Apparatus and method for controlling spectral separation

Abstract

An apparatus and method for rapidly achieving a target peak wavelength separation in a system for producing laser radiation having two or more wavelengths (colors) in which one or more actuators control the wavelengths in response to an applied waveform, wherein the waveform characteristics are determined using a model-based control system.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 63 / 395,368, filed August 5, 2022, the entire contents of which are incorporated herein by reference.

[0002] FIELD OF THE DISCLOSURE

[0002] This disclosure relates to laser systems, such as excimer lasers, that generate light, and to systems and methods for controlling the center wavelength of such lasers. [Background technology]

[0003] A lithographic apparatus applies a desired pattern onto a substrate, such as a wafer made of semiconductor material, typically onto a target portion of the substrate. A patterning device, which may be referred to as a mask or reticle, can be used to generate the circuit pattern formed on an individual layer of the wafer. Transfer of the pattern is typically achieved by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain adjacent target portions that are successively patterned.

[0004] Lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the "scan" direction) while simultaneously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0005]

[0005] The light source used to illuminate the pattern and project this pattern onto the substrate can have any one of a number of configurations. Deep ultraviolet (DUV) 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.

[0006]

[0006] Lithography apparatus can operate at a single wavelength in what may be called a monochromatic mode. However, for some applications, it is desirable to have the ability to change wavelength, i.e., operate in a polychromatic mode, to control the depth of focus (DoF). For example, in the fabrication of 3D NAND memory, structures similar to NAND gates are stacked on top of each other, extending fabrication in three dimensions orthogonal to the xy plane of the 2D substrate. The transition from 2D to 3D NAND architecture requires significant changes in the fabrication process.

[0007] These considerations necessitate a larger DoF. The DoF in lithography is given by DoF=±m2λ / (NA) 2 where λ is the wavelength of the illumination light, NA is the numerical aperture, and m2 is the actual coefficient depending on the resist process. Due to the larger DoF requirements in 3D NAND lithography, multiple exposure passes may be performed on the wafer, using a different laser wavelength for each pass.

[0008]

[0008] Multifocal imaging (MFI) uses multiple focus levels (e.g., via multiple wavelengths) to effectively increase the DoF for a particular NA of the objective. This technique can be specifically tuned to provide the required amount of wavelength separation (peak separation) for a particular DoF requirement. This allows for an increase in imaging NA, and therefore exposure latitude (process window), while also allowing the DoF to be optimized by MFI according to production layer requirements.

[0009]

[0009] Furthermore, the materials that make up the lenses that focus the laser radiation are dispersive, so different wavelengths are focused to different depths, another reason why it may be desirable to have the ability to change the wavelength.

[0010] To achieve MFI, an element in the optical train is moved back and forth between two angular positions, with the light source (1) producing light having a first wavelength when the element is in one of the two positions and (2) producing light having a second wavelength when the element is in the other of the two positions. The element is moved under the control of a command voltage generated by an electrically actuatable element (EAE), such as a piezoelectric transducer (PZT), stepper motor, valve, pressure control device, electromagnet, solenoid, another type of piezoelectric device, linear motor, hydraulic actuator, voice coil, and / or other type of device capable of producing a driving force under the command of a control signal.

[0011]

[0011] In monochromatic mode, two actuators, a stepper motor and a PZT, work together to stabilize the center wavelength. During operation, the PZT is used as the primary actuator because the stepper motor has limited resolution. However, in bichromatic mode, wavelength stability is based on the center or peak wavelength, i.e., the average of two alternating spectra, and in this mode, it is up to the PZT to generate the waveform that produces the alternating wavelengths.

[0012]

[0012] As a specific example, in an application for generating DUV light at two different wavelengths, the reference wavelength has two set points during an exposure: a first set point at a first wavelength and a second set point at a second wavelength. The reference wavelength will be adjusted between these two set points. Each change in wavelength target requires a certain settling time.

[0013]

[0013] DUV light sources include systems for controlling the wavelength of the DUV light. Typically, such wavelength control systems include a feedforward compensator to promote wavelength stability. The feedforward compensator compensates for commanded changes to the wavelength target, i.e., wavelength change events. When such an event occurs, a settling time is required for the system to stabilize and settle to the new wavelength.

[0014]

[0014] Typically, MFI algorithms assume that the laser will operate in MFI mode only at (or substantially near) a particular repetition rate (e.g., 6 kHz), so the PZT dither base waveform is calibrated and optimized for performance at this single operating point. This base waveform is then modified on a burst-by-burst basis using an iterative learning control (ILC) algorithm to compensate (within reason) for drift and operation outside the expected operating point.

[0015]

[0015] The desired peak separation performance can be achieved by using an MFI algorithm that relies on accurate knowledge of PZT calibration results. However, there is uncertainty (nonlinearity) in the PZT's performance at repetition rates at the PZT resonance frequency or its harmonics. As a result, the calibrated gain of the PZT voltage is unreliable at these frequencies. Sequences that use accurately calibrated results from existing MFI control algorithms exhibit slow transient responses with large overshoots when the laser is fired at repetition rates near (2*PZT resonance) Hz. In fact, it can take approximately 100 pulses for the peak separation, a variation used as a measure of system stability, to converge to the desired value. This behavior essentially precludes the use of repetition rates at or near the PZT resonance and its harmonics.

[0016]

[0016] It is in these circumstances that the need for the subject matter disclosed herein arises. Summary of the Invention

[0017] The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of the embodiments. This summary is not an extensive overview of all contemplated embodiments. It is not intended to identify any elements of the embodiments as key or critical elements or to delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

[0018]

[0018] According to one aspect of an embodiment, a laser system is disclosed that includes a source of laser radiation, wherein the laser radiation is emitted in one or more bursts, each burst consisting of a plurality of pulses; a wavelength controller arranged to receive the pulses and control a dominant wavelength of some of the pulses toward a first value and to control a dominant wavelength of other of the pulses toward a second value that differs from the first value by a target dominant wavelength separation amount, the wavelength controller including at least one actuator operative in response to control signals that cause the wavelength control of the pulses; and a model reference adaptive control system adapted to cause the wavelength controller to achieve the target dominant wavelength separation amount by generating control signals based at least in part on a measured dominant wavelength separation amount.

[0019]

[0019] The source of laser radiation may be an excimer laser. The actuator may include a piezoelectric transducer. The wavelength controller may be a line narrowing module. The wavelength controller may be a line narrowing module including an optical element mechanically coupled to at least one actuator. The at least one actuator may include a piezoelectric transducer.

[0020]

[0020] According to another aspect of the embodiment, a multi-focal imaging photolithography system is disclosed that generates first wavelength pulses of deep ultraviolet light having a first dominant wavelength and second wavelength pulses of deep ultraviolet light having a second dominant wavelength that differs from the first dominant wavelength by a dominant separation distance amount, the multi-focal imaging photolithography system including: a wavelength controller arranged to receive input pulses of deep ultraviolet light and, in response to a control signal, control the dominant wavelength of a first subset of pulses to obtain first wavelength pulses, and control the dominant wavelength of a second subset of input pulses to obtain second wavelength pulses; and a model-based adaptive control system adapted to generate a control signal based at least in part on a measured dominant wavelength separation distance of the first wavelength pulses and the second wavelength pulses, thereby causing the wavelength controller to achieve and maintain a target dominant separation distance amount.

[0021]

[0021] The source of laser radiation may be an excimer laser. The wavelength controller may include an electrically actuatable component. The wavelength controller may be a line narrowing module. The line narrowing module may include an electrically actuatable component. The electrically actuatable component may include a piezoelectric transducer.

[0022]

[0022] According to another aspect of an embodiment, a system is disclosed for controlling the wavelength of laser radiation emitted in one or more bursts, each burst consisting of a plurality of pulses, the system including a wavelength controller arranged to receive the pulses and control the dominant wavelength of some of the pulses toward a first value and to control the dominant wavelength of other of the pulses toward a second value that differs from the first value by a target dominant wavelength separation amount, the wavelength controller including at least one actuator operating in response to control signals that cause the wavelength control of the pulses, and a model reference adaptive control system adapted to cause the wavelength controller to achieve the target dominant wavelength separation amount by generating control signals based at least in part on a measured dominant separation amount.

[0023]

[0023] The actuator may include a piezoelectric transducer. The wavelength controller may be a line narrowing module. The wavelength controller may be a line narrowing module including an optical element mechanically coupled to the actuator. The actuator may include a piezoelectric transducer.

[0024] Each burst may include multiple pulses fired at a repetition rate, and the model-based adaptive control system may be adapted to generate control signals based at least in part on the measured dominant wavelength separation amount so that the wavelength controller achieves the target dominant wavelength separation amount even when the repetition rate is within a critical range where operation of the electrically actuatable component becomes unstable. The critical range may be + / - 10% of the resonant frequency of the electrically actuatable component or a harmonic of the resonant frequency of the electrically actuatable component. The electrically actuatable component may include a piezoelectric transducer.

[0025]

[0025] According to another aspect of an embodiment, a method for controlling a multi-focus imaging photolithography system that generates first wavelength pulses of radiation having a first dominant wavelength and second wavelength pulses of radiation having a second dominant wavelength that differs from the first dominant wavelength by a dominant separation amount is disclosed, the method including generating input pulses of laser radiation; using a wavelength controller to control the dominant wavelength of a first subset of the input pulses in response to a control signal to obtain first wavelength pulses, and to control the dominant wavelength of the second subset of input pulses to obtain second wavelength pulses; comparing the dominant wavelength separation of the first wavelength pulses and the second wavelength pulses with a dominant wavelength separation obtained from a reference model controlled by a reference signal to obtain an error signal; and modifying one or more parameters of the control signal based at least in part on the error signal so that the response of the wavelength controller to the control signal tracks the response of the reference model to the reference signal.

[0026]

[0026] Generating the input pulses of laser radiation may be performed using an excimer laser. Using a wavelength controller may include using a line narrowing module.

[0027]

[0027] Further features and exemplary aspects of the embodiments, together with the structure and operation of various embodiments, will be described in detail below with reference to the accompanying drawings. It should be noted that the scope of all possible embodiments is not limited to the specific embodiments described herein. Such specific embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the art based on the teachings contained herein. [Brief explanation of the drawings]

[0028]

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments and, together with the description, serve to explain the principles of the embodiments and enable those skilled in the art to make and use the embodiments.

[0029] [Figure 1A]

[0029] FIG. 1 shows a schematic diagram of a lithographic apparatus according to an embodiment. [Figure 1B]

[0029] FIG. 1 shows a schematic diagram of a lithographic apparatus according to an embodiment. [Figure 1C]

[0029] FIG. 1 shows a schematic diagram of a lithographic apparatus according to an embodiment. [Figure 2A]

[0030] 1 is a schematic diagram of a light source device according to an embodiment. [Figure 2B]

[0031] FIG. 1 is a schematic diagram of a spectral feature actuation system according to one embodiment. [Figure 2C]

[0032] 1 is a schematic cross-sectional view of a line narrowing module according to an embodiment. [Figure 3A]

[0033] FIG. 1 is a diagram of a laser burst composed of laser pulses illustrating certain principles underlying the operation of one aspect of an embodiment. [Figure 3B]

[0033] A diagram of a laser burst composed of laser pulses illustrating certain principles underlying the operation of one aspect of one embodiment. [Figure 3C]

[0033] A diagram of a laser burst composed of laser pulses illustrating certain principles underlying the operation of one aspect of one embodiment. [Figure 4]

[0034] FIG. 1 is a conceptual schematic diagram of a photolithography system according to an aspect of an embodiment. [Figure 5]

[0035] 1 is a graph of a single peaked optical spectrum of laser emission in accordance with an aspect of an embodiment; [Figure 6]

[0036] 1 is a graph of a two-peak optical spectrum of laser emission according to an aspect of an embodiment. [Figure 7]

[0037] 1 illustrates an example of an average optical spectrum at a wafer, according to an aspect of an embodiment. [Figure 8]

[0038] FIG. 1 is a diagram of a model-based adaptive control system for controlling an LNM for an MFI, according to an aspect of an embodiment. [Figure 9]

[0039] 1 is a flowchart of a process for operation of a model reference adaptive control system to control an LNM for an MFI, according to an aspect of an embodiment. [Figure 10]

[0040] FIG. 1 is a functional block diagram of a computer control system according to an aspect of an embodiment.

[0030]

[0041] Features and exemplary aspects of the embodiments will become more apparent from the following detailed description when considered in conjunction with the drawings, in which like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. The drawings are not to be construed as being to scale unless otherwise indicated. DETAILED DESCRIPTION OF THE INVENTION

[0031]

[0042] References to the described embodiment(s), and to "one embodiment," "an embodiment," "an exemplary embodiment," "an example embodiment," etc. in the specification, indicate that the described embodiment may include a particular feature, structure, or characteristic, but not all embodiments may include that particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it will be understood that it is within the knowledge of one skilled in the art that such feature, structure, or characteristic may also be provided in connection with other embodiments, whether expressly stated or not.

[0032]

[0043] Spatially relative terms are used herein for ease of description and may describe the relationship of one element or feature to another element or feature as shown in the figures. Spatially relative terms are intended to encompass various orientations of the device in use or operation in addition to the orientation shown. The device may be oriented differently (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly.

[0033]

[0044] As used herein, the terms "about" or "substantially" or "approximately" refer to a given quantity value that may vary based on a particular technique. Based on a particular technique, the terms "about" or "substantially" or "approximately" may refer to a given quantity value that varies, for example, within 1% to 15% of the value (e.g., ±1%, ±2%, ±5%, ±10%, or ±15% of the value).

[0034]

[0045] Embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Also, embodiments of the present disclosure may be implemented as instructions stored on a tangible, machine-readable medium and readable and executable by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Also, firmware, software, routines, and / or instructions may be described herein as performing certain operations. However, it should be understood that such description is merely for convenience and that such operations are actually performed by a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc.

[0035]

[0046] However, before describing such embodiments in more detail, it is beneficial to present an exemplary environment in which embodiments of the present disclosure may be implemented.

[0036]

[0047] Referring to FIG. 1A , photolithography system 100 includes an optical source (or light source) 105 that provides a light beam 160 to a lithography exposure apparatus 169, which processes a wafer 170 received by a wafer holder or stage 171. Light beam 160 is a pulsed light beam that includes pulses of light that are spaced apart in time. Lithography exposure apparatus 169 includes a projection optical system 175 through which light beam 160 passes before reaching wafer 170, and a metrology system 172. Metrology system 172 may include, for example, a camera or other device capable of capturing an image of wafer 170 and / or light beam 160 at wafer 170, or a photodetector capable of capturing data indicative of properties of light beam 160, such as the intensity of light beam 160 in the x-y plane at wafer 170. Lithography exposure apparatus 169 may be an immersion system or a dry system. The photolithography system 100 may also include a control system 150 for controlling the light source 105 and / or the lithography exposure tool 169 .

[0037]

[0048] Microelectronic features are formed on wafer 170, for example, by exposing a layer of radiation-sensitive photoresist material on wafer 170 to light beam 160. Referring also to FIG. 1B, projection optical system 175 includes slit 176, mask 174, and a projection objective including lens 177. Light beam 160 enters optical system 175 and impinges on slit 176, with at least a portion of beam 160 passing through slit 176. In the example of FIGS. 1A and 1B, slit 176 is rectangular and shapes light beam 160 into an elongated rectangular light beam. A pattern is formed on mask 174, and this pattern determines which portions of the shaped light beam are transmitted through mask 174 and which portions are blocked by mask 174. The design of the pattern is determined by the design of the particular microelectronic circuit to be formed on wafer 170.

[0038]

[0049] The shaped light beam interacts with mask 174. A portion of the shaped light beam that is transmitted through mask 174 passes through (and may be focused by) projection lens 177, exposing wafer 170. The portion of the shaped light beam that is transmitted through mask 174 forms an aerial image in the xy plane of wafer 170. The aerial image is the intensity pattern formed by light that reaches wafer 170 after interacting with mask 174.

[0039]

[0050] System 100 can form multiple aerial images during a single exposure pass, with each aerial image located at a spatially distinct location along the z-axis within wafer 170. Also referring to Figure 1C, which shows a cross-sectional view of wafer 170 in the yz-plane, projection optical system 175 forms two aerial images 173a, 173b at different planes along the z-axis during a single exposure pass. As described in more detail below, each of aerial images 173a, 173b is formed from light having a different dominant wavelength.

[0040]

[0051] The location of the aerial image along the z-axis is determined by the characteristics of optical system 175 (including projection lens 177 and mask 174) and the wavelength of light beam 160. The focal position of lens 177 is determined by the wavelength of light incident on lens 177. Therefore, by varying or controlling the wavelength of light beam 160, the location of the aerial image can be controlled. By providing pulses with different dominant wavelengths during a single exposure pass, multiple (two or more) aerial images at different locations along the z-axis can be formed in a single exposure pass without moving optical system 175 (or any component of optical system 175) and wafer 170 relative to each other along the z-axis.

[0041]

[0052] In the example of FIG. 1B , light passing through mask 174 is focused onto a focal plane by projection lens 177. The focal plane of projection lens 177 is between projection lens 177 and wafer stage 171, and the location of the focal plane along the z-axis is determined by the characteristics of optical system 175 and the wavelength of light beam 160. Because aerial images 173 a, 173 b are formed from light having different wavelengths, aerial images 173 a, 173 b are at different locations within wafer 170. Aerial images 173 a, 173 b are separated from each other along the z-axis by separation distance 179. Separation distance 179 is determined by the difference between the wavelength of the light forming aerial image 173 a and the wavelength of the light forming aerial image 173 b.

[0042]

[0053] Separation distance 179 is formed due to the ability to control the dominant wavelength of the pulses passing through mask 174 during an exposure pass. Furthermore, aerial images 173a and 173b are both present on wafer 170 during the same exposure pass. In other words, system 100 does not require that aerial image 173a be formed in a first exposure pass and aerial image 173b be formed in a second, subsequent exposure pass.

[0043]

[0054] Light in first aerial image 173a interacts with the wafer at depth 178a, and light in second aerial image 173b interacts with the wafer at depth 178b. These interactions can result in the formation of electronic features or other physical features, such as openings or holes, on wafer 170. Because aerial images 173a, 173b are formed at offset locations along the z-axis, forming aerial images 173a, 173b can be used as part of a process to form three-dimensional features on wafer 170. For example, aerial image 173a can be used to form a peripheral region, and aerial image 173b can be used to form a channel, trench, or recess at a different location along the z-axis. As such, the techniques discussed herein can be used to form three-dimensional semiconductor components, such as three-dimensional NAND flash memory components.

[0044]

[0055] Before discussing additional details regarding forming multiple aerial images in a single exposure pass, an example implementation of light source 105 and photolithography system 100 will be described with respect to Figures 2A-2C, 3A-3C, and 4.

[0045]

[0056] Referring to FIG. 2A, a block diagram of a photolithography system 200 is shown. System 200 is an example of one implementation of system 100 (FIG. 1A). For example, in photolithography system 200, optical source 205 is used as optical source 105 (FIG. 1A). Optical source 205 generates a pulsed light beam 260, which is provided to lithography exposure tool 169. Optical source 205 may be, for example, an excimer optical source that outputs pulsed light beam 260 (which may be a laser beam). Upon entering lithography exposure tool 169, pulsed light beam 260 passes through projection optical system 175 and is projected onto wafer 170. In this manner, one or more microelectronic features are patterned on photoresist on wafer 170, which is then developed and washed before subsequent process steps, and the process is repeated. Photolithography system 200 also includes a control system 250, which in the example of Figure 2A is connected to components of optical source 205 and lithography exposure apparatus 169 to control various operations of system 200. Control system 250 is an example of one implementation of control system 150 of Figure 1A.

[0046]

[0057] 2A , optical source 205 is a two-stage laser system that includes a master oscillator (MO) 212 that provides a seed light beam 224 to a power amplifier (PA) 230. MO 212 and PA 230 may be considered to be subsystems of optical source 205 or systems that are part of optical source 205. Power amplifier 230 receives seed light beam 224 from master oscillator 212 and amplifies seed light beam 224 to generate light beam 260 for use in lithography exposure apparatus 169. For example, master oscillator 212 may emit a pulsed seed light beam, with seed pulse energy of about 1 millijoule (mJ) per pulse, and these seed pulses may be amplified by power amplifier 230 to about 10-15 mJ.

[0047]

[0058] Master oscillator 212 includes a discharge chamber 240 with two elongated electrodes 217, a gain medium 219 that is a gas mixture, and a fan for circulating the gas between electrodes 217. A resonator is formed between a line narrowing module (LNM) 216 on one side of discharge chamber 240 and an output coupler 218 on a second side of discharge chamber 240. LNM 216 may include a diffractive optical element such as a grating to fine-tune the spectral output of discharge chamber 240. Figures 2B and 2C provide further details about LNM 216.

[0048]

[0059] 2B is a block diagram illustrating an example of one implementation of the spectral feature selection module 258. The spectral feature selection module 258 couples to light propagating within the optical source 205. In some implementations (such as that shown in FIG. 2B), the spectral feature selection module 258 receives light from the chamber 214 of the master oscillator 212 to allow fine tuning of spectral features, such as wavelength and bandwidth, within the master oscillator 212.

[0049]

[0060] The spectral feature selection module 258 may include a control module, such as a spectral feature control module 254, which includes electronics in the form of any combination of firmware and software. The control module 254 is connected to one or more actuation systems, such as spectral feature actuation systems 255_1-255_n. Each of the actuation systems 255_1-255_n may include one or more actuators connected to respective optical features 256_1-256_n of the optical system 257. The optical features 256_1-256_n are configured to adjust specific characteristics of the generated light beam 260, thereby adjusting the spectral features of the light beam 260. The control module 254 receives control signals from the control system 250, which include specific instructions for operating or controlling one or more of the actuation systems 255_1-255_n. The actuation systems 255_1-255_n can be selected and designed to operate together, i.e., in conjunction, or the actuation systems 255_1-255_n may be configured to operate individually. Furthermore, each actuation system 255_1 to 255_n may be optimized to respond to a particular type of disturbance.

[0050]

[0061] Each actuator of actuation systems 255_1-255_n may be an EAE for moving or controlling a respective optical feature 256_1-256_n of optical system 257. The actuators receive energy from control module 254 and convert the energy into some movement imparted to optical features 256_1-256_n of optical system 257.

[0051]

[0062] Each optical feature 256_1-256_n is optically coupled to the light beam 260 generated by the optical source 105. The optical system 257 may be implemented as an LNM 216c as shown in FIG. 2C. The line narrowing module includes, as the optical features 256_1-256_n, a dispersive optical element, such as a reflective grating 291, and a refractive optical element, such as prisms 292, 293, 294, and 295. One or more of the prisms 292, 293, 294, and 295 may be rotatable. An example of this line narrowing module is described in U.S. Patent No. 8,144,739, entitled "System Method and Apparatus for Selecting and Controlling Light Source Bandwidth," issued March 27, 2012 (the '739 patent). The '739 patent describes a line narrowing module that includes a beam expander (including one or more prisms 292 , 293 , 294 , and 295 ) and a dispersive element such as a grating 291 .

[0052]

[0063] All patent applications, patents, and publications cited herein are incorporated by reference in their entirety, except for definitions, subject matter disclaimers, or disclaimers, and except to the extent that the incorporated material conflicts with the disclosure expressly set forth herein. In the case of a conflict, the language of the disclosure herein will control.

[0053]

[0064] The actuation systems for each of the optical features, such as one or more of prisms 292, 293, 294, and 295, are represented in FIG. 2C by EAEs 292a, 293a, 294a, and 295a. Mirrors are also present and can rotate to change the angle of incidence of the light beam on grating 291 and, therefore, the dominant wavelength of the emitted light. The common factor is the presence of an EAE that causes operation under the command of a voltage command signal. Thus, a line-narrowing module typically includes one or more optical elements that rotate to change the dominant wavelength of the light exiting the module. These EAEs must be able to move the optical element very rapidly between two positions (usually two angular positions) in a process called dithering.

[0054]

[0065] 2A , master oscillator 212 also includes a line center analysis module 220 that receives the output light beam from output coupler 218 and a beam combining optical system 222 that optionally modifies the size or shape of the output light beam to form seed light beam 224. Line center analysis module 220 is a measurement system that can be used to measure or monitor the wavelength of seed light beam 224. Line center analysis module 220 may be located elsewhere within optical source 205 or at the output of optical source 205.

[0055]

[0066] The power amplifier 230 includes a beam combining optical system 232 that receives the seed light beam 224 from the master oscillator 212 and directs the seed light beam 224 through the discharge chamber 240 to the beam rotation optics 248. The beam rotation optics 248 corrects or changes the direction of the seed light beam 224 and sends it back to the discharge chamber 240. The discharge chamber 240 includes a pair of elongated electrodes 241, a gain medium which is a gas mixture, and a fan for circulating the gas mixture between the electrodes 241.

[0056]

[0067] Output light beam 260 is directed through a bandwidth analysis module 262, where various parameters of beam 260 (such as bandwidth or wavelength) may be measured. Output light beam 260 may be directed through a beam preparation system 263. Beam preparation system 263 may include, for example, a pulse stretcher, where each pulse of output light beam 260 is stretched in time, for example, in an optical delay unit, to adjust the performance characteristics of the light beam impinging on lithography exposure apparatus 169. Beam preparation system 263 may also include other components that can act on beam 260, such as reflective and / or refractive optical elements (e.g., lenses and mirrors), filters, and optical apertures (including automatic shutters).

[0057]

[0068] Photolithography system 200 may also include a control system 250. In the implementation shown in FIG. 2A , control system 250 is connected to various components of optical source 205. For example, control system 250 may send one or more trigger signals to optical source 205 to control the timing at which optical source 205 emits a light pulse or a light pulse burst comprising one or more light pulses. Control system 250 is also connected to lithography exposure apparatus 169. Thus, control system 250 may also control various aspects of lithography exposure apparatus 169. For example, control system 250 may control the exposure of wafer 170 and thus may be used to control how electronic features are printed on wafer 170. In some implementations, control system 250 may control the scanning of wafer 170 by controlling the movement of slit 176 in the x-y plane ( FIG. 1B ). Additionally, control system 250 may exchange data with metrology system 172 and / or optical system 175.

[0058]

[0069] Lithography exposure apparatus 169 may also include, for example, temperature control devices (such as air conditioning and / or heating devices) and / or power supplies for various electrical components. Control system 250 may also control these components. In some implementations, control system 250 is implemented to include multiple sub-control systems, with at least one sub-control system (lithography controller) dedicated to controlling aspects of lithography exposure apparatus 169. In these implementations, control system 250 may be used to control aspects of lithography exposure apparatus 169 instead of, or in addition to, using a lithography controller.

[0059]

[0070] Control system 250 includes electronic processor 251, electronic storage 252, and I / O interface 253. Electronic processor 251 includes one or more processors suitable for executing computer programs, such as general-purpose or special-purpose microprocessors, and any one or more processors of any type of digital computer. Typically, an electronic processor receives instructions and data from a read-only memory, a random-access memory, or both. Electronic processor 251 can be any type of electronic processor.

[0060]

[0071] Electronic storage 252 may be volatile memory, such as RAM, or nonvolatile memory. Depending on the implementation, electronic storage 252 includes both nonvolatile and volatile portions or components. Electronic storage 252 may store data and information used in the operation of control system 250, components of control system 250, and / or systems controlled by control system 250. The information may be stored, for example, in a lookup table or database. For example, electronic storage 252 may store data indicating values ​​of various properties of beam 260 under different operating conditions and performance scenarios.

[0061]

[0072] Additionally, electronic storage 252 may store various recipes or process programs 259 that dictate parameters of light beam 260 during use. For example, electronic storage 252 may store a recipe that indicates the wavelength of each pulse in light beam 260 for a particular exposure pass. The recipe may indicate different wavelengths for different exposure passes. Wavelength control techniques discussed below may be applied on a pulse-by-pulse basis. In other words, the wavelength content may be controlled for individual pulses within an exposure pass to facilitate the formation of an aerial image at a desired location along the z-axis.

[0062]

[0073] The electronic storage 252 may also store instructions, possibly as a computer program, that when executed cause the processor 251 to communicate with the control system 250 , the optical system 205 , and / or components within the lithographic exposure apparatus 169 .

[0063]

[0074] I / O interface 253 is any type of electronic interface that allows control system 250 to receive and / or provide data and signals from an operator, optical system 205, lithography exposure apparatus 169, any component or system within optical system 205 and / or lithography exposure apparatus 169, and / or an automated process running on another electronic device. For example, I / O interface 253 may include one or more of a visual display, a keyboard, and a communication interface.

[0064]

[0075] Light beam 260 (and light beam 160) is a pulsed light beam and may include one or more pulse bursts spaced apart in time. Each burst may include one or more light pulses. In some implementations, a burst may include hundreds of pulses (e.g., 100-400 pulses). Figures 3A-3C show an overview of pulse and burst generation in optical source 205. Figure 3A shows the amplitude of wafer exposure signal 300 as a function of time, Figure 3B shows the amplitude of gating signal 315 as a function of time, and Figure 3C shows the amplitude of trigger signal 330 as a function of time.

[0065]

[0076] The control system 250 may be configured to send a wafer exposure signal 300 to the optical source 205 to control the optical source 205 to generate the light beam 260. In the example shown in Figure 3A, the wafer exposure signal 300 has a high value 305 (e.g., a logic 1) during a period 307 when the optical source 205 generates a pulse burst of light. Otherwise, the wafer exposure signal 300 has a low value 310 (e.g., a logic 0) when the wafer 170 is not being exposed.

[0066]

[0077] 3B, the control system 250 also controls the duration and frequency of the pulse bursts by sending a gating signal 315 to the optical source 205. The gating signal 315 has a high value 320 (e.g., logic 1) during a pulse burst and a low value 325 (e.g., logic 0) during the time between successive bursts. In the illustrated example, the period when the gating signal 315 has a high value is also the period of a burst 316. The bursts are separated in time by an inter-burst time interval. During the inter-burst time interval, the lithography exposure apparatus 169 may position the next die on the wafer 170 for exposure.

[0067]

[0078] 3C, control system 250 also controls the repetition rate of the pulses within each burst using trigger signal 330. Trigger signal 330 includes a trigger 340 that is provided to optical source 205 to cause optical source 205 to generate a light pulse. Control system 250 may send trigger 340 to optical source 205 each time a pulse is generated. Thus, the repetition rate of the pulses generated by optical source 205 (the time between two consecutive pulses), or other timing of the pulses, may be set by trigger signal 330.

[0068]

[0079] As described above, when gain medium 219 is pumped by applying a voltage to electrode 217, gain medium 219 emits light. When voltage is applied to electrode 217 in pulses, the light emitted from medium 219 also pulses. Thus, the repetition rate of pulsed light beam 260 is determined by the rate at which voltage is applied to electrode 217, generating an optical pulse each time voltage is applied. The optical pulses propagate through gain medium 219 and exit chamber 214 via output coupler 218. Thus, a pulse train is generated by periodically repeating the application of voltage to electrode 217. For example, trigger signal 330 may be used to control the application of voltage to electrode 217 and the repetition rate of the pulses, which may range from approximately 500 Hz to 6,000 Hz for most applications. In some implementations, the repetition rate may exceed 6,000 Hz, e.g., 12,000 Hz or greater.

[0069]

[0080] Signals from control system 250 may be used to control electrodes 217, 241 in master oscillator 212 and power amplifier 230, respectively, thereby controlling the pulse energy of each of master oscillator 212 and power amplifier 230, and thus the energy of light beam 260. There may be a delay between the signal provided to electrode 217 and the signal provided to electrode 241. The amount of delay may affect the properties of pulsed light beam 260, such as the amount of coherence of beam 260.

[0070]

[0081] The pulsed light beam 260 may have an average output power of tens of watts, for example, in the range of about 50 W to about 130 W. The irradiance (i.e., average power per unit area) of the light beam 260 at the output may be greater than 60 W / cm. 2 to 80W / cm 2 It can reach.

[0071]

[0082] Referring also to FIG. 4, the wafer 170 is illuminated by a light beam 260. The lithography exposure apparatus 169 includes an optical system 175 (FIGS. 1A and 1B). In the example of FIG. 4, the optical system 175 (other parts not shown in FIG. 4) includes an illumination system 429, which includes an objective lens arrangement 432. The objective lens arrangement 432 includes a projection lens 177 (FIG. 1B) and enables image transfer from the mask 174 to the photoresist on the wafer 170. The illumination system 429 adjusts the angular range of the light beam 260 impinging on the mask 174. The illumination system 429 can also homogenize (uniformize) the intensity distribution of the light beam 260 in the x-y plane across the mask 174.

[0072]

[0083] In some implementations, an immersion medium may be provided to cover wafer 170. The immersion medium may be a liquid (such as water) for immersion lithography. In other implementations where the lithography is dry, the immersion medium may be a gas, such as dry nitrogen, dry air, or clean air. In other implementations, wafer 170 may be exposed to a pressure-controlled environment (such as a vacuum or partial vacuum).

[0073]

[0084] A plurality of N pulses of the light beam 260 illuminate the same area of ​​the wafer 170, where N can be any integer greater than or equal to 2. The number N of pulses of the light beam 110 illuminating the same area is sometimes referred to as an exposure window or exposure pass 400. The size of the window 400 can be controlled by the slit 176. For example, the slit 176 can include a plurality of movable blades that form an aperture that is open in one configuration and closed in another configuration. By arranging the blades of the slit 176 to form an aperture of a particular size, the size of the window 400 can also be controlled.

[0074]

[0085] The N pulses also determine the illumination dose of the exposure pass. The illumination dose is the amount of optical energy delivered to the wafer during an exposure pass. Therefore, characteristics of the N pulses, such as the optical energy of each pulse, determine the illumination dose. Furthermore, as described in more detail below, the N pulses can also be used to determine the amount of light in each aerial image 173a, 173b (FIG. 1C). In particular, a recipe may specify that, of the N pulses, a certain number of pulses have a first dominant wavelength that forms aerial image 173a, and a certain number of pulses have a second dominant wavelength that forms aerial image 173b. These pulses with different wavelengths may be interspersed, for example, pulse by pulse, or in some other manner, i.e., within alternating pulse groups.

[0075]

[0086] Additionally, the slit 176 and / or mask 174 may move in a scan direction in the xy plane so that only a portion of the wafer 170 is exposed at a given time or during a particular exposure scan (or exposure pass). The size of the area on the wafer 170 exposed by the light beam 160 is determined by the distance between the blades in the non-scanning direction and the length (distance) of the scan in the scanning direction. In some implementations, the value of N is in tens, so that, for example, each point on the wafer may receive light from 10 to 100 successive pulses during the scan of the slit relative to that point. In other implementations, the value of N is greater than 100 pulses, such as 100 to 500 pulses. The exposure field 479 of the wafer 170 is the physical area of ​​the wafer 170 that is exposed in one scan of the exposure slit or window in the lithography exposure tool 169.

[0076]

[0087] The wafer stage 171, mask 174, and objective lens arrangement 432 are fixed to associated motion systems, thereby forming a scanning configuration in which one or more of the mask 174, objective lens arrangement 432, and wafer 170 (via stage 171) may move relative to one another in the xy plane. However, except for incidental relative motion between the wafer stage 171, mask 174, and objective lens arrangement 432, these elements do not move relative to one another along the z-axis during an exposure pass.

[0077]

[0088] Referring again to FIG. 2A, tuning of the wavelength of beam 224, and therefore of light beam 260, typically occurs in LNM 216. A common technique used to narrow or tune the linewidth of a laser is to provide a window in the back of the laser's discharge cavity and pass a portion of the laser beam through this window into LNM 216. There, a portion of the beam is expanded with a prism beam expander and directed onto a grating. The grating reflects a selected, narrow portion of the laser's broader spectrum back into the discharge chamber, where it is amplified as described in connection with LNM 216c in FIG. 2C. The laser is typically tuned by changing the angle at which the beam illuminates grating 291 using an actuator, such as a piezoelectric actuator.

[0078]

[0089] In some embodiments, multiple prisms 292-295 can be used to adjust the final angle of incidence, and consequently, the selected wavelength. For example, prism 292 may provide more precise control of the final angle of incidence compared to prism 293. That is, in some embodiments, controller 250 uses prisms 292 and 293 in a dual-stage configuration, with prism 292 being used for large jumps and desaturation, and prism 293 being used for finer changes to the final angle of incidence. Controlling prisms 292 and 293 is particularly important for MFI operations, which require more than adjustment around a set point; rather, precise control of the center point (i.e., center wavelength) of the sine wave as well as precise tracking of the sine wave at the Nyquist frequency exists. Processes exist for controlling the center wavelength for imaging operations, such as MFI operations.

[0079]

[0090] Multifocal imaging operations can include a two-color mode, in which a wavelength target can alternate between two known set points within a burst (e.g., pulse by pulse, between pulses), and an electrically actuatable component, which can be implemented as a piezoelectric transducer (PZT), can be used to track (i.e., tune to) the rapidly changing wavelength target. As noted above, in some applications, it is beneficial to be able to generate one or more pulses having one wavelength and then switch to generating one or more pulses having a different wavelength.

[0080]

[0091] In some implementations, MFI operations provide for moving an actuator that controls the motion of prism 293 during a burst. Thus, these processes provide an intra-burst solution for addressing changes in center wavelength. A dynamic model of the actuator can be used to calculate optimal control waveforms for actuating the actuator to minimize the difference between the actual wavelength and the wavelength target.

[0081]

[0092] In some embodiments, a dither waveform (or sequence) can be combined with an offset for moving the actuator of prism 293. For example, the dither waveform can be an application of noise used to randomize quantization. The offset can be updated at the end of burst (EOB) and / or at a set pulse interval. In some embodiments, the EOB update can move the actuator of prism 293 to null out an estimated center wavelength drift obtained by averaging wavelength measurements over the burst. In some embodiments, the interval update can be based on an estimation process.

[0082]

[0093] The optimal control waveform can be calculated using any of several methods. For example, the optimal control waveform can be calculated using dynamic programming. This method is well adapted to handle complex models that include nonlinear dynamics. When an actuator model with strong nonlinear dynamics is employed, dynamic programming can be used to generate optimal control signals for a specific wavelength target. However, dynamic programming has the challenge of requiring significant computational resources that may not be feasible in real time. To overcome this issue, a data storage device such as a pre-populated look-up table or a pre-programmed field-programmable gate array (FPGA) containing optimal control parameters for at least some of the different repetition rates at which the source can operate can be used.

[0083]

[0094] As another example, optimal control waveforms can be determined using model inversion feedforward control. This method relies on a dynamic model of the actuator to build a digital filter that inverts the actuator dynamics. By passing the desired waveform for the desired actuator trajectory through this filter, optimal control waveforms can be generated in real time to achieve zero steady-state error tracking.

[0084]

[0095] As another example, an optimal solution for stably achieving two separate wavelengths is achieved using a learning algorithm to ensure error convergence over several learning iterations. Embodiments of the systems and methods disclosed herein can potentially achieve two separate wavelengths 1000 femtometers (fins) apart with a separation error of less than 20 fins.

[0085]

[0096] 5, an optical spectrum 601A of an optical pulse 600A is shown. The optical pulse 600A has a non-zero intensity within a wavelength band, which may also be referred to as the bandwidth of the pulse 600A.

[0086]

[0097] The information shown in FIG. 5 is the instantaneous optical spectrum 601A (or emission spectrum) of pulse 600A. Optical spectrum 601A contains information about how the optical energy or power of a pulse of light beam 260 is distributed across various wavelengths (or frequencies). Optical spectrum 601A is represented in the form of a diagram in which spectral intensity (not necessarily with absolute calibration) is plotted as a function of wavelength or optical frequency. Optical spectrum 601A is sometimes referred to as the spectral shape or intensity spectrum of the pulse of light beam 260. Pulse 600A has a dominant wavelength 602A, which in the example of FIG. 5 is the peak intensity. While the descriptions of the pulse of light beam 260 and the aerial image formed by the pulse of light beam 260 refer to the dominant wavelength of the pulse, the pulse includes wavelengths other than the dominant wavelength, and the pulse has a finite bandwidth that can be characterized by a measurement system. For example, the full width of spectrum 601A at a fraction of the maximum peak intensity (X) of the spectral shape (referred to as FWXM) may be used to characterize the bandwidth of the light beam. As another example, the width of the spectrum (referred to as EY) that comprises a portion of the integrated spectral intensity (Y) may be used to characterize the bandwidth of a light beam.

[0087]

[0098] Pulse 600A is shown as an example of a pulse that may be present in light beam 260.

[0088]

[0099] When pulse 600A is used to expose a portion of wafer 170, the light within the pulse forms an aerial image. The z-direction location of the aerial image (FIGS. 1A-1C) is determined by the value of dominant wavelength 602A. The various pulses within light beam 260 may have different dominant wavelengths. For example, to generate two aerial images during a single exposure pass, some of the pulses of light beam 260 have one dominant wavelength (first dominant wavelength) and other pulses of light beam 260 have another dominant wavelength (second dominant wavelength). The first and second dominant wavelengths are distinct wavelengths. The wavelength difference between the first dominant wavelength and the second dominant wavelength is sometimes referred to as the spectral separation. Although the wavelengths of the various pulses within light beam 260 may be distinct, the shape of the optical spectrum of the pulses may be the same.

[0089]

[0100] Light source 205 may dither or switch between the first and second dominant wavelengths on a burst-by-burst, pulse-by-pulse, or intra-pulse basis. In the pulse-by-pulse case, each pulse has a different dominant wavelength than the pulse immediately preceding or following it in time. In these implementations, assuming all of the pulses in light beam 260 have the same intensity, this distribution of the first and second dominant wavelengths results in two aerial images with the same intensity but at different locations in the z-direction.

[0090]

[0101] In some implementations, a certain portion of the pulses (e.g., 33%) have a first dominant wavelength, and the remaining portion (67% in this example) have a second dominant wavelength. Here and elsewhere, “first” and “second” are used merely to distinguish between labels and not temporal order, unless the context suggests otherwise. In these implementations, assuming all of the pulses in light beam 260 have the same intensity, two aerial images of different intensities are formed. The aerial image formed by pulses having the first dominant wavelength has approximately half the intensity of the aerial image formed by pulses having the second dominant wavelength. In this way, the dose delivered to a particular location within wafer 170 along the z-axis can be controlled by controlling the portion of the N pulses having the first dominant wavelength and the portion of the N pulses having the second dominant wavelength.

[0091]

[0102] The portion of the pulses having a particular dominant wavelength for a given exposure pass may be specified in a recipe file 259 stored in electronic storage 252 (see FIG. 2A). The recipe file 259 specifies the ratios of the various dominant wavelengths for the exposure pass. The recipe file 259 may also specify ratios for other exposure passes, so that different ratios may be used for other exposure passes and the aerial image may be adjusted or controlled on a field-by-field basis.

[0092]

[0103] Referring to FIG. 6 , optical spectrum 601B of pulse 600B is shown. Pulse 600B is another example of a pulse of light beam 260. Optical spectrum 601B of pulse 600B has a different shape than optical spectrum 601A. In particular, optical spectrum 601B has two peaks corresponding to two dominant wavelengths 602B_1 and 602B_2 of pulse 600B. Pulse 600B is part of light beam 260. When pulse 600B is used to expose a portion of wafer 120, the light in the pulse forms two aerial images at different locations along the z-axis on the wafer. The locations of the aerial images are determined by the wavelengths of dominant wavelengths 602B_1 and 602B_2. Therefore, one goal of one embodiment of a control system is to control the dominant wavelengths toward their respective target values, i.e., to converge each dominant wavelength to its target value, thereby achieving a separation amount that achieves a target amount.

[0093]

[0104] The pulses shown in FIGS. 5 and 6 can be formed by any hardware capable of forming such pulses. For example, a pulse train such as pulse 600A can be formed using a line-narrowing module similar to LNM 216C in FIG. 2C. As described above, the wavelength of light diffracted by grating 291 depends on the angle of light incident on the grating. A mechanism for changing the angle of incidence of light interacting with grating 291 can be used with such a line-narrowing module to create a pulse train including N pulses for an exposure pass, where at least one of the N pulses has a dominant wavelength that is different from the dominant wavelength of another of the N pulses. For example, one of prisms 292, 293, 294, and 295 can be rotated to change the angle of light incident on grating 291 from pulse to pulse. In some implementations, the line-narrowing module includes a mirror in the path of beam 260 that is movable to change the angle of light incident on grating 291. An example of such an implementation is described, for example, in US Pat. No. 6,192,064, issued Feb. 20, 2001, entitled "Narrow Band Laser with Fine Wavelength Control."

[0094]

[0105] Referring again to FIG. 4 , a series of light pulses travels through the mask 174 toward the wafer 170 during a single exposure pass. As described above, N light pulses may be provided to the wafer 170 during this exposure pass. The N light pulses may be consecutive light pulses within the beam 260. The exposed portion of the wafer 170 will see an average of the light spectra of each of the N pulses across the entire exposure pass. Thus, if some of the N pulses have a first dominant wavelength and the remaining N pulses have a second dominant wavelength, the average light spectrum at the wafer 170 will be an optical spectrum that includes a peak at the first dominant wavelength and a peak at the second dominant wavelength. Similarly, if all or some of the individual pulses of the N pulses have two or more dominant wavelengths, those dominant wavelengths may form peaks in the average light spectrum. FIG. 7 shows an example of an average light spectrum 701 at the wafer 170. The average light spectrum 701 includes a first dominant wavelength 702_1 and a second dominant wavelength 702_2. 7, the first dominant wavelength 702_1 and the second dominant wavelength 702_2 are separated by a spectral separation 703. The spectral separation 703 exists such that the first dominant wavelength 702_1 and the second dominant wavelength 702_2 are separate, and the average optical spectrum 701 includes a spectral region with little or no intensity between the wavelengths 702_1 and 702_2.

[0095]

[0106] As noted above, a technical challenge presented by attempting to base control signals and standard mathematical models for feedforward control is that the behavior of the PZT in the LNM exhibits a lack of predictability at the PZT resonant frequency and harmonics (integer multiples) of that frequency, and a lack of predictability near the PZT resonant frequency and harmonics (integer multiples) of that frequency. The PZT resonant frequency may be, for example, about 2100 Hz. This means that the behavior of the PZT is unpredictable at or near that repetition rate, and at or near repetition rates such as 4200 Hz. The practical effect of this is that the user must be able to predict the repetition rate n*f r Frequency at ±Δf or their repetition rate n*f rThe constraint is to avoid frequencies around ±Δf, where n is a positive integer and f r is the PZT's resonant frequency, and ±Δf is the repetition rate range around the resonance or harmonic where the PZT's behavior is unpredictable, typically within 10% of the PZT's resonant frequency or within a harmonic of the PZT's resonant frequency. Otherwise, the peak separation may not settle until later in the burst. Here, the term "critical range" refers to repetition rates within 10% of the PZT's resonant frequency or within a harmonic of the PZT's resonant frequency.

[0096]

[0107] According to one aspect of the embodiment, the uncertainty in the PZT parameters is addressed using model-based adaptive control (MRAC) to adjust the laser to a constant speed, e.g., 2*f r The desired peak separation is achieved quickly, even when firing in the range including and around 500 Hz. The unknown behavior of the PZT near resonance is treated as a parameter uncertainty in the PZT reference model. The control system can adapt the control parameters according to the resonance uncertainty and therefore does not rely on accurate PZT calibration results. Such a control system also allows real-time feedback control that can better manage disturbances. Using such a control system, the desired peak separation can be achieved early in the burst, for example by the third pulse. In practice, this removes the constraint on operation at the repetition rate associated with the PZT resonance frequency. In particular, this allows for a repetition rate of 2*f r provides sufficiently reliable operation to allow operation in MFI mode at such repetition rates.

[0097]

[0108] 8, an MRAC system 1000 is configured to control the operation of a controlled system (e.g., an actuator) 1010. The output of the controlled system 1010 is provided as a feedback signal to an adaptive controller 1040. However, because the behavior of the controlled system 1010 lacks predictability while operating within a certain range of repetition rates, according to one aspect of an embodiment, the illustrated embodiment of the MRAC system 1000 includes a reference model 1020, a parameter adaptation module 1030, and an adaptive controller 1040.

[0098]

[0109] A reference input is applied to a reference model 1020 and an adaptive controller 1020. The adaptive controller 1020 generates a control law signal u(t) based on the reference input. The reference model 1020 generates a reference output in response to the reference input. The controlled system 1010 (e.g., a line-narrowing module with one or more actuators) generates an output in response to the signal u(t) and a feedback signal. The output y(t) is provided to a parameter adaptation module 1030. The parameter adaptation module 1030 determines the difference between the reference output and the output y(t) as a tracking error and provides adapted target operating parameters to the adaptive controller 1020. The adaptive controller 1020 generates a control law u(t) based on the adapted target operating parameters. The parameter adaptation module 1030 automatically adjusts the controller parameters so that the behavior of the output y(t) of the closed-loop controlled system 1010 closely follows the behavior of the reference model 1020. In other words, as the control parameters are adjusted, the tracking error converges such that the behavior of the controlled system 1010 tracks the behavior of the reference model 1020 .

[0099]

[0110] In this example, the controlled system 1010 is an actuator tuned to control the peak separation of two wavelengths produced by a laser. A parameter adaptation module 1030 determines the difference between the peak separation of the reference output and the output y(t) as a tracking error and provides the adaptive operating parameter to an adaptive controller 1040. As noted above, ideally, this peak separation should settle to a stable value quickly at the beginning of the burst. Also, as noted above, achieving such a rapid onset of stability is difficult when the laser is operating at or near the repetition rate of the actuator (e.g., a PZT actuator) and its harmonics. However, using the described system, a stable peak separation can be achieved quickly after the start of the burst, even at repetition rates at or near the resonant frequency and its harmonics.

[0100]

[0111] FIG. 9 is a flowchart illustrating an adaptive model-based adaptive control system according to one aspect of an embodiment. In step S10, a reference model is created. In step S20, a reference signal is applied to the reference model and an adaptive controller. In step S30, the adaptive controller generates a control signal based on the reference signal. In practice, it is advantageous to have the parameters of the operational control signal as close to expected values ​​as possible. In step S40, the controlled actuator is driven using the control signal. In step S50, an error or difference between the output of the reference model and the output of the controlled actuator is determined. In step S60, the operational control parameters are adjusted to reduce the error or difference signal between the output of the reference model and the output of the controlled actuator. In this way, the error converges and the behavior of the controlled actuator matches the behavior of the reference model.

[0101]

[0112] 10, various embodiments and components thereof may be implemented using one or more well-known computer systems, such as the example embodiments, systems, and / or devices shown or otherwise described. Computer system 1200 may be any well-known computer capable of performing the functions described herein.

[0102]

[0113] Computer system 1200 includes one or more processors (also referred to as central processing units or CPUs), such as processor 1210. Processor 1210 is connected to a communication infrastructure or bus 1220.

[0103]

[0114] Each of the one or more processors 1210 may be a graphics processing unit (GPU). In one embodiment, a GPU is a processor that is a specialized electronic circuit designed to process mathematically intensive applications. A GPU may have a parallel structure that is efficient for parallel processing of large blocks of data, such as mathematically intensive data common in computer graphics applications, images, video, etc.

[0104]

[0115] The computer system 1200 also includes user input / output devices 1230 , such as a monitor, keyboard, pointing device, etc., that communicate with the communications infrastructure 1220 via a user input / output interface 1240 .

[0105]

[0116] Computer system 1200 also includes main or primary memory 1250, such as random access memory (RAM). Main memory 1250 may include one or more levels of cache. Main memory 1250 stores control logic (i.e., computer software) and / or data.

[0106]

[0117] Computer system 1200 may also include one or more secondary storage devices or memory 1260. Secondary storage device 1260 may include, for example, a hard disk drive 1280 and / or a removable storage device or drive 1290. Removable storage drive 1290 may be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, a tape backup device, and / or other storage device / drive.

[0107]

[0118] The removable storage drive 1290 may interface with a removable storage unit 1300. The removable storage unit 1300 comprises a computer-usable or readable storage device on which computer software (control logic) and / or data are stored. The removable storage unit 1300 may be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, and other computer data storage device. The removable storage drive 1290 reads from and / or writes to the removable storage unit 1300 in a well-known manner.

[0108]

[0119] According to one example embodiment, secondary memory 1260 may include other means, techniques, or approaches for making computer programs and / or other instructions and / or data accessible by computer system 1200. Such means, techniques, or approaches may include, for example, removable storage unit 1310. Examples of removable storage unit 1310 include program cartridges and cartridge interfaces (such as those found in video game devices), removable memory chips (such as EPROMs or PROMs) and associated sockets, memory sticks and USB ports, memory cards and associated memory card slots, and / or other removable storage units and associated interfaces.

[0109]

[0120] Computer system 1200 may further include a communications or network interface 1320. Communications interface 1320 enables computer system 1200 to communicate and interact with any combination of remote devices, remote networks, remote entities, etc. (individually and collectively referred to by reference numeral 1330). For example, communications interface 1320 enables computer system 1200 to communicate with remote devices 1330 over communications path 1340, which may be wired and / or wireless, and which may include any combination of a LAN, a WAN, the Internet, etc. Control logic and / or data may be transmitted to and received from computer system 1200 via communications path 1340.

[0110]

[0121] In one embodiment, a non-transitory, tangible apparatus or article of manufacture includes a non-transitory, tangible, computer-usable or readable medium having stored thereon control logic (software), also referred to herein as a computer program product or program storage device, including, but not limited to, exemplary computer system 1200, main memory 1008, secondary memory 1010, and removable storage units 1018 and 1022, as well as tangible articles of manufacture embodying any combination of the above. Such control logic, when executed by one or more data processing devices (e.g., computer system 1200), causes such data processing devices to operate as described herein.

[0111]

[0122] Based on the teachings contained herein, it will be apparent to one skilled in the art how to make and use embodiments of the present disclosure using data processing devices, computer systems and / or computer architectures other than those shown in Figure 10. In particular, embodiments may operate with software, hardware and / or operating system implementations other than those described herein.

[0112]

[0123] Although specific reference has been made above to the use of embodiments in the context of optical lithography, it will be appreciated that embodiments may be used in other applications, for example imprint lithography, and are not limited to optical lithography where circumstances permit.

[0113]

[0124] It is to be understood that the phrases or terms herein are for purposes of description and not of limitation, and that the terms or terms herein should be interpreted by one of ordinary skill in the art in light of the teachings herein.

[0114]

[0125] It is understood that the Detailed Description section is intended to be used to interpret the claims, and not the Summary and Abstract sections. The Summary and Abstract sections may describe one or more exemplary embodiments, but may not describe all exemplary embodiments, as contemplated by the inventors, and thus are not intended to limit the scope of the embodiments and appended claims in any way.

[0115]

[0126] The embodiments of the present invention have been described using functional building blocks that illustrate the implementation of specific functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of description. Alternative boundaries may be defined as long as the specific functions and relationships thereof are appropriately implemented.

[0116]

[0127] The above description of specific embodiments sufficiently clarifies the general nature of the embodiments so that others, by applying knowledge within the art, can readily modify and / or adapt such specific embodiments for various uses without undue experimentation and without departing from the general concept of the embodiments. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0117]

[0128] The breadth and scope of embodiments should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

[0118]

[0129] The embodiments can be further described using the following clauses. 1. A source of laser radiation, the laser radiation being emitted in one or more bursts, each burst consisting of a plurality of pulses; a wavelength controller arranged to receive the pulses and to control a dominant wavelength of some of the pulses toward a first value and to control a dominant wavelength of other of the pulses toward a second value that differs from the first value by a target dominant wavelength separation amount, the wavelength controller including at least one actuator operative in response to a control signal to cause wavelength control of the pulses; a model-based adaptive control system adapted to generate control signals based at least in part on the measured dominant wavelength separation so that the wavelength controller achieves the target dominant wavelength separation; 1. A laser system comprising: 2. The laser system of clause 1, wherein the source of laser radiation is an excimer laser. 3. The laser system of claim 1, wherein the actuator includes a piezoelectric transducer. 4. The laser system of clause 1, wherein the wavelength controller is a line narrowing module. 5. The laser system of clause 1, wherein the wavelength controller is a line narrowing module including an optical element mechanically coupled to at least one actuator. 6. The laser system of clause 5, wherein at least one actuator includes a piezoelectric transducer. 7. A multi-focus imaging photolithography system that generates first wavelength pulses of deep ultraviolet light having a first dominant wavelength and second wavelength pulses of deep ultraviolet light having a second dominant wavelength that differs from the first dominant wavelength by a dominant separation amount, comprising: a wavelength controller arranged to receive deep ultraviolet input pulses and to control, in response to a control signal, a dominant wavelength of a first subset of the pulses to obtain first wavelength pulses and a dominant wavelength of a second subset of the input pulses to obtain second wavelength pulses; a model-based adaptive control system adapted to generate a control signal based at least in part on the measured dominant wavelength separation of the first wavelength pulse and the second wavelength pulse so that the wavelength controller achieves and maintains a target dominant wavelength separation amount; A multi-focus imaging photolithography system comprising: 8. The multi-focus imaging photolithography system of clause 7, wherein the source of laser radiation is an excimer laser. 9. The multi-focal imaging photolithography system of clause 7, wherein the wavelength controller includes an electrically actuatable component. 10. The multi-focus imaging photolithography system of clause 7, wherein the wavelength controller is a line narrowing module. 11. The multi-focus imaging photolithography system of clause 10, wherein the line narrowing module includes an electrically actuatable component. 12. The multi-focal imaging photolithography system of clause 11, wherein the electrically actuatable component comprises a piezoelectric transducer. 13. A system for controlling the wavelength of laser radiation emitted in one or more bursts, comprising: Each burst consists of multiple pulses, and the system: a wavelength controller arranged to receive the pulses and to control a dominant wavelength of some of the pulses toward a first value and to control a dominant wavelength of other of the pulses toward a second value that differs from the first value by a target dominant wavelength separation amount, the wavelength controller including at least one actuator operative in response to a control signal to cause wavelength control of the pulses; a model-based adaptive control system adapted to generate control signals based at least in part on the measured primary separation amount so that the wavelength controller achieves the target primary separation amount; A system including: 14. The system of clause 13, wherein the actuator includes a piezoelectric transducer. 15. The system of clause 13, wherein the wavelength controller is a line narrowing module. 16. The system of clause 13, wherein the wavelength controller is a line narrowing module that includes an optical element mechanically coupled to an actuator. 17. The system of clause 16, wherein the actuator includes a piezoelectric transducer. 18. The system of clause 13, wherein each burst includes a plurality of pulses fired at a repetition rate, and wherein the model-based adaptive control system generates a control signal based at least in part on the measured dominant wavelength separation amount, such that the wavelength controller is adapted to achieve the target dominant wavelength separation amount even when the repetition rate is within a critical range where operation of the electrically actuatable component becomes unstable. 19. The system of clause 18, wherein the critical range is + / - 10% of the resonant frequency of the electrically actuatable component or a harmonic of the resonant frequency of the electrically actuatable component. 20. The system of clause 18, wherein the electrically actuatable component includes a piezoelectric transducer. 21. A method of controlling a multi-focus imaging photolithography system that generates first wavelength pulses of radiation having a first dominant wavelength and second wavelength pulses of radiation having a second dominant wavelength that differs from the first dominant wavelength by a dominant separation amount, comprising: generating an input pulse of laser radiation; using a wavelength controller to control, in response to the control signal, a dominant wavelength of a first subset of the input pulses to obtain first wavelength pulses and a dominant wavelength of a second subset of the input pulses to obtain second wavelength pulses; comparing a dominant wavelength separation between the first wavelength pulse and the second wavelength pulse with a dominant wavelength separation obtained from a reference model controlled by a reference signal to obtain an error signal; modifying one or more parameters of the control signal based at least in part on the error signal so that the response of the wavelength controller to the control signal tracks the response of the reference model to the reference signal; A method comprising: 22. The method of clause 21, wherein generating the input pulses of laser radiation is performed using an excimer laser. 23. The method of clause 22, wherein using a wavelength controller includes using a line narrowing module.

[0119]

[0130] These and other implementations are within the scope of the following claims.

Claims

1. a source of laser radiation, the laser radiation being emitted in one or more bursts, each burst consisting of a plurality of pulses; a wavelength controller arranged to receive the pulses and to control a dominant wavelength of some of the pulses toward a first value and to control a dominant wavelength of other of the pulses toward a second value that differs from the first value by a target dominant wavelength separation amount, the wavelength controller comprising at least one actuator operative in response to a control signal to cause wavelength control of the pulses; a model-based adaptive control system adapted to generate the control signal based at least in part on a measured dominant wavelength separation so that the wavelength controller achieves the target dominant wavelength separation; and 1. A laser system comprising:

2. 10. The laser system of claim 1, wherein the source of laser radiation is an excimer laser.

3. The laser system of claim 1 , wherein the actuator comprises a piezoelectric transducer.

4. 10. The laser system of claim 1, wherein the wavelength controller is a line narrowing module.

5. 10. The laser system of claim 1, wherein said wavelength controller is a line narrowing module including an optical element mechanically coupled to said at least one actuator.

6. 6. The laser system of claim 5, wherein the at least one actuator includes a piezoelectric transducer.

7. 1. A multi-focus imaging photolithography system that generates a first wavelength pulse of deep ultraviolet light having a first dominant wavelength and a second wavelength pulse of deep ultraviolet light having a second dominant wavelength that differs from the first dominant wavelength by a dominant separation amount, comprising: a wavelength controller arranged to receive deep ultraviolet input pulses and to control, in response to a control signal, a dominant wavelength of a first subset of the pulses to obtain the first wavelength pulses and a dominant wavelength of a second subset of the input pulses to obtain the second wavelength pulses; a model-based adaptive control system adapted to generate the control signal based at least in part on a measured dominant wavelength separation of the first wavelength pulse and the second wavelength pulse so that the wavelength controller achieves and maintains a target dominant wavelength separation amount; and A multi-focus imaging photolithography system comprising:

8. The multi-focus imaging photolithography system of claim 7 , wherein the source of laser radiation is an excimer laser.

9. The multi-focus imaging photolithography system of claim 7 , wherein the wavelength controller includes an electrically actuatable component.

10. The multi-focus imaging photolithography system of claim 7 , wherein the wavelength controller is a line narrowing module.

11. The multi-focus imaging photolithography system of claim 10 , wherein the line narrowing module includes an electrically actuatable component.

12. The multi-focus imaging photolithography system of claim 11 , wherein the electrically actuatable component comprises a piezoelectric transducer.

13. 1. A system for controlling the wavelength of laser radiation emitted in one or more bursts, comprising: Each burst is comprised of a plurality of pulses, and the system comprises: a wavelength controller arranged to receive the pulses and to control a dominant wavelength of some of the pulses toward a first value and to control a dominant wavelength of other of the pulses toward a second value that differs from the first value by a target dominant wavelength separation amount, the wavelength controller comprising at least one actuator operative in response to a control signal to cause wavelength control of the pulses; a model-based adaptive control system adapted to generate the control signal based at least in part on a measured primary separation amount so that the wavelength controller achieves the target primary separation amount; A system including:

14. The system of claim 13 , wherein the actuator comprises a piezoelectric transducer.

15. The system of claim 13 , wherein the wavelength controller is a line narrowing module.

16. The system of claim 13 , wherein the wavelength controller is a line narrowing module that includes an optical element mechanically coupled to the actuator.

17. The system of claim 16 , wherein the actuator comprises a piezoelectric transducer.

18. 14. The system of claim 13, wherein each burst comprises the plurality of pulses fired at a repetition rate, and wherein the model based adaptive control system generates the control signal based at least in part on a measured dominant wavelength separation amount, such that the wavelength controller is adapted to achieve the target dominant wavelength separation amount even when the repetition rate is within a critical range such that operation of the electrically actuatable component becomes unstable.

19. 20. The system of claim 18, wherein the critical range is + / -10% of the resonant frequency of the electrically actuatable component or a harmonic of the resonant frequency of the electrically actuatable component.

20. The system of claim 18 , wherein the electrically actuatable component includes a piezoelectric transducer.

21. 1. A method of controlling a multi-focus imaging photolithography system that generates first wavelength pulses of radiation having a first dominant wavelength and second wavelength pulses of radiation having a second dominant wavelength that differs from the first dominant wavelength by a dominant separation amount, comprising: generating an input pulse of laser radiation; using a wavelength controller to control, in response to a control signal, a dominant wavelength of a first subset of the input pulses to obtain the first wavelength pulses, and a dominant wavelength of a second subset of the input pulses to obtain the second wavelength pulses; comparing a dominant wavelength separation between the first wavelength pulse and the second wavelength pulse with a dominant wavelength separation obtained from a reference model controlled by a reference signal to obtain an error signal; modifying one or more parameters of the control signal based at least in part on the error signal such that a response of the wavelength controller to the control signal tracks a response of the reference model to the reference signal; A method comprising:

22. 22. The method of claim 21, wherein generating the input pulses of laser radiation is performed using an excimer laser.

23. 23. The method of claim 22, wherein using a wavelength controller comprises using a line narrowing module.

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