DUV light source and method of operation

Abstract

A process for replacing a gas lasing medium in a laser chamber of a deep ultraviolet (DUV) light source includes: selecting a target pumpdown pressure for replacing the gas lasing medium including fluorine in the laser chamber based on at least one of: (a) a temporal age and / or a pulse- count age of the laser chamber, (b) a temporal age and / or a pulse-count age of the gas in the laser chamber, and (c) one or more performance measures of the laser chamber; reducing the pressure of the gas in the laser chamber to the target pumpdown pressure; and adding more gas to the laser chamber to increase the pressure of the gas in the laser chamber up to an operating pressure.

Description

DUV LIGHT SOURCE AND METHOD OF OPERATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Application No. 63 / 569,396, filed March 25, 2024, titled DUV LIGHT SOURCE AND METHOD OF OPERATION, which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The disclosed subject matter relates to laser-based light sources such as those used for integrated circuit photolithographic manufacturing processes or for inspection and metrology processes during the manufacturing processes, including deep ultraviolet (DUV) light sources, and to the operation thereof.BACKGROUND

[0003] Light, which can be laser radiation, that is used for semiconductor photolithography or for metrology process can be supplied by a system that may be referred to as a light source. These light sources produce light as a series of pulses at specified repetition rates, for example, in the range of about 500 Hz to about 6 kHz or more. Additionally, such light sources 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] Light sources for producing light, such as laser radiation, at wavelengths useful for semiconductor photolithography (such as at deep-ultraviolet (DUV) wavelengths) or for metrology and inspection process can involve use of a master oscillator power amplifier (MOPA), a master oscillator power oscillator (MOPO), and a master oscillator power ring amplifier (MOPRA) dual gasdischarge chamber configuration. These configurations have two laser chambers, a master oscillator chamber (MO chamber) and a power amplifier (PA), a power oscillator (PO) or a power ring amplifies (PRA) chamber. These chambers each contain a lasing medium in the form of a gas mixture. To maintain the performance of the light source, the respective gas mixtures in the MO chamber and the PO, PA or PRA chamber require periodic replacement.SUMMARY

[0005] In some general aspects, a process is provided for replacing a gas lasing medium in a laser chamber of a deep ultraviolet (DUV) light source, the process including: selecting a target pumpdown pressure for replacing the gas lasing medium in the laser chamber of the DUV light source wherein the gas includes fluorine, wherein the target pumpdown pressure is selected based on at least on at least one of: (a) a temporal age and / or a pulse-count age of the laser chamber, (b) a temporal age and / or a pulse-count age of the gas in the laser chamber, or (c) one or more performance measures ofthe laser chamber; reducing the pressure of the gas in the laser chamber only to the target pumpdown pressure; and then adding gas to the laser chamber to increase the pressure of the gas in the laser chamber up to an operating pressure.

[0006] Implementations can include one or more of the following.

[0007] The target pumpdown pressure can be selected based on at least a combination of (a), (b), and (c). If the temporal age and / or a pulse-count age of the laser chamber is greater than a corresponding chamber age upper limit, the target pumpdown pressure can be kept at a reference, but if not, if a temporal age and / or a pulse-count age of the gas in the laser chamber is greater than a corresponding gas age limit, the target pumpdown pressure can be set at the reference value plus a first increase amount, but if not, if the one or more performance measures of the laser chamber is or are above one or more corresponding thresholds, the target pumpdown pressure can be set at the reference value plus a second increase amount greater than the first increase amount, but if not, the target pumpdown pressure can be set at the reference value plus the first increase amount, alternatively, at the reference value plus a third increase amount. The first increase amount can be in the range of 5 to 20 kPa (kilopascal). The second increase amount can be in the range of 20 to 40 kPa. The reference pressure can be in the range of 10 to 30 kPa. The one or more performance measures can include one or more of laser chamber efficiency, laser chamber electrode voltage, laser chamber electrode voltage trend, laser chamber timing performance, laser chamber or laser beam quality, and frequency and / or amount of gas injections into the laser chamber. The reference pressure is adjusted downward one or more times during the life of the laser chamber. The target pumpdown pressure can be selected further based at least in part on presence or absence of a chamber break-in mode.

[0008] Adding gas to the laser chamber can include adding a first gas mixture not containing fluorine then adding a second gas mixture containing fluorine, and the process can further include completing the adding of the first gas prior to completing a rethermalization of the gas in the chamber.

[0009] In additional aspects, a process is provided for replacing gas containing fluorine in a DUV light source laser chamber, the process including: pumping down the laser chamber to a target pumpdown pressure, the target pumpdown pressure being higher when a detected health and / or performance of the laser or laser chamber has been higher and lower when the detected health and / or performance of the laser or laser chamber has been lower; and refilling the laser chamber at least to an operating pressure with a gas including fluorine.

[0010] Implementations can include one or more of the following.

[0011] The process can further include detecting the health and / or performance of the laser or laser chamber over a time period preceding pumping down the laser chamber and setting the target pumpdown pressure equal to a reference pressure plus a pressure increase amount, the pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of the laser or laser chamber, the pressure increase amount being higher when the detected health and / or performance is higher. Detecting the health and / or performance of thelaser chamber can include one or more of (a) comparing a temporal age and / or a pulse-count age of the laser chamber to one or more laser chamber age standards, (b) comparing a time since and / or a pulse count since the last refdl of the laser chamber to a gas refdl pulse count standard, (c) measuring an energy stability of the laser chamber and comparing to one or more energy stability standards, and (d) comparing one or more of the following additional performance measures of the laser chamber to respective standards: (1) laser chamber efficiency, (2) laser chamber electrode voltage, (3) laser chamber electrode voltage trend, (4) laser chamber timing performance, (5) laser chamber or laser beam quality, and (6) frequency or amount of gas injections for the laser chamber. Detecting the health and / or performance of the laser chamber can further include determining the presence of a chamber break-in mode.

[0012] Detecting the health and / or performance of the laser chamber can include (all of) (a) comparing a temporal age and / or a pulse-count age of the laser chamber to one or more laser chamber age standards, (b) comparing a time since and / or a pulse count since the last refdl of the laser chamber to a gas refdl pulse count standard, (c) measuring an energy stability of the laser chamber and comparing to one or more energy stability standards, and (d) comparing one or more of the following additional performance measures of the laser chamber to respective standards: (1) laser chamber efficiency, (2) laser chamber electrode voltage, (3) laser chamber electrode voltage trend, (4) laser chamber timing performance, (5) laser chamber or laser beam quality, and (6) frequency or amount of gas injections for the laser chamber. The reference pressure can be adjusted downward one or more times during the life of the laser chamber. The process can further include refilling the chamber with gas by adding a first gas mixture not containing fluorine then adding a second gas mixture containing fluorine and completing the adding of the first gas prior to completing a rethermalization of the gas in the chamber.

[0013] In still other aspects, a process is provided for replacing gas in a deep ultraviolet (DUV) light source laser chamber, the process including: removing gas from the chamber until a pressure of the gas in the chamber reaches a target pumpdown pressure; then adding to the chamber a first gas mixture not containing fluorine; while adding the first gas mixture to the chamber, circulating the gas in the chamber; only after the completion of adding the first gas mixture to the chamber, completing a rethermalization of the gas in the chamber by continuing to circulate the gas in the chamber for a time period TP2; and adding a second gas mixture containing fluorine to the chamber.

[0014] Implementations can include one or more of the following.

[0015] The process can further include: detecting the health and / or performance of the laser or laser chamber over a time period preceding removing gas from the laser chamber and setting the target pumpdown pressure equal to a reference pressure plus a pressure increase amount, the pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of the laser or laser chamber, the pressure increase amount being higher when the detected health and / or performance is higher.

[0016] Circulating the gas in the chamber can optionally be performed only when the pressure of the gas in the chamber is at or above a circulation pressure, and the process can further include, if and when the circulation pressure is first reached, pausing adding to the chamber the first gas mixture for a time period TP1, TP1 being less than 10 times TP2.

[0017] In still other aspects, a DUV laser-based light source for use in photolithography is provided, the light source including: a first laser chamber; two or more gas supplies connected to the first laser chamber; one or more vacuum pumps connected to the first chamber; a circulation fan or blower within or connected to the first laser chamber configured to recirculate gas within the first laser chamber; and a controller in communication with the first laser chamber, the one or more vacuum pumps, the two or more gas supplies, and the circulation fan or blower, the controller being configured to (1) cause one or more of the one or more vacuum pumps to remove gas from the first laser chamber until a pressure in the first laser chamber reaches a target pumpdown pressure, (2) cause addition to the chamber a first gas mixture not containing fluorine; (3) while adding the first gas mixture to the chamber, cause the circulation fan or blower to circulate the gas in the chamber; (4) only after the completion of adding the first gas mixture to the chamber, cause completion of a rethermalization of the gas in the chamber by continuing to circulate the gas in the chamber for a time period TP2; and (5) then cause addition of a second gas mixture containing fluorine to the chamber.

[0018] Implementations can include one or more of the following.

[0019] The light source can further include performance and / or condition sensors connected to the first laser chamber and / or the light source to detect the health and / or performance of the first laser chamber, wherein the controller can be further configured to (1) receive data from the performance and / or condition sensors and to detect the health and / or performance of the laser chamber before removing gas from the laser chamber; and (2) set the target pumpdown pressure equal to a reference pressure plus a pressure increase amount, the pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of the laser or laser chamber, the pressure increase amount being higher when the detected health and / or performance is higher.

[0020] In still more aspects, a DUV laser-based light source for use in photolithography is provided, the light source including: a first laser chamber; one or more gas supplies connected to the first laser chamber; one or more vacuum pumps connected to the first laser chamber; performance and / or condition sensors connected to the first laser chamber and / or the light source to detect the health and / or performance of the first laser chamber; and a controller in communication with the first laser chamber, the one or more vacuum pumps, the one or more gas supplies, and the performance and / or condition sensors, the controller configured (1) to receive data from the performance and / or condition sensors, (2) to detect or assess the health and / or performance of the first laser chamber based on the received data, (3) to select or determine a relatively higher target pumpdown pressure when the assessed health and / or performance has been relatively higher and a relatively lower target pumpdownpressure when the assessed health and / or performance has been relatively lower, (4) to cause one or more of the one or more vacuum pumps to pump down the first laser chamber to the selected or determined target pumpdown pressure, and (5) to cause one or more of the one or more gas supplies to refill the first laser chamber to an operating pressure.

[0021] 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

[0022] FIG. 1 is a schematic cross-sectional diagram of aspects of a light source.

[0023] FIG. 2 is a schematic diagram of a lithography exposure apparatus that can be used with a light source such as the light source of FIG. 1.

[0024] FIG. 3 is a flow chart of a process for refilling a chamber of a light source according to the present disclosure.

[0025] FIG. 4 is a flow chart of an aspect of a process for refining a chamber of a light source.

[0026] FIG. 5 is a flow chart of another process for refilling a chamber of a light source.

[0027] FIG. 6 is a graph of gas pressure over time in another process for refilling a chamber of a light source.DETAILED DESCRIPTION

[0028] Referring to FIG. 1, a light source 100, which can be a deep UV (DUV) light source 100, can be in the form of a dual stage pulsed light source that produces a light beam 105 in the form of a pulsed amplified beam. The light source 100 can include a gas discharge master oscillator (MO) system 160, a power amplification (PA) system 165 which can be a power oscillator (PO) or a power ring amplifier (PRA) system, relay optics 170, and an optical output subsystem 175.

[0029] The MO system 160 can include, for example, an MO chamber 161. In the MO chamber, electrical discharges between electrodes (not shown) can generate an inverted population of high energy molecules in a lasing gas which discharges and lases to produce relatively broadband radiation. The relatively broadband radiation can be line-narrowed to a relatively very narrow bandwidth, and center-wavelength selected, in a line narrowing module (LNM) 162.

[0030] The MO system 160 can also include an MO output coupler (MO OC) 162, which can include a partially reflective mirror, forming, with a reflective grating in the LNM 162 (not shown), an oscillator cavity in which light oscillates to generate a seed output pulse. The MO system 160 can also include a line-center analysis module (LAM) 163. The LAM 163 can include, for example, an etalon spectrometer for fine wavelength measurement and a coarser resolution grating spectrometer.

[0031] The relay optics 170 can include an MO wavefront engineering box (WEB) 171 that serves to redirect the output of the MO system 160 toward the PA, PO or PRA system 165, and can include, forexample, beam expansion with, for example, a multi prism beam expander (not shown) and coherence busting, for example, in the form of an optical delay path (not shown).

[0032] The PA, PO or PRA system 165 includes a power amplifier (PA) or power ring amplifier (PRA) chamber 166. Like the MO chamber 161, the PA or PRA chamber 166 is an oscillator, oscillating in response to injection of the output light pulse or pulses from the MO system 160, and due to output coupling optics that can be incorporated into a PRA WEB 167 and can be redirect pulses back through a gain medium in the chamber 166, in cooperation with a beam reverser 168. The PRA WEB 167 can incorporate a partially reflective input / output coupler (not shown) and a maximally reflective mirror for the nominal operating wavelength, (which can be at around 193 nm for an ArF system, and one or more prisms. The PA, PO or PRA system 165 optically amplifies the output light beam from the MO system 160.

[0033] The optical output subsystem 175 can include a bandwidth analysis module (BAM) 176 at the output of the PA, PO or PRA system 165. The BAM 176 can pick off for metrology purposes a portion of the light beam it receives. For example, the BAM can use the portion of the light beam to measure the output bandwidth and pulse energy of the light. The output light beam of pulses then passes through an optical pulse stretcher module (OPuS) 177 and an output combined autoshutter metrology module (CASMM) 178, which can include a pulse energy meter. One purpose of the OPuS 177 can be to convert a single output pulse into a pulse train. Secondary pulses created from the original single output pulse can 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 light beam can be expanded and at the same time the peak pulse intensity of the beam can be reduced.

[0034] The light source 100 is made up of modules. Each of the components (such as the MO chamber 161, the LNM 162, the MO WEB 171, the PRA chamber 166, the PRA WEB 167, the OPuS 177, the BAM 176) of the light source 100 are or can be considered to be modules. The overall performance of the light source 100 is the direct result of the performance of these individual modules making up the light source 100. A controller 120 monitors these modules so that they can be adjusted, refreshed, or replaced, generally before they fail, in order to maintain the operation of the light source 100 and optimize and improve efficiency of an output apparatus such as a metrology apparatus and a lithography apparatus described below with respect to FIG. 2. The controller 120 can record, and store over time, features and performance data of the light source and / or of the modules. Performance data can include wavelength, wavelength stability, output bandwidth and pulse energy, energy efficiency, electrode operating voltage, and other variables and / or data received from sensors in or associated with the modules.

[0035] Referring to FIG. 2, the amplified light beam (105, FIG. 1) can be useful as a light beam 205 used by a photolithography exposure apparatus 210 to pattern features on a substrate or wafer 211. In some instances, the amplified light beam is used as a light beam by a metrology apparatus for inspecting and measuring target dimensions on a substrate (e.g., a mask, a reticle, or a semiconductorwafer). The wafer 211 is placed on a wafer table 212 constructed to hold the wafer 211 and connected to a positioner configured to position the wafer 211 accurately in accordance with certain parameters. The light beam 205 can have a wavelength in the deep ultraviolet (DUV) range, which can include wavelengths from, for example, about 100 nanometers (nm) to about 400 run. For example, the light source 100 that produces such a light beam 105, 205 can be a gas discharge light source such as an excimer light source, or excimer laser that uses a combination of one or more noble gases, which can include argon, krypton, or xenon, and a reactive gas, which can include fluorine or chlorine as the gain medium. The light source 100 can be an excimer light source. The gain medium can include argon fluoride (ArF), krypton fluoride (KrF), or xenon chloride (XeCl), for example. If the gain medium includes argon fluoride, then the wavelength of the amplified light beam 205 is about 193 nm and if the gain medium includes krypton fluoride, then the wavelength of the amplified light beam 205 is about 248 nm. The size of the microelectronic features patterned on the wafer 211 depends on the wavelength of the light beam 205, with a lower wavelength resulting in a smaller minimum feature size. When the wavelength of the light beam 205 is 248 nm or 193 nm, the minimum size of the microelectronic features can be, for example, 50 nm or less. The bandwidth of the light beam 205 can be the actual, instantaneous bandwidth of its optical spectrum (or emission spectrum), which contains information on how the optical energy of the light beam 205 is distributed over different wavelengths.

[0036] The photolithography exposure apparatus 210 includes an optical arrangement having, for example, one or more condenser lenses, a mask, and an objective arrangement. The mask is movable along one or more directions, such as along an optical axis of the light beam 205 or in a plane that is perpendicular to the optical axis. The objective arrangement includes a projection lens and enables an image transfer to occur from the mask to the photoresist on the wafer 211. The photolithography exposure apparatus 210 also includes an illumination system that adjusts the range of angles for the light beam 205 impinging on the mask. The illumination system also homogenizes (makes uniform) the intensity distribution of the light beam 205 across the mask. During lithography, a plurality of pulses of the light beam 205 illuminates the same area of the wafer 211 to together constitute an illumination dose.

[0037] The quality of the features produced on the wafer 211 by the photolithography exposure apparatus 210 depends directly upon the quality and reliability of the light pulses from the light source 100. Pulses having lower than desired power can result in underexposure of an area of the wafer 211. Missing pulses can similarly result in underexposure. Shifts in wavelength or bandwidth distribution can result in shifts in image position and alterations in patterns produced at the wafer 211. Also, downtime of the light source 100 decreases the productivity of the lithography exposure apparatus 210.

[0038] Referring again to FIG. 1, information or data from the various modules and other sources in the light source 100, both information at a current time and information collected and stored over agiven time range up to a current time, can be used to assess the need for replacing the gas in the MO chamber module 161 or in the PRA chamber module 166. Gas replacement in a respective chamber can be performed whenever the performance of the respective chamber, or of the light source as a whole, is sufficiently degraded. Gas replacement can also be performed for other reasons, such as prespecified gas age limits, gas replacement scheduling considerations, and so forth. Thus for many users of a light source such as light source 100, a proportion of gas replacements are not performed specifically because of performance degradation. In such cases, the controller 120 can use measurement(s) of the performance of a chamber to alter the process of replacing the gas, based on the chamber’s performance. Specifically, the controller 120 can be in communication, such as via communication line(s) 120v, with one or more valves such as vacuum valves 121, 126, and one or more vacuum pumps 122, by which the MO chamber 161 and the PRA chamber 166 can be selectively evacuated. The controller can also be in communication, such as via communication line(s) 120g, with one or more gas supplies 161g, 166g, by which the MO chamber 161 and the PRA chamber 166 can be selectively refilled with a gas lasing medium.

[0039] The controller 120 can be configured (1) to receive data from performance and / or condition sensors, (2) to detect or assess the current and / or most recent health and / or performance of a first laser chamber (such as the MO chamber 161) based on the received data, (3) to select or determine a relatively higher target pumpdown pressure when the assessed health and / or performance has been relatively higher and a relatively lower target pumpdown pressure when the assessed health and / or performance has been relatively lower, (4) to cause one or more of the one or more vacuum pumps to pump down the first laser chamber to the selected or determined target pumpdown pressure, and (5) to cause one or more of the one or more gas supplies to refill the first laser chamber to an operating pressure. By pumping down to a higher target pumpdown pressure when the assessed health and / or performance of the laser chamber is higher, the light source 100 has a shorter pumpdown time as well as a shorter refill time to reach operating pressure. The light source 100 is thus back up and available for use in lithography operations more quickly, as long as the health / and or performance was relatively higher before, without sacrificing the performance or longevity of the chamber after the gas replacement operation. This increases the total uptime and hence the productivity of the light source.

[0040] In one aspect or implementation, the controller can set the target pumpdown pressure equal to a reference pressure plus a pressure increase amount, with the pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of the chamber (or of the laser as representative of the chamber), with the pressure increase amount being set higher when the detected health and / or performance is higher.

[0041] With continuing reference to FIG. 1, the controller 120 optionally can also be configured to control, such as via control lines 120h, heaters 16 Ih, 166h that can be present in and configured to heat gas within the chambers 161, 166 . Similarly, the controller 120 can further be configured to control, such as via control lines 120f, respective circulation fans or blowers 16 If, 166f, configured tocirculate gas within the chambers 161, 166. Independently of whether the controller is configured to sometimes use a higher target pumpdown pressure, the controller 120 can be configured to add gas to the laser chamber by adding a first gas mixture not containing fluorine then adding a second gas mixture containing fluorine, and to complete the adding of the first gas prior to completing a rethermalization of the gas in the chamber. “Rethermalization” as used herein means achieving sufficiently low variation of temperature of the gas within the chamber such that temperature variation of the gas in the chamber is limited to ± 3 °C, ± 2 °C, ± 1 °C, ± 0.5 °C, or less. Completing rethermalization means completing a process or processes resulting in rethermalization. Such processes can include circulating the gas in a respective chamber, such as by one of fans or blowers 16 If, 166f, while little or no gas is added to the chamber, for a sufficient time to ensure rethermalization; circulating the gas while little or no gas is added to the chamber until rethermalization has been achieved as detected by temperature measurements of the gas within the chamber, and / or circulating the gas while little or no gas is added to the chamber while heating the gas within the chamber using one of heaters 16 Ih, 166h, for example. Refilling and rethermalization are discussed in more detail below with reference to FIG. 6.

[0042] Note that the controller 120 can be implemented in software, firmware, hardware, or other forms and combinations thereof. The communications of controller 120 can be wireless, wired, optical, or others and combinations. The controller can be remote from the light source. The controller need not be implemented in a single location or mode, for example, it can be any of local, remote, virtual, cloud-based, other similar, and combinations. The controller can comprise control functions distributed across two or more controllers, including embedded controllers.

[0043] Another aspect of the present disclosure includes processes for operating light sources. FIG. 3 is a flow chart of one such process, With reference to FIG. 3, a process 330 includes selecting a target pumpdown pressure for replacing the gas lasing medium in the laser chamber of a DUV light source, wherein the target pumpdown pressure is selected based on at least on at least one of: (a) a temporal age and / or a pulse-count age of the laser chamber, (b) a temporal age and / or a pulse-count age of the gas in the laser chamber, or (c) one or more performance measures of the laser chamber (331); reducing the pressure of the gas in the laser chamber only to the target pumpdown pressure (332); and then adding gas to the laser chamber to increase the pressure of the gas in the laser chamber up to an operating pressure (333). In variations of the process 330, the target pumpdown pressure is selected based on at least a combination of (a), (b), and (c).

[0044] FIG. 4 is a flow chart of a process or sub-process 431 that can be used as an implementation of, or as a substitution for, features item 331 of process 330 of FIG. 3. With reference to FIG. 4, in process 431 beginning with item 434, the temporal or pulse-count age, or both, of the chamber is checked against corresponding limit or limits. If the age limit or limits are exceeded, or if two are used, if one, or if both are exceeded, depending on the implementation (item 434, “yes” branch), the target pumpdown pressure is kept at the reference value. If the age limit(s) is / are not exceeded (item434, “no” branch), the temporal or pulse-count age (or both) of the gas is checked against corresponding limits (436). If a limit is exceeded in item 436, or in other implementations if two limits are exceeded, (item 436, “yes” branch), the target pressure is set to the reference value plus a first, lower increase amount (437). If no limits are exceeded, or in other implementations, if two limits are not exceeded, (item 436 “no” branch), one or more performance parameters are compared to relevant thresholds (item 438). If one or more thresholds are exceeded (item 438, “no” branch), the target pressure is set to the reference value plus a first, lower increase amount (437). If none of the one or more thresholds are exceeded (item 438, “yes” branch), the target pressure is set to the reference value plus a second, higher increase amount (item 439). Item 440 is optional (hence the dashed outline) and functions as a pre-screening in which the current mode or condition of the light source is compared with a list of conditions under which it is desirable not to use higher-than- reference-value target pumpdown pressures. Such conditions or modes can include early operation or break-in modes after a chamber replacement, for example.

[0045] In the process 431 of FIG. 4, the first increase amount can be in the range of 1 to 40 kPa, 1 to 30 kPa, or 5 to 20 kPa, for example. Keeping the first increase amount in the range of 5 to 20 kPa can allow sufficient replacement of gas for continued good performance under the conditions of gas beyond a gas age limit and a chamber below a chamber age limit. The second increase amount can be greater than the first increase amount and can be in the range of 2 to 100 kPa, 10 to 50 kPa, or 20 to 40 kPa, for example. Keeping the second increase amount above 20 kPa and below 40 kPa can allow a lesser but still sufficient replacement of gas for continued good performance when the gas and the chamber are both below their respective age limits and one or more performance measures are at or above thresholds. In the case that the one or more performance measures are not (each) above their thresholds, the first increase amount can be used, or, optionally, a third increase amount (not shown) less than the second increase amount but different from the first increase amount can be used. The reference pressure can be in the range of 5 to 40 Pa or 10 to 30 kPa, for example, or any value within a normal operating range of the chamber. The one or more performance measures can include one or more of laser chamber efficiency, laser chamber electrode voltage, laser chamber electrode voltage trend, laser chamber timing performance, laser chamber or laser beam quality, and frequency and / or amount of gas injections into the laser chamber. Also, the reference pressure can vary overtime, for example, the reference pressure can be adjusted downward one or more times during the life of the laser chamber.

[0046] FIG. 5 is a flow chart of another version of a process according to the present disclosure. In FIG. 5, a process 541 includes detecting the health and / or performance of the laser or laser chamber over a time period preceding pumping down the laser chamber (542), setting a pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of the laser or laser chamber, with the pressure increase amount being higherwhen the detected health and / or performance is higher (543), and setting a target pumpdown pressure equal to a reference pressure plus the pressure increase amount (544).

[0047] Detecting the health and / or performance of the laser chamber can include one or more of (a) comparing a temporal age and / or a pulse-count age of the laser chamber to one or more laser chamber age standards, (b) comparing a time since and / or a pulse count since the last refdl of the laser chamber to a gas refdl pulse count standard, (c) measuring an energy stability of the light pulses of the laser or the laser chamber and comparing to one or more energy stability standards, and (d) comparing one or more of the following additional performance measures of the laser chamber to respective standards: (1) laser chamber efficiency, (2) laser chamber electrode voltage, (3) laser chamber electrode voltage trend, (4) laser chamber timing performance, (5) laser chamber or laser beam quality, and (6) frequency or amount of gas injections for the laser chamber. Detecting the health and / or performance of the laser chamber can further include determining the presence of one or more chamber conditions or modes, such as break-in mode after chamber replacement and the like.

[0048] Alternatively, detecting the health and / or performance of the laser chamber can include (a) comparing a temporal age and / or a pulse-count age of the laser chamber to one or more laser chamber age standards, (b) comparing a time since and / or a pulse count since the last refdl of the laser chamber to a gas refdl pulse count standard, (c) measuring an energy stability of the light pulses of the laser or the laser chamber and comparing to one or more energy stability standards, and (d) comparing one or more of the following additional performance measures of the laser chamber to respective standards: (1) laser chamber efficiency, (2) laser chamber electrode voltage, (3) laser chamber electrode voltage trend, (4) laser chamber timing performance, (5) laser chamber or laser beam quality, and (6) frequency or amount of gas injections for the laser chamber.

[0049] FIG. 6 is a graph of gas pressure over time related to aspects of a process for refilling and rethermalization of the gas in a chamber of a light source. The pressure vs. time graph of FIG. 6 represents a portion of the process of refilling a laser chamber of a DUV source. For detailed background information, see for example U.S. Patent No. 8,873,600, “SYSTEM AND METHOD FOR HIGH ACCURACY GAS REFILL IN A TWO CHAMBER GAS DISCHARGE LASER SYSTEM” incorporated herein by reference.

[0050] In FIG. 6, the y axis shows the pressure P of gas within a laser chamber as a function of time T during a portion of a refilling process. During the refilling process, as shown, a first gas mixture not containing fluorine is added to the chamber during the segments labeled FGM, and a second gas mixture containing fluorine is added to the chamber during the segment labeled SGM. During at least a later portion, or during all, of the segments labeled FGM, the gas in the chamber is circulated by a fan or blower within the chamber. Only after the completion of adding the first gas mixture to the chamber, at time T3, rethermalization of the gas in the chamber is completed by continuing to circulate the gas in the chamber for a time period TP2 (from time T3 to time T4) during which no or essentially no gas is added.

[0051] The completion of adding the first gas mixture (at time T3) can be determined by measurements within the gas delivery system(s) providing the first gas mixture, by measurement of a target pressure P2 within the chamber for addition of the first gas mixture, or in other suitable ways.

[0052] Completion of rethermalization during time period TP2 (by time T4) can be ensured by setting the time period TP2 to a predetermined time, such as a predetermined time within the range of at least 5 seconds to 60 seconds, 10 seconds to 50 seconds, at least 15 seconds to 40 seconds, 15 seconds to 30 seconds, or 15 seconds to 20 seconds, for some examples. Longer times can also be used if needed. Alternatively, rethermalization (by time T4) can be ensured by measuring (i.e., estimating based on measurements) the temperature variation within the chamber during the time period TP2 until a desired low level of temperature variation is reached. Temperature variation in the chamber can be measured (or estimated based on measurements) by measuring the temperature at a single location, overtime, during circulation of the gas in the chamber, or by measuring the temperature of the gas in the chamber at multiple locations at the same time, or over time (or both), for example.

[0053] Once rethermalization is completed (during time period TP2 or by time T4), then, at time T4, the total gas present in the chamber is measured by measuring the pressure and temperature of the gas within the chamber. Rethermalization is needed to ensure the accuracy of this measurement. Based on this measurement, a desired amount of the second gas mixture (containing fluorine) to be added is determined. The desired amount of the second gas mixture is an amount that will result in a desired gas composition within the chamber upon completion of refilling. The desired amount of the second gas mixture is then added to the chamber (segment SGM) while continuing to circulate the gas within the chamber. Completion (at time T5 and pressure P3) of adding the second mixture is determined by continually or continuously detecting the temperature and pressure of the gas in the chamber until a desired amount of total gas in the chamber is reached that corresponds to the addition of the desired amount of the second gas mixture. Measuring the total gas in the chamber by the measurement of temperature and pressure, at both time T4 and at time T5 and at times leading up to T5, in a rethermalized chamber, enables precise determination of the total amount of gas present and precise control of the final gas composition achieved within the chamber by time T5. With precise control of gas composition accomplished, precise control over a final gas pressure can then be achieved by gradually lowering the pressure from pressure P3 to a desired operating pressure by bleeding out a small amount of the gas in the chamber (not shown), thus allowing both pressure and composition to be controlled precisely.

[0054] Circulating the gas in the chamber while adding the first gas mixture to the chamber can optionally be performed only when the pressure of the gas in the chamber is at or above a “circulation pressure,” which can be a pressure at which a fan or blower has a desired level of effectiveness or can properly operate within the chamber, such as pressure Pl in FIG. 6. Pressure Pl can be pressure within the range of about 30 ± 10 kPa, for example. Optionally, the refilling process can include that,if or when a given instance of refilling of the chamber starts below such a pressure Pl, when the circulation pressure Pl is first reached, adding the first gas mixture can be paused for a time period TP1 (from time T1 to T2) during which the gas in the chamber is circulated. Previously, as in U.S. Patent No. 8,873,600 referenced above, rethermalization of the gas in the chamber was completed within the time period TP1, and the time period TP1 was ten times longer than the time period TP2. In the process disclosed herein and represented in some aspects in FIG.6, rethermalization of the gas in the chamber is completed instead within the time period TP2, and the time period TP1, if present, is decreased relative to the time period TP2.

[0055] Completing the rethermalization of the gas in the chamber only after completion of adding the first gas mixture (after time T3, during the time period TP2) as in the present disclosure, rather than at an earlier time (such as during the time period TP1) allows for a shorter overall time used during the refilling process to rethermalize the gas in the chamber to a desired maximum (low) level of temperature variation. In the methods disclosed herein, the temperature of the gas in the chamber can begin equalizing from whenever the fan or blower is first activated to recirculate the gas until completion of rethermalization within the time period TP2. Accordingly, the time between time T2 and time T3 in which the first gas mixture is added (or continues to be added) to the chamber can be used to assist in rethermalization, such that the overall time used for rethermalization but not for adding gas (time period TP2, plus time period TP1, if present) is less in the present method than the time that would be required for rethermalization to be completed within the time period TP1, for a given maximum level of temperature variation. Time period TP1, if present, can have reduced length relative to time period TP2. For example, the time period TP1 can be less than 10 times the time period TP2, even less than 8 times, 4 times, or 2 times the length of time period TP2. This reflects the shifting, of a significant portion of the needed time for achieving a desired low temperature variation in the chamber, from the time period TP1 to the interval between the time T2 and the time T3, and to the time period TP2. Changing the relationship between the lengths of the time period TP1 and the time period TP2 such that the time period TP1 is at least less than 10 times the length of the time period TP2 tends to ensure that some degree of time savings is realized in achieving a given low maximum level of temperature variation. Changing the relationship between the lengths of the time period TP1 and the time period TP2 such that the time period TP1 is at least less than 2 times the length of the time period TP2 tends to maximize the time savings realized in achieving a given low maximum level of temperature variation.

[0056] Shorter downtime for gas refills that can be provided by the methods and / or apparatuses of the present disclosure provides higher productivity and thus higher value when the light sources of the present disclosure are used in photolithographic processing.

[0057] Aspects and implementations of the present disclosure can be further described using the following numbered clauses:1. A process for replacing a gas lasing medium in a laser chamber of a deep ultraviolet (DUV) light source in a photolithographic facility, the process including: selecting a target pumpdown pressure for replacing the gas lasing medium in the laser chamber of the DUV light source wherein the gas includes fluorine, wherein the target pumpdown pressure is selected based on at least on at least one of: (a) a temporal age and / or a pulse-count age of the laser chamber, (b) a temporal age and / or a pulse-count age of the gas in the laser chamber, or (c) one or more performance measures of the laser chamber; reducing the pressure of the gas in the laser chamber only to the target pumpdown pressure; and then adding gas to the laser chamber to increase the pressure of the gas in the laser chamber up to an operating pressure.2. The process of clause 1, wherein the target pumpdown pressure is selected based on at least a combination of (a), (b), and (c).3. The process of clause 2, wherein (1) if the temporal age and / or a pulse-count age of the laser chamber is greater than a corresponding chamber age upper limit, the target pumpdown pressure is kept at a reference; but if not (2) if a temporal age and / or a pulse-count age of the gas in the laser chamber is greater than a corresponding gas age limit, the target pumpdown pressure is set at the reference value plus a first increase amount; but if not (3) if the one or more performance measures of the laser chamber is or are above one or more corresponding thresholds, the target pumpdown pressure is set at the reference value plus a second increase amount greater than the first increase amount; but if not (4) the target pumpdown pressure is set at the reference value plus the first increase amount.4. The process of clause 3, wherein the first increase amount is in the range of 5 to 20 kPa.5. The process of clause 3, wherein the second increase amount is in the range of 20 to 40 kPa.6. The process of clause 3, wherein the reference pressure is in the range of 10 to 30 kPa.7. The process of clause 3, wherein the one or more performance measures include one or more of laser chamber efficiency, laser chamber electrode voltage, laser chamber electrode voltage trend, laser chamber timing performance, laser chamber or laser beam quality, and frequency and / or amount of gas injections into the laser chamber.8. The process of clause 3 wherein the reference pressure is adjusted downward one or more times during the life of the laser chamber.9. The process of clause 2, wherein (1) if the temporal age and / or a pulse-count age of the laser chamber is greater than a corresponding chamber age upper limit or less than a corresponding chamber age lower limit, the target pumpdown pressure is kept at a reference value; but if not (2) if a temporal age and / or a pulse-count age of the gas in the laser chamber is greater than a corresponding gas age limit, the target pumpdown pressure is set at the reference value plus a first increase amount; but if not (3) if the one or more performance measures of the laser chamber is or are above one or more corresponding thresholds, the target pumpdown pressure is set at the reference value plus asecond increase amount greater than the first increase amount; but if not (4) the target pumpdown pressure is set at the reference value plus the first increase amount.10. The process of clause 2, wherein the target pumpdown pressure is selected further based at least in part on presence or absence of a chamber break-in mode.11. The process of clause 1, wherein adding gas to the laser chamber includes adding a first gas mixture not containing fluorine then adding a second gas mixture containing fluorine, and further including completing the adding of the first gas prior to completing a rethermalization of the gas in the chamber.12. A process for replacing gas containing fluorine in a deep ultraviolet (DUV) light source laser chamber in a photolithographic facility, the process including: pumping down the laser chamber to a target pumpdown pressure, the target pumpdown pressure being higher when a detected health and / or performance of the laser or laser chamber has been higher and lower when the detected health and / or performance of the laser or laser chamber has been lower; and refilling the laser chamber at least to an operating pressure with a gas including fluorine.13. The process of clause 12, further including detecting the health and / or performance of the laser or laser chamber over a time period preceding pumping down the laser chamber; and setting the target pumpdown pressure equal to a reference pressure plus a pressure increase amount, the pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of the laser or laser chamber, the pressure increase amount being higher when the detected health and / or performance is higher.14. The process of clause 13, wherein detecting the health and / or performance of the laser chamber includes one or more of (a) comparing a temporal age and / or a pulse-count age of the laser chamber to one or more laser chamber age standards, (b) comparing a time since and / or a pulse count since the last refill of the laser chamber to a gas refill pulse count standard, (c) measuring an energy stability of the laser chamber and comparing to one or more energy stability standards, and (d) comparing one or more of the following additional performance measures of the laser chamber to respective standards: (1) laser chamber efficiency, (2) laser chamber electrode voltage, (3) laser chamber electrode voltage trend, (4) laser chamber timing performance, (5) laser chamber or laser beam quality, and (6) frequency or amount of gas injections for the laser chamber.15. The process of clause 14 wherein detecting the health and / or performance of the laser chamber further includes determining the presence of a chamber break-in mode.16. The process of clause 13, wherein detecting the health and / or performance of the laser chamber includes (a) comparing a temporal age and / or a pulse-count age of the laser chamber to one or more laser chamber age standards, (b) comparing a time since and / or a pulse count since the last refill of the laser chamber to a gas refill pulse count standard, (c) measuring an energy stability of the laser chamber and comparing to one or more energy stability standards, and (d) comparing one or more of the following additional performance measures of the laser chamber to respective standards: (1) laserchamber efficiency, (2) laser chamber electrode voltage, (3) laser chamber electrode voltage trend, (4) laser chamber timing performance, (5) laser chamber or laser beam quality, and (6) frequency or amount of gas injections for the laser chamber.17. The process of clause 13 wherein the reference pressure is adjusted downward one or more times during the life of the laser chamber.18. The process of clause 12, further including refilling the chamber with gas by adding a first gas mixture not containing fluorine then adding a second gas mixture containing fluorine and completing the adding of the first gas prior to completing a rethermalization of the gas in the chamber.19. A process for replacing gas in a deep ultraviolet (DUV) light source laser chamber in a photolithographic facility, the process including: removing gas from the chamber until a pressure of the gas in the chamber reaches a target pumpdown pressure, then: adding to the chamber a first gas mixture not containing fluorine; while adding the first gas mixture to the chamber, circulating the gas in the chamber; only after the completion of adding the first gas mixture to the chamber, completing a rethermalization of the gas in the chamber by continuing to circulate the gas in the chamber for a time period TP2; and then adding a second gas mixture containing fluorine to the chamber.20. The process of clause 19, further including: detecting the health and / or performance of the laser or laser chamber over a time period preceding removing gas from the laser chamber; and setting the target pumpdown pressure equal to a reference pressure plus a pressure increase amount, the pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of the laser or laser chamber, the pressure increase amount being higher when the detected health and / or performance is higher.21. The process of clause 19, wherein in circulating the gas in the chamber is performed only when the pressure of the gas in the chamber is at or above a circulation pressure, and further including, if and when the circulation pressure is first reached, pausing adding to the chamber the first gas mixture for a time period TP1, TP1 being less than 10 times TP2.22. A DUV laser-based light source for use in photolithography, the light source including: a first laser chamber; two or more gas supplies connected to the first laser chamber; one or more vacuum pumps connected to the first chamber; a circulation fan or blower within or connected to the first laser chamber configured to recirculate gas within the first laser chamber; and a controller in communication with the first laser chamber, the one or more vacuum pumps, the two or more gas supplies, and the circulation fan or blower, the controller being configured to (1) cause one or more of the one or more vacuum pumps to remove gas from the first laser chamber until a pressure in the first laser chamber reaches a target pumpdown pressure, (2) cause addition to the chamber a first gas mixture not containing fluorine; (3) while adding the first gas mixture to the chamber, cause the circulation fan or blower to circulate the gas in the chamber; (4) only after the completion of adding the first gas mixture to the chamber, cause completion of a rethermalization of the gas in the chamberby continuing to circulate the gas in the chamber for a time period TP2; and (5) then cause addition of a second gas mixture containing fluorine to the chamber.23. The light source of clause 22 further including performance and / or condition sensors connected to the first laser chamber and / or the light source to detect the health and / or performance of the first laser chamber, wherein the controller is further configured to (1) receive data from the performance and / or condition sensors and to detect the health and / or performance of the laser chamber before removing gas from the laser chamber; and (2) set the target pumpdown pressure equal to a reference pressure plus a pressure increase amount, the pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of the laser or laser chamber, the pressure increase amount being higher when the detected health and / or performance is higher.24. A DUV laser-based light source for use in photolithography, the light source including: a first laser chamber; one or more gas supplies connected to the first laser chamber; one or more vacuum pumps connected to the first laser chamber; performance and / or condition sensors connected to the first laser chamber and / or the light source to detect the health and / or performance of the first laser chamber; and a controller in communication with the first laser chamber, the one or more vacuum pumps, the one or more gas supplies, and the performance and / or condition sensors, the controller configured (1) to receive data from the performance and / or condition sensors, (2) to detect or assess the health and / or performance of the first laser chamber based on the received data, (3) to select or determine a relatively higher target pumpdown pressure when the assessed health and / or performance has been relatively higher and a relatively lower target pumpdown pressure when the assessed health and / or performance has been relatively lower, (4) to cause one or more of the one or more vacuum pumps to pump down the first laser chamber to the selected or determined target pumpdown pressure, and (5) to cause one or more of the one or more gas supplies to refill the first laser chamber to an operating pressure.

[0058] The above-described aspects and implementations and other implementations are within the scope of the following claims.

Claims

CLAIMS1. A process for replacing a gas lasing medium in a laser chamber of a deep ultraviolet (DUV) light source, the process comprising: selecting a target pumpdown pressure for replacing the gas lasing medium in the laser chamber of the DUV light source wherein the gas includes fluorine, wherein the target pumpdown pressure is selected based on at least one of: (a) a temporal age and / or a pulse-count age of the laser chamber, (b) a temporal age and / or a pulse-count age of the gas in the laser chamber, and (c) one or more performance measures of the laser chamber; reducing a pressure of the gas in the laser chamber to the target pumpdown pressure; and adding more gas to the laser chamber to increase the pressure of the gas in the laser chamber up to an operating pressure.

2. The process of claim 1, wherein (1) if the temporal age and / or a pulse-count age of the laser chamber is greater than a corresponding chamber age upper limit, the target pumpdown pressure is kept at a reference; but if not, (2) if the temporal age and / or a pulse-count age of the gas in the laser chamber is greater than a corresponding gas age limit, the target pumpdown pressure is set at a reference value plus a first increase amount; but if not, (3) if the one or more performance measures of the laser chamber is or are above one or more corresponding thresholds, the target pumpdown pressure is set at the reference value plus a second increase amount greater than the first increase amount; but if not, (4) the target pumpdown pressure is set at the reference value plus the first increase amount.

3. The process of claim 2, wherein the first increase amount is in the range of 5 to 20 kPa, and the second increase amount is in the range of 20 to 40 kPa.

4. The process of claim 2, wherein the one or more performance measures include one or more of laser chamber efficiency, laser chamber electrode voltage, laser chamber electrode voltage trend, laser chamber timing performance, laser chamber or laser beam quality, and frequency and / or amount of gas injections into the laser chamber.

5. The process of claim 2, wherein the reference pressure is adjusted downward one or more times during the life of the laser chamber.

6. The process of claim 1, wherein (1) if the temporal age and / or a pulse-count age of the laser chamber is greater than a corresponding chamber age upper limit or less than a corresponding chamber age lower limit, the target pumpdown pressure is kept at a reference value; but if not, (2) ifthe temporal age and / or a pulse-count age of the gas in the laser chamber is greater than a corresponding gas age limit, the target pumpdown pressure is set at the reference value plus a first increase amount; but if not, (3) if the one or more performance measures of the laser chamber is or are above one or more corresponding thresholds, the target pumpdown pressure is set at the reference value plus a second increase amount greater than the first increase amount; but if not, (4) the target pumpdown pressure is set at the reference value plus the first increase amount.

7. The process of claim 1, wherein the target pumpdown pressure is selected further based at least in part on presence or absence of a chamber break-in mode.

8. The process of claim 1, wherein adding the more gas to the laser chamber comprises adding a first gas mixture not containing fluorine then adding a second gas mixture containing fluorine, and further comprising completing the adding of the first gas mixture prior to completing a rethermalization of the gas in the laser chamber.

9. A process for replacing gas containing fluorine in a deep ultraviolet (DUV) light source laser chamber, the process comprising: pumping down the laser chamber to a target pumpdown pressure, the target pumpdown pressure being higher when a detected health and / or performance of the laser or laser chamber has been higher and lower when the detected health and / or performance of the laser or laser chamber has been lower; and refilling the laser chamber at least to an operating pressure with a gas including fluorine.

10. The process of claim 9, further comprising detecting the health and / or performance of the laser or laser chamber over a time period preceding pumping down the laser chamber; and setting the target pumpdown pressure equal to a reference pressure plus a pressure increase amount, the pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of the laser or laser chamber, the pressure increase amount being higher when the detected health and / or performance is higher.

11. The process of claim 10, wherein detecting the health and / or performance of the laser chamber comprises one or more of (a) comparing a temporal age and / or a pulse-count age of the laser chamber to one or more laser chamber age standards, (b) comparing a time since and / or a pulse count since the last refill of the laser chamber to a gas refill pulse count standard, (c) measuring an energy stability of the laser chamber and comparing to one or more energy stability standards, and (d) comparing one or more of the following additional performance measures of the laser chamber to respective standards:(1) laser chamber efficiency, (2) laser chamber electrode voltage, (3) laser chamber electrode voltage trend, (4) laser chamber timing performance, (5) laser chamber or laser beam quality, and (6) frequency or amount of gas injections for the laser chamber.

12. The process of claim 11, wherein detecting the health and / or performance of the laser chamber further comprises determining presence of a chamber break-in mode.

13. The process of claim 10, wherein the reference pressure is adjusted downward one or more times during the life of the laser chamber.

14. The process of claim 9, further comprising refilling the laser chamber with more gas by adding a first gas mixture not containing fluorine then adding a second gas mixture containing fluorine and completing the adding of the first gas prior to completing a rethermalization of the gas in the laser chamber.

15. A process for replacing gas in a deep ultraviolet (DUV) light source chamber, the process comprising: removing gas from the chamber until a pressure of the gas in the chamber reaches a target pumpdown pressure, then; adding to the chamber a first gas mixture not containing fluorine; while adding the first gas mixture to the chamber, circulating the gas in the chamber; only after the completion of adding the first gas mixture to the chamber, completing a rethermalization of the gas in the chamber by continuing to circulate the gas in the chamber for a first time period; and then adding a second gas mixture containing fluorine to the chamber.

16. The process of claim 15, further comprising: detecting a health and / or performance of an output laser or the chamber over a time period preceding removing gas from the chamber; and setting the target pumpdown pressure equal to a reference pressure plus a pressure increase amount, the pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of the output laser or the chamber, the pressure increase amount being higher when the detected health and / or performance is higher.

17. The process of claim 15, wherein circulating the gas in the chamber is performed only when the pressure of the gas in the chamber is at or above a circulation pressure, and further comprising, whenthe circulation pressure is reached, pausing adding to the chamber the first gas mixture for a second time period, the second time period being less than 10 times of the first time period.

18. A DUV laser-based light source, the light source comprising: a first laser chamber; two or more gas supplies connected to the first laser chamber; at least one vacuum pump connected to the first chamber; a circulation fan or blower within or connected to the first laser chamber configured to recirculate gas within the first laser chamber; and a controller in communication with the first laser chamber, the at least one vacuum pump, the two or more gas supplies, and the circulation fan or blower, the controller being configured to (1) cause the at least one vacuum pump to remove gas from the first laser chamber until a pressure in the first laser chamber reaches a target pumpdown pressure, (2) cause addition to the first laser chamber a first gas mixture not containing fluorine, (3) while adding the first gas mixture to the first laser chamber, cause the circulation fan or blower to circulate the gas in the first laser chamber, (4) cause completion of a rethermalization of the gas in the first laser chamber by continuing to circulate the gas in the first laser chamber, and (5) then cause addition of a second gas mixture containing fluorine to the first laser chamber.

19. The light source of claim 18, further comprising performance and / or condition sensors connected to the first laser chamber and / or the light source to detect a health and / or performance of the first laser chamber, wherein the controller is further configured to (1) receive data from the performance and / or condition sensors and to detect the health and / or performance of the first laser chamber before removing gas from the first laser chamber; and (2) set the target pumpdown pressure equal to a reference pressure plus a pressure increase amount, the pressure increase amount varying from zero to a maximum pressure increase amount based on the detected health and / or performance of an output laser or the first laser chamber, the pressure increase amount being higher when the detected health and / or performance is higher.

20. The light source of claim 18, wherein continuing to circulate the gas in the first laser chamber for a time period is performed after adding the first gas mixture to the first laser chamber.

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