of the present disclosure.

[0014] Fig. 5 illustrates an example flow chart of a process for updating a target temperature in a laser system, consistent with embodiments of the present disclosure.DETAILED DESCRIPTION

[0015] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplaryembodiments do not represent all implementations consistent with the disclosure. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the subject matter recited in the appended claims. For example, although some embodiments are described in the context of DUV-based lithographic apparatuses, the present disclosure is not so limited. Unless infeasible, embodiments described herein can be implemented in any type of lithographic apparatus or other laser application.

[0016] As used herein, unless specifically stated otherwise, the term “or” encompasses all possible combinations, except where infeasible. For example, if it is stated that a component can comprise A or B, then, unless specifically stated otherwise or infeasible, the component can comprise A, or B, or A and B. As a second example, if it is stated that a component can comprise A, B, or C, then, unless specifically stated otherwise or infeasible, the component can comprise A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0017] Electronic devices are constructed of circuits formed on a substrate. The substrate is typically of a semiconductor material (e.g., silicon) and is often referred to as a wafer by persons of skill in the art. Many circuits may be formed together on the same piece of silicon and are called integrated circuits or ICs. With advancements in technology, the size of these circuits has decreased dramatically so that many more of them can fit on the substrate. For example, an IC chip in a smart phone can be as small as a fingernail and yet may include over 2 billion transistors, the size of each transistor being less than 1 / 1, 000th the width of a human hair.

[0018] Making these ICs with extremely small structures or components is a complex, timeconsuming, and expensive process, often involving hundreds of individual steps. Errors in even one step have the potential to result in defects in the finished IC, rendering it useless. Thus, one goal of the manufacturing process is to avoid such defects to maximize the number of functional ICs made in the process, that is, to improve the overall yield of the process.

[0019] Speed, or throughput, has been a traditionally important metric alongside yield. Throughput is a measurable quantity that characterizes the manufacture speed of a fab (e.g., number of IC units produced per unit time). Throughput has become even more important in view of recent global chip shortages. As there are multiple steps in the fabrication of a chip device (e.g., multiple steps for multiple layers), each step can have a characteristic throughput. For example, a throughput value can be assigned to how quickly a lithographic system can conduct an illumination optimization process. Innovations in the design or functions of source optimizers can increase throughput or resolve problems in another aspect while mitigating adverse impact to throughput.

[0020] Yield is a metric that characterizes failure rate in device fabrication, which relates to cost and efficiency. Yield can be defined as a ratio of all the wafers that are produced by a fab to the number of wafers that were introduced to the fab. Or yield can be the number of working chips that survive the device fabrication process performed on a wafer to the number of potential chips that can be fabricated from that wafer in the ideal case of zero failure. As some wafers or chips fail duringfabrication, the overall yield is less than 100%. For example, to obtain a 75% yield for a 50-step process (where a step can be indicative of the number of layers formed on a wafer), each individual step should have a yield greater than 99.4%. In contrast, if individual steps have a yield of 95%, the compounding errors at each step result in an overall process yield as low as 7-8%. Every wafer or chip lost during fabrication is a sunk cost and lost time for the fab.

[0021] One parameter of the device manufacturing process that can impact the throughput and yield of a fab is temperature control of laser light sources. To avoid unwanted changes in beam characteristics and damage to the laser system components, it may be desirable to maintain a laser system at a predetermined operating temperature. However, due to the large amount of heat that is generated during laser operation, this temperature control may consume excessive resources such as water and energy.

[0022] For example, a typical laser temperature control system may comprise a gas heater and a water (or other coolant) distribution system. The gas heater may be configured to heat the gas in a chamber of a laser system to a predetermined target temperature (such as, in one example, 65° C). The gas may be circulated in the chamber by a blower module to maintain uniformity of, e.g., temperature, gas mixture, density, pressure, etc. Excess heat is generated during laser firing, which may be removed by thermal contact between the circulating gas and a continuous flow of cooling water from the water distribution system. Temperature adjustment within the chamber may be performed using a flow control valve to increase or decrease the flow rate of the cooling water. The flow rate may be increased to lower the chamber temperature and decreased to raise the chamber temperature.

[0023] However, conventional temperature control arrangements may suffer several drawbacks. First, the amount of water that is consumed can be excessive. For instance, each chamber of each laser system in a fab might use, e.g., approximately 3-5 liters of water per minute while operating 24 hours per day. Combined with other uses of water in semiconductor manufacturing (such as wafer rinsing), a typical fab can consume millions of liters of water each day. Second, because laser manufacturers may lack the time or resources to calibrate the optimal operating temperatures for each individual chamber, laser systems may be operated at a pre-selected target temperature (such as, e.g., 65° C as discussed above) that is not the most optimal. For instance, some higher operating temperatures may offer improved suppression of acoustic resonance issues, burst transients, cold start problems, etc. Thus, a cooling system may be consuming more water and energy than necessary simply to cool the laser chambers to sub-optimal temperatures, resulting in degraded performance and increased operational cost. Third, even if the laser system is initially set at an optimal temperature value for each chamber, these optimal values may drift over time as the laser system is used.

[0024] Embodiments of the present disclosure provide systems and methods for monitoring a laser system to continuously update the target temperatures of chambers or other modules. In some embodiments, a series of measurements or other health checks may be periodically performed on a laser system to determine whether it is acceptable to update a temperature control system byincrementally increasing the target temperature. This process may be repeated iteratively until the measurements or other health checks indicate that further increases are not acceptable, or that an incremental decrease in the target temperature is warranted. By incrementally raising the target temperature to its maximum allowable value within prescribed tolerances, it may be possible to reduce water consumption, improve laser performance, and keep pace with drifts in the optimal temperature values.

[0025] As an illustrative example of potential water savings, assume a two-chambered laser initially operates at a target temperature of 65° C. A water flow control valve may provide a maximum flow rate of 11.4 L / min when the valve is 100% open, and may be set at an opening ratio of 35% to maintain the 65° C target temperature, resulting in (11.4 x 0.35) = 3.99 L / min of water consumed. If it can be determined that the laser’s target temperature may be safely increased to, e.g., 75° C, the temperature increase may be achieved by closing the valve by, e.g., a further 10% to an opening ratio of 25%. Thus it may be possible to reduce water consumption by (11.4 x 0.10) = 1.14 L / min per chamber. In a continuously operating fab, this may result in a savings of (2 chambers) x (1.14 L) x (60 minutes) x (24 hours) x (365 days) = 1,198,368 liters of water per laser per year.

[0026] Embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine -readable medium, such as a computer-readable medium, 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, 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.

[0027] Systems such as those described herein may render benefits in a wide range of applications and implementations. For the sake of having a specific nonlimiting example to facilitate description, one such application is in semiconductor photolithography. Fig. 1 schematically illustrates a photolithography system 100 that includes an illumination system 105. As described more fully below, the illumination system 105 may include 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 may be 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.

[0028] 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 may include an optical arrangement 117 having, for example, one or more condenser lenses, a mask, and an objective arrangement. The mask may be 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 may include a projection lens and may enable an image transfer to occur from the mask to photoresist on the wafer 120. The illumination system 105 may adjust the range of angles for the pulsed light beam 110 impinging on the mask. The illumination system 105 may also homogenize (make uniform) the intensity distribution of the pulsed light beam 110 across the mask.

[0029] 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 may illuminate the same area of the wafer 120 to constitute an illumination dose.

[0030] 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.

[0031] Fig. 2 schematically illustrates a pulsed laser source that produces a pulsed laser beam as the light beam 110 as an example of an illumination system 105, consistent with embodiments of the present disclosure. 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, e.g., a solid state or gas discharge master oscillator (“MO”) seed laser system 140, an amplification stage, e.g., a power ring amplifier (“PRA”) stage 145, relay optics 150, and laser system output subsystem 160. The seed system 140 may include, e.g., an MO chamber 165 which includes a pair of electrodes 167 and 168.

[0032] 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 165 with an oscillator cavity defined by a reflective grating (not shown) in an LNM 170 that oscillates to form the seed laser output pulse. The MO seed laser system 140 may also include a line-center 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).

[0033] 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 beincorporated into a PRA WEB 210. The beam may be redirected back through the gain medium in the 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.

[0034] 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 251. 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.

[0035] The PRA lasing chamber 200 and the MO 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.

[0036] Pulse energy meter 251 within CASMM 250 may be used to monitor performance parameters of the laser apparatus based on pulse energy measurements. Alternatively or additionally, one or more pulse energy meters 251 may be located in other subsystems for monitoring laser performance parameters, such as in, e.g., seed laser system 140, amplification stage 145, relay optics 150, output subsystem 160, or one or more modules contained therein.

[0037] The PRA lasing chamber 200 and the MO 165 may generate large amounts of heat during the lasing process. Similarly, other modules or sub-systems of illumination system 105 may comprise purge gas that becomes heated when the optical elements of such module or sub-systems are irradiated, or through optical absorption in the gas itself. Thus, illumination system 105 may comprise a temperature control system as discussed below.

[0038] Fig. 3 schematically illustrates an example temperature control system 300 for a laser system, consistent with embodiments of the present disclosure. For example, the temperature control system 300 may be used in illumination systems 105 of Figs. 1 and 2, and may be operated by, e.g., control system 135 of Fig. 1. Temperature control system 300 may comprise: a water inlet 310; water piping 311; blower module 312; gas chamber 313; pulse power module 314; flow meter 315; flow control valve 316; heater 317 and temperature sensor 318.

[0039] Gas chamber 313 may represent a chamber of a laser apparatus in which gas discharge occurs such as, e.g., PRA lasing chamber 200 or MO 165 of illumination system 105. Therefore it should be understood that in some embodiments there may be a plurality of gas chambers 313, such as a first gas chamber and a second gas chamber. In some embodiments, each gas chamber may comprise its own dedicated components such as blower module 312, flow control valve 316, or heater 317. In some embodiments, a laser system may use a single gas chamber, for example in a KrF laser.

[0040] Blower module 312 may comprise a fan or other system configured to circulate the chamber gas (illustrated in dashed lines) through heater 317 and gas chamber 313. Heater 317 may be configured to heat the gas at a fixed rate corresponding to a predetermined operating temperature. For example, in some embodiments, the predetermined operating temperature may be, e.g., 65° C. In some embodiments, a temperature of gas exiting gas chamber 313 may be monitored by temperature sensor 318.

[0041] Cooling water may be introduced into temperature control system 300 through water inlet 310 and circulated to various chambers and modules by a network of water piping 311. For example, water piping 311 may distribute cooling water to blower module 312, gas chamber 313, pulse power module 314, or other unillustrated chambers or modules. The cooling water may absorb heat from the environment of the module through which it passes by, e.g., heat exchange with gas inside the chamber or module. A flow rate of the cooling water may be controlled using flow control valve 316 and may be monitored by one or more flow meters 315. For example, flow control valve 316 may comprise a hydraulic proportioning valve or other valve configured to precisely regulate a flow rate of cooling water. By adjusting the flow rate of water passing through gas chamber 313, it may be possible to increase or reduce the amount of heat that is absorbed by the flow of cooling water and thereby control the temperature of gas chamber 313. For example, the flow rate may be adjusted according to a target temperature based on a temperature measurement, such as from sensor 318. While it may also be possible to adjust a temperature of gas chamber 313 by changing a heat output of heater 317, adjustment of the water flow may be a more responsive and accurate technique. Therefore, in some embodiments a heat output of heater 317 may be kept substantially constant while the water flow rate is adjusted to achieve a target temperature in the gas chamber 313.

[0042] Fig. 4 illustrates a simple flow chart of a process 400 for maintaining a temperature at a fixed target in a laser system, consistent with embodiments of the present disclosure. The process 400 of Fig. 4 may be performed using, e.g., temperature control system 300 of Fig.3, and may be controlled by, e.g., control system 135 of Fig. 1. At step 401, a chamber gas temperature may be determined (such as by temperature sensor 318 of Fig. 3). At step 402, it may be determined whether the chamber gas temperature is within an allowable range of a predetermined target temperature (such as the example target temperature of 65° C discussed above). For example, the allowable range may be within, e.g., 2° C, 1° C, 0.5° C, 0.1° C, etc. if the temperature is within the allowable range, the process may revert to step 401 and repeat. If the temperature is outside the allowable range, theprocess may move on to a step 403 of adjusting the flow rate. For example, the flow rate may be increased or decreased by an amount corresponding to the difference between the determined temperature and the target temperature.

[0043] In a comparative laser system, temperature control may continue indefinitely based on a predetermined fixed target temperature. However, as discussed above, this arrangement may not be optimal in view of the high water consumption and failure to tune the target temperature to an optimal range. For example, if it were determined that it would be feasible to raise the target temperature of an individual chamber, sub-system, or laser system to higher target such as, e.g., 70, 75, 80, or 85° C, it may be possible to drastically reduce water consumption while simultaneously improving acoustic resonance issues and other parameters. However, increasing the target temperature to an improper level runs the risk of increasing such acoustic resonance problems along with, e.g., light beam parameters and laser energy efficiency. Additionally, increasing the target temperature may potentially lead to other issues, such as lifetime of a chamber or other components such as bearing lubricants.

[0044] Embodiments of the present disclosure provide systems and methods for safely and continuously monitoring and updating a target temperature of a laser system or its subcomponents. The systems and methods may operate in cycles comprising, e.g. an initial check process and a performance monitoring process. The initial check process may be used to confirm basic eligibility, i.e., that the laser system is in a suitable condition to perform continuous updates to the target temperature. If the laser system passes the initial check, then a performance monitoring process may be initiated. The performance monitoring process may be designed to ensure that an increase to the target temperature will not negatively affect laser health or performance parameters. After performance monitoring is completed, a decision may be made to either raise the target temperature by a first incremental amount, lower the target temperature by a second incremental amount, or leave the target temperature unchanged. The cycles may be performed at regular intervals during operation of the laser system such as, e.g., every second, every minute, every ten minutes, every hour, every four hours, every day, etc. Alternatively or additionally, the regular intervals may be determined based on, e.g., a predetermined pulse count.

[0045] Fig. 5 illustrates an example flow chart of a process 500 for updating a target temperature in a laser system, consistent with embodiments of the present disclosure. The process 500 may be used to update a set target temperature in a temperature control process, such as process 400 of Fig. 4.Process 500 may be performed using, e.g., temperature control system 300 of Fig. 3, and may be controlled by, e.g., control system 135 of Fig. 1. For example, control system 135 may comprise an initial check module 501, a performance monitor module 510, and a decision module 520. Initial check module 501 may perform an initial check process to confirm basic eligibility of the laser system as illustrated in steps 502-506. Performance monitoring module 510 may monitor and evaluate various performance parameters of the laser system as illustrated in steps 511-513. Decision module520 may process and output a decision on whether to increase, decrease, or maintain the target temperature based on the results of the performance monitoring as illustrated in steps 521-524.

[0046] It should be understood that the method steps discussed below need not necessarily be performed in the order displayed or presented. For example, some initial check steps 502-506 may be performed in another order or simultaneously. Some initial check steps may be omitted entirely while others may be added. The same may be true for performance monitoring steps 511-513. Further, the various method steps may not necessarily occur on a 1:1 basis. For example, in some embodiments the performance monitoring steps may be performed with a higher frequency than the initial check steps.

[0047] In step 502, a chamber age check may determine whether the laser system or one of its components is within a safe age range for performing target temperature updates. For example, it may be desirable that an update to the target temperature is not performed until the laser (or at least a monitored component, such as an MO chamber or PRA lasing chamber) has been operated and observed for a minimum period. In some embodiments, the minimum period may be measured in terms of, e.g., pulse count. For example, the minimum period may comprise a period during which the laser has emitted, e.g., one billion, two billion, or three billion pulses or more. Alternatively or additionally, the minimum period may be measured in terms of total operation time. Further, it may be desirable that an update to the target temperature is not performed after the laser or a component has aged to the point that such changes could result in undue stress or damage to the system. Therefore a chamber age check may further comprise determining whether the laser or component has exceeded a maximum period, which may be evaluated in terms of, e.g., a percentage of expected lifetime. In some embodiments, the maximum period may correspond to a threshold percentage of the expected lifetime such as, e.g., 70%, 80%, or 90% of the expected lifetime. Alternatively or additionally, the maximum period may correspond to a pulse count or total operation time.

[0048] In step 503, a data availability check may determine whether sufficient data has been collected about the performance of the laser system or its components for a proper evaluation. For example, the data may relate to the performance parameters that are monitored in the performance monitoring steps 511-513 discussed below. The data availability check may comprise, e.g. a threshold pulse count over which such data has been. For example, the pulse count may comprise, e.g. a minimum of one million, five million, or ten million pulses, etc. In some embodiments, the data availability check may comprise determining that such data from the threshold pulse count was collected at a repetition rate of interest, such as the repetition rate at which the laser system is presently operating, or within a prescribed range of said repetition rate. In some embodiments, the data availability check may comprise determining that the available data has been collected within a sufficiently recent period such as, e.g., with the last 10 million, 50 million, or 100 million pulses. The data availability check may be used to ensure that a baseline set of data exists such that any new data gathered during performance monitoring may be appropriately analyzed or characterized.

[0049] In step 504, a temperature range check may be performed. For example, the temperature range check may set upper or lower limits on the operating temperatures at which further target temperature updates may be allowed. For example, the temperature range check may determine whether the present temperature of a laser system or one of its components is above a predetermined baseline temperature or below a predetermined maximum allowable temperature. This may be used to, e.g., ensure that process 500 does not unintentionally deviate a target temperature into levels that may be harmful or may result in degraded laser performance.

[0050] In step 505, it may be determined whether each of the chamber age check, data availability check, and temperature range check has passed. If at least one of the chamber age check, data availability check, or temperature range check does not pass, the cycle may be terminated at step 506 with no change in the target temperature. Then the cycle may begin again at, e.g., a predetermined regular interval such as, e.g., one second, one minute, ten minutes, one hour, four hours, one day, etc. If instead each of the chamber age check, data availability check, and temperature range check has passed, the process may proceed to the performance monitoring steps 511-513 and decision steps 521-524. The performance monitoring and decision steps may be used to determine whether it is allowable to increase a target temperature based on various performance metrics, as well as whether the target temperature should be decreased, or whether it should remain unchanged.

[0051] For example, in step 511, a beam quality check may measure one or more parameters related to beam quality. For example, beam quality check step may be designed to ensure that the one or more beam parameters do not exceed a predetermined threshold. The predetermined thresholds may indicate that beam quality has unacceptably degraded at the present target temperature. Alternatively or additionally, the predetermined thresholds may indicate that beam quality would unacceptably degrade if the target temperature were increased by an incremental amount. The beam quality check may comprise measuring beam parameters such as, e.g., energy, center wavelength, BQ sigma, divergence, beam uniformity, spot size, beam parameter product, M2factor, and other laser beam quality parameters known to persons having ordinary skill in the art.

[0052] In some embodiments, the beam quality check may comprise evaluating each selected parameter individually and judging the laser to have passed the beam quality check only when each individual parameter has met its respective predetermined threshold. In some embodiments, the beam quality check may comprise assigning a score based on a weighted combination of a plurality of monitored parameters. In such a case, the laser may be judged to have passed the beam quality check when the score meets a predetermined threshold score. In some embodiments, the beam quality check may be judged based on the score as well as on one or more critical threshold parameter values. For example, critical threshold parameter values may be assigned to certain beam quality parameters such that the beam quality check will fail when that parameter value is exceeded, even when the score meets the predetermined threshold score. The outcomes that result from the laser passing or failing the beam quality check are discussed further below with respect to steps 521-524 of decision module 520.

[0053] In step 512, an acoustic resonance check may determine whether increasing the target temperature by an incremental amount would have an unacceptable effect on acoustic resonance issues in a chamber. Acoustic resonance may occur when the frequency of a sound wave in a chamber corresponds to a natural frequency of the chamber, such that standing waves may be amplified. This may result in unwanted mechanical stress or vibration of optical elements and other components in the chamber. The natural frequencies of the chamber may shift according to, inter alia, gas parameters such as temperature and pressure. Thus, acoustic resonance properties may change, for better or worse, as a function of the operating temperature of a laser. In some embodiments, an acoustic resonance check may comprise analyzing acoustic resonance properties via, error checks on wavelength, energy output, or another beam parameter. For example, the acoustic resonance check may comprise performing a fast Fourier transform (FFT) error check on the wavelength, energy output, etc. In some embodiments, the acoustic resonance check may result in a pass or fail scenario based on such error checks or on a weighted combination of such error checks.

[0054] In step 513, an efficiency check may determine whether increasing the target temperature by an incremental amount would have an unacceptable effect on laser efficiency. For example, the efficiency check may comprise performing a check of the change in output energy as a function of input voltage (dV / dT) in a laser chamber.

[0055] The decision module 520 may be configured to output decisions based on the performance monitoring steps of the performance module 510. For example, the decision module may output a target temperature adjustment command to a temperature control system of a laser apparatus, such as temperature control system 300 of Fig. 3. The target temperature adjustment command may increase or decrease a target temperature value of the temperature control system by an incremental amount, such as, e.g., between 0.5° C and 5° C.

[0056] For example, when each performance monitor check of steps 511-513 is judged to have passed, the process may proceed to step 524 in which the decision module outputs an incremental increase command to increase the target temperature. In some embodiments, the incremental increase may comprise a fixed amount (such as, e.g., 2° C or some other value) that is independent of the values measured during the performance monitor checks. In some embodiments, the incremental increase amount may vary based on different factors such as, e.g., the results of one or more performance monitor checks, or on the value of the present target temperature. For example, if the results of the performance monitor checks are close to exceeding their threshold values, the incremental increase command may be smaller than if the results of the performance monitor checks are well within acceptable tolerances. Alternatively or additionally, the incremental increase command may become smaller as the present target temperature approaches a maximum allowable target temperature. Such dynamic increases may allow a laser system to reach an ideal target temperature more rapidly than by increasing the temperature in fixed increments. However, in someembodiments it may be undesirable to increase a target temperature too rapidly, and therefore the incremental increase command may comprise a fixed amount.

[0057] When one or more performance checks fails, the decision module may output an incremental decrease command (such as seen at steps 521 or 522), or it may output no command or a “no change” command (such as seen at step 523). For example, if at least one of the beam quality check or the acoustic resonance check fails, the decision module may output an incremental decrease command. In some embodiments the amount of the incremental decrease command may comprise a fixed amount that is the same as, or different from, a fixed incremental increase command. For example, in some embodiments where the amount of incremental increase is, e.g., 2° C, the incremental decrease may be, e.g., 1° C. In some embodiments, the incremental decrease amount may be dynamic in a similar manner as discussed above with respect to the incremental increase amount. For example, if the results of the performance monitor checks greatly exceed their threshold values, the amount of the incremental decrease command may be larger than if the results of the performance monitor checks only narrowly exceed these thresholds. Alternatively or additionally, the incremental decrease command may become smaller as the present target temperature approaches a minimum allowable target temperature. In some embodiments, rather than outputting a command to decrease the target temperature, the decision module may output a “no change” command, or simply output no command at all. For example, as illustrated, a failure of the efficiency check at step 513 may result in no change to a target temperature rather than a decrease. It should be understood that embodiments of the present disclosure are not limited to the scenarios illustrated in Fig. 5. For example, a failure at step 513 may result in an incremental decrease command, or a failure at one of steps 511 or 512 may result in no change.

[0058] By continuously or periodically running process 500, it may be possible to automatically optimize a target temperature of a laser system without requiring any system downtime or manual inspection processes. For example, process 500 may be repeated at predetermined regular intervals such as, e.g., one second, one minute, ten minutes, one hour, four hours, one day, etc. Alternatively or additionally, the regular intervals may be determined based on, e.g., a predetermined pulse count.

[0059] A non-transitory computer-readable medium may be provided that stores instructions for one or more processors of a controller (e.g., control system 135 in Fig. 1) for monitoring laser performance and updating a target temperature using embodiments of the present disclosure. For example, the instructions stored in the non-transitory computer-readable medium may be executed by the circuitry of the controller for performing methods 400 or 500 in part or in entirety. Common forms of non-transitory media include, for example, a floppy disk, a flexible disk, hard disk, solid-state drive, magnetic tape, or any other magnetic data storage medium, a Compact Disc Read-Only Memory (CD-ROM), any other optical data storage medium, any physical medium with patterns of holes, a Random Access Memory (RAM), a Programmable Read-Only Memory (PROM), and Erasable Programmable Read-Only Memory (EPROM), a FLASH-EPROM or any other flashConfidentialmemory, Non-Volatile Random Access Memory (NVRAM), a cache, a register, any other memory chip or cartridge, and networked versions of the same. The one or more processors can include any combination of any number of a central processing unit (“CPU”), a graphics processing unit (“GPU”), a neural processing unit (“NPU”), a microcontroller unit (“MCU”), an optical processor, a programmable logic controller, a microcontroller, a microprocessor, a digital signal processor, an intellectual property (IP) core, a Programmable Logic Array (PL A), a Programmable Array Logic (PAL), a Generic Array Logic (GAL), a Complex Programmable Logic Device (CPLD), a Field-Programmable Gate Array (FPGA), a System On Chip (SoC), an Application-Specific Integrated Circuit (ASIC), or the like. In some embodiments, the one or more processors can also be a set of processors grouped as a single logical component.

[0060] The embodiments may further be described using the following clauses:1. A laser apparatus, comprising:a laser chamber comprising a gas;a temperature control system configured to control a temperature of the gas based on a target temperature of the gas; anda controller comprising one or more processors and configured to cause the laser apparatus to perform operations comprising:performing a monitoring of a performance parameter of the laser apparatus; and updating the target temperature based on a value of the performance parameter. 2. The laser apparatus of clause 1, wherein the temperature control system comprises: a water distribution system configured to circulate cooling water in thermal contact with the gas; anda flow control valve configured to adjust a flow rate of the cooling water to adjust a temperature of the gas and maintain the gas at the target temperature.3. The laser apparatus of clause 1, wherein the laser chamber comprises one of a master oscillator or a power ring amplifier.4. The laser apparatus of clause 1 , wherein the laser apparatus is configured to output deep ultraviolet (DUV) light.5. The laser apparatus of clause 1, further comprising:a pulse energy meter;wherein the controller is configured to perform the monitoring of the performance parameter based on an output from the pulse energy meter.6. The laser apparatus of clause 5, further comprising:a combined autoshutter metrology module (CASMM);wherein the pulse energy meter is located in the CASMM.7. The laser apparatus of clause 1, wherein performing the monitoring of the performance parameter comprises performing a beam quality check on a beam of the laser apparatus.Confidential8. The laser apparatus of clause 7, wherein performing the beam quality check comprises measuring one of an energy, a center wavelength, a BQ sigma, a divergence, a beam uniformity, a spot size, a beam parameter product, or an M2factor of the beam.9. The laser apparatus of clause 1, wherein performing the monitoring of the performance parameter comprises performing an acoustic resonance check on a beam of the laser apparatus.10. The laser apparatus of clause 1, wherein performing the monitoring of the performance parameter comprises performing an efficiency check on a beam of the laser apparatus.11. The laser apparatus of clause 1 , wherein updating the target temperature comprises increasing the target temperature by a predetermined fixed amount that is independent of the value of the performance parameter.12. The laser apparatus of clause 1, wherein updating the target temperature comprises increasing the target temperature by an amount that depends on the value of the performance parameter.13. The laser apparatus of clause 1, wherein updating the target temperature comprises decreasing the target temperature by a predetermined fixed amount that is independent of the value of the performance parameter.14. The laser apparatus of clause 1, wherein updating the target temperature comprises decreasing the target temperature by an amount that depends on the value of the performance parameter.15. The laser apparatus of clause 1, the operations further comprising:performing an initial check of the laser apparatus, anddetermining whether to perform monitoring of performance parameter based on a result of the initial check.16. The laser apparatus of clause 15, wherein performing the initial check comprises performing an age check on the laser chamber.17. The laser apparatus of clause 16, wherein performing the age check comprises determining whether an age of the laser chamber is greater than a predetermined minimum age.18. The laser apparatus of clause 17, wherein the predetermined minimum age is based on a minimum pulse count of the laser chamber.19. The laser apparatus of clause 16, wherein performing the age check comprises determining whether an age of the laser chamber is less than a predetermined maximum age.20. The laser apparatus of clause 19, wherein the predetermined maximum age is based on a percentage of an expected lifetime of the laser chamber.21. The laser apparatus of clause 15, wherein performing the initial check comprises performing a data availability check on the laser chamber.Confidential22. The laser apparatus of clause 21, wherein performing the data availability check comprises determining whether a predetermined amount of data about the performance parameter has been collected.23. The laser apparatus of clause 22, wherein the predetermined amount of data is based on a predetermined pulse count of the laser chamber.24. The laser apparatus of clause 15, wherein performing the initial check comprises performing a temperature range check on the laser chamber.25. The laser apparatus of clause 24, wherein performing the temperature range check comprises determining whether a present temperature of the laser chamber is greater than a predetermined minimum temperature.26. The laser apparatus of clause 24, wherein performing the temperature range check comprises determining whether a present temperature of the laser chamber is less than a predetermined maximum temperature.27. The laser apparatus of clause 15, further comprising performing the initial check at predetermined intervals.28. The laser apparatus of clause 1, further comprising performing the monitoring over predetermined intervals.29. A non-transitory computer-readable medium that stores a set of instructions that is executable by at least one processor of an apparatus to cause the apparatus to perform operations comprising:operating a laser apparatus,operating a temperature control system to control a temperature of a gas in a laser chamber of the laser apparatus based on a target temperature of the gas;performing a monitoring of a performance parameter of the laser apparatus; and updating the target temperature based on a value of the performance parameter.30. The non-transitory computer-readable medium of clause 29, wherein operating the temperature control system comprises:operating a water distribution system to circulate cooling water in thermal contact with the gas; andoperating a flow control valve to adjust a flow rate of the cooling water to adjust a temperature of the gas and maintain the gas at the target temperature.31. The non-transitory computer-readable medium of clause 29, wherein performing the monitoring of the performance parameter is based on an output from a pulse energy meter.32. The non-transitory computer-readable medium of clause 29, wherein performing the monitoring of the performance parameter comprises performing a beam quality check on a beam of the laser apparatus.Confidential33. The non-transitory computer-readable medium of clause 32, wherein performing the beam quality check comprises measuring one of an energy, a center wavelength, a BQ sigma, a divergence, a beam uniformity, a spot size, a beam parameter product, or an M2factor of the beam.34. The non-transitory computer-readable medium of clause 29, wherein performing the monitoring of the performance parameter comprises performing an acoustic resonance check on a beam of the laser apparatus.35. The non-transitory computer-readable medium of clause 29, wherein performing the monitoring of the performance parameter comprises performing an efficiency check on a beam of the laser apparatus.36. The non-transitory computer-readable medium of clause 29, wherein updating the target temperature comprises increasing the target temperature by a predetermined fixed amount that is independent of the value of the performance parameter.37. The non-transitory computer-readable medium of clause 29, wherein updating the target temperature comprises increasing the target temperature by an amount that depends on the value of the performance parameter.38. The non-transitory computer-readable medium of clause 29, wherein updating the target temperature comprises decreasing the target temperature by a predetermined fixed amount that is independent of the value of the performance parameter.39. The non-transitory computer-readable medium of clause 29, wherein updating the target temperature comprises decreasing the target temperature by an amount that depends on the value of the performance parameter.40. The non-transitory computer-readable medium of clause 29, the operations further comprising:performing an initial check of the laser apparatus, anddetermining whether to perform monitoring of performance parameter based on a result of the initial check.41. The non-transitory computer-readable medium of clause 40, wherein performing the initial check comprises performing an age check on the laser chamber.42. The non-transitory computer-readable medium of clause 41, wherein performing the age check comprises determining whether an age of the laser chamber is greater than a predetermined minimum age.43. The non-transitory computer-readable medium of clause 42, wherein the predetermined minimum age is based on a minimum pulse count of the laser chamber.44. The non-transitory computer-readable medium of clause 41, wherein performing the age check comprises determining whether an age of the laser chamber is less than a predetermined maximum age.Confidential45. The non-transitory computer-readable medium of clause 44, wherein the predetermined maximum age is based on a percentage of an expected lifetime of the laser chamber.46. The non-transitory computer-readable medium of clause 40, wherein performing the initial check comprises performing a data availability check on the laser chamber.47. The non-transitory computer-readable medium of clause 46, wherein performing the data availability check comprises determining whether a predetermined amount of data about the performance parameter has been collected.48. The non-transitory computer-readable medium of clause 47, wherein the predetermined amount of data is based on a predetermined pulse count of the laser chamber.49. The non-transitory computer-readable medium of clause 40, wherein performing the initial check comprises performing a temperature range check on the laser chamber.50. The non-transitory computer-readable medium of clause 49, wherein performing the temperature range check comprises determining whether a present temperature of the laser chamber is greater than a predetermined minimum temperature.51. The non-transitory computer-readable medium of clause 49, wherein performing the temperature range check comprises determining whether a present temperature of the laser chamber is less than a predetermined maximum temperature.52. The non-transitory computer-readable medium of clause 40, wherein the set of instructions that is executable by the at least one processor of the apparatus cause the apparatus to further perform:performing the initial check at predetermined intervals.53. The non-transitory computer-readable medium of clause 52, wherein the set of instructions that is executable by the at least one processor of the apparatus cause the apparatus to further perform:performing the monitoring over predetermined intervals.54. A method, comprising:operating a laser apparatus,operating a temperature control system to control a temperature of a gas in a laser chamber of the laser apparatus based on a target temperature of the gas;performing a monitoring of a performance parameter of the laser apparatus; and updating the target temperature based on a value of the performance parameter.55. The method of clause 54, wherein operating the temperature control system comprises:operating a water distribution system to circulate cooling water in thermal contact with the gas; andoperating a flow control valve to adjust a flow rate of the cooling water to adjust a temperature of the gas and maintain the gas at the target temperature.Confidential56. The method of clause 54, wherein performing the monitoring of the performance parameter is based on an output from a pulse energy meter.57. The method of clause 54, wherein performing the monitoring of the performance parameter comprises performing a beam quality check on a beam of the laser apparatus.58. The method of clause 57, wherein performing the beam quality check comprises measuring one of an energy, a center wavelength, a BQ sigma, a divergence, a beam uniformity, a spot size, a beam parameter product, or an M2factor of the beam.59. The method of clause 54, wherein performing the monitoring of the performance parameter comprises performing an acoustic resonance check on a beam of the laser apparatus.60. The method of clause 54, wherein performing the monitoring of the performance parameter comprises performing an efficiency check on a beam of the laser apparatus.61. The method of clause 54, wherein updating the target temperature comprises increasing the target temperature by a predetermined fixed amount that is independent of the value of the performance parameter.62. The method of clause 54, wherein updating the target temperature comprises increasing the target temperature by an amount that depends on the value of the performance parameter.63. The method of clause 54, wherein updating the target temperature comprises decreasing the target temperature by a predetermined fixed amount that is independent of the value of the performance parameter.64. The method of clause 54, wherein updating the target temperature comprises decreasing the target temperature by an amount that depends on the value of the performance parameter.65. The method of clause 54, the operations further comprising:performing an initial check of the laser apparatus, anddetermining whether to perform monitoring of performance parameter based on a result of the initial check.66. The method of clause 65, wherein performing the initial check comprises performing an age check on the laser chamber.67. The method of clause 66, wherein performing the age check comprises determining whether an age of the laser chamber is greater than a predetermined minimum age.68. The method of clause 67, wherein the predetermined minimum age is based on a minimum pulse count of the laser chamber.69. The method of clause 66, wherein performing the age check comprises determining whether an age of the laser chamber is less than a predetermined maximum age.70. The method of clause 69, wherein the predetermined maximum age is based on a percentage of an expected lifetime of the laser chamber.Confidential71. The method of clause 65, wherein performing the initial check comprises performing a data availability check on the laser chamber.72. The method of clause 71, wherein performing the data availability check comprises determining whether a predetermined amount of data about the performance parameter has been collected.73. The method of clause 72, wherein the predetermined amount of data is based on a predetermined pulse count of the laser chamber.74. The method of clause 65, wherein performing the initial check comprises performing a temperature range check on the laser chamber.75. The method of clause 74, wherein performing the temperature range check comprises determining whether a present temperature of the laser chamber is greater than a predetermined minimum temperature.76. The method of clause 74, wherein performing the temperature range check comprises determining whether a present temperature of the laser chamber is less than a predetermined maximum temperature.77. The method of clause 65, further comprising:performing the initial check at predetermined intervals.78. The method of clause 77, further comprising:performing the monitoring over predetermined intervals.

[0061] Some embodiments of the present disclosure have been described with respect to DUV excimer laser systems, such as for use in photolithography illumination systems. However, the present disclosure is not limited to such systems. It should be understood that the above disclosed embodiments may be applicable to other laser systems, such as other non-DUV or non-lithography illumination systems, and that other classes of lasers are contemplated within the scope of the present disclosure.

[0062] Block diagrams in the figures may illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. In this regard, each block in a schematic diagram may represent certain arithmetical or logical operation processing that may be implemented using hardware such as an electronic circuit. Blocks may also represent a module, segment, or portion of code that comprises one or more executable instructions for implementing the specified logical functions. It should be understood that in some alternative implementations, functions indicated in a block may occur out of the order noted in the figures. For example, two blocks shown in succession may be executed or implemented substantially concurrently, or two blocks may sometimes be executed in reverse order, depending upon the functionality involved. Some blocks may also be omitted. It should also be understood that each block of the block diagrams, and combination of the blocks, may be implemented by special purpose hardware-based systems thatConfidentialperform the specified functions or acts, or by combinations of special purpose hardware and computer instructions.

[0063] It will be appreciated that the embodiments of the present disclosure are not limited to the exact construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes can be made without departing from the scope thereof. For example, a DUV laser system may be but one example of a laser system consistent with embodiments of the present disclosure.Confidential

Claims

CLAIMS1. A laser apparatus, comprising:a laser chamber comprising a gas;a temperature control system configured to control a temperature of the gas based on a target temperature of the gas; anda controller comprising one or more processors and configured to cause the laser apparatus to perform operations comprising:performing a monitoring of a performance parameter of the laser apparatus; and updating the target temperature based on a value of the performance parameter.

2. The laser apparatus of claim 1, wherein the temperature control system comprises: a water distribution system configured to circulate cooling water in thermal contact with the gas; anda flow control valve configured to adjust a flow rate of the cooling water to adjust a temperature of the gas and maintain the gas at the target temperature.

3. The laser apparatus of claim 1, further comprising:a pulse energy meter;wherein the controller is configured to perform the monitoring of the performance parameter based on an output from the pulse energy meter.

4. The laser apparatus of claim 3, further comprising:a combined autoshutter metrology module (CASMM);wherein the pulse energy meter is located in the CASMM.

5. The laser apparatus of claim 1, wherein performing the monitoring of the performance parameter comprises performing a beam quality check on a beam of the laser apparatus.

6. The laser apparatus of claim 1, wherein performing the monitoring of the performance parameter comprises performing an acoustic resonance check on a beam of the laser apparatus.

7. The laser apparatus of claim 1, wherein performing the monitoring of the performance parameter comprises performing an efficiency check on a beam of the laser apparatus.

8. The laser apparatus of claim 1, the operations further comprising:Confidentialperforming an initial check of the laser apparatus, anddetermining whether to perform monitoring of performance parameter based on a result of the initial check.

9. A non-transitory computer-readable medium that stores a set of instructions that is executable by at least one processor of an apparatus to cause the apparatus to perform operations comprising:operating a laser apparatus,operating a temperature control system to control a temperature of a gas in a laser chamber of the laser apparatus based on a target temperature of the gas;performing a monitoring of a performance parameter of the laser apparatus; and updating the target temperature based on a value of the performance parameter.

10. The non-transitory computer-readable medium of claim 9, wherein operating the temperature control system comprises:operating a water distribution system to circulate cooling water in thermal contact with the gas; andoperating a flow control valve to adjust a flow rate of the cooling water to adjust a temperature of the gas and maintain the gas at the target temperature.

11. The non-transitory computer-readable medium of claim 9, wherein performing the monitoring of the performance parameter is based on an output from a pulse energy meter.

12. The non-transitory computer-readable medium of claim 9, wherein performing the monitoring of the performance parameter comprises performing a beam quality check on a beam of the laser apparatus.

13. The non-transitory computer-readable medium of claim 9, wherein performing the monitoring of the performance parameter comprises performing an acoustic resonance check on a beam of the laser apparatus.

14. The non-transitory computer-readable medium of claim 9, wherein performing the monitoring of the performance parameter comprises performing an efficiency check on a beam of the laser apparatus.

15. A method, comprising:operating a laser apparatus,Confidentialoperating a temperature control system to control a temperature of a gas in a laser chamber of the laser apparatus based on a target temperature of the gas;performing a monitoring of a performance parameter of the laser apparatus; and updating the target temperature based on a value of the performance parameter.

16. The method of claim 15, wherein operating the temperature control system comprises:operating a water distribution system to circulate cooling water in thermal contact with the gas; andoperating a flow control valve to adjust a flow rate of the cooling water to adjust a temperature of the gas and maintain the gas at the target temperature.

17. The method of claim 15, wherein performing the monitoring of the performance parameter is based on an output from a pulse energy meter.

18. The method of claim 15, wherein performing the monitoring of the performance parameter comprises performing a beam quality check on a beam of the laser apparatus.

19. The method of claim 15, wherein performing the monitoring of the performance parameter comprises performing an acoustic resonance check on a beam of the laser apparatus.

20. The method of claim 15, wherein performing the monitoring of the performance parameter comprises performing an efficiency check on a beam of the laser apparatus.Confidential

Images