Control systems for light sources

Abstract

A light source includes: a light-generating device configured to be in an active state during a first time period, in an idle state during a second time period, and in an active state during a third time period; 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-generating device in the active state, but not applied to the light-generating device in the idle state. The control system is configured to estimate a property of the excitation signal applied to the light-generating device during the third time period based on the duration of the second time period and the value of the property during the first time period.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 62 / 984,433, filed on March 3, 2020, entitled “CONTROL SYSTEM FOR A LIGHT SOURCE,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to a control system for a light source, such as a deep ultraviolet light source. Background Art

[0004] Photolithography is a process for patterning semiconductor circuit systems on substrates such as silicon wafers. An optical source generates deep ultraviolet (DUV) light for exposing the photoresist on the wafer. The DUV light can include, for example, a wavelength from about 100 nanometers (nm) to about 400 nm. Typically, the optical source is a laser source (e.g., an excimer laser), and the DUV light is a pulsed laser beam. The DUV light from the optical source interacts with a projection optical system that projects the light beam onto the photoresist on the silicon wafer through a mask. In this way, the chip design layer is patterned onto the photoresist. The photoresist and wafer are then etched and cleaned, and the photolithography process is repeated. Summary of the Invention

[0005] In one aspect, a light source includes: a light-generating device configured to be in an active state during a first time period, in an idle state during a second time period, and in an active state during a third time period; 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-generating device in the active state and not applied to the light-generating device in the idle state. The control system is configured to estimate a property to be applied to the light-generating device during the third time period based on the duration of the second time period and the value of the property of the excitation signal during the first time period.

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

[0007] A light-generating device may include a discharge chamber configured to contain a gaseous gain medium and a plurality of electrodes in the discharge chamber. An excitation signal may include a voltage signal applied to at least one of the plurality of electrodes, and a property of the excitation signal may include an amplitude of the voltage signal. The voltage signal may include a time-varying voltage signal. A control system may include a memory module configured to store at least one value representing the amplitude of the voltage signal applied to the electrode during a first time period. The value of the property during the first time period may include a minimum voltage applied to the electrode during the first time period. The control system may be configured to estimate a property of the excitation signal applied to the light-generating device during a third time period based on a duration of a second time period, the minimum voltage applied to the electrode during the first time period, and an adaptive parameter associated with the first time period. The gaseous gain medium may include a gain medium configured to emit deep ultraviolet (DUV) light in response to the 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).

[0008] The control system may be further configured to determine an error metric based on the estimated property of the excitation signal and an actual value of the property of the excitation signal applied to the light generating device during the third time period. The control system may be configured to update a value of an adaptive parameter based on the error metric. The control system may be configured to update the value of each of a plurality of adaptive parameters, and each of the plurality of adaptive parameters may be associated with a different duration of the second time period.

[0009] The control system may be configured to determine whether to initiate a preheating process based on the estimated properties of the excitation signal. If the preheating process is initiated, the control system may be configured to determine a preheating process metric related to the duration of the preheating process. The preheating process metric may be the number of times the light generating device is activated during the preheating process.

[0010] The light generating device may include a master oscillator and a power amplifier.

[0011] The light generating device may comprise a single discharge chamber.

[0012] The light generating device may include a plurality of discharge cells, and each of the discharge cells may be configured to emit a pulsed light beam towards the beam combiner.

[0013] In another aspect, a controller for a light source includes a control system configured to: access information related to a duration of an idle period of the light source; access information related to a value of a property of an excitation signal applied to the light source during a time period occurring before the idle period; and estimate an updated value of the property of the excitation signal based on the duration of the idle period and the value of the property of the excitation signal during the time period occurring before the idle period.

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

[0015] The control system may be configured to apply an excitation signal having an updated value of the property 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 property and the actual value of the property applied to the excitation signal of the light generating device after the idle period. The control system may be configured to update a value of an adaptive parameter based on the error metric. The control system may be configured to update a value of each of a plurality of adaptive parameters, each of the plurality of adaptive parameters being associated with a different duration of the second time period.

[0016] The control system may be further configured to determine whether to initiate a warm-up process for the light source based on the estimated updated value of the property.

[0017] The control system may be configured to access from the computer readable memory module information relating to the duration of the idle period of the light source and information relating to the value of the property of the excitation signal during a time period occurring prior to the idle period.

[0018] The control system may also include: a computer-readable memory module; and one or more electronic processors coupled to the computer-readable memory module.

[0019] On the other hand, a method includes accessing information related to the duration of an idle period of a light source; accessing information related to a value of a property of an excitation signal applied to the light source during a time period occurring before the idle period; and estimating an updated value of the property of the excitation signal based on the duration of the idle period and the value of the property of the excitation signal during the time period occurring before the idle period.

[0020] Implementations of any of the above techniques may include DUV light sources, systems, methods, processes, devices, or apparatuses. Details of one or more implementations are set forth in the accompanying drawings and the following description. Other features will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figures 1A to 1C It is a block diagram of the light source at three different times.

[0022] Figures 2A to 2C This is a block diagram of another light source at three different times.

[0023] Figure 3 is a flow chart of a process for estimating a value of a property of an excitation signal.

[0024] Figure 4 is a flow chart of a process for determining whether to initiate a warm-up process.

[0025] Figure 5A is a plot of idle time as a function of time.

[0026] Figure 5B is a plot of the voltage metric as a function of time.

[0027] Figure 5C is a plot of the voltage applied to the electrodes of the first DUV light source as a function of time.

[0028] Figure 5D is a plot of the voltage applied to the electrodes of the second DUV light source as a function of time.

[0029] Figure 5E is the error metric used for Figure 5D Plot of the second DUV light source as a function of the idle time.

[0030] Figure 5F is the error metric used for Figure 5D Plot of the second DUV light source as a function of the idle time.

[0031] Figure 6 It is a block diagram of a lithography system.

[0032] Figure 7A is a block diagram of an optical lithography system.

[0033] Figure 7B is used for Figure 7A Block diagram of the projection optical system of an optical lithography system. DETAILED DESCRIPTION

[0034] Figures 1A to 1C Each of the figures is a block diagram of the light source 100 at different times. Figure 1A The light source 100 is shown at time t1 . Figure 1B The light source 100 is shown at time t2. Figure 1CLight source 100 is shown at time t3. Time t1 occurs during a first time period, time t2 occurs during a second time period, and time t3 occurs during a third time period. The first time period occurs before the second time period, and the second time period occurs before the third time period. For illustrative purposes, three time periods are shown. However, light source 100 can operate for more than three time periods.

[0035] Light source 100 includes a light generating device 110 and a control system 150 that estimates properties of an excitation signal 109. Excitation signal 109 may be generated by control system 150 or a separate device (such as a voltage source or a 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 may be an excitation mechanism (such as a current source) applied to light generating device 110. Figures 2A to 2C Incentive Agency 211, Figure 6 7 ). Light beam 105 may be, for example, a pulsed or continuous wave laser beam. Light generating device 110 may be a deep ultraviolet (DUV) optical system that emits a pulsed light beam in the DUV range (e.g., a wavelength from approximately 100 nanometers (nm) to approximately 400 nm). In some implementations, light generating device 110 emits a pulse train during each active period. The pulse train includes hundreds or thousands of light pulses.

[0036] When the light generating device 110 is in an active state, the excitation signal 109 is applied to the light generating device 110 or a component of the light generating device 110. The light generating device 110 generates the light beam 105 during the active state. The light generating device 110 also has an inactive or idle state. When in the inactive or idle state, the excitation signal 109 is not applied to the light generating device 110 or its components, and the light generating device 110 does not generate the light beam 105. During the idle or inactive state, the light generating device 110 can, for example, be powered off or turned off, or powered on without generating any light. Figures 1A to 1C In the example of , the light generating device 110 is in the active state in the first and third time periods, and in the idle state in the second time period. The duration of the second time period is also referred to as the idle time, and the second time period is also referred to as the idle period.

[0037] As discussed in more detail below, the control system 150 estimates a property of the excitation signal 109 applied to the light generating device 110 during the third time period based on the duration of the idle period and the value of the property of the excitation signal 109 applied to the light generating device 110 during the previous active time period (e.g., the first time period). The property may be, for example, the amplitude of a voltage and / or current signal provided to an excitation mechanism in the light generating device 110.

[0038] By using the idle time and the value of the property during the first time period to determine the property of the excitation signal 109, the control system 150 improves the performance of the light source 100. For example, some prior art techniques determine the excitation signal based solely on the 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 cause the light generating device 110 to enter a preheating mode when the idle time is greater than a predetermined idle time threshold.

[0039] On the other hand, control system 150 implements a technique for estimating an updated value of excitation signal 109 by taking into account previous values ​​of the property of excitation signal 109. The method employed by control system 150 results in a more accurate determination of the property of excitation signal 109 to be applied during the third time period and improves the use of the preheating process. For example, control system 150 reduces or eliminates unnecessary performance of the preheating process while also helping to ensure that the preheating process is properly invoked.

[0040] In addition, the control system 150 can also determine adaptive parameters that take into account changes in one or more characteristics of the light generating device 110 over time. For example, the energy efficiency of the light generating device 110 can change over time. Energy efficiency is the relationship between the amount of energy provided to the light generating device 110 to generate light having a certain amount of energy. For example, in an implementation where the excitation signal 109 is a voltage signal applied to electrodes in the light generating device 110, as the energy efficiency of the light generating device 110 decreases, a larger amount of voltage is required to generate the light beam 105. The energy efficiency of the light generating device 110 may also decrease during idle time. 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 time-varying characteristics of the light generating device 110, the control system 150 improves the accuracy of its estimate of the properties of the excitation signal 109.

[0041] refer to Figures 2A to 2C , shows a block diagram of a light source 200 . The light source 200 is an implementation of the light source 100 . Figures 2A to 2C Each of the figures shows the light source 200 at a different time. Figure 2A and Figure 2C is shown as active in Figure 2BThe light source 200 includes a light generating device 210 and a control system 250. The light generating device 210 includes an excitation mechanism 211 and a gain medium 212.

[0042] The light generating device 210 generates the light beam 205 in the active state. The excitation signal 209 is applied to the light generating device 210, and when the light generating device 210 is in the active state ( Figure 2A and Figure 2C ) when the excitation mechanism 211 is activated. The light generating device 210 also has an inactive or idle state ( Figure 2B ). When the light generating device 210 is in an idle state, the excitation signal 209 is not applied to the light generating device and the excitation mechanism 211 is not excited. Figures 2A to 2C In the example shown in FIG, light source 200 is in an active state during a first time period (including time t1) and a third time period (including time t3). Light source 200 is in an idle state during a second time period (including time t2). The duration of the second time period is also referred to as the idle time. For illustrative purposes, three time periods are shown. However, light source 200 can operate over more than three time periods.

[0043] The excitation mechanism 211 excites the gain medium 212 in response to the excitation signal 209. The gain medium 212 is any medium suitable for generating a light beam at the wavelength, energy, and bandwidth required by the application. For example, the gain medium 212 can be a gas, crystal, glass, semiconductor, or liquid.

[0044] The excitation mechanism 211 is any mechanism capable of exciting the gain medium 212. For example, the excitation mechanism 211 may be a plurality of electrodes that excite a gaseous gain medium. The 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 provided to the excitation mechanism 211. The excitation signal 209 may be a direct current (DC) electrical signal or an alternating current (AC) electrical signal that varies with time, such as a sinusoidal voltage signal or a square wave voltage signal. In these implementations, the properties of the excitation signal 209 may be the maximum amplitude of the time-varying signal, the average amplitude of the time-varying signal, the minimum amplitude of the time-varying signal, the frequency of the time-varying signal, the duty cycle of the time-varying signal, and / or any other property related to the time-varying signal.

[0045] The control system 250 estimates a property of the excitation signal 209. The property may be, for example, the amplitude, frequency, and / or duty cycle of a voltage and / or current signal provided to the excitation mechanism 211 in the light generating device 210. The control system 250 estimates the property of the excitation signal 209 based on a previous or earlier idle time and a previous or earlier value of the property of the excitation signal 209. To estimate the property of the excitation signal 209, the control system 250 may implement, for example, Figure 3 The control system 250 may also implement other processes, such as Figure 4 The process 400 is discussed as a standalone process or in conjunction with the process 300. Furthermore, the control system 250 can be used with any type of light source. For example, the control system 250 can be used with the photolithography system 600 ( Figure 6 ) or optical lithography system 700 (Figure 7).

[0046] The control system 250 includes an electronic processing module 251, a computer-readable memory module 252, and an I / O interface 253. The electronic processing module 251 includes one or more processors suitable for executing computer programs (such as general-purpose or special-purpose microprocessors), as well as any one or more processors of any type of digital computer. Typically, the electronic processor receives instructions and data from a read-only memory, a random access memory (RAM), or both. The electronic processing module 251 can include any type of electronic processor. The one or more electronic processors of the electronic processing module 251 execute instructions and access data stored on the memory module 252. The one or more electronic processors can also write data to the memory module 252.

[0047] Memory module 252 can be volatile memory (such as RAM) or non-volatile memory. In some implementations, memory module 252 includes both non-volatile and volatile portions or components. Memory module 252 can store data and information used in the operation of control system 250. For example, memory module 252 can store information related to idle periods and information related to the values ​​of properties of excitation signal 209 applied to light generating device 210 during one or more time periods occurring in the past and immediately preceding the most recent idle period. Memory module 252 can store one or more values ​​associated with excitation signal 209 applied during the active period occurring immediately preceding the most recent idle period. For example, excitation signal 209 can be a voltage signal or a signal specifying a voltage generated by a voltage source. In this example, memory module 252 can store the average, minimum, and maximum values ​​of the voltage signal during the most recent active period. Memory module 252 can also store information received from light source 200 and / or light generating device 210.

[0048] The I / O interface 253 is any type of interface that allows the control system 250 to exchange data and signals with an operator, the light generating device 210, and / or an automated process running on another electronic device. For example, in an implementation where the rules or instructions stored on the memory module 252 can be edited, the editing can be performed via the I / O interface 253. In another example, the I / O interface 253 receives data from the light generating device 210 and / or the hardware and / or software subsystems of the light generating device 210. For example, the light generating device 210 can provide idle time and other information about the light generating device 210 to the control system 250 via the I / O interface 253. The I / O interface 253 can include one or more of a visual display, a keyboard, and a communication interface, such as a parallel port, a universal serial bus (USB) connection, and / or any type of network interface, such as Ethernet. The I / O interface 253 can also allow for contactless communication via, for example, IEEE 802.11, Bluetooth, or near-field communication (NFC) connections.

[0049] Control system 250 is coupled to light generating device 210 via data connection 254. Data connection 254 can be a physical cable or other physical data conduit (such as a cable supporting data transmission based on IEEE 802.3), a wireless data connection (such as a data connection providing 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 provided using any type of protocol or format. Data connection 254 is connected to light generating device 210 at a corresponding communication interface (not shown). The communication interface can be any type of interface capable of sending and receiving 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 allows for data communication via a wireless data connection. For example, the data interface can be an IEEE 811.11 transceiver, a Bluetooth, or an NFC connection. Control system 250 can be connected to systems and / or components within light generating device 210. For example, control system 250 can be connected to actuation mechanism 211.

[0050] exist Figures 2A to 2C In the example shown, the control system 250 is shown as being separate from the light generating device 210 and connected via a data connection 254. However, in some implementations, the control system 250 is implemented as part of the light generating device 210, such that the light generating device 210 and the control system 250 are part of a single integrated package (e.g., enclosed within the same housing). In these implementations, the data connection 254 can be a data path that allows communication between software modules, including one of the software modules that implements aspects of the control system 250 and another of the software modules that implement other functionality of the light generating device 210.

[0051] Figure 3 300 is a flow chart of process 300. Process 300 is an example of a process for estimating a value of a property 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 ( Figures 2A to 2C ) is executed. In the following discussion, process 300 is discussed with respect to control system 250 and light generating device 210. For example, referring to Figures 2A to 2C , process 300 may be implemented as a set of instructions (eg, a computer program or computer software) stored on memory module 252 and executed by one or more electronic processors in electronic processing module 251 .

[0052] Information related to the duration of idle periods 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 continuous period of time during which the light generating device 210 is idle or inactive. The idle time relates to idle periods that occurred in the past and may be the duration of a recent idle period. For example, the idle time may include Figure 2B The duration of the second time period is shown at time t2.

[0053] The idle time may be stored in the memory module 252. In these implementations, the control system 250 accesses the idle time value from the memory module 252. The idle time value may not necessarily be accessed from the memory module 252. For example, in some implementations, the idle time is provided by an operator via the I / O interface 253. Furthermore, the information related to the idle time may be a numerical value representing the idle time, or the information may take other forms. For example, the information related to the idle time may include the time when the idle period begins and the time when the idle time ends. In these implementations, the control system 250 is configured to determine the idle time based on the accessed information.

[0054] Information about the value of the property of the excitation signal 209 applied to the light generating device 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 more than one value of the property during the previous active period. For example, the information may include the maximum and minimum voltages applied to the excitation mechanism 211 during the previous active period. In another example, the information may include a time series representing the voltages applied to the excitation mechanism 211 at regular intervals during the active period. The information about the value of the property of the excitation signal 209 may be accessed from the memory module 252 or may be accessed through the I / O interface 253.

[0055] An updated value of the property of the excitation signal 209 is estimated (330) based on the duration of the idle period and the value of the property of the excitation signal 209 during a time period that occurred before the idle period. The following discussion relates to an example in which the excitation signal 209 is a time-varying voltage signal applied to the excitation mechanism 211. The property of the excitation signal 209 that is estimated is the maximum magnitude (V max ). The excitation signal 209 generates a pulse train comprising many individual pulses (e.g., hundreds or thousands). Each pulse is created by a corresponding pulse in the time-varying voltage excitation signal 209. In the following discussion, the maximum voltage (V max ) is the maximum amplitude of the voltage applied to the excitation mechanism 211 to form the light pulse during the active period, and the minimum voltage (V min ) is applied to the excitation mechanism 211 to form a light pulse during the active period. Maximum voltage (V max ) typically occurs relatively early in a particular pulse train while the light generating device 210 is experiencing transient effects associated with starting to generate the light beam 205 after an idle period. After the transient effects have ended and the light generating device 210 is in a steady state, the minimum voltage (V min ) typically occurs later in the pulse train.

[0056] The value of the voltage signal of the excitation signal 209 to be applied to the excitation mechanism 211 after the idle time ends can be estimated as shown in equation (1):

[0057]

[0058] where i is an integer value that indexes the active period of the light generating device 210, is an estimated value of the maximum voltage of the excitation signal 209 used in the i-th active period, V min (i-1) is the value of the minimum voltage of the excitation signal 209 during the (i-1)th active period, α(i-1) is the value of the adaptive parameter α associated with the (i-1)th active period, and ΔT(i) is the idle time of the idle period immediately preceding the i-th active period. The i-th active period is the current active period, and the (i-1)th active period is the active period immediately preceding the current active period. The idle period having the idle time ΔT(i) is between the i-th active period and the (i-1)th active period.

[0059] For example, the current or i-th activity period may include Figure 2C The third time period is t3 as shown, and the previous activity time period may be a time period including Figure 2A Continuing with this example, the idle time is the time period including Figure 2B The second time period t2 is shown. Therefore, in this example, V min (i-1) is the minimum voltage applied to the excitation mechanism 211 during the first time period (and based on the information accessed at (320)), ΔT(i) is the duration of the second time period or idle time (and based on the information accessed at (310)), and the estimated property of the excitation signal is the maximum voltage to be applied to the excitation mechanism 211 during the third time period.

[0060] The above discussion relates to an example in which the excitation signal 209 is a time-varying voltage signal applied to the excitation mechanism 211, and the metric of the excitation signal 209 being estimated is the maximum voltage (V max ) value. However, other metrics can 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 estimated after the idle period based on knowledge of the idle time and the output energy of the light beam 205 before the idle time. In other words, the above method can be used to predict the light energy generated by the light beam 205 after the idle period.

[0061] The adaptive parameter a(i-1) is the value of the adaptive parameter associated with the first time period. The value of the adaptive parameter associated with the first time period can be stored on the memory module 252 or provided to the control system 250 via the I / O interface 253. The process 300 can end, return to (310), or continue to (340).

[0062] In some implementations, the adaptive parameter α is updated for each active period. In these implementations, an error metric is determined (340). The error metric is based on the estimated property of the excitation signal 209 to be applied to the excitation mechanism 211 during the active period (as estimated in 330) and the actual value of the property of the excitation signal 209 applied during the active period. The error metric can be determined as shown in equation (2):

[0063]

[0064] where i is an integer value that indexes the active period of the light generating device 210, e v (i) is the error metric associated with the i-th activity period, V max (i) is the actual value of the applied maximum 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 the excitation signal 209 for the i-th active period.

[0065] The value of the adaptive parameter may be updated (350). An adaptive parameter is any parameter that represents a characteristic of the light generating device 210 that changes over time. For example, the adaptive parameter may be an estimate of the energy efficiency of the light generating device 210. The energy efficiency relates the input energy (the voltage supplied to the excitation mechanism 211) to the output energy (the light energy in the light beam 205). This relationship may be approximately linear. The slope of the linear relationship with respect to or relative to the idle time may be used as the adaptive parameter.

[0066] The value of the adaptive parameter (α) can be updated as shown in equation (3):

[0067] α(i)=α(i-1)+ηe V (i), Equation (3),

[0068] Where i is an integer value that indexes the active period of the light generating device 210, η is the step size or weighting factor, and e v (i) is the error metric for the i-th activity period. In the example of equation (3), i is the current activity period (e.g., including Figure 2C t3 in the third time period), and i-1 is the immediately preceding activity period (e.g., including Figure 2A The first time period of time t1 in the example is shown in FIG.

[0069] The step size or weighting factor η remains constant over time unless it is intentionally changed by the operator of the light source 200. The step size or weighting factor η determines the error value e v (i) The degree to which the adaptive parameter α is affected. A relatively large value of the step size or weighting factor η results in a larger change in the adaptive parameter α than a relatively small value. When the light generating device 210 is assembled, the step size or weighting factor η can be set by the manufacturer and stored on the memory module 252, and / or the operator can update the step size or weighting factor via the I / O interface 253.

[0070] The updated value of the adaptive parameter α may be stored on the memory module 252 in association with the i-th activity period so that the control system 250 may access the value of the adaptive parameter for later use.

[0071] In some implementations, more than one instance of the adaptive parameter α is used, where each instance is associated with a particular idle time or idle time range. For example, two (2), five (5), seven (7), or more instances of the adaptive parameter α may be initialized and then updated based on equations (4), (5), and (6):

[0072]

[0073]

[0074] α j (i) = α j (i-1)+η j e V (i) Equation (6),

[0075] where j is an instance, and α j is the adaptive parameter corresponding to the jth instance, and ΔT is the idle time range associated with the jth instance. The idle time ranges do not have to be the same. For example, in one implementation, the adaptive parameter α j Five (j=5) instances of are initialized, where the adaptive parameter α j An example of is used for each of the following idle time ranges ΔT(i): 0 to 60 seconds (s), 61 to 120 s, 121 to 600 s, 601 to 3600 s, and greater than 3600 s. Thus, if the idle time is 60 seconds or less, α(1) is used as α j If the idle time is 3600 seconds or longer, α(5) is used as α j .

[0076] Using the adaptive parameter α j More than one instance of improves the overall accuracy of process 300. For example, the energy efficiency of light generating device 210 generally decreases as the idle time increases. Although the relationship between energy efficiency and idle time is generally linear for relatively short idle times (e.g., idle times less than 10 minutes), for relatively long idle times, energy efficiency decreases in a manner that is not necessarily linear with respect to the idle time. To this end, an adaptive parameter α may be used. j , each associated with a different range of idle times. Since the ranges of idle times can be selected so that the energy efficiency is linear or approximately linear over each of these ranges, so that equation (3) can be used to update various adjustable parameters, this approach can lead to a more efficient process and ensure accurate results for longer idle times.

[0077] In some implementations, the control system 250 intentionally does not update the adaptive parameters under certain conditions, even if the control system 250 updates the adaptive parameters under other conditions. For example, the light generating device 210 may have one or more calibration modes and / or maintenance modes in which the light generating device 210 is active but performs under conditions that do not reflect typical usage conditions. If the adaptive parameters are updated during the calibration and / or maintenance modes, the values ​​of the adaptive parameters may become inaccurate after the light generating device 210 exits the maintenance and / or calibration mode and may affect the accuracy of the calculation of the properties of the excitation signal. Therefore, the control system 250 can be configured to skip portions of process 300, such as (340) and (350), when the light generating device 210 is in the maintenance and / or calibration mode. The control system 250 can receive instructions to enter and exit the maintenance and / or calibration mode from the light generating device 210 or the operator via the I / O interface 253.

[0078] refer to Figure 4 , a flow chart of process 400 is shown. Process 400 can be performed by a control system associated with a light generating device. For example, process 400 can 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 can be implemented as a set of instructions (e.g., a computer program or computer software) stored on memory module 252 and executed by one or more electronic processors in electronic processing module 251.

[0079] Process 400 is an example of a process for determining whether to initiate a warm-up process. When light generating device 210 begins generating light beam 205 immediately after an idle period, one or more properties of light beam 205 (e.g., wavelength, bandwidth, energy, and / or temporal pulse duration) may not meet specifications associated with the application in which light beam 205 is used. In this case, light generating device 210 can be considered to be in a cold start condition. In a cold start condition, light generating device 210 generates light beam 205, but light beam 205 is insufficient for the application. A warm-up process is applied to light generating device 210 to remedy the cold start condition. During the warm-up process, excitation signal 209 is provided to excitation mechanism 211, but light beam 205 is not provided to (or used by) a downstream tool or system until light beam 205 meets performance specifications. For example, light beam 205 can be blocked or redirected while the warm-up process is performed.

[0080] Some existing technologies initiate the warm-up process based solely on idle time. For example, if the idle time immediately preceding an active period exceeds a threshold, these existing technologies may initiate the warm-up process. However, because idle time itself does not always provide an accurate indication of whether the warm-up process should be initiated, this approach may result in the warm-up process being unnecessarily invoked during relatively long idle periods. Furthermore, this approach may result in the warm-up process being erroneously omitted during relatively short idle periods. Figure 5A and Figure 5B This illustrates an example of how relying solely on idle time may lead to an incorrect determination of whether to initiate a warm-up process. Alternatively, as described below, control system 250 implements process 400 that uses an estimate of a property of excitation signal 209 to determine whether to initiate a warm-up process.

[0081] The estimated property of the excitation signal 209 is analyzed to determine whether to initiate a preheating process (410). The estimated property of the excitation signal 209 can be determined at (330) of process 300 and passed to process 400 (e.g., via a function call). In some implementations, process 400 is performed independently of process 300. In these implementations, the estimated property of the excitation signal 209 can be provided by an operator of the light source 200 via the I / O interface 253 or read from the memory module 252.

[0082] The estimated value of the property of the excitation signal 209 can be analyzed by comparing the estimated value with a threshold value. For example, the estimated value can be the maximum voltage value estimated In this example, a higher value of the estimated maximum voltage indicates relatively low efficiency and a warm-up process should be performed. On the other hand, a relatively low estimated maximum voltage indicates relatively high efficiency and no warm-up process is required.

[0083] At (420), the process 400 determines whether to initiate a warm-up process based on the analysis performed at (410). If the warm-up process is not to be performed, the process 400 ends or returns to Figure 3 If a preheating process is performed, a preheating process metric is determined (430). The preheating process metric may be, for example, one or more characteristics of the excitation signal 209 to be applied to the excitation mechanism 211 during the preheating process. For example, the metric may indicate the time duration of the excitation signal 209 and / or the number of voltage pulses applied to the excitation mechanism 211 during the preheating process. In some implementations, the estimated maximum voltage value may be used to determine the preheating process metric. The number of voltage pulses is calculated based on the voltage expected after the preheating process (e.g., as estimated by Equation 1) and the voltage expected after the preheating process. The number of voltage pulses can be estimated by comparing the voltage expected after the preheating process with the actual voltage achieved after the preheating process. Specifically, the voltage error between the voltage expected after the preheating process and the actual voltage achieved after the preheating process can be adaptively updated to estimate the number of voltage pulses to be applied to the excitation mechanism 211 during the next preheating process. In some implementations, the preheating process metric is a predetermined value stored on the memory module 252.

[0084] The excitation signal 209 having the determined properties is applied to the excitation mechanism 211 (440) to perform preheating. After the preheating process is completed, the process 400 ends or returns to the process 300.

[0085] Figure 5A and Figure 5B It is shown that relying solely on idle time is insufficient to accurately detect cold start conditions and accurately determine whether to initiate a warm-up process. Figure 5A is a plot of idle time in seconds as a function of time. Figure 5B is a plot of the voltage metric as a function of time. Figure 5B In the example of , the voltage metric is the voltage applied to the electrode immediately after the idle period. Figure 5A and Figure 5B have the same X-axis.

[0086] The light source has a first active period ta_1. The light source is in a first idle period t1_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 t1_2 after the second active period. During the first active period, the duty cycle of the light beam generated by the light source is relatively low, as shown by the hollow circle symbols. During the second active period, the duty cycle of the light beam is higher, as shown by the solid circle symbols, which are closer together in time. This indicates that the excitation mechanism is excited more quickly in the second active period than in the first active period. The first idle time ( Figure 5A and Figure 5B t1) is less than the second idle time ( Figure 5A and Figure 5Bt2 on ). However, the first voltage metric (ΔV1) is greater than the second voltage metric (ΔV2), and a process such as process 400 will determine that a warm-up process would be beneficial after the first idle time rather than after the second idle time. However, a method that only considers the idle time and compares the idle time to a threshold value having a value between the first idle time and the second idle time would produce the opposite result. Thus, a conventional method that only considers the idle time would initiate an unnecessary warm-up process after the second idle time, rather than initiating a beneficial warm-up process after the first idle time. Thus, a process such as process 400 allows for greater use of the warm-up process in a more efficient manner by taking into account an estimate of the value of a property of the excitation signal (such as the amount of voltage applied immediately after the idle period).

[0087] Figure 5C and Figure 5D An example of actual measurement results for a process such as process 300 is shown. Figure 5C is a plot of the voltage applied to the electrodes of the first DUV light source as a function of time. Figure 5D is a plot of the voltage applied to the electrodes of the second DUV light source as a function of time. Figure 5C and Figure 5D In each of the embodiments, the actual voltage applied to the electrode is represented by the line with the hollow circle symbol labeled 596. Each data point in the series labeled 596 is the maximum burst average voltage over multiple consecutive bursts. The voltage value predicted at element (330) of process 300 using a single adaptive parameter α is represented by the line with the hollow square symbol labeled 594. The voltage value predicted at element (330) of process 300 using multiple instances of the adaptive parameter α is represented by the line with the x symbol labeled 595. In both implementations, process 300 estimates the value of the property of the excitation signal with reasonable accuracy, and the implementation with multiple instances of the adaptive parameter α results in improved accuracy in some cases.

[0088] Figure 5E and Figure 5F shows the idle time in seconds as a function of the Figure 3 The error metric determined at (340) of process 300 is used. Figure 5D The second DUV light source discussed, simulated Figure 5E and Figure 5F The data shown in Figure 5E and Figure 5F In FIG, the open circles represent the error metrics for an implementation of process 300 in which a single adaptive parameter α is used, and the x symbols represent the error metrics for an implementation in which multiple instances of the adaptive parameter α are used. Figure 5EAs shown, for idle times of about 18 seconds or less, the single adaptive parameter and multiple adaptive parameter methods predict the value of the property of the stimulus signal with similar accuracy (within about 2%). Figure 5F As shown, for idle times greater than about 50 seconds, the multiple adaptive parameter methods achieve better accuracy.

[0089] Figure 3 and Figure 4 The examples discussed above are related to light generating device 210. However, control system 250 can be used with other light sources. For example, control system 250 can be used with a DUV laser that includes a single discharge chamber enclosing a gas gain medium and an electrode configured to excite the gain medium. In these examples, control system 250 estimates the voltage applied to the electrode during an active period immediately following an idle period. In another example, control system 250 can be used with a DUV light source that includes more than one discharge chamber, each of which encloses a gas gain medium and an electrode configured to excite the medium. In these examples, control system 250 estimates the voltage applied to the electrodes in one, more than one, or all of the discharge chambers during an active period immediately following an idle period. Figure 6 、 Figure 7A and Figure 7B An example of a DUV light source that includes more than one discharge chamber and that can be used with control system 150 or control system 250 is shown.

[0090] refer to Figure 6 , a block diagram of a lithography system 600 is shown. A light source 610 generates a pulsed light beam 605, which is provided to a lithography exposure device 669. The light source 610 may be, for example, an excimer light source that outputs a pulsed light beam 605 (which may be a laser beam). When the pulsed light beam 605 enters the lithography exposure device 669, it is guided through a projection optical system 675 and projected onto a wafer 670 to form one or more microelectronic features on a photoresist on the wafer 670. The lithography system 600 further includes a control system 250, which is used to control the photoresist. Figure 6 In the example shown, control system 250 is connected to components of photolithographic exposure apparatus 669 and light source 610. In this example, control system 250 can receive data or other information related to pulsed beam 605 from photolithographic exposure apparatus 669 and / or can send commands to photolithographic exposure apparatus 669. In other examples, control system 250 is connected only to light source 610.

[0091] exist Figure 6In the example shown, the light source 610 is a two-stage laser system that includes a master oscillator (MO) 631 that provides a seed beam 624 to a power amplifier (PA) 630. The MO 631 and the PA 630 can be considered a subsystem of the light source 610 or a system that is part of the light source 610. The power amplifier 630 receives the seed beam 624 from the master oscillator 631 and amplifies the seed beam 624 to generate a beam 605 for a lithographic exposure apparatus 669. For example, the master oscillator 631 can emit a pulsed seed beam having a seed pulse energy of approximately 1 millijoule (mJ) per pulse, and these seed pulses can be amplified to approximately 10 to 15 mJ by the power amplifier 630.

[0092] Master oscillator 631 includes a discharge chamber 614 having two elongated electrodes 611A, a gain medium 612 as a gas mixture, and a fan for circulating the gas between electrodes 611A. A resonator is formed between a line-narrowing module 616 on one side of discharge chamber 614 and an output coupler 618 on a second side of discharge chamber 614. Line-narrowing module 616 may include a diffractive optical device, such as a grating, that fine-tunes the spectral output of discharge chamber 614.

[0093] The master oscillator 631 also includes a line center analysis module 620 that receives the output beam from the output coupler 618 and a beam coupling optical system 622 that modifies the size or shape of the output beam as needed to form a seed beam 624. The line center analysis module 620 is a measurement system that can be used to measure or monitor the wavelength of the seed beam 624. The line center analysis module 620 can be placed elsewhere in the light source 610, or it can be placed at the output of the light source 610.

[0094] The gas mixture used in the discharge chamber 614 can be any gas suitable for generating a light beam at the wavelength and bandwidth required by the application. For an excimer source, the gas mixture can include an inert gas (rare gas) as a buffer gas, such as, for example, argon or krypton, a halogen gas, such as, for example, fluorine or chlorine, and a trace amount of xenon in addition to helium and / or neon. Specific examples of gas mixtures include argon fluoride (ArF), which emits light at a wavelength of approximately 193 nm, krypton fluoride (KrF), which emits light at a wavelength of approximately 248 nm, or xenon chloride (XeCl), which emits light at a wavelength of approximately 351 nm. The excimer gain medium (gas mixture) is pumped with short (e.g., nanosecond) current pulses in a high-voltage discharge by applying a voltage 609 to the elongated electrode 611A.

[0095] The power amplifier 630 includes a beam coupling optical system 632 that receives the seed beam 624 from the master oscillator 631 and directs the beam through the discharge chamber 640 and to the beam steering optical element 648, which modifies or changes the direction of the seed beam 624 so that it is sent back to the discharge chamber 640. The discharge chamber 640 includes a pair of elongated electrodes 611B, a gain medium 612 that is a gas mixture, and a fan for circulating the gas mixture between the electrodes 611B.

[0096] The output beam 605 is directed through a bandwidth analysis module 662, where various parameters of the beam 605 (such as bandwidth or wavelength) can be measured. The output beam 605 can also be directed through a beam preparation system 663. The beam preparation system 663 can include, for example, a pulse stretcher, where each of the pulses of the output beam 605 is stretched in time, for example, in an optical delay unit, to adjust the performance properties of the beam incident on the lithographic exposure apparatus 669. The beam preparation system 663 can also include other components capable of acting on the beam 605, such as, for example, reflective and / or refractive optical elements (such as, for example, lenses and mirrors), filters, and optical apertures (including automated shutters).

[0097] Light beam 605 is a pulsed light beam and can include one or more pulse trains separated from each other in time. Each pulse train can include one or more light pulses. In some implementations, the pulse train includes hundreds of pulses, for example, 100 to 400 pulses.

[0098] As described above, when gain medium 612 is pumped by applying voltage 609 to electrode 611A, gain medium 612 emits light. When voltage 609 is applied to electrode 611A in a pulsed form, the light emitted from medium 612 is also pulsed. Therefore, the repetition rate of pulsed light beam 605 is determined by the rate at which voltage 609 is applied to electrode 611A, where each application of voltage 609 produces a light pulse. The light pulse propagates through gain medium 612 and exits chamber 614 through output coupler 618. Thus, a pulse train is created by periodically and repeatedly applying voltage 609 to electrode 611A. The repetition rate of the pulses can range between approximately 500 Hz and 6000 Hz. In some implementations, the repetition rate is greater than 6000 Hz and can be, for example, 12000 Hz or greater.

[0099] Signals from the control system 250 can also be used to control the electrodes 611A, 611B within the master oscillator 631 and the power amplifier 630, respectively, for controlling the respective pulse energies of the master oscillator 631 and the power amplifier 630, thereby controlling the energy of the light beam 605. There may be a delay between the signal provided to the electrode 611A and the signal provided to the electrode 611B. The amount of delay can affect the properties of the light beam 605, such as the amount of coherence in the pulsed light beam 605. The average output power of the pulsed light beam 605 can be in the range of tens of watts, for example, from about 50W to about 130W. The irradiance of the light beam 605 at the output (i.e., the average power per unit area) can range from 60W / cm 2 Up to 80W / cm 2 .

[0100] refer to Figure 7A , shows a block diagram of a lithography system 700. The lithography system 700 includes a light source system 710 that generates an exposure beam 705 that is provided to a scanner device 780. The scanner device 780 uses the exposure beam 705 to expose a wafer 770. In the example shown, the control system 250 is connected to both the light source system 710 and the scanner device 780. In other examples, the control system 250 is connected only to the light source system 710.

[0101] The scanner device 780 exposes the wafer 770 using the shaped exposure beam 705'. The shaped exposure beam 705' is formed by passing the exposure beam 705 through the projection optical system 781.

[0102] Light source system 710 includes optical oscillators 740-1 through 740-N, where N is an integer greater than 1. Each optical oscillator 740-1 through 740-N generates a corresponding light beam 704-1 through 704-N. Details of optical oscillator 740-1 are discussed below. The other N-1 optical oscillators in light source system 710 may include the same or similar features.

[0103] Optical oscillator 740-1 includes a discharge chamber 715-1 that encloses a cathode 711-1a and an anode 711-1b. Discharge chamber 715-1 also contains a gas gain medium 712-1. A potential difference between cathode 711-1a and anode 711-1b creates an electric field in gas gain medium 712-1. The potential difference can be generated by controlling a voltage source 797 coupled to control system 250 to apply a voltage 709 to cathode 711-1a and / or anode 711-1b. The electric field provides energy to gain medium 712-1 sufficient to cause a population inversion and generate light pulses via stimulated emission. This repetitive creation of a potential difference creates a sequence of light pulses to form light beam 704-1. The repetition rate of pulsed light beam 704-1 is determined by the rate at which voltage 709 is applied to electrodes 711-1a and 711-1b. The duration of the pulses in pulsed beam 704-1 is determined by the duration of application of voltage 709 to electrodes 711-1a and 711-1b. The repetition rate of the pulses can range, for example, from about 500 Hz to 6000 Hz. In some implementations, the repetition rate can be greater than 6000 Hz, and can be, for example, 12000 Hz or greater. Each pulse emitted from optical oscillator 740-1 can have a pulse energy of, for example, about 1 millijoule (mJ).

[0104] The gaseous gain medium 712-1 can be any gas suitable for generating a beam at the wavelength, energy, and bandwidth required for the application. For an excimer source, the gaseous gain medium 712-1 can include an inert gas (rare gas) such as argon or krypton, a halogen gas such as fluorine or chlorine, and a trace amount of xenon, in addition to a buffer gas such as helium. Specific examples of the gaseous gain medium 712-1 include argon fluoride (ArF), which emits light at a wavelength of approximately 193 nm, krypton fluoride (KrF), which emits light at a wavelength of approximately 248 nm, or xenon chloride (XeCl), which emits light at a wavelength of approximately 351 nm. By applying a voltage 709 to electrodes 711-1a and 711-1b, the gain medium 712-1 is pumped with short (e.g., nanosecond) current pulses in a high-voltage discharge.

[0105] The 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. The line-narrowing module 716-1 can include a diffractive optical device, such as a grating and / or a prism, that fine-tunes the spectral output of the discharge chamber 715-1. In some implementations, the line-narrowing module 716-1 includes multiple diffractive optical elements. For example, the line-narrowing module 716-1 can include four prisms, some of which are configured to control the central wavelength of the light beam 704-1, while other prisms are configured to control the spectral bandwidth of the light beam 704-1.

[0106] Optical oscillator 740-1 also includes a line center analysis module 720-1 that receives the output 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, and control system 250 can determine metrics related to light beam 704-1 based on the data from line center analysis module 720-1. For example, control system 250 can determine a beam quality metric or spectral bandwidth based on the data measured by line center analysis module 720-1.

[0107] Light source system 710 also includes a gas supply system 790, which is fluidically coupled to the interior of discharge chamber 715-1 via fluid conduit 789. Fluid conduit 789 is any conduit capable of conveying a gas or other fluid with minimal or no fluid loss. For example, fluid conduit 789 may be a tube made of, or coated with, a material that is non-reactive with the one or more fluids conveyed in conduit 789. Gas supply system 790 includes a chamber 791 that contains and / or is configured to receive a supply of one or more gases used in gain medium 712-1. Gas supply system 790 also 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. Gas supply system 790 is coupled to control system 250. Gas supply system 790 can be controlled by control system 250 to perform, for example, a refilling procedure.

[0108] The other N-1 optical oscillators are similar to optical oscillator 740-1 and have similar or identical components and subsystems. For example, each of optical oscillators 740-1 to 740-N includes electrodes similar to electrodes 711-1a, 711-1b, a line narrowing module similar to line narrowing module 716-1, and an output coupler similar to output coupler 718-1. Optical oscillators 740-1 to 740-N can be tuned or configured so that all light beams 704-1 to 704-N have the same properties, or optical oscillators 740-1 to 740-N can be tuned or configured so that at least some of the optical oscillators have at least some properties that are different from the other optical oscillators. For example, all light beams 704-1 to 704-N can have the same central wavelength, or the central wavelength of each light beam 704-1 to 704-N can be different. The center wavelength generated by a particular one of the optical oscillators 740 - 1 to 740 -N may be set using a corresponding line-narrowing module.

[0109] Furthermore, the voltage source 797 may be electrically connected to an electrode in each of the optical oscillators 740-1 to 740-N, or the voltage source 797 may be implemented as a voltage system comprising N individual voltage sources, each of which is electrically connected to an electrode of one of the optical oscillators 740-1 to 740-N.

[0110] The light source system 710 also includes a beam control device 787 and a beam combiner 788. The beam control device 787 is located between the gas gain medium of the optical oscillators 740-1 to 740-N and the beam combiner 788. The beam control device 787 determines which of the light beams 704-1 to 704-N is incident on the beam combiner 788. The beam combiner 788 forms the exposure beam 705 from the (multiple) light beams incident on the beam combiner 788. In the example shown, the beam control device 787 is represented as a single element. However, the beam control device 787 can be implemented as a collection of separate beam control devices. For example, the beam control device 787 can include a collection of shutters, one shutter being associated with each optical oscillator 740-1 to 740-N.

[0111] The light source system 710 may include other components and systems. For example, the light source system 710 may include a beam preparation system 763, which includes a bandwidth analysis module that measures various properties of the light beam (such as bandwidth or wavelength). The beam preparation system 763 may also include a pulse stretcher (not shown) that temporally stretches each pulse that interacts with the pulse stretcher. The beam preparation system 763 may also include other components capable of acting on light, such as, for example, reflective and / or refractive optical elements (such as, for example, lenses and mirrors), and / or filters. In the example shown, the beam preparation system 763 is located in the path of the exposure beam 705. However, the beam preparation system 763 can be placed elsewhere within the optical lithography system 700. In addition, other implementations are possible. For example, the light source system 710 may include N instances of the beam preparation system 763, each instance being positioned to interact with one of the light beams 704-1 to 704-N. In another example, the light source system 810 can include optical elements, such as mirrors, that steer the light beams 704 - 1 through 704 -N toward the beam combiner 788 .

[0112] The scanner device 780 can be a liquid immersion system or a dry system. The scanner device 780 includes: a projection optical system 781, through which the exposure beam 705 passes before reaching the wafer 770; and a sensor system or measurement system 799. The wafer 770 is held or received on a wafer holder 783. Also refer to Figure 7B, the projection optical system 781 includes a slit 784, a mask 785, and a projection objective including a lens system 786. The lens system 786 includes one or more optical elements. The exposure beam 705 enters the scanner device 780 and is incident on the slit 784, and at least some of the beam 705 passes through the slit 784 to form a shaped exposure beam 705'. Figure 7A and Figure 7B In the example shown, slit 784 is rectangular and shapes exposure beam 705 into an elongated rectangular beam, which is shaped exposure beam 705′. Mask 785 includes a pattern that determines which portions of the shaped beam are transmitted by 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 with exposure beam 705′. The design of the pattern on the mask is determined by the specific microelectronic circuit features desired.

[0113] The metrology system 799 includes a sensor 771. The sensor 771 can be configured to measure properties of the shaped exposure beam 705', such as, for example, bandwidth, energy, pulse duration, and / or wavelength. The sensor 771 can be, for example, a camera or other device capable of capturing an image of the shaped exposure beam 705' at the wafer 770, or an energy detector capable of capturing data describing the amount of light energy at the wafer 770 in the xy plane.

[0114] Further aspects of the invention are set out in the following numbered clauses.

[0115] 1. A light source, comprising:

[0116] a light generating device configured to be in an active state during a first time period, in an idle state during a second time period, and in an active state during a third time period, the first time period occurring before the second time period, and the second time period occurring before the third time period, and wherein the excitation signal is applied to the light generating device in the active state and not applied to the light generating device in the idle state; and

[0117] A control system is configured to estimate a property of the excitation signal applied to the light generating device during a third time period based on a duration of the second time period and a value of the property of the excitation signal during the first time period.

[0118] 2. A light source according to clause 1, wherein the light generating device comprises:

[0119] a discharge chamber configured to contain a gaseous gain medium; and

[0120] A plurality of electrodes in the discharge chamber, and wherein the excitation signal comprises a voltage signal applied to at least one electrode of the plurality of electrodes, and the property of the excitation signal comprises an amplitude of the voltage signal.

[0121] 3. The light source according to clause 2, wherein the voltage signal comprises a time-varying voltage signal.

[0122] 4. The light source according to clause 2, wherein the control system comprises a memory module configured to store at least one value representing the amplitude of the voltage signal applied to the electrode during the first time period.

[0123] 5. The light source of clause 2, wherein the value of the property during the first time period comprises a minimum voltage applied to the electrode during the first time period.

[0124] 6. A light source according to clause 5, wherein the control system is configured to estimate a property of the excitation signal applied to the light generating device during the third time period based on the duration of the second time period, the minimum voltage applied to the electrode during the first time period, and an adaptive parameter associated with the first time period.

[0125] 7. The light source of clause 2, wherein the gas 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.

[0126] 8. The light source of clause 7, wherein the gaseous gain medium comprises argon fluoride (ArF), krypton fluoride (KrF), or xenon chloride (XeCl).

[0127] 9. Light source according to clause 1, wherein the control system is further configured to determine an error metric based on the estimated property of the excitation signal and an actual value of the property of the excitation signal applied to the light generating device during the third time period.

[0128] 10. The light source according to clause 9, wherein the control system is further configured to update the value of the adaptive parameter based on the error metric.

[0129] 11. The luminaire of clause 10, wherein the control system is configured to update a value of each of the plurality of adaptive parameters, and each of the plurality of adaptive parameters is associated with a different duration of the second time period.

[0130] 12. The light source according to clause 1, wherein the control system is further configured to determine whether to initiate a preheating process based on the estimated properties of the excitation signal.

[0131] 13. Luminaire according to clause 12, wherein if a warm-up process is initiated, the control system is further configured to determine a warm-up process metric related to a duration of the warm-up process.

[0132] 14. The light source according to clause 13, wherein the warm-up process metric is the number of times the light generating device is activated during the warm-up process.

[0133] 15. The light source according to clause 1, wherein the light generating device comprises a master oscillator and a power amplifier.

[0134] 16. The light source according to clause 1, wherein the light generating device comprises a single discharge chamber.

[0135] 17. The light source according to clause 1, wherein the light generating device comprises a plurality of discharge cells, and each of the discharge cells is configured to emit a pulsed light beam towards the beam combiner.

[0136] 18. A controller for a light source, the controller comprising a control system, wherein the control system is configured to:

[0137] accessing information related to durations of idle periods of the light source;

[0138] accessing information relating to a value of a property of an excitation signal applied to the light source during a time period occurring prior to the idle period; and

[0139] An updated value of the property of the excitation signal is estimated based on the duration of the idle period and a value of the property of the excitation signal during a time period occurring before the idle period.

[0140] 19. A controller according to clause 18, wherein the control system is further configured to apply an excitation signal having an updated value of the property to the light source after the idle period.

[0141] 20. The controller according to clause 19, wherein the control system is further configured to determine an error metric based on the estimated updated value of the property and an actual value of the property of the excitation signal applied to the light generating device after the idle period.

[0142] 21. The controller according to clause 20, wherein the control system is further configured to update the value of the adaptive parameter based on the error metric.

[0143] 22. The controller of clause 21, wherein the control system is configured to update a value of each of the plurality of adaptive parameters, and each of the plurality of adaptive parameters is associated with a different duration of the second time period.

[0144] 23. The controller according to clause 18, wherein the control system is further configured to determine whether to initiate a warm-up process for the light source based on the estimated updated value of the property.

[0145] 24. A controller according to clause 18, wherein the control system is configured to access from the computer readable memory module information relating to the duration of the idle period of the light source and information relating to the value of the property of the excitation signal during a time period occurring before the idle period.

[0146] 25. The controller according to clause 18, wherein the control system comprises:

[0147] a computer readable memory module; and

[0148] One or more electronic processors are coupled to the computer-readable memory module.

[0149] 26. A method comprising:

[0150] accessing information related to durations of idle periods of the light source;

[0151] accessing information relating to a value of a property of an excitation signal applied to the light source during a time period occurring prior to the idle period; and

[0152] An updated value of the property of the excitation signal is estimated based on the duration of the idle period and a value of the property of the excitation signal during a time period occurring before the idle period.

[0153] Other implementations are within the scope of the following claims.

Claims

1. A light source, comprising: a light generating device configured to be in an active state during a first time period, in an idle state during a second time period, and in the active state during a third time period, the first time period occurring before the second time period, and the second time period occurring before the third time period, and wherein an excitation signal is applied to the light generating device in the active state and not applied to the light generating device in the idle state; as well as A control system is configured to estimate the property applied to the light generating device during the third time period based on the duration of the second time period and the value of the property of the excitation signal during the first time period.

2. The light source of claim 1 , wherein the light generating device comprises: a discharge chamber configured to contain a gaseous gain medium; as well as A plurality of electrodes in the discharge cell, and wherein the excitation signal comprises a voltage signal applied to at least one electrode of the plurality of electrodes, and the property of the excitation signal comprises an amplitude of the voltage signal. The light source of claim 2 , wherein the voltage signal comprises a time-varying voltage signal. 4 . The light source of claim 2 , wherein the control system comprises a memory module configured to store at least one value representing the magnitude of the voltage signal applied to the electrode during the first time period.

5. The light source of claim 2, wherein the value of the property during the first time period comprises a minimum voltage applied to the electrode during the first time period.

6. A light source according to claim 5, wherein the control system is configured to estimate the property of the excitation signal applied to the light generating device during the third time period based on the duration of the second time period, the minimum voltage applied to the electrode during the first time period, and an adaptive parameter associated with the first time period. 7 . The light source of claim 2 , wherein the gaseous gain medium comprises a gain medium configured to emit deep ultraviolet (DUV) light in response to the voltage signal applied to at least one of the electrodes.

8. The light source of claim 7, wherein the gaseous gain medium comprises argon fluoride (ArF), krypton fluoride (KrF), or xenon chloride (XeCl).

9. The light source of claim 1 , wherein the control system is further configured to determine an error metric based on the estimated property of the excitation signal and an actual value of the property of the excitation signal applied to the light generating device during the third time period.

10. The light source of claim 9, wherein the control system is further configured to update a value of an adaptive parameter based on the error metric.

11. The light source of claim 10, wherein the control system is configured to update a value of each of a plurality of adaptive parameters, and each of the plurality of adaptive parameters is associated with a different duration of the second time period.

12. The light source of claim 1, wherein the control system is further configured to determine whether to initiate a preheating process based on the estimated property of the excitation signal.

13. The light source of claim 12, wherein if the warm-up process is initiated, the control system is further configured to determine a warm-up process metric related to a duration of the warm-up process.

14. The light source of claim 13, wherein the warm-up process metric is the number of times the light generating device is activated during the warm-up process.

15. The light source of claim 1, wherein the light generating device comprises a master oscillator and a power amplifier.

16. The light source of claim 1, wherein the light generating device comprises a single discharge chamber.

17. The light source of claim 1, wherein the light generating device comprises a plurality of discharge chambers, and each of the discharge chambers is configured to emit a pulsed light beam towards a beam combiner.

18. A controller for a light source, the controller comprising a control system, wherein the control system is configured to: accessing information related to durations of idle periods of the light source; accessing information relating to a value of a property of an excitation signal applied to the light source during a time period occurring prior to the idle period; and An updated value of the property of the excitation signal is estimated based on the duration of the idle period and the value of the property of the excitation signal during a time period occurring before the idle period.

19. The controller of claim 18, wherein the control system is further configured to apply the excitation signal having the updated value of the property to the light source after the idle period.

20. The controller of claim 19, wherein the control system is further configured to determine an error metric based on the estimated updated value of the property and an actual value of the property of the excitation signal applied to the light generating device after the idle period.

21. The controller of claim 20, wherein the control system is further configured to update a value of an adaptive parameter based on the error metric.

22. The controller of claim 21, wherein the control system is configured to update a value of each of a plurality of adaptive parameters, and each of the plurality of adaptive parameters is associated with a different duration of the idle period.

23. The controller of claim 18, wherein the control system is further configured to determine whether to initiate a warm-up process for the light source based on the estimated updated value of the property.

24. The controller of claim 18, wherein the control system is configured to access from the computer readable memory module information regarding the duration of an idle period of the light source and information regarding a value of a property of the excitation signal during a time period occurring prior to the idle period.

25. The controller of claim 18, wherein the control system comprises: a computer readable memory module; as well as One or more electronic processors are coupled to the computer-readable memory module.

26. A method for controlling a light source, comprising: accessing information related to durations of idle periods of the light source; accessing information relating to a value of a property of an excitation signal applied to the light source during a time period occurring prior to the idle period; as well as An updated value of the property of the excitation signal is estimated based on the duration of the idle period and the value of the property of the excitation signal during a time period occurring before the idle period.

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