JP7430799B2 - Control system for light sources - Google Patents

Description

Cross-reference of related applications
[0001] This application claims priority to U.S. patent application Ser. Incorporated herein.

[0002] The present disclosure relates to a control system for a light source, such as a deep ultraviolet light source.

[0003] Photolithography is a process in which semiconductor circuits are patterned on a substrate such as a silicon wafer. An optical source produces deep ultraviolet (DUV) light that is used to expose photoresist on the wafer. DUV light can include wavelengths from about 100 nanometers (nm) to about 400 nm, for example. Often the optical source is a laser source (eg, an excimer laser) and the DUV light is a pulsed laser beam. DUV light from an optical source interacts with a projection optical system that projects a beam through a mask onto a photoresist on a silicon wafer. In this way, a layer of chip designs is patterned onto the photoresist. Subsequently, the photoresist and wafer are etched and cleaned, and then the photolithography process is repeated.

[0004] In one aspect, the light source is configured to generate light that is active during a first period, idle during a second period, and active during a third period. including an apparatus and a control system. The first time period occurs before the second time period, and the second time period occurs before the third time period. An excitation signal is applied to the light generator in the active state and not applied to the light generator in the idle state. The control system is configured to estimate a characteristic of the excitation signal for applying to the light generating device during the third period based on the duration of the second period and the value of the characteristic during the first period. Ru.

[0005] Implementations can include one or more of the following features.

[0006] A light generating device may include a discharge chamber configured to hold a gaseous gain medium and a plurality of electrodes within the discharge chamber. The excitation signal may include a voltage signal applied to at least one of the plurality of electrodes, and the characteristic of the excitation signal may include a magnitude of the voltage signal. The voltage signal may include a time-varying voltage signal. The control system may include a memory module configured to store at least one value representative of the magnitude of the voltage signal applied to the electrode during the first period. The value of the characteristic during the first period may include a minimum voltage applied to the electrode during the first period. The control system determines the characteristics of the excitation signal for applying to the light generating device during the third period, the duration of the second period, the minimum voltage applied to the electrode during the first period and the first period. may be configured to estimate based on an adaptive parameter associated with. The gaseous gain medium may include a gain medium configured to emit deep ultraviolet (DUV) light in response to a voltage signal applied to at least one of the electrodes. The gaseous gain medium may include argon fluoride (ArF), krypton fluoride (KrF) or xenon chloride (XeCl).

[0007] The control system is also configured to determine an error metric based on the estimated characteristic of the excitation signal and the actual value of the characteristic of the excitation signal applied to the light generating device during the third period. obtain. The control system may be configured to update the value of the adaptive parameter based on the error metric. The control system may be configured to update a value for each of the plurality of adaptation parameters, and each of the plurality of adaptation parameters may be associated with a different duration of the second time period.

[0008] The control system may be configured to determine whether to initiate a warm-up procedure based on the estimated characteristics of the excitation signal. When a warm-up procedure is initiated, the control system may be configured to determine a warm-up procedure metric related to a duration of the warm-up procedure. The warm-up procedure metric may be the number of times the light generator is excited during the warm-up procedure.

[0009] The light generating device may include a main oscillator and a power amplifier.

[0010] The light generating device may include a single discharge chamber.

[0011] The light generating device may include a plurality of discharge chambers, and each of the discharge chambers may be configured to emit a pulsed light beam toward a beam combiner.

[0012] In another aspect, a controller for a light source includes a control system. The control system is configured to access information related to the duration of the idle period of the light source and to access information related to a value of a characteristic of the excitation signal applied to the light source during a period that occurred before the idle period. , and estimating an updated value of the characteristic of the excitation signal based on the duration of the idle period and the value of the characteristic of the excitation signal during a period that occurred before the idle period.

[0013] Implementations may include one or more of the following features.

[0014] The control system may be configured to apply an excitation signal having an updated value of the characteristic to the light source after the idle period. The control system may be configured to determine an error metric based on the estimated updated value of the characteristic and the actual value of the characteristic of the excitation signal applied to the light generator after the idle period. The control system may be configured to update the value of the adaptive parameter based on the error metric. The control system may be configured to update a value for each of the plurality of adaptation parameters, each of the plurality of adaptation parameters being associated with a different duration of the second time period.

[0015] The control system may also be configured to determine whether to initiate a warm-up procedure for the light source based on the estimated updated value of the characteristic.

[0016] The control system is configured to access from the computer readable memory module information related to the duration of the idle period of the light source and information related to the value of the characteristic of the excitation signal during periods occurring before the idle period. may be configured.

[0017] The control system may also include a computer readable memory module and one or more electronic processors coupled to the computer readable memory module.

[0018] In another aspect, a method includes accessing information related to the duration of an idle period of a light source and relating to a value of a characteristic of an excitation signal applied to the light source during a period that occurred before the idle period. and estimating an updated value of the characteristic of the excitation signal based on the duration of the idle period and the value of the characteristic of the excitation signal during a period that occurred before the idle period.

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

[0020] FIG. 4 is a block diagram of a light source at different times. [0020] FIG. 4 is a block diagram of a light source at different times. [0020] FIG. 4 is a block diagram of a light source at different times. [0021] FIG. 4 is a block diagram of another light source at different times. [0021] FIG. 4 is a block diagram of another light source at different times. [0021] FIG. 4 is a block diagram of another light source at different times. [0022] FIG. 3 is a flowchart of a process for estimating the value of a characteristic of an excitation signal. [0023] FIG. 3 is a flowchart of a process for determining whether to initiate a warm-up procedure. [0024] FIG. 3 is a plot of idle time as a function of time. [0025] FIG. 3 is a plot of voltage metrics as a function of time. [0026] FIG. 4 is a plot of the voltage applied to the electrodes of the first DUV light source as a function of time. [0027] FIG. 4 is a plot of voltage applied to the electrodes of a second DUV light source as a function of time. [0028] FIG. 5D is a plot of error metrics as a function of idle time for the second DUV light source of FIG. 5D. [0029] FIG. 5D is a plot of error metrics as a function of idle time for the second DUV light source of FIG. 5D. [0030] FIG. 1 is a block diagram of a photolithography system. [0031] FIG. 2 is a block diagram of an optical lithography system. [0032] FIG. 7B is a block diagram of a projection optical system for the optical lithography system of FIG. 7A.

[0033] Each of FIGS. 1A-1C is a block diagram of light source 100 at different times. FIG. 1A shows light source 100 at time t1. FIG. 1B shows light source 100 at time t2. FIG. 1C shows light source 100 at time t3. Time t1 occurs during the first time period, time t2 occurs during the second time period, and time t3 occurs during the third time period. The first time period occurs before the second time period, and the second time period occurs before the third time period. Three time periods are shown for illustrative purposes. However, light source 100 can operate for more than four periods.

[0034] Light source 100 includes a light generating device 110 and a control system 150 that estimates characteristics of excitation signal 109. Excitation signal 109 may be generated by control system 150 or by a separate device (such as a voltage or current source) controlled by control system 150. Excitation signal 109 is any type of signal sufficient to cause light generating device 110 to generate light beam 105. For example, excitation signal 109 is applied to an excitation mechanism within light generating device 110 (such as excitation mechanism 211 in FIGS. 2A-2C, electrodes 611A and 611b in FIG. 6 or electrodes 711-1a and 711-1b in FIG. 7). It can be a signal that Light beam 105 may be, for example, a pulsed laser beam or a continuous wave laser beam. Light generator 110 may be a deep ultraviolet (DUV) optical system that emits a pulsed light beam within the DUV range (eg, wavelengths from about 100 nanometers (nm) to about 400 nm). In some implementations, light generator 110 emits a burst of pulses during each active period. A burst of pulses includes hundreds or thousands of light pulses.

[0035] Excitation signal 109 is applied to light generating device 110 or a component of light generating device 110 when light generating device 110 is in an active state. Light generator 110 generates a light beam 105 during an active state. Light generating device 110 also has an inactive or idle state. While in the inactive or idle state, excitation signal 109 is not applied to light generating device 110 or its components, and light generating device 110 does not generate light beam 105. During an idle or inactive state, light generating device 110 may be powered off or shut off, or powered on and not producing any light, for example. In the example of FIGS. 1A-1C, light generating device 110 is active during the first and third time periods and idle during the second time period. The temporal duration of the second period is also referred to as an idle time, and the second period is also referred to as an idle period.

[0036] As discussed in more detail below, the control system 150 controls the characteristics of the excitation signal 109 applied to the light generating device 110 during the third time period to match the duration of the idle period and the previous active period (e.g. , the value of the characteristic of the excitation signal 109 applied to the light generating device 110 during the first period). The characteristic may be, for example, the amplitude of the voltage and/or current signal supplied to the excitation mechanism within the light generating device 110.

[0037] By determining the characteristics of the excitation signal 109 using the idle time and the value of the characteristic during the first period, the control system 150 improves the performance of the light source 100. For example, some prior art techniques determine excitation signals based only on idle time. These prior art techniques, for example, use a predetermined excitation signal when the idle time is greater than a predetermined threshold, and/or when the idle time is greater than a predetermined idle time threshold. to enter warm-up mode.

[0038] On the other hand, the control system 150 implements a technique for estimating the updated value of the excitation signal 109, taking into account the previous values of the characteristics of the excitation signal 109. The approach taken by the control system 150 results in a more accurate determination of the characteristics of the excitation signal 109 applied during the third period and improves the use of the warm-up procedure. For example, control system 150 reduces or eliminates unnecessary execution of warm-up procedures while also facilitating ensuring that warm-up procedures are properly invoked.

[0039] Furthermore, control system 150 may also determine adaptive parameters that account for changes in one or more characteristics of light generating device 110 over time. For example, the energy efficiency of light generating device 110 may change over time. Energy efficiency is the relationship between the amount of energy delivered to light generating device 110 to produce light with a certain amount of energy. For example, in implementations where the excitation signal 109 is a voltage signal applied to the electrodes of the light generating device 110, as the energy efficiency of the light generating device 110 decreases, more voltage is required to generate the light beam 105. Is required. The energy efficiency of light generating device 110 may also decrease during idle times. As discussed in more detail below, the adaptive parameters can estimate and track changes in the energy efficiency of the light generating device 110. By taking into account the characteristics of light generation 110 that change over time, control system 150 improves the accuracy of the estimation of the characteristics of excitation signal 109.

[0040] Referring to FIGS. 2A-2C, a block diagram of a light source 200 is shown. Light source 200 is an implementation of light source 100. Each of FIGS. 2A-2C shows light source 200 at a different time. Light source 200 is shown in an active state in FIGS. 2A and 2C and in an idle state in FIG. 2B. Light source 200 includes a light generating device 210 and a control system 250. Light generating device 210 includes an excitation mechanism 211 and a gain medium 212.

[0041] Light generating device 210 generates light beam 205 in an active state. Excitation signal 209 is applied to light generator 210 to excite excitation mechanism 211 when light generator 210 is in the active state (FIGS. 2A and 2C). Light generating device 210 also has an inactive or idle state (FIG. 2B). When the light generator 210 is idle, the excitation signal 209 is not applied to the light generator and does not excite the excitation mechanism 211. In the example of FIGS. 2A-2C, light source 200 is active during a first period (including time t1) and a third period (including time t3). Light source 200 is idle during the second period (including time t2). The duration of the second period is also referred to as idle time. Three time periods are shown for illustrative purposes. However, light source 200 can operate for more than four periods.

[0042] Excitation mechanism 211 excites gain medium 212 in response to excitation signal 209. Gain medium 212 is any medium suitable for producing a beam of light at the wavelength, energy, and bandwidth required for the application. For example, gain medium 212 can be a gas, crystal, glass, semiconductor, or liquid.

[0043] Excitation mechanism 211 is any mechanism capable of exciting gain medium 212. For example, excitation mechanism 211 can be a plurality of electrodes that excite a gaseous gain medium. Excitation signal 209 may be, for example, an electrical signal (such as a voltage signal) or a command signal that causes an additional element (such as a voltage or current source) to generate an electrical signal that is supplied to excitation mechanism 211. . Excitation signal 209 can be a time-varying direct current (DC) or alternating current (AC) electrical signal, such as a sinusoidal or square wave voltage signal. In these implementations, the characteristics of the excitation signal 209 include a maximum amplitude of the time-varying signal, an average amplitude of the time-varying signal, a minimum amplitude of the time-varying signal, a frequency of the time-varying signal, a duty cycle of the time-varying signal, and/or a time-variant signal. It could be any other characteristic associated with the variable signal.

[0044] Control system 250 estimates characteristics of excitation signal 209. The characteristics may be, for example, the amplitude, frequency and/or duty cycle of the voltage and/or current signal supplied to the excitation mechanism 211 within the light generating device 210. Control system 250 estimates the characteristics of excitation signal 209 based on the previous or preceding idle time and the previous or previous value of the characteristics of excitation signal 209 . To estimate the characteristics of excitation signal 209, control system 250 may implement a process such as process 300 discussed with respect to FIG. Control system 250 may also implement other processes, such as process 400 discussed with respect to FIG. 4, as a standalone process or in conjunction with process 300. Additionally, control system 250 can be used with any type of optical source. For example, control system 250 can be used with photolithography system 600 (FIG. 6) or optical lithography system 700 (FIG. 7).

[0045] Control system 250 includes an electronic processing module 251, a computer readable memory module 252, and an I/O interface 253. Electronic processing module 251 includes one or more processors suitable for the execution of a computer program, such as a general purpose or special purpose microprocessor, and any one or more processors of any type of digital computer. Generally, electronic processors receive instructions and data from read-only memory, random access memory (RAM), or both. Electronic processing module 251 may include any type of electronic processor. One or more electronic processors in electronic processing module 251 execute instructions and access data stored in memory module 252. One or more electronic processors can also write data to memory module 252.

[0046] Memory module 252 may be volatile memory, such as RAM, or may be non-volatile memory. In some implementations, memory module 252 includes non-volatile and volatile parts or components. Memory module 252 can store data and information used in the operation of control system 250. For example, the memory module 252 may store information related to idle periods and values of characteristics of the excitation signal 209 applied to the light generating device 210 during one or more periods occurring prior to the past and most recent idle times. information can be stored. Memory module 252 can store one or more values associated with excitation signal 209 applied during an active period that occurred immediately before the most recent idle period. For example, excitation signal 209 can be a voltage signal or a signal specifying a voltage produced by a voltage source. In this example, memory module 252 may store the average, minimum, and maximum values of the voltage signal during the most recent active period. Memory module 252 may also store information received from light source 200 and/or light generating device 210.

[0047] I/O interface 253 is an optional interface that allows control system 250 to exchange data and signals with an operator, an automated process operating on light generator 210, and/or another electronic device. This is a type of interface. For example, in implementations where rules or instructions stored in memory module 252 may be edited, the editing may occur via I/O interface 253. In another example, I/O interface 253 receives data from light generating device 210 and/or from hardware and/or software subsystems of light generating device 210. For example, light generating device 210 may provide idle time and other information about light generating device 210 to control system 250 via I/O interface 253. I/O interface 253 may include one or more of any type of interface, such as a visual display, a keyboard, and a communication interface, such as a parallel port, a universal serial bus (USB) connection, and/or an Ethernet. I/O interface 253 may also enable communication without physical contact, for example, via IEEE 802.11, Bluetooth, or near field communication (NFC) connections.

[0048] Control system 250 is coupled to light generating device 210 via data connection 254. Data connection 254 may include a physical cable or other physical data conduit (e.g., a cable that supports data transfer based on IEEE 802.3), a wireless data connection (e.g., a data connection that provides data via IEEE 802.11 or Bluetooth) or a combination of wired and wireless data connections. The data provided via the data connection can be configured via any type of protocol or format. Data connection 254 is connected to light generating device 210 at a corresponding communication interface (not shown). A communication interface can be any type of interface that can send and receive data. For example, the data interface can be an Ethernet interface, a serial port, a parallel port or a USB connection. In some implementations, the data interface enables data communication via a wireless data connection. For example, the data interface may be an IEEE 811.11 transceiver, Bluetooth or NFC connection. Control system 250 may be connected to systems and/or components within light generating device 210. For example, control system 250 can be connected to excitation mechanism 211.

[0049] In the example of FIGS. 2A-2C, control system 250 is shown as being separate from light generating device 210 and connected via data connection 254. However, in some implementations, the control system 250 is configured such that the light generating device 210 and the control system 250 are part of a single integrated package (e.g., confined within the same housing). It is implemented as part of the generator 210. In these implementations, the data connection 254 may be connected to one software module of the software modules that implements aspects of the control system 250 and to another of the software modules that implements other functionality for the light generating device 210. may be a data path that allows communication between

[0050] FIG. 3 is a flowchart of process 300. Process 300 is an example of a process for estimating the value of a characteristic of excitation signal 209. Process 300 may be performed by a control system associated with a light generating device. For example, process 300 may be performed by control system 150 (FIG. 1) or control system 250 (FIGS. 2A-2C). In the following discussion, process 300 is discussed with respect to control system 250 and light generating device 210. For example, with reference to FIGS. 2A-2C, process 300 is a collection of instructions (e.g., computer programs or software) stored in memory module 252 and executed by one or more electronic processors within electronic processing module 251. It can be realized as

[0051] Information regarding the duration of an idle period of the light generating device 210 is accessed (310). The duration of an idle period (also referred to as idle time) is the length of a consecutive period during which light generating device 210 is idle or inactive. Idle time may relate to idle periods that have occurred in the past and may be the duration of the most recent idle period. For example, the idle time may be the duration of a second time period that includes time t2 shown in FIG. 2B.

[0052] Idle time may be stored in memory module 252. In these implementations, control system 250 accesses the idle time value from memory module 252. The idle time value is not necessarily accessed from memory module 252. For example, in some implementations, idle time is provided by an operator via I/O interface 253. Additionally, the information regarding idle time may be a numerical value representing idle time, and the information may be in other formats. For example, information regarding idle time may include a time when the idle period started and a time when the idle time ended. In these implementations, control system 250 is configured to determine idle time based on the accessed information.

[0053] Information regarding the value of the characteristic of the excitation signal 209 applied to the light generator 210 during the active period that occurred before the idle period is accessed (320). For example, the information may be the maximum voltage applied to the excitation mechanism 211 during the most recent active period. The information may include multiple values of the characteristic during previous active periods. For example, the information may include the maximum and minimum voltages applied to the excitation mechanism 211 during previous active periods. In another example, the information may include a time series representing voltages applied to the excitation mechanism 211 at regular time intervals during active periods. Information related to the values of the characteristics of excitation signal 209 may be accessed from memory module 252 or the information may be accessed via I/O interface 253.

[0054] An updated value of the characteristic of the excitation signal 209 is estimated (330) based on the duration of the idle period and the value of the characteristic of the excitation signal 209 during a period that occurred before the idle period. The following discussion relates to an example in which excitation signal 209 is a time-varying voltage signal applied to excitation mechanism 211. The characteristic of the excitation signal 209 that is estimated is the maximum amplitude (V _max ) of the voltage applied to the excitation mechanism 211 after the idle period has ended. Excitation signal 209 generates a burst of pulses that includes a large number of individual pulses (eg, hundreds or thousands). Each pulse is formed by a corresponding pulse in time-varying voltage excitation signal 209. In the following discussion, the maximum voltage (V _max ) is the maximum magnitude of the voltage applied to the excitation mechanism 211 to form a light pulse during the active period, and the minimum voltage (V _min ) is the maximum magnitude of the voltage applied to the excitation mechanism 211 to form a light pulse during the active period. is applied to the excitation mechanism 211 to form a light pulse during. The maximum voltage (V _max ) typically occurs relatively early in a particular burst after an idle period, during a transient period associated with light generator 210 beginning to generate light beam 205. . The minimum voltage (V _min ) typically occurs during the second half of the burst, after the transient effects have ended and when the light generator 210 is in steady state.

[0055] The value of the voltage signal of the excitation signal 209 applied to the excitation mechanism 211 after the end of the idle time can be estimated as shown in equation (1).
where i is an integer value that indexes the active period of light generating device 210;
is the estimate of the maximum voltage of the excitation signal 209 for use in the ith active period, and V _min (i-1) is the minimum voltage of the excitation signal 209 during the (i-1)th active period. , α(i-1) is the value of the adaptation parameter α associated with the (i-1)th active period, and ΔT(i) is the idle period immediately before the i-th active period. This is idle time. The i-th active period is the current active period, and the (i-1)th active period is the active period immediately before the current active period. An idle period with idle time ΔT(i) is between the i-th active period and the (i-1)-th active period.

[0056] For example, the current or i-th active period may be the third period including t3 as shown in FIG. 2C, and the previous active period may be the first period including t1 as shown in FIG. 2A. It can be a period. Continuing with this example, the idle time is a second period that includes t2 as shown in FIG. 2B. Therefore, in this example, V _min (i-1) is the minimum voltage applied to the excitation mechanism 211 during the first period (based on the information accessed at (320)) and ΔT(i) is , the duration of the second period or idle time (based on the information accessed at (310)), and the estimated characteristic of the excitation signal is the maximum voltage applied to the excitation mechanism 211 during the third period. It is.

[0057] The above discussion relates to an example where the excitation signal 209 is a time-varying voltage signal applied to the excitation mechanism 211 and the metric of the estimated excitation signal 209 is the value of the maximum voltage (V _max ). However, other metrics may be estimated. For example, in some implementations, a constant voltage is applied to the excitation mechanism 211 and the output energy of the light beam 205 is adjusted during the idle period based on knowledge of the idle time and the output energy of the light beam 205 before the idle time. Estimated later. In other words, the techniques discussed above can be used to predict the light energy generated in light beam 205 after an idle period.

[0058] The adaptation parameter α(i-1) is the value of the adaptation parameter associated with the first period. The value of the adaptation parameter associated with the first time period may be stored in memory module 252 or provided to control system 250 via I/O interface 253. Process 300 may end, return to (310), or continue to (340).

[0059] In some implementations, the adaptation parameter α is updated every active period. In these implementations, an error metric is determined (340). The error metric is based on the estimated characteristic (estimated at 330) of the excitation signal 209 applied to the excitation mechanism 211 during the active period and the actual value of the characteristic of the excitation signal 209 applied during the active period. Based on. The error metric can be determined as shown in equation (2).
where i is an integer value that indexes the active period of light generating device 210, e _v (i) is the error metric associated with the i-th active period, and V _max (i) is is the actual value of the maximum applied voltage of the excitation signal 209 applied to the light generating device 210 during the i-th active period;
is the estimated maximum voltage of excitation signal 209 for the i-th active period.

[0060] The value of the adaptation parameter may be updated (350). An adaptive parameter is any parameter representative of a characteristic of light generating device 210 that changes over time. For example, the adaptation parameter may be an estimate of the energy efficiency of light generating device 210. Energy efficiency relates input energy (voltage supplied to excitation mechanism 211) to output energy (light energy in light beam 205). This association may be approximately linear. The slope of the linear relationship to or against idle time can be used as an adaptation parameter.

[0061] The value of the adaptation parameter (α) can be updated as shown in equation (3).
α(i)=α(i-1)+ηe _v (i) Equation (3)
where i is an integer value that indexes the active period of light generating device 210, η is the step size or weighting factor, and e _v (i) is the error metric for the i-th active period. . In the example of equation (3), i is the current active period (e.g., the third period including time t3 in FIG. 2C) and i-1 is the previous active period (e.g., time t1 in FIG. 2A). (first period including the first period).

[0062] The step size or weighting factor η remains constant over time unless intentionally changed by the operator of the light source 200. The step size or weighting factor η determines how much the error value e _v (i) influences the adaptation parameter α. A relatively large value of the step size or weighting factor η results in a large change in the adaptation parameter α compared to a relatively small value. The step size or weighting factor η may be set by the manufacturer when the light generating device 210 is assembled and stored in the memory module 252, and/or the operator may set the step size or weighting factor via the I/O interface 253. Coefficients may be updated.

[0063] The updated value of the adaptation parameter α may be stored in the memory module 252 associated with the i-th active period so that the control system 250 can access the value of the adaptation parameter for later use.

[0064] In some implementations, multiple instances of the adaptive parameter are used, each instance being associated with a particular idle time or range of idle time. For example, two, five, seven or more instances of the adaptation parameter α may be initialized and then updated based on equations (4), (5) and (6).
where j is one instance, α _j is the adaptation parameter corresponding to the jth instance, and ΔT is the idle time range associated with the jth instance. The idle time ranges are not necessarily the same. For example, in one implementation, five ( _j = 5) instances of the adaptation parameter α For each super, it is initialized with one instance of the adaptation parameter α _j . Therefore, if the idle time is 60 seconds or less, α(1) is used as α _j . If the idle time is 3600 seconds or more, α(5) is used as α _j .

[0065] By using one or more instances of adaptation parameters α _j , the overall accuracy of process 300 is improved. For example, the energy efficiency of light generating device 210 generally decreases as idle time increases. The relationship between energy efficiency and idle time is often linear when idle time is relatively short (e.g., idle time less than 10 minutes), but when idle time is relatively long, energy efficiency is not necessarily linear. Degrades with idle time in a non-linear manner. To account for this, multiple instances of the adaptation parameter α _j can be used, each associated with a different range of idle times. This approach can result in a more efficient process and ensure accurate results for longer idle times. This is because the range of idle time can be chosen such that the energy efficiency is linear or nearly linear in each range, and therefore Equation (3) can be used to update the various tunable parameters. .

[0066] In some implementations, control system 250 does not intentionally update the adaptive parameters under certain conditions, even if control system 250 updates the adaptive parameters under other conditions. For example, light generating device 210 may have one or more calibration modes and/or maintenance modes in which light generating device 210 is active but under conditions that do not reflect typical conditions of use. It works. If the adaptive parameters are updated during the calibration and/or maintenance mode, the values of the adaptive parameters may become inaccurate and the characteristics of the excitation signal may become inaccurate after the light generator 210 exits the maintenance and/or calibration mode. calculation accuracy may be affected. Accordingly, when light generating device 210 is in maintenance and/or calibration mode, control system 250 may be configured to skip portions of process 300, such as (340) and (350). Control system 250 can receive indications of entering and exiting maintenance and/or calibration modes from light generating device 210 or an operator via I/O interface 253 .

[0067] Referring to FIG. 4, a flowchart of a process 400 is shown. Process 400 may be performed by a control system associated with a light generating device. For example, process 400 may be performed by control system 150 (FIG. 1) or control system 250 (FIG. 2). In the following discussion, process 400 is discussed with respect to control system 250 and light generating device 210. Process 400 may be implemented as a collection of instructions (eg, computer programs or software) stored in memory module 252 and executed by one or more electronic processors within electronic processing module 251.

[0068] Process 400 is an example of a process for determining whether to begin a warm-up procedure. If light generator 210 begins generating light beam 205 immediately after an idle period, one or more characteristics of light beam 205 (e.g., wavelength, bandwidth, energy, and/or temporal pulse duration) may The specifications associated with the application for which beam 205 is used may not be met. In such a situation, light generating device 210 may be considered to be in a cold start condition. In a cold start condition, light generator 210 generates light beam 205, which is unsuitable for its application. A warm-up procedure is applied to the light generating device 210 to improve cold start conditions. During a warm-up procedure, an excitation signal 209 is provided to the excitation mechanism 211, but the light beam 205 is not provided to (or by) the downstream tool or system until the light beam 205 meets the performance specifications. not used). For example, light beam 205 may be interrupted or diverted while a warm-up procedure is being performed.

[0069] Some prior art initiates a warm-up procedure based only on idle time. For example, these prior art techniques may initiate a warm-up procedure if the idle time immediately preceding the active period exceeds a threshold. However, since idle time alone is not always an accurate indicator of whether a warm-up procedure should be initiated, such a procedure may cause the warm-up procedure to be called unnecessarily if the idle time is relatively long. There is. Furthermore, such a procedure may result in the warm-up procedure being erroneously not performed if the idle time is relatively short. 5A and 5B show an example of how relying solely on idle time can lead to an incorrect decision whether to initiate a warm-up procedure. In contrast, as discussed below, control system 250 uses estimates of the characteristics of excitation signal 209 to implement process 400 of determining whether to initiate a warm-up procedure.

[0070] The estimated characteristics of the excitation signal 209 are analyzed to determine whether to initiate a warm-up procedure (410). The estimated characteristics of excitation signal 209 may be determined (330) of process 300 and passed to process 400 (eg, via a function call). In some implementations, process 400 is performed independently of process 300. In these implementations, the estimated characteristics of excitation signal 209 may be provided by an operator of light source 200 via I/O interface 253 or read from memory module 252.

[0071] Estimates of the properties of excitation signal 209 can be analyzed by comparing the estimates to thresholds. For example, the estimated value is the estimated maximum voltage value
It can be. In this example, a higher value of estimated maximum voltage indicates relatively lower efficiency and a need to perform a warm-up procedure. In contrast, a relatively low estimated maximum voltage indicates relatively high efficiency and no need for a warm-up procedure.

[0072] At (420), process 400 determines whether to initiate a warm-up procedure based on the analysis performed at (410). If the warm-up procedure is not performed, process 400 ends or returns to (330) of FIG. 3. If a warm-up procedure is performed, a warm-up procedure metric is determined (430). The warm-up procedure metric may be, for example, one or more characteristics of the excitation signal 209 applied to the excitation mechanism 211 during the warm-up procedure. For example, the metric may indicate the temporal duration and/or number of voltage pulses of the excitation signal 209 applied to the excitation mechanism 211 during a warm-up procedure. In some implementations, the number of voltage pulses is equal to the estimated maximum voltage value (e.g., estimated by Equation 1)
and the desired voltage after a warm-up procedure. The number of voltage pulses can be estimated by comparing the desired voltage after the warm-up procedure with the actual voltage achieved after the warm-up procedure. Specifically, the voltage error between the desired voltage after the warm-up procedure and the actual voltage achieved after the warm-up procedure is adaptively updated to be applied to the excitation mechanism 211 during the next warm-up procedure. The number of voltage pulses generated can be estimated. In some implementations, the warm-up procedure metric is a predetermined value stored in memory module 252.

[0073] To perform a warm-up, an excitation signal 209 having the determined characteristics is applied to the excitation mechanism 211 (440). After the warm-up procedure is complete, process 400 ends or returns to process 300.

[0074] FIGS. 5A and 5B illustrate that relying solely on idle time is insufficient to accurately detect cold start conditions and accurately determine whether to initiate a warm-up procedure. . FIG. 5A is a plot of idle time in seconds as a function of time. FIG. 5B is a plot of voltage metrics as a function of time. In the example of FIG. 5B, the voltage metric is the voltage applied to the electrodes immediately after the idle period. 5A and 5B have the same X-axis.

[0075] The light source has a first active period ta_1. The light source is in a first idle period ti_1 after the first active period. The light source is in a second active period ta_2 after the first idle period. The light source is in a second idle period ti_2 after the second active period. During the first active period, the duty cycle of the light beam produced by the light source is relatively low, as indicated by the open circle symbol. During the second active period, the duty cycle of the light beams is higher and closer in time, as indicated by the filled symbols. This indicates that the excitation mechanism is excited more rapidly in the second active period than in the first active period. The first idle time (t1 in FIGS. 5A and 5B) is shorter than the second idle time (t2 in FIGS. 5A and 5B). However, the first voltage metric (ΔV1) is greater than the second voltage metric (ΔV2), such that a process such as process 400 may benefit from a warm-up procedure after the first idle time, but after the second idle time. After some time it will be decided that it is not beneficial. However, an approach that only considers the idle time and compares the idle time with a threshold having a value between the first idle time and the second idle time would yield the opposite result. Therefore, a conventional approach that only considers idle time would initiate an unnecessary warm-up procedure after the second idle time and would not initiate a useful warm-up procedure after the first idle time. Thus, a process such as process 400 that takes into account an estimate of the value of a characteristic of the excitation signal (e.g., the amount of voltage to apply immediately after an idle period) allows a warm-up procedure to be used more effectively. Become.

[0076] FIGS. 5C and 5D illustrate examples of actual measurements for a process, such as process 300. FIG. 5C is a plot of the voltage applied to the electrodes of the first DUV light source as a function of time. FIG. 5D is a plot of the voltage applied to the electrodes of the second DUV light source as a function of time. In each of FIGS. 5C and 5D, the actual voltage applied to the electrodes is represented by the line with the open circle symbol labeled 596. Each point in the series of data labeled 596 is the maximum burst average voltage over multiple consecutive bursts. The predicted voltage value at element (330) of process 300 using a single adaptation parameter α is represented by a line with an open square symbol labeled 594. The predicted voltage value at element (330) of process 300 using multiple instances of adaptation parameter α is represented by a line with an x symbol labeled 595. In both implementations, the process 300 estimates the value of the excitation signal characteristic with reasonable accuracy, and implementations with multiple instances of the adaptation parameter α yield improved accuracy in some situations.

[0077] FIGS. 5E and 5F illustrate the error metrics determined at (340) of process 300 of FIG. 3 as a function of idle time in seconds. The data shown in FIGS. 5E and 5F were simulated using the second DUV light source discussed with respect to FIG. 5D. 5E and 5F, open circles represent error metrics for implementations of process 300 using a single adaptation parameter α, and x symbols represent error metrics for implementations using multiple instances of adaptation parameter α. represent. As shown in Figure 5E, when the idle time is about 18 seconds or less, the single adaptive parameter approach and the multiple adaptive parameter approach predict the value of the excitation signal characteristic with similar accuracy (within about 2%). do. As shown in FIG. 5F, the multiple adaptive parameter approach archives higher accuracy when idle time exceeds about 50 seconds.

[0078] The examples of FIGS. 3 and 4 are discussed with respect to light generating device 210. However, control system 250 may be used with other light sources. For example, control system 250 can be used with a DUV laser that includes a single discharge chamber surrounding a gaseous gain medium and an electrode configured to excite the gain medium. In these examples, control system 250 estimates the voltage to be applied to the electrodes for an active period that immediately follows an idle period. In another example, the control system 250 includes two or more discharge chambers, each discharge chamber surrounding a gaseous gain medium, and an electrode configured to excite the medium. It can be used with DUV light sources including. In these examples, control system 250 estimates the voltage applied to the electrodes in one, more than one, or all of the discharge chambers for an active period that immediately follows an idle period. 6, 7A, and 7B illustrate examples of DUV light sources that include multiple discharge chambers and can be used with control system 150 or control system 250.

[0079] Referring to FIG. 6, a block diagram of a photolithography system 600 is shown. Optical source 610 generates a pulsed light beam 605 that is provided to lithographic exposure apparatus 669. Optical source 610 may be, for example, an excimer optical source that outputs pulsed light beam 605 (which may be a laser beam). Once pulsed light beam 605 enters lithographic exposure apparatus 669 , it is directed through projection optical system 675 and projected onto wafer 670 to form one or more microelectronic features on photoresist on wafer 670 . Photolithography system 600 also includes a control system 250, which in the example of FIG. 6 is connected to components of optical source 610 and lithographic exposure apparatus 669. In this example, control system 250 may receive data or other information related to pulsed light beam 605 from lithographic exposure apparatus 669 and/or may send commands to lithographic exposure apparatus 669. In other examples, control system 250 is connected only to optical source 610.

[0080] In the example shown in FIG. 6, optical source 610 is a two-stage laser system that includes a master oscillator (MO) 631 that provides a seed light beam 624 to a power amplifier (PA) 630. MO 631 and PA 630 can be considered a subsystem of optical source 610 or a system that is part of optical source 610. Power amplifier 630 receives seed light beam 624 from master oscillator 631 and amplifies seed light beam 624 to produce light beam 605 for use in lithographic exposure apparatus 669. For example, master oscillator 631 may emit a pulsed seed light beam having a seed pulse energy of approximately 1 millijoule (mJ) per pulse, and these seed pulses are amplified by power amplifier 630 to approximately 10-15 mJ. can do.

[0081] The main oscillator 631 includes a discharge chamber 614 having two elongated electrodes 611A, a gain medium 612 which is a gas mixture, and a fan to circulate the gas between the electrodes 611A. A resonator is formed between a line narrowing module 616 on one side of the discharge chamber 614 and an output coupler 618 on a second side of the discharge chamber 614. Line narrowing module 616 can include diffractive optics, such as a diffraction grating, to fine tune the spectral output of discharge chamber 614.

[0082] Master oscillator 631 also includes a line center analysis module 620 that receives the output light beam from output coupler 618 and beam combination that changes the size or shape of the output light beam as necessary to form seed light beam 624. optical system 622. Line center analysis module 620 is a measurement system that can be used to measure or monitor the wavelength of seed light beam 624. Line center analysis module 620 may be located elsewhere within optical source 610 or may be located at the output of optical source 610.

[0083] The gas mixture used within the discharge chamber 614 can be any gas suitable for producing a beam of light at the wavelength and bandwidth required for the application. In the case of an excimer source, the gas mixture may contain, for example, noble gases such as argon or krypton, halogens such as fluorine or chlorine, and traces of xenon other than helium and/or neon as a buffer gas. . Examples of gas mixtures include argon fluoride (ArF), which emits at a wavelength of about 193 nm, krypton fluoride (KrF), which emits at a wavelength of about 248 nm, or xenon chloride (XeCl), which emits at a wavelength of about 351 nm. . The excimer gain medium (gas mixture) is pumped with short (eg, nanosecond) current pulses in a high voltage discharge by applying voltage 609 to elongated electrode 611A.

[0084] Power amplifier 630 includes a beam-combining optical system 632 that receives a seed light beam 624 from a master oscillator 631 and directs the light beam through a discharge chamber 640 to a beam-rotating optical element 648. The direction of the seed light beam 624 is changed or changed so that the light beam is sent back into the discharge chamber 640. The discharge chamber 640 includes a pair of elongate electrodes 611B, a gas mixture gain medium 612, and a fan for circulating the gas mixture between the electrodes 611B.

[0085] Output light beam 605 is directed through a bandwidth analysis module 662 that can measure various parameters (eg, bandwidth or wavelength) of beam 605. Output light beam 605 may also be directed through beam preparation system 663. Beam preparation system 663 may include, for example, a pulse stretcher, in which each pulse of output light beam 605 is stretched in time, for example in an optical delay unit, to form a light beam impinging on lithographic exposure apparatus 669. The performance characteristics of are adjusted. Beam preparation system 663 also includes other components that can act on beam 605, such as, for example, reflective and/or refractive optical elements (e.g., lenses and mirrors, etc.), filters, and optical apertures (including automatic shutters). obtain.

[0086] Light beam 605 is a pulsed light beam and may include one or more bursts of pulses separated from each other in time. Each burst may include one or more pulses of light. In some implementations, the burst includes several hundred pulses, such as 100-400 pulses.

[0087] As discussed above, when gain medium 612 is pumped by applying voltage 609 to electrode 611A, gain medium 612 emits light. When voltage 609 is applied in pulses to electrode 611A, the light emitted from medium 612 is also pulsed. The repetition frequency of pulsed light beam 605 is therefore determined by the frequency at which voltage 609 is applied to electrode 611A, with each application of voltage 609 producing a light pulse. The light pulse propagates through gain medium 612 and exits chamber 614 through output coupler 618. Therefore, by periodically and repeatedly applying voltage 609 to electrode 611A, a train of pulses is formed. The repetition frequency of the pulses can range from about 500Hz to 6,000Hz. In some implementations, the repetition frequency can be greater than 6,000 Hz, such as 12,000 Hz or more.

[0088] Signals from control system 250 cause electrodes 611A, 611B in master oscillator 631 and power amplifier 630 to control the pulse energy of master oscillator 631 and power amplifier 630, respectively, and thus the energy of light beam 605. They can also be used to control each. There may be a delay between the signal provided to electrode 611A and the signal provided to electrode 611B. The amount of delay may affect the properties of pulsed light beam 605, such as the amount of coherence of pulsed light beam 605. Pulsed light beam 605 may have an average output power in the range of tens of watts, for example from about 50W to about 130W. The irradiance (ie, average power per unit area) of the light beam 605 at the output can range from 60 W/cm ² to 80 W/cm ² .

[0089] Referring to FIG. 7A, a block diagram of an optical lithography system 700 is shown. Optical lithography system 700 includes an optical source system 710 that generates an exposure beam 705 that is provided to a scanner device 780. Scanner device 780 exposes wafer 770 with exposure beam 705 . In the example shown, control system 250 is connected to optical source system 710 and scanner device 780. In other examples, control system 250 is connected only to optical source system 710.

[0090] Scanner device 780 exposes wafer 770 with shaped exposure beam 705'. Shaped exposure beam 705' is formed by passing exposure beam 705 through projection optical system 781.

[0091] Optical source system 710 includes optical oscillators 740-1 to 740-N, where N is an integer greater than 1. Each optical oscillator 740-1 to 740-N generates a light beam 704-1 to 704-N, respectively. Details of optical oscillator 740-1 are discussed below. The other N-1 optical oscillators in optical source system 710 include the same or similar features.

[0092] Optical oscillator 740-1 includes a discharge chamber 715-1 surrounding a cathode 711-1a and an anode 711-1b. Discharge chamber 715-1 also includes gaseous gain medium 712-1. The potential difference between cathode 711-1a and anode 711-1b creates an electric field in gaseous gain medium 712-1. The potential difference can be generated by controlling a voltage source 797 coupled to control system 250 to apply voltage 709 to cathode 711-1a and/or anode 711-1b. The electric field provides sufficient energy to the gain medium 712-1 to cause population inversion and generate light pulses via stimulated emission. By repeatedly forming such a potential difference, a series of light pulses is formed to create light beam 704-1. The repetition frequency of pulsed light beam 704-1 is determined by the frequency at which voltage 709 is applied to electrodes 711-1a, 711-1b. The duration of the pulses in pulsed light beam 704-1 is determined by the duration of application of voltage 709 to electrodes 711-1a and 711-1b. The repetition frequency of the pulses can range, for example, from about 500Hz to 6,000Hz. In some implementations, the repetition frequency may be greater than 6,000 Hz, such as 12,000 Hz or more. Each pulse emitted from optical oscillator 740-1 may have a pulse energy of, for example, approximately 1 millijoule (mJ).

[0093] Gaseous gain medium 712-1 may be any gas suitable for producing a beam of light at the wavelength, energy and bandwidth required for the application. In the case of an excimer source, the gaseous gain medium 712-1 may contain trace amounts of xenon other than a noble gas such as argon or krypton, a halogen such as fluorine or chlorine, and a buffer gas such as helium. can. Specific examples of the gaseous gain medium 712-1 include argon fluoride (ArF) that emits light at a wavelength of about 193 nm, krypton fluoride (KrF) that emits light at a wavelength of about 248 nm, or xenon chloride (KrF) that emits light at a wavelength of about 351 nm. XeCl). Gain medium 712-1 is pumped with short (eg, nanosecond) current pulses in a high voltage discharge by applying voltage 709 to electrodes 711-1a, 711-1b.

[0094] A resonator is formed between a line narrowing module 716-1 on one side of the discharge chamber 715-1 and an output coupler 718-1 on a second side of the discharge chamber 715-1. Ru. Line narrowing module 716-1 may include diffractive optics, such as a diffraction grating and/or prism, to fine tune the spectral output of discharge chamber 715-1. In some implementations, line narrowing module 716-1 includes multiple diffractive optical elements. For example, line narrowing module 716-1 may include four prisms, some of which are configured to control the center wavelength of light beam 704-1, and others configured to control the spectrum of light beam 704-1. Configured to control bandwidth.

[0095] Optical oscillator 740-1 also includes a line center analysis module 720-1 that receives an output optical beam from output coupler 718-1. Line center analysis module 720-1 is a measurement system that can be used to measure or monitor the wavelength of light beam 704-1. Line center analysis module 720-1 can provide data to control system 250, which determines metrics associated with light beam 704-1 based on the data from line center analysis module 720-1. can be determined. For example, control system 250 can determine beam quality metrics or spectral bandwidth based on data measured by line center analysis module 720-1.

[0096] Optical source system 710 also includes a gas supply system 790 fluidly coupled to the interior of discharge chamber 715-1 via fluid conduit 789. Fluid conduit 789 is any conduit capable of transporting gas or other fluid with no or minimal loss of fluid. For example, fluid conduit 789 can be a pipe made or coated with a material that does not react with the fluid or fluids transported within conduit 789. Gas supply system 790 includes a chamber 791 configured to contain and/or receive a supply of the gas used in gain medium 712-1. Gas supply system 790 includes devices (such as pumps, valves and/or fluid switches) that enable gas supply system 790 to remove gas from or inject gas into discharge chamber 715-1. Also included. Gas supply system 790 is coupled to control system 250. Gas supply system 790 may be controlled by control system 250 to perform replenishment procedures, for example.

[0097] The other N-1 optical oscillators are similar to optical oscillator 740-1 and have similar or the same components and subsystems. For example, each of the optical oscillators 740-1 to 740-N includes electrodes similar to electrodes 711-1a and 711-1b, a line narrowing module similar to line narrowing module 716-1, and a line narrowing module similar to output coupler 718-1. Includes an output coupler. The optical oscillators 740-1 through 740-N may be tuned or configured such that all optical beams 704-1 through 704-N have the same characteristics, or the optical oscillators 740-1 through 740-N may have at least several An optical oscillator may be tuned or configured to have at least some characteristics that are different from other optical oscillators. For example, all of the light beams 704-1 to 704-N may have the same center wavelength, or the center wavelength of each of the light beams 704-1 to 704-N may be different. The center wavelength produced by a particular one of optical oscillators 740-1 to 740-N can be set using a corresponding line narrowing module.

[0098] Furthermore, the voltage source 797 may be electrically connected to the electrode of each of the optical oscillators 740-1 to 740-N, or the voltage source 797 may be connected as a voltage system including N individual voltage sources. Each of the power sources may be electrically connected to one electrode of the optical oscillators 740-1 to 740-N.

[0099] Optical source system 710 also includes a beam controller 787 and a beam combiner 788. Beam control device 787 is located between the gaseous gain medium of optical oscillators 740-1 to 740-N and beam combiner 788. Beam controller 787 determines which of light beams 704-1 to 704-N is incident on beam combiner 788. Beam combiner 788 forms exposure beam 705 from one or more light beams incident on beam combiner 788 . In the example shown, beam controller 787 is represented as a single element. However, beam controller 787 can be implemented as a collection of individual beam controllers. For example, beam controller 787 may include a collection of shutters, one shutter associated with each of optical oscillators 740-1 through 740-N.

[0100] Optical source system 710 may include other components and systems. For example, optical source system 710 can include a beam preparation system 763 that includes a bandwidth analysis module that measures various properties (such as bandwidth or wavelength) of the light beam. Beam preparation system 763 may also include a pulse stretcher (not shown) that stretches in time each pulse that interacts with the pulse stretcher. Beam preparation system 763 may also include other components that can act on light, such as reflective and/or refractive optical elements (eg, lenses and mirrors, etc.) and/or filters. In the example shown, beam preparation system 763 is positioned within the path of exposure beam 705. However, beam preparation system 763 may be located elsewhere within optical lithography system 700. Additionally, other implementations are possible. For example, optical source system 710 may include N instances of beam preparation system 763, each instance positioned to interact with one of light beams 704-1 through 704-N. In another example, optical source system 810 may include optical elements (such as mirrors) that direct light beams 704-1 through 704-N toward beam combiner 788.

[0101] Scanner device 780 may be an immersion system or a dry system. Scanner apparatus 780 includes a projection optical system 781 through which exposure beam 705 passes before reaching wafer 770, and a sensor or metrology system 799. Wafer 770 is held or housed on wafer holder 783. Referring also to FIG. 7B, projection optical system 781 includes a projection objective that includes a slit 784, a mask 785, and a lens system 786. Lens system 786 includes one or more optical elements. Exposure beam 705 enters scanner device 780 and impinges on slit 784, with at least a portion of beam 705 passing through slit 784 to form a shaped exposure beam 705'. In the example of FIGS. 7A and 7B, slit 784 is rectangular and shapes exposure beam 705 into an elongated rectangular shaped light beam, which is shaped exposure beam 705'. Mask 785 includes a pattern that determines which portions of the shaped light beam are transmitted through mask 785 and which portions are blocked by mask 785. Microelectronic features are formed on wafer 770 by exposing a layer of radiation-sensitive photoresist material on wafer 770 to exposure beam 705'. The design of the pattern on the mask is determined by the specific microelectronic circuit characteristics desired.

[0102] Metrology system 799 includes sensor 771. Sensor 771 may be configured to measure characteristics of shaped exposure beam 705', such as, for example, bandwidth, energy, pulse duration and/or wavelength. Sensor 771 captures, for example, a camera or other device capable of capturing an image of shaped exposure beam 705' at wafer 770 or data describing the amount of light energy in the xy plane at wafer 770. can be an energy detector.

[0103] Other aspects of the invention are described in the numbered sections below.
Clause 1. A light source,
A light generating device configured to be active during a first period, idle during a second period, and active during a third period, wherein the first period is , occurring before a second period, and the second period occurring before a third period, the excitation signal being applied to the light generating device in the active state and not being applied to the light generating device in the idle state. a generator;
a control system configured to estimate a characteristic of an excitation signal for application to the light generating device during a third period based on the duration of the second period and the value of the characteristic during the first period; A light source containing.
Clause 2. The light generator is
a discharge chamber configured to hold a gaseous gain medium;
a plurality of electrodes in the discharge chamber, an excitation signal comprising a voltage signal applied to at least one of the plurality of electrodes, and a characteristic of the excitation signal including a magnitude of the voltage signal; A light source according to clause 1, including:
Clause 3. 3. The light source of clause 2, wherein the voltage signal comprises a time-varying voltage signal.
Clause 4. 3. The light source of clause 2, wherein the control system includes a memory module configured to store at least one value representative of the magnitude of the voltage signal applied to the electrode during the first period.
Clause 5. 3. A light source according to clause 2, wherein the value of the characteristic during the first period comprises the minimum voltage applied to the electrode during the first period.
Clause 6. The control system determines the characteristics of the excitation signal for applying to the light generating device during the third period, the duration of the second period, the minimum voltage applied to the electrode during the first period and the first period. The light source according to clause 5, configured to estimate based on an adaptive parameter associated with.
Clause 7. 3. The light source of clause 2, wherein the gaseous gain medium comprises a gain medium configured to emit deep ultraviolet (DUV) light in response to a voltage signal applied to at least one of the electrodes.
Clause 8. 8. A light source according to clause 7, wherein the gaseous gain medium comprises argon fluoride (ArF), krypton fluoride (KrF) or xenon chloride (XeCl).
Clause 9. Clause, wherein the control system is further configured to determine an error metric based on the estimated characteristic of the excitation signal and the actual value of the characteristic of the excitation signal applied to the light generating device during the third period. 1. The light source according to 1.
Clause 10. 10. The light source of clause 9, wherein the control system is further configured to update the value of the adaptive parameter based on the error metric.
Clause 11. 11. The light source of clause 10, wherein the control system is configured to update the value for each of the plurality of adaptation parameters, and each of the plurality of adaptation parameters is associated with a different duration of the second time period.
Clause 12. The light source of clause 1, wherein the control system is further configured to determine whether to initiate a warm-up procedure based on the estimated characteristics of the excitation signal.
Clause 13. 13. The light source of clause 12, wherein, when a warm-up procedure is initiated, the control system is further configured to determine a warm-up procedure metric related to a duration of the warm-up procedure.
Clause 14. 14. The light source of clause 13, wherein the warm-up procedure metric is the number of times the light generating device is excited during the warm-up procedure.
Clause 15. The light source according to clause 1, wherein the light generating device includes a main oscillator and a power amplifier.
Clause 16. 2. The light source of clause 1, wherein the light generating device comprises a single discharge chamber.
Clause 17. 2. The light source of clause 1, wherein the light generating device includes a plurality of discharge chambers, and each of the discharge chambers is configured to emit a pulsed light beam towards a beam combiner.
Article 18. A controller for a light source, comprising a control system, the control system comprising:
accessing information related to the duration of the light source's idle period;
accessing information related to a value of a characteristic of an excitation signal applied to the light source during a period occurring before the idle period;
A controller configured to estimate an updated value of a characteristic of the excitation signal based on a duration of an idle period and a value of the characteristic of the excitation signal during a period that occurred before the idle period.
Article 19. 19. The controller of clause 18, wherein the control system is further configured to apply an excitation signal having an updated value of the characteristic to the light source after the idle period.
Article 20. The control system is further configured to determine an error metric based on the estimated updated value of the characteristic and the actual value of the characteristic of the excitation signal applied to the light generating device after the idle period. controller.
Clause 21. 21. The controller of clause 20, wherein the control system is further configured to update the value of the adaptive parameter based on the error metric.
Clause 22. 22. The controller of clause 21, wherein the control system is configured to update a value for each of the plurality of adaptation parameters, and each of the plurality of adaptation parameters is associated with a different duration of the second time period.
Clause 23. 19. The controller of clause 18, wherein the control system is further configured to determine whether to initiate a warm-up procedure for the light source based on the estimated updated value of the characteristic.
Article 24. The control system is configured to access from the computer readable memory module information related to the duration of the idle period of the light source and information related to the value of the characteristic of the excitation signal during periods occurring before the idle period. 18.
Article 25. The control system is
a computer readable memory module;
and one or more electronic processors coupled to a computer readable memory module.
Article 26. A method,
accessing information related to the duration of the light source's idle period;
accessing information related to a value of a characteristic of an excitation signal applied to the light source during a period occurring before the idle period;
Estimating an updated value of a characteristic of the excitation signal based on the duration of an idle period and a value of the characteristic of the excitation signal during a period that occurred before the idle period.

[0104] Other implementations are within the scope of the claims.

Claims (17)

A light source,
a light generating device that is active during a first time period, idle during a second time period, and in the active state during a third time period; 2 time periods, and the second time period occurs before the third time period, and an excitation signal is applied to the light generating device in the active state and to the light generating device in the idle state. a light generating device with no applied voltage;
A control system that estimates a characteristic of the excitation signal for application to the light generating device during the third period based on the duration of the second period and the value of the characteristic during the first period. including
The light source , wherein the control system further determines whether to initiate a warm-up procedure based on the estimated characteristic of the excitation signal . The light generating device includes:
a discharge chamber holding a gaseous gain medium;
a plurality of electrodes in the discharge chamber, the excitation signal includes a voltage signal applied to at least one of the plurality of electrodes, and the characteristic of the excitation signal determines the magnitude of the voltage signal. 2. The light source of claim 1, comprising a plurality of electrodes. 3. The light source of claim 2, wherein the voltage signal comprises a time-varying voltage signal. 3. The light source of claim 2, wherein the value of the characteristic during the first period includes a minimum voltage applied to the electrode during the first period. The control system determines the characteristics of the excitation signal for applying to the light generating device during the third time period, the duration of the second time period, and the characteristics of the excitation signal for applying to the electrode during the first time period. 5. The light source of claim 4, wherein the estimation is based on an adaptive parameter associated with the minimum voltage determined and the first period. 3. The light source of claim 2, wherein the gaseous gain medium includes a gain medium that emits deep ultraviolet (DUV) light in response to the voltage signal applied to at least one of the electrodes. The control system further determines an error metric based on the estimated characteristic of the excitation signal and an actual value of the characteristic of the excitation signal applied to the light generating device during the third time period. , the light source according to claim 1. 8. The light source of claim 7, wherein the control system further updates values of adaptive parameters based on the error metric. 2. The light source of claim 1 , wherein when the warm-up procedure is initiated, the control system further determines a warm-up procedure metric related to a duration of the warm-up procedure. 10. The light source of claim 9, wherein the warm-up procedure metric is the number of times the light generating device is excited during the warm-up procedure. The light source according to claim 1, wherein the light generating device includes a main oscillator and a power amplifier. 2. The light source of claim 1, wherein the light generating device includes a plurality of discharge chambers, and each of the discharge chambers emits a pulsed light beam toward a beam combiner. A controller for a light source, comprising a control system, the control system comprising:
accessing information related to the duration of an idle period of the light source;
accessing information related to a value of a characteristic of an excitation signal applied to the light source during a period that occurred before the idle period;
estimating an updated value of the characteristic of the excitation signal based on the duration of the idle period and the value of the characteristic of the excitation signal during the period that occurred before the idle period. stomach ,
The controller, wherein the control system further determines whether to initiate a warm-up procedure for the light source based on the estimated updated value of the characteristic . 14. The controller of claim 13, wherein the control system further applies the excitation signal having the updated value of the characteristic to the light source after the idle period. 15. The control system further determines an error metric based on the estimated updated value of the characteristic and an actual value of the characteristic of the excitation signal applied to the light generating device after the idle period. Controller described in. 14. The controller of claim 13 , wherein if the warm-up procedure is initiated, the control system further determines a warm-up procedure metric related to a duration of the warm-up procedure . The control system includes:
a computer readable memory module;
and one or more electronic processors coupled to the computer readable memory module.

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