Reducing energy consumption of gas discharge chamber blowers

Abstract

In some general aspects, an apparatus for a light source includes a monitoring module configured to monitor a fault condition of one or more operating conditions of the light source, a decrement module configured to reduce an operating speed of a blower disposed in a gas discharge chamber of the light source when the fault condition for the one or more operating conditions of the light source is clear and a reduced operating speed is equal to or greater than a baseline speed, and an increment module configured to increase an operating speed of the blower when a fault condition for the one or more operating conditions of the light source is flagged, The blower is configured to move a gas mixture including a gain medium through the gas discharge chamber from an energy source configured to provide energy to the gas mixture.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 63 / 129,122, entitled REDUCING ENERGY CONSUMPTION OF A GAS DISCHARGE CHAMBER BLOWER, filed December 22, 2020, and is incorporated by reference in its entirety herein.

[0002] The disclosed subject matter relates to reducing the energy consumed by a blower disposed in a gas discharge chamber of a light source during operation of the light source by controlling the blower. [Background technology]

[0003]

[0003] One type of gas discharge light source used in photolithography is called an excimer light source or laser. Typically, an excimer laser uses a combination of one or more noble gases, which may include argon, krypton, or xenon, and a reactive gas, which may include fluorine or chlorine. Under the proper conditions of electrical simulation (energy provided) and high pressure (of the gas mixture), an excimer laser can generate excimers (pseudo-molecules), which exist only in an excited state. The excited state of the excimer produces amplified light in the ultraviolet range. An excimer light source may use a single gas discharge chamber or multiple gas discharge chambers. When an excimer light source is operating, it generates a deep ultraviolet (DUV) light beam. DUV light may include wavelengths, for example, from about 100 nanometers (nm) to about 400 nm.

[0004]

[0004] The DUV light beam may be directed to a photolithography exposure tool or scanner, which is a machine that applies a desired pattern onto a target portion of a substrate (such as a silicon wafer). The DUV light beam interacts with a projection optical system that projects the DUV light beam through a mask onto the photoresist of the wafer. In this way, one or more layers of a chip design are patterned onto the photoresist, and the wafer is then etched and cleaned. Summary of the Invention

[0005] In some general aspects, an apparatus for a light source includes a monitoring module configured to monitor a fault condition of one or more operating conditions of the light source, a decrement module configured to reduce an operating speed of a blower disposed in a gas discharge chamber of the light source when the fault condition for the one or more operating conditions of the light source is clear and when a reduced operating speed is equal to or greater than a baseline speed, and an increment module configured to increase an operating speed of the blower when a fault condition for the one or more operating conditions of the light source is flagged. The blower is configured to move a gas mixture including a gain medium through the gas discharge chamber from an energy source configured to provide energy to the gas mixture.

[0006]

[0006] Implementations can include one or more of the following features: For example, the baseline speed of the blower can be related to the age of the gas discharge chamber, the baseline speed changing as the gas discharge chamber ages over time.

[0007]

[0007] Each of the one or more operating states may be defined by a performance metric for the light source or for a light beam generated by the light source. The one or more performance metric may include a wavelength histogram associated with the light beam, an energy dose error associated with the light beam, an energy error associated with the light beam, and an operating point of a gas discharge chamber in the light source. A fault condition may be flagged if at least one of the associated performance metric is not within a threshold range for that performance metric, and the fault condition is cleared when all of the associated performance metric are within their corresponding threshold ranges. At least one of the operating states of the light source may be proactive such that an operating speed of a blower is adjusted before a value of the associated performance metric falls outside a threshold range for the performance metric. At least one of the operating states may be reactive such that an operating speed of a blower is adjusted after a value of the associated performance metric falls outside a threshold range for the performance metric. Each active operating state may be associated with a limited threshold range that is narrower than the actual threshold range of the performance metric, and the operating speed of the blower may be adjusted before the value of the associated performance metric falls outside the actual threshold range by determining a fault condition of the active operating state based on the limited threshold range.

[0008] A fault condition relating to one or more operational states of a light source may be determined using a low pass filter or a weighted sum filter.

[0009]

[0009] The decrement module may be configured to decrease the operating speed of the blower by a decrement speed step size, and the increment module may be configured to increase the operating speed of the blower by an increment speed step size. The increment speed step size may be greater than the decrement speed step size. The increment speed step size may be 25 revolutions per minute (rpm) or less, and the decrement speed step size may be approximately one-half, one-third, one-quarter, or one-fifth the increment speed step size.

[0010]

[0010] The operating speed of the blower may be adjusted by an increment module and a decrement module within a blower speed range defined by a minimum blower speed and a maximum blower speed.

[0011]

[0011] The decrement module and the increment module may each be configured to avoid a blower operating speed at which an aliased frequency of the blower's second harmonic interferes with a spectral feature control system associated with the light source. The interfering blower operating speed may depend on a repetition rate at which the light source generates the light beam.

[0012]

[0012] The apparatus may also include a baseline module configured to increase the operating speed of the blower when the operating speed of the blower is below the baseline speed.

[0013]

[0013] The apparatus may be a state machine for a light source, where the monitoring module is in a monitoring state, the decrement module is in a decrement state, and the increment module may be in an increment state. After reducing the operating speed of the blower in the decrement state, the state machine may transition from the decrement state to the increment state if a fault condition is flagged for one or more operating conditions of the light source. The state machine may include a baseline state configured to increase the operating speed of the blower if the operating speed of the blower falls below a baseline speed, and the state machine may transition from the decrement state to the baseline state if the operating speed of the blower falls below the baseline speed. After the baseline state increases the operating speed of the blower in the baseline state, the state machine may transition from the baseline state to the increment state if a fault condition is flagged for one or more operating conditions of the light source. The state machine may transition from the monitoring state to the baseline state if the operating speed of the blower falls below the baseline speed. After increasing the operating speed of the blower in the increment state, the state machine can transition from the increment state to the monitoring state if the increased operating speed of the blower is greater than the target speed. The state machine can transition from the monitoring state to the increment state if a fault condition is flagged for one or more operating conditions of the light source. The state machine can transition from the monitoring state to the decrement state if one or more exit criteria are met, the exit criteria being based on one or more of a baseline speed, a number of light beam pulses generated by the light source, and an event that results in an improvement in the performance of the light source.

[0014] In another general aspect, a blower controller for a light source includes a control system in communication with a blower disposed within a gas discharge chamber of the light source, the blower configured to move a gas mixture including a gain medium through the gas discharge chamber from an energy source configured to provide energy to the gas mixture, the control system configured to monitor for a fault condition of one or more operating conditions of the light source, reduce an operating speed of the blower in a decrement state when the fault condition for one or more operating conditions of the light source is clear and the reduced operating speed is equal to or greater than a baseline speed, and increase an operating speed of the blower in an increment state when a fault condition for one or more operating conditions of the light source is flagged.

[0015]

[0015] Implementations may include one or more of the following features: For example, a control system may include a computer-readable memory module and one or more electronic processors coupled to the computer-readable memory module.

[0016]

[0016] A fault condition for one or more operational states may be defined using a binary system in which the fault condition is assigned a value of 0 if the fault condition is clear and a value of 1 if the fault condition is flagged.

[0017]

[0017] The control system may be configured to increase the operating speed of the blower in incremental steps if the reduced operating speed of the blower falls below the baseline speed.

[0018] In another general aspect, a method is performed to control a blower disposed in a gas discharge chamber of a light source, the method including monitoring a fault condition for one or more operating conditions of the light source, decrementing an operating speed of the blower when the fault condition for one or more operating conditions of the light source is clear and a reduced operating speed is equal to or greater than a baseline speed, and incrementing the operating speed of the blower when a fault condition for one or more operating conditions of the light source is flagged.

[0019]

[0019] Implementations may include one or more of the following features. For example, the operating speed of the blower may be decremented by reducing an amount of vibration in the light source caused by movement of the blower. The operating speed of the blower may be decremented by decreasing the operating speed of the blower by a decrement speed step size, and the operating speed of the blower may be incremented by increasing the operating speed of the blower by an increment speed step size. The method may further include determining an increment speed step size and a decrement speed step size of the blower, each dependent on a fault condition related to one or more operational conditions of the light source.

[0020]

[0020] The operating speed of the blower may be decremented and incremented by adjusting the operating speed of the blower within a blower speed range defined by a minimum blower speed and a maximum blower speed. The method may also include determining a blower speed range for the blower that is dependent on a fault condition of one or more operational conditions of the light source.

[0021]

[0021] The method may further include incrementing the operating speed of the blower if the reduced operating speed of the blower is below the baseline speed.

[0022]

[0022] A fault condition for one or more operating conditions may be monitored by monitoring one or more termination criteria to reduce the operating speed of the blower only if one or more of the termination criteria are met. The termination criteria may be based on a baseline speed and a number of light beam pulses generated by the light source, and the termination criteria are met when the operating speed of the blower is greater than the baseline speed and the number of light beam pulses is greater than a minimum number of pulses.

[0023] In another general aspect, an ultraviolet light source includes one or more gas discharge chambers configured to hold a gas mixture including a gain medium, house an energy source configured to provide energy to the gas mixture, and generate a light beam, at least one of which is configured to hold a blower configured to move the gas mixture from the energy source through the gas discharge chamber, and an apparatus configured to adjust an operating speed of the blower, the apparatus including a monitoring module configured to monitor a fault condition for one or more operating conditions of the light source, a decrement module configured to decrease the operating speed of the blower when the fault condition for one or more operating conditions of the light source is clear and a decreased operating speed is equal to or greater than a baseline speed, and an increment module configured to increase the operating speed of the blower when a fault condition for one or more operating conditions of the light source is flagged.

[0024]

[0024] Embodiments may include one or more of the following features. For example, the gain medium may be configured to emit deep ultraviolet (DUV) light in response to a voltage signal being applied to the energy source. The gas gain medium may include argon fluoride (ArF), krypton fluoride (KrF), or xenon chloride (XeCl). The light-generating device may include two gas discharge chambers with a master oscillator configured to generate a seed light beam and a power amplifier configured to generate an output light beam from the seed light beam. The light-generating device may include a plurality of gas discharge chambers, each of which may be configured to emit a light beam toward the beam combiner.

[0025]

[0025] The apparatus may include a baseline module configured to increase the operating speed of the blower when the reduced operating speed of the blower is below the baseline speed. [Brief description of the drawings]

[0026] [Figure 1]

[0026] A block diagram of an ultraviolet light source that generates a light beam used by a lithography exposure apparatus, the ultraviolet light source including a light generating device having one or more gas discharge chambers, each having a blower and a device configured to at least partially control the speed of the blower. [Diagram 2]

[0027] FIG. 2 is a block diagram of an embodiment of the device of FIG. 1 including a monitor module, a decrement module, an increment module, and optionally a baseline module. [Diagram 3]

[0028] FIG. 3 is a schematic diagram illustrating how the overall fault condition of a light source is determined based on one or more operational states of the light source for use by the device of FIGS. 1 and 2. [Figure 4A]

[0029] 1 is an exemplary graph showing how baseline rates change with discharge chamber age for various discharge chambers. [Figure 4B] 1 is an exemplary graph showing how baseline rates change with discharge chamber age for various discharge chambers. [Figure 4C] 1 is an exemplary graph showing how baseline rates change with discharge chamber age for various discharge chambers. [Diagram 5]

[0030] FIG. 1 is a state machine diagram illustrating an embodiment of an apparatus, the state machine including a monitoring state (performed by a monitoring module), a decrement state (performed by a decrement module), and an increment state (performed by an increment module). [Figure 6A]

[0031] 11 is a flow chart of a procedure performed by the decrement module while the state machine is in the decrement state. [Figure 6B]

[0032] 11 is a flow chart of the procedure performed by the monitor module while the state machine is in the monitor state. [Figure 6C]

[0033] 1 is a flow chart of a procedure performed by the baseline module while the state machine is in the baseline state. [Figure 6D]

[0034] 11 is a flow chart of a procedure performed by the increment module while the state machine is in the increment state. [Figure 7A]

[0035] 3 is a flow chart of a procedure executed by the apparatus for controlling the blower speed of the light source of FIGS. 1 and 2. [Figure 7B]

[0036] 7B is an additional step that may be included in the procedure of FIG. 7A. [Figure 8]

[0037] FIG. 1 is a block diagram of an embodiment of a light source in which the light-generating device comprises two gas discharge chambers in a master oscillator-power amplifier configuration. [Figure 9A]

[0038] 1 is a block diagram of an embodiment of a light source in which the light-generating device comprises multiple gas discharge chambers and an embodiment of a lithographic exposure apparatus; [Figure 9B]

[0039] FIG. 9B is a block diagram of an embodiment of a projection optical system of the lithographic exposure apparatus of FIG. 9A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027]

[0040] Referring to FIG. 1, an ultraviolet light source 100 includes a light-generating device 105 that includes one or more gas discharge chambers 104 and a device 110. In the example of FIG. 1, the light-generating device 105 includes one discharge chamber 104, but may include multiple discharge chambers 104 (as shown in FIGS. 8 and 9A). The gas discharge chamber 104 is configured to hold a gas mixture 107 including a gain medium within an internal cavity 104i of the gas discharge chamber 104 and to accommodate an energy source 106 configured to generate a light beam 102 by providing energy to the gas mixture 107. The gain medium of the gas mixture 107 is configured to emit deep ultraviolet (DUV) light in response to a voltage signal being applied to the energy source 106. The energy source 106 may be configured to provide energy to the gas mixture 107 in short (e.g., nanosecond) current pulses using a high-voltage discharge interspersed with periods of no energy. The gas mixture 107 generates pulses of light beam 102 from a population inversion that occurs in the gain medium of the gas mixture 107 by stimulated emission when energy from the energy source 106 is provided to the gas mixture 107. Thus, the light beam 102 is a pulsed light beam that includes pulses of light centered at wavelengths in the DUV range, including wavelengths of 248 nanometers (nm) or 193 nm. For a DUV light source, the gas gain medium of the gas mixture 107 may include, for example, argon fluoride (ArF), krypton fluoride (KrF), or xenon chloride (XeCl). The light beam 102 is directed along a path to a lithography exposure tool 101. The light beam 102 is used to pattern microelectronic features on a substrate or wafer received in the lithography exposure tool 101. The size of the microelectronic features patterned on the wafer depends on the wavelength of the pulsed light beam 102, with lower wavelengths resulting in smaller minimum feature sizes or critical dimensions. For example, if the wavelength of the pulsed light beam 102 is 248 nm or 193 nm, the minimum size of the microelectronic features may be, for example, 50 nm or less.

[0028]

[0041] Specifically, the energy source 106 may include a cathode and an anode, where a potential difference between the cathode and the anode creates an electric field in the gas mixture 107. The electric field provides sufficient energy to the gain medium in the gas mixture 107 to cause a population inversion and enable the generation of light pulses by stimulated emission. Such a potential difference is repeatedly created to produce a train of light pulses that ultimately constitute the light beam 102. A "discharge event" is the application of a voltage that creates a potential difference sufficient to cause a discharge in the gain medium of the gas mixture 107 and the emission of light pulses.

[0029]

[0042] When a light pulse is generated from the gas mixture 107 near the energy source 106, there is a period of time during which the molecules in the gas mixture 107 recover. This recovery period is longer than the time between pulses of the energy source 106. Also, if another pulse of energy is provided to the recovering gas mixture 107 residing closest to the energy source 106, the output quality of the light pulse in the resulting light beam 102 will be reduced, which may lead to failure of the light-generating device 105. To solve this problem, the gas discharge chamber 104 carries a blower 108 that is attached to the walls 103A, 103B of the gas discharge chamber 104. In various embodiments, the blower 108 may comprise a rotating structure such as a fan. See, for example, U.S. Patent No. 6,765,946, issued July 20, 2004, in the name of Partlo, et. al., which is incorporated herein by reference in its entirety. The blower 108 is configured to periodically move the portion of the recovering gas mixture 107 away from the energy source 106 within the gas discharge chamber 104 so that fresh gas mixture 107 can interact with the energy source 106 before the next pulse of the energy source 106 is generated. If the speed of the blower 108 is too slow, arcing, dropouts, and inefficiencies can occur in the gas discharge chamber 104, and the gas discharge chamber 104 can fail if the blower 108 is unable to sufficiently remove the portion of the recovering gas mixture 107. Another consideration is that the rotation or movement of the blower 108 can cause vibrations within the gas discharge chamber 104 that can affect one or more spectral characteristics of the light beam 102 and the dosing performance of the light beam 102 in the lithography exposure apparatus 101.

[0030]

[0043] During operation of the light source 100, the operating speed of the blower 108 (which is the speed or rate at which the blower 108 rotates about its axis of rotation) may be maintained constant at a preset speed. In particular, the operating speed of the blower 108 may be maintained at a maximum blower speed such that the operating speed of the blower 108 does not change over time as the light source 100 operates. Under such conditions, the blower 108 may consume an approximately constant amount of energy over time, in other words, may require constant power as the light source 100 operates, which may be expensive or at least cost ineffective. Thus, as discussed herein, the operating speed of the blower 108 is changed or adjusted over time (as the light source 100 operates) by the device 110 based on fault conditions of one or more operational states of the light source 100 and the baseline speed of the blower 108 (which is the minimum acceptable speed of the blower 108). In this manner, the device 110 functions as a blower controller that controls the operating speed of the blower 108 by adjusting the operating speed between a minimum blower speed and a maximum blower speed that together define a safe blower speed range for the blower 108 during operation of the light source 100. In other words, when the light source 100 is in operation, the device 110 adjusts the operating speed of the blower 108 within a safe blower speed range that does not cause any faults and / or problems within the light source 100, and also adjusts the operating speed of the blower 108 such that more energy is conserved by the blower 108, and, as a result, less energy is consumed by the light source 100. Details of the device 110 will now be provided.

[0031]

[0044] Referring to FIG. 2, the device 110 (ie, the blower controller) includes a monitor module 112, a decrement module 114, and an increment module .

[0032]

[0045] In general, the monitoring module 112 is configured to monitor for fault conditions associated with one or more operational conditions of the light source 100. For example, each of the one or more operational conditions may be defined by a performance metric associated with the light source 100 or with the light beam 102 generated by the light source 100. A fault condition may be considered to be flagged if at least one of the associated performance metric is not within a threshold range for that performance metric, and the fault condition is considered to be clear if all of the associated performance metric are within their respective threshold ranges. Thus, as the light source 100 operates, the monitoring module 112 may monitor one or more operational conditions of the light source 100 by monitoring one or more associated performance metric.

[0033]

[0046] In general, the decrement module 114 is configured to decrease the operating speed of the blower 108 when a fault condition for one or more operational states of the light source 100 is clear and when the decreased operating speed is equal to or greater than the baseline speed of the blower 108 (which is the minimum allowable speed of the blower 108). For example, the decrement module 114 may be configured to decrease the operating speed of the blower 108 by a decrement speed step size.

[0034]

[0047] In general, the increment module 116 is configured to increase the operating speed of the blower 108 when a fault condition in one or more operational conditions of the light source 100 is flagged. The increment module 116 may be configured to increase the operating speed of the blower 108 by an increment speed step size. In one example, the increment step size may be, for example, 25 revolutions per minute (rpm) or less. In this example, the increment speed step size is greater than the decrement speed step size, and the decrement speed step size may be approximately one-half, one-third, one-quarter, or one-fifth the increment speed step size.

[0035]

[0048] The apparatus 110 may also include a baseline module 118 configured to increase the operating speed of the blower 108 if the operating speed of the blower 108 is below the baseline speed.

[0036]

[0049] When the light source 100 operates, the operating speed of the blower 108 is adjusted by the increment and decrement modules 114, 116 and the baseline module 118 within a blower speed range defined by a minimum blower speed and a maximum blower speed. The blower speed range is a safe range within which the light source 100 operates properly without problems and / or failures. In this manner, the device 110 controls the operating speed of the blower 108 by adjusting the operating speed within the safe blower speed range such that minimal energy is consumed by the blower 108 and less energy is consumed by the light source 100.

[0037]

[0050] The modules 112, 114, 116, 118 of the apparatus 110 may be implemented in a control system that is in communication with and thereby controls the blower 108. Thus, the control system of the blower controller 108 is configured to monitor a fault condition for one or more operational conditions of the light source 100, decrementally decrease the operating speed of the blower 108 if the fault condition for one or more operational conditions of the light source 100 is clear and the reduced operating speed is equal to or greater than the baseline speed, and incrementally increase the operating speed of the blower 108 if a fault condition for one or more operational conditions of the light source 100 is flagged. The control system of the blower controller 110 may also be configured to incrementally increase the operating speed of the blower 108 if the reduced operating speed of the blower 108 is below the baseline speed.

[0038]

[0051] The device 110 may, for example, comprise a computer-readable memory module and one or more electronic processors coupled to the computer-readable memory module. Each of the modules 112, 114, 116, 118 may be in communication with the memory module and may be controlled by one or more electronic processors. For example, each module 112, 114, 116, 118 may comprise or have access to one or more programmable processors, each capable of executing a program of instructions that perform a desired function by operating on input data and generating appropriate output. Each module 112, 114, 116, 118 may be implemented in any of digital electronic circuitry, computer hardware, firmware, or software. In further embodiments, each module 112, 114, 116, 118 accesses memory in a memory module that is also configured to store information output from one or more of the modules 112, 114, 116, 118, information from the gas discharge chamber 104, or information about other aspects of the light-generating device 105 that can be used by the modules 112, 114, 116, 118 in various ways during operation of the device 110. The memory in the memory module may be read-only memory and / or random access memory and may provide suitable storage devices for tangibly embodying computer program instructions and data. The device 110 may also include one or more input devices (such as a keyboard, a touch-enabled device, a voice input device, etc.) and one or more output devices, such as an audio output or a video output.

[0039]

[0052] In the example where device 110 functions as a blower controller, the fault conditions for one or more operational states may be defined (by the control system) using a binary system. Specifically, the fault conditions may be assigned a value of zero (0) if the fault condition is clear and a value of one (1) if the fault condition is flagged. Details of the fault conditions for one or more operational states of light source 100 are provided below.

[0040]

[0053] 3, an overall fault status 327 of the light source 100 is determined by the apparatus 110 at each iteration based on one or more operational states of the light source 100. Each of the one or more operational states is defined by performance metrics 320_1-320_N related to the light source 100 or to the light beam 102 generated by the light source 100. The fault status 327 used by the apparatus 110 to control the blower 108 should be based on system parameters, metrics, and signals that are significantly affected by changes in the speed of the blower 108.

[0041]

[0054] In the example of FIG. 3, the one or more performance metrics 320_1-320_N include a spectral feature accuracy associated with the light beam 102, an energy dose error associated with the light beam 102, an energy error associated with the light beam 102, an actuator operating point of the light generating device 105 in the light source 100, and a gas discharge chamber dropout rate.

[0042]

[0055] Spectral feature accuracy describes the stability and precision of the spectral features (e.g., wavelength) of the light beam 102 generated by the light source 100. Specifically, the spectral feature accuracy with respect to wavelength is based on the mean and standard deviation of the error of the wavelength of the light beam 102 calculated over a moving window of M pulses of the light beam 102, where M is an integer equal to or greater than 1. The value of the spectral feature accuracy may be measured / calculated directly or may be estimated from other measurement data.

[0043]

[0056] The energy dose error represents the difference between the desired or target dose at the wafer and the actual dose at the wafer received by the lithography exposure tool 107. The dose at the wafer is the amount of light energy per unit area that the light beam 102 delivers over the exposure time or a specific number of pulses at the wafer. While the energy dose error may be measured / calculated directly, it is alternatively possible to estimate the energy dose error from other measurement data.

[0044]

[0057] The energy error represents the standard deviation of the measured energy of the light beam 102. Specifically, the energy error may be considered as the difference between the energy of a pulse of the light beam 102 and a target amount of energy. While the energy error may be measured directly, the energy error may alternatively be estimated from other data.

[0045]

[0058] The actuator operating point of the light-generating device 105 characterizes where within a range of possible settings, values, or conditions the actuator in the light-generating device 105 is operating. In some embodiments, as discussed below with reference to FIG. 8, the actuator may be a timing module coupled to a first stage including a first discharge chamber 804A (the first stage constitutes a master oscillator) and a second stage including a second discharge chamber 804B (the second stage constitutes a power amplifier) ​​of the light-generating device 805. Such a timing module controls the relative timing between a first trigger signal sent to a first energy source 806A of the first discharge chamber 804A and a second trigger signal sent to a second energy source 806B of the second discharge chamber 804B. This relative timing may be referred to as differential timing. In these embodiments, the metric of the actuator operating point of the light-generating device 805 may quantify the deviation of the actual relative timing from the peak efficiency differential timing (Tpeak). Here, Tpeak is the relative timing value when the light-generating device 805 (via energy sources 806A, 806B) generates the light beam 802 with maximum energy at a particular input energy applied to the light-generating device 805. This actuator operating point metric may be calculated or estimated based on the voltage or energy supplied to the energy sources 806A, 806B, the output energy of the light beam 802, and the differential timing.

[0046]

[0059] The gas discharge chamber dropout rate quantifies a failure mechanism in which the blower 108 is unable to sufficiently remove the portion of the recovering gas mixture 107, causing the gas mixture to not move through the gas discharge chamber 104 fast enough, resulting in arcing and energy loss in the gas discharge chamber 104.

[0047]

[0060] In some embodiments, as discussed above, one or more of the performance metrics 320_1-320_N for the light source 100 may not be available at a particular moment during operation or within a particular system, and the apparatus 110 may estimate values ​​of the unavailable performance metrics based on other available data to determine the fault condition 327. To calculate the overall fault condition 327, the apparatus 110 receives the performance metrics 320_1, 320_2, ... 320_N.

[0048]

[0061] Each of the one or more performance metrics 320_1-320_N is associated with a corresponding value 321_1-321_N that is passed through a corresponding filter 322_1-322_N to remove noise effects or temporary performance issues that may occur during operation. For example, each of the filters 322_1-322_N may be a low pass filter or a weighted sum filter, such that a fault condition 327 for one or more operational states 320_1-320_N of the light source 100 is determined using the filters 322_1-322_N (including the low pass filter or the weighted sum filter). Also, each of the filters 322_1-322_N may have a configurable transfer function for filtering the values ​​321_1-321_N of the performance metrics 320_1-320_N.

[0049]

[0062] Filtered values ​​323_1-323_N of the performance metric 320_1-320_N are output from each of the corresponding filters 322_1-322_N. Each of the filtered values ​​323_1-323_N is compared to a corresponding threshold range 324_1-324_N associated with the corresponding performance metric 320_1-320_N to determine a corresponding fault condition 325_1-325_N associated with each of the performance metric 320_1-320_N (i.e., an operating state). If it is determined that the corresponding performance metric 320_1-320_N is not within the threshold range 324_1-324_N of that performance metric 320_1-320_N, then the fault condition 325_1-325_N of that performance metric 320_1-320_N is flagged. A fault condition 325_1-325_N for a performance metric 320_1-320_N is clear if the corresponding performance metric 320_1-320_N is determined to be within the threshold range 324_1-324_N for that performance metric 320_1-320_N. As described above, the fault conditions 325_1-325_N may be assigned a value of zero (0) if the fault condition 325_1-325_N is clear, or a value of one if the fault condition 325_1-325_N is flagged.

[0050]

[0063] Each fault status 325_1-325_N is input to a fault status module 326 (which may be a controller) that determines an overall fault status 327 of the light source 100 based on the fault statuses 325_1-325_N of the performance metrics 320_1-320_N associated with the light source 100. For example, in some embodiments, the overall fault status 327 of the light source 100 is flagged (i.e., given a value of 1) if any one of the fault statuses 325_1-325_N is flagged (i.e., given a value of 1). And, the overall fault status 327 of the light source 100 is clear (i.e., has a value of 0) if all of the fault statuses 325_1-325_N are clear (i.e., have a value of 0). In this manner, the overall fault status 327 of the light source 100 may be determined and the apparatus 110 may control the blower 108 based on the fault status 327 of the light source 100, thereby reducing energy consumption by the blower 108 during operation. In other embodiments, the fault condition module 326 may be configured to flag the entire fault condition 325 only if multiple fault conditions 325_1-325_N are flagged.

[0051]

[0064] Next, the baseline speed of the blower 108 is detailed.

[0052]

[0065] 4A-4C, the baseline speed of the blower 108 may be related to the age of the gas discharge chamber 104. In the examples of FIGS. 4A-4C, the baseline speed changes as the gas discharge chamber 104 ages over time. In other words, the baseline speed changes as the number of pulses of the light beam 102 generated by the gas discharge chamber 104 increases over time (and as the gas discharge chamber 104 ages). In these examples, the apparatus 110 adjusts the baseline operating speed of the blower 108 between a minimum baseline speed bmin and a maximum baseline speed bmax. Any of the modules 114, 116, 118 of the apparatus 110 or another module may perform this adjustment. In general, the baseline speed of the blower 108 should be increased as the gas discharge chamber 104 ages and performance failures, problems, and / or errors occur more frequently in the aging light source 100 (and in the gas discharge chamber 104). By increasing the baseline velocity of the gas discharge chamber 104 as the discharge chamber 104 ages, performance impairments, problems, and / or errors that may occur within the aging light source 100 are reduced or mitigated.

[0053]

[0066] In the example of Figure 4A, the apparatus 110 adjusts the baseline speed from a maximum baseline speed bmax to a minimum baseline speed bmin at time tla, where the apparatus 110 begins to gradually increase the baseline speed. The baseline speed of the blower 108 is incremented at a constant rate 429a (i.e. slope) as the gas discharge chamber 104 ages over time (or as pulses of the light beam 102 are generated by the gas discharge chamber 104). The baseline speed of the blower 108 is increased or incremented from the minimum baseline speed bmin to the maximum baseline speed bmax such that the baseline speed reaches the maximum baseline speed bmax at time t2a, which is the end of the life of the gas discharge chamber 104.

[0054]

[0067] 4B, apparatus 110 adjusts the baseline speed from a maximum baseline speed bmax to a minimum baseline speed bmin at time tlb. While gas discharge chamber 104 is new for a period of time dL between times tlb and t2b, the baseline speed of blower 108 does not change and remains constant at the minimum baseline speed bmin. Because gas discharge chamber 104 is new between times tlb and t2b, in this example, there is no need to increase the baseline speed to reduce or alleviate the performance problem in light source 100.

[0055]

[0068] At time t2b, the apparatus 110 begins to increase or increment the baseline speed. The baseline speed of the blower 108 is incremented at a constant rate 429b (i.e., slope) as the gas discharge chamber 104 ages and degrades over time (and as pulses of the light beam 102 are generated by the gas discharge chamber 104). The baseline speed of the blower 108 is increased or incremented from a minimum baseline speed bmin to a maximum baseline speed bmax such that the baseline speed reaches a maximum baseline speed bmax at time t3b, which is the end of the life of the gas discharge chamber 104.

[0056]

[0069] The example of Figure 4C is similar to the example of Figure 4B except that the baseline speed of the blower 108 remains constant for a shorter time dS and the baseline speed is incremented at a slower rate 429c than rate 429b. After decrementing the baseline speed to a minimum baseline speed bmin at time tlc and maintaining this minimum baseline speed bmin for time dS, at time t2c the baseline speed increases at a constant rate 429c as the gas discharge chamber 104 ages over time until the baseline speed of the blower 108 reaches a maximum baseline speed bmax at time t3c which is the end of the life of the gas discharge chamber 104.

[0057]

[0070] 5, the apparatus 110 (FIG. 2) is represented as a state machine 510 for the light source 100. In this representation of the state machine 510, the monitor module 112 is represented by a monitor state 512, the decrement module 114 is represented by a decrement state 514, and the increment module 116 is represented by an increment state 516. The state machine 510 may also include a baseline state 518, which represents the baseline module 118 (FIG. 2). In this embodiment, the state machine 510 also includes a passive state 511, in which there is no command or instruction from the state machine 510 to change or adjust the operating speed of the blower 108.

[0058]

[0071] The state machine 510 transitions from the passive state 511 to the decrement state 514 when the number of pulses in the light beam 102 produced from the gas discharge chamber 104 exceeds a threshold value or after the state machine 510 has been in the passive state 511 for a threshold period of time (T(PD)). In general, the decrement state 514 is configured to reduce the operating speed of the blower 108 when the fault condition 327 for one or more operational conditions of the light source 100 is clear and when the reduced operating speed is equal to or greater than the baseline speed.

[0059]

[0072] 6A , in the decrement state 514, the decrement module 114 determines (532) whether the fault status 327 of the light source 100 is clear (e.g., is 0). If the fault status 327 is not clear (i.e., is flagged or has a value of 1) (532), the decrement module 114 exits the decrement state 514 and the state machine 510 transitions (T(DI)) from the decrement state 514 to the increment state 516 such that the operating speed of the blower 108 is incremented to a safe operating speed where no problems and / or faults will occur within the light source 100.

[0060]

[0073] If the fault condition is clear (i.e., has a value of 0) (532), the decrement module 114 determines whether the operating speed of the blower 108 is greater than the baseline speed (533). If the operating speed of the blower 108 is not greater than the baseline speed (i.e., is equal to or less than the baseline speed of the blower 108), the decrement module 114 exits the decrement state 514 and the state machine 510 transitions (T(DB)) from the decrement state 514 to the baseline state 518 such that the operating speed of the blower 108 is incremented to a safe operating speed above the baseline speed at which no problems and / or faults will occur within the light source 100.

[0061]

[0074] If the operating speed of the blower 108 is greater than the baseline speed (533), the decrement module 114 determines whether the proposed new blower speed is greater than the baseline speed (534). The proposed new blower speed is the operating speed of the blower 108 minus the decrement speed step size. If the proposed new speed of the blower 108 is not greater than the baseline speed (i.e., the proposed new blower speed is the baseline speed or is less than the baseline speed) (534), the decrement module 114 exits the decrement state 514 and the state machine 510 transitions from the decrement state 514 to the monitor state 512 (T(DM)) so that one or more operating conditions of the light source 100 and the operating speed of the blower 108 can be monitored.

[0062]

[0075] On the other hand, if the proposed new blower speed is greater than the baseline speed (534), the decrement module 114 determines whether the number of pulses of the light beam 102 generated by the gas discharge chamber 104 since the last time the blower speed was changed is greater than a threshold number of pulses (541). The threshold number of pulses may be preset to a positive integer to reduce the frequency at which the blower speed is changed. For example, the frequency at which the blower speed is changed may be set to ensure that the light-generating device 105, and similarly the performance metric, have sufficient time to adjust to the effects of the blower speed change. It is also possible to operate in the decrement state 514 without performing this step 541.

[0063]

[0076] If the number of pulses of the light beam 102 produced by the gas discharge chamber 104 is not greater than (i.e., is less than or equal to) the threshold number of pulses (541), the decrement module 114 returns to step 532 and repeats steps 532, 533, and 534. If the number of pulses of the light beam 102 produced by the gas discharge chamber 104 is greater than the threshold number of pulses (541), the decrement module 114 instructs the blower 108 to slow down or decrement its operating speed (542). For example, the decrement state 514 may decrement the operating speed of the blower 108 by the decrement speed step size.

[0064]

[0077] After reducing (542) the operating speed of the blower 108 in the decrement state 514, the decrement module 114 returns to querying (532) whether the fault status 327 for one or more operating conditions of the light source 100 is clear (e.g., has a value of 0).

[0065]

[0078] Thus, in summary, decrement module 114 reduces (524) the speed of blower 108 if there is no fault (532), if the speed of blower 108 is greater than the baseline speed (533), if the proposed new blower speed is greater than the baseline speed (534), and if a certain number of pulses of light beam 102 have been generated since the last change in blower speed (541). In this manner, the energy consumed by blower 108 is significantly reduced, especially early in the life of light source 100 and gas discharge chamber 104.

[0066]

[0079] Referring again to FIG. 5, as discussed above with reference to FIG. 6A, if the proposed new speed of the blower 108 is not greater than the baseline speed (i.e., the proposed new blower speed is at or less than the baseline speed) (534), the decrement module 114 exits the decrement state 514 and the state machine 510 transitions from the decrement state 514 to the monitoring state 512 (T(DM)) so that one or more operational conditions of the light source 100 and the operating speed of the blower 108 can be monitored.

[0067]

[0080] Generally, in the monitoring state 512, the monitoring module 112 is configured to monitor for the exit criteria and remain in the monitoring state 512 while there are no faults, the blower speed is greater than the baseline speed, and there are no occurrences of the exit criteria events. With reference to FIGURE 6B, in the monitoring state 512, the monitoring module 112 determines (537) whether the fault condition 327 for one or more operational conditions of the light source 100 is clear (e.g., has a value of 0). If the fault condition 327 is not clear (i.e., flagged) (537), the state machine 510 transitions (T(MI)) from the monitoring state 512 to the increment state 516 such that the operating speed of the blower 108 is increased to a safe operating speed where no problems and / or faults occur within the light source 100.

[0068]

[0081] If the fault condition is clear (i.e., has a value of 0) (537), the monitoring module 112 determines whether the operating speed of the blower 108 is greater than the baseline speed (538). If the operating speed of the blower 108 is less than, or falls below, the baseline speed (538), the state machine 510 transitions from the monitoring state 512 to the baseline state 518 such that the operating speed of the blower 108 is increased to a safe operating speed where no problems and / or faults occur within the light source 100 (T(MB)). If the operating speed of the blower 108 is greater than the baseline speed (538), the monitoring module 112 determines whether one or more exit criteria are met (536). For example, the exit criteria may be based on one or more of the baseline speed, the number of pulses of the light beam 102 generated by the light source 100, and an event that results in an improvement in the performance of the light source 100. If the termination criteria are met, the state machine 510 transitions (T(MD)) from the monitor state 512 to the decrement state 514 (because it is determined that the light source 100 is in a safe state to reduce the operating speed of the blower 108). If the termination criteria are not met, the monitor module 112 returns to determining (537) whether the fault condition 327 for one or more operating conditions of the light source 100 is clear (e.g., has a value of 0). One possible termination criterion that may be evaluated in step 536 is a determination of whether the speed of the blower 108 is greater than a baseline speed plus a lower threshold (e.g., 200 rpm). In this case, it may be more appropriate to reduce the blower speed (by the decrement state 514). Another possible termination criterion that may be evaluated in step 536 is to determine whether the number of pulses of the light beam 102 currently being generated is greater than a predetermined threshold, such as 100 million pulses. Alternatively, instead of evaluating the set of termination criteria in step 536 based on the number of pulses of the light beam 102 generated, the monitoring module 112 can evaluate whether a particular performance improvement event has occurred. For example, the performance improvement event could be a gas refill or gas injection, where the gas mixture 107 is at least partially or completely replaced.Such an event may result in improved performance of the light source 100 .

[0069]

[0082] Referring back to FIG. 5, as discussed above with reference to FIG. 6A, if the operating speed of the blower 108 is equal to or less than the baseline speed (533), the decrement module 114 exits the decrement state 514 and the state machine 510 transitions (T(DB)) from the decrement state 514 to the baseline state 518 such that the operating speed of the blower 108 is incremented to a safe operating speed above the baseline speed where no issues and / or faults will occur within the light source 100. The baseline state 518 is discussed with reference to FIG. 6C. In general, the baseline state 518 is configured to increase the operating speed of the blower 108 if the operating speed of the blower 108 is equal to or less than the baseline speed. The baseline module 118 determines (539) whether the fault status 327 of the light source 100 is clear (e.g., equal to 0). If the fault condition 327 is not clear (and thus is flagged or has a value of 1) (539), the state machine 510 transitions from the baseline state 518 to the increment state 516 so that the operating speed of the blower 108 is incremented to a safe operating speed at which no problems and / or faults will occur within the light source 100 (T(BI)).

[0070]

[0083] If the fault condition is clear (i.e., has a value of 0) (539), the baseline module 118 determines whether the operating speed of the blower 108 is less than the baseline speed (540). If the operating speed of the blower 108 is equal to or greater than the baseline speed (540), the state machine 510 transitions (T(BM)) from the baseline state 518 to the monitoring state 512 (because there is no need to increase the operating speed). On the other hand, if the operating speed of the blower 108 is less than the baseline speed (540), the baseline module 118 determines whether the number of pulses of the light beam 102 generated by the gas discharge chamber 104 since the last time the blower speed was changed is greater than a threshold number of pulses (548). As discussed above, the threshold number of pulses may be preset to a positive integer to reduce the frequency of changing the blower speed. If the number of pulses of the light beam 102 generated by the gas discharge chamber 104 is less than or equal to the threshold number of pulses (548), the baseline module 118 continues to query whether the number of pulses of the light beam 102 generated by the gas discharge chamber 104 has been greater than the threshold number of pulses since the last time the blower speed was changed.

[0071]

[0084] If the number of pulses of the light beam 102 produced by the gas discharge chamber 104 is greater than the threshold number of pulses (548), then the baseline module 118 increases or increments (549) the operating speed of the blower 108. For example, the baseline module 118 may increment the operating speed of the blower 108 by an increment speed step size. As an example, the increment speed step size may be about 5 revolutions per minute (rpm). After increasing the operating speed of the blower 108, the baseline module 118 returns to step 439 again to determine whether the fault status 327 of the light source 100 is clear (e.g., equal to 0).

[0072]

[0085] 5, as discussed above with reference to FIGS. 6A-6C, the state machine 510 can transition to the increment state 516 from any one of the decrement state 514, the monitor state 512, and the baseline state 518. For example, while in the decrement state 514, if the fault condition 327 is not clear (i.e., flagged or has a value of 1) (532), the decrement module 114 exits the decrement state 514 and the state machine 510 transitions (T(DI)) from the decrement state 514 to the increment state 516. Generally, in the increment state 516, the operating speed of the blower 108 is incremented to a safe operating speed at which no problems and / or faults will occur within the light source 100. The increment state 516 will now be considered with reference to the embodiment shown in FIG. 6D.

[0073]

[0086] Specifically, in the increment state 516, the increment module 116 determines (544) whether the fault status 327 of the light source 100 is clear (e.g., 0). If the fault status 327 is not clear (e.g., the fault status is 1) (544), the increment module 116 sets (545) a new target speed for the blower 108. The new target speed for the blower 108 may be equal to the operating speed of the blower 108 plus a large increment speed step size (e.g., 100 rpm). The idea is to increase the speed of the blower 108 significantly when a fault occurs. After the new target speed for the blower 108 is set (545) or after the increment module 116 determines (544) that the fault status is clear (e.g., the fault status is 0), the increment module 116 determines (535) whether the operating speed of the blower 108 is less than the new target speed. If the operating speed of the blower 108 is not less than the new target speed (535), i.e., the operating speed of the blower 108 is greater than or equal to the new target speed (535), the state machine 510 transitions from the increment state 516 to the monitor state 512 (T(IM)).

[0074]

[0087] If the operating speed of the blower 108 is less than the target speed (535), the increment module 116 determines whether the number of pulses of the light beam 102 generated by the gas discharge chamber 104 is greater than a threshold number of pulses (546). If the number of pulses of the light beam 102 generated by the gas discharge chamber 104 is less than or equal to the threshold number of pulses, the increment module 116 continues to query whether the number of pulses of the light beam 102 generated by the gas discharge chamber 104 is greater than a threshold number of pulses (546). If the number of pulses of the light beam 102 generated by the gas discharge chamber 104 is greater than the threshold number of pulses, the increment module 116 increases or increments the operating speed of the blower 108 by a specified amount (547). For example, the increment module 116 may increment the operating speed of the blower 108 by an increment speed step size, for example, 25 rpm. After increasing (547) the operating speed of the blower 108, the increment module 116 returns to step 535 to determine whether the increased operating speed of the blower 108 is less than the target speed (535).

[0075]

[0088] 7A more generally, the apparatus 110 performs a procedure 760 for controlling the blower 108. The procedure 760 may be performed for the apparatus 110 (FIG. 2) and for the light source 100 (FIG. 1) that includes the blower 108 in the gas discharge chamber 104. The procedure 760 may also be performed for the state machine 510 (FIG. 5). Below, the procedure 760 is described for the light source 100 that includes the blower 108.

[0076]

[0089] Procedure 760 includes monitoring 761 one or more operational conditions of the light source for fault conditions. As discussed above, e.g., with reference to FIG. 6B, the monitoring module 112 monitors 537 one or more operational conditions of the light source 100 for fault conditions 327 (FIG. 3).

[0077]

[0090] The apparatus 110 then decrements (763) the operating speed of the blower 108 if the fault condition for one or more operational conditions of the light source 100 is clear and if the reduced operating speed is equal to or greater than the baseline speed. For example, with reference to FIG. 6A , the decrement module 114 decrements (542) the operating speed of the blower 108 if the fault condition 327 for one or more operational conditions of the light source 100 is clear (532) and if the reduced operating speed of the blower 108 is greater than the baseline speed (534). Decrementing the operating speed of the blower 108 may include decreasing the operating speed of the blower 108 by a decrement speed step size. Decrementing the operating speed of the blower 108 may also include reducing an amount of vibration in the light source 100 caused by the movement of the blower 108.

[0078]

[0091] Meanwhile, referring back to Figure 7, the apparatus 110 increments (765) the operating speed of the blower 108 if a fault condition is flagged for one or more operational conditions of the light source. For example, referring to Figure 6D, the increment module 116 increments (547) the operating speed of the blower 108 if a fault condition 327 of the light source 100 is flagged. Incrementing the operating speed of the blower 108 may include increasing the operating speed of the blower 108 by an increment speed step size. In this manner, the increment module 116 prevents the blower 108 from operating at an operating speed that may cause problems and / or failures within the light source 100.

[0079]

[0092] 7B, procedure 760 may further include incrementing (767) the operating speed of the blower if the reduced operating speed of the blower is below the baseline speed. For example, with reference to FIG. 6C, if the baseline module 118 determines (540) that the reduced operating speed of the blower 108 (which the decrement module 114 reduced) is below the baseline speed, the baseline module 118 increases or increments (549) the operating speed of the blower 108. Thus, similar to the increment module 116, the baseline module 118 prevents the blower 108 from operating at an operating speed that may cause problems and / or failures within the light source 100.

[0080]

[0093] In one example, decrementing and incrementing the operating speed of the blower 108 may include adjusting the operating speed of the blower 108 within a blower speed range defined by a minimum blower speed and a maximum blower speed. In other words, the operating speed of the blower 108 is adjusted between the minimum blower speed and the maximum blower speed by the increment and decrement modules 114, 116 (as well as the baseline module 118). As explained above, the blower speed range is a safe range in which the light source 100 operates properly without problems and / or failures. In this manner, the device 110 can control the operating speed of the blower 108 by adjusting the operating speed within the safe blower speed range such that minimal energy is consumed by the blower 108 and the energy consumed by the light source 100 is reduced.

[0081]

[0094] In some embodiments, procedure 760 may further include determining an increment speed step size and a decrement speed step size for the blower 108, each of which is dependent on the fault condition 327 for one or more operational states of the light source 100. In particular, one or more studies of the light source 100 may be performed, for example, by a user determining maximum increment speed step sizes and decrement speed step sizes that both maintain the stability of the light source 100 and do not adversely affect the performance of the light source 100 (so that the fault condition 327 of the light source 100 remains clear). Additionally, procedure 760 may further include determining a blower speed range for the blower 108, which is dependent on the fault condition 327 for one or more operational states of the light source 100. Similarly, one or more studies of the light source 100 may be performed, for example by a user, to determine a minimum and maximum blower speed (and thus a blower speed range) such that the performance of the light source 100 is not adversely affected when the blower 108 is operated within the blower speed range (so that the fault condition 327 of the light source 100 remains clear).

[0082]

[0095] 3, in some embodiments, at least one of the operating states (associated with each performance metric 320_1-320_N) of the light source 100 is active and at least one of the operating states is reactive. Specifically, in an active operating state, the operating speed of the blower 108 is adjusted (e.g., by the increment module 116 or the decrement module 114) before the value 323_1-323_N of the associated performance metric 320_1-320_N falls outside the threshold range 324_1-324_N of the performance metric 320_1-320_N. In a reactive operating state, the operating speed of the blower 108 is adjusted (eg, by the increment module 116 or the decrement module 114) after the value 323_1-323_N of the associated performance metric 320_1-320_N falls outside the threshold range 324_1-324_N of the performance metric 320_1-320_N. Also, in some embodiments, each active operating state is associated with a limited threshold range that is narrower than the actual threshold range 324_1-324_N of the performance metric 320_1-320_N, and the operating speed of the blower 108 is adjusted (e.g., by the increment module 116 or the decrement module 114) before the value 323_1-323_N of the associated performance metric 320_1-320_N falls outside the actual threshold range 324_1-324_N by determining a fault condition 325_1-325_N of the active operating state based on the limited threshold range.

[0083]

[0096] 8, an embodiment 800 of light source 100 (FIG. 1) includes a light-generating apparatus 805 with two gas discharge chambers 804A, 804B that generates a pulsed output light beam 802 that is directed to a lithography exposure tool 801. The pulsed output light beam 802 has a wavelength in the ultraviolet range (e.g., in the deep ultraviolet range) that is used by the lithography exposure tool 801 to pattern a semiconductor substrate or wafer 870. In the example of FIG. 8, the gas discharge chamber 804A is part of a master oscillator configured to generate a seed light beam 802s, and the gas discharge chamber 804B is part of a power amplifier configured to generate an output light beam 802 from the seed light beam 802s. Each of the discharge chambers 804A, 804B includes a corresponding blower 808A, 808B configured to move a corresponding gas mixture 807A, 807B including the gain medium from a corresponding energy source 806A, 806B through the corresponding gas discharge chamber 804A, 804B. In the example of Fig. 8, the apparatus 110 is configured to control the operating speed of the two blowers 808A, 808B. In particular, the apparatus 110 controls the blowers 808A, 808B to consume a minimum amount of energy or power during operation of the light source 800 while ensuring that problems and / or failures in the light source 800 do not occur (or are at least mitigated). Other embodiments of the light source 800 are possible.

[0084]

[0097] Each discharge chamber 804A, 804B is configured to hold a corresponding gas mixture 807A, 807B in a corresponding internal cavity 873A, 873B. The gas mixture 807A, 807B used in the corresponding discharge chamber 804A, 804B may be a combination of gases suitable for generating a corresponding light beam 802s, 802 centered on a desired wavelength, bandwidth, and energy. For example, the gas mixture 807A, 807B may include argon fluoride (ArF), which emits light at a wavelength of about 193 nm. Each discharge chamber 804A, 804B is defined by a corresponding chamber wall 803A_1, 803A_2, 803B_1, 803B_2 configured to hold a corresponding blower 808A, 808B and a corresponding optical component 875A, 876A, 877A, 875B, 876B, 877B in this example. Each discharge chamber 804A, 804B houses a corresponding energy source 806A, 806B configured to provide energy to the gas mixture 807A, 807B within each internal cavity 873A, 873B. For example, each energy source 806A, 806B may comprise a pair of electrodes that create a potential difference to excite the gain medium of the gas mixture 807A, 807B during operation.

[0085]

[0098] Each discharge chamber 804A, 804B may include one or more optical components. For example, the discharge chamber 804A includes optical components 875A, 876A associated with the internal cavity 873A of the discharge chamber 804A. The optical components 875A, 876A may include windows that allow the light beam to enter and exit the internal cavity 873A of the discharge chamber 804A. The optical component 875A may be a partially reflective / partially transmissive optical coupler that allows the seed light beam 802s to exit the discharge chamber 804A. The light source 800 may also include other optical components outside the discharge chamber 804A, such as an optical component 877A corresponding to a spectral feature selection module that selects the wavelength and / or bandwidth of the seed light beam 802s output from the discharge chamber 804A. For example, the spectral feature selection module 877A may include one or more of a beam expanding prism or a beam splitter. In this example, optical component 875A is held within chamber wall 803A_1, and optical component 876A is held within chamber wall 803A_2.

[0086]

[0099] Discharge chamber 804B includes optical components 875B, 876B associated with internal cavity 873B of discharge chamber 804B. Optical components 875B, 876B may include windows that allow light beams (such as seed light beam 802s and light beam 802) to enter and exit internal cavity 873B of discharge chamber 804B. Light source 800 may also include other optical components that are external to discharge chamber 804B, such as optical component 877B corresponding to a beam reverser or rotator configured to direct light beam 802 back through discharge chamber 804B. In the example of FIG. 8, optical component 875B is held within chamber wall 803B_1 and optical component 876B is held within chamber wall 803B_2.

[0087]

[0100] During operation of the light source 800, the apparatus 110 controls the operating speed of each of the two blowers 808A, 808B. In some embodiments, control of the operating speed of the blower 808A may be independent of control of the operating speed of the blower 808B. In some embodiments, each blower 808A, 808B is independently controlled by a dedicated apparatus (810A, 810B). Also, the apparatus 810B may be designed differently from the apparatus 810A to account for differences in how the discharge chambers 804A, 804B each affect the parameters of the output light beam. Furthermore, while the control of the blowers 808A, 808B is not coupled in these embodiments, simultaneous control by the apparatus 810A, 810B may couple differently in performance than controlling only one of them due to the different way each blower 808A, 808B drives vibrations in the frame of the chambers 804A, 804B.

[0088]

[0101] In other embodiments, control of the operating speed of blower 808A and / or blower 808B may depend on a performance metric associated with the light-generating device 105, and thus the control of the two blowers 808A, 808B may be coupled.

[0089]

[0102] In some embodiments, it may be possible to have a single device 110 configured to control the blower 810A of the first discharge chamber 804A, but not use a device 110 to control the blower 810B of the second discharge chamber 804B.

[0090]

[0103] Specifically, in the example of Figure 8, the apparatus 110 (Figure 2) comprises a monitor module 112 that monitors for a fault condition of one or more operational conditions of the light source 800, a decrement module 114 that reduces the operating speed of the appropriate blower 808A, 808B if the fault condition for one or more operational conditions of the light source 800 is clear and if the reduced operating speed of the corresponding blower 808A, 808B is equal to or greater than the baseline speed, and an increment module 116 that increases the operating speed of the appropriate blower 808A, 808B if a fault condition for one or more operational conditions of the light source 800 is flagged. In this manner, the apparatus 110 controls the blowers 808A, 808B to consume a minimum amount of energy or power during operation of the light source 800, whereby problems and / or faults within the light source 800 are mitigated or mitigated based on the fault condition of the light source 800 and the baseline speed of the blowers 808A, 808B.

[0091]

[0104] 9A, an embodiment 900 of light source 100 (FIG. 1) includes a light generating device 905 that includes a plurality of optical oscillators 909-1 to 909-N, each with a corresponding gas discharge chamber 904-1 to 904-N, generating a pulsed light beam 902 that is directed to a lithography exposure tool 901, and a control system 950. The light source 900 is configured to generate an output light beam 902 in the ultraviolet range that is used by, for example, the lithography exposure tool 901 to pattern a semiconductor substrate or wafer 970. In particular, the lithography exposure tool 901 exposes the wafer 970 with a shaped exposure beam 902′ that is formed by passing the light beam 902 (which in this example is an exposure beam) through a projection optical system 995. 9A, the light-generating apparatus 905 comprises N optical oscillators 909_1 to 909_N and thus N gas discharge chambers 904-1 to 904-N, where N is an integer greater than 1. Each of the gas discharge chambers 904-1 to 904-N is configured to emit a corresponding light beam 978-1 to 978-N towards the beam combiner 993. In the example shown, a control system 950 is connected to the light-generating apparatus 905 and to the lithographic exposure apparatus 901. Other embodiments of the light source 900 are possible.

[0092]

[0105] Each of the gas discharge chambers 904-1-904-N includes a corresponding blower 908-1-908-N, each configured to move a corresponding gas mixture 907-1-907-N including a gain medium from a corresponding energy source 906-1-906-N through the corresponding gas discharge chamber 904-1-904-N. In the example of FIG. 9A, the apparatus 110 (FIG. 2) is included as part of a control system 950 that is a blower controller that controls the operating speed of each of the blowers 908-1-908-N. The apparatus 110 is configured to control the operating speed of the blowers 908-1-908-N. In particular, the apparatus 110 controls each blower 908-1-908-N to consume a minimum amount of energy or power during operation of the light source 900 while ensuring that problems and / or failures within the light source 900 do not occur (or are at least mitigated).

[0093]

[0106] The details of optical oscillator 909-1 are discussed below. The other N-1 optical oscillators of light-generating device 905 have the same or similar characteristics.

[0094]

[0107] The optical oscillator 909-1 comprises a gas discharge chamber 904-1 housing an energy source 906-1, which may include, for example, a cathode and an anode, and a blower 908-1. The discharge chamber 904-1 also contains a gas mixture 907-1, which includes a gain medium. A resonator is formed between a spectral feature selection module 977-1 on one side of the discharge chamber 904-1 and an output coupler 980-1 on a second side of the discharge chamber 904-1. The spectral feature selection module 977-1 may comprise a diffractive optical element, such as, for example, a grating and / or a prism, that finely tunes the spectral output of the discharge chamber 904-1. In some embodiments, the spectral feature selection module 977-1 comprises multiple diffractive optical elements. For example, the spectral feature selection module 977-1 may comprise four prisms, some of which are configured to control the central wavelength of the optical beam 978-1 and others of which are configured to control the spectral bandwidth of the optical beam 978-1.

[0095]

[0108] In some embodiments, the spectral feature selection module 977-1 may include or be in communication with a spectral feature control system configured to, for example, control various components within the spectral feature selection module 977-1. In these embodiments, the decrement module 114 and the increment module 116 of the apparatus 110 (which are part of the control system 950 in this example) may each be configured to avoid an interference blower operating speed at which the aliased frequency of the second harmonic of the blower 908-1 interferes with the spectral feature control system associated with the light source 900. For example, the interference blower operating speed may be dependent on the repetition rate at which the light source 900 generates a light beam (which in this example includes the light beam 902 or the exposure beam 902').

[0096]

[0109] The optical oscillator 909-1 also includes a line center analysis module 981-1 that receives the output optical beam from the output coupler 980-1. The line center analysis module 981-1 is a measurement system that may be used to measure or monitor the wavelength of the optical beam 978-1. The line center analysis module 981-1 may provide data to the control system 950, which may determine metrics associated with the optical beam 978-1 based on the data from the line center analysis module 981-1. For example, the control system 950 may determine a beam quality metric or a spectral bandwidth based on the data measured by the line center analysis module 981-1.

[0097]

[0110] The light-generating device 905 also includes a gas supply system 990 that is fluidly coupled to the interior of the discharge chamber 904-1 via a fluid line 998. The fluid line 998 is any conduit that can transport a gas or other fluid with no or minimal loss of the fluid. For example, the fluid line 998 can be a pipe made of or coated with a material that does not react with the fluid or fluids transported in the conduit 998. The gas supply system 990 includes a chamber 991 that is configured to contain and / or receive a supply of one or more gases used in the gas mixture 907-1. The gas supply system 990 also includes devices (pumps, valves, and / or fluidic switches) that allow the gas supply system 990 to remove gas from the discharge chamber 904-1 and / or inject gas into the discharge chamber 904-1. The gas supply system 990 is coupled to a control system 950. The gas supply system 990 can be controlled by the control system 950, for example to perform a refill procedure.

[0098]

[0111] The other N-1 optical oscillators are similar to optical oscillator 904-1 and have similar or the same components and subsystems. For example, each of optical oscillators 909-1 to 909-N includes an energy source similar to energy source 906-1, a spectral feature selection module similar to spectral feature selection module 977-1, and an output coupler similar to output coupler 980-1. Optical oscillators 909-1 to 909-N may be tuned or configured such that all of optical beams 978-1 to 978-N have the same characteristics, or optical oscillators 909-1 to 909-N may be tuned or configured such that at least some of the optical oscillators have at least some characteristics that are different from the other optical oscillators. For example, all of optical beams 978-1 to 978-N may have the same center wavelength, or the center wavelength of each optical beam 978-1 to 978-N may be different. The center wavelength generated by a particular one of the optical oscillators 909-1 through 909-N may be set using a corresponding spectral feature selection module.

[0099]

[0112] The light generating device 905 also includes a beam controller 992 and a beam combiner 993. The beam controller 992 is between the gas mixtures of the optical oscillators 909-1 to 909-N and the beam combiner 993. The beam controller 992 determines which of the optical beams 978-1 to 978-N are incident on the beam combiner 993. The beam combiner 993 forms the exposure beam 902 from one or more optical beams incident on the beam combiner 993. In the illustrated example, the beam controller 992 is depicted as a single element. However, the beam controller 992 could be implemented as a collection of individual beam controllers. For example, the beam controller 992 could be a collection of shutters, one shutter associated with each optical oscillator 909-1 to 909-N.

[0100]

[0113] The light generating device 905 may include other components and systems. For example, the light generating device 905 may include a beam preparation system 994 with a bandwidth analysis module that measures various characteristics of the light beam (such as bandwidth or wavelength). The beam preparation system 994 may also include a pulse stretcher (not shown), which stretches in time each pulse that interacts with the pulse stretcher. The beam preparation system 994 may also include other components that may act on the light, such as reflective and / or refractive optical elements (such as lenses and mirrors), and / or filters. In the example shown, the beam preparation system 994 is positioned in the path of the exposure beam 902. However, the beam preparation system 994 may be located elsewhere in the light source 900. Other implementations are also possible. For example, the light generating device 905 may include N instances of the beam preparation system 994, each of which is positioned to interact with one of the light beams 978-1 to 978-N. In another example, light generating device 905 may include optical elements (such as mirrors) that direct light beams 978-1 through 978-N toward beam combiner 993.

[0101]

[0114] The lithography exposure apparatus 901 can be an immersion system or a dry system. The lithography exposure apparatus 901 comprises a projection optical system 995 through which the exposure beam 902 passes before reaching the wafer 970, and a sensor system or metrology system 997. The wafer 970 is held or accommodated on a wafer holder 996. Referring also to FIG. 9B, the projection optical system 995 comprises a projection objective including a slit 995a, a mask 995b, and a lens system 995c. The lens system 995c includes one or more optical elements. The exposure beam 902 enters the lithography exposure apparatus 901 and impinges on the slit 995a, and at least a portion of the beam 902 passes through the slit 995a to form a shaped exposure beam 902'. In the example of FIG. 9A and FIG. 9B, the slit 995a is rectangular and shapes the exposure beam 902 into an elongated rectangular shaped light beam, which is the shaped exposure beam 902'. Mask 995b contains a pattern that determines which portions of the shaped light beam are transmitted through mask 995b and which portions are blocked by mask 995b. Microelectronic features are formed on wafer 970 by exposing a layer of radiation-sensitive photoresist material on wafer 970 to exposure beam 902'. The design of the pattern on the mask is determined by the particular microelectronic circuit characteristics desired.

[0102]

[0115] The embodiments may be further described using the following clauses: 1. An apparatus for a light source, comprising: a monitoring module that monitors one or more operational conditions of the light source for a fault condition; a decrement module that reduces an operating speed of a blower disposed within a gas discharge chamber of the light source, the blower moving a gas mixture containing a gain medium through the gas discharge chamber from an energy source that provides energy to the gas mixture when a fault condition associated with one or more operational states of the light source is clear and when the reduced operating speed is equal to or greater than a baseline speed; and an increment module that increases an operating speed of the blower if a fault condition is flagged relating to one or more operational conditions of the light source. 2. The apparatus of clause 1, wherein the baseline speed of the blower is related to the age of the gas discharge chamber, the baseline speed changing as the gas discharge chamber ages over time. 3. An apparatus according to clause 1, wherein each of the one or more operating states is defined by a performance metric relating to the light source or to a light beam generated by the light source. 4. The apparatus of clause 3, wherein the one or more performance metrics include a wavelength histogram associated with the light beam, an energy dose error associated with the light beam, an energy error associated with the light beam, and an operating point of a gas discharge chamber within the light source. 5. The apparatus of clause 3, wherein a fault condition is flagged if at least one of the relevant performance metrics is not within a threshold range for that performance metric, and the fault condition is cleared if all of the relevant performance metrics are within their corresponding threshold ranges. 6. The apparatus of clause 5, wherein at least one of the operating states of the light source is active such that the operating speed of the blower is adjusted before the value of the associated performance metric falls outside the performance metric threshold range, and at least one of the operating states is reactive such that the operating speed of the blower is adjusted after the value of the associated performance metric falls outside the performance metric threshold range. 7. The apparatus of clause 6, wherein each active operating condition is associated with a limited threshold range that is narrower than the actual threshold range of the performance metric, and the operating speed of the blower is adjusted before the value of the associated performance metric falls outside the actual threshold range by determining a fault condition of the active operating condition based on the limited threshold range. 8. The apparatus of clause 1, wherein a fault condition relating to one or more operational states of the light source is determined using a low pass filter or a weighted sum filter. 9. The apparatus of clause 1, wherein the decrement module decreases the operating speed of the blower by the decrement speed step size and the increment module increases the operating speed of the blower by the increment speed step size. 10. The apparatus of clause 9, wherein the increment rate step size is greater than the decrement rate step size. 11. The apparatus of clause 9, wherein the increment speed step size is 25 revolutions per minute (rpm) or less and the decrement speed step size is approximately one-half, one-third, one-quarter, or one-fifth the increment speed step size. 12. The apparatus of clause 1, wherein the operating speed of the blower is regulated by an increment module and a decrement module within a blower speed range defined by a minimum blower speed and a maximum blower speed. 13. The apparatus of clause 1, wherein the decrement module and the increment module each avoid a blower operating speed at which an aliased frequency of the blower's second harmonic interferes with a spectral characteristic control system associated with the light source. 14. An apparatus according to clause 13, in which the interfering blower operating speed is dependent on the repetition rate at which the light source generates the light beam. 15. The apparatus of clause 1, further comprising a baseline module that increases an operating speed of the blower if the operating speed of the blower is below the baseline speed. 16. The apparatus of clause 1, wherein the apparatus is a state machine for a light source, wherein the monitor module is in a monitor state, the decrement module is in a decrement state, and the increment module is in an increment state. 17. The apparatus of clause 16, wherein after reducing the operating speed of the blower in the decrement state, the state machine transitions from the decrement state to the increment state if a fault condition is flagged relating to one or more operational conditions of the light source. 18. The apparatus of clause 16, wherein the state machine further includes a baseline state that increases the operating speed of the blower if the operating speed of the blower falls below the baseline speed, and wherein the state machine transitions from the decrement state to the baseline state if the operating speed of the blower falls below the baseline speed. 19. The apparatus of clause 18, wherein the state machine transitions from the baseline state to the increment state if a fault condition is flagged for one or more operational conditions of the light source after the baseline state increases the operating speed of the blower in the baseline state. 20. The apparatus of clause 18, wherein the state machine transitions from the monitoring state to the baseline state if the operating speed of the blower falls below the baseline speed. 21. The apparatus of clause 16, wherein after increasing the operating speed of the blower in the Increment State, the state machine transitions from the Increment State to the Monitor State if the increased operating speed of the blower is greater than the target speed. 22. The apparatus of clause 16, wherein the state machine transitions from the monitor state to the increment state if a fault condition is flagged relating to one or more operational states of the light source. 23. The apparatus of clause 16, wherein the state machine transitions from the monitoring state to the decrementing state when one or more exit criteria are met, the exit criteria being based on one or more of a baseline rate, a number of light beam pulses produced by the light source, and an event that results in an improvement in performance of the light source. 24. A blower controller for a light source, comprising: a blower disposed within a gas discharge chamber of the light source, the blower moving the gas mixture including the gain medium through the gas discharge chamber from an energy source that provides energy to the gas mixture, the control system being in communication with the blower; Monitor one or more operational states of the light source for fault conditions; reducing the operating speed of the blower in a decrement state when a fault condition related to one or more operational states of the light source is clear and when the reduced operating speed is equal to or greater than the baseline speed; A blower controller that incrementally increases the operating speed of the blower when a fault condition is flagged relating to one or more operational conditions of the light source. 25. The control system a computer readable memory module; and one or more electronic processors coupled to a computer readable memory module. 26. A blower controller of clause 24, wherein a fault condition for one or more operational conditions is defined using a binary system in which a fault condition is assigned a value of 0 if the fault condition is clear and a value of 1 if the fault condition is flagged. 27. The blower controller of clause 24, wherein the control system further increases the operating speed of the blower in an incremental manner if the reduced operating speed of the blower is below the baseline speed. 28. A method of controlling a blower disposed within a gas discharge chamber of a light source, comprising the steps of: monitoring one or more operational states of the light source for a fault condition; decrementing the operating speed of the blower when a fault condition related to one or more operational states of the light source is clear and when the reduced operating speed is equal to or greater than the baseline speed; and The method includes incrementing an operating speed of a blower if a fault condition is flagged relating to one or more operational conditions of the light source. 29. The method of clause 28, wherein decrementing the operating speed of the blower includes reducing an amount of vibration in the light source caused by movement of the blower. 30. The method of clause 28, wherein decrementing the operating speed of the blower includes decreasing the operating speed of the blower by a decrement speed step size, and wherein incrementing the operating speed of the blower includes increasing the operating speed of the blower by an increment speed step size. 31. The method of clause 30, further comprising determining an increment speed step size and a decrement speed step size for the blower, each of which is dependent on a fault condition related to one or more operational conditions of the light source. 32. The method of clause 28, wherein decrementing and incrementing the operating speed of the blower includes adjusting the operating speed of the blower within a blower speed range defined by a minimum blower speed and a maximum blower speed. 33. The method of clause 32, further comprising determining a blower speed range for the blower dependent on a fault condition of one or more operational conditions of the light source. 34. The method of clause 28, further comprising incrementing the operating speed of the blower if the reduced operating speed of the blower is below the baseline speed. 35. The method of clause 28, wherein monitoring for a fault condition relating to one or more operating conditions includes monitoring one or more exit criteria such that the operating speed of the blower is reduced only if one or more of the exit criteria are satisfied. 36. The method of clause 35, wherein the termination criterion is based on a baseline speed and a number of light beam pulses generated by the light source, and the termination criterion is met when the operating speed of the blower is greater than the baseline speed and the number of light beam pulses is greater than a minimum number of pulses. 37. A light generating device comprising one or more gas discharge chambers for holding a gas mixture including a gain medium, housing an energy source for providing energy to the gas mixture, and producing a light beam, at least one of the gas discharge chambers housing a blower for moving the gas mixture from the energy source through the gas discharge chamber; A device for adjusting the operating speed of a blower, comprising: a monitoring module that monitors for fault conditions relating to one or more operational states of the light source; a decrement module that reduces the operating speed of the blower when a fault condition related to one or more operational states of the light source is clear and when the reduced operating speed is equal to or greater than the baseline speed; and and an apparatus having an increment module that increases the operating speed of a blower if a fault condition in one or more operational conditions of the light source is flagged. 38. The ultraviolet light source of clause 37, wherein the gain medium emits deep ultraviolet (DUV) light in response to a voltage signal being applied to the energy source. 39. The ultraviolet light source of clause 38, wherein the gas gain medium comprises argon fluoride (ArF), krypton fluoride (KrF), or xenon chloride (XeCl). 40. The ultraviolet light source of clause 37, wherein the light generating apparatus comprises two gas discharge chambers with a master oscillator for generating a seed light beam and a power amplifier for generating an output light beam from the seed light beam. 41. The ultraviolet light source of clause 37, wherein the light generating device comprises a plurality of gas discharge chambers, each of the gas discharge chambers emitting a light beam toward the beam combiner. 42. An ultraviolet light source according to clause 37, wherein the device increases the operating speed of the blower if the reduced operating speed of the blower is below the baseline speed.

[0103]

[0116] Other embodiments are within the scope of the claims.

Claims

1. 1. An apparatus for a light source, comprising: a monitoring module configured to monitor one or more operational conditions of the light source for a fault condition; a decrement module configured to reduce an operating speed of a blower disposed in a gas discharge chamber of the light source, the blower configured to move the gas mixture including a gain medium through the gas discharge chamber from an energy source configured to provide energy to the gas mixture when the fault condition for one or more operational states of the light source is clear and when the reduced operating speed is equal to or greater than a baseline speed; an increment module configured to increase the operating speed of the blower if the fault condition relating to one or more operational conditions of the light source is flagged.

2. The apparatus of claim 1 , wherein each of the one or more operating conditions is defined by a performance metric related to the light source or to a light beam generated by the light source.

3. 3. The apparatus of claim 2, wherein the one or more performance metrics include a wavelength histogram associated with the light beam, an energy dose error associated with the light beam, an energy error associated with the light beam, and an operating point of the gas discharge chamber in the light source.

4. The apparatus of claim 1 , wherein the fault condition for the one or more operational states of the light source is determined using a low pass filter or a weighted sum filter.

5. 2. The apparatus of claim 1, wherein the decrement module is configured to decrease the operating speed of the blower by a decrement speed step size and the increment module is configured to increase the operating speed of the blower by an increment speed step size.

6. The apparatus of claim 5 , wherein the increment rate step size is greater than the decrement rate step size.

7. 2. The apparatus of claim 1, wherein the decrement module and the increment module are each configured to avoid blower operating speeds at which aliased frequencies of the blower's second harmonic interfere with a spectral feature control system associated with the light source.

8. The apparatus of claim 7 , wherein the blower operating speed that is interfered with depends on a repetition rate at which the light source generates the light beam.

9. The apparatus of claim 1 , further comprising a baseline module configured to increase the operating speed of the blower if the operating speed of the blower is below the baseline speed.

10. 2. The apparatus of claim 1, wherein the apparatus is a state machine for the light source, with the monitoring module in a monitoring state, the decrement module in a decrement state, and the increment module in an increment state, and after reducing the operating speed of the blower in the decrement state, the state machine transitions from the decrement state to the increment state if the fault condition is flagged for one or more operating states of the light source.

11. 2. The apparatus of claim 1, wherein the apparatus is a state machine for the light source, wherein the monitoring module is in a monitoring state, the decrement module is in a decrement state, and the increment module is in an increment state, the state machine further comprising a baseline state configured to increase the operating speed of the blower if the operating speed of the blower falls below the baseline speed, the state machine transitioning from the decrement state to the baseline state if the operating speed of the blower falls below the baseline speed.

12. The apparatus of claim 11 , wherein the state machine transitions from the monitoring state to the baseline state if the operating speed of the blower falls below the baseline speed.

13. 2. The apparatus of claim 1, wherein the apparatus is a state machine for the light source, with the monitoring module in a monitoring state, the decrement module in a decrement state, and the increment module in an increment state, and the state machine transitions from the monitoring state to the decrement state when one or more termination criteria are met, the termination criteria being based on one or more of the baseline speed, the number of light beam pulses generated by the light source, and an event that results in an improvement in performance of the light source.

14. 1. A blower controller for a light source, comprising: a control system in communication with a blower disposed within a gas discharge chamber of the light source, the blower configured to move the gas mixture including the gain medium through the gas discharge chamber from an energy source configured to provide energy to the gas mixture, the control system comprising: monitoring one or more operational conditions of the light source for a fault condition; reducing the operating speed of the blower in a decrement state when the fault condition for one or more operational states of the light source is clear and when the reduced operating speed is equal to or greater than a baseline speed; a blower controller configured to incrementally increase the operating speed of the blower if the fault condition relating to one or more operational conditions of the light source is flagged.

15. 15. The blower controller of claim 14, wherein the fault conditions for the one or more operational conditions are defined using a binary system in which the fault condition is assigned a value of 0 if the fault condition is clear and a value of 1 if the fault condition is flagged.

16. The blower controller of claim 14 , wherein the control system is further configured to increase the operating speed of the blower in the incremental state if the reduced operating speed of the blower is below the baseline speed.

17. a light-generating device comprising one or more gas discharge chambers configured to hold a gas mixture including a gain medium, house an energy source configured to provide energy to the gas mixture, and generate a light beam, at least one of the gas discharge chambers configured to hold a blower configured to move the gas mixture from the energy source through the gas discharge chamber; 1. An apparatus configured to adjust an operating speed of the blower, comprising: a monitoring module configured to monitor for fault conditions relating to one or more operational conditions of the light source; a decrement module configured to reduce the operating speed of the blower when the fault condition related to one or more operational states of the light source is clear and when the reduced operating speed is equal to or greater than a baseline speed; and and an apparatus comprising an increment module configured to increase the operating speed of the blower if the fault condition of one or more operational conditions of the light source is flagged.

18. 20. The ultraviolet light source of claim 17, wherein the light-generating device comprises a plurality of gas discharge chambers, each of the gas discharge chambers configured to emit a light beam toward a beam combiner.

19. 20. The ultraviolet light source of claim 17, wherein the apparatus comprises a baseline module configured to increase the operating speed of the blower if the reduced operating speed of the blower is below the baseline speed.

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