Method and system for wavelength measurement for a lithographic apparatus or an inspection apparatus

Abstract

A lithographic apparatus includes an illumination system that includes a metrology system. The illumination system generates a beam of radiation to illuminate a pattern of a patterning device for projecting an image of the pattern onto a substrate. The metrology system includes an etalon, a detector having an array of pixels, and a computing system. The etalon generates a fringe pattern and a next fringe pattern respectively corresponding to a pulse and a next pulse of the beam. The array of pixels generate intensity signals based on fringe pattern intensities at positions of the pixels. The computing system determines a predicted range of pixel positions corresponding to intensity peaks of the next fringe pattern based on pixel positions of intensity peaks of the fringe pattern and performs an abbreviated analysis of the next fringe pattern. The abbreviated analysis is delimited by the predicted range of pixel positions.

Description

METHOD AND SYSTEM FOR WAVELENGTH MEASUREMENT FOR A LITHOGRAPHIC APPARATUS OR AN INSPECTION APPARATUSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Application No. 63 / 561,576, filed March 5, 2024, titled METHOD AND APPARATUS FOR WAVELENGTH MEASUREMENTS, which is incorporated herein by reference in its entirety.FIELD

[0002] The present disclosure relates to metrology systems, for example, a wavelength measurement device and post processing system for lithographic apparatuses or inspection apparatuses.BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which can be a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiationsensitive material (photoresist or simply “resist”) provided on the substrate . In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”- direction) while synchronously scanning the target portions parallel or anti-parallel to this scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] During lithographic operation, different processing steps can entail different layers to be sequentially formed on the substrate. Accordingly, it can be necessary to position the substrate relative to prior patterns formed thereon with a high degree of accuracy. Generally, alignment marks are placed on the substrate to be aligned and are located with reference to a second object. A lithographic apparatus can use an alignment apparatus for detecting positions of the alignment marks and for aligning the substrate using the alignment marks to ensure accurate exposure from a mask. Misalignment between the alignment marks at two different layers is measured as overlay error.

[0005] In order to monitor the lithographic process, parameters of the patterned substrate are measured. Parameters can include, for example, the overlay error between successive layers formed in or on the patterned substrate and critical linewidth of developed photosensitive resist. This measurement can be performed on a product substrate and / or on a dedicated metrology target. There are various techniquesfor making measurements of the microscopic structures formed in lithographic processes, including the use of scanning electron microscopes and various specialized tools. A fast and non -invasive form of a specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Spectroscopic scatterometers direct a broadband radiation beam onto the substrate and measure the spectrum (intensity as a function of wavelength) of the radiation scattered into a particular narrow angular range. By contrast, angularly resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

[0006] Such optical scatterometers can be used to measure parameters, such as critical dimensions of developed photosensitive resist or overlay error between two layers formed in or on the patterned substrate. Properties of the substrate can be determined by comparing the properties of an illumination beam before and after the beam has been reflected or scattered by the substrate. A lithographic process is sensitive to instabilities in the wavelength of the radiation used in pattern transfer.

[0007] During a semiconductor manufacturing process, specifically during various stages such as lithography, etching, deposition, and chemical mechanical polishing, an inspection or a metrology apparatus can leverage radiation to scan a surface of the wafer, pattern defects, or any anomalies that may impact yield. For reticle inspection, the inspection or the metrology apparatus examines the reticles for defects such as missing features, extra features, or contamination, which could be transferred to the substrate during the lithography processes. In some embodiments, the metrology can even provide overlay measurement, ensuring that different layers of the devices are aligned with each other during the manufacturing process. Moreover, the inspection or the metrology apparatus offers in-line process control by providing real-time feedback, allowing users to adjust process parameters on the fly.SUMMARY

[0008] Accordingly, in order to monitor a wavelength of radiation used in lithographic processes or metrology processes, it is desirable for a wavelength measurement tool to measure the wavelength accurately and swiftly.

[0009] In some aspects, a lithographic apparatus can comprise an illumination system comprising a metrology system. The illumination system can generate a beam of radiation to illuminate a pattern of a patterning device for projecting an image of the pattern onto a substrate. The beam can be pulsed. The illumination system can comprise an etalon, a detector comprising an array of pixels, and a computing system. The etalon can generate a fringe pattern corresponding to a pulse of the beam and a next fringe pattern corresponding to a next pulse of the beam after the pulse. The array of pixels can generate intensity signals based on intensities of the fringe pattern and the next fringe pattern at positions of thepixels. The computing system can determine a predicted range of pixel positions corresponding to intensity peaks of the next fringe pattern based on pixel positions of intensity peaks of the fringe pattern. The computing system can also perform an abbreviated analysis of the next fringe pattern. The abbreviated analysis is delimited by the predicted range of pixel positions to reduce a measurement time of the metrology system.

[0010] In some aspects, a metrology system can comprise an etalon, a detector comprising an array of pixels, and a computing system. The etalon can generate a fringe pattern corresponding to a pulse of a beam of radiation and a next fringe pattern corresponding to a next pulse of the beam after the pulse. The array of pixels can generate intensity signals based on intensities of the fringe pattern and the next fringe pattern at positions of the pixels. The computing system can determine a range of pixel positions for intensity peaks of the next fringe pattern based on pixel positions of intensity peaks of the fringe pattern. The computing system can also perform an abbreviated analysis of the next fringe pattern, wherein the abbreviated analysis is delimited by the range pixel position to reduce a measurement time of the metrology system.

[0011] In some aspects, a method can comprise determining a range of pixel positions corresponding to intensity peaks of a fringe pattern based on pixel positions of intensity peaks of the fringe pattern. The pixel positions correspond to an array of pixels of a detector of a metrology system. An etalon of the metrology system is configured to generate the fringe pattern corresponding to a pulse of a beam of radiation and a next fringe pattern corresponding to a next pulse of the beam after the pulse. The array of pixels is configured to generate intensity signals based on intensities of the fringe pattern and the next fringe pattern at positions of the pixels. The method can also comprise performing an abbreviated analysis of the next fringe pattern, wherein the abbreviated analysis is delimited by the range pixel position.

[0012] Further features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to those skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0013] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use aspects described herein.

[0014] FIG. 1 shows a lithographic apparatus, according to some aspects.

[0015] FIG. 2 shows a lithographic cell, according to some aspects.

[0016] FIG. 3 shows a radiation source, according to some aspects.

[0017] FIG. 4 shows a radiation source, according to some aspects.

[0018] FIG. 5 shows a radiation source, according to some aspects.

[0019] FIG. 6 shows a metrology system, according to some aspects.

[0020] FIG. 7 shows a graph for an intensity peak profile of a fringe pattern, according to some aspects.

[0021] FIG. 8 shows a computer system that can be used to implement metrology operations described herein, according to some aspects.

[0022] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0023] The aspects described herein, and references in the specification to “one aspect,” “an aspect,” “an exemplary aspect,” “an example aspect,” etc., indicate that the aspects described can include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0024] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

[0025] The terms “about,” “approximately,” or the like can be used herein to indicate the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the terms “about,” “approximately,” or the like can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0026] Enumerative adjectives (e.g., “first,” “second,” “third,” or the like) can be used as labels to distinguish like elements without establishing an order, hierarchy, quantity, or permanent numeric assignment (unless otherwise noted). For example, a given element can be referred to as a “second target” in one labeling scheme while the same element can be referred to as a “first target” in another labeling scheme.

[0027] Aspects of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure can also be implemented as instructions stored on a computer-readable medium, which can be read and executed by one or more processors. A machine- readable medium can 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 can include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and / or instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. The term “machine -readable medium” can be interchangeable with similar terms, for example, “computer program product,” “computer-readable medium,” “non-transitory computer- readable medium,” or the like . The term “non-transitory” can be used herein to characterize one or more forms of computer readable media except for a transitory, propagating signal.

[0028] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.

[0029] Example Lithographic Systems

[0030] FIG. 1 shows a lithographic apparatus 100, in which aspects of the present disclosure can be implemented. Lithographic apparatus 100 can comprise one ormore ofthe following: an illuminator IL to condition a radiation beam B (e.g., deep ultra violet (DUV) radiation); a support structure MT (e.g., a mask table) to support a patterning device MA (e.g., a mask, a reticle, or a dynamic patterning device); a first positioner PM to accurately position patterning device MA; a substrate table WT (e.g., a wafer table) to hold a substrate W (e.g., a resist-coated wafer); and a second positioner PW to accurately position substrate W. Lithographic apparatus 100 can also comprise a projection system PS to project patterned radiation onto a target portion C (e.g., comprising one or more dies) of substrate W. The pattern can be imparted to radiation beam B by patterning device MA. In lithographic apparatus 100, patterning device MA and projection system PS can be transmissive.

[0031] In some aspects, illuminator IL can comprise various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

[0032] In some aspects, support structure MT can hold patterning device MA in a manner that depends on the orientation of patterning device MA with respect to a reference frame, a design of lithographic apparatus 100, and other conditions, such as whether or not patterning device MA is held in a vacuum environment. Support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. Support structure MT can be, for example, a frame or a table (e.g., can be fixed ormovable). By using one ormore positioning sensors (e.g., alignment sensor),support structure MT can ensure that patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0033] In some aspects, the term “patterning device” can refer to a device that can be used to create a pattern of radiation at a cross-section of radiation beam B, such as to create a pattern at target portion C of substrate W. The pattern imparted to radiation beam B can correspond to a particular functional layer in a device being created at target portion C to form an integrated circuit. Examples of patterning devices MA include, for example, reticles, masks, or programmable LCD panels. Masks types used in lithography can include binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types.

[0034] In some aspects, the term “projection system” can refer to any type of projection system (e.g., refractive, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof) suitable for the exposure radiation being used. Features of projection systems can account for additional factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. For example, a projection system can be designed for use in a controlled gas environment such that the beam path can be conditioned as desired.

[0035] In some aspects, lithographic apparatus 100 can be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table.

[0036] In some aspects, lithographic apparatus 100 can also be of a type in which at least a portion of substrate W can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between projection system PS and substrate W. An immersion liquid can also be applied to other spaces in lithographic apparatus 100, for example, between patterning device MA and projection system PS. Immersion techniques can increase the numerical aperture (NA) of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid. For example, a liquid can be disposed between projection system PS and substrate W during exposure.

[0037] In some aspects, illuminator IL can receive a radiation beam from source SO (e.g., radiation source). Source SO and lithographic apparatus 100 can be separate physical entities. For example, source SO can be a detached excimer laser. In such cases, source SO is not considered to be part of the lithographic apparatus 100 and radiation beam B passes from source SO to illuminator IL with the aid of a beam delivery system BD. Beam delivery system BD can include, for example, suitable directing mirrors and / or a beam expander.

[0038] In some aspects, source SO can be an integral part ofthe lithographic apparatus 100. A radiation system (or illumination system) can comprise source SO, illuminator IL, and / or beam delivery system BD.

[0039] In some aspects, illuminator IL can comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as “n-outer” and “n-inner,” respectively) of the intensity distribution in a pupil plane of illuminator IL can be adjusted. In addition, illuminator IL can comprise various other components, such as an integrator IN and a condenser CO. Illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

[0040] In some aspects, radiation beam B can be incident on patterning device MA, which is held on support structure MT, and is patterned by patterning device MA. Having traversed patterning device MA, radiation beam B can pass through projection system PS, which focuses the beam onto a target portion C of substrate W. Projection System PS has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

[0041] In some aspects, projection system PS can project an image of a pattern MP of patterning device MA. The image can be formed by diffracted beams produced from the pattern MP by radiation from the intensity distribution. The image can be projected on a photoresist layer coated on the substrate W. For example, pattern MP can comprise an array of lines and spaces. A diffraction of radiation at the array and different from zeroth order diffraction can generate diverted diffracted beams with a change of direction in a direction perpendicular to the lines. Undiffracted beams (i.e., so-called zeroth order diffracted beams) can traverse the pattern without any change in propagation direction. The zeroth order diffracted beams can traverse an upper lens or upper lens group of projection system PS, upstream of pupil conjugate PPU of projection system PS, to reach pupil conjugate PPU. The portion of the intensity distribution in the plane of pupil conjugate PPU and associated with the zeroth order diffracted beams is an image of the intensity distribution in the illumination system pupil IPU of the illuminator IL. An aperture device PD, for example, can be disposed at or substantially at a plane that includes pupil conjugate PPU of projection system PS.

[0042] In some aspects, projection system PS can capture the zeroth order diffracted beams, first order diffracted beams, and / or higher order diffracted beams (not shown) (e.g., capture using a lens or lens group L). In some aspects, dipole illumination for imaging line patterns extending in a direction perpendicular to a line can be used to utilize the resolution enhancement effect of dipole illumination. For example, first-order diffracted beams can interfere with corresponding zeroth-order diffracted beams at the level of substrate W to create an image of pattern MP at a highest possible resolution and process window (e.g., usable depth of focus in combination with tolerable exposure dose deviations). In some aspects, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of illumination system pupil IPU. Further, in some aspects, astigmatism aberration can be reduced by blocking the zeroth order beams, at pupil conjugate PPU, that are associated withradiation poles in opposite quadrants. This is is described in more detail in US 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

[0043] In some aspects, with the aid of second positioner PW and position sensor IFD (for example, an interferometric device, linear encoder, or capacitive sensor), substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of radiation beam B). Similarly, first positioner PM and another position sensor (not shown) can be used to accurately position patterning device MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).

[0044] In some aspects, movement of support structure MT can be achieved using a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of first positioner PM. Similarly, movement of substrate table WT can be achieved using a long-stroke module and a short-stroke module, which form part of second positioner PW. In the case of a stepper (as opposed to a scanner), support structure MT can be connected to a short-stroke actuator or can be fixed. Patterning device MA and substrate W can be aligned using measurement targets, for example, mask alignment marks Ml, M2, and substrate alignment marks Pl, P2. Although targets as illustrated (e.g., substrate alignment marks Pl, P2) can occupy dedicated target portions, targets can be located in spaces between target portions (referred to as scribe -lane targets or alignment marks). Similarly, in situations in which more than one die is provided on patterning device MA, the mask alignment marks can be located between the dies.

[0045] In some aspects, support structure MT and patterning device MA can be in a vacuum chamber V. An in-vacuum robot IVR can be used to move patterning devices, such as a mask, in and out of vacuum chamber V. Alternatively, when support structure MT and patterning device MA are outside of the vacuum chamber, an out-of-vacuum robot can be used for various transportation operations, similar to in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots can be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0046] In some aspects, lithographic apparatus 100 can be used in at least one of the following modes:

[0047] 1. In step mode, the support structure (for example, mask table) MT and substrate table WT can be kept substantially stationary, while an entire pattern imparted to radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). Substrate table WT can then be shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0048] 2. In scan mode, support structure MT and substrate table WT can be scanned synchronously while a pattern imparted to radiation beam B is projected onto a target portion C (e.g., a single dynamic exposure). The velocity and direction of substrate table WT relative to support structure MT can be determined by the (de-)magnification and image reversal characteristics of projection system PS.

[0049] 3. In another mode, support structure MT can be kept substantially stationary holding a programmable patterning device, and substrate table WT can be moved or scanned while a patternimparted to radiation beam B is projected onto a target portion C. A pulsed radiation source for source SO can be employed and the programmable patterning device can be updated as needed after each movement of substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0050] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0051] In some aspects, lithographic apparatuses can comprise a deep ultraviolet (DUV) source, which is configured to generate a beam of DUV radiation for DUV lithography. In general, the DUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the DUV radiation beam of the DUV source.

[0052] Example Uithographic Cell

[0053] FIG. 2 shows a lithographic cell 200, also sometimes referred to a lithocell or cluster, according to some aspects. Uithographic apparatus 100 can form part of lithographic cell 200. Uithographic cell 200 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Examples of such apparatuses can include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO can pick up substrates from input / output ports I / Ol, I / O2, move them between the different process apparatuses and deliver the substrates to a loading bay LB of lithographic apparatus 100. The different apparatuses, which are often collectively referred to as the track, can be under the control of a track control unit TCU, which can itself be controlled by a supervisory control system SCS. Supervisory control system can also control lithographic apparatus 100 via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0054] Example Radiation Source

[0055] There are many applications of pulsed-discharge radiation sources. In some aspects, a pulsed-discharge laser can be used for lithographic processes, medical procedures, machining via laser ablation, laser imprinting, and more. A lithographic apparatus is one example in which a stable radiation source is desirable. Instabilities of the radiation beam can cause a lithographic process to introduce errors in a pattern transfer. Examples of instabilities can include, but are not limited to, wavelength fluctuations, dose or intensity fluctuations, or the like.

[0056] FIG. 3 shows a radiation source 300, according to some aspects. In some aspects, radiation source 300 is a pulsed-discharge radiation source. A gas discharge laser is an example of a pulsed-discharge radiation source. Source SO of lithographic apparatus 100 (FIG. 1) can use implement radiation source 300. Radiation source 300 can comprise a gas chamber 302, a window 304, and one or more electrodes 310.

[0057] In some aspects, gas chamber 302 can confine a gas 308. Gas 308 can comprise fluorine, neon, krypton, argon, and the like. Gas 308 can be rarified via a pressure control system (e.g., vacuum system)that controls a pressure within gas chamber 302. A voltage / current can be supplied to gas 308 (e.g., via one or more electrodes 310) to generate radiation 312. The voltage / current can be in the form of pulse with sufficient power to strike a plasma of gas 308. The plasma can generate radiation with a set of wavelengths that depend on energy states of the plasma. The type of gas 308 (e.g., fluorine) can determine the wavelengths that are produced (e.g., DUV wavelengths). Window 304 can allow radiation 312 to exit gas chamber 302.

[0058] FIG. 4 shows a radiation source 400, according to some aspects. In some aspects, radiation source 400 can include a gas chamber 402, a gas 408, electrodes 410, a gas circulator 414, and a plasma region 416. Gas circulator 414 can be blower or an external pressure system that is connected to gas chamber 402 via ducting. Gas can comprise fluorine, neon, krypton, argon, or other similar species (for example, argon fluoride). For radiation source 400 to generate radiation, an electrical pulse can be supplied to gas 408 via electrodes 410, thereby igniting a plasma of gas 408 at plasma region 416. The generated plasma can release radiation, thereby operating as a radiation source. The perspective in FIG. 4 can be considered as being 90 degrees with respect to the perspective of FIG. 3 (e.g., whereas radiation 312 is shown in FIG. 3 traveling to the right of the page (can also be left of the page), radiation can travel in / out of the page in FIG. 4).

[0059] In some aspects, in the process of generating radiation, gas 408 and electrodes 410 can interact chemically. For example, a material of electrodes 410 (e.g., copper) can chemically interact with a chemical content of gas 408 (e.g., fluoride) to create a dust-like byproduct (e.g., metal -fluoride by product). The airborne byproduct can become a contaminant that absorbs radiation in subsequent radiation pulses. Therefore, a gas flow 418 (indicated by arrows) can be implemented in order to optimize the production of radiation by circulating the expended portion of gas 408 away from plasma region 416, while also supplying unspent gas for the next pulse of plasma ignition. Gas circulator 414 can generate gas flow 418. Additional details about blower functions are described in WO 2022 / 140074, published on June 30, 2022, which is incorporated by reference herein in its entirety.

[0060] FIG. 5 shows a radiation source 500, according to some aspects. In some aspects, radiation source 500 can include gas chamber 502, gas 508, radiation 512, gas circulator 514, an output coupler 520, a wavelength selector 522, and a controller 524. Wavelengths selector 522 can comprise a wavelength-dependent reflector 526. For example, wavelength-dependent reflector 526 can comprise a refractive element (e.g., one or more prisms) and / or a diffractive element (e.g., one or more gratings).

[0061] In some aspects, an electrical pulse is applied to gas 508 to ignite a plasma and generate radiation 512. Molecules of gas 508 can have electron energy levels capable of decaying with the release of photons (photon wavelengths correspond to the multiple energy levels). Subsequently, a portion of radiation 512 is output as a beam of radiation 528 from radiation source 500. In the context of lithographic processes, beam of radiation 528 can be used as radiation beam B of FIG. 1. A narrow and stable wavelength is desirable for lithographic processes. Wavelength instabilities can adversely impact the accuracy of patterns that are printed on a substrate. As a non -limiting example, beam of radiation528 can have a DUV wavelength of approximately 193 nm, which can be used for a lithographic process. It is desirable to have access to a variety of wavelengths to choose from.

[0062] In some aspects, wavelength selector 522 can be used to perform wavelength selection. The wavelength selection process can rely on lasing to further amplify the radiation at the desired wavelength while suppressing unselected wavelengths (e.g., higher signal-to-noise (SNR)). The process can begin by allowing radiation 512 to propagate toward wavelength selector 522, which can be achieved via implementation of window(s) (e.g., see window 304 (FIG. 3)). Wavelength-dependent reflector 526 can reflect a portion of radiation 512 (the portion that has the selected wavelength) along a “gain path” while rejecting other portions of radiation 512 that have undesirable wavelengths (e.g., diverting unselected wavelengths toward a beam dump). Hence, the wavelength of radiation 512 can be narrowed to a narrowband having a peak central wavelength and a small full -width at half-maximum (FWHM). Wavelength selector 522 can be referred to as a narrowing device, narrowing module, line narrowing module (LNM), or the like.

[0063] In some aspects, the “gain path” can be the space where radiation 512 bounces back and forth between wavelength-dependent reflector 526 and output coupler 520, with the plasma of gas 508 being the gain medium. Lasing can be achieved as radiation 512 (at the selected wavelength) bounces back and forth between wavelength -dependent reflector 526 and output coupler 520 (output coupler 520 can have a reflective property). Output coupler 520 can comprise a partial reflector that allows a fraction of the, now amplified, radiation 512 (at the selected wavelength) to be output as beam of radiation 528.

[0064] In some aspects, gas chamber 502 can be referred to as a master oscillator (MO) chamber since radiation 512 is generated at gas chamber 502 and oscillates back and forth through gas chamber 502 to achieve intensity gains.

[0065] In some aspects, adjusting the wavelength (e.g., selecting another wavelength) can be achieved by adjusting a position of wavelength-dependent reflector 526 (e.g., rotating a diffractive or refractive element). Diffractive and refractive elements have wavelength-dependent scattering directions. As the position of the diffractive (or refractive) element is changed, a different wavelength can be aligned along the gain path while other wavelengths are directed away from the gain path. The lasing process can then amplify radiation 512 for the adjusted wavelength.

[0066] In some aspects, wavelength selector 522 can also comprise an actuator 530 (e.g., a piezo device), wavelength-dependent reflector 526 can be disposed on actuator 530. Controller 524 can be used in to perform the wavelength selection or adjustment by actuating wavelength -dependent reflector 526 via actuator 530. It is desirable for actuator 530 to be capable of high positional accuracy, as well as high speed adjustments (e.g., greater than 1 kHz, 10 kHz, or the like). Controller 524 can send a control signal 532 (e.g., a command, instructions, voltage / current signal, or the like). Actuator 530 can move according to control signal 532.

[0067] In some aspects, radiation source 500 can comprise a detector 534 to interrogate a portion of radiation 512. Detector 534 can be disposed at wavelength selector 522. Detector 534 can be referredto as a line-center analysis module or a bandwidth analysis module for analyzing one or more performance criteria (e.g., wavelength, bandwidth, intensity, and energy distribution) of wavelength selector 522. In some aspects, detector 534 can be disposed at other suitable locations for receiving a portion of radiation 512 or a portion of beam of radiation 528. While detector 534 is illustrated as being in the path of radiation 512, it is to be appreciated that detector 534 can be disposed elsewhere and a beam splitter can be implemented to direct a portion of radiation 512 toward detector 534. In one instance, detector 534 generates a measurement signal 536 that is indicative of the wavelength of beam of radiation 528. Measurement signal 536 can be received at controller 524, as well as at other processing systems. Measurement signal 536 can be used for reporting a real-team status of the wavelength of beam of radiation 528.

[0068] In some aspects, radiation source 500 can also comprise one or more additional amplification chambers 540. Amplification chambers 540 can provide additional amplification of beam of radiation 528. Amplification chambers 540 can also be referred to as power oscillator (PO) chambers, power amplifier (PA) chambers, or power ring amplifier (PRA) chambers.

[0069] Additional details about wavelength-selection are described in U.S. Patent No. 8,254,420, issued on August 28, 2012, which is incorporated by reference herein in its entirety.

[0070] Example Measurement Signal Processing

[0071] In scenarios in which the actual wavelength of a radiation source is inaccurate and different from a prescribed wavelength, it is desirable to re-establish the selected wavelength via corrective action. In order to initiate corrective procedures, it is desirable for the wavelength measurement tool to measures the wavelength accurately and swiftly. For a pulsed radiation source, it is desirable to be able to measure the wavelength of one pulse and be able to take corrective action before the firing of the immediate next pulse. If kilohertz repetition rates are used (e.g., 1-10 kHz), a constraint would be to detect wavelength and move the wavelength selector in a time frame no more than 0. 1 to 1 millisecond. In this manner, the number of pulses with incorrect wavelengths can be minimized. Aspects disclosed herein can be used to shorten measurement times for wavelength measurements.

[0072] FIG. 6 shows a metrology system 600, according to some aspects. In some aspects, metrology system 600 can be used as detector 534. Metrology system 600 can comprise an etalon 602, a detector 604, and computing system 606. Etalon 602 can comprise a first component 608 and a second component 610. In some embodiments, first component 608 and second component 610 have a same refraction index. First component 608 and second component 610 are separated by a medium. The medium has a different refraction index than components 608 and 610. Detector 604 can comprise an array of pixels 612. Detector 604 can comprise a photodiode array. The array of pixels can be a onedimensional (1-D) photodiode array (e.g., a plurality of photodiodes arranged in a line). Other types of detector arrays can be used (e.g., a camera having a two-dimensional (2-D) array of pixels).

[0073] In some aspects, etalon 602 can receive a beam of radiation 614. Beam of radiation 614 has a wavelength that is to be measured by metrology system 600. Beam of radiation 614 can correspond toa portion radiation that is used as input for metrology system 600. At least one of first component 608 and second component 610 has a partially reflective surface facing the medium. Radiation 614 is reflected back and forth between first component 608 and second component 610. A portion of the bouncing radiation can exit etalon 602 via second component 610 and propagate toward detector 604. The exiting radiation can interfere to generate a fringe pattern 616 at detector 604. Fringe pattern 616 includes a plurality of concentric rings having fringe features 620, 622, 624 and 626. The pixels of detector 604 can generate intensity signals 618 based on intensities of fringe pattern 616 at respective positions of the pixels. In some aspects, a portion of a beam radiation exiting output coupler propagate toward a coarse diffractive element, such as a grating, and form a coarse feature 628 on a plane of fringe pattern 616. Coarse feature 628 can be a spot pattern or have a grain shape. The course feature 628 provides a lower-resolution of the wavelength information. To generate coarse feature 628, a portion of radiation that is injected into metrology system 600 can be split off as beam of radiation 630 (e.g., using a beam splitter). Beam of radiation 630 can be reflected off or passed through a grating 632 so as to deflect beam of radiation 630.

[0074] In some aspects, computing system 606 can receive intensity signals 618. As will be appreciated by those skilled in the art, each pixel can essentially be considered an independent measurement channel and each of intensity signals 618 can be considered independent signals to be analyzed. For example, for an array of 1024 pixels, computing system 606 analyzes 1024 signals, extracts 1024 different intensities, and so on. For a computing system to read off elements of a detector array such as pixels, a simple and cost-efficient method is to scan across the pixels. For example, in the case of a 2-D array, a raster pattern can be used to read from one pixel at a time. For a 1-D array, pixels can be read in order, from one pixel to the next. As will be appreciated by those skilled in the art, reading off of pixels of a detector has an associated finite time period (that is, it can be time consuming). The requisite time can be compounded by additional analysis and computations as the number of pixels are increased (e.g., doubling the number of pixels on detector 604 can double the measurement time).

[0075] Reducing measurement times can aid efforts to detect wavelength and also adjust the wavelength selector in atime between pulses — with pulses repeating at kilohertz rates. Therefore, rather than reading off of every pixel of detector 604, computing system 606 can be configured to predict a range of pixel positions for intensity peaks of the next fringe pattern based on pixel positions of intensity peaks of a prior fringe pattern. In some aspects, the prediction of computing system 606 is further based on a shift of an optics component, such as a grating or a prism in a wavelength selector, or grating 632. With the predicted range of pixel positions determined, computing system 606 can perform an abbreviated analysis of the next fringe pattern. The abbreviated analysis is delimited by the predicted range pixel position, thereby increasing a measurement speed of the metrology system.

[0076] To appreciate the reduction of computational burden reduction and measurement time, it is instructive to consider an example measurement of intensity peaks of a fringe pattern at array of pixels

[0077] FIG. 7 shows a graph 700 for an intensity peak profile of a fringe pattern, according to some aspects. The features of graph 700 shall be described with reference to FIGS. 5 and 6. However, the features of graph 700 are not limited to the apparatus illustrated in FIGS. 5 and 6. Moreover, while features of graph 700 are described in relation to detector 604 and computing system 606, data acquisition and analysis thereof can be performed using any suitable detector and computing device within the scope of the present disclosure.

[0078] In some aspects, the horizontal axis represents a position of pixels of detector 604. The vertical axis represents an intensity of radiation detected at a given pixel position. Fringe peaks 720, 722, 724, and 726 respectively match fringe features 620, 622, 624, and 626 of FIG. 6. Fringe peaks 720 and 724 correspond to opposite sides of a ring pattern having fringe features 620 and 624. The ring is characterized by a diameter d in both of FIGS. 6 and 7. It is to be appreciated that each of measurement signals 618 can correspond a position of a pixel of detector 604.

[0079] In some aspects, a wavelength of radiation detected by detector 604 can be determined using Equation 1:A = (2ND / m)cos (d / 2FD) Eq. 1.

[0080] Here, A is the wavelength, N and D are parameters fixed by hardware and known ahead of time (such as refraction index and etalon spacing, respectively), FD refers to focal distance from lens to the plane of fringe pattern, which is also known ahead of time, and m is the order of fringe, and d is the diameter of fringe ring as described in FIGS. 6 and 7. To accurately determine the wavelength A, the values of diameter d and order m are calculated from the features of graph 700 (that is, by analyzing measurement signals 618).

[0081] In some aspects, analysis of a coarse peak 728 is enough to determine the order m. Coarse peak 728 can correspond to coarse feature 628 in FIG. 6. Since the amount of deflection of beam of radiation 630 is dependent upon wavelength, knowing the pixel position of coarse feature 628 is enough to approximate the wavelength A (hence the names of the elements coarse feature 628 and coarse peak 728). A fringe pattern looks exactly the same if the wavelength undergoes a change by what is known as a free spectral range (FSR). Since fringe pattern 616 looks the same from order to order (e.g., over one FSR), knowing the pixel position of coarse peak 728 is enough information to uniquely determine the value of order m by eliminating incompatible values.

[0082] In some aspects, once the value of order m is determined, the value of diameter d is used in order to determine a finer value of the wavelength A, using Eq. 1. The measured wavelength can then be sent back to a radiation source as feedback information (e.g., as measurement signal 536).

[0083] As explained above, the processing of the fringe information can involve scanning through pixels of detector 604 to search for the pixel location of peak 720. In the absence of historical fringe information, a large scan range of Ax pixel positions can be implemented, starting from an initial pixelposition xo to a final pixel position Xf. The large range of Ax pixels can be chosen based on how the fringe rings are expected to change over one FSR (e.g., based on the point at which center peak fringe 722 “separates” enough to no longer be a spot, but a ring).

[0084] However, in order to reduce computing burden and time of scanning through a large number of pixels, an estimate of a narrower scan range in a future fringe measurement can be made based on available information of a most recently measured fringe pattern. That is, based on the observed pixel positions of intensity peak 720 of a present pulse of radiation, a predicted range of pixel positions Ax' is determined for an intensity peak of the next fringe pattern of a next pulse of radiation. The predicted range of pixel positions Ax' can be just wide enough to accommodate fluctuations due to noise. Then, computing system 606 can perform and abbreviated analysis of the next fringe pattern, the abbreviated analysis being based on the narrower predicted range of pixel positions Ax' rather than a full scan of Ax pixel positions. In some aspects, the predicted range of pixel positions Ax' is determined by a set number of pixels prior to and after a pixel of a intensity peak (i.e., an intensity center). The set number of pixels ranges from about 20 to about 200 pixels. If the set number is greater than 200, there is no significant improvement in saving measurement time, in some instances. If the set number is smaller than 20, the likelihood of missing the peak intensity increases, in some instances. However, in some aspects, if a peak intensity is still positioned in a center of the predicted range of pixel positions Ax', the set number of pixels ranges can even reduce to 5 pixels. Reducing the set number of pixels further will lead to a significant increase in errors. In some aspects, a thermal expansion effect of detector 604 is considered. The same abbreviated analysis can be performed for fringe peak 724, thereby extracting a value of the distance in a shorter time frame as compared to performing a full of pixel positions. Having determined the distance d, computing system 606 can then determine an accurate value of the wavelength 2 using Eq. 1. Furthermore, the method of limiting the scan range can also be applied to analysis of coarse peak 728 and future pulses thereof. While measuring and analyzing of coarse peak 728 on every pulse provide comprehensive results, it may be unnecessary to detect coarse peak 728 every single pulse. In some aspects, a detection of coarse peak 728 every two to four pulses offers a more efficient approach. However, in some aspects, the measurement and analysis of coarse peak 728 are optional. For example, the analysis of coarse peak 728 is performed by an estimation of timeframe when the wavelength changes by about a half of the FSR of the etalon. In some aspects, the predicted range of pixel position Ax” for coarse peak 728 is smaller than predicted range of pixel positions Ax' for fringe peaks 720, 724 and 726. A ratio of Ax' to Ax” ranges from about 4 to about 40.

[0085] The predicted range can be further determined by a movement of a prism or a variation in voltage levels of a stepper inside the wavelength selector. An algorithm, provided with information about changing position of these actuators can determine movements of fringe peaks, narrowing the search. An example of this would be a case where scanner commands a wavelength target change. In some cases, the wavelength will be making large changes between pulses. Knowing the actuatormovements to achieve the new target, the algorithm could predict where peaks would show up and thereby narrow the search.

[0086] The above operations can be performed independent or dependent of a processor in computing system 606, or the measured data can be stored in a memory in another computing system, such that computing system 606 can reduce the number of measurement and / or analysis.

[0087] In some aspects, computing system 606 can delimit the abbreviated analysis of the next fringe pattern by selecting a set number of pixels prior to and after intensity peaks of the fringe pattern (e.g., excluding intensity signals originating from pixel locations outside of the predicted range of pixel positions Ax').

[0088] In some aspects, computing system 606 can down sample analysis of intensity signals 618 by disregarding positions of the pixels with a predetermined periodicity. For example, every other pixel position or every third pixel position may be skipped in the analysis . It is to be appreciated that a tradeoff could be the accuracy of the wavelength measurement, but down sampling can be useful when the wavelength value is consistent or when wavelength tolerances can be relaxed for faster measurement speed.

[0089] It was described previously in reference to FIG. 5 that a wavelength of radiation source 500 is selectable via adjustment of actuator 530 to adjust wavelength-dependent reflector 526. The inverse of this mechanism can also be used to back infer wavelength information and increase the speed of metrology system 600. For example, computing system 600 can determine the predicted range of pixel positions Zix' by analyzing a setting of wavelength selector 522. For example, control signal 532 can also be received as input by computing system 606. The command in control signal 532 comprises information about the target wavelength of the radiation source. The information about the setting of wavelength selector 522 can also be used to limit a scan / search for coarse peak 728. The analysis of the setting of wavelength selector 522 can increase the speed of wavelength measurements, for example, when the wavelength is intentionally changed by a user of the radiation system.

[0090] When a new wavelength is selected, the mechanical process of changing the wavelength can be fast to the extent that predictions of narrower pixel ranges for future scans are more accurate if relying on a position of actuator 530 instead of a fringe pattern that has abruptly changed due to the new wavelength setting. Computing system 606 can be programmed with information about the rate of change of the wavelength with respect to a change of actuator 530 (e.g., wavelength per volt / step). As actuator 530 is in the process of moving, computing system 606 can calculate approximately how much the wavelength has shifted. With an estimate of the change in wavelength, an estimate of the new value of diameter d can be inferred via Eq. 1. From the estimate of the new value of diameter d, computing system 606 can predict the shift in pixel positions of fringe peaks, thereby predicting the new range of pixel positions Ax'.

[0091] In some aspects, the argument inside the cosine of Eq. 1 (e.g., d / 2FD) can be made close to zero, allowing for faster, yet accurate, calculations using small angle approximation (e.g., Taylor series expansion) in lieu of an exact cosine calculation.

[0092] In some aspects, the hardware and operations of radiation system 500 can be implemented such that an exact position of actuator 530 is unknowable until a pulse of radiation is generated. In such a scenario, rather than scanning the full extent of pixel positions Ax to ascertain the position of actuator 530, a brief time delay can be implemented instead in order to determine the value of diameter d. Then, the predicted range of pixel positions Ax' can be determined as described above. The implementation of the time delay is useful in circumstances where information about the predicted range of pixel positions Ax' can greatly speed up the search for fringe peaks, thereby offsetting the adverse effects of the time delay.

[0093] FIG. 8 shows a computer system 800, according to some aspects. Various aspects and components therein can be implemented, for example, using computer system 800 or any other well- known computer systems. For example, the operations of computing system 606 described above can be implemented via computer system 800.

[0094] In some aspects, computer system 800 can comprise one or more processors (also called central processing units, or CPUs), such as a processor 804. Processor 804 can be connected to a communication infrastructure or bus 806.

[0095] In some aspects, one or more processors 804 can each be a graphics processing unit (GPU). In some aspects, a GPU is a processor that is a specialized electronic circuit designed to process mathematically intensive applications. The GPU can have a parallel structure that is efficient for parallel processing of large blocks of data, such as mathematically intensive data common to computer graphics applications, images, videos, etc.

[0096] In some aspects, computer system 800 can further comprise user input / output device(s) 803, such as monitors, keyboards, pointing devices, etc., that communicate with communication infrastructure 806 through user input / output interface(s) 802. Computer system 800 can further comprise a main or primary memory 808, such as random access memory (RAM). Main memory 808 can comprise one or more levels of cache. Main memory 808 has stored therein control logic (z.e., computer software) and / or data.

[0097] In some aspects, computer system 800 can further comprise one or more secondary storage devices or memory 810. Secondary memory 810 can comprise, for example, a hard disk drive 812 and / or a removable storage device or drive 814. Removable storage drive 814 can be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, tape backup device, and / or any other storage device / drive. Removable storage drive 814 can interact with a removable storage unit 818. Removable storage unit 818 can comprise a computer usable or readable storage device having stored thereon computer software (control logic) and / or data. Removable storage unit 818 can be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, and / any other computer datastorage device. Removable storage drive 814 reads from and / or writes to removable storage unit 818 in a well-known manner.

[0098] In some aspects, secondary memory 810 can comprise other means, instrumentalities or other approaches for allowing computer programs and / or other instructions and / or data to be accessed by computer system 800. Such means, instrumentalities or other approaches can comprise, for example, a removable storage unit 822 and an interface 820. Examples of the removable storage unit 822 and the interface 820 can comprise a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a memory stick and USB port, a memory card and associated memory card slot, and / or any other removable storage unit and associated interface.

[0099] In some aspects, computer system 800 can further comprise a communication or network interface 824. Communication interface 824 enables computer system 800 to communicate and interact with any combination of remote devices, remote networks, remote entities, etc. (individually and collectively referenced by reference number 828). For example, communication interface 824 can allow computer system 800 to communicate with remote devices 828 over communications path 826, which can be wired and / or wireless, and which can comprise any combination of LANs, WANs, the Internet, etc. Control logic and / or data can be transmitted to and from computer system 800 via communications path 826.

[0100] In some aspects, a non-transitory, tangible apparatus or article of manufacture comprising a non-transitory, tangible computer useable or readable medium having control logic (software) stored thereon is also referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system 800, main memory 808, secondary memory 810, and removable storage units 818 and 822, as well as tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (such as computer system 800), causes such data processing devices to operate as described herein.

[0101] Based on the teachings contained in this disclosure, it will be apparent to those skilled in the relevant art(s) how to make and use aspects of this disclosure using data processing devices, computer systems and / or computer architectures other than that shown in FIG. 8. In particular, aspects described herein can operate with software, hardware, and / or operating system implementations other than those described herein.

[0102] The terms “radiation,” “beam,” “light,” “illumination,” or the like can be used herein to refer to one or more types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength X of 365, 248, 193, 157 or 126 nm). Generally, radiation having wavelengths between about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to thewavelengths that can be produced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm; and / or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in some aspects, an excimer laser can generate DUV radiation used within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 180-200 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 180-200 nm.

[0103] Although some aspects of the present disclosure are described in the context of lithographic apparatuses in the manufacture of ICs, it should be understood that lithographic apparatuses described herein can be used in other applications, for example, in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, UCDs, thin-fdm magnetic heads, etc. Those skilled in the art will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion”, respectively. A substrate can be processed before or after exposure in, for example, a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and / or a metrology unit. Where applicable, aspects disclosed herein can be applied to such and other substrate processing tools. Furthermore, a substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

[0104] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0105] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. The foregoing description of specific aspects will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein.

[0106] It is to be understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections can set forth one or more, but not necessarily all, aspects of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way. Thebreadth and scope of the protected subject matter should not be limited by any of the above -described aspects, but should be defined in accordance with the following claims and their equivalents.

Claims

CLAIMS1. A lithographic apparatus comprising: an illumination system configured to generate a beam of radiation to illuminate a pattern of a patterning device for projecting an image of the pattern onto a substrate, wherein the beam is pulsed and the illumination system comprises a metrology system comprising: an etalon configured to generate a fringe pattern corresponding to a pulse of the beam and a next fringe pattern corresponding to a next pulse of the beam after the pulse; a detector comprising an array of pixels configured to generate intensity signals based on intensities of the fringe pattern and the next fringe pattern at positions of the pixels; and a computing system configured to: determine a predicted range of pixel positions corresponding to intensity peaks of the next fringe pattern based on pixel positions of intensity peaks of the fringe pattern; and perform an abbreviated analysis of the next fringe pattern, wherein the abbreviated analysis is delimited by the predicted range of pixel positions to reduce a measurement time of the metrology system.

2. The lithographic apparatus of claim 1, wherein the computing system is further configured to delimit the abbreviated analysis of the next fringe pattern by excluding intensity signals from pixel locations outside of the predicted range of pixel positions.

3. The lithographic apparatus of claim 1, wherein the computing system is further configured to determine a wavelength of the beam based on the abbreviated analysis of the next fringe pattern.

4. The lithographic apparatus of claim 1, wherein the computing system is further configured to down sample analysis of the intensity signals by disregarding positions of the pixels that correspond to a predetermined periodicity.

5. The lithographic apparatus of claim 1, further comprising a wavelength selector configured to adjust a wavelength of the beam, wherein: the computing system is further configured to determine the predicted range of pixel positions based on a setting of the wavelength selector.

6. The lithographic apparatus of claim 5, wherein: the wavelength selector is further configured to perform an adjustment from a first wavelength value to a second wavelength value; and the computing system is further configured to calculate a shift of the next fringe pattern based on the adjustment from the first wavelength value to the second wavelength value.

7. The lithographic apparatus of claim 1, wherein the computing system is further configured to execute a delay operation prior to determining the predicted range of pixel positions.

8. The lithographic apparatus of claim 1, wherein the abbreviated analysis comprises a Taylor series expansion.

9. A metrology system comprising: an etalon configured to generate a fringe pattern corresponding to a pulse of a beam of radiation and a next fringe pattern corresponding to a next pulse of the beam after the pulse; a detector comprising an array of pixels configured to generate intensity signals based on intensities of the fringe pattern and the next fringe pattern at positions of the pixels; and a computing system configured to: determine a range of pixel positions for intensity peaks of the next fringe pattern based on pixel positions of intensity peaks of the fringe pattern; and perform an abbreviated analysis of the next fringe pattern, wherein the abbreviated analysis is delimited by the range pixel position to reduce a measurement time of the metrology system.

10. The metrology system of claim 9, wherein the computing system is further configured to delimit the abbreviated analysis of the next fringe pattern by selecting a set number of pixels prior to and after intensity peaks of the fringe pattern.

11. The metrology system of claim 10, wherein the set number of pixels ranges from about 20 to about 200 pixels.

12. The metrology system of claim 9, wherein the detector is further configured to generate an additional intensity signals based on intensities of a spot pattern having a lower-resolution wavelength information.

13. The metrology system of claim 9, wherein the computing system is further configured to determine the range of pixel positions based on a movement of a prism or a variation in voltage levels of a stepper in a wavelength selector.

14. The metrology system of claim 13, wherein: the wavelength selector is further configured to perform an adjustment from a first wavelength value to a second wavelength value; andthe computing system is further configured to determine a shift of the next fringe pattern based on the adjustment from the first wavelength value to the second wavelength value.

15. The metrology system of claim 9, wherein the computing system is further configured to execute a delay operation prior to determining the range of pixel positions.

16. A method comprising: determining a predicted range of pixel positions corresponding to intensity peaks of a fringe pattern based on pixel positions of intensity peaks of the fringe pattern, wherein the pixel positions correspond to an array of pixels of a detector of a metrology system, wherein an etalon of the metrology system is configured to generate the fringe pattern corresponding to a pulse of a beam of radiation and a next fringe pattern corresponding to a next pulse of the beam after the pulse, and wherein the array of pixels is configured to generate intensity signals based on intensities of the fringe pattern and the next fringe pattern at positions of the pixels; and performing an abbreviated analysis of the next fringe pattern, wherein the abbreviated analysis is delimited by the predicted range pixel positions.

17. The method of claim 16, further comprising delimiting the abbreviated analysis of the next fringe pattern by excluding intensity signals from pixel locations outside of the predicted range of pixel positions.

18. The method of claim 16, further comprising down sampling analysis of the intensity signals by disregarding positions of the pixels that correspond to a predetermined periodicity.

19. The method of claim 16, further comprising: adjusting a wavelength of the beam using a wavelength selector; and determining the predicted range of pixel positions based on a setting of the wavelength selector.

20. The method of claim 16, further comprising introducing a delay prior to determining the predicted range of pixel positions.

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