Deformable optical component actuation and modulation in a metrology system

Abstract

A metrology apparatus includes an optical component, a wafer, a sensor, and a processor. The optical component, which can actuate between multiple aberration modes, provides a wavefront correction to light incident on the optical component. Light reflected and / or transmitted by the optical component is scattered by a target on the wafer. The scattered light forms a measurement signal that is collected by a sensor. The processor uses the measurement signal to determine an aberration correction for the optical component.

Description

DEFORMABLE OPTICAL COMPONENT ACTUATION AND MODULATION IN A METROLOGY SYSTEMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 553,824 which was filed on February 15, 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to actuation and modulation of optical components, for example, optical components in metrology and lithographic apparatuses and systems.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 is alternatively referred to as 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 radiation- sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus 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 may require 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 may 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.

[0005] In order to monitor the lithographic process, parameters of the patterned substrate are measured. Parameters may 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 techniques for making measurements of the microscopic structures formed in lithographic processes, including theuse 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] In some scatterometers, optical components can cause aberrations that affect the quality of a measurement. An adaptive optical component, such as a deformable mirror can be introduced into an illumination branch of a scatterometer. The shape of the adaptive optical component can be actuated to perform an aberration correction. However, any unwanted perturbance of the scatterometer during this measurement sequence can affect individual measurements, thereby reducing performance.SUMMARY

[0007] Accordingly, an aberration correction is determined by measuring aberration modes of an adaptive optical component in parallel. For example, measuring aberration modes in parallel allows for faster setup of a scatterometer or similar metrology apparatus in a lithography system.

[0008] In some aspects, a lithography apparatus comprises an optical component, a wafer, a sensor, and a processor. The optical component can be configured to provide a wavefront correction to light reflected and / or transmitted by the optical component. In some embodiments, the optical component can be configured to generate multiple aberration modes in parallel through fast actuation. The wafer can comprise a target. Light reflected and / or transmitted by the optical component can be scattered and / or diffracted by the target and captured by the sensor. The processor can determine an aberration correction for the lithography apparatus using light captured by the sensor.

[0009] In some aspects, a method of correcting aberrations comprises modulating a shape of an optical component, illuminating a target on a wafer, measuring light scattered from the target, demultiplexing the measured light, and determining a preferred aberration mode of the optical component. In some aspects, light transmitted and / or reflected by the optical component contains information about aberration modes of the optical component. Light transmitted and / or reflected by the optical component can be scattered by the target on the wafer to form a measurement signal. The measurement signal can be demultiplexed to obtain multiple demodulated signals. Each demodulated signal can correspond to an aberration mode of the optical component. The demodulated signals can be used to determine a preferred aberration mode or weighted combination of aberration modes of an optical component.

[0010] In some aspects, a method of correcting aberrations comprises determining an aberration correction and applying an aberration correction to an optical component or measurement signal. The aberration correction can be determined by processing a measurement signal scattered and / or diffracted from a wafer using a machine learning model. The measurement signal can comprise images of one or more point spread functions and / or images of a target on the wafer. The machine learning model can be trained using simulation data and wafer target and / or stack data. The output of the machine learning model can comprise an aberration correction, which can be physically applied to an adaptive optical component or computationally applied to a measurement signal.

[0011] Further features of the present disclosure, as well as the structure and operation of various embodiments / aspects, are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific embodiments / aspects described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments / aspects will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0012] 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 a person skilled in the relevant art(s) to make and use embodiments / aspects described herein.

[0013] FIG. 1A shows a schematic of a reflective lithographic apparatus, according to some aspects.

[0014] FIG. IB shows a schematic of a transmissive lithographic apparatus, according to some aspects.

[0015] FIG. 2 shows a more detailed schematic of the reflective lithographic apparatus, according to some aspects.

[0016] FIG. 3 shows a schematic of a lithographic cell, according to some aspects.

[0017] FIGS. 4 A and 4B show schematics of a metrology apparatus, according to some aspects.

[0018] FIGS. 5a, 5b, and 5c show a grating light valve, according to some aspects.

[0019] FIG. 6a, 6b, and 6c show a schematic of color switching with a grating light valve, according to some aspects.

[0020] FIG. 7 shows a deformable mirror, according to some aspects.

[0021] FIG. 8 shows a first method of correcting aberrations in a metrology system, according to some aspects.

[0022] FIG. 9 shows a second method of correcting aberrations in a metrology system, according to some aspects.

[0023] FIG. 10 shows a computer system, according to some aspects.

[0024] 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 indicateidentical, functionally similar, and / or structurally similar elements. Additionally, generally, the left-most 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

[0025] This specification discloses one or more embodiments that incorporate the features of the present disclosure. The disclosed embodiment(s) are provided as examples. The scope of the present disclosure is not limited to the disclosed embodiment(s). Claimed features are defined by the claims appended hereto.

[0026] The embodiment(s) described, and references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” aspect, etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0027] 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 may likewise be interpreted accordingly.

[0028] The term “about” as used herein indicates the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the term “about” 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).

[0029] Embodiments of the disclosure can be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the disclosure may also be implemented as instructions stored on a machine-readable medium, which can be read and executed 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, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, and / or instructions can be described herein as performing certain actions. However, it should beappreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[0030] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present disclosure can be implemented.

[0031] Example Lithographic Systems

[0032] FIGS. 1 A and IB show schematic illustrations of a lithographic apparatus 100 and lithographic apparatus 100’, respectively, in which embodiments of the present disclosure can be implemented. Lithographic apparatus 100 and lithographic apparatus 100’ each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100’ also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100’, the patterning device MA and the projection system PS are transmissive.

[0033] The illumination system IL can include 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.

[0034] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatus 100 and 100’, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable, as required. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0035] The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0036] The terms “inspection apparatus,” “metrology system,” or the like may be used herein to refer to, e.g., a device or system used for measuring a property of a structure (e.g., overlay error, critical dimension parameters) or used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment apparatus).

[0037] The patterning device MA can be transmissive (as in lithographic apparatus 100’ of FIG. IB) or reflective (as in lithographic apparatus 100 of FIG. 1A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B, which is reflected by a matrix of small mirrors.

[0038] The term “projection system” PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. A vacuum environment can be used for EUV or electron beam radiation since other gases can absorb too much radiation or electrons. A vacuum environment can therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0039] Lithographic apparatus 100 and / or 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 WT.

[0040] The lithographic apparatus can also be of a type wherein at least a portion of the substrate can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid can also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.

[0041] Referring to FIGS. 1A and IB, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100’ can be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 100’, and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (in FIG. IB) including, for example,suitable directing mirrors and / or a beam expander. In other cases, the source SO can be an integral part of the lithographic apparatus 100, 100’, for example, when the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD, if required, can be referred to as a radiation system.

[0042] The illuminator IL can include an adjuster AD (in FIG. IB) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as “o-outer” and “o-inner,” respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL can comprise various other components (in FIG. IB), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

[0043] Referring to FIG. 1A, the radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device (for example, mask) MA and substrate W can be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2.

[0044] Referring to FIG. IB, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system 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.

[0045] The projection system PS projects an image of the mask pattern MP, where the image is formed by diffracted beams produced from the mark pattern MP by radiation from the intensity distribution, onto a photoresist layer coated on the substrate W. For example, the mask pattern MP can include an array of lines and spaces. A diffraction of radiation at the array and different from zeroth order diffraction generates 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) traverse the pattern without any change in propagation direction. The zeroth order diffracted beams traverse an upper lensor upper lens group of the projection system PS, upstream of the pupil conjugate PPU of the projection system PS, to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the 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 illumination system IL. The aperture device PD, for example, is disposed at or substantially at a plane that includes the pupil conjugate PPU of the projection system PS.

[0046] The projection system PS is arranged to capture, by means of a lens or lens group L, not only the zeroth order diffracted beams, but also first-order or first- and higher-order diffracted beams (not shown). In some embodiments, 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 interfere with corresponding zeroth-order diffracted beams at the level of the wafer W to create an image of the line pattern MP at highest possible resolution and process window (i.e., usable depth of focus in combination with tolerable exposure dose deviations). In some embodiments, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some embodiments, astigmatism aberration can be reduced by blocking the zeroth order beams in the pupil conjugate PPU of the projection system associated with radiation poles in opposite quadrants. This is described in more detail in US 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

[0047] With the aid of the second positioner PW and position sensor IFD (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown in FIG. IB) can be used to accurately position the mask MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).

[0048] In general, movement of the mask table MT can be realized with the aid of a long-stroke module (coarse positioning) and a short- stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected to a short- stroke actuator only or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks Ml, M2, and substrate alignment marks Pl, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

[0049] Mask table MT and patterning device MA can be in a vacuum chamber V, where an in-vacuum robot IVR can be used to move patterning devices such as a mask in and out of vacuum chamber. Alternatively, when mask table MT and patterning device MA are outside of the vacuum chamber, anout-of-vacuum robot can be used for various transportation operations, similar to the in- vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0050] The lithographic apparatus 100 and 100’ can be used in at least one of the following modes:1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de- jmagnification and image reversal characteristics of the projection system PS.3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated as required after each movement of the 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.

[0051] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0052] In a further embodiment, lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0053] FIG. 2 shows the lithographic apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector apparatus SO. An EUV radiation emitting plasma 210 can be formed by a discharge produced plasma source. EUV radiation can be produced by a gas or vapor, for example Xe gas, Li vapor, or Sn vapor in which the very hot plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 is created by, for example, an electrical discharge causing at least a partially ionized plasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor can be required for efficient generation of the radiation. In some embodiments, a plasma of excited tin (Sn) is provided to produce EUV radiation.

[0054] The radiation emitted by the hot plasma 210 is passed from a source chamber 211 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap), which is positioned in or behind an opening in source chamber 211. The contaminant trap 230 can include a channel structure. Contamination trap 230 can also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure.

[0055] The collector chamber 212 can include a radiation collector CO, which can be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point INTF. The virtual source point INTF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus INTF is located at or near an opening 219 in the enclosing structure 220. The virtual source point INTF is an image of the radiation emitting plasma 210. Grating spectral filter 240 is used in particular for suppressing infra-red (IR) radiation.

[0056] Subsequently the radiation traverses the illumination system IL, which can include a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to provide a desired angular distribution of the radiation beam 221, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation 221 at the patterning device MA, held by the support structure MT, a patterned beam 226 is formed and the patterned beam 226 is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by the wafer stage or substrate table WT.

[0057] More elements than shown can generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 240 can optionally be present, depending upon the type of lithographic apparatus. Further, there can be more mirrors present than those shown in the FIG. 2, for example there can be one to six additional reflective elements present in the projection system PS than shown in FIG. 2.

[0058] Collector optic CO, as illustrated in FIG. 2, is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are disposed axially symmetric around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

[0059] Exemplary Lithographic Cell

[0060] FIG. 3 shows a lithographic cell 300, also sometimes referred to a lithocell or cluster, according to some embodiments. Lithographic apparatus 100 or 100’ can form part of lithographic cell 300. Lithographic cell 300 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. In some examples, these 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 picks up substrates from input / output ports I / Ol, I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus 100 or 100’. These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0061] Exemplary Metrology Apparatus

[0062] FIG. 4A shows a metrology apparatus 400, according to some embodiments. A target T and diffracted rays of measurement radiation used to illuminate the target are illustrated in more detail in FIG. 4B. The metrology apparatus illustrated is of a type known as a dark field metrology apparatus. The metrology apparatus depicted here is purely exemplary, to provide an explanation of dark field metrology. The metrology apparatus may be a stand-alone device or incorporated in either lithographic apparatus 100 or 100’, or the lithographic cell 300. An optical axis, which has several branches throughout the apparatus, is represented by a dotted line O. In this apparatus, light emitted by source 11 (e.g., a xenon lamp) is directed onto substrate W via a beam splitter 15 by an optical system comprising lenses 12, 14 and objective lens 16. These lenses are arranged in a double sequence of a 4F arrangement. A different lens arrangement can be used, provided that it still provides a substrate image onto a detector, and simultaneously allows for access of an intermediate pupil-plane for spatial-frequency filtering. Therefore, the angular range at which the radiation is incident on the substrate can be selected by defining a spatial intensity distribution in a plane that presents the spatial spectrum of the substrate plane, here referred to as a (conjugate) pupil plane. In particular, this can be done by inserting an aperture plate 13 of suitable form between lenses 12 and 14, in a plane which is a back-projected image of the objective lens pupil plane. In the example illustrated, aperture plate 13 has different forms, labeled 13N and 13S, allowing different illumination modes to be selected. The illumination system in the present examples forms an off-axis illumination mode. In the first illumination mode, aperture plate 13N provides off-axis from a direction designated, for the sake of description only, as ‘north’. In a second illumination mode, aperture plate 13S is used to provide similar illumination, but from an opposite direction, labeled ‘south’. Other modes of illumination are possible by using different apertures. The rest of the pupil plane is desirably dark as any unnecessary light outside the desired illumination mode will interfere with the desired measurement signals.

[0063] As shown in Figure 4B, target T is placed with substrate W normal to the optical axis O of objective lens 16. The substrate W may be supported by a support (not shown). A ray of measurement radiation I impinging on target T from an angle off the axis O gives rise to a zeroth order ray (solid line 0) and two first order rays (dot-chain line +1 and double dot-chain line -1). It should be remembered that with an overfilled small target, these rays are just one of many parallel rays covering the area of thesubstrate including metrology target T and other features. Since the aperture in plate 13 has a finite width (necessary to admit a useful quantity of light, the incident rays I will in fact occupy a range of angles, and the diffracted rays 0 and +1 / -1 will be spread out somewhat. According to the point spread function of a small target, each order +1 and -1 will be further spread over a range of angles, not a single ideal ray as shown. Note that the grating pitches of the targets and the illumination angles can be designed or adjusted so that the first order rays entering the objective lens are closely aligned with the central optical axis. The rays illustrated in FIG. 4 A are shown somewhat off axis, purely to enable them to be more easily distinguished in the diagram.

[0064] At least the 0 and +1 orders diffracted by the target T on substrate W are collected by objective lens 16 and directed back through beam splitter 15. Returning to FIG. 4A, both the first and second illumination modes are illustrated, by designating diametrically opposite apertures labeled as north (N) and south (S). When the incident ray I of measurement radiation is from the north side of the optical axis, that is when the first illumination mode is applied using aperture plate 13N, the +1 diffracted rays, which are labeled +1(N), enter the objective lens 16. In contrast, when the second illumination mode is applied using aperture plate 13S the -1 diffracted rays (labeled 1(S)) are the ones which enter the lens 16.

[0065] A second beam splitter 17 divides the diffracted beams into two measurement branches. In a first measurement branch, optical system 18 forms a diffraction spectrum (pupil plane image) of the target on first sensor 19 (e.g., a CCD or CMOS sensor) using the zeroth and first order diffractive beams. Each diffraction order hits a different point on the sensor, so that image processing can compare and contrast orders. The pupil plane image captured by sensor 19 can be used for focusing the metrology apparatus and / or normalizing intensity measurements of the first order beam. The pupil plane image can also be used for many measurement purposes such as reconstruction.

[0066] In the second measurement branch, optical system 20, 22 forms an image of the target T on sensor 23 (e.g., a CCD or CMOS sensor). In the second measurement branch, an aperture stop 21 is provided in a plane that is conjugate to the pupil-plane. Aperture stop 21 functions to block the zeroth order diffracted beam so that the image of the target formed on sensor 23 is formed only from the -1 or +1 first order beam. The images captured by sensors 19 and 23 are output to processor PU which processes the image, the function of which will depend on the particular type of measurements being performed. Note that the term ‘image’ is used here in a broad sense. An image of the grating lines as such will not be formed, if only one of the -1 and +1 orders is present.

[0067] The particular forms of aperture plate 13 and field stop 21 shown in FIG. 4 are purely examples. In another embodiment of the invention, on-axis illumination of the targets is used and an aperture stop with an off-axis aperture is used to pass substantially only one first order of diffracted light to the sensor. In other examples, a two quadrant aperture may be used. This may enable simultaneous detection of plus and minus orders, as described in U.S. Patent No. 8,705,007 B2 published on April 22, 2014 and herein incorporated by reference. Embodiments with optical wedges (segmented prisms or othersuitable elements) in the detection branch can be used to separate the orders for imaging spatially in a single image, as described in U.S. Patent No. 8,786,825 B2 published on July 22, 2014 and herein incorporated by reference. In yet other embodiments, 2nd, 3rd and higher order beams can be used in measurements, instead of or in addition to the first order beams. In yet other embodiments, a segmented prism can be used in place of aperture stop 21, enabling both +1 and -1 orders to be captured simultaneously at spatially separate locations on image sensor 23.

[0068] In order to make the measurement radiation adaptable to these different types of measurement, the aperture plate 13 may comprise a number of aperture patterns formed around a disc, which rotates to bring a desired pattern into place. Note that aperture plate 13N or 13S can only be used to measure gratings oriented in one direction (X or Y depending on the set-up). For measurement of an orthogonal grating, rotation of the target through 90° and 270° might be implemented.

[0069] A light source for metrology applications usable for concepts disclosed herein may comprise any broadband source and a color selection arrangement to select one or more colors from the broadband output. By way of an example, the radiation source may be based on a hollow core or solid core fiber such as a hollow core photonic crystal fiber (HC-PCF) or solid core photonic crystal fiber (SC-PCF). For example, in the case of a HC-PCF, the hollow core of the fiber may be filled with a gas acting as a broadening medium for broadening input radiation. Such a fiber and gas arrangement may be used to create a supercontinuum radiation source. Radiation input to the fiber may be electromagnetic radiation, for example radiation in one or more of the infrared, visible, UV, and extreme UV spectra. The output radiation may consist of or comprise broadband radiation, which may be referred to herein as white light. This is only one example of a broadband light source technology usable in methods and apparatuses disclosed herein, and other suitable technologies may instead be employed.

[0070] When using metrology sensors, including those described above and / or other types of metrology sensors (e.g., alignment sensors, levelling sensors), it is often desirable to control the illumination spectrum, e.g., to switch the illumination between different wavelengths (colors) and / or wavefront profiles.

[0071] To perform color selection, a color selection module has been proposed that uses grating light valve (GLV) technology such as marketed by Silicon Light Machines (SLM), e.g., as described in U.S. Pat. No. 6,947,613 Bl, published on September 20, 2005 and incorporated herein by reference. A GLV is an electrically-programmable diffraction grating based on Micro-Electro-Mechanical Systems (MEMS) technology. Figure 5 illustrates the principal. Figure 5 is a schematic illustration of a GLV pixel or component 500 from (a) above and (b), (c) end-on. The GLV component comprises alternating GLV reflective ribbons of two types: static or bias ribbons 510 that are typically grounded along with a common electrode and driven or active ribbons 520, which are driven by an electronic driver channel. A GLV module can comprise any number of these GLV components 500 arranged in an array. The active and bias ribbons can be essentially identical other than in how they are driven. When no voltage is applied to the active ribbons 520, they are co-planar with the bias ribbons, a configuration illustratedin Figure 5(b). In this configuration, the GLV acts like a mirror, with incident light being specularly reflected. When a voltage is applied to the active ribbons 520, as illustrated in Figure 5(c), they deflect relative to the bias ribbons 510, establishing a square- well diffraction grating. In this state, incident light is diffracted into fixed diffraction angles. The ratio of light reflected with respect to light diffracted can be continuously varied by controlling the voltage on the active ribbons 520, which controls the magnitude of their deflection. As such, the amount of light diffracted by the GLV can be controlled in an analog fashion from zero (full specular reflection) to all incident light (zero specular reflection).

[0072] The GLV module can be used in a zeroth order mode such that the diffracted radiation is blocked / dumped and the specularly reflected (zeroth order) radiation is provided to the metrology tool. This has the advantage of preserving etendue.

[0073] A GLV-based color selection module is an example of a type of color selection module that can be used in any suitable metrology device. Other fast-switching color section arrangements can also be used instead of a GLV, such as other light valve technologies, or more generally other spatial light modulation devices (e.g., acousto-optical modulation devices such as an acousto-optical tunable filter, digital micromirror device (DMD) technologies and / or LCOS (Liquid Crystal on Silicon) devices.

[0074] A proposed method and illumination module is provided that synchronizes the wavelength selection (spectral configurations of the illumination) with a programmable or configurable range of illumination angles and / or detection angles such that only wavelengths are selected at any time which result in proper detection (i.e., for a particular structure pitch of a diffractive structure being measured) or desired detection condition. The module can comprise: a grating light valve module (or other color selection module such as a fast-switching MEMS or other light valve color selection module) for controllably configuring a spectral configuration (e.g., a wavelength, combination or weighted combination of wavelengths) of said measurement illumination, a configurable illumination module operable to provide measurement illumination over a configurable range of illumination angles, and a controller for controlling the configurable illumination module and grating light valve module.

[0075] The configurable illumination module can comprise a beam steering device, e.g., which scans a beam over the illumination pupil (e.g., over a range of illumination angles) sufficiently fast to define a desired range of illumination angles or illumination shape in a pupil plane. In an embodiment, such a module can comprise both of a beam scanning device, a GLV module and a controller, the controller configured to scan over a range of illumination angles while controlling the GLV module to select wavelengths (single wavelengths or combinations of multiple wavelengths), which will be properly detected by the detection mask (within the detection NA), the colors being selected in dependence on the illumination angle (beam position in the illumination pupil) during scanning. Properly detected (i.e., the desired detection condition) in this context can comprise maintaining the detection regions (detection NA) to be overfilled. Overfilled in this context may mean being substantially filled (e.g., as defined above) with detected radiation or diffracted order radiation resulting from the scanned illumination being diffracted by a target or other diffractive structure for each of a plurality of desiredwavelengths. Alternatively or in addition, properly detected may mean that the diffracted radiation of a plurality of desired wavelengths are detected in a substantially common region in the detection pupil plane.

[0076] The detection mask / detection NA may be fixed, or it may be configurable / movable such that the GLV color selection is synchronized with the illumination beam position and / or detection mask position.

[0077] A GLV can have a switching speed of a few ps, which is much faster than the scanning speed of a MEMS mirror (e.g., 0.5-lms) and may be used for scanning the illumination over the illumination region. As such, if the scanning of the MEMS mirror over an illumination region takes 1ms or more, the GLV module can switch colors on and off about 50-100 times during a single scan. This may comprise switching colors individually and / or switching multiple colors simultaneously, and may further optionally comprise a non-binary control of each wavelength such that intensity of individual wavelengths may be attenuated by less than 100% (e.g., attenuation at multiple values or continuously between 0% and 100%).

[0078] Figure 6 schematically illustrates the principle. Figure 6(a) shows a first instant or snapshot during a scan through a range of illumination angles, at a point where the beam steering element BS is steering the beam IB, i through a first angle 0i, and therefore a first position in the illumination pupil plane IPP of objective lens OL. Based on this angle (and target pitch), the controller CO controls the GLV module, which receives a broadband illumination beam IB, to select an appropriate one or more wavelengths for illumination beam IB, i . Figure 6(b) shows a second instant during the same scan where the beam steering element BS is steering the beam IB,2 through a second angle 02 and therefore a second position in the illumination pupil plane IPP. Based on this angle (and target pitch), the controller CO controls the GLV module to select an appropriate one or more wavelengths for illumination beam IB,2. Similarly, Figure 6(c) shows a third instant during the scan where the beam steering element BS is steering the beam IB, ; through a third angle 03 and therefore a third position in the illumination pupil plane IPP. Based on this angle (and target pitch), the controller CO controls the GLV module to select an appropriate one or more wavelengths for illumination beam IB, ;.

[0079] Color selection modules are further described in International Appl. No. WO2023 / 222328A1, published on Nov. 23, 2023, and herein incorporated by reference.

[0080] Exemplary Aberration Correction Methods

[0081] In a metrology or lithography apparatus, aberrations can refer to deviations from ideal system behavior, such as errors in the light wavefront. Aberrations can be corrected by adding an adaptive optical component to the metrology apparatus, or by applying a computational correction to an image during processing.

[0082] In some aspects, point spread functions can be used to infer aberration corrections. Typically, point spread functions originate from an infinitely small point source. However, in practice, point spreadfunctions can be generated from light diffracted by pinhole structures comprising a diameter smaller than the wavelength of incident light. One or more pinhole structures can be introduced on and / or near target T on substrate W. Light diffracted by the pinhole structures (e.g., point spread functions) can be captured by a sensor, such as sensor 19 or 23. A processor can analyze captured images of point spread functions to determine a preferred aberration correction to be applied to a component in a metrology apparatus and / or a computational correction to be applied to a captured image.

[0083] In some aspects, an adaptive optical component is added to a metrology apparatus, such as metrology apparatus 400. The adaptive optical component can be configured to provide a wavefront correction to light transmitted and / or reflected by the adaptive optical component. The provided correction can be related to the shape of the adaptive optical component, which can be adjusted.

[0084] In some aspects, an adaptive optical component can comprise a deformable mirror. FIG. 7 shows a schematic of a deformable mirror 700, according to some aspects. Deformable mirror 700 can comprise a mirror sheet 702, an actuator array 704, actuator electrodes 706, and a substrate 708. Actuator array 704 can be suspended above electrodes 706 on a series of supports 710. In some aspects, actuator array 704 is a PZT actuator array. Electrodes 706 can apply a voltage to actuator array 704, causing actuator array 704 to deform under an electrostatic force. Because mirror sheet 702 can be connected to actuator array 704 through supports 712, mirror sheet 702 deforms simultaneously. In some aspects, the shape of deformable mirror 700 can be actuated to switch between different aberration modes. Each aberration mode can apply a distinct aberration correction to light reflected from the mirror.

[0085] In some aspects, an aberration correction for an adaptive optical component and / or a computational correction for a captured image can be inferred using a machine learning model, such as a convolutional neural network (CNN). Method 800, as shown in FIG. 8, describes a method of determining an aberration correction using a machine learning model, according to some aspects. Method 800 can include steps 802 and 804.

[0086] In step 802, an aberration correction can be determined using a trained machine learning model. The machine learning model can process a measurement signal (e.g., image of a point spread function and / or target) to infer an aberration correction. The machine learning model can be trained using simulation data and wafer target and / or stack data. Simulation data can estimate how optical properties of a metrology apparatus, such as aberrations and detection noise, affect measured images of a target and / or point spread functions.

[0087] In step 804, the calculated aberration correction can be applied to an adaptive optical component or to the measurement signal. For example, the shape of the adaptive optical component can be altered to match the shape specified by the aberration correction. Similarly, a measurement signal can be computationally corrected to account for aberrations predicted by the machine learning model.

[0088] The method steps of FIG. 8 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 8 described above merely reflect anexample of steps and are not limiting. That is, further method steps and functions are envisaged based aspects described in reference to FIGS. 1-7.

[0089] In some aspects, shapes (e.g., aberration modes) of an adaptive optical component can be sequentially actuated to determine an aberration correction. However, any perturbance of a metrology apparatus during this measurement sequence can affect individual measurements, thereby reducing performance. To enable faster measurement setup and reduce system perturbances, an adaptive optical component can undergo fast modulation.

[0090] In some aspects, a modulated signal illuminates a target and / or one or more pinhole structures on a wafer. Fast modulation generates a multiplexed signal that contains images of the target / pinhole structures for multiple aberration modes. After detection, the multiplexed signal is demultiplexed to extract an image corresponding to each aberration mode.

[0091] In some aspects, a second optical component, may be modulated at the same time as the adaptive optical component. The resulting multiplexed signal contains information relating to modes of both optical components. For example, the second optical component may comprise a grating light value module, which alters the wavelength and / or angle of illuminating light incident on a target / pinhole structure. The multiplexed signal reflected and / or scattered from the target / pinhole structures contains wavelength / angle specific information for each aberration mode. When the signal is demultiplexed, each demultiplexed signal can correspond to an aberration mode of the adaptive optical component at a specific wavelength.

[0092] FIG. 9 shows a method 900 of determining an aberration correction for an optical metrology system. For example method 900 can determine an aberration correction for metrology apparatus 400. Method 900 can include steps 902, 904, 906, 908, 910 and 912.

[0093] In step 902, the shape of an adaptive optical component can be modulated. The shape of the optical component can be modulated at a frequency of at least 1 kHz. In some aspects, the shape of the optical component can be modulated at a frequency of 100 kHz. Fast modulation can generate a multiplexed signal comprising information on multiple aberration modes. The aberration modes can be described by Zernike coefficients. In some aspects, the adaptive optical component is an actuated, deformable mirror, as shown in FIG. 7.

[0094] A second optical component, such as a programmable depth valve (e.g., grating light valve), can be modulated in sync with the adaptive optical component, according to some aspects. The second optical component can modulate the wavelength and / or angle of illumination of light incident on the adaptive optical component.

[0095] In step 904, a target can be illuminated with light reflected and / or transmitted by the adaptive optical component. Illuminating light can be scattered by the target (e.g., an overlay target on a wafer). Additionally, illuminating light can be diffracted by one or more pinhole structures on and / or near the target. In some aspects, the pinhole structures are located on a wafer.

[0096] In step 906, light scattered and / or diffracted from the target and / or pinhole structure(s) on the wafer can be measured by a sensor. In some aspects, the sensor measures a multiplexed signal comprising information on multiple aberration modes of the adaptive optical component. In some aspects, the sensor is a multi-channel lock-in camera. In additional aspects, the sensor is a high speed camera. The high speed camera can comprise a framerate similar to the update frequency of the adaptive optical component.

[0097] In step 908, light measured by the sensor can be demultiplexed to generate a set of demodulated signals. The light measured by the senor can be demultiplexed using a Fourier transform. Demultiplexing can take place inside the sensor, and / or may be carried out by a processor. In some aspects, each demodulated signal can correspond to an aberration mode of the adaptive optical component. The demodulated signals may each comprise an image of the target and / or one or more images of a point spread function diffracted from one or more pinhole structures on the wafer.

[0098] In step 910, a preferred aberration mode of the optical component is determined based on the set of demodulated signals. In some aspects, the demodulated signals can be analyzed to determine which demodulated signal or weighted combination of demodulated signals comprises the sharpest image of the target and / or point spread function. A sharp image of a target can comprise an image with a small, defined edge and / or a steep transition between the edge and surrounding area of the image. A sharp image of a point spread function can comprise an image where multiple point spread functions are the same size, and / or an image where point spread function images are small in diameter and spherically symmetric.

[0099] In some aspects, the preferred aberration mode of the optical component can be determined for different wavelengths and / or angles of light incident on the optical component.

[0100] In step 912, the preferred aberration correction can be implemented into a measurement sequence. In some aspects, implementing the aberration correction into a measurement sequence can comprise setting the adaptive optical component to the preferred aberration mode and remeasuring the light scattered and / or diffracted from the target and / or pinhole structure(s) on the wafer without any modulation. In additional aspects, the combination of demodulated signals corresponding to the preferred aberration mode can be further processed to determine system corrections and / or calibrations for a lithography system and / or to infer overlay.

[0101] In some aspects, the steps of method 900 can be completed during layer / recipe setup or at the start of wafer / lot production.

[0102] The method steps of FIG. 9 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 9 described above merely reflect an example of steps and are not limiting. That is, further method steps and functions are envisaged based aspects described in reference to FIGS. 1-7.

[0103] In some aspects, a combination of method 800 and method 900 can be used to determine an aberration correction for a lithography apparatus. For example, measured data (e.g., measured imagesof point spread functions / wafer overlay targets) can improve the simulations used to train the machine learning model. Similarly, prior knowledge from simulations can be used to initialize settings of components in a metrology apparatus before measurements are taken.

[0104] In some aspects, aberrations can be corrected using a computational image correction calculated based on one or more images of a point spread function. A computational image correction may be applied instead of or in addition to a physical correction by an adaptive optical component. Computational image corrections may be based outputs of a CNN (as described in method 800) or measurements from a set of images (as described in method 900). More information on computational corrections can be found in International Patent Application WO2023 / 194036A1 published on October 12, 2023, and European Patent Publication EP4184426A1 published on May 24, 2023, which are herein incorporated in their entirety by reference.

[0105] FIG. 10 shows a computer system 1000. One or more computer systems 1000 may be used, for example, to implement any of the aspects discussed herein, as well as combinations and subcombinations thereof. For example, computer system 1000 can be integrated to facilitate in- camera / sensor processing or be a stand-alone computer.

[0106] Computer system 1000 may include one or more processors (also called central processing units, or CPUs), such as a processor 1004. Processor 1004 may be connected to a communication infrastructure or bus 1006.

[0107] Computer system 1000 may also include user input / output device(s) 1003, such as monitors, keyboards, pointing devices, etc., which may communicate with communication infrastructure 1006 through user input / output interface(s) 1002.

[0108] One or more of processors 1004 may be a graphics processing unit (GPU). In an embodiment, a GPU may be a processor that is a specialized electronic circuit designed to process mathematically intensive applications. The GPU may 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.

[0109] Computer system 1000 may also include a main or primary memory 1008, such as random access memory (RAM). Main memory 1008 may include one or more levels of cache. Main memory 1008 may have stored therein control logic (i.e., computer software) and / or data.

[0110] Computer system 1000 may also include one or more secondary storage devices or memory 1010. Secondary memory 1010 may include, for example, a hard disk drive 1012 and / or a removable storage device or drive 1014. Removable storage drive 1014 may 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.

[0111] Removable storage drive 1014 may interact with a removable storage unit 1018. Removable storage unit 1018 may include a computer usable or readable storage device having stored thereon computer software (control logic) and / or data. Removable storage unit 1018 may be a floppy disk,magnetic tape, compact disk, DVD, optical storage disk, and / any other computer data storage device. Removable storage drive 1014 may read from and / or write to removable storage unit 1018.

[0112] Secondary memory 1010 may include other means, devices, components, instrumentalities or other approaches for allowing computer programs and / or other instructions and / or data to be accessed by computer system 1000. Such means, devices, components, instrumentalities or other approaches may include, for example, a removable storage unit 1022 and an interface 1020. Examples of the removable storage unit 1022 and the interface 1020 may include 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 or other port, a memory card and associated memory card slot, and / or any other removable storage unit and associated interface.

[0113] Computer system 1000 may further include a communication or network interface 1024. Communication interface 1024 may enable computer system 1000 to communicate and interact with any combination of external devices, external networks, external entities, etc. (individually and collectively referenced by reference number 1028). For example, communication interface 1024 may allow computer system 1000 to communicate with external or remote devices 1028 over communications path 1026, which may be wired and / or wireless (or a combination thereof), and which may include any combination of LANs, WANs, the Internet, etc. Control logic and / or data may be transmitted to and from computer system 1000 via communication path 1026.

[0114] Computer system 1000 may also be any of a personal digital assistant (PDA), desktop workstation, laptop or notebook computer, netbook, tablet, smart phone, smart watch or other wearable, appliance, part of the Internet-of-Things, and / or embedded system, to name a few non-limiting examples, or any combination thereof.

[0115] Computer system 1000 may be a client or server, accessing or hosting any applications and / or data through any delivery paradigm, including but not limited to remote or distributed cloud computing solutions; local or on-premises software (“on-premise” cloud-based solutions); “as a service” models (e.g., content as a service (CaaS), digital content as a service (DCaaS), software as a service (SaaS), managed software as a service (MSaaS), platform as a service (PaaS), desktop as a service (DaaS), framework as a service (FaaS), backend as a service (BaaS), mobile backend as a service (MBaaS), infrastructure as a service (laaS), etc.); and / or a hybrid model including any combination of the foregoing examples or other services or delivery paradigms.

[0116] Any applicable data structures, file formats, and schemas in computer system 1000 may be derived from standards including but not limited to JavaScript Object Notation (JSON), Extensible Markup Language (XML), Yet Another Markup Language (YAML), Extensible Hypertext Markup Language (XHTML), Wireless Markup Language (WML), MessagePack, XML User Interface Language (XUL), or any other functionally similar representations alone or in combination. Alternatively, proprietary data structures, formats or schemas may be used, either exclusively or in combination with known or open standards.

[0117] In some embodiments, a tangible, non-transitory apparatus or article of manufacture comprising a tangible, non-transitory computer useable or readable medium having control logic (software) stored thereon may also be referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system 1000, main memory 1008, secondary memory 1010, and removable storage units 1018 and 1022, 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 1000 or processor(s) 1004), may cause such data processing devices to operate as described herein.

[0118] Based on the teachings contained in this disclosure, it will be apparent to persons skilled in the relevant art(s) how to make and use embodiments of this disclosure using data processing devices, computer systems and / or computer architectures other than that shown in FIG. 10. In particular, embodiments may operate with software, hardware, and / or operating system implementations other than those described herein.

[0119] The embodiments may further be described using the following clauses:1. A metrology apparatus comprising: an optical component configured to provide a wavefront correction to light reflected and / or transmitted by the optical component, wherein the optical component is configured to generate plural aberration modes at a same time; a sensor configured to capture a measurement signal scattered from a target; and a processor, configured to use the measurement signal to determine an aberration correction.2. The metrology apparatus of clause 1 , wherein the measurement signal is demultiplexed to generate a set of demodulated signals, wherein each demodulated signal corresponds to an aberration mode of the optical component.3. The metrology apparatus of clause 2, wherein the target and / or a wafer comprising the target comprise one or more pinhole structures, wherein the diameter of the one or more pinhole structures is less than the wavelength of light incident on the one or more pinhole structures.4. The metrology apparatus of clause 3, wherein the one or more pinhole structures generate one or more point spread functions, wherein images of the one or more point spread functions are captured by the sensor.5. The metrology apparatus of clause 3, wherein the aberration correction comprises a combination of aberration modes corresponding to a combination of demodulated signals in the one or more demodulated signals where the images of the one or more point spread functions are sharpest and circularly symmetric and / or where an image of the target is sharpest.6. The metrology apparatus of clause 1 , wherein the optical component is an actuated, deformable mirror.7. The metrology apparatus of clause 6, wherein the deformable mirror comprises an update frequency of at least 1 kHz.8. The metrology apparatus of clause 1, wherein an aberration correction is determined for different wavelengths of illuminating light.9. The metrology apparatus of clause 1, wherein the processor utilizes a convolutional neural network to predict an aberration correction for the optical component and / or a computational correction for the measurement signal.10. The metrology apparatus of clause 9, wherein the convolutional neural network is trained using simulation data and information on a wafer stack and / or wafer target.11. A method of correcting aberrations, the method comprising: modulating a shape of an optical component, wherein light reflected and / or transmitted by the optical component comprises information on aberration modes of the optical component; illuminating a target on with the light reflected and / or transmitted by the optical component; measuring light diffracted and / or scattered from the target with a sensor; demultiplexing the measured light to obtain a set of demodulated signals, wherein each demodulated signal in the set of demodulated signals corresponds to an aberration mode of the optical component; and determining a preferred aberration mode of the optical component based on the set of demodulated signals.12. The method of clause 11, wherein the preferred aberration mode is determined for different wavelengths of light reflected and / or transmitted by the optical component.13. The method of clause 11, wherein the modulating the shape of the optical component comprises modulating the shape of a deformable mirror.14. The method of clause 11, wherein the determining comprises determining which demodulated signal or combination of demodulated signals in the set of demodulated signals contains a steepest edge transition of a selected feature within the image.15. The method of clause 11, wherein the set of demodulated signals comprises one or more images of a point spread function diffracted from one or more pinhole structures on the wafer.16. The method of clause 15, wherein the determining comprises determining a demodulated signal or weighted combination of demodulated signals in the set of demodulated signals where the one or more images of a point spread function comprise the smallest diameter and / or highest circular symmetry.17. The method of clause 15, wherein the determining comprises determining a demodulated signal or weighted combination of demodulated signals in the set of demodulated signals where the one or more images of a point spread function comprises images of point spread functions of similar size.18. The method of clause 11, wherein the modulating comprises modulating the shape of the optical component at a frequency of at least 1 kHz.19. The method of clause 11, the method additionally comprising ceasing modulation and applying the preferred aberration correction to the optical component and repeating the illuminating and measuring.20. The method of clause 11 , the method additionally comprising further processing a combination of demodulated signals corresponding to the preferred aberration mode.21. A method of correcting aberrations, the method comprising: determining an aberration correction by using a machine learning model to process a measurement signal scattered and / or diffracted from a target, wherein the measurement signal contains one or more images of a point spread function and / or one or more images of the target; and applying the aberration correction to an adaptive optical component and / or to the measurement signal, wherein the convolutional neural network is trained using simulation data and wafer target and / or stack data.

[0120] Although specific reference can be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. The skilled artisan 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. The substrate referred to herein 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, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0121] Although specific reference may have been made above to the use of embodiments of the present disclosure in the context of optical lithography, it will be appreciated that the present disclosure can be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device can be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0122] 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 disclosure is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0123] The terms “radiation,” “beam of radiation” or the like as used herein can encompass all types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelengthX of 365, 248, 193, 157 or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (for example, having a wavelength in the range of 5-20 nm such as, for example, 13.5 nm), or hard X-ray working at less than 5 nm, as well as matter beams, such as ion beams or electron beams. The terms “light,” “illumination,” or the like may refer to non-matter radiation (e.g., photons, UV, X-ray, or the like). 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 the wavelengths 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 embodiments, 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, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.

[0124] It is to be appreciated 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 may set forth one or more but not all exemplary embodiments 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.

[0125] 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.

[0126] While specific embodiments of the disclosure have been described above, it will be appreciated that embodiments of the present disclosure may be practiced otherwise than as described. The descriptions are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the disclosure as described without departing from the scope of the claims set out below.

[0127] The foregoing description of the specific embodiments 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 embodiments, without undue experimentation, 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 embodiments, based on the teaching and guidance presented herein.

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

Claims

CLAIMS1. A metrology apparatus comprising: an optical component configured to provide a wavefront correction to light reflected and / or transmitted by the optical component, wherein the optical component is configured to generate plural aberration modes at a same time; a sensor configured to capture a measurement signal scattered from a target; and a processor, configured to use the measurement signal to determine an aberration correction.

2. The metrology apparatus of claim 1 , wherein the measurement signal is demultiplexed to generate a set of demodulated signals, wherein each demodulated signal corresponds to an aberration mode of the optical component.

3. The metrology apparatus of claim 2, wherein the target and / or a wafer comprising the target comprise one or more pinhole structures, wherein the diameter of the one or more pinhole structures is less than the wavelength of light incident on the one or more pinhole structures.

4. The metrology apparatus of claim 3, wherein the one or more pinhole structures generate one or more point spread functions, wherein images of the one or more point spread functions are captured by the sensor.

5. The metrology apparatus of claim 3, wherein the aberration correction comprises a combination of aberration modes corresponding to a combination of demodulated signals in the one or more demodulated signals where the images of the one or more point spread functions are sharpest and circularly symmetric and / or where an image of the target is sharpest.

6. The metrology apparatus of claim 1 , wherein the optical component is an actuated, deformable mirror.

7. The metrology apparatus of claim 6, wherein the deformable mirror comprises an update frequency of at least 1 kHz.

8. The metrology apparatus of claim 1, wherein an aberration correction is determined for different wavelengths of illuminating light.

9. The metrology apparatus of claim 1, wherein the processor utilizes a convolutional neural network to predict an aberration correction for the optical component and / or a computational correction for the measurement signal.

10. The metrology apparatus of claim 9, wherein the convolutional neural network is trained using simulation data and information on a wafer stack and / or wafer target.

11. A method of correcting aberrations, the method comprising: modulating a shape of an optical component, wherein light reflected and / or transmitted by the optical component comprises information on aberration modes of the optical component; illuminating a target on with the light reflected and / or transmitted by the optical component; measuring light diffracted and / or scattered from the target with a sensor; demultiplexing the measured light to obtain a set of demodulated signals, wherein each demodulated signal in the set of demodulated signals corresponds to an aberration mode of the optical component; and determining a preferred aberration mode of the optical component based on the set of demodulated signals.

12. The method of claim 11, wherein the preferred aberration mode is determined for different wavelengths of light reflected and / or transmitted by the optical component.

13. The method of claim 11, wherein the modulating the shape of the optical component comprises modulating the shape of a deformable mirror.

14. The method of claim 11, wherein the determining comprises determining which demodulated signal or combination of demodulated signals in the set of demodulated signals contains a steepest edge transition of a selected feature within the image.

15. The method of claim 11, wherein the set of demodulated signals comprises one or more images of a point spread function diffracted from one or more pinhole structures on the wafer.

Images