Apparatus and method for modulating the wavelength of a light source

Abstract

To provide an apparatus and method for modulating a light source wavelength.SOLUTION: A laser system comprises: an actuator having a first state, in which the actuator causes the laser system to generate a first burst of one or more pulses of laser radiation having a first wavelength, and a second state, in which the actuator causes the laser system to generate a second burst of one or more pulses of laser radiation having a second wavelength different from the first wavelength; and an actuator controller arranged to supply a signal to the actuator to cause the actuator to assume a third state between bursts which is intermediate between the first state and the second state.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] (Cross-reference of related applications)

[0001] This application claims priority to U.S. Patent Application No. 62 / 847,464, filed on 14 May 2019, entitled "APPARATUS FOR AND METHOD OF MODULATING A LIGHT SOURCE WAVELENGTH," which is included in its entirety by reference.

[0002]

[0002] This disclosure relates to a system and method for generating multiple laser beams, for example, used in a lithography apparatus. [Background technology]

[0003]

[0003] A lithography apparatus applies a desired pattern to a substrate, such as a semiconductor wafer, usually to a target area of ​​the substrate. Alternatively, a patterning device, also called a mask or reticle, can be used to generate the circuit pattern to be formed on individual layers of the wafer. The transfer of the pattern is usually performed by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Generally, a single substrate contains adjacent target areas to which patterns are sequentially applied.

[0004]

[0004] A lithography apparatus includes a so-called stepper, which illuminates each target portion by exposing the entire pattern to the target portion in a single pass, and a so-called scanner, which illuminates each target portion by scanning the pattern with a radiation beam in a given direction ("scanning direction") while synchronously scanning the substrate in a given direction ("scanning direction") parallel or counter-parallel to that direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. In this specification, for simplicity, both the stepper and the scanner are simply referred to as scanners.

[0005]

[0005] The light source used to illuminate the pattern and project it onto the substrate can be one of a number of configurations. Deep ultraviolet excimer lasers commonly used in lithography systems include krypton fluoride (KrF) lasers with a wavelength of 248 nm and argon fluoride (ArF) lasers with a wavelength of 193 nm. Generally, excimer lasers are designed to operate with specific gas mixtures, and therefore changing the wavelength can be complex. In particular, changing the central wavelength with each discharge ("shot-to-shot") is difficult.

[0006]

[0006] However, there are cases where it is desirable to have the ability to change the wavelength. For example, in 3D NAND layers of memory (i.e., memory with a structure similar to NAND (not AND) gates stacked on top of each other). Transitioning from 2D to 3D NAND architecture requires significant changes to the manufacturing process. The problems in 3D NAND manufacturing are mainly caused by etching and deposition processes at extreme aspect ratios (ratio of hole diameter to depth). Generating complex 3D structures with extremely high-aspect-ratio (HAR) features is complex, requires extremely high precision, and ultimately requires process uniformity and repeatability to achieve large scale. Furthermore, as the height of multilayer stacks increases, the difficulty of obtaining consistent etching and deposition results at the top and bottom of the stack increases, such as in memory arrays.

[0007]

[0007] These considerations necessitate increasing the depth of focus. The depth of focus (DOF) in lithography is given by the relationship DOF = ±m²λ / (NA) 2 This is determined by the following formula: where λ is the wavelength of the illumination light, NA is the numerical aperture, and m1 and m2 are actual factors that depend on the resist process. In 3D NAND lithography, a large depth of field is required, so two or more exposure passes may be performed on the wafer, with different laser wavelengths used in each pass.

[0008]

[0008] Furthermore, since the material constituting the lens that focuses the laser radiation is dispersive, different wavelengths are focused at different depths. This is another reason why it is desirable to have the ability to change the wavelength.

[0009]

[0009] A DUV light source includes a system for controlling the wavelength of DUV light. Typically, such wavelength control systems include a feedback compensator and a feedforward compensator to promote wavelength stability. Characteristically, the target or reference wavelength, i.e., the wavelength required by the wavelength control system, is not expected to change rapidly during laser operation. Therefore, the controller is primarily involved in the rejection of transient disturbances. The feedforward compensator also compensates for required changes in the wavelength target, i.e., wavelength change events that are not expected to occur frequently. If such an event occurs and, for example, a wavelength setpoint change of 600 fm is achieved, the system must typically allow a settling time of the order of about 100 ms for the system to settle stably at the new wavelength. Typically, this exceeds the time between pulses, so in applications where the target wavelength setpoint is changed by about 500 fm between pulses, such a control system cannot provide the desired wavelength tracking performance.

[0010]

[0010] As a specific example, in an application where DUV light is generated at two different wavelengths, the reference wavelength has two set points during exposure: a first set point for the first wavelength and a second set point for the second wavelength. Therefore, the reference wavelength is modulated between these two set points. Every wavelength target change requires a predetermined settling time, which limits the rate at which the reference wavelength can be modulated. Furthermore, the wavelength is essentially uncontrolled during the transient settling period, which imposes constraints on the acceptable waiting time between wavelength target changes.

[0011]

[0011] It is desirable to have the ability to change the reference wavelength between pulses, that is, with each pulse. This ability can be achieved by shortening the transient settling period. It is also desirable to shorten or eliminate the waiting time between changes in the reference wavelength. [Overview of the project]

[0012]

[0012] The following provides a simplified overview of one or more embodiments in order to provide a basic understanding of such embodiments. This overview is not intended to provide a broad overview of all conceivable embodiments, nor is it intended to identify important or essential elements of all embodiments, nor is it intended to define the scope of any or all embodiments. Its sole purpose is to provide a simplified version of some concepts of one or more embodiments as a prelude to the more detailed descriptions that will be presented later.

[0013]

[0013] According to one embodiment, in order to shorten the transient period caused by changing the reference wavelength, the actuator is prepared by pre-positioning the actuator between bursts to achieve the next new target wavelength between bursts.

[0014]

[0014] In another embodiment, wavelength control is achieved in the line narrowing module by using an actuator such as a piezo actuator. Based on a dynamic model of the actuator, an optimal control waveform is calculated to operate the actuator so as to minimize the difference between the actual wavelength and the wavelength target. The optimal control waveform can be calculated using one of several methods. For example, the optimal control waveform may be calculated using quadratic programming with constraints and / or dynamic programming that generates an optimal control signal for a given wavelength target. A pre-populated lookup table can be used that includes optimal control parameters for at least some of the various repetition rates that can operate the radiation source.

[0015]

[0015] As another example, the optimal control waveform can be determined using model inversion feedforward control. This method constructs a digital filter using an actuator dynamic model to invert the actuator dynamics. By passing the waveform of the desired actuator trajectory through this filter, the optimal control waveform can be generated in real time to achieve steady-state error-free tracking. Here and elsewhere, the term "trajectory" is used to describe the characteristics of the actuator's movement, including acceleration.

[0016]

[0016] As another example, the optimal solution for achieving two distinct wavelengths is achieved by using a learning algorithm and performing error convergence through several learning iterations. The proposed method can achieve two distinct wavelengths separated by 1000 fm with a separation error of less than 20 fm.

[0017] According to another aspect, the optimal control waveform can be supplied to the actuator at a very high rate using a field programmable gate array (FPGA).

[0018]

[0018] Other features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, will be described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are described herein for illustrative purposes only. Those skilled in the art will readily conceive of further embodiments based on the teachings contained herein.

Brief Description of the Drawings

[0019]

[0019] The accompanying drawings incorporated herein and forming a part of this specification illustrate, by way of example and not limitation, methods and systems of embodiments of the present invention. The drawings, in conjunction with the detailed description, also serve to explain the principles of the methods and systems presented herein and to enable one skilled in the art to make and use these methods and systems. In the drawings, like reference numerals represent identical or functionally similar elements.

[0020] [Figure 1]

[0020] A schematic diagram that is not to scale showing the overall broad concept of a photolithography system according to one aspect of the disclosed subject matter. [Figure 2]

[0021] A schematic diagram that is not to scale showing the overall broad concept of an illumination system according to one aspect of the disclosed subject matter. [Figure 3]

[0022] A functional block diagram of a two-chamber laser system according to one aspect of an embodiment. [Figure 4]

[0023] A diagram of the relative discharge timing that can occur in two laser chambers according to one aspect of an embodiment. [Figure 5] ​A diagram of another relative discharge timing that can occur in two laser chambers according to one aspect of the embodiment.

[0021]

[0025] Other features and advantages of the present invention and the structure and operation of various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are described herein for illustrative purposes only. Those skilled in the art will readily conceive of additional embodiments based on the teachings contained herein.

MODE FOR CARRYING OUT THE INVENTION

[0022]

[0026] This specification discloses one or more embodiments incorporating features of the present invention. The one or more disclosed embodiments merely exemplify the present invention. The scope of the present invention is not limited to the one or more disclosed embodiments. The present invention is defined by the claims appended hereto. 【0​​​​​​​Before describing embodiments in detail, it is beneficial to show exemplary environments in which embodiments of the present invention can be carried out. Referring to Figure 1, the photolithography system 100 includes an illumination system 105. As will be described more fully below, the illumination system 105 includes a light source that generates a pulsed light beam 110 and directs it to a photolithography exposure apparatus or scanner 115. The photolithography exposure apparatus or scanner 115 patterns microelectronic features on a wafer 120. The wafer 120 is placed on a wafer table 125. The wafer table 125 is constructed to hold the wafer 120 and is connected to a positioner configured to precisely position the wafer 120 according to specific parameters.

[0025]

[0029] The photolithography system 100 uses a light beam 110 having a wavelength in the deep ultraviolet (DUV) range, such as 248 nanometers (nm) or 193 nm. The minimum size of microelectronic features that can be patterned on the wafer 120 depends on the wavelength of the light beam 110, with shorter wavelengths allowing for smaller minimum feature sizes. When the wavelength of the light beam 110 is 248 nm or 193 nm, the minimum size of microelectronic features may be, for example, 50 nm or less. The bandwidth of the light beam 110 may be the actual instantaneous bandwidth of the optical spectrum (or emission spectrum) containing information about how the light energy of the light beam 110 is distributed across various wavelengths. The scanner 115 includes an optical mechanism having, for example, one or more condenser lenses, a mask, and an objective system mechanism. The mask is movable along one or more directions, for example, along the optical axis of the light beam 110 or in a plane perpendicular to the optical axis. The objective system mechanism includes a projection lens that enables image transfer from the mask to the photoresist on the wafer 120. The illumination system 105 adjusts the angular range of the light beam 110 incident on the mask. The illumination system 105 also homogenizes (makes uniform) the intensity distribution of the light beam 110 in the mask.

[0026]

[0030] The scanner 115 may include, among several features, a lithography controller 130, an air conditioning device, and a power supply for various electrical components. The lithography controller 130 controls how layers are printed on the wafer 120. The lithography controller 130 includes a memory that stores information such as a process recipe. The process program or recipe determines the exposure length for the wafer 120, for example, based on the mask used and other factors that affect exposure. During lithography, multiple pulses of the light beam 110 illuminate the same area of ​​the wafer 120 to form an illumination dose.

[0027]

[0031] Furthermore, the photolithography system 100 preferably also includes a control system 135. Generally, the control system 135 includes one or more of the following: digital electronic circuits, computer hardware, firmware, and software. The control system 135 also includes memory, which may be read-only memory and / or random-access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, but examples include semiconductor memory devices such as EPROMs, EEPROMs, and flash memory devices, magnetic disks such as internal hard disks and removable disks, magneto-optical disks, and CD-ROM disks.

[0028]

[0032] The control system 135 may also include one or more input devices (such as a keyboard, touchscreen, microphone, mouse, or handheld input device) and one or more output devices (such as a speaker or monitor). Furthermore, the control system 135 may include one or more programmable processors and one or more computer program products tangibly embodied in a machine-readable storage device for execution by the one or more programmable processors. Each of the one or more programmable processors can execute a program of instructions and perform a desired function by performing actions on input data and generating appropriate outputs. Generally, the processors receive instructions and data from memory. Any of the above can be supplemented by or incorporated into a specially designed ASIC (Application-Specific Integrated Circuit). The control system 135 can be centralized or distributed partially or entirely throughout the photolithography system 100.

[0029]

[0033] Referring to Figure 2, the exemplary illumination system 105 is a pulsed laser source that generates a pulsed laser beam as an optical beam 110. Figure 2 illustrates a gas discharge laser system in an exemplary block diagram according to an embodiment of a particular aspect of the subject matter disclosed. The gas discharge laser system may include, for example, a solid or gas discharge seed laser system 140, an amplification stage such as a power ring amplifier ("PRA") stage 145, a relay optical system 150, and a laser system output subsystem 160. The seed system 140 may include, for example, a master oscillator ("MO") chamber 165.

[0030]

[0034] The seed laser system 140 may also include a master oscillator output coupler ("MOOC") 175. The MOOC 175 may include a partial reflection mirror and, together with a reflection grating (not shown) in a line narrowing module ("LNM") 170, form an oscillator cavity. Within this cavity, the seed laser 140 oscillates to form seed laser output pulses, i.e., the master oscillator ("MO"). The system may also include a line-center analysis module ("LAM") 180. The LAM 180 may include an etalon spectrometer for fine wavelength measurements and a coarse-resolution grating spectrometer. The MO wavefront engineering box ("WEB:wavefront engineering box") 185 functions to redirect the output of the MO seed laser system 140 to the amplification stage 145, which may include, for example, beam expansion by a multiprism beam expander (not shown) and coherence busting in the form of, for example, an optical delay path (not shown).

[0031]

[0035] The amplification stage 145 may include, for example, a PRA laser oscillation chamber 200. This can be an oscillator formed by a seed beam incidence and output coupling optical system (not shown), which may be incorporated into, for example, a PRA web 210, and can be redirected backward through a gain medium in the beam chamber 200 by a beam inverter 220. The PRA web 210 may incorporate a partial reflection input / output coupler (not shown), a maximum reflection mirror for the nominal operating wavelength (e.g., about 193 nm in an ArF system), and one or more prisms.

[0032]

[0036] A bandwidth analysis module ("BAM") 230 at the output of the amplification stage 145 receives the output laser beam pulse from the amplification stage and can select a portion of the beam for metronome purposes, such as measuring the output bandwidth and pulse energy. The laser output beam pulse then passes through an optical pulse stretcher ("OPuS") 240 and a combined autoshutter metronome module ("CASMM") 250, which may be located at the position of the pulse energy meter. One purpose of the OPuS 240 is, for example, to convert a single output laser pulse into a pulse train. Secondary pulses generated from the initial single output pulse can be delayed relative to each other. By distributing the initial laser pulse energy within the secondary pulse train, the effective pulse length of the laser can be extended while simultaneously reducing the peak pulse intensity. Thus, the OPuS 240 can receive the laser beam from the PRA WEB 210 via the BAM 230 and guide the output of the OPuS 240 to the CASMM 250. Other appropriate configurations may be used in other embodiments.

[0033]

[0037] The PRA laser oscillation chambers 200 and MO165 are configured as chambers, within which a discharge between electrodes induces a laser oscillation gas discharge in the laser oscillation gas, generating a population inversion of high-energy molecules, such as Ar, Kr, and / or Xe, thereby producing radiation with a relatively broad bandwidth. This radiation can be line-narrowed to a relatively very narrow bandwidth and center wavelength selected in the line-narrowing module ("LNM") 170. This is known in the art.

[0034]

[0038] Typically, adjustments are made in LNMs. A common technique used for line narrowing and laser adjustment is to create a window at the rear of the laser discharge cavity through which a portion of the laser beam passes when it enters the LNM. Here, a portion of the beam is expanded by a prism beam expander and guided to a grating, which reflects a narrow selection of the laser's broad spectrum back into the discharge chamber, where it is amplified. Laser adjustment is typically performed by changing the angle at which the beam illuminates the grating, for example, using an actuator such as a piezo actuator.

[0035]

[0039] As described above, in some applications, it is beneficial to be able to generate bursts of one or more pulses having a single wavelength, and then switch to generating bursts of one or more pulses having different wavelengths. However, achieving this between pulses is difficult. This is because the settling time, i.e., the amount of time required for the system to stabilize after a wavelength change, is typically longer than the interval between pulses. In one embodiment, the transient settling time caused by the change in reference wavelength is shortened by preparing the actuators in advance between bursts to achieve the next new target wavelength between bursts.

[0036]

[0040] In another embodiment, a dynamic model of the actuator is used to calculate the optimal control waveform for operating the actuator in such a way as to minimize the difference between the actual wavelength and the wavelength target.

[0037]

[0041] The optimal control waveform can be calculated using one of several methods. For example, the optimal control waveform can be calculated using dynamic programming. This method is well-suited to handling complex models involving nonlinear dynamics. When employing actuator models with strong nonlinear dynamics, dynamic programming can be used to generate the optimal control signal for a given wavelength target. However, dynamic programming has the challenge of requiring significant computational resources, which may be impossible to implement in real time. To overcome this, a prepopulated lookup table or a preprogrammed data storage device such as a field-programmable gate array (FPGA) can be used, which contains the optimal control parameters for at least some of the various repetition rates that can operate the radiation source.

[0038]

[0042] As another example, the optimal control waveform can be determined using model-inverted feedforward control. This method constructs a digital filter using an actuator dynamic model to invert the actuator dynamics. By passing the desired waveform of the desired actuator trajectory through this filter, the optimal control waveform can be generated in real time, achieving tracking without steady-state error.

[0039]

[0043] As another example, an optimal solution for stably achieving two distinct wavelengths is achieved by using a learning algorithm and ensuring error convergence through several learning iterations. Embodiments of the systems and methods disclosed herein may be able to achieve two distinct wavelengths separated by 1000 fm with a separation error of less than 20 fm.

[0040]

[0044] In another embodiment, the optimal control waveform can be supplied to the actuator at an extremely high rate using an FPGA.

[0041]

[0045] The control system may include a combination of feedforward control and iterative learning control (ILC). As shown in Figure 3, the ILC module 300 calculates the feedforward control signal A offline using wavelength measurements from the streaming data acquisition unit 330 and an ILC update law. This is described below. The bandwidth wavelength control module (BWCM) 340 updates predefined data in a data storage unit such as an FPGA contained within the BWCM 340 using the feedforward control signal A. The BWCM 340 then operates the PZT 350 at, for example, 60 kHz when the laser is pulsed. The wavelength of the laser emission is measured by the line-center (center wavelength) analysis module (LAM) 360 and the fire control platform or processor (FCP) 370, and the wavelength measurements are collected by the data acquisition unit 330 at 6 kHz.

[0042]

[0046] It will be acknowledged that the system shown in Figure 3 can be configured to encompass multiple frequency regimes. The area within the dashed box indicates a process that can essentially be performed offline. The PZT350 can be driven at approximately 60 kHz. Wavelength data can be acquired at approximately 6 kHz.

[0043]

[0047] To take into account the constraints on changes in the PZT voltage, constrained quadratic programming can be used to help find the optimal feedforward signal within the feasible operating region. Quadratic programming is a technique for finding the optimal solution for a given quadratic cost function with mathematical constraints.

[0044]

[0048] A standard QP solver can solve the problems associated with the following structure.

[0045]

number

[0046] Here, X is a design parameter that can be freely chosen, but it must satisfy LX ≤ b. In other words, the QP solver finds the optimal X that minimizes the cost function within the feasible region defined by LX ≤ b.

[0047]

[0049] The objective in the application examples described here is to find a feedforward control that satisfies actuator constraints while minimizing the error between the actuator position and the desired control waveform. PZT dynamics can be represented in the following state-space form. x(k+1)=Ax(k)+Bu(k) y(k+1)=Cx(k+1) Here, A, B, and C are the state matrix, input matrix, and output matrix describing the PZT dynamics, respectively, x is the state vector, u is the input vector, and y is the output from the PZT.

[0048]

[0050] By substituting the dynamic model above, the initial cost function can be rewritten as follows:

[0049]

number

[0050]

[0051] This fits the following standard QP format. H=P T QP f = -P T QR X=U L=D b=l P describes the PZT input / output dynamics, Q is the weight function, R represents the desired control waveform, D represents the actuator constraint, and l is the threshold of the actuator constraint.

[0051]

[0052] In another embodiment, ILC control can be described by the following equation. Uk = U k-1 + LE k-1 Here, U k is the feed-forward control signal used in the k-th iteration, L is the learning function that determines the convergence of the ILC algorithm, and E k is the error in the k-th iteration.

[0052]

[0053] The stability and convergence characteristics of ILC control can be derived as follows by combining the ILC control method and the dynamic model of the system. E k = (I - PL)E k-1

[0053]

[0054] Here, P is the matrix that describes the relationship between the input and output of the system, and I is the identity matrix. Stability is guaranteed when the absolute value of all eigenvalues of (I - PL) is less than 1. Also, the convergence rate is obtained by the matrix (I - PL). When (I - PL) = 0, the error converges to zero after one iteration.

[0054]

[0055] Figure 4 is a flowchart showing a method for controlling a radiation source according to an aspect of the embodiment. In step S100, the burst preceding the pulse ends. In step S110, the actuator is prepared by pre-positioning it at a position between the position where it must be placed to generate a pulse having a first frequency and the position where it must be placed to generate a pulse having a second frequency. In step S120, an optimal control waveform is calculated using one or more of the techniques described above. In step S130, it is determined whether a new burst has been triggered. If "yes", that is, if a new burst has been triggered, then in step S140, parameters for operating at the required repetition rate and frequency are transmitted to the radiation source, for example, using an FPGA. In step S150, it is determined whether the current burst has ended. If the current burst has not ended, step S140 is repeated. When the burst has ended, the process ends in step S160.

[0055]

[0056] Figure 5 shows the method performed by the ILC to calculate the update method using the initial QP feedforward control signal. In step S210, the initial feedforward control signal is generated using a quadratic design. In step S220, the laser is fired using the feedforward control signal. In step S230, it is determined whether the error in the feedforward signal has converged. If the error has not converged, the control signal is updated using iterative learning in step S250. Then, the laser is fired in step S220 using the new control signal. If the error has converged, the process ends in step S240.

[0056]

[0057] It will be acknowledged that the section "Modes for Carrying Out the Invention" is intended to be used to interpret the claims, rather than the sections "Summary of the Invention" and "Abstract." The sections "Summary of the Invention" and "Abstract" may describe one or more exemplary embodiments of the invention as envisioned by the inventor, but not all of those exemplary embodiments, and are therefore not intended to limit the invention and the attached claims in any sense.

[0057]

[0058] The present invention has been described above using function building blocks that illustrate examples of specified functions and their relationships. The boundaries of these function building blocks are arbitrarily defined in this specification for the sake of clarity. Alternative boundaries may also be defined, as long as the specified functions and their relationships are properly performed.

[0058]

[0059] The above-mentioned descriptions of specific embodiments fully illustrate the overall nature of the invention, and by applying knowledge in the art, such specific embodiments can be readily modified and / or adapted for various uses without excessive experimentation and without departing from the overall concept of the invention. Accordingly, based on the teachings and guidance presented herein, such adaptations and modifications are intended to be within the meaning and scope of equivalents of the disclosed embodiments. Since the expressions or terms herein are for illustrative purposes only and not limitation, it will be understood that the expressions or terms herein should be interpreted in light of the teachings and guidance by those skilled in the art.

[0059]

[0060] Other aspects of the present invention are described in the following numbered clauses. 1. A laser system, An actuator having a first state in which a first burst of one or more pulses of laser radiation having a first wavelength is generated in the laser system, and a second state in which a second burst of one or more pulses of laser radiation having a second wavelength different from the first wavelength is generated in the laser system, An actuator controller configured to supply a signal to the actuator in order to move the actuator to a third state between the first and second states, which is a burst state, A laser system equipped with [the following features]. 2. The laser system as described in Clause 1, wherein the first state is the first position, the second state is the second position, and the third state is the third position between the first and second positions. 3. A laser system, An actuator having a first state in which a first burst of one or more pulses of laser radiation having a first wavelength is generated in the laser system, and a second state in which a second burst of one or more pulses of laser radiation having a second wavelength different from the first wavelength is generated in the laser system, An actuator controller configured to supply a signal to an actuator in order to transition the actuator from a first state to a second state, comprising a module configured to calculate an optimal control waveform for the signal that causes the actuator to transition from the first state to the second state, and transitioning the actuator along a trajectory from the first state to the second state under the control of the optimal control waveform, A laser system equipped with [the following features]. 4. The module is adapted to calculate the optimal control waveform using a constrained quadratic programming method, as described in Clause 3 of the laser system. 5. The module is adapted to calculate the optimal control waveform using dynamic programming, as described in Clause 3 of the laser system. 6. The module is adapted to calculate the optimal control waveform using model inverted feedforward control, as described in Clause 3 of the laser system. 7. The module is adapted to calculate the optimal control waveform using iterative learning control, as described in Clause 3 of the laser system. 8. The laser system according to any one of clauses 3 to 7, further comprising means for storing at least one optimal control parameter for each of a plurality of repetition rates. 9. The laser system according to Clause 8, wherein means for storing at least one optimal control parameter for each of a plurality of repetition rates include a prepopulated lookup table. 10. The laser system according to Clause 8, wherein means for storing at least one optimal control parameter for each of a plurality of repetition rates include a field-programmable gate array. 11. A method for controlling a laser system, The steps of placing an actuator in a first state that causes a first burst of one or more pulses of laser radiation having a first wavelength to be generated in the laser system, The process includes the step of placing an actuator in a second state that causes the laser system to generate a second burst of one or more pulses of laser radiation having a second wavelength different from a first wavelength, Furthermore, the method includes a third step of placing the actuator in a third state, which is an intermediate state between the first and second states, between the step of placing the actuator in a first state and the step of placing the actuator in a second state. 12. A method for controlling the laser system described in Clause 11, wherein the first state is the first position, the second state is the second position, and the third state is the third position between the first and second positions. 13. A method for controlling a laser system, The steps of placing an actuator in a first state that causes a first burst of one or more pulses of laser radiation having a first wavelength to be generated in the laser system, The process includes the step of placing an actuator in a second state that causes the laser system to generate a second burst of one or more pulses of laser radiation having a second wavelength different from a first wavelength, A method for placing an actuator into a second state, comprising the steps of calculating an optimal control waveform for the actuator to transition from a first state to a second state, and transitioning the actuator from the first state to the second state along a trajectory under the control of the optimal control waveform. 14. A method for controlling the laser system described in Clause 13, which includes using a constrained quadratic programming to calculate the optimal control waveform for the actuator to transition from a first state to a second state. 15. A method for controlling the laser system described in Clause 13, which includes using dynamic programming to calculate the optimal control waveform for the actuator to transition from a first state to a second state. 16. A method for controlling the laser system described in Clause 13, comprising using model inverted feedforward control to calculate the optimal control waveform for the actuator to transition from a first state to a second state. 17. A method for controlling the laser system described in Clause 13, comprising using iterative learning control to calculate the optimal control waveform for the actuator to transition from a first state to a second state. 18. A method for controlling a laser system according to any one of clauses 13 to 17, comprising calculating an optimal control waveform for the actuator to transition from a first state to a second state, and including means for storing at least one optimal control parameter for each of a plurality of repetition rates. 19. A method for controlling the laser system described in Clause 18, wherein storing at least one optimal control parameter for each of a plurality of repetition rates is performed using a prepopulated lookup table. 20. A method for controlling the laser system described in Clause 18, comprising using a field-programmable gate array to store at least one optimal control parameter for each of a plurality of repetition rates. 21. A method for controlling a laser system, The steps of placing an actuator in a first state that causes a first burst of one or more pulses of laser radiation having a first wavelength to be generated in the laser system, The process includes the step of placing an actuator in a second state that causes the laser system to generate a second burst of one or more pulses of laser radiation having a second wavelength different from a first wavelength, Furthermore, between the step of placing the actuator in the first state and the step of placing the actuator in the second state, there is a third step of placing the actuator in a third state which is an intermediate state between the first and second states. A method comprising the step of placing an actuator in a second state, which includes calculating an optimal control waveform for transitioning the actuator from a first state to a second state along an optimal trajectory.

Claims

1. It is a source of radiation, Discharge chamber and A line narrowing module (LNM) coupled to the discharge chamber, An actuator within the LNM having a first state corresponding to a first wavelength of a first burst of one or more pulses, and a second state corresponding to a second wavelength of a second burst of one or more pulses, wherein the second wavelength is different from the first wavelength, An actuator controller coupled to the actuator, wherein the actuator controller is configured to supply a feedforward control signal to transition the actuator from a first state to a second state, and to update the feedforward control signal until the error converges, A radiation source equipped with [the necessary components].

2. The radiation source according to claim 1, wherein the actuator controller is coupled to a data acquisition unit and configured to receive wavelength measurements from the data acquisition unit, and the actuator controller includes an iterative learning control module configured to calculate the feedforward control signal using the wavelength measurements and an iterative learning control update method.

3. The radiation source according to claim 2, wherein the iterative learning control module calculates an initial feedforward control signal using a constrained quadratic programming.

4. The radiation source according to claim 1, wherein the actuator controller includes a prepopulated lookup table configured to store control parameters for at least some of the different repetition rates in which the radiation source operates.

5. The radiation source according to claim 1, wherein the feedforward control signal is not calculated in real time.

6. The radiation source according to claim 1, wherein the actuator controller includes a pre-programmed field-programmable gate array (FPGA) configured to store control parameters for a plurality of repetition rates in which the radiation source operates.

7. The radiation source according to claim 1, wherein the feedforward control signal is configured to cause the actuator to transition from a first state to a second state with each pulse.

8. A central wavelength analysis module coupled to the actuator, A launch control platform or processor coupled to the central wavelength analysis module and the data acquisition unit, The radiation source according to claim 1, further comprising a bandwidth control module coupled to the actuator.

9. A radiation source, Discharge chamber and A line narrowing module (LNM) coupled to the discharge chamber, An actuator within the LNM having a first state corresponding to a first wavelength of a first burst of one or more pulses, and a second state corresponding to a second wavelength of a second burst of one or more pulses, An actuator controller coupled to the actuator and a data acquisition unit, configured to receive wavelength measurements from the data acquisition unit and to supply a feedforward control signal for transitioning the actuator from a first state to a second state, A central wavelength analysis module coupled to the actuator, A launch control platform or processor coupled to the central wavelength analysis module and the data acquisition unit, A bandwidth control module coupled to the actuator, Equipped with, The actuator controller is configured to supply the feedforward control signal at a frequency higher than the reception of the wavelength measurement, and is a radiation source.

10. A method for achieving two distinct wavelengths of a radiation source, Setting an actuator to a first state, wherein in the first state, the actuator causes the radiation source to generate a first burst of one or more pulses having a first wavelength. The calculation of a feedforward control signal for the actuator to transition from the first state to the second state, wherein the calculation of the feedforward control signal includes updating the feedforward control signal until the error converges. A method comprising setting the actuator to a second state, wherein in the second state, the actuator causes the radiation source to generate a second burst of one or more pulses having a second wavelength different from the first wavelength.

11. The method according to claim 10, wherein updating the feedforward control signal includes calculating the feedforward control signal using wavelength measurement and an iterative learning control update method.

12. The method according to claim 10, wherein the calculation of the feedforward control signal is performed offline.

13. The method according to claim 10, further comprising storing at least one control parameter for each of a plurality of repetition rates in which the radiation source operates.

14. The method according to claim 13, wherein storing the at least one control parameter includes using a prepopulated lookup table or a preprogrammed field-programmable gate array (FPGA).

15. The method according to claim 13, wherein calculating the feedforward control signal includes calculating an initial feedforward control signal using a constrained quadratic programming.

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