CN115210970A

CN115210970A - Control system for light sources

Info

Publication number: CN115210970A
Application number: CN202180018978.9A
Authority: CN
Inventors: M·T·莫赫比
Original assignee: Cymer LLC
Current assignee: Cymer LLC
Priority date: 2020-03-03
Filing date: 2021-02-02
Publication date: 2022-10-18
Also published as: TWI804817B; KR20220109471A; JP2023515743A; TW202138933A; WO2021178091A1; JP7430799B2

Abstract

A light source, comprising: a light generating device configured to: active during a first time period, idle during a second time period, and active 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. The excitation signal is applied to the light generating device in an active state and is not applied to the light generating device in an 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

Control system for light sources

Cross Reference to Related Applications

This application claims priority from U.S. application No.62/984,433, entitled "CONTROL SYSTEM FOR a LIGHT SOURCE" filed 3/2020, which is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to a control system for a light source (e.g., a deep ultraviolet light source).

Background

Photolithography is a process of patterning semiconductor circuitry on a substrate, such as a silicon wafer. The optical source generates Deep Ultraviolet (DUV) light for exposing a photoresist on a wafer. The DUV light may include wavelengths from about 100 nanometers (nm) to about 400nm, for example. Typically, the optical source is a laser source (e.g., an excimer laser) and the DUV light is a pulsed laser beam. DUV light from an optical source interacts with projection optics that project a beam of light through a mask onto a photoresist on a silicon wafer. 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.

Disclosure of Invention

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

Implementations may include one or more of the following features.

The light generating device may include: a discharge chamber configured to accommodate a gaseous gain medium; and a plurality of electrodes in the discharge cells. The excitation signal may comprise a voltage signal applied to at least one of the plurality of electrodes, and the property of the excitation signal may comprise an amplitude of the voltage signal. The voltage signal may comprise a time-varying voltage signal. The control system may include a memory module configured to store at least one value indicative of the magnitude of the voltage signal applied to the electrode during the first time period. The value of the property during the first time period may comprise a minimum voltage applied to the electrode during the first time period. The control system may be configured to: a property of the excitation signal applied to the light generating device during the third time period is estimated based on the duration of the second time period, the minimum voltage applied to the electrode during the first time period, and the 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 a voltage signal applied to at least one of the electrodes. The gaseous gain medium may comprise argon fluoride (ArF), krypton fluoride (KrF), or xenon chloride (XeCl).

The control system may be further configured to: an error metric is determined 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: based on the error metric, the value of the adaptive parameter is updated. The control system may be configured to: the value of each of the plurality of adaptive parameters is updated, and each of the plurality of adaptive parameters may be associated with a different duration of the second time period.

The control system may be configured to: based on the estimated property of the excitation signal, it is determined whether to initiate a warm-up process. If the warm-up process is initiated, the control system may be configured to determine a warm-up process metric related to a duration of the warm-up process. The pre-heating process metric may be a number of times the light generating device is activated during the pre-heating process.

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

The light generating device may comprise a single discharge cell.

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 toward the beam combiner.

In another aspect, a controller for a light source includes a control system. The control system is configured to: accessing information related to a duration of an idle period of a light source; accessing information related to a value of a property of an excitation signal applied to a light source during a time period occurring before an idle time period; and estimating an updated value of the property of the excitation signal 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.

Implementations may include one or more of the following features.

The control system may be configured to: an excitation signal having an updated value of the property is applied to the light source after the idle period. The control system may be configured to: an error metric is determined 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. The control system may be configured to: based on the error metric, the value of the adaptive parameter is updated. The control system may be configured to: the value of each of the plurality of adaptive parameters is updated, each of the plurality of adaptive parameters being associated with a different duration of the second time period.

The control system may be further configured to: based on the estimated updated value of the property, it is determined whether to initiate a warm-up procedure for the light source.

The control system may be configured to: accessing, from the computer-readable memory module, information relating to a duration of an idle period of the light source and information relating to a value during a time period in which a property of the excitation signal occurs prior to the idle period.

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

In another aspect, a method comprises: accessing information relating to a duration of an idle period of a light source; accessing information related to a value of a property of an excitation signal applied to a light source during a time period occurring before an idle time period; and estimating an updated value of the property of the excitation signal based on the duration of the idle period and a value during a time period in which the property of the excitation signal occurs before the idle period.

Implementations of any of the above techniques may include a DUV light source, system, method, process, apparatus, or device. 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.

Drawings

Fig. 1A to 1C are block diagrams of a light source at three different times.

Fig. 2A to 2C are block diagrams of another light source at three different times.

Fig. 3 is a flow chart of a process for estimating a value of a property of an excitation signal.

Fig. 4 is a flowchart of a process for determining whether to initiate a warm-up procedure.

Fig. 5A is a plot of idle time as a function of time.

Fig. 5B is a plot of voltage measurements as a function of time.

FIG. 5C is a plot of 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.

Fig. 5E is a plot of error metric as a function of idle time for the second DUV light source of fig. 5D.

Fig. 5F is a plot of an error metric as a function of idle time for the second DUV light source of fig. 5D.

FIG. 6 is a block diagram of a lithography system.

FIG. 7A is a block diagram of an optical lithography system.

FIG. 7B is a block diagram of a projection optical system for use in the optical lithography system of FIG. 7A.

Detailed Description

Each of fig. 1A to 1C is a block diagram of the light source 100 at different times. Fig. 1A shows light source 100 at time t 1. Fig. 1B shows light source 100 at time t 2. Fig. 1C shows light source 100 at time t 3. 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. For purposes of illustration, three time periods are shown. However, the light source 100 may operate for more than three periods of time.

The light source 100 comprises a light generating device 110 and a control system 150, the control system 150 estimating properties of the excitation signal 109. The excitation signal 109 may be generated by the control system 150 or a separate device (such as a voltage source or current source) controlled by the control system 150. The excitation signal 109 is any type of signal sufficient for the light generating device 110 to generate the light beam 105. For example, the excitation signal 109 may be a signal that is applied to an excitation mechanism in the light-generating device 110 (such as the excitation mechanism 211 of fig. 2A-2C, the electrodes 611A and 611b of fig. 6, or the electrodes 711-1A, 711-1b of fig. 7). The light beam 105 may be, for example, a pulsed or continuous wave laser beam. The light-generating device 110 may be a Deep Ultraviolet (DUV) optical system that emits a pulsed light beam in the DUV range (e.g., wavelengths from about 100 nanometers (nm) to about 400 nm). In some implementations, the light generating device 110 transmits a burst of pulses during each activity period. A pulse train comprises hundreds or thousands of light pulses.

When the light generating device 110 is in the active state, the excitation signal 109 is applied to the light generating device 110 or to 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 an inactive or idle state, the excitation signal 109 is not applied to the light generating device 110 or components thereof, and the light generating device 110 does not produce the light beam 105. During an idle or inactive state, the light-generating device 110 may, for example, be powered off or off, or powered on without generating any light. In the example of fig. 1A-1C, the light generating device 110 is in an active state during the first and third time periods and is in an idle state during the second time period. The duration of the second time period is also referred to as an idle time, and the second time period is also referred to as an idle period.

As discussed in more detail below, the control system 150 estimates the 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 a previous active time period (e.g., the first 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.

By using the values of the property during the idle time and 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 only on idle time. These prior art techniques, for example, use a predetermined excitation signal if the idle time is greater than a predetermined threshold and/or cause the light generating device 110 to enter a preheat mode if the idle time is greater than a predetermined idle time threshold.

On the other hand, the control system 150 implements techniques to estimate an updated value of the excitation signal 109 that take into account previous values of the properties of the excitation signal 109. The approach taken by the control system 150 results in a more accurate determination of the nature of the excitation signal 109 to be applied in the third time period and improves the use of the warm-up process. For example, the control system 150 reduces or eliminates unnecessary performance of the warm-up process while also helping to ensure that the warm-up process is properly invoked.

Furthermore, the control system 150 may also determine adaptive parameters that take into account the time variation of one or more characteristics of the light generating device 110. For example, the energy efficiency of the light generating device 110 may change over time. Energy efficiency is the relationship between the amount of energy provided to the light generating device 110 to produce light having a certain amount of energy. For example, in implementations where the excitation signal 109 is a voltage signal applied to an electrode in the light generating device 110, as the energy efficiency of the light generating device 110 decreases, a greater amount of voltage is required to produce the light beam 105. The energy efficiency of the light generating device 110 may also decrease during idle times. As discussed in more detail below, the adaptive parameters may 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 generation 110, the control system 150 improves the accuracy of the estimation of the properties of the excitation signal 109.

Referring to fig. 2A-2C, block diagrams of light source 200 are shown. Light source 200 is an implementation of light source 100. Each of fig. 2A-2C shows the light source 200 at a different time. The light source 200 is shown in an active state in fig. 2A and 2C and in an idle state in fig. 2B. The light source 200 comprises a light generating device 210 and a control system 250. The light generating device 210 comprises an excitation mechanism 211 and a gain medium 212.

The light generating device 210 generates the light beam 205 in an active state. The excitation signal 209 is applied to the light generating device 210 and excites the excitation mechanism 211 when the light generating device 210 is in an active state (fig. 2A and 2C). The light generating device 210 also has an inactive or idle state (FIG. 2B). When the light generating device 210 is in the idle state, the excitation signal 209 is not applied to the light generating device and the excitation mechanism 211 is not excited. In the example of fig. 2A-2C, the light source 200 is in an active state during a first time period (including time t 1) and a third time period (including time t 3). The light source 200 is in an idle state during a second time period (including time t 2). The duration of the second time period is also referred to as idle time. For purposes of illustration, three time periods are shown. However, the light source 200 may operate over more than three time periods.

The excitation mechanism 211 excites the gain medium 212 in response to the excitation signal 209. Gain medium 212 is any medium suitable for producing an optical beam at the wavelength, energy, and bandwidth required for the application. For example, the gain medium 212 may be a gas, a crystal, a glass, a semiconductor, or a liquid.

Excitation mechanism 211 is any mechanism capable of exciting gain medium 212. For example, the excitation mechanism 211 may be a plurality of electrodes that excite the gas 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 time-varying Direct Current (DC) electrical signal or an Alternating Current (AC) electrical signal, such as a sine wave voltage signal or a square wave voltage signal. In these implementations, the property of the excitation signal 209 may be 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 any other property related to the time-varying signal.

The control system 250 evaluates the properties of the excitation signal 209. The property may be, for example, the amplitude, frequency and/or duty cycle of the voltage and/or current signal provided to the excitation mechanism 211 in the light generating device 210. The control system 250 estimates the properties of the excitation signal 209 based on previous or earlier idle times and previous or earlier values of the properties of the excitation signal 209. To estimate the properties of the excitation signal 209, the control system 250 may implement a process such as the process 300 discussed with respect to fig. 3. The control system 250 may also implement other processes, such as the process 400 discussed with respect to fig. 4, as a standalone process or in conjunction with the process 300. Further, the control system 250 may be used with any type of light source. For example, control system 250 may be used with lithography system 600 (FIG. 6) or optical lithography system 700 (FIG. 7).

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 (such as general or special purpose microprocessors) adapted to execute a computer program, as well as any one or more processors of any kind of digital computer. Generally, an electronic processor receives instructions and data from a read-only memory, a Random Access Memory (RAM), or both. The electronic processing module 251 may include any type of electronic processor. One or more electronic processors of electronic processing module 251 execute instructions and access data stored on memory module 252. The one or more electronic processors can also write data to the memory module 252.

The memory module 252 may be volatile memory (such as RAM) or non-volatile memory. In some implementations, the memory module 252 includes non-volatile and volatile portions or components. The memory module 252 may store data and information used in the operation of the control system 250. For example, the memory module 252 may store information related to idle periods and information related to values of properties of the excitation signal 209 applied to the light generating device 210 during one or more time periods that occurred before the past and most recent idle times. The memory module 252 may store one or more values associated with the stimulus signal 209 applied during an active period that occurs immediately prior to the most recent idle period. For example, the excitation signal 209 may be a voltage signal or a signal specifying the voltage generated by a voltage source. In this example, the memory module 252 may store the average, minimum, and maximum values of the voltage signal during the most recent activity period. The memory module 252 may also store information received from the light source 200 and/or the light generating device 210.

The I/O interface 253 is any kind 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 apparatus. For example, in implementations where rules or instructions stored on the memory module 252 may be edited, the editing may be done through the I/O interface 253. In another example, the I/O interface 253 receives data from the light generating device 210 and/or a hardware and/or software subsystem of the light generating device 210. For example, the light generating device 210 may provide idle time and other information about the light generating device 210 to the control system 250 through the I/O interface 253. The I/O interface 253 may include one or more of a visual display, a keyboard, and a communications interface, such as a parallel port, a Universal Serial Bus (USB) connection, and/or any type of network interface, such as, for example, ethernet. The I/O interface 253 may also allow contactless communication over, for example, IEEE802.11, bluetooth, or Near Field Communication (NFC) connections.

The control system 250 is coupled to the light generating device 210 by a data connection 254. The data connection 254 may be a physical cable or other physical data conduit (such as a cable supporting IEEE 802.3-based data transmission), a wireless data connection (such as a data connection providing data via IEEE802.11 or bluetooth), or a combination of wired and wireless data connections. The data provided over the data connection may be arranged by any type of protocol or format. The data connections 254 are connected to the light generating device 210 at respective communication interfaces (not shown). The communication interface may be any kind of interface capable of sending and receiving data. For example, the data interface may be an ethernet interface, a serial port, a parallel port, or a USB connection. In some implementations, the data interface allows data communication over a wireless data connection. For example, the data interface may be an IEEE 811.11 transceiver, bluetooth, or NFC connection. The control system 250 may be connected to systems and/or components within the light generating device 210. For example, the control system 250 may be connected to the excitation mechanism 211.

In the example of fig. 2A-2C, the control system 250 is shown 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 may be a data path that allows communication between software modules having one of the software modules implementing aspects of the control system 250 and another of the software modules implementing other functionality of the light-generating device 210.

Fig. 3 is a flow chart of a process 300. The process 300 is an example of a process for estimating a value of a property of the excitation signal 209. The process 300 may be performed by a control system associated with the light generating device. For example, process 300 may be performed by control system 150 (fig. 1) or control system 250 (fig. 2A-2C). In the following discussion, the process 300 is discussed with respect to the control system 250 and the light generating device 210. For example, referring to fig. 2A-2C, process 300 may 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.

Information relating to the duration of the idle period of the light generating device 210 is accessed (310). The duration of the idle period (also referred to as idle time) is the length of the continuous period of time during which the light generating device 210 is in an idle or inactive state. The idle time is related to the idle period that 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.

The idle time may be stored on 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 is not necessarily accessed from the memory module 252. For example, in some implementations, idle time is provided by an operator through the I/O interface 253. Further, the information relating to the idle time may be a numerical value indicating the idle time, or the information may take other forms. For example, the information related to the idle time may include a time when the idle period starts and a 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.

Information regarding a value of a property of the excitation signal 209 applied to the light generating device 210 during an active period occurring before an idle period is accessed (320). For example, the information may be the maximum voltage applied to the excitation mechanism 211 during the most recent activity period. The information may include more than one value of the property during a previous activity period. For example, the information may include maximum and minimum voltages applied to the excitation mechanism 211 during a previous activity period. In another example, the information may include a time series representing the voltage applied to energizing mechanism 211 at regular intervals during the active period. Information relating to the value of the property of the stimulus signal 209 may be accessed from the memory module 252 or may be accessed through the I/O interface 253.

An updated value of the property of the excitation signal 209 is estimated based on the duration of the idle period and the value of the property of the excitation signal 209 during a time period that occurs before the idle period (330). 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 being estimated is the maximum amplitude (V) of the voltage to be applied to the excitation mechanism 211 after the end of the idle period _max ). The excitation signal 209 is generated to include a number of individual pulses (e.g.,hundreds or thousands) of bursts. 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 the light pulses during the active period. Maximum voltage (V) _max ) Typically relatively early in a particular pulse train, while the light generating device 210 is experiencing transient effects associated with beginning to produce the light beam 205 after an idle period. After the transient effect has ended and the light generating device 210 is in a steady state, the minimum voltage (V) _min ) Usually later in the burst.

The value of the voltage signal of the excitation signal 209 to be applied to the excitation mechanism 211 after the end of the idle time may be estimated as shown in equation (1):

where i is an integer value indexing the activity period of the light-generating device 210,

is an estimate of the maximum voltage, V, of the excitation signal 209 used during the i-th active period _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 Δ T (i) is the idle time of the idle period immediately preceding the i-th active period. The ith activity period is a current activity period, and the (i-1) th activity period is an activity period immediately preceding the current activity period. The idle period with idle time Δ T (i) is between the ith active period and the (i-1) th active period.

For example, the current or ith activity period may be a third time period including t3 as shown in fig. 2C, and the previous activity period may be a first time period including t1 as shown in fig. 2A. Continuing the example, the idle time is includingA second period of time at t2 as shown in fig. 2B. Thus, 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)), Δ T (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.

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 estimated excitation signal 209 is the maximum voltage (V) _max ) The value of (c). However, other metrics may be estimated. For example, in some implementations, a constant voltage is applied to excitation mechanism 211, and the output energy of beam 205 is estimated after the idle time based on the idle time and knowledge of the output energy of beam 205 before the idle time. In other words, the above-described method may be used to predict the optical energy generated by beam 205 after an idle period.

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

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

where i is an integer value indexing the activity period of the light generating device 210, e _v (i) Is associated with the ith activity periodError metric of (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 activity period,

is the estimated maximum voltage of the excitation signal 209 for the i-th active period.

The value of the adaptive parameter may be updated (350). The adaptive parameter is any parameter representing the time-varying characteristics of the light generating device 210. For example, the adaptive parameter may be an estimate of the energy efficiency of the light generating device 210. Energy efficiency relates the input energy (voltage supplied to the excitation mechanism 211) to the output energy (light energy in the beam 205). The relationship may be approximately linear. The slope of the linear relationship with respect to or with respect to the idle time may be used as an adaptation parameter.

The value of the adaptive parameter (α) may be updated as shown in equation (3):

α(i)＝α(i-1)+ηe _V (i) The results of equation (3),

where i is an integer value indexing the activity period of the light-generating device 210, η is a step size or weighting factor, and e _v (i) Is the error metric for the ith activity period. In the example of equation (3), i is the current activity period (e.g., the third time period including time t3 in fig. 2C), and i-1 is the immediately preceding activity period (e.g., the first time period including time t1 in fig. 2A).

The step size or weighting factor η remains constant over time unless it is intentionally changed by the operator of the light source 200. Step size or weighting factor eta determines an error value e _v (i) The degree of the adaptation parameter alpha is influenced. A relatively large value of the step size or weighting factor η results in a large change of the adaptation parameter α compared to a relatively small value. When the light generating device 210 is assembled, the step size or weighting factor η may be set by the manufacturer and stored on the memory module 252, and/or an operator may update the step size or weighting factor via the I/O interface 253.

The updated value of the adaptive parameter a may be stored on the memory module 252 in association with the ith activity period so that the control system 250 may access the value of the adaptive parameter for later use.

In some implementations, more than one instance of the adaptive parameter 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):

α _j (i)＝α _j (i-1)+η _j e _V (i) In the equation (6),

wherein j is an example, and α _j Is the adaptive parameter corresponding to the jth instance, and Δ T is the idle time range associated with the jth instance. The idle time ranges need not be the same. For example, in one implementation, the adaptive parameter α _j Is initialized with the adaptive parameter a _j For each of the following idle time ranges Δ T (i): 0 to 60 seconds(s), 61 to 120s, 121 to 600s, 601 to 3600s, and greater than 3600s. 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 。

Using an adaptive parameter alpha _j More than one instance of (a) improves the overall accuracy of the process 300. For example, the energy efficiency of the light generating device 210 generally decreases with increasing idle time. While 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 idle time. For this purpose, canTo use the adaptive parameter alpha _j Each associated with a different range of idle times. Since the ranges of idle time may be selected such that the energy efficiency is linear or nearly linear over each of these ranges, so that equation (3) may be used to update the various adjustable parameters, this approach may result in a more efficient process and ensure accurate results for longer idle times.

In some implementations, the control system 250 intentionally does not update the adaptive parameters under certain conditions, even though 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 mode, the values of the adaptive parameters may become inaccurate and may affect the computational accuracy of the properties of the excitation signal after the light generating device 210 exits the maintenance and/or calibration mode. Accordingly, the control system 250 may be configured to: when the light-generating device 210 is in maintenance and/or calibration mode, portions of the process 300, such as (340) and (350), are skipped. The control system 250 may receive indications from the light generating device 210 or an operator via the I/O interface 253 to enter and exit the maintenance and/or calibration mode.

Referring to fig. 4, a flow chart of a process 400 is shown. The process 400 may be performed by a control system associated with the light generating device. For example, process 400 may be performed by control system 150 (fig. 1) or control system 250 (fig. 2). In the discussion that follows, the process 400 is discussed with respect to the control system 250 and the light generating device 210. Process 400 may 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.

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

Some prior art techniques initiate the 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, 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 for some relatively long idle time. Furthermore, this approach may result in the warm-up process being erroneously not performed for some relatively short idle time. Fig. 5A and 5B show examples of how relying on idle time alone may result in an incorrect determination of whether to initiate a warm-up procedure. On the other hand, as described below, the control system 250 implements a process 400 that uses the estimate of the property of the excitation signal 209 to determine whether to initiate the warm-up process.

The estimated properties of the excitation signal 209 are analyzed to determine whether to initiate a warm-up process (410). The estimated property of the excitation signal 209 may be determined at (330) of the process 300 and passed to the process 400 (e.g., through 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 may be provided by an operator of the light source 200 through the I/O interface 253 or read from the memory module 252.

The estimate of the property of the excitation signal 209 may be analyzed by comparing the estimate to a threshold. For example, the estimated value may be an estimated maximum voltage value

In this example, a higher value of the estimated maximum voltage indicates a relatively low efficiency and the warm-up process should be performed. On the other hand, a relatively low estimated maximum voltage indicates a relatively high efficiency without the need for a warm-up process.

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, then the 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 pre-heating 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 pre-heating process. For example, the metric may indicate a time duration of the excitation signal 209 and/or a number of voltage pulses applied to the excitation mechanism 211 during the warm-up process. In some implementations, the maximum voltage value may be estimated based on the maximum voltage value

The number of voltage pulses is calculated (e.g., as estimated by equation 1) and the desired voltage after the preheating process. The number of voltage pulses may be estimated by comparing the expected voltage after the preheating process with the actual voltage achieved after the preheating process. In particular, the voltage error between the desired voltage after the preheating process and the actual voltage achieved after the preheating process may 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 warm-up process metric is a predetermined value stored on the memory module 252.

The excitation signal 209 having the determined property is applied to the excitation mechanism 211 (440) to perform the preheating. After the preheating process is complete, the process 400 ends or returns to the process 300.

Fig. 5A and 5B show that relying on idle time alone is not sufficient to accurately detect cold start conditions and accurately determine whether to initiate a warm-up process. Fig. 5A is a plot of idle time in seconds as a function of time. Fig. 5B is a plot of voltage measurements as a function of time. In the example of fig. 5B, the voltage metric is the voltage applied to the electrode immediately after the idle period. Fig. 5A and 5B have the same X-axis.

The light source has a first activity 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 indicated by the open circle symbol. 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 energizing mechanism is more rapidly energized in the second activity period than in the first activity period. The first idle time (t 1 on fig. 5A and 5B) is smaller than the second idle time (t 2 on fig. 5A and 5B). However, the first voltage metric (Δ V1) is greater than the second voltage metric (Δ V2), and a process such as process 400 would determine that a warm-up process would be beneficial after the first idle time, but not after the second idle time. However, a method 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, the opposite result will occur. Thus, a conventional approach that only considers idle times would initiate unnecessary warm-up procedures after the second idle time, without initiating beneficial warm-up procedures after the first idle time. Thus, a process such as process 400, which takes into account an estimate of the value of a property of the excitation signal (such as the amount of voltage applied immediately after an idle period), allows for greater use of the warm-up process in a more efficient manner.

Fig. 5C and 5D show examples of actual measurements for a process such as process 300. 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. In each of fig. 5C and 5D, the actual voltage applied to the electrodes is represented by the line with the open circle symbol labeled 596. Each data point in the series labeled 596 is the maximum burst average voltage over a plurality of consecutive bursts. The voltage values predicted at element (330) of process 300 using a single adaptive parameter a are represented by the line labeled 594 with the open square symbol. The voltage values predicted at element (330) of process 300 using multiple instances of the adaptive parameter a are represented by the line with the x symbol labeled 595. In both implementations, the process 300 estimates the value of the property of the excitation signal with reasonable accuracy, and implementations with multiple instances of the adaptive parameter a result in improved accuracy in some cases.

Fig. 5E and 5F illustrate the error metric determined at (340) of the process 300 of fig. 3 as a function of idle time in seconds. The data shown in fig. 5E and 5F were simulated using the second DUV light source discussed with respect to fig. 5D. In fig. 5E and 5F, the open circles represent error metrics for implementations of process 300 in which a single adaptive parameter a is used, and the x symbols represent error metrics for implementations in which multiple instances of adaptive parameter a are used. As shown in fig. 5E, the single adaptive parameter and multiple adaptive parameter methods predict values of the property of the excitation signal with similar accuracy (within about 2%) for idle times of about 18 seconds or less. As shown in fig. 5F, the multiple adaptive parameter approach achieves better accuracy for idle times greater than about 50 seconds.

The examples of fig. 3 and 4 are discussed with respect to light-generating device 210. However, the control system 250 may be used with other light sources. For example, the control system 250 may be used with a DUV laser that includes a single discharge chamber enclosing a gaseous 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 that occurs immediately after the idle period. In another example, the control system 250 may be used with a DUV light source that includes more than one discharge cell, and each discharge cell encloses a gaseous 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 cells during an active period that occurs immediately after an idle period. Fig. 6, 7A and 7B show examples of DUV light sources that include more than one discharge cell and that may be used with control system 150 or control system 250.

Referring to FIG. 6, a block diagram of a lithography system 600 is shown. The light source 610 generates a pulsed light beam 605, and the pulsed light beam 605 is provided to a lithographic exposure apparatus 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 pulsed beam 605 enters lithographic exposure apparatus 669, it is directed through projection optics 675 and projected onto wafer 670 to form one or more microelectronic features on the photoresist on wafer 670. The lithography system 600 further comprises a control system 250, in the example of fig. 6, the control system 250 is connected to components of the lithography exposure apparatus 669 and the light source 610. 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, the control system 250 is connected only to the light source 610.

In the example shown in fig. 6, 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 PA 630 may be considered subsystems of the light source 610 or systems that are part of the light source 610. Power amplifier 630 receives seed beam 624 from master oscillator 631 and amplifies seed beam 624 to generate beam 605 for lithographic exposure apparatus 669. For example, the master oscillator 631 may emit a pulsed seed beam having a seed pulse energy of about 1 millijoule (mJ) per pulse, and these seed pulses may be amplified to about 10 to 15mJ by the power amplifier 630.

The 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 gas between the electrodes 611A. The resonator is formed between a line narrowing module 616 on one side of the discharge cell 614 and an output coupler 618 on a second side of the discharge cell 614. Line narrowing module 616 may include diffractive optics, such as a grating, that fine-tunes the spectral output of discharge cells 614.

The master oscillator 631 further includes a line center analysis module 620, the line center analysis module 620 receiving the output beam from the output coupler 618 and the beam coupling optics 622, the beam coupling optics 622 modifying the size or shape of the output beam as needed to form a seed beam 624. Line center analysis module 620 is a measurement system that may be used to measure or monitor the wavelength of seed beam 624. The line center analysis module 620 may be placed at other locations in the light source 610, or it may be placed at the output of the light source 610.

The gas mixture used in the discharge cells 614 may be any gas suitable for producing a light beam at the wavelength and bandwidth required for the application. For excimer sources, the gas mixture may comprise an inert gas (noble gas) as a buffer gas, such as for example argon or krypton, a halogen gas, such as for example fluorine or chlorine and traces of xenon in addition to helium and/or neon. Specific examples of gas mixtures include argon fluoride (ArF) emitting light at a wavelength of about 193nm, krypton fluoride (KrF) emitting light at a wavelength of about 248nm, or xenon chloride (XeCl) emitting light at a wavelength of about 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 elongated electrode 611A.

The power amplifier 630 includes beam coupling optics 632 that receives the seed beam 624 from the master oscillator 631 and directs the beam through the discharge cell 640 and to beam steering optics 648, which beam steering optics 648 modify or change the direction of the seed beam 624 so that it is transmitted back to the discharge cell 640. The discharge chamber 640 includes a pair of elongated electrodes 611B, a gain medium 612 as a gas mixture, and a fan for circulating the gas mixture between the electrodes 611B.

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

Beam 605 is a pulsed beam and may comprise one or more pulse trains separated in time from each other. Each burst may include one or more optical pulses. In some implementations, the pulse train includes hundreds of pulses, e.g., 100 to 400 pulses.

As described above, when the gain medium 612 is pumped by applying the voltage 609 to the electrode 611A, the gain medium 612 emits light. When a voltage 609 is applied to the electrode 611A in a pulse form, light emitted from the medium 612 is also pulsed. Thus, the repetition rate of pulsed light beam 605 is determined by the rate at which voltage 609 is applied to electrode 611A, with each application of voltage 609 producing a pulse of light. The optical pulses propagate through the gain medium 612 and exit the chamber 614 through the output coupler 618. Thus, a pulse sequence is created by periodically, repeatedly applying the voltage 609 to the electrode 611A. The repetition rate of the pulses may range between about 500Hz and 6000 Hz. In some implementations, the repetition rate is greater than 6000Hz, and may be, for example, 12000Hz or greater.

The signals from the control system 250 may also be used to control the

electrodes

611A, 611B within the master oscillator 631 and power amplifier 630, respectively, for controlling the respective pulse energies of the master oscillator 631 and power amplifier 630, and thus the energy of the beam 605. 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 a property 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 may be in the range of tens of watts, for example from about 50W to about 130W. The irradiance (i.e., average power per unit area) of light beam 605 at the output may range from 60W/cm ² To 80W/cm ² 。

Referring to FIG. 7A, a block diagram of a lithography system 700 is shown. Lithography system 700 includes a light source system 710, which light source system 710 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, the control system 250 is connected to a light source system 710 and a scanner device 780. In other examples, the control system 250 is connected only to the light source system 710.

Scanner device 780 exposes wafer 770 with shaped exposure beam 705'. The shaped exposure beam 705' is formed by passing the exposure beam 705 through a projection optical system 781.

The light 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 respective optical beam 704-1 to 704-N. Details of optical oscillator 740-1 are discussed below. The other N-1 optical oscillators in the light source system 710 include the same or similar features.

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

The gas gain medium 712-1 may be any gas suitable for producing a beam at the wavelength, energy, and bandwidth required for the application. For excimer sources, the gas gain medium 712-1 may contain an inert gas (noble 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 a buffer gas, such as helium. Specific examples of the gaseous gain medium 712-1 include argon fluoride (ArF) that emits light having a wavelength of about 193nm, krypton fluoride (KrF) that emits light having a wavelength of about 248nm, or xenon chloride (XeCl) that emits light having a wavelength of about 351 nm. The gain medium 712-1 is pumped with short (e.g., nanosecond) current pulses in a high voltage discharge by applying a voltage 709 to the electrodes 711-1a, 711-1 b.

The resonator is formed between the line narrowing module 716-1 on one side of the discharge cell 715-1 and the output coupler 718-1 on a second side of the discharge cell 715-1. Line narrowing module 716-1 may include diffractive optics, such as, for example, gratings and/or prisms, that fine-tune the spectral output of discharge cell 715-1. In some implementations, the line narrowing module 716-1 includes a plurality of 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 of which are configured to control the spectral bandwidth of light beam 704-1.

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 may be used to measure or monitor the wavelength of light beam 704-1. The line center analysis module 720-1 can provide data to the control system 250, and the control system 250 can determine a metric related to the beam 704-1 based on the data from the line center analysis module 720-1. For example, the control system 250 may determine a beam quality metric or spectral bandwidth based on the data measured by the hub-of-line analysis module 720-1.

The light source system 710 further includes a gas supply system 790, the gas supply system 790 being fluidly coupled to the interior of the discharge chamber 715-1 via a fluid conduit 789. Fluid conduit 789 is any conduit capable of transporting a gas or other fluid with no or minimal fluid loss. For example, fluid conduit 789 may be a tube made of or coated with a material that is non-reactive with the fluid or fluids being conveyed in conduit 789. The gas supply system 790 includes a chamber 791, the chamber 791 containing and/or configured to receive a supply of one or more gases used in the gain medium 712-1. The gas supply system 790 also includes devices (such as pumps, valves, and/or fluid switches) that enable the gas supply system 790 to remove gas from the discharge chamber 715-1 or inject gas into the discharge chamber 715-1. The gas supply system 790 is coupled to the control system 250. The gas supply system 790 may be controlled by the control system 250 to perform, for example, a refill procedure.

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 an electrode 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. The optical oscillators 740-1 to 740-N may be tuned or configured such that all of the optical beams 704-1 to 704-N have the same properties, or the optical oscillators 740-1 to 740-N may be tuned or configured such that at least some of the optical oscillators have at least some properties different from other optical oscillators. For example, all of the beams 704-1 to 704-N may have the same center wavelength, or the center wavelength of each of the beams 704-1 to 704-N may be different. The center wavelength generated by a particular optical oscillator of optical oscillators 740-1 to 740-N can be set using a corresponding line narrowing module.

Further, voltage source 797 may be electrically connected to an electrode in each of optical oscillators 740-1 through 740-N, or voltage source 797 may be implemented as a voltage system including N separate voltage sources, each of which is electrically connected to an electrode of one of optical oscillators 740-1 through 740-N.

Light source system 710 also includes a beam control device 787 and a beam combiner 788. A beam control device 787 is located between the gas gain media 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 beam(s) incident on the beam combiner 788. In the example shown, beam control device 787 is represented as a single element. However, beam control device 787 may be implemented as a collection of individual beam control devices. For example, beam control device 787 may include a set of shutters, one associated with each optical oscillator 740-1 to 740-N.

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, the beam preparation system 763 including a bandwidth analysis module that measures various properties of the light beam (such as bandwidth or wavelength). The beam preparation system 763 can 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 the light, such as, for example, reflective and/or refractive optical elements (such as, for example, lenses and mirrors), and/or optical 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 may be placed elsewhere within the optical lithography system 700. Further, other implementations are possible. For example, light 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, the light source system 810 may include optical elements (such as mirrors) that divert the light beams 704-1 to 704-N to the beam combiner 788.

The scanner device 780 may be a liquid immersion system or a drying 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 metrology system 799. The wafer 770 is held or received on a wafer holder 783. Referring also to fig. 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 beams 705 enter the scanner device 780 and are incident on the slits 784, and at least some of the beams 705 pass through the slits 784 to form shaped exposure beams 705'. In the example of fig. 7A and 7B, the slit 784 is rectangular and shapes the exposure beam 705 into an elongated rectangular shaped beam, which is the shaped exposure beam 705'. The mask 785 includes a pattern that determines which portions of the shaped beam are transmitted by the mask 785 and which portions are blocked by the 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.

The metrology system 799 includes a sensor 771. The sensor 771 may 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 may 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 optical energy at the wafer 770 in the x-y plane.

Other aspects of the invention are set forth in the following numbered clauses.

1. A light source, comprising:

a light generating device configured to: 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

a control system configured to: based on the duration of the second time period and the value of the property of the excitation signal during the first time period, a property of the excitation signal applied to the light-generating device during the third time period is estimated.

2. The light source according to clause 1, wherein the light generating device comprises:

a discharge chamber configured to accommodate a gaseous gain medium; and

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.

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

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

5. The light source according to 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.

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

7. The light source according to 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.

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

9. The light source according to clause 1, wherein the control system is further configured to: an error metric is determined 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 according to clause 9, wherein the control system is further configured to: based on the error metric, the value of the adaptive parameter is updated.

11. The light source according to clause 10, wherein the control system is configured to update the 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.

12. The light source according to clause 1, wherein the control system is further configured to: based on the estimated property of the excitation signal, it is determined whether to initiate a warm-up process.

13. The light source according to clause 12, wherein if the pre-heating process is initiated, the control system is further configured to determine a pre-heating process metric related to a duration of the pre-heating process.

14. The light source according to clause 13, wherein the pre-heating process metric is a number of times the light generating device is activated during the pre-heating process.

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

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

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.

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

accessing information relating to a duration of an idle period of a light source;

accessing information related to a value of a property of an excitation signal applied to a light source during a time period occurring before an idle time period; and

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.

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

20. The controller of clause 19, wherein the control system is further configured to: an error metric is determined 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 clause 20, wherein the control system is further configured to: based on the error metric, the value of the adaptive parameter is updated.

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

23. The controller of clause 18, wherein the control system is further configured to: based on the estimated updated value of the property, it is determined whether to initiate a warm-up procedure for the light source.

24. The controller of clause 18, wherein the control system is configured to: accessing, from the computer-readable memory module, information relating to a duration of an idle period of the light source and information relating to a value during a time period in which a property of the excitation signal occurs before the idle period.

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

a computer-readable memory module; and

one or more electronic processors coupled to the computer-readable memory module.

26. A method, comprising:

accessing information related to a duration of an idle period of a light source;

Other implementations are within the scope of the following claims.

Claims

1. A light source, comprising:

a light generating device configured to: a first time period during which an excitation signal is applied to the light-generating device, a second time period during which the excitation signal is applied to the light-generating device, and an idle state during which the excitation signal is applied to the light-generating device, and a third time period during which the excitation signal is applied to the light-generating device, the first time period occurring before the second time period and the second time period occurring before the third time period; and

a control system configured to: estimating the property applied to the light-generating device during the third time period based on a duration of the second time period and a value of a 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 accommodate a gaseous gain medium; and

3. 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 representative of the magnitude of the voltage signal applied to the electrode during the first time period.

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

6. The light source of claim 5, wherein the control system is configured to: estimating the property of the excitation signal applied to the light-generating device during the third time period based on a 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: determining 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: updating 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: determining whether to initiate a warm-up process based on the estimated property of the excitation signal.

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

14. The light source of claim 13, wherein the pre-heat process metric is a number of times the light generating device is energized during the pre-heat 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 cell.

17. The light source of claim 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 toward a beam combiner.

accessing information related to a duration of an idle period 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 before the idle period; and

estimating an updated value of the property of the excitation signal based on a duration of the idle period and a value during a time period in which the property of the excitation signal occurs before the idle period.

19. The controller of claim 18, wherein the control system is further configured to: applying 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: determining 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: updating a value of an adaptive parameter based on the error metric.

22. The controller of claim 21, wherein the control system is configured to: updating 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.

23. The controller of claim 18, wherein the control system is further configured to: determining 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: accessing from a computer readable memory module information relating to the duration of an idle period of a light source and information relating to a value of a property of an excitation signal during a time period occurring before the idle period.

25. The controller of claim 18, wherein the control system comprises:

a computer-readable memory module; and

26. A method, comprising: