Control system for multiple deep ultraviolet oscillators

Abstract

To provide a control system for multiple deep ultraviolet (DUV) optical oscillators.SOLUTION: A deep ultraviolet (DUV) optical system includes an optical source system including: multiple optical oscillators; a beam combiner; and a beam control apparatus between the optical oscillators and the beam combiner. The beam combiner is configured to receive light emitted from any of the optical oscillators and direct it toward a scanner apparatus as an exposure light beam. The beam control apparatus is configured to determine whether the beam combiner has received light from a particular one of the optical oscillators. The DUV optical lithography system also includes a control system coupled to the optical source system, the control system configured to: determine whether a condition exists in the DUV optical system; and, based on a determination that the condition exists, perform a calibration action in a subset of the optical oscillators.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. application Ser. No. 62 / 851,147, entitled CONTROL SYSTEM FOR A PLURALITY OF DEEP ULTRAVIOLET OPTICAL OSCILLATORS, filed May 22, 2019, and U.S. application Ser. No. 63 / 006,162, entitled CONTROL SYSTEM FOR A PLURALITY OF DEEP ULTRAVIOLET OPTICAL OSCILLATORS, filed April 7, 2020, each of which is incorporated by reference in its entirety herein.

[0002] This disclosure relates to a control system for multiple deep ultraviolet (DUV) optical oscillators. [Background technology]

[0003]

[0003] Photolithography is the process of patterning semiconductor circuits onto a substrate, such as a silicon wafer. A light source produces deep ultraviolet (DUV) light that is used to expose photoresist on the wafer. The DUV light may include wavelengths, for example, from about 100 nanometers (nm) to about 400 nm. The light source is a laser source (e.g., an excimer laser), and the DUV light is often a pulsed laser beam. The DUV light from the light source interacts with a projection optical system, which projects the beam through a mask onto the photoresist on the silicon wafer. In this way, layers of the chip design are patterned onto the photoresist. The photoresist and wafer are then etched and cleaned, and the photolithography process repeats. Summary of the Invention

[0004] In one aspect, a deep ultraviolet (DUV) optical system includes a light source system including a plurality of optical oscillators, a beam combiner, and a beam control device between the optical oscillators and the beam combiner. The beam combiner is configured to receive light emitted from any of the optical oscillators and direct it as an exposure beam toward a scanner device, and the beam control device is configured to determine whether the beam combiner receives light from a particular one of the optical oscillators. The DUV optical lithography system also includes a control system coupled to the light source system, the control system configured to determine whether a condition exists in the DUV optical system and, based on a determination that the condition exists, perform a calibration operation on a subset of the optical oscillators.

[0005]

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

[0006] The calibration operation may include bringing the wavelength of the light generated by at least one of the optical oscillators within a target range.

[0007] The calibration operation may include bringing the bandwidth of the light generated by at least one of the optical oscillators within a target range.

[0008] The calibration operation may include bringing the pulse energy of light generated by at least one of the optical oscillators within a target range.

[0009]

[0009] The condition may be a time-based condition or an event-based condition. The condition may be an event-based condition, and a control system may be coupled to the light source system and the scanner device, and the control system may be configured to receive a status signal from the DUV optical system, and the control system may determine whether the event-based condition exists based on the status signal from the scanner device. The status signal may include information related to an upcoming event at the scanner device, and the control system may perform a calibration action based on the information related to the upcoming event. The information related to the upcoming event may include a time until the upcoming event occurs and an indication identifying the upcoming event, and the control system may perform the calibration action before the upcoming event occurs. The upcoming event may include a change in an operating condition of the scanner device, and the change in the operating condition may include a change in a repetition rate of the exposure beam, a change in a power of the exposure beam, or a change in an operating mode of the scanner device. The performed calibration action may be one of a plurality of available calibration actions, and the performed calibration action may be determined from the plurality of available calibration actions based on the indication identifying the upcoming event.

[0010]

[0010] The condition may be a time-based condition, and the control system may be configured to monitor a status of the DUV optical system, and the control system may be configured to determine the condition of the DUV optical system based on the monitored status of the light source system. The control system configured to monitor the status of the DUV optical system may include a control system configured to monitor a time elapsed from a start time, and the control system may determine the condition of the DUV optical system based on the time elapsed from the start time. The start time may include a time at which a previous calibration event occurred. In some embodiments, to determine the condition of the DUV optical system, the control system is further configured to compare the elapsed time with a specification, and the control system is configured to perform a calibration action if the elapsed time meets the specification.

[0011]

[0011] Each optical oscillator may include a gain medium, the gain medium may include a gas gain medium, and the calibration operation may include a refill operation. In these embodiments, the refill operation includes replacing the gas gain medium in a subset of the optical oscillators.

[0012]

[0012] The beam control apparatus may comprise a beam blocking device for each of the plurality of optical oscillators, each of the beam blocking devices may be coupled to a control system, which may be further configured to control the beam blocking device to determine whether the beam combiner receives light from a particular one of the optical oscillators. Each beam blocking device may include a shutter having a first state that transmits the DUV light and a second state that blocks the DUV light, and each shutter may be configured to be positioned at an output of one of the optical oscillators such that each shutter prevents the corresponding one of the optical oscillators from emitting light toward the beam combiner when the corresponding one of the optical oscillators is in the second state and allows the corresponding one of the optical oscillators to emit light toward the beam combiner when the corresponding one of the optical oscillators is in the first state.

[0013]

[0013] In some embodiments, the subset of optical oscillators does not include any of the multiple optical oscillators generating a light beam that is part of the exposure beam.

[0014] In some embodiments, the calibration operation is performed only when the beam combiner does not receive light from a subset of the optical oscillators.

[0015]

[0015] In some embodiments, the DUV optical system is configured for use in a DUV photolithography system. Further, the DUV optical system may include a scanner device configured to receive the exposure beam from the beam combiner.

[0016] In another aspect, a method of controlling a plurality of optical oscillators in a deep ultraviolet (DUV) optical system includes monitoring the DUV optical system to determine whether a condition exists, determining if any of the plurality of optical oscillators are in a wait state if the condition exists, and performing a calibration operation on a subset of the plurality of optical oscillators that are in a wait state. One or more of the optical oscillators that are not in a wait state continue to generate an exposure beam while the calibration operation is performed.

[0017]

[0017] Implementations may include one or more of the following features: The method may also include determining whether the calibration operation was successful.

[0018]

[0018] The DUV optical system may be configured for use in conjunction with a DUV photolithography system, and monitoring the DUV optical system may include receiving a command signal from a scanner apparatus and determining whether a condition exists based on the command signal.

[0019] In some embodiments, at least one optical oscillator is placed in a wait state if a condition exists and none of the multiple optical oscillators are in a wait state.

[0020]

[0020] In another aspect, an optical lithography system includes a deep ultraviolet (DUV) optical lithography system including a light source system including a plurality of optical oscillators each including a gain medium, a beam combiner, and a beam control device between the gain medium and the beam combiner. The beam combiner is configured to receive light emitted from any of the optical oscillators and direct it as an exposure beam toward a scanner device, and the beam control device is configured to determine whether the beam combiner has received light from a particular one of the optical oscillators. The DUV optical lithography system also includes a scanner device and a control system coupled to the light source system and the scanner device, the control system configured to determine whether a condition exists in the optical lithography system and to perform a calibration operation on a subset of the optical oscillators if the condition is determined to exist.

[0021] Implementations may include one or more of the following features: The optical lithography system may also include a gas supply system fluidly coupled to the multiple optical oscillators.

[0022]

[0022] In another aspect, a method for controlling multiple optical oscillators in a deep ultraviolet (DUV) optical lithography system includes receiving a request for an exposure beam configured to provide a requested dose of DUV light to a wafer, determining whether a cold start condition exists, and if a cold start condition exists, activating more than a nominal number of optical oscillators, which is the number of optical oscillators that can provide the requested dose under steady state conditions, and directing a light beam from each of the activated optical oscillators toward a scanner device to provide an exposure beam during the cold start period.

[0023] In some embodiments, if a cold start condition exists, the method also includes:

[0024] Determining whether the cold-start period has expired and deactivating at least one of the activated optical oscillators if the cold-start period has expired.

[0024]

[0025] In another aspect, the control system includes an interface configured to communicate with the DUV optical system.

[0026] The system is configured to control the DUV optical system by determining whether a condition exists in the DUV optical system, and, based on a determination that the condition exists, performing a calibration operation in a subset of optical oscillators of the DUV optical system while at least one optical oscillator that is not in the subset of optical oscillators generates an exposure beam.

[0025]

[0027] In some embodiments, the control system also includes one or more electronic processors and computer-readable electronic storage coupled to the one or more electronic processors that includes executable instructions that, when executed, cause the control system to communicate with the DUV optical system via the interface.

[0026]

[0028] Implementations of any of the techniques described above and herein may include processes, apparatus, control systems, instructions stored on a non-transitory machine-readable computer medium, and / or methods. 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. [Brief description of the drawings]

[0027] [Figure 1]

[0029] FIG. 1 is a block diagram of an example optical lithography system. [Figure 2A]

[0030] FIG. 2 is a block diagram of another example of an optical lithography system. [Figure 2B]

[0031] 2B is a block diagram of an example of a projection optical system used in the optical lithography system of FIG. 2A. [Diagram 3]

[0032] FIG. 1 is a block diagram of an example of a light source system. [Figure 4]

[0033] 1 is a flowchart of an example process for performing a calibration operation during manufacturing in an optical lithography system. [Diagram 5]

[0034] 1 is a flow chart of an example of a process for generating an exposure beam during a cold start in an optical lithography system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028]

[0035] 1, there is shown a block diagram of an optical lithography system 100. The optical lithography system 100 includes a light source system 110 that generates an exposure beam 111 that is provided to a scanner device 180. The scanner device 180 exposes a wafer 182 with the exposure beam 111.

[0029]

[0036] The light source system 110 includes N optical oscillators 112-1 to 112-N, where N is an integer greater than 1. Each optical oscillator 112-1 to 112-N includes a corresponding gas gain medium 114-1 to 114-N that generates a respective light beam 116-1 to 116-N. The light source system 110 also includes a beam combiner 118 that directs incident light onto a beam path 179 to form the exposure beam 111. The beam path 179 is between the beam combiner 118 and a scanner device 180. The beam combiner 118 is any optical element capable of directing the light beams 116-1 to 116-N onto the beam path 179. For example, the beam combiner 118 may be a collection of refractive and / or reflective optical elements.

[0030]

[0037] Beam combiner 118 is positioned to receive all of light beams 116-1-116-N. However, the light incident on beam combiner 118 (and included in exposure beam 111) may include one of light beams 116-1-116-N, all of light beams 116-1-116-N, or any combination of the various light beams 116-1-116-N. Additionally, the particular one or more of light beams 116-1-116-N incident on beam combiner 118 (and included in exposure beam 111) may change during operation of optical lithography system 100. For example, in some applications, the dose delivered by one of light beams 116-1-116-N is sufficient to expose wafer 182. Dose is the amount of optical energy delivered to an area. In these applications, light source system 110 is configured to allow only one of light beams 116-1 through 116-N to reach beam combiner 118. In other applications, the dose delivered by one of light beams 116-1 through 116-N is not sufficient to expose wafer 182. In these applications, two or more of light beams 116-1 through 116-N reach beam combiner 118 and contribute to exposure beam 111.

[0031]

[0038] The optical oscillators 112-1-112-N are independent of one another, and the control system 150 determines which of the optical beams 116-1-116-N enter the beam combiner 118. The particular one or some of the optical beams 116-1-116-N that enter the beam combiner 118 is determined, for example, by controlling the light source system 110, the optical oscillators 112-1-112-N, and / or components of the light source system 110. For example, the configuration of the beam control device 117 (between the gain media 114-1-114-N and the beam combiner 118) may be controlled to determine which of the optical beams 116-1-116-N reach the beam combiner 118. In some embodiments, the beam control device 117 includes a shutter for each optical oscillator 112-1-112-N. Each shutter is controlled by a control system 150 to determine whether a corresponding light beam 116-1 through 116-N is blocked or enters a beam combiner 118. Figure 3 shows an example of a beam control device 117 implemented as N shutters.

[0032]

[0039] The control system 150 causes the calibration operation to occur on one or more of the optical oscillators 112-1-112-N that are not contributing to the exposure beam 111. In this manner, the control system 150 takes advantage of the independence of the optical oscillators 112-1-112-N to perform the calibration operation while the exposure beam 111 is being generated. The control system 150 monitors the optical lithography system 100 to determine whether a condition exists in the optical lithography system 100. If the condition exists, the control system 150 performs the calibration operation. The control system 150 causes the calibration operation to occur only on the subset of the optical oscillators 112-1-112-N associated with the optical beams 116-1-116-N that are not incident on the beam combiner 118. For example, if optical beam 116-1 is not incident on beam combiner 118 and all of the other (N-1) optical beams are incident on beam combiner 118, control system 150 may initiate a calibration operation on optical oscillator 112-1 rather than the other (N-1) optical oscillators.

[0033]

[0040] Thus, while the calibration operation is being performed on optical oscillator 112-1, exposure beam 111 continues to be generated and wafer 182 continues to be exposed. This allows calibration operations that would previously have required the entire optical lithography system 100 to be taken offline to be performed while exposure beam 111 is being generated. Control system 150 improves the performance of optical lithography system 100 by reducing the amount of downtime, allowing exposure beam 111 to be generated more consistently and for a longer period of time. Furthermore, because optical lithography system 100 does not need to be taken offline to perform the calibration operation, the calibration operation may be performed more frequently and more easily. By performing the calibration operation more frequently, the life of optical oscillators 112-1 through 112-N may be extended.

[0034]

[0041] The control system 150 may monitor one or more of a variety of conditions. The optical lithography system 100 does not necessarily include the scanner device 180. Thus, a condition in the optical lithography system 100 may be a condition in one or more of the optical oscillators 112-1-112-N and / or a condition in the scanner device 180. The condition may be a time-based condition or an event-based condition. A time-based condition is a condition that exists when a predetermined time has elapsed. For example, the control system 150 may determine that a time-based condition exists in one of the optical oscillators 112-1-112-N when a predetermined time has elapsed since a most recent calibration operation was performed in that optical oscillator. In another example, a time-based condition may be a condition that occurs based on a predetermined schedule. For example, a calibration operation may be scheduled to occur every time a certain amount of time has elapsed. An event-based condition is a condition that exists when an event occurs. Examples of event-based conditions include receiving a command from scanner device 180 and / or receiving a command from one or more of optical oscillators 112-1-112-N. An event-based condition may have a time aspect. For example, an event-based condition may exist after a certain number of pulses are generated by any of optical oscillators 112-1-112-N at a particular repetition rate.

[0035]

[0042] A calibration operation is any type of procedure that calibrates or otherwise refines or enhances the performance of the optical oscillators 112-1-112-N. A calibration operation may be, for example, a procedure to bring one or more parameters (such as energy, bandwidth, and / or center wavelength) to a specified or target range. In another example, a calibration operation is a refill procedure that includes removing and replacing one or more of the gas gain media 114-1-114-N. In yet another example, a calibration operation is a warm-up procedure that prepares one or more of the optical oscillators 112-1-112-N for steady-state operation. An in-manufacturing calibration technique that includes performing one or more calibration operations is discussed with respect to FIG. 4.

[0036]

[0043] In some embodiments, the control system 150 is configured to generate the exposure beam 111 during a cold start period by activating more than a nominal number of the optical oscillators 112-1 through 112-N. The nominal number of the optical oscillators is the number of the optical oscillators 112-1 through 112-N that are activated to generate the exposure beam 111 under normal steady state conditions. By activating more than the nominal number of the optical oscillators 112-1 through 112-N, the control system 150 compensates for energy inefficiencies that may be present during the cold start period. The generation of the exposure beam during the cold start period is discussed in more detail with respect to FIG. 5.

[0037]

[0044] Control system 150 includes electronic processing module 151, electronic storage 152, and I / O interface 153. Electronic processing module 151 includes one or more processors suitable for executing computer programs, such as general purpose or special purpose microprocessors, and any one or more processors of any type of digital computer. Typically, an electronic processor receives instructions and data from a read-only memory, a random access memory (RAM), or both. Electronic processing module 151 may include any type of electronic processor. The one or more electronic processors of electronic processing module 151 execute instructions and access data stored in electronic storage 152. The one or more electronic processors may also write data to electronic storage 152.

[0038]

[0045] Electronic storage 152 may be volatile memory, such as RAM, or non-volatile memory. In some embodiments, electronic storage 152 includes non-volatile and volatile parts or components. Electronic storage 152 may store data and information used in the operation of control system 150. For example, electronic storage 152 may store specification information for optical oscillators 112-1 through 112-N. The specification information may include, for example, target energy, wavelength, bandwidth, and / or beam quality ranges for various operating modes of optical lithography system 100 and scanner device 180. Electronic storage 152 may also store instructions (e.g., in the form of a computer program) associated with a particular calibration operation.

[0039]

[0046] Electronic storage 152 may also store instructions (e.g., in the form of a computer program) that cause control system 150 to interact with other components and subsystems within optical lithography system 100 to perform calibration operations. For example, the instructions may be for electronic processing module 151 to provide command signals to light source system 110 such that a calibration operation is performed on one or more of optical oscillators 112-1 through 112-N. Electronic storage 152 may also store information received from optical lithography system 100, scanner device 180, and / or light source system 110.

[0040]

[0047] I / O interface 153 is any type of interface that allows control system 150 to exchange data and signals with an operator, light source system 110, scanner device 180, and / or an automated process running on another electronic device. For example, in an embodiment in which rules or instructions stored in electronic storage 152 may be edited, the editing may be performed via I / O interface 153. I / O interface 153 may include one or more of a 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, e.g., Ethernet. I / O interface 153 may also enable communication without physical contact, e.g., via an IEEE 802.11, Bluetooth, or Near Field Communication (NFC) connection.

[0041]

[0048] The control system 150 is coupled to the light source system 110 and / or the scanner device 180 via a data connection 154. The data connection 154 may be a physical cable or other physical data conduit (such as a cable supporting transmission of IEEE 802.3-based data), 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. Data provided via the data connection may be set via any type of protocol or format. The data connection 154 is connected to the light source system 110 and / or the scanner device 180 at a corresponding communication interface (not shown). The communication interface may be any type 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 embodiments, the data interface allows data communication via a wireless data connection. For example, the data interface may be an IEEE 811.11 transceiver, a Bluetooth, or an NFC connection. The control system 150 may be connected to systems and / or components within the light source system 110 and / or the scanner device 180. For example, control system 150 may be directly connected to each of optical oscillators 112-1 through 112-N.

[0042]

[0049] 2A and 2B, optical lithography system 200 includes a light source system 210 that provides an exposure beam 211 to a scanner apparatus 280. Light source system 210 is an implementation of light source system 110 (FIG. 1). Scanner apparatus 280 is an implementation of scanner apparatus 180 (FIG. 1). Scanner apparatus 280 exposes a wafer 282 with a shaped exposure beam 211′. Shaped exposure beam 211′ is formed by passing exposure beam 211 through a projection optical system 281.

[0043]

[0050] Light source system 210 includes optical oscillators 212-1 through 212-N, where N is an integer greater than 1. Each optical oscillator 210-1 through 210-N generates a corresponding light beam 216-1 through 216-N. Details of optical oscillator 212-1 are discussed below. The other (N-1) optical oscillators in light source system 210 include the same or similar features.

[0044]

[0051] The optical oscillator 212-1 includes a discharge chamber 215-1, which surrounds the cathode 213-1a and the anode 213-1b. The discharge chamber 215-1 also includes a gas gain medium 214-1. A potential difference between the cathode 213-1a and the anode 213-1b creates an electric field in the gas gain medium 214-1. The potential difference may be created by controlling a voltage source 297, coupled to the control system 150, to apply a voltage to the cathode 213-1a and / or the anode 213-1b. The electric field provides sufficient energy to the gain medium 214-1 to cause population inversion and to enable the generation of light pulses via stimulated emission. By repeatedly creating such a potential difference, a train of light pulses is formed to create the light beam 216-1. The repetition rate of the pulsed light beam 216-1 is determined by the rate at which voltages are applied to the electrodes 213-1a, 213-1b. The duration of a pulse in pulsed light beam 216-1 is determined by the time that a voltage is applied to electrodes 213-1a and 213-1b. The repetition rate of the pulses may be, for example, in the range of about 500-6,000 Hz. In some embodiments, the repetition rate may be greater than 6,000 Hz, for example, 12,000 Hz or greater. Each pulse emitted from optical oscillator 212-1 may have a pulse energy of, for example, approximately 1 millijoule (mJ).

[0045]

[0052] The gas gain medium 214-1 may be any gas suitable for producing a light beam of the wavelength, energy, and bandwidth required for application. In the case of an excimer source, the gas gain medium 214-1 may include a noble gas, such as argon or krypton, a halogen, such as fluorine or chlorine, and traces of xenon, other than a buffer gas, such as helium. Specific examples of the gas gain medium 214-1 include argon fluoride (ArF), which emits light at a wavelength of about 193 nm, krypton fluoride (KrF), which emits light at a wavelength of about 248 nm, or xenon chloride (XeCl), which emits light at a wavelength of about 351 nm. The gas gain medium 214-1 is excited with a short (e.g., nanosecond) current pulse in a high-voltage discharge by application of a voltage to the electrodes 213-1a, 213-1b.

[0046]

[0053] A resonator is formed between a line narrowing module 295-1 on one side of the discharge chamber 215-1 and an output coupler 296-1 on a second side of the discharge chamber 215-1. The line narrowing module 295-1 may include diffractive optical components, such as, for example, a grating and / or a prism, that finely tune the spectral output of the discharge chamber 215-1. In some embodiments, the line narrowing module 295-1 includes multiple diffractive optical elements. For example, the line narrowing module 295-1 may include four prisms, some of which are configured to control the central wavelength of the light beam 216-1 and some of which are configured to control the spectral bandwidth of the light beam 216-1.

[0047]

[0054] The optical oscillator 212-1 also includes a line center analysis module 298-1 that receives the output light beam from the output coupler 296-1. The line center analysis module 298-1 is a measurement system that may be used to measure or monitor the wavelength of the light beam 216-1. The line center analysis module 298-1 may provide data to the control system 150, which may determine metrics associated with the light beam 216-1 based on the data from the line center analysis module 298-1. For example, the control system 150 may determine a beam quality metric or a spectral bandwidth based on the data measured by the line center analysis module 298-1.

[0048]

[0055] The light source system 210 also includes a gas supply system 290 that is fluidly coupled to the interior of the discharge chamber 215-1 via a fluid conduit 289. The fluid conduit 289 is any conduit that can transport a gas or other fluid without or with minimal loss. For example, the fluid conduit 289 can be a pipe made of or coated with a material that does not react with one or more fluids transported in the fluid conduit 289. The gas supply system 290 includes a chamber 291 that is configured to contain and / or receive a supply of one or more gases used in the gain medium 214-1. The gas supply system 290 also includes devices (such as pumps, valves, and / or fluidic switches) that allow the gas supply system 290 to remove gas from or inject gas into the discharge chamber 215-1. The gas supply system 290 is coupled to the control system 150. The gas supply system 290 can be controlled by the control system 150 to perform, for example, a refill procedure.

[0049]

[0056] The other (N-1) optical oscillators are similar to optical oscillator 212-1 and have similar or the same components and subsystems. For example, each of optical oscillators 212-1-212-N includes electrodes similar to electrodes 213-1a, 213-1b, a line narrowing module similar to line narrowing module 295-1, and an output coupler similar to output coupler 296-1. Optical oscillators 212-1-212-N may be tuned or configured such that optical beams 216-1-216-N all have the same characteristics, or optical oscillators 212-1-212-N may be tuned or configured such that at least some of the optical oscillators have at least some characteristics that differ from the other optical oscillators. For example, optical beams 216-1-216-N may all have the same center wavelength, or the center wavelength of each optical beam 216-1-216-N may be different. The center wavelength generated by a particular one of the optical oscillators 212-1 through 212-N may be set using a corresponding line narrowing module.

[0050]

[0057] Further, the voltage source 297 may be electrically connected to an electrode of each of the optical oscillators 212-1 to 212-N, or the voltage source 297 may be implemented as a voltage system including N individual voltage sources, each electrically connected to an electrode of one of the optical oscillators 212-1 to 212-N.

[0051]

[0058] The light source system 210 also includes a beam controller 217 and a beam combiner 218. The beam controller 217 is between the gas gain media of the optical oscillators 212-1 through 212-N and the beam combiner 218. The beam controller 217 determines which of the optical beams 216-1 through 216-N are incident on the beam combiner 218. The beam combiner 218 forms the exposure beam 211 from one or more optical beams incident on the beam combiner 218. In the illustrated example, the beam controller 217 is represented as a single element. However, the beam controller 217 may be implemented as a collection of individual beam controllers. For example, the beam controller 217 may include a collection of shutters, with one shutter associated with each optical oscillator 212-1 through 212-N.

[0052]

[0059] The light source system 210 may include other components and systems. For example, the light source system 210 may include a beam formation system 299 that includes a bandwidth analysis module that measures various characteristics of the light beam (such as bandwidth and wavelength). The beam formation system may also include a pulse stretcher (not shown) that stretches each pulse, with which each pulse interacts in time. The beam formation system may also include other components that can act on the light, such as reflective and / or refractive optical elements (such as lenses and mirrors), and / or filters. In the illustrated example, the beam formation system 299 is positioned in the path of the exposure beam 211. However, the beam formation system 299 may be located elsewhere in the optical lithography system 200. Additionally, other implementations are possible. For example, the light source system 210 may include N instances of the beam formation system 299, each positioned to interact with one of the light beams 216-1 to 216-N. In another example, light source system 210 may include optical elements (such as mirrors) that direct light beams 216-1 through 216-N toward beam combiner 218.

[0053]

[0060] The scanner apparatus 280 may be an immersion system or a dry system. The scanner apparatus 280 includes a projection optical system 281 through which the exposure beam 211 passes before reaching the wafer 282, and a sensor system or metrology system 270. The wafer 282 is held or received in a wafer holder 283. Also referring to FIG. 2B, the projection optical system 281 includes a projection objective including a slit 284, a mask 285, and a lens system 286. The lens system 286 includes one or more optical elements. The exposure beam 211 enters the scanner apparatus 280 and impinges on the slit 284. At least a portion of the beam 211 then passes through the slit 284 to form a shaped exposure beam 211'. In the example of FIGS. 2A and 2B, the slit 284 is rectangular and shapes the exposure beam 211 into an elongated rectangular light beam, which is the shaped exposure beam 211'. Mask 285 contains a pattern that determines which portions of the shaped light beam are transmitted and which portions are blocked by mask 285. Microelectronic features are formed on wafer 282 by exposing a layer of radiation-sensitive photoresist material on wafer 282 to exposure beam 211'. The design of the pattern on the mask is determined by the particular microelectronic circuit features desired.

[0054]

[0061] Metrology system 270 includes sensor 271. Sensor 271 may be configured to measure characteristics of shaped exposure beam 211', such as, for example, bandwidth, energy, pulse duration, and / or wavelength. Sensor 271 may be, for example, a camera or other device capable of capturing an image of shaped exposure beam 211' at wafer 282, or an energy detector capable of collecting data describing the amount of optical energy at wafer 282 in the xy plane.

[0055]

[0062] Metrology system 270 also includes electronic processing module 272 and electronic storage 273. Electronic processing module 272 is similar to electronic processing module 151, and electronic storage 273 is similar to electronic storage 152 (FIG. 1). Electronic storage 273 may store information that, for example, causes electronic processing module 272 to generate a command or trigger signal that is provided to control system 150 via data connection 254. The trigger signal causes control system 150 to initiate a calibration operation in one or more of optical oscillators 212-1 to 212-N, as discussed with respect to FIG. 4. The command signal generated by metrology system 270 may be based, for example, on time-based rules and / or on the occurrence of an event. For example, metrology system 270 may generate and provide a command signal to control system 150 periodically or whenever a certain amount of time has passed. The command signal may be generated based on an event. For example, a command signal may be generated if a dose determined based on data from sensor 271 is outside of the specification for this application. In this example, the command signal includes information that causes control system 150 to perform a calibration operation to correct the pulse energy of one or more of light beams 216-1 through 216-N.

[0056]

[0063] The scanner device 280 may include, for example, temperature control devices (such as air conditioning and / or heating devices) and / or power sources for various electrical components.

[0057]

[0064] 3, light source system 310 is shown. Light source system 310 is another example of an embodiment of light source system 110. Light source system 310 includes optical oscillators 312-1 to 312-N, where N is an integer greater than 1. Each optical oscillator 312-1 to 312-N includes a discharge chamber 315-1 to 315-N and generates a respective light beam 316-1 to 316-N.

[0058]

[0065] Light source system 310 includes beam control device 317 between optical oscillators 312-1 to 312-N and beam combiner 318. Beam control device 317 includes N shutters 319-1 to 319-N. In the example of Fig. 3, each of shutters 319-1 to 319-N is located within corresponding discharge chamber 315-1 to 315-N. However, in other embodiments, each of shutters 319-1 to 319-N is located outside corresponding discharge chamber 315-1 to 315-N.

[0059]

[0066] Each shutter 319-1-319-N has at least two stable states including a first state in which the shutter 319-1-319-N transmits the corresponding light beam 316-1-316-N and a second state in which the shutter 319-1-319-N blocks the corresponding light beam 316-1-316-N. Each shutter 319-1-319-N is coupled to the control system 150. The beam controller 317 and / or the shutters 319-1-319-N may send information to and receive information from the control system 150. For example, the beam controller 317 may send information about the state of the shutter to the control system 150, and the shutters 319-1-319-N may change state in response to receiving a command signal from the control system 150.

[0060]

[0067] Beam controller 317 may be a mechanical device or an electro-optical device. In an embodiment where beam controller 317 is a mechanical device, each shutter 319-1-319-N is made of a material that is opaque to the wavelength of light generated by the corresponding optical oscillator 312-1-312-N. The mechanical shutters are configured to move in and out of the path of the corresponding optical beam 316-1-316-N. When a mechanical shutter 319-1-319-N is in the path of a corresponding optical beam 316-1-316-N, the light is blocked. When a mechanical shutter 319-1-319-N is not in the path of a corresponding optical beam 316-1-316-N, the light is not blocked and enters beam combiner 318. Beam controller 317 also includes various associated components for operating mechanical shutters 319-1-319-N. For example, the beam control device 317 may include a mechanical actuator coupled to the control system 150 and configured to move the mechanical shutters 319-1 to 319-N based on commands from the control system 150.

[0061]

[0068] In embodiments in which beam controller 317 is an optical device, each shutter 319-1-319-N may be, for example, a Pockels cell that allows a corresponding optical beam 316-1-316-N to exit discharge chamber 315-1-315-N only when a voltage greater than a threshold voltage is applied. In these embodiments, beam controller 317 also includes various associated components for operating shutters 319-1-319-N. For example, beam controller 317 may include one or more voltage sources and associated electronic circuitry coupled to control system 150 and configured to change the state of optical shutters 319-1-319-N.

[0062]

[0069] Additionally, in some embodiments, each shutter 319-1-319-N may include or be a light sensor. In these embodiments, each shutter 319-1-319-N may sense light propagating through a corresponding optical oscillator 312-1-312-N. In these embodiments, the shutters 319-1-319-N provide information about the sensed light (e.g., data representing a measurement of energy and / or power) to control system 350.

[0063]

[0070] FIG. 4 is a flow chart of process 400. Process 400 is an exemplary process for performing an in-production calibration operation in an optical lithography system. In-production calibration is a calibration operation that is performed while the optical lithography system is exposing a wafer. Process 400 may be performed by control system 150. For example, process 400 may be implemented as a collection of instructions (e.g., a computer program or computer software) stored in electronic storage 152 and executed by one or more electronic processors in electronic processing module 151. Process 400 is discussed with respect to optical lithography system 200 of FIG. 2 and light source system 310 of FIG. 3. However, process 400 may be performed in other optical lithography systems.

[0064]

[0071] The optical lithography system 200 is monitored 410 for the occurrence or presence of a condition. The condition may be a time-based condition. For example, a schedule of calibration operations may be stored in a lookup table or database in electronic storage 152. The lookup table or database stores a time period in association with one or more calibration operations. For example, the lookup table or database may store a schedule of refill operations indicating that each gain medium 214-1-214-N should be replaced at least once a month. In this example, the control system 150 monitors the time elapsed since the most recent refill operation for each optical oscillator 212-1-212-N and declares that the condition exists for a particular one of the optical oscillators 212-1-212-N if the time elapsed since the most recent refill operation for that optical oscillator equals the time defined by the schedule.

[0065]

[0072] In another example, the control system 150 monitors the optical lithography system 200 by monitoring for the occurrence of an event. One example of an event is the receipt of a command signal from the metrology system 270 for the scanner device 280. The command signal indicates that an event has occurred or will occur shortly in the scanner device 280. For example, the command signal may indicate that the scanner device 280 will shortly switch to a different operating mode, such as an operating mode requiring more optical energy or a larger dose, or a multi-focal imaging (MFI) operating mode in which the shaped exposure beam 211' includes an optical beam of a different wavelength. In another example, the command signal indicates that the scanner device 280 will shortly switch to an application requiring a different repetition rate of the exposure beam 211. If the command signal from the metrology system 270 relates to an event that has not yet occurred, the command signal includes an indication of the time until the event occurs.

[0066]

[0073] The control system 150 determines (420) whether one or more conditions exist. The condition is determined to exist based on the existence of an event-based condition (e.g., receiving a command signal from the metrology system 270 of the scanner device 280) or the existence of a time-based condition (e.g., by determining that a predetermined time has passed). If the condition exists, the control system 150 determines (430) whether any of the optical oscillators 212-1 through 212-N are in a wait state. An optical oscillator is in a wait state when the optical beam generated by that optical oscillator does not contribute significantly to the exposure beam 211. For example, an optical oscillator is in a wait state when the optical beam generated by that optical oscillator does not enter the beam combiner 218. An optical oscillator is in a wait state when, for example, the beam control device 217 prevents the optical beam generated by that optical oscillator from reaching the beam combiner. For example, referring also to FIG. 3, the optical oscillator 312-1 is in a wait state when the shutter 319-1 is in a second state. Meanwhile, the optical oscillator 312-1 is in a ready state when the shutter 319-1 is in a first state, and the optical oscillator 312-1 provides the optical beam 316-1 to the beam combiner 318. In another example, the optical oscillator is in a wait state when the optical oscillator is offline or not generating a light beam at all. In yet another example, the optical oscillator is in a wait state when a small or very small amount of light from the optical oscillator reaches the beam combiner 218. For example, the small or very small amount of light may be less than 1% or less than 0.1% of the amount of light that the optical oscillator normally provides, and the small or very small amount of light does not contribute significantly to the dose provided to the wafer 282.

[0067]

[0074] The control system 150 may determine whether a particular one of the optical oscillators 212-1-212-N is in a wait state by determining a state or configuration of the beam controller 217. For example, the control system 150 may determine a state of a shutter associated with each of the optical oscillators 212-1-212-N. In the example of FIG. 4, if none of the optical oscillators 212-1-212-N is in a wait state, the process 400 returns to (410) to continue monitoring the optical lithography system 200. Other implementations are possible. For example, the process 400 may end if none of the optical oscillators 212-1-212-N is in a wait state. In some implementations, if none of the optical oscillators 212-1-212-N is in a wait state, the control system 150 places at least one of the optical oscillators 212-1-212-N in a wait state by controlling the configuration of the beam controller 217.

[0068]

[0075] If a subset of the optical oscillators 212-1 through 212-N is in a wait state and one or more conditions exist, the control system 150 causes one or more calibration operations to be performed on the subset of the optical oscillators (440). The subset includes no more than (N-1) of the optical oscillators 212-1 through 212-N, and the subset includes only the optical oscillators that are in a wait state. The subset may include, for example, one optical oscillator. Because the subset includes no more than (N-1) optical oscillators, the exposure beam 211 continues to be provided to the scanner device 280. Thus, the calibration operation is a manufacturing calibration.

[0069]

[0076] A calibration operation is any type of operation that calibrates or enhances the performance of a subset of optical oscillators. For example, when a condition exists that results from the control system 150 receiving a command signal indicating that the scanner device 180 will switch to MFI mode in a few minutes, the control system 150 performs a calibration operation that includes setting one or more beam parameters for an optical oscillator in the subset. The beam parameters may include, for example, beam quality, energy, bandwidth, and / or center wavelength.

[0070]

[0077] To provide a more specific example, optical oscillator 212-1 is part of the subset and is in a wait state. Control system 150 commands optical oscillator 212-1 to begin pulse formation (while still in the wait state), and control system 150 receives data from optical oscillator 212-1 and determines characteristics of optical beam 216-1 based on the data. The data may be received, for example, from line center analysis module 298-1. Control system 150 continues to monitor the characteristics of optical beam 216-1 before switching to MFI mode and for a period of time determined by the command signal.

[0071]

[0078] Additionally, different calibration operations may be performed on individual optical oscillators in the subset. For example, optical oscillators 210-1 and 210-2 (not shown, but one of the N optical oscillators of light source system 210) may be included in the subset. Control system 350 may cause a calibration operation to cause the wavelength of optical beam 216-1 generated by optical oscillator 210-1 to fall within a target wavelength band. At the same time, or nearly the same time, control system 350 may cause a calibration operation to cause the pulse energy of optical beam 216-2 (not shown) generated by optical oscillator 210-2 to fall within a target energy band.

[0072]

[0079] In another example, a condition exists due to the scanner device 280 receiving a command signal from the metrology system 270 indicating that it will switch to high dose application in 2-3 minutes. Any optical oscillator 212-1-212-N that is in off mode or standby mode is activated and a calibration operation, such as a warm-up procedure, is performed to ensure that the characteristics of the optical beam generated by the activated oscillator are within specifications. By activating one or more additional oscillators, the control system 150 ensures that more energy, and therefore a higher dose, is delivered to the wafer 282. The warm-up procedure ensures that the newly activated optical oscillator functions within specifications before contributing to the exposure beam 211.

[0073]

[0080] When the optical oscillator is activated after a long period of inactivity, the optical oscillator may have an abnormally low energy efficiency when activated again (e.g., when a voltage is applied to the electrodes after a long period of no voltage applied). Thus, the first light pulses generated by the newly activated optical oscillator may have less than a normal amount of energy, for example, even if a voltage above normal magnitude is applied to the electrodes. These low energy pulses may adversely affect the automatic control algorithms and / or the exposure beam 211. By performing a warm-up procedure while the optical oscillator is in a wait state, the control system 150 ensures that the light beam emitted from the newly activated laser does not contribute to the exposure beam 211 until the emitted light beam is within specifications. Thus, the warm-up procedure improves the performance of the scanner device 280.

[0074]

[0081] In some embodiments, electronic storage 152 stores instructions for multiple possible event-based conditions in association with one or more calibration actions to be performed when the event-based condition exists. Each calibration action is a collection of instructions (e.g., a computer program or computer software) that, when performed by electronic processing module 151, causes components of light source system 110 and / or scanner device 280 to perform a particular operation. For example, the instructions may cause electronic processing module 151 to generate commands for one or more of line narrowing modules 295-1 through 295-N, gas supply system 290, and / or one or more of optical oscillators 210-1 through 210-N.

[0075]

[0082] In another example, the condition is a time-based condition that exists due to a certain amount of time having passed. For example, the control system 150 may determine that a scheduled refill of the optical oscillator 212-1 is due due to a threshold time having passed since the most recent refill procedure. In this example, the control system 150 issues a command signal to the optical oscillator 212-1 to enter an off state in which the electrodes 213-1a and 213-1b are not energized. The control system 150 also commands the optical oscillator 212-1 to release the gas gain medium 214-1. After the gain medium 214-1 is released or removed from the discharge chamber 215-1, the control system 150 commands the gas supply system 290 to fill the discharge chamber 215-1 with gas from the chamber 291. While the refill procedure is taking place, the other (N-1) optical oscillators continue to generate optical beams that are incident on the beam combiner 218. In this manner, gain medium 214-1 within discharge chamber 215-1 is removed and replaced while exposure beam 211 continues to be generated.

[0076]

[0083] The success of the calibration operation is evaluated (450). For example, if the calibration operation is successful, the characteristics of the light beam generated by the optical oscillator on which the calibration operation was performed are within the specifications for the operating mode of the scanner device 280. Thus, in some embodiments, the measured characteristics of the light beam are compared to the specifications to determine whether the calibration operation was successful. The characteristics of the light beam may be determined from measurements obtained by the line center analysis module 298-1. In another example, the calibration operation is a warm-up procedure. In these embodiments, the control system 150 monitors the magnitude of the voltage applied to the electrodes and / or the energy of the generated light beam while the optical oscillator is in a wait state or after the warm-up procedure has ended to determine whether the warm-up procedure was successful.

[0077]

[0084] In some embodiments, if the calibration operation is successful, the process 400 returns to (410) and continues monitoring the optical lithography system 200. In some embodiments, if the calibration operation is not successful, the process 400 returns to (440) and the calibration operation is performed again. For example, in an example where the scanner device 280 transitions to the MFI mode and the calibration operation is performed on the optical oscillator 210-1, if the characteristics of the optical beam 216-1 (e.g., beam quality, wavelength, and / or pulse energy) are not within specifications before a time period defined in the command signal, the control system 150 sends a command signal to the metrology system 270 of the scanner device 280 to delay the transition to the MFI mode to allow more time for the characteristics of the optical beam 216-1 to meet specifications. In the example of a refill operation of discharge chamber 215-1, if the refill is not completed successfully, control system 150 may send a command signal to the metrology system of scanner device 280 to prevent scanner device 280 from entering a mode requiring light beam 216-1.

[0078]

[0085] In some embodiments, the process 400 may also end or return to (410) if the calibration operation fails. For example, an equipment malfunction or an unrecoverable error may cause the calibration operation to fail, and the control system 150 may place the optical oscillator on which the calibration operation was performed in an off state and inform the scanner device 280 that the optical oscillator on which the calibration operation was performed is unavailable.

[0079]

[0086] The optical oscillator on which the calibration operation is performed may generate an acceptable optical beam even if the calibration operation fails. In some embodiments, a clock or timer in the control system 150 is started when the calibration operation is initiated, and the calibration operation is terminated if one or more success criteria of the calibration operation are not achieved within a predetermined period of time. For example, in these embodiments, the electronic storage 152 stores a period of time in association with at least some of the calibration operations. Each period is a predetermined period of time that occurs before the calibration operation is terminated if one or more success criteria are not met. The use of the exposure beam 211 may be acceptable even if the calibration operation is terminated without one or more success criteria being met. For example, the calibration operation may be associated with a non-critical characteristic of the exposure beam 211 that is not required for the use of the exposure beam 211 to be acceptable.

[0080]

[0087] 5 is a flow chart of a process 500. Process 500 is an exemplary process for generating an exposure beam during a cold start period in an optical lithography system. Process 500 may be performed by control system 150. For example, process 500 may be implemented as a collection of instructions (e.g., a computer program or computer software) stored in electronic storage 152 and executed by one or more electronic processors in electronic processing module 151. Process 500 is discussed with respect to optical lithography system 200 of FIG. 2 and light source system 310 of FIG. 3. However, process 500 may be performed in other optical lithography systems.

[0081]

[0088] If any of the optical oscillators 212-1-212-N has not been operated for a long continuous period of time or has never been operated, the optical oscillator is considered to be in a cold start state. The optical oscillators 212-1-212-N are operated by applying a voltage to the electrodes that excites the corresponding gain medium in each of the oscillators 212-1-212-N. When an optical oscillator in a cold start state is operated, the optical oscillator has an abnormally low energy efficiency during the cold start period. Due to the low energy efficiency, more energy (or voltage) is required to produce the expected characteristics of the corresponding optical beams 216-1-216-N. As a result, during the cold start period, the optical beams 216-1-216-N may have lower pulse energy than expected and / or may exhibit transient effects such as abnormal temporal changes in pulse energy. These effects are generally temporary and disappear when the optical oscillators 212-1-212-N reach steady state operation. The time between initial activation and steady state operation after the idle time is the cold start period. The duration of the cold start period depends on one or more conditions associated with the optical oscillators 212-1-212-N. The one or more conditions may include, for example, the amount of time the oscillators 212-1-212-N have been idle and / or the age of the optical oscillators 212-1-212-N. The process 500 enables an acceptable exposure beam 211 to be generated during the cold start period.

[0082]

[0089] The light source system 210 receives (510) a request for an exposure beam 211. The request may be, for example, a command signal from the metrology system 270 of the scanner device 280. In another example, the request may be a command signal generated based on operator input received at the I / O interface 273. The request for the exposure beam 211 includes an indication of a requested dose. The dose provided by the light source system 210 depends in part on how many of the N optical oscillators 212-1 to 212-N contribute to the exposure beam 211.

[0083]

[0090] It is determined (520) whether a cold start condition exists. A cold start condition exists in light source system 210 if the number of optical oscillators (m) operating under steady state and normal conditions (i.e., not in a cold start condition) is less than the nominal number of optical oscillators (M) required to generate the requested dose, where m is an integer less than M, and M is an integer less than N. M optical oscillators is the nominal number of optical oscillators operated under normal steady state conditions to generate an exposure beam having a particular dose. A look-up table or database may store the nominal number of optical oscillators (M) associated with each of a number of possible doses.

[0084]

[0091] A cold start condition exists in the light source system 210 if all of the N optical oscillators 212-1 to 212-N have been inactive for an extended period of time. Additionally, a cold start condition exists in the light source system 210 if the N optical oscillators 212-1 to 212-N do not include a group of M optical oscillators 212-1 to 212-N that are not in a cold start state. That is, a cold start condition exists in the light source system 210 if m is less than M (the number of optical oscillators that are not in a cold start state is less than the nominal number of optical oscillators required to generate the requested dose).

[0085]

[0092] Whether a cold start condition exists in the light source system 210 may be determined by evaluating whether m is less than M. To determine which (if any) of the optical oscillators 212-1-212-N are in a cold start state, the control system 150 may determine whether the voltage source 297 is applying a voltage signal to the electrodes of the various optical oscillators 212-1-212-N. If the voltage source 297 is not applying a voltage signal to the electrodes of a particular one of the optical oscillators 212-1-212-N, the time since the voltage source 297 applied a voltage signal to the electrodes is measured to determine how long that optical oscillator has been idle. The time since the last operation is referred to as the idle time. The idle time is compared to a cold start threshold stored in the electronic storage 152. The cold start threshold may vary depending on the age of the chamber and / or the type of chamber. The cold start threshold may be stored in a look-up table or database that associates various cold start threshold times with various conditions. If the length of the idle time exceeds the cold start threshold, then a cold start condition exists for that optical oscillator. Each of optical oscillators 212-1 through 212-N may be evaluated to determine whether a cold start condition exists for that optical oscillator.

[0086]

[0093] In some embodiments, an operator of lithography system 200 inputs an indication of a cold start condition into I / O interface 153, and based on the indication, it is determined that a cold start condition exists in one or more of optical oscillators 210-1 through 210-N.

[0087]

[0094] In the example of process 500, under normal steady-state operating conditions, the required dose is achieved by combining M (where M is an integer smaller than N) of the light beams 216-1 to 216-N. In other words, under normal steady-state operating conditions, the required dose can be less than all N light beams 216-1 to 216-N. When there is no cold start condition in the light source system 210, M of the optical oscillators 212-1 to 212-N are activated (540).

[0088]

[0095] However, when there is a cold start condition (where m is smaller than M), the control system 150 activates P of the optical oscillators 212-1 to 212-N that have the cold start condition (530). The relationship among P, M, N, and m is provided by Equation 1. M - m < P ≤ N - m Equation (1) Two examples are considered to show further details of using the P optical oscillators with cold start conditions to provide all or part of the exposure beam 211 during the cold start period.

[0089]

[0096] In a first example, N is 10, the light source system 210 includes optical oscillators 210-1 to 210-10, m is 3, which means that 3 of the N optical oscillators 210-1 to 210-10 are not in a cold start state, and 7 of the N optical oscillators 210-1 to 210-10 are in a cold start state, and the requested dose is associated with a nominal number (M) of 5, which means that nominally, the requested dose requires light beams from 5 of the 10 optical oscillators 210-1 to 210-10. Thus, in this example, the light source system 210 has fewer than M=5 optical oscillators that are not in a cold start state. The number of available optical oscillators (m) is compared to the nominal number (M) of optical oscillators. Because m=3 is less than M=5, a cold start condition is declared in the light source system 210. In this example, the equivalent of two additional steady-state optical oscillators in optical power is required to bring the dose of the exposure beam 211 to the required dose. The deficit in steady-state optical power is determined by Mm. In this example, Mm is 2, so the equivalent of two steady-state optical oscillators in power will compensate for the cold start condition.

[0090]

[0097] The control system 150 operates the P oscillators in a cold start state. Because the P oscillators are in a cold start state, they also have a lower efficiency during the cold start period. Thus, the value P chosen by the control system 150 may be greater than (Mm) rather than simply being equal to (Mm). The value P depends on the inefficiency caused by the cold start condition. For example, the efficiency of the optical oscillators 212-1 to 212-N is known to drop by 50% during the cold start period. In this example, where the efficiency drops by 50% during the cold start period and the equivalent optical output of two optical oscillators needs to be provided, P is 4, which is twice the difference between the available optical oscillators (m) and the nominal number of optical oscillators (M). In this example, P is 2*(Mm) since the efficiency is known to drop by 50% during the cold start period. Other examples may also have a greater or lesser decrease in efficiency during the cold start period. In any case, by activating the P optical oscillators that are in the cold start state during the cold start period (in addition to the m optical oscillators that are not in the cold start state), the control system 150 ensures that the exposure beam 211 provides the required dose during the cold start period.

[0091]

[0098] In another example, N is 2 and the light source system 210 includes optical oscillators 212-1 and 212-2. In this example, both optical oscillators 212-1 and 212-2 are in a cold start state. Thus, m is 0 in this example. The requested dose is the dose that one of the optical oscillators 210-1 or 210-2 can provide during a normal steady state operating condition. Thus, M is 1 in this example. Since M is greater than m, a cold start condition exists in the light source system 210. To compensate for the temporary effect of the cold start condition, the control system 150 commands the voltage source 297 to apply a train of voltage pulses to the electrodes of the optical oscillators 210-1 and 212-2, and the beam controller 217 is set so that both the resulting light beams 216-1 and 216-2 reach the beam combiner 218 and contribute to the exposure beam 211. In other words, the control system 150 compensates for the transient effects of the cold start condition by using both optical beams 216-1 and 216-2 during the cold start period. In this example, a command signal from the metrology system 270 of the scanner device 280 triggers the control system 150 to cause both optical oscillators 212-1 and 212-2 to generate optical beams during the cold start period.

[0092]

[0099] It is determined whether the cold start period has ended (550). The cold start period may be determined to have ended after the characteristics of the light beams generated by each of the P activated optical oscillators are within steady state specifications and / or when the magnitude of the voltage applied by voltage source 297 is within steady state specifications. The steady state specifications may be stored in electronic storage 152. In some embodiments, the cold start period is predetermined and stored in electronic storage 152. In these embodiments, the cold start period is determined to have ended when more than a predetermined amount of time has elapsed. If the cold start period has not ended, control system 150 continues to activate (530) the (m+P) optical oscillators.

[0093]

[0100] After the cold start period ends, process 500 returns to (540) to continue generating exposure beam 211 under normal steady state conditions. Some of the P optical oscillators may be deactivated because they are no longer needed, so that exposure beam 211 is generated from M optical oscillators.

[0094]

[0101] Other aspects of the invention are described in the following numbered clauses. 1. A light source system; a control system coupled to a light source system, the control system comprising: The light source system A plurality of optical oscillators; A beam combiner; a beam control device between the optical oscillators and a beam combiner, the beam combiner being configured to receive light emitted from any of the optical oscillators and direct it as an exposure beam toward the scanner device, the beam control device being configured to determine whether the beam combiner has received light from a particular one of the plurality of optical oscillators; The control system Determining whether a condition exists in a DUV optical system; A deep ultraviolet (DUV) optical system configured to perform a calibration operation on a subset of the optical oscillators based on a determination that the condition exists. 2. The DUV optical system of clause 1, wherein the calibration operation includes bringing the wavelength of light generated by at least one of the optical oscillators within a target range. 3. The DUV optical system of clause 1, wherein the calibration operation includes bringing a bandwidth of light generated by at least one of the optical oscillators within a target range. 4. The DUV optical system of clause 1, wherein the calibration operation includes bringing a pulse energy of light generated by at least one of the optical oscillators within a target range. 5. The DUV optical system of clause 1, wherein the condition is a time-based condition or an event-based condition. 6. The DUV optical system of clause 5, wherein the condition is an event-based condition, and the control system is coupled to the light source system and the scanner device, the control system being configured to receive a status signal from the DUV optical system, and the control system determining whether the event-based condition exists based on the status signal from the scanner device. 7. The DUV optical system of clause 6, wherein the status signal includes information relating to an upcoming event in the scanner device, and the control system performs a calibration action based on the information relating to the upcoming event. 8. A DUV optical system as claimed in clause 7, wherein the information relating to the upcoming event includes an indication of a time until the upcoming event occurs and an identification of the upcoming event, and wherein the control system performs a calibration action before the upcoming event occurs. 9. A DUV optical system according to clause 8, wherein the event to occur comprises a change in an operating condition of the scanner apparatus, the change in operating condition comprising a change in the repetition rate of the exposure beam, a change in the power of the exposure beam, or a change in the operating mode of the scanner apparatus. 10. The DUV optical system of clause 8, wherein the calibration action performed is one of a plurality of available calibration actions, and the calibration action performed is determined from the plurality of available calibration actions based on an indication identifying an upcoming event. 11. The DUV optical system of clause 5, wherein the condition is a time-based condition, and the control system is configured to monitor a status of the DUV optical system, and the control system is configured to determine the condition of the DUV optical system based on the monitored status of the light source system. 12. The DUV optical system of clause 11, wherein the control system configured to monitor a status of the DUV optical system includes a control system configured to monitor a time elapsed since a start time, and the control system determines a condition of the DUV optical system based on the time elapsed since the start time. 13. A DUV optical system according to clause 12, the start time of which includes the time at which the immediately preceding calibration event occurred. 14. The DUV optical system of clause 13, wherein the control system is further configured to compare the elapsed time with a specification to determine the condition of the DUV optical system, and the control system is configured to perform a calibration action if the elapsed time meets the specification. 15. The DUV optical system of clause 1, wherein each optical oscillator includes a gain medium, the gain medium includes a gas gain medium, and the calibration operation includes a refill operation, the refill operation includes replacing the gas gain medium in a subset of the optical oscillators. 16. A beam control device comprising a beam blocking device for each of the plurality of optical oscillators, each of the beam blocking devices coupled to a control system; 13. The DUV optical system of claim 1, wherein the control system is further configured to control the beam blocking device to determine whether the beam combiner receives light from a particular one of the optical oscillators. 17. The DUV optical system of clause 16, wherein each beam blocking device is a shutter including a first state that transmits DUV light and a second state that blocks DUV light, and each shutter is configured to be positioned at the output of one of the optical oscillators such that each shutter prevents the corresponding one of the optical oscillators from emitting light towards the beam combiner when in the second state, and such that the corresponding one of the optical oscillators can emit light towards the beam combiner when in the first state. 18. The DUV optical system of clause 1, wherein the subset of optical oscillators does not include any of the multiple optical oscillators generating a light beam that is part of the exposure beam. 19. The DUV optical system of clause 1, wherein the calibration operation is performed only when the beam combiner does not receive light from a subset of the optical oscillators. 20. The DUV optical system of clause 1, wherein the DUV optical system is configured for use in a DUV photolithography system. 21. The DUV optical system of clause 20, further comprising a scanner device configured to receive the exposure beam from the beam combiner. 22. A method for controlling multiple optical oscillators in a deep ultraviolet (DUV) optical system, comprising: monitoring the DUV optical system to determine whether a condition exists; determining if any of the plurality of optical oscillators is in a wait state if the condition exists; and 11. A method comprising performing a calibration operation on a subset of a plurality of optical oscillators that are in a wait state, wherein one or more of the optical oscillators that are not in a wait state continue to generate an exposure beam while the calibration operation is performed. 23. The method of clause 22, further comprising determining whether the calibration operation was successful. 24. The method of clause 22, wherein the DUV optical system is configured for use with a DUV photolithography system, and monitoring the DUV optical system includes receiving a command signal from the scanner device and determining whether a condition exists based on the command signal. 25. The method of clause 22, wherein at least one optical oscillator is placed in a wait state if a condition exists and none of the plurality of optical oscillators is in a wait state. 26. A deep ultraviolet (DUV) optical lithography system having a light source system; A scanner device; a control system coupled to a light source system and a scanner device, The light source system a plurality of optical oscillators each including a gain medium; A beam combiner; a beam control device between the gain medium and the beam combiner, the beam combiner configured to receive light emitted from any of the optical oscillators and direct it as an exposure beam towards the scanner device, the beam control device configured to determine whether the beam combiner has received light from a particular one of the optical oscillators; The control system Determining whether a condition exists in the optical lithography system; The optical lithography system is configured to perform a calibration operation on a subset of the optical oscillators if the condition is determined to exist. 27. The optical lithography system of clause 26, further comprising a gas supply system fluidly coupled to the plurality of optical oscillators. 28. A method of controlling a plurality of optical oscillators in a deep ultraviolet (DUV) optical lithography system, comprising: receiving a request for an exposure beam configured to provide a requested dose of DUV light to the wafer; determining whether a cold start condition exists; and If a cold start condition exists, activating more than the nominal number of optical oscillators, which is the number of optical oscillators capable of providing the required dose under steady state conditions; and directing a light beam from each of the activated optical oscillators toward a scanner device to provide an exposure beam during a cold start period. 29. When a cold start condition exists, determining whether a cold start period has ended; and 29. The method of clause 28, further comprising deactivating at least one of the activated optical oscillators when the cold start period expires. 30. A control system having an interface configured to communicate with a DUV optical system, the control system comprising: Determining whether a condition exists in a DUV optical system; and performing a calibration operation in a subset of optical oscillators of the DUV optical system while at least one optical oscillator not in the subset of optical oscillators generates an exposure beam based on a determination that the condition exists; A control system configured to control the DUV optical system. 31. One or more electronic processors; The control system of clause 30, further comprising: computer readable electronic storage coupled to the one or more electronic processors, the computer readable electronic storage including executable instructions that, when executed, cause the control system to communicate with the DUV optical system via the interface. 32. N optical oscillators (N is an integer equal to or greater than 2); a beam combiner configured to generate an exposure beam from one or more light beams received from one or more of the N optical oscillators; and a control system configured to control the plurality of optical oscillators to determine which M of the plurality of optical oscillators (M is an integer between 1 and N) will generate light for the exposure beam. 33. The control system further comprises: configured to determine whether a condition exists in the light source system and, if the condition exists, perform a calibration operation on one or more of the plurality of optical oscillators; 33. The light source system of claim 32, wherein the calibration operation adjusts a characteristic of the light beam emitted by one of the plurality of optical oscillators, the characteristic including a central wavelength, an energy, or a spectral bandwidth. 34. A light source system according to clause 33, in which the calibration operation is performed only when one or more of the optical oscillators for which a condition exists is not generating light. 35. The light source system of clause 34, wherein each of the plurality of optical oscillators includes an excimer laser. 36. The light source system of clause 32, wherein a beam combiner is between the multiple optical oscillators and a scanner configured to expose a semiconductor wafer. 37. The light source system of clause 32, wherein the optical oscillators generate light beams having different central wavelengths.

[0095]

[0102] Other embodiments are within the scope of the claims.

Claims

1. A method of controlling a plurality of optical oscillators in a deep ultraviolet (DUV) optical system comprising: a beam combiner configured to receive light emitted from at least one of the plurality of optical oscillators and to emit a combined exposure beam, the method comprising: monitoring the DUV optical system to determine if a condition exists; identifying a subset of the plurality of optical oscillators from which the beam combiner is not receiving light if a condition exists; and 11. The method of claim 10, further comprising: performing a calibration operation on the subset of the plurality of optical oscillators, wherein at least one optical oscillator not in the subset continues to generate a combined exposure beam while the calibration operation is performed.

2. 2. The method of claim 1, wherein the DUV optical system is configured for use with a DUV photolithography system, and monitoring the DUV optical system includes receiving a command signal from a scanner device and determining whether the condition exists based on the command signal.

3. The method of claim 1 , wherein if the condition exists and none of the plurality of optical oscillators is included in the subset, then at least one optical oscillator is included in the subset.

4. A control system having an interface configured to communicate with a DUV optical system comprising a plurality of optical oscillators and a beam combiner configured to receive light emitted from at least one of the plurality of optical oscillators and emit a combined exposure beam, the control system comprising: determining whether a condition exists in the DUV optical system; identifying a subset of the plurality of optical oscillators from which the beam combiner is not receiving light based on a determination that the condition exists; and performing a calibration operation in the subset of optical oscillators of the plurality of optical oscillators while at least one optical oscillator not in the subset of optical oscillators generates a combined exposure beam; A control system configured to control the DUV optical system.

5. N optical oscillators (N is an integer equal to or greater than 2); a beam combiner configured to generate a combined exposure beam from one or more light beams received from one or more of the N optical oscillators; a control system configured to control the N optical oscillators to determine which M of the N optical oscillators (M is an integer between 1 and N, inclusive) will generate light for the exposure beam, The control system comprises: determining whether a condition exists for the light source system; identifying a subset of the N optical oscillators from which the beam combiner is not receiving light based on a determination that the condition exists; A light source system configured to perform a calibration operation on the subset of optical oscillators while at least one optical oscillator not in the subset of optical oscillators generates a combined exposure beam.

6. The control system further comprises: The light source system of claim 5 , wherein the calibration operation adjusts a characteristic of the light beam emitted by the one of the N optical oscillators, the characteristic including a central wavelength, an energy, or a spectral bandwidth.

7. 6. The light source system of claim 5, wherein the beam combiner is between the N optical oscillators and a scanner configured to expose a semiconductor wafer.

8. The light source system of claim 5 , wherein the optical oscillators generate light beams having different center wavelengths.

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