System and method for controlling center wavelength

Abstract

The present disclosure relates to systems and methods for controlling center wavelength. In one example, a method includes estimating a center wavelength error. The method also includes determining, based on the estimated center wavelength error, a first actuation amount of a first actuator that controls movement of a first prism. The method also includes actuating the first actuator based on the actuation amount. The method also includes determining whether the first prism is off-center. The method also includes, in response to determining that the first prism is off-center, determining a second actuation amount of the first actuator and determining a third actuation amount of a second actuator that controls movement of a second prism. The method also includes actuating the first actuator and the second actuator based on the second actuation amount and the third actuation amount, respectively. The method finds application in a multi-focal imaging operation.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Application No. 63 / 036,700, filed June 9, 2020, and also to U.S. Application No. 63 / 079,191, filed September 16, 2020, both of which are entitled “SYSTEMSAND METHODS FOR CONTROLLING A CENTER WAVELENGTH”, and both are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure relates to laser systems (such as excimer lasers that generate light) and systems and methods for controlling their center wavelength. Background Technology

[0004] A photolithography apparatus is a machine configured to apply a desired pattern onto a substrate. Photolithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A photolithography apparatus can, for example, project a patterning device (e.g., a mask, a photomask) onto a radiation-sensitive material (resist) layer provided on a substrate.

[0005] To project patterns onto a substrate, photolithography equipment can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features that can be formed on the substrate. Photolithography equipment can use extreme ultraviolet (EUV) radiation with wavelengths in the range of 4-20 nm (e.g., 6.7 nm or 13.5 nm), or deep ultraviolet (DUV) radiation with wavelengths in the range of about 120 nm to about 400 nm (e.g., 193 nm or 248 nm).

[0006] A master oscillator power amplifier (MOPA) is a two-stage optical resonator arrangement that produces a highly coherent amplified beam. The performance of a MOPA depends primarily on the alignment of the master oscillator (MO). MO alignment can include the alignment of the gas discharge chamber, the alignment of the input / output optics, and the alignment of the spectral characterizer.

[0007] However, MO alignment can be time-consuming and requires several hours of manual maintenance. Furthermore, monitoring and adjusting MO alignment can suppress or block, for example, the output beam to a DUV lithography device.

[0008] Furthermore, wavelength stability is affected when the device experiences thermal transients and other transients. In monochromatic mode, two actuators (i.e., a stepper motor and a piezoelectric transducer (PZT)) work together to stabilize the center wavelength. During operation, the stepper motor has limited resolution, and therefore, the PZT acts as the primary actuator. However, in dual-color mode, wavelength stability is based on the center wavelength, i.e., the average of two alternating spectra, and in this mode, the PZT's task is to generate a waveform that produces the alternating wavelengths. Summary of the Invention

[0009] Therefore, it is necessary to control the center wavelength.

[0010] In some embodiments, this disclosure relates to a system and method for controlling the center wavelength of an imaging operation. The system may include: a first actuator configured to control movement of a first prism, a second actuator configured to control movement of a second prism, and a controller configured to: determine a first actuation amount of the first actuator based on an estimated center wavelength error; cause the first actuator to actuate based on the first actuation amount; determine whether the first prism is off-center; in response to determining that the first prism is off-center, determine a second actuation amount of the first actuator and a third actuation amount of the second actuator; and cause the first and second actuators to actuate based on the second and third actuation amounts, respectively.

[0011] The method may include estimating a center wavelength error. The method may further include determining a first actuation amount of a first actuator for controlling movement of a first prism based on the estimated center wavelength error. The method may further include actuating the first actuator based on the first actuation amount. The method may further include determining whether the first prism is off-center. The method may further include: in response to determining that the first prism is off-center, determining a second actuation amount of the first actuator and determining a third actuation amount of a second actuator for controlling movement of a second prism. The method may further include actuating the first and second actuators based on the second and third actuation amounts, respectively. In some embodiments, the method may be performed using the system.

[0012] In some embodiments, estimating the center wavelength error may include calculating a first average value of the center wavelength at odd bursts and a second average value of the center wavelength at even bursts, and determining an average of the first average value and the second average value, wherein the center wavelength error is based on the average of the first average value and the second average value.

[0013] In some embodiments, determining the first actuation amount may include determining the difference between the target center wavelength and the estimated center wavelength, and determining the first actuation amount based on the difference between the target center wavelength and the estimated center wavelength.

[0014] In some embodiments, determining the difference between the target center wavelength and the estimated center wavelength may include using a digital filter to determine the difference.

[0015] In some embodiments, determining a third actuation amount of the second actuator may be based on the position of the first prism after the first actuator is actuated based on the second actuation amount.

[0016] In some embodiments, determining the third actuation amount may further include determining the third actuation amount to reduce the difference between the target center wavelength and the estimated wavelength.

[0017] In some embodiments, the imaging operation includes multifocal imaging, and the method may further include operating the light source in a dual-color mode. In some embodiments, operating the light source in a dual-color mode may include: generating a first laser radiation beam of a first wavelength using a first laser chamber module; generating a second laser radiation beam of a second wavelength using a second laser chamber module; and combining the first and second laser radiation beams along a common output beam path using a beam combiner. In some embodiments, estimating the center wavelength error may include estimating the center wavelength error of the first laser radiation beam. In some embodiments, in dual-color mode, the wavelength target may alternate between two known setpoints within a burst (e.g., per pulse), and the PZT may be used to track a rapidly changing target with little margin to control the center wavelength.

[0018] In some embodiments, this disclosure relates to a system and method for controlling a center wavelength. The system may include: a light source configured to generate a light beam; a first actuator configured to control movement of a first prism; a second actuator configured to control movement of a second prism; and a controller. The controller may be configured to: determine a wavelength error of the light beam generated by the light source; determine whether the wavelength error is greater than a first threshold; in response to determining that the wavelength error is greater than the first threshold, cause the first actuator to move by a first step; in response to determining that the wavelength error is less than the first threshold, determine an average wavelength error; determine whether the average wavelength error is greater than a second threshold different from the first threshold; in response to determining that the average wavelength error is greater than the second threshold, cause the first actuator to move by a second step and enable a low-pass filter; and in response to determining that the average wavelength error is less than the second threshold, enable the low-pass filter, update the voltage applied to the second actuator, and cause the first actuator to move by a third step.

[0019] The method may include determining a wavelength error of a light beam generated by a light source. The method may also include determining whether the wavelength error is greater than a first threshold. The method may further include: in response to determining that the wavelength error is greater than the first threshold, moving a first actuator by a step size, the first actuator being configured to control movement of a first prism. In response to determining that the wavelength error is less than the first threshold, the method may further include: determining an average wavelength error; determining whether the average wavelength error is greater than a second threshold different from the first threshold; in response to determining that the average wavelength error is greater than the second threshold, moving the first actuator by a second step size and enabling a low-pass filter; and in response to determining that the average wavelength error is less than the second threshold, enabling the low-pass filter, updating the voltage applied to a second actuator, and moving the first actuator by a third step size, the second actuator being configured to control movement of a second prism. In some embodiments, the method may be performed using this system.

[0020] In some embodiments, determining the wavelength error may include measuring the center wavelength of the light beam generated by the light source and determining the difference between the center wavelength and the target center wavelength.

[0021] In some embodiments, the method may further include determining whether the number of pulses emitted by the light source is a multiple of the update interval, and updating the voltage applied to the second actuator in response to determining that the number of emission times is equal to the update interval.

[0022] In some embodiments, the method may further include disabling the movement of the low-pass filter and the second actuator in response to determining that the wavelength error is greater than a first threshold.

[0023] In some embodiments, the first step length is a fixed step length of the actuator.

[0024] In some embodiments, the second step length is based on wavelength error.

[0025] In some embodiments, the third step length is based on the voltage applied to the second actuator.

[0026] In some embodiments, moving the first actuator in a second step includes moving the first actuator every n pulses, where n is greater than 1.

[0027] In some embodiments, the average wavelength error is based on the average of the wavelength error and the average of the wavelength errors over multiple pulses.

[0028] In some embodiments, the method includes controlling the center wavelength during multifocal imaging operation, and the method may further include operating the light source in a dual-color mode. In some embodiments, operating the light source in a dual-color mode may include: generating a first laser radiation beam of a first wavelength using a first laser chamber module; generating a second laser radiation beam of a second wavelength using a second laser chamber module; and combining the first and second laser radiation beams along a common output beam path using a beam combiner. In some embodiments, determining the wavelength error of the beam generated by the light source includes determining the center wavelength error of the first laser radiation beam. In some embodiments, in dual-color mode, the wavelength target may alternate between two known setpoints within a burst (e.g., per pulse), and a PZT may be used to track a rapidly changing target with little margin to control the center wavelength.

[0029] In some embodiments, this disclosure relates to a system and method for controlling the center wavelength of multifocal imaging operation. The system may include: an actuator configured to control movement of a prism; and a controller configured to: combine a jitter waveform with an offset value for moving the actuator; generate an inter-pulse wavelength based on the jitter waveform and the offset value; generate a rolling average of the center wavelength based on the inter-pulse wavelengths of a plurality of pulses; estimate a drift rate to predict the center wavelength of future pulses; and update the offset value based on the estimated drift rate.

[0030] The method may include combining a jitter waveform with an offset value of an actuator used to move a control prism. The method may also include generating an inter-pulse wavelength based on the jitter waveform and the offset value. The method may further include generating a rolling average of the center wavelength based on the inter-pulse wavelengths of multiple pulses. The method may further include estimating a drift rate to predict the center wavelength of future pulses. The method may further include updating the offset value based on the estimated drift rate. In some embodiments, the method may be performed using this system.

[0031] In some embodiments, the offset value is based on a direct current (DC) voltage.

[0032] In some embodiments, the initial value of the DC voltage is zero volts.

[0033] In some embodiments, the offset value includes a first offset value, and estimating the drift rate may include estimating the drift rate based on the rolling average value of the center wavelength, the first offset value, and a second offset value of the second actuator that moves the second prism.

[0034] In some embodiments, estimating the drift rate may include using a Kalman filter framework to estimate the cumulative center wavelength drift rate.

[0035] In some embodiments, estimating the drift rate may include predicting the center wavelength N pulses prior to the current pulse.

[0036] In some embodiments, estimating the drift rate may include converting a Kalman filter framework into a Kalman predictor to predict the center wavelength N pulses prior to the current pulse.

[0037] In some embodiments, the inter-pulse wavelength of the plurality of pulses includes the wavelength of the current pulse.

[0038] In some embodiments, updating the offset value may include updating the offset value based on a rolling average of the center wavelength at the end of the burst.

[0039] In some embodiments, multifocal imaging operation includes a dual-color mode, and the method may further include operating the light source in dual-color mode. In some embodiments, operating the light source in dual-color mode may include: generating a first laser radiation beam of a first wavelength using a first laser chamber module; generating a second laser radiation beam of a second wavelength using a second laser chamber module; and combining the first and second laser radiation beams along a common output beam path using a beam combiner.

[0040] Other features and exemplary aspects of the embodiments, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. Note that the embodiments are not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Other embodiments will be readily apparent to those skilled in the art based on the teachings included herein. Attached Figure Description

[0041] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate embodiments and, together with the specification, further serve to explain the principles of the embodiments and enable those skilled in the art to make and use the embodiments.

[0042] Figure 1 This is a schematic diagram of a lithography apparatus according to an exemplary embodiment.

[0043] Figure 2 This is a schematic top view of a light source device according to an exemplary embodiment.

[0044] Figure 3 This is according to an exemplary embodiment. Figure 2 A schematic partial cross-sectional view of the gas discharge stage of the light source device shown.

[0045] Figure 4 This is according to an exemplary embodiment. Figure 2 A schematic partial cross-sectional view of the gas discharge stage of the light source device shown.

[0046] Figure 5A method for adjusting the center wavelength of multifocal imaging according to one embodiment is shown.

[0047] Figures 6A-6B , Figure 7 and Figure 8 A method for adjusting the center wavelength of multifocal imaging according to some embodiments is shown.

[0048] Figure 9 A flowchart for aligning a gas discharge stage according to an exemplary embodiment is shown.

[0049] Figure 10 These are example computer systems for implementing various embodiments of the present disclosure.

[0050] The features and exemplary aspects of the embodiments will become more apparent from the detailed description set forth below, taken in conjunction with the accompanying drawings, in which the same reference numerals consistently identify corresponding elements. In the drawings, the same reference numerals generally denote the same, functionally similar, and / or structurally similar elements. Furthermore, the leftmost numeral of the reference numerals generally indicates the figure in which the reference numeral first appears. Unless otherwise stated, the drawings provided throughout this disclosure should not be construed as scale diagrams. Detailed Implementation

[0051] This specification discloses one or more embodiments incorporating features of the invention. The disclosed embodiments are merely illustrative of the invention. The scope of the invention is not limited to the disclosed embodiments. The invention is defined by the appended claims.

[0052] The described embodiments and references to "an embodiment," "embodiment," and "exemplary embodiment" in the specification indicate that the described embodiments may include specific features, structures, or characteristics, but each embodiment does not necessarily include specific features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, it should be understood that implementing such features, structures, and characteristics in conjunction with other embodiments is within the knowledge of those skilled in the art, whether explicitly described or not.

[0053] For ease of description, spatial relative terms such as “below,” “under,” “lower,” and “above,” “upper,” and “upper” are used herein to describe the relationship of an element or feature to another element(s) and feature(s) shown in the figures. In addition to the orientations shown in the figures, the spatial relative terms are intended to cover different orientations of the device in use or operation. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptors used herein may be interpreted accordingly.

[0054] The terms “approximately,” “substantially,” or “approximately” as used herein refer to a given quantity of value that may vary depending on the specific technology used. Based on the specific technology used, the terms “approximately,” “substantially,” or “approximately” may refer to a given quantity of value that varies, for example, within a range of 1-15% of that value (e.g., ±1%, ±2%, ±5%, ±10%, or ±15% of that value).

[0055] Embodiments of this disclosure can be implemented in hardware, firmware, software, or any combination thereof. Embodiments of this disclosure can also be implemented as instructions stored on a tangible machine-readable medium, which can be read and executed by one or more processors. The machine-readable medium can include any mechanism for storing or transmitting information in a machine-readable form (e.g., a computing device). For example, a machine-readable medium can include read-only memory (ROM); random access memory (RAM); disk storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagation signals (e.g., carrier waves, infrared signals, digital signals, etc.). Furthermore, firmware, software, routines, and / or instructions can be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and such actions are actually generated by a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc.

[0056] However, it is instructive to present an example environment in which embodiments of this disclosure may be implemented before describing such embodiments in more detail.

[0057] Exemplary lithography system

[0058] Figure 1 A lithography system including a radiation source SO and a lithography apparatus LA is shown. The radiation source SO is configured to generate EUV and / or DUV radiation beams B and supply EUV and / or DUV radiation beams B to the lithography apparatus LA. The lithography apparatus LA includes an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate stage WT configured to support a substrate W.

[0059] The illumination system IL is configured to modulate the EUV and / or DUV radiation beam B before it is incident on the patterning device MA. Therefore, the illumination system IL may include a faceted field mirror assembly 10 and a faceted pupil mirror assembly 11. Together, the faceted field mirror assembly 10 and the faceted pupil mirror assembly 11 provide the EUV and / or DUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. In addition to or instead of the faceted field mirror assembly 10 and the faceted pupil mirror assembly 11, the illumination system IL may include other mirrors or devices.

[0060] After such adjustment, the EUV and / or DUV radiation beam B interacts with the patterning device MA (e.g., a transmission mask for DUV or a reflection mask for EUV). As a result of this interaction, a patterned EUV and / or DUV radiation beam B' is generated. A projection system PS is configured to project the patterned EUV and / or DUV radiation beam B' onto a substrate W. For this purpose, the projection system PS may include a plurality of mirrors 13, 14, configured to project the patterned EUV and / or DUV radiation beam B' onto the substrate W held by a substrate stage WT. The projection system PS may apply a reduction factor to the patterned EUV and / or DUV radiation beam B', thereby forming an image with features smaller than the corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS in Figure 1 The projection system PS is shown as having only two mirrors 13 and 14, but the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[0061] The substrate W may include a previously formed pattern. In this case, the lithography apparatus LA aligns the image formed by the patterned EUV and / or DUV radiation beams B' with the pattern previously formed on the substrate W.

[0062] A relative vacuum, i.e., a small amount of gas (e.g., hydrogen) at a pressure much lower than atmospheric pressure, can be provided in the radiation source SO, the lighting system IL, and / or the projection system PS.

[0063] Exemplary light source device

[0064] As described above, the master oscillator power amplifier (MOPA) is a two-stage optical resonator arrangement. The master oscillator (MO) (e.g., the first optical resonator stage) generates a highly coherent beam (e.g., from a seed laser). The power amplifier (PA) (e.g., the second optical resonator stage) increases the optical power of the beam while maintaining the beam characteristics. The MO may include a gas discharge chamber, input / output optics (e.g., an optical coupler (OC)), and a spectral characterization modulator (e.g., a linewidth narrowing module (LNM)). The input / output optics and the spectral characterization modulator may surround the gas discharge chamber to form an optical resonator.

[0065] The performance of MOPA depends primarily on the alignment of MOs. MO alignment can include the alignment of the gas discharge chamber, the OC, and the LNM. Each alignment (e.g., chamber, OC, LNM, etc.) results in alignment errors and MO variations over time. However, MO calibration can be time-consuming and require several hours of manual maintenance (e.g., Synchronous Performance Maintenance (SPM)). Furthermore, initial alignment can be difficult (e.g., trial and error) if the chamber, OC, and LNM are severely misaligned (e.g., no initial reference point). Additionally, monitoring and adjusting MO alignment can suppress (e.g., block) the output beam to DUV lithography equipment (e.g., the DUV beam).

[0066] Imaging light (e.g., a visual laser beam) can be projected onto the chamber, OC, and LNM (e.g., sequentially or simultaneously) to illuminate the OC and / or LNM and guide their alignment along the optical axis of the chamber (e.g., the first and second optical ports). Amplified spontaneous emission (ASE) from the gas discharge chamber can act as a beacon (e.g., a reference point) to facilitate aiming of the imaging light along the optical axis of the MO cavity (e.g., along the optical axis of the chamber, OC, and LNM) (e.g., laser aiming). Furthermore, ASE can be used to initially align the chamber with the optical axis of the MO cavity (e.g., coarse alignment). Additionally, sensing devices (e.g., cameras) can be used to visually survey different object planes within the MO (e.g., chamber ports, OC apertures, LNM apertures, etc.) and quantify any alignment errors (e.g., image comparison). For example, the sensing devices can survey the near-field (NF) and far-field (FF) regions of the imaging light on various object planes and apply adjustments (e.g., fine alignment) for example, by beam profile (e.g., horizontal symmetry, vertical symmetry, etc.).

[0067] The light source devices and systems described below can reduce the alignment time (e.g., SPM) of the master oscillator, reduce alignment variations of the master oscillator over time, and monitor and dynamically control the quantifiable alignment error of the master oscillator to provide, for example, a highly coherent beam to a DUV lithography apparatus.

[0068] Figures 2 to 4 A light source device 200 according to various exemplary embodiments is shown. Figure 2 This is a schematic top view of a light source device 200 according to an exemplary embodiment. Figure 3 and Figure 4 This is according to an exemplary embodiment. Figure 2 A schematic partial cross-sectional view of the gas discharge stage 220 of the light source device 200 shown.

[0069] Figure 2A light source device 200 according to various exemplary embodiments is illustrated. The light source device 200 can be configured to monitor and dynamically control quantifiable alignment errors of a gas discharge stage 220 (e.g., MO), and, for example, provide a highly coherent and aligned beam (e.g., beam 202, amplified beam 204) to a DUV lithography apparatus (e.g., LA). The light source device 200 can be further configured to reduce the alignment time of the gas discharge stage 220 (e.g., MO) and reduce alignment variations of the gas discharge stage 220 (e.g., MO) over time. Although the light source device 200 in… Figure 2 While illustrated as a standalone device and / or system, embodiments of this disclosure can be used in conjunction with other optical systems, such as, but not limited to, a radiation source SO, a lithography apparatus LA, and / or other optical systems. In some embodiments, the light source device 200 may be a radiation source SO within the lithography apparatus LA. For example, the DUV radiation beam B may be beam 202 and / or amplified beam 204.

[0070] The light source device 200 may be a MOPA formed by a gas discharge stage 220 (e.g., MO) and a power loop amplifier (PRA) stage 280 (e.g., PA). The light source device 200 may include the gas discharge stage 220, a line analysis module (LAM) 230, a master oscillator wavefront engineering box (MoWEB) 240, the power loop amplifier (PRA) stage 280, and a controller 290. In some embodiments, all of the above components may be housed within a three-dimensional (3D) frame 210. In some embodiments, the 3D frame 210 may include metal (e.g., aluminum, steel, etc.), ceramic, and / or any other suitable rigid material.

[0071] Gas discharge stage 220 can be configured to output a highly coherent beam (e.g., beam 202). Gas discharge stage 220 may include a first optical resonator element 254, a second optical resonator element 224, an input / output optics element 250 (e.g., OC), an optical amplifier 260, and a spectral feature modulator 270 (e.g., LNM). In some embodiments, the input / output optics element 250 may include the first optical resonator element 254, and the spectral feature modulator 270 may include the second optical resonator element 224. The first optical resonator 228 may be defined by the input / output optical element 250 (e.g., via the first optical resonator element 254) and the spectral feature modulator 270 (e.g., via the second optical resonator element 224). The first optical resonator element 254 may be partially reflective (e.g., a partial mirror), and the second optical resonator element 224 may be reflective (e.g., a mirror or grating) to form the first optical resonator 228. The first optical resonator 228 can guide light generated by the optical amplifier 260 (e.g., amplified spontaneous emission (ASE) 201) into the optical amplifier 260 a fixed number of times to form a beam 202. In some embodiments, such as Figure 2 As shown, the gas discharge stage 220 can output the beam 202 to the PRA stage 280 as part of the MOPA arrangement.

[0072] PRA stage 280 can be configured to amplify beam 202 from gas discharge stage 220 via a multi-pass arrangement and output amplified beam 204. PRA stage 280 may include a third optical resonator element 282, a power loop amplifier (PRA) 286, and a fourth optical resonator element 284. A second optical resonator 288 may be defined by the third optical resonator element 282 and the fourth optical resonator element 284. The third optical resonator element 282 may be partially reflective (e.g., a partial beam splitter), and the fourth optical resonator element 284 may be reflective (e.g., a mirror, prism, or beam inverter) to form the second optical resonator 288. The second optical resonator 282 can guide beam 202 from gas discharge stage 220 into PRA 286 a fixed number of times to form the amplified beam 204. In some embodiments, PRA stage 280 can output the amplified beam 204 to a lithography apparatus, such as a lithography (LA) apparatus. For example, the magnified beam 204 can be an EUV and / or DUV radiation beam B from a radiation source SO in a lithography device LA.

[0073] like Figures 2-4Optical amplifier 260 can be optically coupled to input / output optics 250 and spectral characteristic modulator 270. Optical amplifier 260 can be configured to output ASE 201 and / or beam 202. In some embodiments, optical amplifier 260 can utilize ASE 201 as a beacon to guide the alignment of the optical axis of chamber 261 and / or the optical axis of gas discharge stage 220 (e.g., MO cavity). Optical amplifier 260 may include chamber 261, gas discharge medium 263, and chamber modulator 265. Gas discharge medium 263 may be disposed within chamber 261, and chamber 261 may be disposed on chamber modulator 265.

[0074] The chamber 261 can be configured to hold the gas discharge medium 263 within a first chamber optical port 262a and a second chamber optical port 262b. The chamber 261 may include a first chamber optical port 262a and a second chamber optical port 262 opposite to the first chamber optical port 262a. In some embodiments, the first chamber optical port 262a and the second chamber optical port 262b may form the optical axis of the chamber 261.

[0075] like Figure 3 As shown, the first chamber optical port 262a can optically communicate with the input / output optical element 250. The first chamber optical port 262a may include a first chamber wall 261a, a first chamber window 266a, and a first chamber aperture 264a. In some embodiments, such as Figure 3 As shown, the first chamber orifice 264a can be a rectangular opening.

[0076] like Figure 4 As shown, the second chamber optical port 262b can optically communicate with the spectral feature modulator 270. The second chamber optical port 262b may include a second chamber wall 261b, a second chamber window 266b, and a second chamber aperture 264b. In some embodiments, such as Figure 4 As shown, the second chamber aperture 264b can be a rectangular opening. In some embodiments, the optical axis of the chamber 261 passes through the first chamber aperture 264a and the second chamber aperture 264b.

[0077] The gas discharge medium 263 can be configured to output ASE 201 (e.g., 193 nm) and / or beam 202 (e.g., 193 nm). In some embodiments, the gas discharge medium 263 may include a gas for excimer lasers (e.g., Ar2, Kr2, F2, Xe2, ArF, KrCl, KrF, XeBr, XeCl, XeF, etc.). For example, the gas discharge medium 263 may include ArF or KrF and output ASE 201 (e.g., 193 nm) and / or beam 202 (e.g., 193 nm) through a first chamber optical port 262a and a second chamber optical port 262b when excited (e.g., by an applied voltage) from a peripheral electrode (not shown) in chamber 261. In some embodiments, the gas discharge stage 220 may include a voltage power supply (not shown) configured to apply a high-voltage electrical pulse across electrodes (not shown) in chamber 261.

[0078] The chamber adjuster 265 can be configured to spatially adjust (e.g., laterally, angularly, etc.) the optical axis of the chamber 261 (e.g., along the first chamber optical port 262a and the second chamber optical port 262b). Figure 2 As shown, chamber adjuster 265 can be coupled to chamber 261 and first chamber optical port 262a and second chamber optical port 262b. In some embodiments, chamber adjuster 265 can have six degrees of freedom (e.g., six axes). For example, chamber adjuster 265 can include one or more linear motors and / or actuators to adjust the optical axis of chamber 261 in six degrees of freedom (e.g., forward / backward, up / down, left / right, yaw, pitch, roll). In some embodiments, chamber adjuster 265 can adjust chamber 261 laterally and angularly so that the optical axis of chamber 261 (e.g., along the first chamber optical port 262a and second chamber optical port 262b) is aligned with the optical axis of gas discharge stage 220 (e.g., MO cavity). For example, as Figure 2 As shown, the optical axis of the gas discharge stage 220 (e.g., MO cavity) can be defined by the optical axis of the chamber 261 (e.g., along the first chamber optical port 262a and the second chamber optical port 262b), the input / output optical element 250 (e.g., OC aperture 252), and the spectral feature modulator 270 (e.g., LNM aperture 272).

[0079] The input / output optics 250 can be configured to optically communicate with the first chamber optical port 262a. In some embodiments, the input / output optics 250 can be an optical coupler (OC) configured to partially reflect the beam and form a first optical resonator 228. For example, an OC has previously been described in U.S. Patent No. 7,885,309, published February 8, 2011, which is incorporated herein by reference in its entirety. Figure 2 As shown, the input / output optical element 250 may include a first optical resonator element 254 for guiding (e.g., reflecting) light into the optical amplifier 260 and transmitting light (e.g., beam 202, ASE 201) from the optical amplifier 260 to outside the gas discharge stage 220 (e.g., MO cavity).

[0080] like Figure 3 As shown, the input / output optics 250 may include an OC aperture 252 and a first optical resonator element 254. The first optical resonator element 254 may be configured to be angled (e.g., tilted and / or tilted) relative to the cavity 261 (e.g., the first cavity optical port 262a) in the vertical and / or horizontal directions to allow light passing through the OC aperture 252. In some embodiments, the OC aperture 252 may be a rectangular opening. In some embodiments, the alignment of the gas discharge stage 220 may be based on the alignment of the first cavity aperture 264a and the OC aperture 252. In some embodiments, the first optical resonator element 254 may be angled (e.g., tilted and / or tilted) the input / output optics 250 such that reflections from the input / output optics 250 are parallel to the optical axis of the gas discharge stage 220 (e.g., the MO cavity). In some embodiments, the first optical resonator element 254 may be an adjustable mirror (e.g., a partial reflector, beam splitter, etc.) capable of being angled (e.g., tilted and / or tilted). In some embodiments, the OC aperture 252 may be fixed, and the first optical resonator element 254 may be adjustable. In some embodiments, the OC aperture 252 may be adjustable. For example, the OC aperture 252 may be spatially adjustable relative to the chamber 261 in the vertical and / or horizontal directions.

[0081] The spectral feature modulator 270 (e.g., an LNM) can be configured to optically communicate with the second chamber optical port 262b. In some embodiments, the spectral feature modulator 270 can be a line narrowing module (LNM) configured to provide spectral line narrowing to the beam. For example, an LNM has been previously described in U.S. Patent No. 8,126,027, published February 28, 2012, which is incorporated herein by reference in its entirety.

[0082] like Figure 2 As shown, the spectral feature modulator 270 may include a second optical resonator element 224 for directing (e.g., beam 202, ASE 201) light from the optical amplifier 260 toward the input / output optical element 250 (e.g., reflecting) it back to the optical amplifier 260.

[0083] like Figure 4As shown, the spectral feature modulator 270 may include an LNM aperture 272 and a tilt angle modulator (TAM) 274. The TAM 274 may be configured to angle the light passing through the LNM aperture 270 relative to the chamber 261 (e.g., the second chamber optical port 262b) in the vertical and / or horizontal directions. In some embodiments, the LNM aperture 272 may be a rectangular opening. In some embodiments, the alignment of the gas discharge stage 220 may be based on the alignment of the second chamber aperture 264b and the LNM aperture 272. In some embodiments, the TAM 274 may angle-adjust (e.g., tilt and / or tilt) the spectral feature modulator 270 such that reflections from the spectral feature modulator 270 are parallel to the optical axis of the gas discharge stage 200 (e.g., the MO cavity). In some embodiments, the TAM 274 may include adjustable mirrors (e.g., partial reflectors, beam splitters, etc.) and / or adjustable prisms capable of angle adjustment (e.g., tilt and / or tilt). In some embodiments, the LNM aperture 272 may be fixed, and the TAM 274 may be adjustable. In some embodiments, the LNM aperture 272 may be adjustable. For example, the LNM aperture 272 may be spatially adjustable relative to the chamber 261 in the vertical and / or horizontal directions.

[0084] In some embodiments, the adjustable mirrors (e.g., partial reflectors, beam splitters, etc.) and / or adjustable prisms of TAM 274 may include a plurality of prisms 276a-d. Prisms 276a-d can be actuated to manipulate the angle of incidence of incident light on the second optical resonator element 224, which can be used to select narrowband wavelengths to be reflected back along the optical path. In some embodiments, prism 276a may be fitted with a stepper motor with finite step resolution and can be used for coarse wavelength control. Prism 276b can be actuated using a piezoelectric transducer (PZT) actuator, which provides improved resolution and bandwidth compared to prism 276a. In operation, controller 290 can use prisms 276a and 276b in a two-stage configuration.

[0085] LAM 230 can be configured to monitor the line center (e.g., center wavelength) of a beam (e.g., beam 202, imaging beam 206). LAM 230 can also be configured to monitor the energy of a beam (e.g., ASE 201, beam 202, imaging beam 206) for wavelength measurement. For example, LAMs have previously been described in U.S. Patent No. 7,885,309, published February 8, 2011, which is incorporated herein by reference in its entirety.

[0086] like Figure 2As shown, LAM 230 can be optically coupled to gas discharge stage 220 and / or MoWEB 240. In some embodiments, LAM 230 can be disposed between gas discharge stage 220 and MoWEB 240. For example, as Figure 2 As shown, LAM 230 can be directly optically coupled to MoWEB 240 and optically coupled to gas discharge stage 220. In some embodiments, such as Figure 2 As shown, beam splitter 212 can be configured to direct ASE 201 and / or beam 202 toward PRA stage 280, and to direct ASE 201 or beam 202 toward imaging device. In some embodiments, such as Figure 2 As shown, the beam splitter 212 can be set in the MoWEB 240.

[0087] MoWEB 240 can be configured to provide beam shaping for a beam (e.g., beam 202, imaging beam 206). MoWEB 240 can be further configured to monitor the forward and / or backward propagation of the beam (e.g., ASE 201, beam 202, imaging beam 206). For example, MoWEB has previously been described in U.S. Patent No. 7,885,309, published February 8, 2011, which is incorporated herein by reference in its entirety. Figure 2 As shown, MoWEB 240 can be optically coupled to LAM 230. In some embodiments, LAM 230, MoWEB 240, and / or imaging devices can be optically coupled to gas discharge stage 220 via a single optical arrangement.

[0088] The controller 290 may be configured to communicate with the input / output optics 250, the chamber modulator 265, and / or the spectral feature modulator 270. In some embodiments, the controller 290 may be configured to provide a first signal 292 to the input / output optics 250, a second signal 294 to the spectral feature modulator 270, and a third signal 296 to the chamber modulator 265. In some embodiments, the controller 290 may be configured to provide signals (e.g., the first signal 292 and / or the second signal 294) to the input / output optics 250 and / or the spectral feature modulator 270 and adjust the input / output optics 250 (e.g., adjust the first optical resonator element 254) and / or the spectral feature modulator 270 (e.g., adjust the TAM 274) based on the output from the imaging device 400 (e.g., two-dimensional (2D) image comparison).

[0089] In some embodiments, the first optical resonator element 254, the chamber adjuster 265, and / or the TAM 274 can physically and / or electronically communicate with the controller 290 (e.g., a first signal 292, a second signal 294, and / or a third signal 296). For example, the first optical resonator element 254, the chamber adjuster 265, and / or the TAM 274 can be adjusted by the controller 290 (e.g., laterally and / or angularly) so that the optical axis of the chamber 261 (e.g., along the first chamber optical port 262a and the second chamber optical port 262b) is aligned with the optical axis of the gas discharge stage 220 (e.g., an MO cavity) defined by the input / output optical element 250 (e.g., OC aperture 252) and the spectral feature adjuster 270 (e.g., LNM aperture 272).

[0090] During normal operation, the laser wavelength may be disturbed and drifted when the optics experience thermal transients and when the laser duty cycle changes. The master wavelength actuator is an LNM (Laser-Nearest Neural Mechanism). As described above, the LNM may include multiple prisms 276a-d and a second optical resonator element 224 (e.g., a grating). The multiple prisms 276a-d can be actuated to manipulate the incident angle of the incident light on the second optical resonator element 224, which is used to select a narrowband wavelength to be reflected back along the optical path. In some embodiments, the magnitude of the incident angle can control the selected wavelength.

[0091] In some embodiments, multiple prisms 276a-d can be used to adjust the final angle of incidence in order to control the size of the angle of incidence and thus the selected wavelength. For example, prism 276a may have more control over the final angle of incidence compared to prism 276b. That is, in some embodiments, controller 290 uses prisms 276a and 276b in a two-stage configuration, where prism 276a is used for large jumps and to desaturate prism 276b, and prism 276b is used for finer changes in the final angle of incidence. Controlling prisms 276a and 276b is particularly important for MFI operation, which requires more than just adjustment around a setpoint; it requires precise tracking of the sine curve at the Nyquist frequency, in addition to precise control of the center point of the sine curve (i.e., the center wavelength). Reference Figure 5 , Figure 6A , Figure 6B and Figures 7-9 The described process provides a method for controlling the center wavelength of imaging operations, such as MFI operations.

[0092] Multifocal imaging operation can include a two-color mode. Operating a light source in two-color mode can include: generating a first laser radiation beam of a first wavelength using a first laser chamber module; generating a second laser radiation beam of a second wavelength using a second laser chamber module; and combining the first and second laser radiation beams along a common output beam path using a beam combiner. In two-color mode, the wavelength target can alternate between two known setpoints within a burst (e.g., per pulse), and the PZT can be used to track rapidly changing targets with little margin to control the center wavelength.

[0093] Figure 5 A method 500 for adjusting the center wavelength of multifocal or other imaging is illustrated according to one embodiment. It should be understood that performing the disclosure provided herein is not required. Figure 5 All steps in the process. Furthermore, some steps can be simultaneous, sequential, and / or combined with... Figure 5 The different execution orders shown are illustrated. (Refer to...) Figures 1-4 Method 500 is described. However, method 500 is not limited to these example embodiments.

[0094] In some embodiments, method 500 involves establishing a feedback loop to adjust the center wavelength of the laser radiation beam by moving actuators to control the movement of prisms 276a and 276b, respectively, based on an average center wavelength error estimated from LAM 230. To achieve this, LAM data can be used to estimate the center wavelength of the most recent pulse. In some embodiments, the difference between the target center wavelength and the estimated center wavelength can be provided to controller 290 to determine the desired actuation of prism 276b to compensate for interference on the center wavelength. Since prism 276b has a limited range of travel, controller 290 can also ensure that prism 276b is centered by actuating it as needed.

[0095] At 510, method 500 may include estimating a center wavelength error. For example, the center wavelength error may be estimated based on a first average of the center wavelengths of odd-numbered bursts and a second average of the center wavelengths of even-numbered bursts, and a third average may be determined based on the first and second averages. In some embodiments, the center wavelength error may be based on the difference between the center wavelength and the third average.

[0096] In 520, method 500 may include determining the actuation amount of a first actuator for controlling the movement of the prism 276b based on an estimated center wavelength. For example, Figure 2 The controller 290 can determine the difference between the target center wavelength and the estimated wavelength, and determine an actuator to actuate the movement of the control prism 276b to compensate for the difference. At 530, method 500 may include an actuator to actuate the movement of the control prism 276b based on the actuation amount.

[0097] At 540, method 500 may include determining whether prism 276b is off-center. In response to determining that prism 276b is centered, method 500 terminates at 550. In response to determining that prism 276b is off-center, at 560, method 500 may include determining a second actuation amount of an actuator controlling movement of prism 276b, and determining a third actuation amount of a second actuator controlling movement of prism 276a based on the second actuation of the first actuator. That is, controller 290 may determine how much actuation is needed from the two prisms 276a, 276b to compensate for the center wavelength error.

[0098] Figures 6A-6B , Figure 7 and Figure 8 A method for adjusting the center wavelength of an imaging operation, such as multifocal imaging, is illustrated according to some embodiments. It should be understood that performing the disclosure provided herein does not necessarily require Figure 6- Figure 8 All steps in the process. Furthermore, some steps can be simultaneous, sequential, and / or combined with... Figures 6A-6B , Figure 7 and Figure 8 The different execution orders shown are illustrated. (Refer to...) Figures 1-4 These methods are described. However, these methods are not limited to these example embodiments.

[0099] Figures 6A-6B , Figure 7 and Figure 8 Methods for adjusting the center wavelength of a laser radiation beam, such as in a two-color MFI mode, are disclosed. Two-color MFI modes can present challenges, such as prism 276b having a small margin for center wavelength control in two-color mode, step disturbances from mode transitions, and / or peak separation variations that can cause transients if handled using pure feedback. Furthermore, the center wavelength controller may interact with (multiple) other controllers (e.g., a peak separation controller), leading to performance degradation or even instability. To address these challenges, in some embodiments, prism 276a can be moved within a burst to compensate for large center wavelength errors, while limiting the movement of prism 276b to compensate for small low-pass filter errors. Additionally, in some embodiments, prism 276a can be moved to desaturate prism 276b. In some embodiments, prism 276a can be moved outside the burst when a two-color mode transition or a peak separation target change is detected. In some embodiments, the control bandwidth between the center wavelength controller and other controllers (e.g., a peak separation controller) can be separated from each other.

[0100] like Figures 6A-6BAs shown, at 610, method 600 may include an excitation source, such as a laser chamber in an MFI system. At 620, method 600 may include determining a wavelength error of the source, which may be a first laser radiation beam of a first wavelength from a first laser chamber module, or a second laser radiation beam of a second wavelength generated using a second laser chamber module. In some embodiments, determining the wavelength error may include measuring the center wavelength of the beam generated by the source and determining the difference between the center wavelength and a target center wavelength.

[0101] In 630, method 600 may include determining whether the wavelength error is greater than a first threshold. For example, the threshold may be 200 nanometers. Those skilled in the art will understand that this is merely an example threshold, and other thresholds may be considered according to aspects of this disclosure.

[0102] In some embodiments, at 640, in response to determining that the wavelength error is greater than a threshold, method 600 may include moving a first actuator for controlling the movement of prism 276a. For example, when a filter, such as a low-pass filter, and the movement of a second actuator for controlling the movement of prism 276b are disabled, the first actuator may be moved by a step length per pulse. For example, the first actuator may move in a direction that reduces the wavelength error. The step length may be a fixed step length, such as a full step length of the first actuator. By moving the first actuator while the filter and the second actuator are disabled, method 600 provides an overall change in the wavelength error and desaturates prism 276b. In some embodiments, after the first actuator is moved by a step length, at 698, method 600 ends by waiting for the next pulse of the light source.

[0103] In some embodiments, at 650, in response to determining that the wavelength error is less than a first threshold, method 600 may include determining an average wavelength error. In some embodiments, the average wavelength error may be a moving average based on a low-pass filtering technique, as will be understood by those skilled in the art. At 660, method 600 may include determining whether the average wavelength error is greater than a second threshold. In some embodiments, the second threshold may be different from the first threshold. For example, the second threshold may be 100 nanometers. It will be understood by those skilled in the art that this is merely an example threshold, and other thresholds may be considered according to aspects of this disclosure. In some embodiments, the average wavelength error may be based on the wavelength error and the average of multiple wavelength errors over n pulses, where n is the number of pulses greater than one (1). That is, the average wavelength error may be a moving average of the wavelength errors.

[0104] In some embodiments, at 670, in response to determining that the average wavelength error is greater than a second threshold, method 600 may include moving the first actuator by a second step size, enabling a low-pass filter, and disabling movement of the second actuator. For example, the first actuator may move in a direction that reduces the wavelength error. In some embodiments, the second step size may be proportional to the wavelength error; for example, the smaller the average wavelength error, the smaller the step size of the first actuator, and vice versa. In some embodiments, the second step size may be less than the full step size. In some embodiments, the second step size may be greater than the full step size. By moving the first actuator by a step size proportional to the average wavelength error, method 600 prevents overshoot of the desired position of prism 276a. In some embodiments, after the first actuator moves by the second step size, at 698, method 600 ends by waiting for the next pulse from the light source.

[0105] In some embodiments, at 680, in response to determining that the average wavelength error is less than a second threshold, method 600 may include moving the first actuator in third steps. In some embodiments, the third step may be proportional to the voltage applied to the second actuator, and the voltage applied to the second actuator may be reset. Therefore, in some embodiments, the third step may be based on the voltage applied to the second actuator, rather than the average wavelength error.

[0106] In some embodiments, at 690, method 600 may include determining whether the number of pulses emitted is a multiple of the update interval. For example, the number of emissions may be the number of beam pulses. In some embodiments, the update interval may be, for example, every five (5) or ten (10) pulses. Those skilled in the art will understand that these are merely example update intervals, and other update intervals may be considered according to aspects of this disclosure. That is, in some embodiments, method 600 may include determining whether the pulse is, for example, the fifth pulse or the tenth pulse. In some embodiments, when the number of emissions is not equal to the update interval, at 698, method 600 ends by waiting for the next pulse from the light source.

[0107] In some embodiments, when the number of emission times equals the update interval, at 695, method 600 may include updating the voltage applied to the second actuator. For example, the voltage applied to the second actuator may be based on an average wavelength error, such that the movement of prism 276b adapts to the average wavelength error in subsequent pulses. In some embodiments, after updating the voltage applied to the second actuator, at 698, method 600 waits for the next pulse from the light source to end.

[0108] In some embodiments, Figure 7Method 700 can be executed between pulses of the light source. During this period, the light source can switch between operating modes, for example, between a monochromatic mode and a dual-color mode, resulting in a change in the center wavelength due to the change in operating state. To solve this problem, such as Figure 7 As shown, method 700 may further include detecting a change in the operating state of the light source at 710. At 720, in response to detecting a change in the operating state of the light source, method 700 may include determining a center wavelength change. For example, determining the center wavelength change may include determining the midpoint of the target peak separation. At 730, method 700 may include moving a first actuator by a step size based on the center wavelength change. In some embodiments, regarding Figure 7 The described process can be performed between bursts of light source activity. By doing so, method 700 reduces wavelength error when the light source is activated again.

[0109] In some embodiments, Figure 8 Method 800 can be performed between pulses of the light source. During this period, the target peak separation may change. To address this issue, such as... Figure 8 As shown, method 800 may include detecting a change in peak separation at 810. At 820, in response to detecting a change in peak separation, method 800 may further include determining a change in center wavelength. For example, determining a change in center wavelength may include determining an average value between a previous peak separation target and a new peak separation target. At 830, method 800 may include moving a first actuator by a step size based on the change in center wavelength. In some embodiments... Figure 7 and Figure 8 The described process can be performed between bursts of light source activity. By doing so, methods 700 and 800 reduce wavelength error when the light source is activated again. Furthermore, using… Figure 7 and Figure 8 The process described herein reduces the number of bursts required to complete the transition between different operating modes.

[0110] Figure 9 A method 900 for adjusting the center wavelength, such as that used in multifocal imaging, according to one embodiment is shown. It should be understood that performing the disclosure provided herein is not required. Figure 9 All steps in the process. Furthermore, some steps can be simultaneous, sequential, and / or combined with... Figure 9 The different execution orders shown are illustrated. (Refer to...) Figures 1-4 Method 900 is described. However, method 900 is not limited to these example embodiments.

[0111] In some embodiments, regarding Figure 9 The discussion process provided an actuator for moving the control prism 276b during emergencies. That is, regarding... Figure 9The discussion process provides a solution for addressing in-burst variations in center wavelength, such as a first laser radiation beam of a first wavelength from a first laser chamber module, or a second laser radiation beam of a second wavelength generated by a second laser chamber module in MFI mode. To achieve this, in some embodiments, regarding... Figure 9 The described process estimates the drift rate of the center wavelength in order to compensate for the measurement delay of the center wavelength.

[0112] In some embodiments, the jitter waveform (or sequence) may be combined with the offset of the actuator used to move prism 276b. For example, the jitter waveform may be an application of noise for randomization quantization. The offset may be updated at the end of burst (EOB) and / or at set pulse intervals. In some embodiments, the EOB update may move the actuator of prism 276b to zero the estimated center wavelength drift obtained by averaging wavelength measurements over the entire burst. In some embodiments, the interval update may be based on the estimation process described herein. In some embodiments, the estimation process described herein may be based on a rolling average estimate of the center wavelength up to the current pulse and may provide access to both the offset of the actuator of prism 276b and a second offset of the actuator of prism 276a. In other words, in some embodiments, the process for estimating the drift rate may be based on the current positions of prisms 276a and 276b, the corresponding offset of each actuator, and a rolling average of the center wavelength, and the total cumulative center wavelength drift may be estimated using a Kalman filter framework. In some embodiments, to compensate for the delay of the LAM 230, the drift two steps before the current burst can be predicted by converting the Kalman filter into a Kalman predictor. That is, the drift rate can be estimated using open-loop propagation by using known inputs and any disturbances, to predict the drift rate two steps before the current burst.

[0113] In some embodiments, the Kalman filter can be modeled using Equations 1 and 2. In some embodiments, at any given point, the center wavelength relative to the center wavelength target can be based on the sum of the positions of prisms 276a and 276b (scaled with an appropriate gain) and the cumulative wavelength drift D(k) at time k. In some embodiments, the cumulative wavelength drift can be modeled as a linear drift with an unknown rate at time k, defined as DSR(k). As a result, the drift rate can vary with time without issue and can be incorporated into the state vector, thus allowing for the estimation of the drift rate.

[0114]

[0115]

[0116] Using this constructed model, the steady-state Kalman filter can be implemented as shown in Equation 3, where A, B, C, and D are defined in Equations 1 and 2, Q and R are tuning parameters, and S is the solution to the algebraic Ricatti equation given in Equation 4.

[0117]

[0118] AS+SA T -SC T R- 1 CS+Q=0 (4)

[0119] In some embodiments, the controller (e.g., controller 290) may be provided with total cumulative drift and estimated drift rate such that changes in the center wavelength can be compensated.

[0120] In some embodiments, offset P3 offset It can be defined using Equation 5. By using known inputs and any disturbances incorporated into the model, the drift rate can be estimated using open-loop propagation of the model two steps prior.

[0121]

[0122] Based on the foregoing, the drift rate can be estimated in real time based on wavelength measurements. The drift rate can be used to predict the magnitude of wavelength drift and compensate for it point-by-point. In some embodiments, the drift rate can be modeled as an accumulator with a variable accumulation rate, and a Kalman filter can be used to estimate the accumulation rate based on an estimate of the center wavelength (e.g., the arithmetic mean of all wavelength measurements in the current burst). In some embodiments, to compensate for measurement delays in LAM 230, N pulses (e.g., two pulses) of the preceding center wavelength can be predicted and used to determine the offset applied to the actuator of prism 276b. For example, in some embodiments, N pulses may be two pulses, but those skilled in the art will understand that this is merely an example number of pulses, and more or fewer pulses are conceivable according to aspects of this disclosure. In some embodiments, this offset can be updated per-emission at sub-nanometer resolution.

[0123] In 910, method 900 may include combining a jitter waveform with an offset value for actuating a prism. In some embodiments, the offset value may be used to move an actuator for controlling the movement of prism 276b. In some embodiments, the offset value is based on a direct current (DC) voltage applied to the actuator for controlling the movement of prism 276b. In some embodiments, the initial value of the DC voltage is zero volts.

[0124] In 920, method 900 may include generating an inter-pulse wavelength based on a jitter waveform and an offset value. For example, the inter-pulse wavelength can be generated using a LAM 230. In some embodiments, the inter-pulse wavelength may also be based on other interference from within the lithography apparatus LA.

[0125] In 930, method 900 may include generating a rolling average of the center wavelength based on the inter-pulse wavelengths of a plurality of pulses. In some embodiments, the inter-pulse wavelengths of the plurality of pulses include the wavelength of the current pulse.

[0126] At 940, method 900 may include estimating a drift rate to predict the center wavelength of a future pulse. In some embodiments, the offset value used to move the actuator associated with prism 276b may be a first offset value, and estimating the drift rate may include estimating the drift rate based on a rolling average of the center wavelength, the first offset value, and a second offset value of the second actuator that controls the movement of the second prism 276a. In some embodiments, estimating the drift rate includes using a Kalman filter framework to estimate the cumulative center wavelength drift rate. For example, the Kalman filter framework may estimate the cumulative center wavelength drift rate based on a rolling average of the center wavelength, the first offset value, and a second offset value. Furthermore, estimating the drift rate may include predicting the center wavelength N pulses (e.g., two pulses) prior to the current pulse. To achieve this, the Kalman filter framework may be converted into a Kalman predictor to predict the center wavelength N pulses (e.g., two pulses) prior to the current pulse.

[0127] At 950, method 900 may include updating the offset value based on the estimated drift rate. In some embodiments, in addition to the estimated drift rate, the updated offset value may also be based on the rolling average of the center wavelength at the end of the burst.

[0128] Example computer system

[0129] The various embodiments and components herein can be implemented, for example, using one or more known computer systems, such as the example embodiments, systems, and / or devices shown in the figures or otherwise discussed. Computer system 1000 can be any known computer capable of performing the functions described herein.

[0130] Computer system 1000 includes one or more processors (also called central processing units or CPUs), such as processor 1004. Processor 1004 is connected to communication infrastructure or bus 1006.

[0131] One or more processors 1004 may each be a graphics processing unit (GPU). In one embodiment, the GPU is a processor designed with dedicated electronic circuitry for processing mathematically intensive applications. The GPU may have a parallel architecture that is efficient for parallel processing of large blocks of data, such as common mathematically intensive data, such as computer graphics applications, images, and videos.

[0132] The computer system 1000 also includes multiple user input / output devices 1003, such as a display, keyboard, pointing device, etc., that communicate with the communication infrastructure 1006 via multiple user input / output interfaces 1002.

[0133] The computer system 1000 also includes main memory or primary memory 1008, such as random access memory (RAM). Main memory 1008 may include one or more levels of cache. Control logic (i.e., computer software) and / or data are stored in main memory 1008.

[0134] The computer system 1000 may also include one or more secondary storage devices or memories 1010. Secondary storage 1010 may include, for example, a hard disk drive 1012 and / or a removable storage device or drive 1014. The removable storage device 1014 may be a flash drive, magnetic tape drive, optical disc drive, optical storage device, tape backup device, and / or any other storage device / drive.

[0135] The removable storage drive 1014 can interact with the removable storage unit 1018. The removable storage device 1018 includes a computer-usable or readable storage device on which computer software (control logic) and / or data are stored. The removable storage unit 1018 can be a floppy disk, magnetic tape, compact disc, DVD, optical disc, and / or any other computer data storage device. The removable storage drive 1014 reads from and / or writes to the removable storage unit 1018 in a known manner.

[0136] According to an example embodiment, secondary storage 1010 may include other means, tools, or other methods for allowing computer system 1000 to access computer programs and / or other instructions and / or data. Such means, tools, and other methods may include, for example, removable storage unit 1022 and interface 1020. Examples of removable storage unit 1022 and interface 1020 may include program boxes and box interfaces (such as those found in video game devices), removable memory chips (such as EPROM or PROM) and associated sockets, memory sticks and USB ports, memory cards and associated memory card slots, and / or any other removable storage modules and associated interfaces.

[0137] Computer system 1000 may also include a communication or network interface 1024. Communication interface 1024 enables computer system 1000 to communicate and interact with any combination of remote devices, remote networks, remote entities, etc. (individually and collectively referenced by reference numeral 1028). For example, communication interface 1024 may allow computer system 1000 to communicate with remote device 1028 via communication path 1026, which may be wired and / or wireless, and may include any combination of LAN, WAN, Internet, etc. Control logic and / or data may be transmitted to and from computer system 1000 via communication path 1026.

[0138] In one embodiment, a non-transitory tangible device or article of manufacture including a non-transitory tangible computer-usable or readable medium on which control logic (software) is stored is also referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system 1000, main memory 1008, secondary storage 1010, removable storage units 1018 and 1022, and tangible articles embodying any combination of the foregoing. When executed by one or more data processing devices (such as computer system 1000), such control logic causes such data processing devices to operate as described herein.

[0139] Based on the teachings included in this disclosure, those skilled in the art will clearly understand how to use it. Figure 10 Embodiments of this disclosure may be made and used with data processing devices, computer systems, and / or computer architectures other than those shown herein. Specifically, embodiments may operate with other software, hardware, and / or operating system implementations besides those described herein.

[0140] While the foregoing may specifically refer to embodiments used in the context of optical lithography, it should be understood that the embodiments can be used in other applications, such as imprint lithography, and are not limited to optical lithography where the context permits. In imprint lithography, the morphology in a patterning apparatus defines a pattern created on a substrate. The morphology of the patterning apparatus can be pressed into a resist layer provided to the substrate, and then the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist has cured, the patterning apparatus is removed from the resist to leave a pattern therein.

[0141] It should be understood that the wording or terminology used herein is for descriptive rather than limiting purposes, and therefore the terms or phrases in this specification shall be interpreted by those skilled in the art based on the teachings herein.

[0142] As used herein, the term "substrate" describes a material on which a layer of material has been added. In some embodiments, the substrate itself may be patterned, and the material added thereon may also be patterned, or it may be left unpatterned.

[0143] The following examples are illustrative but not limiting examples of embodiments of this disclosure. Other suitable modifications and adaptations to various conditions and parameters commonly encountered in the art (which will be apparent to those skilled in the art) are within the spirit and scope of this disclosure.

[0144] While this document may specifically mention the use of such equipment and / or systems in IC manufacturing, it should be clearly understood that such equipment and / or systems have many other possible applications. For example, it can be used to manufacture integrated optical systems, guide and detection patterns for magnetic domain memories, LCD panels, thin-film magnetic heads, etc. Those skilled in the art should understand that, in the context of such alternative applications, any use of the terms “mask,” “wafer,” or “die” herein should be replaced with the more general terms “mask,” “substrate,” and “target portion,” respectively.

[0145] While specific embodiments have been described above, it will be understood that embodiments may be practiced in ways other than those described. This specification is not intended to limit the scope of the claims.

[0146] It should be understood that the "Detailed Description" section, rather than the "Summary" and "Abstract" sections, is intended to be used to interpret the claims. The "Summary" and "Abstract" sections may set forth one or more, but not all, exemplary embodiments contemplated by the inventors, and are therefore not intended to limit the embodiments and the appended claims in any way.

[0147] The above embodiments are described using functional building blocks that illustrate the implementation of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks are arbitrarily defined herein. Alternative boundaries can be defined as long as the specified functions and their relationships are properly performed.

[0148] The above description of the specific embodiments will so fully reveal the general nature of the embodiments that others can readily modify and / or adapt them to various applications by applying the knowledge of those skilled in the art, without excessive experimentation and without departing from the overall concept of the embodiments. Therefore, based on the teachings and guidance presented herein, such adaptations and modifications are intended to be within the meaning and scope of the equivalents of the disclosed embodiments.

[0149] Other aspects of the invention are set forth in the following numbered clauses.

[0150] 1. A method for controlling the center wavelength of an imaging operation, comprising:

[0151] Estimate center wavelength error;

[0152] The first actuation amount of the first actuator that controls the movement of the first prism is determined based on the estimated center wavelength error.

[0153] The first actuator is actuated based on the first actuation amount;

[0154] Determine whether the first prism is off-center;

[0155] In response to determining that the first prism is off-center, a second actuation amount of the first actuator is determined and a third actuation amount of the second actuator for controlling the movement of the second prism is determined; and

[0156] The first actuator and the second actuator are actuated based on the second actuation amount and the third actuation amount, respectively.

[0157] 2. The method according to Clause 1, wherein estimating the center wavelength error comprises:

[0158] Calculate the first average value of the center wavelength at odd-numbered bursts and the second average value of the center wavelength at even-numbered bursts; and

[0159] Determine the average of the first average and the second average, wherein the center wavelength error is based on the average of the first average and the second average.

[0160] 3. The method according to Clause 1, wherein determining the first actuation amount includes:

[0161] Determine the difference between the target center wavelength and the estimated center wavelength; and

[0162] The first actuation amount is determined based on the difference between the target center wavelength and the estimated center wavelength.

[0163] 4. The method according to Clause 3, wherein determining the difference between the target center wavelength and the estimated center wavelength includes determining the difference using a digital filter.

[0164] 5. The method according to Clause 1, wherein the determination of the third actuation amount of the second actuator is based on the position of the first prism after the first actuator is actuated based on the second actuation amount.

[0165] 6. The method according to Clause 5, wherein determining the third actuation amount further comprises determining the third actuation amount to reduce the difference between the target center wavelength and the estimated wavelength.

[0166] 7. The method according to Clause 1, wherein the imaging operation includes a multifocal imaging operation, and the method further includes operating the light source in a dual-color mode, wherein operating the light source in the dual-color mode includes:

[0167] A first laser radiation beam of a first wavelength is generated using the first laser chamber module;

[0168] A second laser radiation beam of a second wavelength is generated using the second laser chamber module; and

[0169] The first laser radiation and the second laser radiation are combined along a common output beam path using a beam combiner.

[0170] The estimated center wavelength error includes the estimated center wavelength error of the first laser radiation beam.

[0171] 8. A method for controlling the center wavelength, comprising:

[0172] Determine the wavelength error of the beam generated by the light source;

[0173] Determine whether the wavelength error is greater than a first threshold;

[0174] In response to determining that the wavelength error is greater than the first threshold, the first actuator is moved by a step length, the first actuator being configured to control the movement of the first prism;

[0175] In response to determining that the wavelength error is less than the first threshold:

[0176] Determine the average wavelength error;

[0177] Determine whether the average wavelength error is greater than a second threshold that is different from the first threshold;

[0178] In response to determining that the average wavelength error is greater than the second threshold, the first actuator is moved a second step and the low-pass filter is enabled; and

[0179] In response to determining that the average wavelength error is less than the second threshold, the low-pass filter is enabled, the voltage applied to the second actuator is updated, and the first actuator is moved by a third step, wherein the second actuator is configured to control the movement of the second prism.

[0180] 9. The method according to Clause 8, wherein determining the wavelength error comprises:

[0181] Measuring the center wavelength of the beam generated by the light source; and

[0182] Determine the difference between the center wavelength and the target center wavelength.

[0183] 10. The method described under Clause 8 further includes:

[0184] Determine whether the number of pulses emitted by the light source is a multiple of the update interval; and

[0185] In response to determining that the number of launches equals the update interval, the voltage applied to the second actuator is updated.

[0186] 11. The method according to Clause 8 further includes disabling movement of the low-pass filter and the second actuator in response to determining that the wavelength error is greater than the first threshold.

[0187] 12. The method according to Clause 8, wherein the first step length is a fixed step length of the actuator.

[0188] 13. The method according to Clause 8, wherein the second step size is a function of the wavelength error.

[0189] 14. The method according to Clause 8, wherein the third step length is a function of the voltage applied to the second actuator.

[0190] 15. The method according to Clause 8, wherein moving the first actuator with the second step size comprises moving the first actuator every n pulses, where n is greater than 1.

[0191] 16. The method according to Clause 8, wherein the average wavelength error is based on the average of the wavelength error and a plurality of wavelength errors over a plurality of pulses.

[0192] 17. The method according to Clause 8, wherein the method includes controlling the center wavelength in multifocal imaging operation, and the method further includes operating the light source in a dual-color mode, wherein operating the light source in the dual-color mode includes:

[0193] A first laser radiation beam of a first wavelength is generated using the first laser chamber module;

[0194] A second laser radiation beam of a second wavelength is generated using the second laser chamber module; and

[0195] The first laser radiation and the second laser radiation are combined along a common output beam path using a beam combiner.

[0196] The determination of the wavelength error of the beam generated by the light source includes determining the center wavelength error of the first laser radiation beam.

[0197] 18. A method for controlling the center wavelength of multifocal imaging operation, comprising:

[0198] Combine the jitter waveform with the offset value of the actuator used to move the control prism;

[0199] Generate inter-pulse wavelengths based on the jitter waveform and the offset value;

[0200] A rolling average of the center wavelength is generated based on the inter-pulse wavelengths of multiple pulses;

[0201] Estimate the drift rate to predict the center wavelength of future pulses; and

[0202] The offset value is updated based on the estimated drift rate.

[0203] 19. The method according to Clause 18, wherein the offset value is based on a direct current (DC) voltage.

[0204] 20. The method according to Clause 19, wherein the initial value of the DC voltage is zero volts.

[0205] 21. The method according to Clause 18, wherein:

[0206] The offset value includes a first offset value, and

[0207] The estimation of the drift rate includes estimating the drift rate based on the rolling average value of the center wavelength, the first offset value, and the second offset value of the second actuator that moves the second prism.

[0208] 22. The method according to Clause 21, wherein estimating the drift rate includes using a Kalman filter framework to estimate the cumulative center wavelength drift rate.

[0209] 23. The method according to Clause 22, wherein the estimation of the drift rate includes predicting the center wavelength N pulses prior to the current pulse.

[0210] 24. The method according to Clause 23, wherein estimating the drift rate comprises converting the Kalman filter frame into a Kalman predictor to predict the center wavelength N pulses prior to the current pulse.

[0211] 25. The method according to Clause 18, wherein the inter-pulse wavelength of the plurality of pulses includes the wavelength of the current pulse.

[0212] 26. The method according to Clause 18, wherein updating the offset value further includes updating the offset value based on the rolling average of the center wavelength at the end of the burst.

[0213] 27. A system comprising:

[0214] The first actuator is configured to control the movement of the first prism;

[0215] A second actuator is configured to control the movement of a second prism; and

[0216] The controller is configured as follows:

[0217] Estimate center wavelength error;

[0218] The first actuation amount of the first actuator is determined based on the estimated center wavelength error;

[0219] This causes the first actuator to be actuated based on the first actuation amount;

[0220] Determine whether the first prism is off-center;

[0221] In response to determining that the first prism is off-center, a second actuation amount of the first actuator is determined and a third actuation amount of the second actuator is determined; and

[0222] This causes the first actuator and the second actuator to be actuated based on the second actuation amount and the third actuation amount, respectively.

[0223] 28. The system according to Clause 27, wherein, in order to estimate the center wavelength error, the controller is further configured to:

[0224] Calculate the first average value of the center wavelength at odd-numbered bursts and the second average value of the center wavelength at even-numbered bursts; and

[0225] Determine the average of the first average and the second average, wherein the center wavelength error is based on the average of the first average and the second average.

[0226] 29. The system according to Clause 27, wherein, in order to determine the first actuation amount, the controller is further configured to:

[0227] Determine the difference between the target center wavelength and the estimated center wavelength; and

[0228] The first actuation amount is determined based on the difference between the target center wavelength and the estimated center wavelength.

[0229] 30. The system according to Clause 29, wherein in order to determine the difference between the target center wavelength and the estimated center wavelength, the controller is further configured to use a digital filter to determine the difference.

[0230] 31. The system according to Clause 27, wherein the third actuation amount of the second actuator is based on the position of the first prism after the first actuator is actuated based on the second actuation amount.

[0231] 32. The system according to Clause 31, wherein, in order to determine the third actuation amount, the controller is further configured to determine the third actuation amount to reduce the difference between the target center wavelength and the estimated wavelength.

[0232] 33. The system as described in Clause 27, wherein:

[0233] The imaging operation includes multifocal imaging operation.

[0234] The system also includes a light source that operates in a dual-color mode.

[0235] The controller is also configured to operate the light source in the dual-color mode in the following manner:

[0236] A first laser radiation beam of a first wavelength is generated using the first laser chamber module;

[0237] A second laser radiation beam of a second wavelength is generated using the second laser chamber module; and

[0238] The first laser radiation and the second laser radiation are combined along a common output beam path using a beam combiner.

[0239] The estimated center wavelength error includes the estimated center wavelength error of the first laser radiation beam.

[0240] 34. A system comprising:

[0241] The light source is configured to generate a beam;

[0242] The first actuator is configured to control the movement of the first prism;

[0243] A second actuator is configured to control the movement of a second prism; and

[0244] The controller is configured as follows:

[0245] Determine the wavelength error of the beam generated by the light source;

[0246] Determine whether the wavelength error is greater than a first threshold;

[0247] In response to determining that the wavelength error is greater than the first threshold, the first actuator is moved by a step length; and

[0248] In response to determining that the wavelength error is less than the first threshold:

[0249] Determine the average wavelength error; and

[0250] Determine whether the average wavelength error is greater than a second threshold that is different from the first threshold;

[0251] In response to determining that the average wavelength error is greater than the second threshold, the first actuator is moved a second step and the low-pass filter is activated; and

[0252] In response to determining that the average wavelength error is less than the second threshold, the low-pass filter is enabled, the voltage applied to the second actuator is updated, and the first actuator is moved by a third step.

[0253] 35. The system according to clause 34, wherein, in order to determine the wavelength error, the controller is further configured to:

[0254] Measuring the center wavelength of the beam generated by the light source; and

[0255] Determine the difference between the center wavelength and the target center wavelength.

[0256] 36. The system according to Clause 34, wherein the controller is further configured to:

[0257] Determine whether the number of pulses emitted by the light source is a multiple of the update interval; and

[0258] In response to determining that the number of launches equals the update interval, the voltage applied to the second actuator is updated.

[0259] 37. The system according to Clause 34, wherein the controller is further configured to disable movement of the low-pass filter and the second actuator in response to determining that the wavelength error is greater than the first threshold.

[0260] 38. The system according to Clause 34, wherein the first step length is a fixed step length of the actuator.

[0261] 39. The system according to Clause 34, wherein the second step size is a function of the wavelength error.

[0262] 40. The system according to Clause 34, wherein the third step length is a function of the voltage applied to the second actuator.

[0263] 41. The system according to Clause 34, wherein in order to cause the first actuator to move with the second step size, the controller is further configured to cause the first actuator to move every n pulses, where n is greater than 1.

[0264] 42. The system according to Clause 34, wherein the average wavelength error is based on the average of the wavelength error and a plurality of wavelength errors over a plurality of pulses.

[0265] 43. The system according to Clause 34, wherein:

[0266] The system is configured to perform multifocal imaging operations, and

[0267] The controller is also configured to operate the light source in a dual-color mode in the following manner:

[0268] A first laser radiation beam of a first wavelength is generated using the first laser chamber module;

[0269] A second laser radiation beam of a second wavelength is generated using the second laser chamber module; and

[0270] The first laser radiation and the second laser radiation are combined along a common output beam path using a beam combiner.

[0271] The determination of the wavelength error of the beam generated by the light source includes determining the center wavelength error of the first laser radiation beam.

[0272] 44. A system for controlling the center wavelength of multifocal imaging operation, comprising:

[0273] An actuator is configured to control the movement of the prism; and

[0274] The controller is configured as follows:

[0275] Combine the jitter waveform with the offset value used to move the actuator;

[0276] Generate inter-pulse wavelengths based on the jitter waveform and the offset value;

[0277] A rolling average of the center wavelength is generated based on the inter-pulse wavelengths of multiple pulses;

[0278] Estimate the drift rate to predict the center wavelength of future pulses; and

[0279] The offset value is updated based on the estimated drift rate.

[0280] 45. The system described in Clause 44, wherein the offset value is based on a direct current (DC) voltage.

[0281] 46. ​​The system according to Clause 45, wherein the initial value of the DC voltage is zero volts.

[0282] 47. The system according to Clause 44, wherein:

[0283] The offset value includes a first offset value, and

[0284] The estimation of the drift rate includes estimating the drift rate based on the rolling average value of the center wavelength, the first offset value, and the second offset value of the second actuator that moves the second prism.

[0285] 48. The system according to Clause 47, wherein, in order to estimate the drift rate, the controller is further configured to use a Kalman filter framework to estimate the accumulated center wavelength drift rate.

[0286] 49. The system according to Clause 48, wherein, in order to estimate the drift rate, the controller is further configured to predict the center wavelength N pulses prior to the current pulse.

[0287] 50. The system according to Clause 49, wherein, in order to estimate the drift rate, the controller is further configured to convert the Kalman filter frame into a Kalman predictor to predict the center wavelength N pulses prior to the current pulse.

[0288] 51. The system according to Clause 44, wherein the inter-pulse wavelength of the plurality of pulses includes the wavelength of the current pulse.

[0289] 52. The system according to Clause 44, wherein, in order to update the offset value, the controller is further configured to update the offset value based on the rolling average of the center wavelength at the end of the burst.

[0290] The breadth and scope of the embodiments should not be limited by any of the exemplary embodiments described above, but should be defined only by the appended claims and their equivalents.

Claims

1. A method for controlling the center wavelength of an imaging operation, comprising: Estimate center wavelength error; Based on the estimated center wavelength error, a first actuation amount of the first actuator controlling the movement of the first prism is determined; Based on the first actuation amount, the first actuator is actuated; Determine whether the first prism is off-center; In response to determining that the first prism is off-center, a second actuation amount of the first actuator is determined and a third actuation amount of the second actuator for controlling the movement of the second prism is determined; as well as The first actuator and the second actuator are actuated based on the second actuation amount and the third actuation amount, respectively.

2. The method of claim 1, wherein estimating the center wavelength error comprises: Calculate the first average value of the center wavelength at odd-numbered bursts and the second average value of the center wavelength at even-numbered bursts; as well as Determine the average of the first average and the second average, wherein the center wavelength error is based on the average of the first average and the second average.

3. The method of claim 1, wherein determining the first actuation amount comprises: Determine the difference between the target center wavelength and the estimated center wavelength; as well as The first actuation amount is determined based on the difference between the target center wavelength and the estimated center wavelength.

4. The method of claim 3, wherein determining the difference between the target center wavelength and the estimated center wavelength comprises determining the difference using a digital filter.

5. The method of claim 1, wherein determining the third actuation amount of the second actuator is based on the position of the first prism after the first actuator is actuated based on the second actuation amount.

6. The method of claim 5, wherein determining the third actuation amount further comprises: The third actuation amount is determined to reduce the difference between the target center wavelength and the estimated wavelength.

7. The method of claim 1, wherein the imaging operation includes a multifocal imaging operation, and the method further includes operating the light source in a dual-color mode, wherein operating the light source in the dual-color mode includes: Using the first laser chamber module, a first laser radiation beam of the first wavelength is generated; Using the second laser chamber module, a second laser radiation beam of the second wavelength is generated; as well as Using a beam combiner, the first laser radiation and the second laser radiation are combined along a common output beam path. The estimation of center wavelength error includes estimating the center wavelength error of the first laser radiation beam.

8. A system comprising: The first actuator is configured to control the movement of the first prism; The second actuator is configured to control the movement of the second prism; as well as The controller is configured as follows: Estimate center wavelength error; Based on the estimated center wavelength error, the first actuation amount of the first actuator is determined; This causes the first actuator to be actuated based on the first actuation amount; Determine whether the first prism is off-center; In response to determining that the first prism is off-center, a second actuation amount of the first actuator is determined and a third actuation amount of the second actuator is determined; as well as This causes the first actuator and the second actuator to be actuated based on the second actuation amount and the third actuation amount, respectively.

9. The system of claim 8, wherein, in order to estimate the center wavelength error, the controller is further configured to: Calculate the first average value of the center wavelength at odd-numbered bursts and the second average value of the center wavelength at even-numbered bursts; and Determine the average of the first average and the second average, wherein the center wavelength error is based on the average of the first average and the second average.

10. The system of claim 8, wherein, in order to determine the first actuation amount, the controller is further configured to: Determine the difference between the target center wavelength and the estimated center wavelength; and The first actuation amount is determined based on the difference between the target center wavelength and the estimated center wavelength.

11. The system of claim 10, wherein, in order to determine the difference between the target center wavelength and the estimated center wavelength, the controller is further configured to use a digital filter to determine the difference.

12. The system of claim 8, wherein the third actuation amount of the second actuator is based on the position of the first prism after the first actuator is actuated based on the second actuation amount.

13. The system of claim 12, wherein, in order to determine the third actuation amount, the controller is further configured to: determine the third actuation amount to reduce the difference between the target center wavelength and the estimated wavelength.

14. The system according to claim 8, wherein: The system also includes a light source that operates in a dual-color mode. The controller is also configured to operate the light source in the dual-color mode in the following manner: Using the first laser chamber module, a first laser radiation beam of the first wavelength is generated; Using the second laser chamber module, a second laser radiation beam of the second wavelength is generated; and Using a beam combiner, the first laser radiation and the second laser radiation are combined along a common output beam path. The estimated center wavelength error includes the estimated center wavelength error of the first laser radiation beam.

Images