WO2024201181A1

WO2024201181A1 - Method and apparatus for replacing gas mixture in a gas discharge chamber

Info

Publication number: WO2024201181A1
Application number: PCT/IB2024/052131
Authority: WO
Inventors: Siyu CHEN; Spencer Ryan WILLIAMS
Original assignee: Cymer LLC
Current assignee: Cymer LLC
Priority date: 2023-03-24
Filing date: 2024-03-05
Publication date: 2024-10-03
Anticipated expiration: 2025-09-24
Also published as: KR20250160972A; EP4690393A1; CN120917634A; TW202509669A

Abstract

A method of replacing a gas mixture in a gas discharge chamber in a light source includes determining a performance of the light source and/or gas discharge chamber based on one or more light source and/or gas discharge chamber performance metrics, determining a next refill pressure based on the determined performance and a current operating pressure of the gas discharge chamber, removing the gas mixture from the gas discharge chamber; and filling the gas discharge chamber with a replacement gas mixture to the determined next refill pressure. An apparatus for replacing the gas mixture is also disclosed.

Description

METHOD AND APPARATUS FOR REPLACING GAS MIXTURE IN A GAS DISCHARGE CHAMBER

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Application No. 63/491,990, filed March 24, 2023, titled METHOD AND APPARATUS FOR REPLACING GAS MIXTURE IN A GAS DISCHARGE CHAMBER, which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

[0002] This disclosure relates to a method of and apparatus for replacing a gas mixture in a gas discharge chamber in a deep ultraviolet (DUV) light source such as a power ring amplifier gas discharge chamber in (DUV) light source.

BACKGROUND

[0003] One kind of gas discharge light source used in photolithography is termed an excimer light source or laser. Typically, an excimer laser uses a mixture of one or more noble gases, which can include argon, krypton, or xenon, and a reactive gas, which can include fluorine or chlorine. The excimer laser can create an excimer, a pseudo-molecule, under appropriate conditions of electrical simulation (energy supplied) and high pressure (of the gas mixture), the excimer only existing in an energized state. The excimer in an energized state gives rise to generation and amplification of light in the ultraviolet range. An excimer light source for photolithography typically includes a plurality of gas discharge chambers. When the excimer light source is performing, the excimer light source produces a deep ultraviolet (DUV) light beam. DUV light can include wavelengths from, for example, about 100 nanometers (nm) to about 400 nm.

[0004] The DUV light beam from the light source can be directed to a photolithography exposure apparatus, which is a machine that produces a desired pattern onto a target portion of a substrate such as a layer of photoresist on a semiconductor wafer. The DUV light beam interacts with a projection optical system, which projects the DUV light beam through a mask or other image forming apparatus onto the photoresist on the wafer. In this way, one or more layers of chip design can be patterned onto the photoresist and thence on or into the wafer or on or into layers built up on the wafer.

SUMMARY

[0005] In some general aspects, a process of replacing a gas mixture in a gas discharge chamber in a light source includes determining a performance of the light source and/or gas discharge chamber based on one or more light source and/or gas discharge chamber performance metrics; determining a next refill pressure based on the determined performance and a current operating pressure of the gas discharge chamber; removing the gas mixture from the gas discharge chamber; and filling the gas discharge chamber with a replacement gas mixture to the determined next refill pressure. Implementations can include one or more of the following.

[0006] The process can further include reducing a gas discharge chamber pressure from a previous refill pressure to the current operating pressure based on one or more performance metrics of the light source and/or the gas discharge chamber. The process can further include determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein when the determined performance indicates that the light source and/or the gas discharge chamber is stable then the margin value is a first value, and when the determined performance indicates that the light source and/or the gas discharge chamber is unstable then the margin value is a second value that is larger than the first value. The gas discharge chamber can be a power amplifier gas discharge chamber. [0007] The process can further include determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein determining the margin value includes comparing the one or more light source and/or gas discharge chamber performance metrics to respective limits; setting the margin value to a first value if any of the one or more light source and/or gas discharge chamber performance metrics is outside its respective limit or limits; and setting the margin value to a second value if each of the one or more light source and/or gas discharge chamber performance metrics is inside its respective limit or limits; wherein the second value is smaller than the first value.

[0008] The process can further include determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein the determined performance indicates a level of stability of the light source and/or the gas discharge chamber, and the determined margin value decreases as the indicated level of stability increases.

[0009] The process can further include determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein determining the margin value includes comparing the one or more light source and/or gas discharge chamber performance metrics to respective limits and setting the margin value to relatively higher values when the one or more light source and/or gas discharge chamber performance metrics are closer to exceeding, or exceed, their respective limits, and to relatively lower values when the one or more light source and/or gas discharge chamber performance metrics are further from exceeding their respective limits.

[0010] Determining the next refill pressure can include determining a margin value that is smaller when the determined performance indicates the light source is more stable and larger when the determined performance indicates that the light source is less stable and setting the next refill pressure to at least the current operating pressure plus the margin value. Determining the performance of the light source and/or gas discharge chamber can include comparing one or more light source and/or gas discharge chamber performance metrics to respective limits. Determining the performance of the light source and/or gas discharge chamber can include collecting the one or more light source and/or gas discharge chamber performance metrics during a standard operation of the light source. [0011] The gas discharge chamber can be a power ring amplifier gas discharge chamber.

[0012] In other general aspects, a gas mixture replacement apparatus associated with a gas discharge chamber within a light source is provided, the apparatus including (1) a monitoring and control system connected to the light source and configured to (a) determine a current operating pressure value of the gas discharge chamber; (b) determine one or more performance metrics of the light source and/or the gas discharge chamber; and (c) determine a next refill pressure value of the gas discharge chamber based on the one or more performance metrics and the current operating pressure value of the gas discharge chamber; (2) a gas mixture removal system configured to remove the gas mixture from the gas discharge chamber; and (3) a gas mixture resupply system connected to the monitoring and control system and configured to fill the gas discharge chamber with a replacement gas mixture to the determined refill pressure value. Implementations can include one or more of the following.

[0013] The gas discharge chamber can be a power amplifier gas discharge chamber. The power amplifier gas discharge chamber can be a power ring amplifier gas discharge chamber. The light source can be a multi-stage light source. The light source can be a multi-stage light source and one of the stages of the multi-stage light source can be a power amplifier stage with the power amplifier stage including the gas discharge chamber and a circulating and looped optical path through the gas discharge chamber. The gas mixture can include argon fluoride (ArF).

[0014] The monitoring and control system can be further configured to determine a margin value that increases the next refill pressure, relative to the current operating pressure, by comparing the one or more performance metrics of the light source and/or gas discharge chamber to respective limits and setting the margin value to a first value if any of the one or more light source and/or gas discharge chamber performance metrics is outside its respective limit or limits and setting the margin value to a second value if each of the one or more light source and/or gas discharge chamber performance metrics is inside its respective limit or limits, wherein the second value is smaller than the first value. [0015] The monitoring and control system can be further configured to determine a margin value that increases the next refill pressure, relative to the current operating pressure, by comparing the one or more light source and/or gas discharge chamber performance metrics to respective limits and setting the margin value to relatively higher values when the one or more light source and/or gas discharge chamber performance metrics are closer to exceeding, or exceed, their respective limits, and to relatively lower values when the one or more light source and/or gas discharge chamber performance metrics are further from exceeding their respective limits.

[0016] 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. DRAWING DESCRIPTION

[0017] FIG. 1 is a block diagram of a gas control apparatus and associated gas discharge chamber and light source that supplies an amplified light beam to an output apparatus;

[0018] FIG. 2 is a flow diagram of a method of the present disclosure;

[0019] FIG. 2 A is a flow diagram of method that can be used in the method of FIG. 2;

[0020] FIG. 2B is a flow diagram of method that can be used in the method of FIG. 2;

[0021] FIG. 3 is a block diagram of an implementation of the output apparatus of FIG. 1 in which the output apparatus is a photolithography exposure apparatus;

[0022] FIG. 4 is a block diagram of an implementation of the gas control apparatus of FIG. 1 and associated gas discharge chamber and light source in which a dual-stage light source is shown;

[0023] FIG. 5 is graph showing a trace representing pressure of a gas mixture in the gas discharge chamber 150 as a function of time illustrating aspects of the present disclosure;

[0024] FIG. 6 is a block diagram showing an aspect of a method of the present disclosure; and [0025] FIG. 7 is a block diagram showing another aspect of a method of the present disclosure.

DETAIEED DESCRIPTION

[0026] Referring to FIG. 1, a gas control apparatus 100 is associated with a gas discharge chamber 150 of a light source 160. The light source 160 is configured as part of an optical system (including optical feedback not shown in FIG. 1) that supplies an amplified light beam 165 (produced at least in part from an output light beam 153 of the gas discharge chamber 150) to an output apparatus 180. The output apparatus 180 can be, for example, a photolithography exposure apparatus that patterns microelectronic features on a substrate such as a wafer. The gas discharge chamber 150 can be configured as part of a gas discharge stage 155, which can be a power amplifier or power amplifier stage, and the light source 160 can contain one or more additional stages such as a master oscillator (MO) stage (not shown in FIG. 1, see FIG. 4 described below).

[0027] The gas control apparatus 100 includes a monitoring system 140, a gas supply system 170, and a control system 105. The control system 105 includes a gas control module 110 that can be configured to a perform gas filling process, a gas replacement process, and a pressure adjustment processes on the gas discharge chamber 150. The gas filling process can be an initial filling of the gas discharge chamber 150 with a gas mixture 151 to prepare for an initial operation or an initial testing of the gas discharge chamber 150 and/or of the light source 160. The gas replacement process can be performed to replace the gas mixture 151 in the gas discharge chamber 150 with a new (fresh) replacement gas mixture 151 after the monitoring system 140 and/or the control system 105 determines the need for a gas replacement to restore the operating performance of the gas discharge chamber 150 and/or the light source 160 to a standard (or to an improved) operating performance. The pressure adjustment process is performed after either the gas filling process or the gas replacement process to optimize and/or to restore the performance of the gas discharge chamber 150 and/or of the light source 160.

[0028] In a gas replacement as understood herein, for example, all or essentially all of a gas mixture 151 within the gas discharge chamber 150 is replaced, by, for example, first emptying the gas discharge chamber 150 via a gas mixture removal system 114, for example, by bleeding an old gas mixture 151 out to a gas dump (not shown) or even evacuating the chamber 150 with a vacuum pump (not shown) or purging with a purge gas (not shown) or combination thereof, and then refilling the gas discharge chamber 150 with a fresh gas mixture 151 from the gas supply system 170.

[0029] The pressure adjustment process is performed to optimize gas pressure within the gas discharge chamber 150 in order to establish standard operation after the initial fill of the gas mixture or to return to or re-establish conditions for standard operation after the replacement of the gas mixture. During the standard mode of operation of the gas discharge chamber 150 which follows the pressure adjustment process, the light beam 165 is produced in accordance with requirements of output apparatus 180. In various implementations, the light beam 165 can be produced in accordance with instructions from or under the control of the output apparatus 180.

[0030] During the pressure adjustment process, after the gas discharge chamber 150 has been supplied with an initial or a fresh replacement gas mixture 151, the gas control module 110 signals an energy source actuator 154 to supply energy to an energy source 152 of the gas discharge chamber 150 to thereby produce a discharge or a light beam (the output light beam) 153 from the gas discharge chamber 150. The discharge or light beam 153 can correspond to the amplified light beam 165 or the amplified light beam 165 can be produced from the discharge or light beam 153 prior to exiting the light source 160. Then, the gas control module 110 analyzes the performance of the gas discharge chamber 150 and/or the light source 160 against a set of performance metrics and thresholds or limits that are specific to the pressure adjustment process. The gas control module 110 can perform this analysis by accessing performance parameters that are tracked or monitored by the monitoring system 140. For example, performance parameters that can be monitored include, for instance, a variation in the energy of the light beam 153 output by the gas discharge chamber 150 and/or the light source 160, a high voltage setting, a wavelength variation of the light beam 153 output from the gas discharge chamber 150 and/or light source 160, and a wavelength or bandwidth of the light beam 153 output from the gas discharge chamber 150 and/or the light source 160.

[0031] If the gas control module 110 determines that the discharge chamber 150 and/or the light source 160 is not performing within the performance thresholds that are specific to the pressure adjustment process, then the gas control module 110 can signal the gas supply system 170 to iteratively bleed the (fresh) gas mixture 151 from the gas discharge chamber 150 (or multiple gas discharge chambers within the light source 160, if multiple chambers are undergoing a pressure adjustment process) until one or more conditions are met. For example, the iterative pressure reduction can continue until one or more performance metrics desirable for standard operation are met, such as performance metrics for power output, wavelength, wavelength bandwidth and the like, or until one or more thresholds or limits for the start of standard operation, such as a minimum pressure, or a maximum voltage, or the like, are reached. These thresholds or limits can sometimes be referred to as recovery settings or gas recovery settings or limits. Once the one or more conditions (of either type) are met or reached, standard operation of the gas discharge chamber 150 and the light source 160 can begin, or can begin again, with the light source 160 supplying the amplified light beam 165 to the output apparatus 180.

[0032] In prior gas control methods and apparatuses for gas discharge chambers such as gas discharge chamber 150, especially in the case that the gas discharge chamber 150 is a power amplifier gas discharge chamber, when the gas mixture 151 is initially supplied into the gas discharge chamber 150 or is replaced, the fresh gas mixture that is supplied to the gas discharge chamber 150 is supplied up to a pre-specified gas mixture initial refill pressure or a pre-specified replacement refill pressure, such as for instance 300 kilopascals (kPa) or more, to allow for a relatively wide (downward) range of pressure adjustment during the pressure adjustment process. The pressure adjustment process, once complete, results in an operating pressure (which may be referred to as a “current operating pressure”) in the gas discharge chamber 150 that is set or optimized, by the pressure adjustment process, for standard operation of the light source. The current operating pressure thus set can fall within a relatively wide range, such as from 220 to 300 kPa, hence the need, in this example, for a refill pressure of at least 300 kPa. However, such a relatively high refill pressure is not required in every instance. Although it may be necessary at the initial filling and at some instances of refilling to fill to such a relatively high pressure, under appropriate conditions, lower refill pressures can be used as explained below. The use of lower refill pressures under appropriate conditions during gas mixture replacement results in resource and cost savings due to a reduction in the amount of gas required for gas mixture replacement.

[0033] According to aspects of the present disclosure and with reference to FIG. 2, a procedure 220 of replacing a gas mixture (such as gas mixture 151 of FIG. 1) in a gas discharge chamber (such as gas discharge chamber 150 of FIG. 1) in a light source (such as light source 160 of FIG. 1) is diagramed and discussed with additional reference to FIG. 1. As shown in FIG. 2, the procedure 220 includes determining a performance of the light source 160 and/or the gas discharge chamber 150 based on one or more light source and/or gas discharge chamber performance metrics (222); determining a next refill pressure based on the determined performance and a current operating pressure of the gas discharge chamber 150 (223); removing the gas mixture 151 from the gas discharge chamber 150 (224); and filling the gas discharge chamber 150 with a replacement gas mixture to the determined next refill pressure (225). In implementations, gas discharge chamber and/or light source performance metrics can be measured by the monitoring system 140 and can include metrics such as wavelength, wavelength variability, bandwidth, power, power variability, and so forth of the light beam 153 produced by the gas discharge chamber 150 and/or the light beam 165 produced by the light source 160, as well as an operating voltage and other operating conditions of the gas discharge chamber 150. Implementations can further include one or more of the following.

[0034] The procedure 220 can include determining the current operating pressure by reducing from a previous refill pressure based on one or more performance metrics of the light source 160 and/or the gas discharge chamber 150 specific to the pressure adjustment process as discussed above with respect to FIG. 1.

[0035] With respect to the procedure of FIG. 2, at some point before removing the gas mixture 151 from the gas discharge chamber 150 (224), a signal is received that a gas mixture replacement is needed. The need for a refill can depend on several complex and often unpredictable variables, including the light source firing pattern and energy, the age of light source modules, and other variables and parameters that will be familiar to those of skill in the art. If desired, refills can be done on a regular schedule, which ensures that the light source operation will never suffer an unanticipated interruption due to the light source reaching its operational limit. In implementations, the relative timing of the receipt of a signal that a refill or gas replacement is needed can be at various positions before the start of removing the gas mixture, including at such relative timing positions as positions A, B, and C indicated in FIG. 2.

[0036] With reference to FIG. 2A, a procedure 223a can be performed for determining the next refill pressure based on determined performance and current operating pressure (223 of FIG. 2). The procedure 223a includes determining a margin value that increases the next refill pressure relative to the current operating pressure (226a and 216a). When the determined performance indicates that the light source is stable (the “yes” branch of 227), the margin value is set to a first value (228a), and when the determined performance indicates that the light source is unstable (the “no” branch of 227), the margin value is set to a second value that is larger than the first value (229a). The gas discharge chamber 150 of the procedure 223a can be a power amplifier gas discharge chamber (that is, a gas discharge chamber of a power amplifier of a light source, including a gas discharge chamber of a power ring amplifier).

[0037] With reference to FIG. 2B, in other implementations, a procedure 223b can be performed for determining the next refill pressure based on determined performance and current operating pressure (223 of FIG. 2). The procedure 223b includes determining a margin value that increases the next refill pressure relative to the current operating pressure (226b and 216b) by comparing the one or more performance metrics to respective limits (217) and setting the margin value to a first value (229a) if any of the one or more performance metrics is outside its respective limit or limits (“no” branch of 218) and setting the margin value to a second value greater than the first value (229b) if none of the one or more performance metrics is outside of its respective limit or limits (“yes” branch of 218).

[0038] In still further implementations, procedure 220 can also include determining a margin value that increases the next refill pressure relative to the current operating pressure wherein (1) the determined performance indicates a level of stability of the light source 160 and/or of the gas discharge chamber 150 and (2) the determined margin value decreases as the indicated level of stability increases. The procedure 220 can also include determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein determining the margin value includes (1) comparing the one or more performance metrics to respective limits and (2) setting the margin value to a value that is relatively lower when the one or more performance metrics are relatively further from exceeding their respective limits, and relatively higher when the one or more performance metrics are relatively closer to exceeding, or are exceeding, their respective limits. The procedure 220can also include determining a margin value that is smaller when the determined performance indicates the light source 160 and/or the gas discharge chamber 150 is more stable and larger when the determined performance indicates that the light source 160 and/or the gas discharge chamber 150 is less stable, and setting the next refill pressure to current operating pressure plus the margin value, or to at least to the current operating pressure plus the margin value. Determining the performance of the light source 160 and/or the discharge chamber 150 can include collecting the one or more performance metrics during a standard operation of the light source 160. The one or more performance metrics can also be compared to their respective targets during standard operation of the light source 160. The next refill pressure can also be continually or even virtually continuously determined and re-determined during standard operation of the light source 160, if desired. As mentioned above, the gas discharge chamber 150 of the procedure 220 can be a power ring amplifier gas discharge chamber.

[0039] Referring again to FIG. 1, the gas control apparatus 100 includes a performance monitoring module 115 that can be configured to continually analyze one or more performance parameters of the light source 160 and/or the gas discharge chamber 150 during a standard operation of the light source 160. The performance analysis can be performed by a performance analyzer PA. As mentioned, the performance monitoring module 115, such as via the performance analyzer PA, can continually update the margin value based on this analysis and store the updated margin value within the control system 105, such as in a memory M. In implementations, the performance monitoring module 115 can continually update the next refill pressure itself and store it, such as in memory M. The performance monitoring module 115 can continually record performance data, such as in memory M, and update the margin value (and the next refill pressure) only whenever a gas mixture replacement is called for. Regardless of the particular implementation, the next time the gas control module 110 performs the gas mixture replacement process, the margin value is available to or stored in the control system 105 to use in setting the next refill pressure relative to the current operating pressure, or the next refill pressure value is itself already available to or stored in the control system 105. Thus, no manual adjustment of the margin value or the associated next refill pressure is required.

[0040] In implementations the memory M can be located other than within the gas control module 110, such as within the control system 105 generally. The memory M can be accessible to one or more of the modules 110, 115 within the control system 105, and to other modules not shown. The memory M can be read-only memory and/or random-access memory and can provide a storage device suitable for tangibly embodying computer program instructions and data. The memory M can be configured to store information that is output from each of the modules and/or information received from the monitoring system 140 for use by various modules of the control system 105 during operation of the control system 105.

[0041] In implementations, the control system 105 also includes one or more input and/or output devices 109 (such as a keyboard, touch-enabled devices, audio input devices as input and audio or video for output), and one or more processors 108. Communication between any of the modules 110, 115, and others and the memory M can be by a direct or physical connection (for example, wired) or by a wireless connection.

[0042] Although the control system 105 is represented as a box in which all of the components appear to be co-located, it is possible for the control system 105 to be made up of components (such as the modules 110, 115, and others not shown) that are physically remote from each other. Each of the modules 110, 115, and others not shown can be a dedicated processing system for receiving data and analyzing data, or one or more of the modules can be combined into a single processing system. Each of the modules can include or have access to one or more programmable processors 108 and can each execute a program of instructions to perform desired functions by operating on input data and generating appropriate output. The modules 110, 115, and others can be implemented in any of digital electronic circuitry, computer hardware, firmware, or software.

[0043] Referring to FIG. 3, in some implementations, the output apparatus 180 is a photolithography exposure apparatus 380. The exposure apparatus 380 includes an optical arrangement that includes an illuminator system 381 having, for example, one or more condenser lenses, a mask, and an objective arrangement through which the light beam 165 is directed on its way to a substrate (wafer) 382. The mask may be movable along one or more directions, such as along an axis of the light beam 165 or in a plane that is perpendicular to the axis of the light beam 165. The objective arrangement includes, for example, a projection lens, and enables the image to transfer from the mask to a photoresist on the wafer 382. The illuminator system 381 adjusts the range of angles for the light beam 165 impinging on the mask. The exposure apparatus 380 can include, among other features, a lithography controller 383 that controls, among other things, how layers are patterned on the wafer 382. The lithography controller 383 can be in communication with the control system 105.

[0044] As mentioned above, the light source 160 can be a multi-stage system. In the implementation shown in FIG. 4, the light source 160 is a two-stage light source 460. The light source 460 includes a master oscillator 461 A as its first stage and a power amplifier 46 IB as its second stage. The master oscillator 461 A includes a master oscillator gas discharge chamber 450A and the power amplifier 46 IB includes a power amplifier gas discharge chamber 450B. The master oscillator gas discharge chamber 450A includes as the energy source 452A two elongated electrodes that provide a source of pulsed energy to a gas mixture 451 A within the chamber 450A. The power amplifier gas discharge chamber 450B includes as the energy source 452B two elongated electrodes that provide a source of pulsed energy to a gas mixture 45 IB within the chamber 450B.

[0045] The master oscillator 461 A provides a pulsed amplified light beam (called a seed light beam) 462 to the power amplifier 46 IB. The master oscillator gas discharge chamber 450A houses the gas mixture 451 A that includes a gain medium in which amplification occurs and the master oscillator 461 A includes an optical feedback mechanism such as an optical resonator. The optical resonator is formed between a spectral optical system 463A on one side of the master oscillator gas discharge chamber 450A and an output coupler 464A on a second side of the master oscillator gas discharge chamber 450A. The power amplifier gas discharge chamber 450B houses the gas mixture 45 IB that includes a gain medium in which amplification occurs when seeded with the seed light beam 462 from the master oscillator 461 A. If the power amplifier 46 IB is designed as a regenerative ring resonator then it is described as a power ring amplifier, and in this case, enough optical feedback can be provided from the ring design. The power amplifier 46 IB can also include a beam return (such as a reflector) 463B that returns (via reflection, for example) the light beam back into the power amplifier gas discharge chamber 452B to form a circulating and looped path (in which the input into the ring amplifier intersects the output out of the ring amplifier) and also an output coupler 464B for inputting the seed light beam 462 and outputting an amplified light beam 465. The light beam 153 can correspond to the seed light beam 462 or the amplified light beam 465.

[0046] The gas mixture (for example, gas mixture 451 A, 45 IB) used in the respective discharge chamber 450A, 450B can be a combination of suitable gases for producing the amplified light beam around the required wavelengths, bandwidth, and energy. For example, the gas mixture 451A, 451B can include argon fluoride (ArF), which emits light at a wavelength of about 193 nm, or krypton fluoride (KrF), which emits light at a wavelength of about 248 nm.

[0047] FIG. 5 shows a graph 590 of arbitrary scale and proportions showing a solid line trace 591 of pressure P of a gas mixture 151 in the gas discharge chamber 150 as a function of time t. The trace 591 is shown through one cycle 592 (the time extent of which is represented by the bracket labeled 592). The cycle 592 extends from completion of an initial gas mixture fill 593 or the immediately previous gas mixture replacement 593, represented by the vertical dashed line 593 marking the time of completion, to completion of the next gas mixture replacement 594, represented by vertical dashed line 594 marking the time of completion (prior to the next pressure adjustment process, not shown). [0048] With continued reference to FIG. 5, after completion of an initial gas mixture fill or the fill for the immediately previous gas mixture replacement 593, a pressure adjustment process 595 (represented by incremental reductions in pressure in trace 591 and indicated by the bracket labeled 595) incrementally reduces the pressure in the gas discharge chamber 150 until a desired performance level is achieved. When the desired performance level is achieved, the pressure adjustment process stops at a current operating pressure 596. The gas discharge chamber 151 then enters a period of standard operation 597. [0049] During normal operation 597, the current operating pressure 596 generally changes only very slightly, and the performance of the gas discharge chamber 150 and/or the light source 160 of which it is a part (see FIGS. 1 and 4) is monitored. Additionally, during normal operation 597, performance metrics are detected and/or calculated and recorded or otherwise stored, and the performance of the gas discharge chamber 150 and/or the light source 160 is evaluated or assessed. As noted above, the margin value MV determined by the performance of the gas discharge chamber 150 and/or the light source 160 — and optionally even the next refill pressure — can also be continually or even essentially continuously determined or calculated during the period of normal operation 597.

[0050] At the end of the period of normal operation 597, when a gas mixture replacement is signaled or otherwise called for, the gas mixture 151 in the gas discharge chamber 150 is emptied and/or purged, represented by the decreasing pressure 598. A fresh gas mixture is then flowed into the gas discharge chamber, represented by the increasing pressure 599a or 599b, up to a next refill pressure NRP determined by the current operating pressure 596 plus a margin value MV. As described above, the margin value MV is determined by the evaluation of the performance during the period of normal operation 597 of the gas discharge chamber 150 and/or the light source 160.

[0051] In implementations, the evaluation can be based on the entire period of normal operation 597, or on only a period of time near the end of the period of normal operation 597, or on a weighted evaluation placing greater or less weight on the later time of the period of operation 597. In implementations, trends and/or variability throughout or at any point in the period of normal operation 597 may also be used in the evaluation metric. If the light source 160 and/or the discharge chamber 150 is evaluated to be (or to have been) relatively more stable during standard operation, a relatively more aggressive gas savings is achieved during the gas mixture replacement process by setting the margin value MV as a relatively smaller margin value MVa, which, added to the current operating pressure 596, determines a relatively lower next refill pressure value NRPa for the next gas mixture replacement. At least the relatively lower next refill pressure value NRPa is less than 300 kPa, or less than an initial fill pressure of the discharge chamber 150, and results in gas savings compared to filling to the initial fill pressure. If the light source operation is evaluated to be relatively less stable, a relatively less aggressive (or more conservative) gas savings is achieved during the gas mixture replacement process by setting a relatively larger margin value MVb, which, added to the current operating pressure 596, determines a relatively higher next refill pressure value NRPb for the next gas mixture replacement. In implementations, the relatively higher next refill pressure is also less than 300kPa, or less than an initial fill pressure of the discharge chamber 150, and results in gas savings compared to the initial fill pressure, just not as much savings as in the case of refill pressure NRPa. [0052] The relatively larger margin value MVb and the associated relatively higher next refill pressure value NRPb provide a larger range of pressure, namely a larger operating window, for the next-following pressure adjustment process (not shown) to find a next-following current operating pressure (not shown) according to recovery settings or gas recovery settings or limits for a next succeeding period of normal operation (not shown). It should be noted, as mentioned above, that graph 590 is illustrative only and not quantitative, and is of essentially arbitrary scale and proportions. (For instance, the increasing pressure represented at 599a and 599b of the trace 591 need not have different slopes — the separation of the lines shown at 599a and 599b is used to allow for better illustration of the principles of this disclosure. Similarly, in practice, changes in pressure over time during gas mixture replacement are not everywhere linear.)

[0053] As described above, the determination of the margin value MV may have an essentially binary outcome or a more continuous outcome. This is illustrated in FIGS. 6 and 7. With reference to FIG. 6, a performance analyzer 630 (such as performance analyzer PA within the gas controller 110 of FIG.

1) receives a signal 631 to replace the gas mixture 151 of the gas discharge chamber 150, as well as one or more performance metrics 632 of the gas discharge chamber 150 and/or the light source 160. If the performance as analyzed is relatively low, the performance analyzer PA triggers a conservative gas saving mode 633 (the upper alternative) in which the next refill pressure is set (634) to the current operating pressure plus a relatively larger (a conservative) margin value. If the performance as analyzed is relatively high, the performance analyzer PA triggers an aggressive gas saving mode 635 (the lower alternative) in which the next refill pressure is set (636) to the current operating pressure plus a relatively smaller (an aggressive) margin value to realize greater gas savings in the next gas replacement.

[0054] With reference to FIG. 7, a performance analyzer 730 (such as performance analyzer PA within the gas controller 110 of FIG. 1) receives a signal 731 to replace the gas mixture 151 of the gas discharge chamber 150, as well as one or more performance metrics 732 of the gas discharge chamber 150 and/or the light source 160. The margin value is set (737) such that higher the performance, as analyzed, the lower (more aggressive) the margin value is. The next refill pressure is set (738) based on the current operating pressure and the margin value so as to realize greater gas savings during the next gas mixture replacement when the performance of the gas discharge chamber 150 and/or the light source 160 is more stable.

[0055] The implementations of the invention can be further described in the following numbered clauses:

1. A method of replacing a gas mixture in a gas discharge chamber in a light source, the method comprising: determining a performance of the light source and/or gas discharge chamber based on one or more light source and/or gas discharge chamber performance metrics; determining a next refill pressure based on the determined performance and a current operating pressure of the gas discharge chamber; removing the gas mixture from the gas discharge chamber; and filling the gas discharge chamber with a replacement gas mixture to the determined next refill pressure.

2. The method as in clause 1, further comprising reducing a gas discharge chamber pressure from a previous refill pressure to the current operating pressure based on one or more performance metrics of the light source and/or the gas discharge chamber. 3. The method as in clause 1, further comprising determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein when the determined performance indicates that the light source and/or the gas discharge chamber is stable then the margin value is a first value, and when the determined performance indicates that the light source and/or the gas discharge chamber is unstable then the margin value is a second value that is larger than the first value.

4. The method as in clause 3, wherein the gas discharge chamber is a power amplifier gas discharge chamber.

5. The method as in clause 1, further comprising determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein determining the margin value comprises: comparing the one or more light source and/or gas discharge chamber performance metrics to respective limits; setting the margin value to a first value if any of the one or more light source and/or gas discharge chamber performance metrics is outside its respective limit or limits; and setting the margin value to a second value if each of the one or more light source and/or gas discharge chamber performance metrics is inside its respective limit or limits; wherein the second value is smaller than the first value.

6. The method as in clause 1, further comprising determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein the determined performance indicates a level of stability of the light source and/or the gas discharge chamber, and the determined margin value decreases as the indicated level of stability increases.

7. The method as in clause 6, wherein the gas discharge chamber is a power amplifier gas discharge chamber.

8. The method as in clause 1, further comprising determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein determining the margin value comprises: comparing the one or more light source and/or gas discharge chamber performance metrics to respective limits; and setting the margin value to relatively higher values when the one or more light source and/or gas discharge chamber performance metrics are closer to exceeding, or exceed, their respective limits, and to relatively lower values when the one or more light source and/or gas discharge chamber performance metrics are relatively further from exceeding their respective limits.

9. The method as in clause 1, wherein determining the next refill pressure comprises: determining a margin value that is smaller when the determined performance indicates the light source is more stable and larger when the determined performance indicates that the light source is less stable; and setting the next refill pressure to at least the current operating pressure plus the margin value.

10. The method as in clause 1 wherein determining the next refill pressure comprises: determining a margin value that is smaller when the determined performance indicates the light source is more stable and larger when the determined performance indicates that the light source is less stable; and setting the next refill pressure to the current operating pressure plus the margin value. 11. The method as in clause 1 , wherein determining the performance of the light source and/or gas discharge chamber comprises comparing one or more light source and/or gas discharge chamber performance metrics to respective limits.

12. The method as in clause 1, wherein determining the performance of the light source and/or gas discharge chamber comprises collecting the one or more light source and/or gas discharge chamber performance metrics during a standard operation of the light source.

13. The method as in clause 1, wherein the gas discharge chamber is a power ring amplifier gas discharge chamber.

14. A gas mixture replacement apparatus associated with a gas discharge chamber within a light source, the apparatus comprising: a monitoring and control system connected to the light source and configured to determine a current operating pressure value of the gas discharge chamber; determine one or more performance metrics of the light source and/or the gas discharge chamber; and determine a next refill pressure value of the gas discharge chamber based on the one or more performance metrics and the current operating pressure value of the gas discharge chamber; a gas mixture removal system configured to remove the gas mixture from the gas discharge chamber; and a gas mixture resupply system connected to the monitoring and control system and configured to fill the gas discharge chamber with a replacement gas mixture to the determined refill pressure value.

15. The apparatus as in clause 14, wherein the gas discharge chamber is a power amplifier gas discharge chamber.

16. The apparatus as in clause 15, wherein the power amplifier gas discharge chamber is a power ring amplifier gas discharge chamber.

17. The apparatus as in clause 15, wherein the light source is a multi-stage light source.

18. The apparatus as in clause 15, wherein the light source is a multi-stage light source and one of the stages of the multi-stage light source is a power amplifier stage, the power amplifier stage including the gas discharge chamber and a circulating and looped optical path through the gas discharge chamber, and wherein the gas mixture comprises argon fluoride (ArF).

19. The apparatus as in clause 15, wherein the monitoring and control system is further configured to determine a margin value, that increases the next refill pressure relative to the current operating pressure, by comparing the one or more performance metrics of the light source and/or gas discharge chamber to respective limits and setting the margin value to a first value if any of the one or more light source and/or gas discharge chamber performance metrics is outside its respective limit or limits and setting the margin value to a second value if each of the one or more light source and/or gas discharge chamber performance metrics is inside its respective limit or limits, wherein the second value is smaller than the first value.

20. The apparatus as in clause 15, wherein the monitoring and control system is further configured to determine a margin value that increases the next refill pressure, relative to the current operating pressure, by comparing the one or more light source and/or gas discharge chamber performance metrics to respective limits and setting the margin value to relatively higher values when the one or more light source and/or gas discharge chamber performance metrics are closer to exceeding, or exceed, their respective limits, and to relatively lower values as the one or more light source and/or gas discharge chamber performance metrics are further from exceeding their respective limits. [0056] The above-described implementations and other implementations are within the scope of the following claims.

Claims

2. The method as in claim 1, further comprising reducing a gas discharge chamber pressure from a previous refill pressure to the current operating pressure based on one or more performance metrics of the light source and/or the gas discharge chamber.

3. The method as in claim 1, further comprising determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein when the determined performance indicates that the light source and/or the gas discharge chamber is stable then the margin value is a first value, and when the determined performance indicates that the light source and/or the gas discharge chamber is unstable then the margin value is a second value that is larger than the first value.

4. The method as in claim 3, wherein the gas discharge chamber is a power amplifier gas discharge chamber.

5. The method as in claim 1, further comprising determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein determining the margin value comprises: comparing the one or more light source and/or gas discharge chamber performance metrics to respective limits; setting the margin value to a first value if any of the one or more light source and/or gas discharge chamber performance metrics is outside its respective limit or limits; and setting the margin value to a second value if each of the one or more light source and/or gas discharge chamber performance metrics is inside its respective limit or limits; wherein the second value is smaller than the first value.

6. The method as in claim 1, further comprising determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein the determined performance indicates a level of stability of the light source and/or the gas discharge chamber, and the determined margin value decreases as the indicated level of stability increases.

7. The method as in claim 6, wherein the gas discharge chamber is a power amplifier gas discharge chamber.

8. The method as in claim 1, further comprising determining a margin value that increases the next refill pressure relative to the current operating pressure, wherein determining the margin value comprises: comparing the one or more light source and/or gas discharge chamber performance metrics to respective limits; and setting the margin value to relatively higher values when the one or more light source and/or gas discharge chamber performance metrics are closer to exceeding, or exceed, their respective limits, and to relatively lower values when the one or more light source and/or gas discharge chamber performance metrics are further from exceeding their respective limits.

9. The method as in claim 1, wherein determining the next refill pressure comprises: determining a margin value that is smaller when the determined performance indicates the light source is more stable and larger when the determined performance indicates that the light source is less stable; and setting the next refill pressure to at least the current operating pressure plus the margin value.

10. The method as in claim 1 wherein determining the next refill pressure comprises: determining a margin value that is smaller when the determined performance indicates the light source is more stable and larger when the determined performance indicates that the light source is less stable; and setting the next refill pressure to the current operating pressure plus the margin value.

11. The method as in claim 1 , wherein determining the performance of the light source and/or gas discharge chamber comprises comparing one or more light source and/or gas discharge chamber performance metrics to respective limits.

12. The method as in claim 1, wherein determining the performance of the light source and/or gas discharge chamber comprises collecting the one or more light source and/or gas discharge chamber performance metrics during a standard operation of the light source.

13. The method as in claim 1, wherein the gas discharge chamber is a power ring amplifier gas discharge chamber.

15. The apparatus as in claim 14, wherein the gas discharge chamber is a power amplifier gas discharge chamber.

16. The apparatus as in claim 15, wherein the power amplifier gas discharge chamber is a power ring amplifier gas discharge chamber.

17. The apparatus as in claim 15, wherein the light source is a multi-stage light source.

18. The apparatus as in claim 15, wherein the light source is a multi-stage light source and one of the stages of the multi-stage light source is a power amplifier stage, the power amplifier stage including the gas discharge chamber and a circulating and looped optical path through the gas discharge chamber, and wherein the gas mixture comprises argon fluoride (ArF).

19. The apparatus as in claim 15, wherein the monitoring and control system is further configured to determine a margin value that increases the next refill pressure relative to the current operating pressure by comparing the one or more performance metrics of the light source and/or gas discharge chamber to respective limits and setting the margin value to a first value if any of the one or more light source and/or gas discharge chamber performance metrics is outside its respective limit or limits and setting the margin value to a second value if each of the one or more light source and/or gas discharge chamber performance metrics is inside its respective limit or limits, wherein the second value is smaller than the first value.

20. The apparatus as in claim 15, wherein the monitoring and control system is further configured to determine a margin value that increases the next refill pressure, relative to the current operating pressure, by comparing the one or more light source and/or gas discharge chamber performance metrics to respective limits and setting the margin value to relatively higher values when the one or more light source and/or gas discharge chamber performance metrics are closer to exceeding, or exceed, their respective limits, and to relatively lower values when the one or more light source and/or gas discharge chamber performance metrics are further from exceeding their respective limits.