WO2025237649A1

WO2025237649A1 - System and method for combined field and pupil intensity-based phase retrieval

Info

Publication number: WO2025237649A1
Application number: PCT/EP2025/061266
Authority: WO
Inventors: Aniruddha Ramakrishna SONDE; Joshua Adams; Krishanu SHOME; Mahesh Upendra AJGAONKAR
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2024-05-16
Filing date: 2025-04-24
Publication date: 2025-11-20
Anticipated expiration: 2026-11-16

Abstract

An alignment system includes an illumination source, an optical module, a detection system, an image processor, and a control system. The illumination source directs a beam toward a target mark disposed on a substrate. The optical module splits one or more diffracted beams from the target mark into a pupil image and a field image. The detection system receives the pupil image and the field image from the optical module. The image processor applies a region of interest to the pupil image and the field image to determine a pupil plane and an image plane. The image processor applies a phase retrieval algorithm to computationally determine a phase of the one or more diffracted beams from the target mark at a target plane. The control system adjusts a position of the substrate based on the determined phase.

Description

SYSTEM AND METHOD FOR COMBINED FIELD AND PUPIL INTENSITY-BASED PHASE RETRIEVAL

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63/648,463 which was filed on May 16, 2024 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present disclosure relates to metrology systems, for example, an alignment system for measuring alignment mark positions in 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 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 may 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 techniques for 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 (OV) 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.

[0007] Current alignment sensors can use self-referencing interferometers to interfere plus and minus orders of diffracted light from a substrate to form an alignment signal. A detection system can measure a location of a peak of the alignment signal and can compare that peak location to an expected peak location to determine a position of an alignment mark on the substrate. As resists increase in thickness on the substrate, material inconsistencies can form a tilted resist covering the alignment marks. The tilted resist can cause alignment signal degradation, which can lead to alignment errors in the detection system.

SUMMARY

[0008] Accordingly, it is desirable to have an alignment system that can monitor an alignment signal without being affected by a tilted resist. For example, optical inspection processes can be performed with the use of a phase retrieval algorithm based on aspects described herein.

[0009] In some aspects, an alignment system can include an illumination source, an optical module, a detection system, an image processor, and a control system. The illumination source can direct a beam toward a target mark disposed on a substrate. The optical module can split one or more diffracted beams from the target mark into a pupil image and a field image. The detection system can receive the pupil image and the field image from the optical module. The image processor can apply a region of interest to the pupil image and the field image to determine a pupil plane and an image plane. The image processor can apply a phase retrieval algorithm to computationally determine a phase of the one or more diffracted beams from the target mark at a target plane. The control system can adjust a position of the substrate based on the determined phase. [0010] In some aspects, a method can include directing a beam with an illumination source toward a target mark disposed on a substrate. The method can further include splitting, with an optical module, one or more diffracted beams from the target mark into a pupil image and a field image. The method can further include receiving the pupil image and the field image from the optical module at a detection system. The method can further include applying, with an image processor, a region of interest to the pupil image and the field image to determine a pupil plane and an image plane. The method can further include applying, with the image processor, a phase retrieval algorithm to computationally determine a phase of the one or more diffracted beams from the target mark at a target plane. The method can further include adjusting a position of the substrate based on the determined phase.

[0011] In some aspects, a pupil metrology method can include directing a beam with an illumination source toward a target mark disposed on a substrate. The method can further include splitting, with an optical module, one or more diffracted beams from the target mark into a pupil image and a field image. The method can further include receiving the pupil image and the field image from the optical module at a detection system. The method can further include applying, with an image processor, a region of interest to the pupil image and the field image to determine a pupil plane and an image plane. The method can further include applying, with the image processor, a phase retrieval algorithm to computationally determine a beam spot profile of the one or more diffracted beams from the target mark at a target plane. The method can further include adjusting a position of the substrate based on the determined beam spot profile.

[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. 1A shows a reflective lithographic apparatus, according to some aspects.

[0015] FIG. IB shows a transmissive lithographic apparatus, according to some aspects.

[0016] FIG. 2 shows more details of a reflective lithographic apparatus, according to some aspects.

[0017] FIG. 3 shows a lithographic cell, according to some aspects.

[0018] FIGS. 4 A and 4B show inspection apparatuses, according to some aspects.

[0019] FIG. 5 shows an alignment system using field and pupil intensity-based phase retrieval, according to some aspects. [0020] FIG. 6 shows a detection system view corresponding to the alignment system of FIG. 5, according to some aspects.

[0021] FIG. 7 shows an alignment system configured to alter a magnification of an image, according to some aspects.

[0022] FIG. 8 shows a detection system view corresponding to the alignment system of FIG. 7, according to some aspects.

[0023] FIG. 9 shows an alignment system configured to use two detectors, according to some aspects. [0024] FIG. 10 shows detector views corresponding to the alignment system of FIG. 9, according to some aspects.

[0025] FIG. 11 shows a method for extracting a phase of an alignment signal, according to some aspects.

[0026] FIG. 12 shows a method for performing pupil metrology with an alignment signal, according to some aspects.

[0027] 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

[0028] 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.

[0029] 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.

[0030] 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).

[0031] 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.

[0032] 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.

[0033] Example Lithographic Systems

[0034] FIGS. 1A and IB show a lithographic apparatus 100 and a lithographic apparatus 100’, respectively, in which aspects 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.

[0035] 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. [0036] 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. 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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. For example, a liquid can be located between the projection system and the substrate during exposure.

[0042] 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. A radiation system can comprise the source SO, the illuminator IL, and/or the beam delivery system BD.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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 lens or 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.

[0047] The projection system PS is arranged to capture (e.g., using a lens or lens group L) the zeroth order diffracted beams, first order diffracted beams, and/or higher order diffracted beams (not shown). 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 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 aspects, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some aspects, 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.

[0048] 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).

[0049] 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 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.

[0050] 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, an out-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 can be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0051] 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-)magnification 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 needed 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.

[0052] Combinations and/or variations on the described modes of use or entirely different modes of use can also be employed.

[0053] In some aspects, 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.

[0054] In some aspects, lithographic apparatus 100’ includes 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.

[0055] 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 EUV radiation emitting plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The EUV radiation emitting 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 used for efficient generation of the radiation. In some aspects, a plasma of excited tin (Sn) (e.g., excited via a laser) is provided to produce EUV radiation.

[0056] The radiation emitted by the EUV radiation emitting 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.

[0057] 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 EUV radiation emitting plasma 210. Grating spectral filter 240 is used in particular for suppressing infra-red (IR) radiation.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Example Lithographic Cell

[0062] FIG. 3 shows a lithographic cell 300, also sometimes referred to a lithocell or cluster, according to some aspects. 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. Conventionally 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.

[0063] Example Inspection Apparatus

[0064] In order to control the lithographic process to place device features accurately on the substrate, alignment marks are generally provided on the substrate, and the lithographic apparatus includes one or more inspection apparatuses for accurate positioning of marks on a substrate. These alignment apparatuses are effectively position measuring apparatuses. Different types of marks and different types of alignment apparatuses and/or systems are known from different times and different manufacturers. A type of system widely used in current lithographic apparatus is based on a self-referencing interferometer as described in U.S. Patent No. 6,961,116 (den Boef et al.). Generally marks are measured separately to obtain X- and Y-positions. A combined X- and Y-measurement can be performed using the techniques described in U.S. Publication No. 2009/195768 A (Bijnen et al.), however. The full contents of both of these disclosures are incorporated herein by reference.

[0065] FIG. 4A shows a cross-sectional view of an inspection apparatus 400 that can be implemented as a part of lithographic apparatus 100 or 100’, according to some aspects. In some aspects, inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). Inspection apparatus 400 can be further configured to detect positions of alignment marks on the substrate and to align the substrate with respect to the patterning device or other components of lithographic apparatus 100 or 100’ using the detected positions of the alignment marks. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0066] The terms “inspection apparatus,” “metrology system,” or the like can be used herein to refer to, e.g., a device used for measuring a property of a structure (e.g., overlay sensor, critical dimension sensor, or the like), a device or system used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment sensor), or the like.

[0067] In some aspects, inspection apparatus 400 can include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and a processor 432. Illumination system 412 can be configured to provide an electromagnetic narrow band radiation beam 413 having one or more passbands. In an example, the one or more passbands can be within a spectrum of wavelengths between about 500 nm to about 900 nm. In another example, the one or more passbands can be discrete narrow passbands within a spectrum of wavelengths between about 500 nm to about 900 nm. Illumination system 412 can be further configured to provide one or more passbands having substantially constant center wavelength (CWL) values over a long period of time (e.g., over a lifetime of illumination system 412). Such configuration of illumination system 412 can help to prevent the shift of the actual CWL values from the desired CWL values, as discussed above, in current alignment systems. And, as a result, the use of constant CWL values can improve long-term stability and accuracy of alignment systems (e.g., inspection apparatus 400) compared to the current alignment apparatuses. [0068] In some aspects, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. For example, radiation beam 413 can be split into radiation sub-beams 415 and 417, as shown in FIG. 4A. Beam splitter 414 can be further configured to direct radiation sub-beam 415 onto a substrate 420 placed on a stage 422. In one example, the stage 422 is movable along direction 424. Radiation sub-beam 415 can be configured to illuminate an alignment mark or a target 418 located on substrate 420. Alignment mark or target 418 can be coated with a radiation sensitive film. In some aspects, alignment mark or target 418 can have one hundred and eighty degrees (i.e., 180°) symmetry. That is, when alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to a plane of alignment mark or target 418, rotated alignment mark or target 418 can be substantially identical to an unrotated alignment mark or target 418. The target 418 on substrate 420 can be (a) a resist layer grating comprising bars that are formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interleaved on a product layer grating. The bars can alternatively be etched into the substrate. This pattern is sensitive to chromatic aberrations in the lithographic projection apparatus, particularly the projection system PL, and illumination symmetry and the presence of such aberrations will manifest themselves in a variation in the printed grating. One in-line method used in device manufacturing for measurements of line width, pitch, and critical dimension makes use of a technique known as “scatterometry”. Methods of scatterometry are described in Raymond et al., “Multiparameter Grating Metrology Using Optical Scatterometry”, J. Vac. Sci. Tech. B, Vol. 15, no. 2, pp. 361-368 (1997) and Niu et al., “Specular Spectroscopic Scatterometry in DUV Lithography”, SPIE, Vol. 3677 (1999), which are both incorporated by reference herein in their entireties. In scatterometry, light is reflected by periodic structures in the target, and the resulting reflection spectrum at a given angle is detected. The structure giving rise to the reflection spectrum is reconstructed, e.g. using Rigorous Coupled- Wave Analysis (RCWA) or by comparison to a library of patterns derived by simulation. Accordingly, the scatterometry data of the printed gratings is used to reconstruct the gratings. The parameters of the grating, such as line widths and shapes, can be input to the reconstruction process, performed by processing unit PU, from knowledge of the printing step and/or other scatterometry processes.

[0069] In some aspects, beam splitter 414 can be further configured to receive diffraction radiation beam 419 and split diffraction radiation beam 419 into at least two radiation sub-beams, according to an aspect. Diffraction radiation beam 419 can be split into diffraction radiation sub-beams 429 and 439, as shown in FIG. 4A.

[0070] It should be noted that even though beam splitter 414 is shown to direct radiation sub-beam 415 towards alignment mark or target 418 and to direct diffracted radiation sub-beam 429 towards interferometer 426, the disclosure is not so limiting. Other optical arrangements can be used to obtain the similar result of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0071] As illustrated in FIG. 4A, interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 through beam splitter 414. In an example aspect, diffracted radiation sub-beam 429 can be at least a portion of radiation sub-beam 415 that can be reflected from alignment mark or target 418. In an example of this aspect, interferometer 426 comprises any appropriate set of optical-elements, for example, a combination of prisms that can be configured to form two images of alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be appreciated that a good quality image need not be formed. It can be enough to have the features of alignment mark 418 resolved. Interferometer 426 can be further configured to rotate one of the two images with respect to the other of the two images 180° and recombine the rotated and unrotated images interferometrically.

[0072] In some aspects, detector 428 can be configured to receive the recombined image via interferometer signal 427 and detect interference as a result of the recombined image when alignment axis 421 of inspection apparatus 400 passes through a center of symmetry (not shown) of alignment mark or target 418. Such interference can be due to alignment mark or target 418 being 180° symmetrical, and the recombined image interfering constructively or destructively, according to an example aspect. Based on the detected interference, detector 428 can be further configured to determine a position of the center of symmetry of alignment mark or target 418 and consequently, detect a position of substrate 420. According to an example, alignment axis 421 can be aligned with an optical beam perpendicular to substrate 420 and passing through a center of image rotation interferometer 426. Detector 428 can be further configured to estimate the positions of alignment mark or target 418 by implementing sensor characteristics and interacting with wafer mark process variations.

[0073] In a further aspect, detector 428 determines the position of the center of symmetry of alignment mark or target 418 by performing one or more of the following measurements:

[0074] 1. measuring position variations for various wavelengths (position shift between colors);

[0075] 2. measuring position variations for various orders (position shift between diffraction orders); [0076] 3. measuring position variations for various polarizations (position shift between polarizations); and

[0077] 4. measuring intensity difference between opposite orders of a diffraction order pair (e.g., to characterize and correct for asymmetry).

[0078] This data can be obtained using any type of alignment sensor, for example, a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Patent No. 6,961,116 that employs a selfreferencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software, or Athena (Advanced Technology using High order ENhancement of Alignment), as described in U.S. Patent No. 6,297,876, which directs each of seven diffraction orders to a dedicated detector, which are both incorporated by reference herein in their entireties.

[0079] In some aspects, beam analyzer 430 can be configured to receive and determine an optical state of diffracted radiation sub-beam 439. The optical state can be a measure of beam wavelength, polarization, or beam profile. Beam analyzer 430 can be further configured to determine a position of stage 422 and correlate the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420 can be accurately known with reference to stage 422. Alternatively, beam analyzer 430 can be configured to determine a position of inspection apparatus 400 or any other reference element such that the center of symmetry of alignment mark or target 418 can be known with reference to inspection apparatus 400 or any other reference element. Beam analyzer 430 can be a point or an imaging polarimeter with some form of wavelength-band selectivity. In some aspects, beam analyzer 430 can be directly integrated into inspection apparatus 400, or connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other aspects. [0080] In some aspects, beam analyzer 430 can be further configured to determine the overlay data between two patterns on substrate 420. One of these patterns can be a reference pattern on a reference layer. The other pattern can be an exposed pattern on an exposed layer. The reference layer can be an etched layer already present on substrate 420. The reference layer can be generated by a reference pattern exposed on the substrate by lithographic apparatus 100 and/or 100’. The exposed layer can be a resist layer exposed adjacent to the reference layer. The exposed layer can be generated by an exposure pattern exposed on substrate 420 by lithographic apparatus 100 or 100’. The exposed pattern on substrate 420 can correspond to a movement of substrate 420 by stage 422. In some aspects, the measured overlay data can also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data can be used as calibration data to calibrate the exposure pattern exposed by lithographic apparatus 100 or 100’, such that after the calibration, the offset between the exposed layer and the reference layer can be minimized.

[0081] In some aspects, beam analyzer 430 can be further configured to determine a model of the product stack profile of substrate 420, and can be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement. The product stack profile contains information on the stacked product such as alignment mark, target 418, or substrate 420, and can include mark process variation-induced optical signature metrology that is a function of illumination variation. The product stack profile can also include product grating profile, mark stack profile, and mark asymmetry information. An example of beam analyzer 430 is Yieldstar™, manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Patent No. 8,706,442, which is incorporated by reference herein in its entirety. Beam analyzer 430 can be further configured to process information related to a particular property of an exposed pattern in that layer. For example, beam analyzer 430 can process an overlay parameter (an indication of the positioning accuracy of the layer with respect to a previous layer on the substrate or the positioning accuracy of the first layer with respective to marks on the substrate), a focus parameter, and/or a critical dimension parameter (e.g., line width and its variations) of the depicted image in the layer. Other parameters are image parameters relating to the quality of the depicted image of the exposed pattern.

[0082] In some aspects, an array of detectors (not shown) can be connected to beam analyzer 430, and allows the possibility of accurate stack profile detection as discussed below. For example, detector 428 can be an array of detectors. For the detector array, a number of options are possible: a bundle of multimode fibers, discrete pin detectors per channel, or CCD or CMOS (linear) arrays. The use of a bundle of multimode fibers enables any dissipating elements to be remotely located for stability reasons. Discrete PIN detectors offer a large dynamic range but each need separate pre-amps. The number of elements is therefore limited. CCD linear arrays offer many elements that can be read-out at high speed and are especially of interest if phase-stepping detection is used.

[0083] In some aspects, a second beam analyzer 430’ can be configured to receive and determine an optical state of diffracted radiation sub-beam 429, as shown in FIG. 4B. The optical state can be a measure of beam wavelength, polarization, or beam profile. Second beam analyzer 430’ can be identical to beam analyzer 430. Alternatively, second beam analyzer 430’ can be configured to perform one or more of the functions of beam analyzer 430, such as determining a position of stage 422 and correlating the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420, can be accurately known with reference to stage 422. Second beam analyzer 430’ can also be configured to determine a position of inspection apparatus 400, or any other reference element, such that the center of symmetry of alignment mark or target 418 can be known with reference to inspection apparatus 400, or any other reference element. [0084] In some aspects, second beam analyzer 430’ can be directly integrated into inspection apparatus 400, or it can be connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other aspects. Alternatively, second beam analyzer 430’ and beam analyzer 430 can be combined to form a single analyzer (not shown) configured to receive and determine the optical states of both diffracted radiation sub-beams 429 and 439.

[0085] In some aspects, processor 432 receives information from detector 428 and beam analyzer 430. Processor 432 can create a basic correction algorithm based on the information received from detector 428 and beam analyzer 430, including but not limited to the optical state of the illumination beam, the alignment signals, associated position estimates, and the optical state in the pupil, image, and additional planes. The pupil plane is the plane in which the radial position of radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Processor 432 can utilize the basic correction algorithm to characterize the inspection apparatus 400 with reference to wafer marks and/or alignment marks 418.

[0086] Example Alignment System Using Field and Pupil Intensity-Based Phase Retrieval

[0087] FIG. 5 shows an alignment system 500 using field and pupil intensity-based phase retrieval, according to some aspects. Alignment system 500 can be configured to measure a position of an alignment target. In some aspects, alignment system 500 can represent a detailed view of inspection apparatus 400 (FIGS. 4A and 4B). Alignment system 500 can be built as a part of lithographic apparatus 100 or 100', or can be built as a stand-alone unit in lithographic cell 300 and work together with other apparatuses during operation. In some aspects, alignment system 500 can include an illumination source 502, an optical module 504, a detection system 506, an image processor 508 and a control system 510. [0088] In some aspects, illumination source 502 can be configured to emit a spatially coherent illumination beam 512. Illumination beam 512 can have an electromagnetic narrow band with one or more pass bands. In some aspects, illumination beam 512 can be visible light or infrared light with a wavelength in a range between about 500 nm to about 700 nm, and about 700 nm to about 2 pm, respectively. In some aspects, illumination source 502 can include one or more sources of radiation, each source producing one or more passbands within a spectrum of wavelengths between about 500 nm to about 2 pm. For example, illumination beam 512 can be a combination of the one or more passbands from the one or more sources of radiation and can have substantially continuous wavelengths. In some aspects, the wavelength range of the illumination beam 512 can also include ultra-violet light.

[0089] In some aspects, illumination source 502 can be configured to direct illumination beam 512 toward a target mark 514 disposed on a substrate 516. In some aspects, illumination source 502 can direct illumination beam 512 toward optical module 504, which can be configured to redirect the illumination beam 512 toward target mark 514.

[0090] In some aspects, a substrate 516 (e.g. a semiconductor wafer) can be disposed on a stage 518 that is adjustable (e.g., a support structure that can move). In some aspects, target mark 514 can be a structure formed on a substrate 516 through pattern transfer using a prior-level lithography mask (not shown). The material and film stack used for the formation of target mark 514 can depend on the layout of target mark 514 on the prior-level lithography mask and the processes that the substrate 516 went through. The design requirement for target mark 514 (e.g., shape and size) can depend on the alignment system and alignment method used. In some aspects, target mark 514 can comprise a diffractive structure (e.g., a grating(s)). Target mark 514 can reflect, refract, diffract, scatter, or the like, radiation (e.g. illumination beam 512). For ease of discussion, and without limitation, radiation that interacts with an alignment target will be termed scattered radiation throughout. In some aspects, scattered radiation can be collected by an objective lens (not shown) within optical module 504.

[0091] In some aspects, target mark 514 can be made of or coated with a radiation sensitive film, for example, a photoresist (“resist”). A non-uniform increase in thickness of a resist layer can cause height differences across substrate 516. A top surface of the resist layer may not be parallel to target mark 514, and may be tilted instead. Accordingly, such a resist layer can be considered a “tilted resist” or “wedged resist.” Resist tilt can occur in scribelanes of substrate 516 where alignment targets are located (e.g., target mark 514). In some aspects, a scribelane may form a trench on a surface of the substrate 516. The resist does not fill the trench uniformly when substrate 516 is covered with resist. As a result, target mark 514 can be located under an area with a tilted resist surface.

[0092] In some aspects, scattered radiation from target mark 514 can include a zero-order diffracted beam 520 and higher-order diffracted beams 521a, 521b. In some aspects, zero-order diffracted beam 520 can be a reflection of illumination beam 512 off target mark 514, in which the zero-order diffracted beam 520 travels transverse to the direction of propagation of illumination beam 512. In some aspects, higher-order diffracted beams 521a, 521b from target mark 514 can include symmetrically distributed high orders of diffraction beams, for example, +1 and -1, +2 and -2, . . ., -i-n and -n, respectively (where n is an integer greater than 2). Different orders of diffraction beams are spatially separated, depending on a diffraction angle. In some aspects, higher-order diffracted beams 521a, 521b can include at least one positive diffraction order or one negative diffraction order.

[0093] In some aspects, however, a resist layer may affect how illumination beam 512 illuminates target mark 514 such as, for example, causing illumination beam 512 to refract before reaching target mark 514. Additionally, higher-order diffracted beams 521a, 521b can reflect from target mark 514 and can subsequently be refracted by the resist layer in an asymmetric manner. Therefore, due to the refraction of illumination beam 512 and the reflection and refraction of higher-order diffracted beams 521a, 521b, the diffraction angles of higher-order diffracted beams 521a, 521b (e.g., +1/-1, . . ., +m/-m, where m is any integer greater than one) with respect to an optical axis of alignment system 500 may not be equal. The magnitude of angular deviations in higher-order diffracted beams 521a, 521b operate according to Snell’s law. In some aspects, phase deltas between the higher-order diffracted beams 521a, 521b (e.g., +1/-1, . . ., +m/-m) may be introduced due to non-equal diffraction angles or different optical path lengths between each pair of the higher-order diffracted beams 521a, 521b (e.g., +1/-1, ..., +m/- m). The phase delta may introduce an aligned position error proportional to the magnitude of the phase delta.

[0094] In some aspects, optical module 504 can be configured to receive illumination beam 512 from illumination source 502 and redirect illumination beam 512 toward target mark 514. In some aspects, optical module 504 can be configured to receive zero-order diffracted beam 520 and higher-order diffracted beams 521a, 521b scattered from target mark 514 and split the zero-order diffracted beam 520 and higher-order diffracted beams 521a, 521b into sub-beams directed toward detection system 506, in which the sub-beams form a pupil image and a field image. In some aspects, optical module 504 can include zero stop 522, a beam splitter 524, one or more mirrors 526, and one or more focusing elements 528.

[0095] In some aspects, zero stop 522 can be configured to receive zero-order diffracted beam 520 and block zero-order diffracted beam 520 from propagating through the rest of optical module 504. In some aspects, zero stop 522 can be an optical element (e.g., lens, aperture, etc.) configured to permit illumination beam 512 to transmit in a first direction but block zero-order diffracted beam 520 from transmitting in an opposite direction. Therefore, zero stop 522 can enable optical module 504 to manipulate higher-order diffracted beams 521a, 521b without interference from zero-order diffracted beam 520.

[0096] In some aspects, beam splitter 524 can be configured to receive illumination beam 512 from illumination source 502 and redirect illumination beam 512 toward target mark 514. For example, illumination beam 512 can be directed with any incident angle toward target mark 514. In some aspects, beam splitter 524 can be configured to receive higher-order diffracted beams 521a, 521b scattered from target mark 514 and produce sub-beams directed toward detection system 506. In some aspects, higher- order diffracted beams 521a, 521b can be split into halves to produce sub-beams. The sub-beams produced by beam splitter 524 can be pupil sub-beams 530a, 530b and field sub-beams 532a, 532b. In some aspects, pupil sub-beams 530a, 530b can be transmitted directly from beam splitter 524 as a pupil image received at detection system 506. In some aspects, field sub-beams 532a, 532b can be redirected by beam splitter 524 toward other optical elements within optical module 504 such as, for example, one or more mirrors 526 and/or one or more focusing elements 528.

[0097] In some aspects, beam splitter 524 can be a spot mirror, formed by a transmissive cube with a reflective metal layer disposed in the center of the cube. It should be noted that even though beam splitter 524 is shown to reflect illumination beam 512 toward target mark 514 and to produce pupil subbeams 530a, 530b and field sub-beams 532a, 532b from higher-order diffracted beams 521a, 521b, the disclosure is not so limiting. It would be apparent to a person skilled in the relevant art that other optical arrangements may be used to obtain a similar result. For example, Fresnel lenses or another type of diffractive optic element may be used as an optical element for directing light beams throughout alignment system 500. Such an example configuration may transmit a first portion of the received scattered radiation as a pupil image at the detection system 506, while simultaneously focusing a second portion of the received scattered radiation to produce a field image at the detection system 506.

[0098] In some aspects, one or more mirrors 526 and one or more focusing elements 528 can be configured to receive field sub-beams 532a, 532b from beam splitter 524. In some aspects, one or more mirrors 526 can be disposed at any angle to redirect field sub-beams 532a, 532b toward detection system 506. It is known to a person skilled in the art that other optical elements within optical module 504 can also be used to provide a similar function. For example, one or more prisms can be used to redirect light beams throughout alignment system 500. In some aspects, one or more focusing elements 528 can be configured to focus, magnify, or redirect field sub-beams 532a, 532b within optical module 504. It is known to a person skilled in the art that other focusing optical elements can also be used to provide a similar function. One or more mirrors 526 and one or more focusing elements 528 can be used in conjunction to transmit field sub-beams 532a, 532b as a field image received at detection system 506. [0099] It should be appreciated the structures drawn within alignment system 500 and optical module 504 are not limited to their depicted positions. The positions of structures can vary as necessary, for example, as designed for a modular assembly.

[0100] In some aspects, detection system 506 can be configured to receive pupil sub-beams 530a, 530b as a pupil image and to receive field sub-beams 532a, 532b as a field image from optical module 504. In some aspects, detection system 506 can simultaneously receive the pupil image and the field image. In some aspects, detection system 506 can include a two-dimensional detector device configured to capture a image within a field of view in X- and Y-dimensions with, for example, a pixel array. A pitch of a target mark 514 may influence where the pupil image and/or field image appear within the field of view of detection system 506. Detection system 506 can be configured to capture intensity data corresponding to the pupil image and the field image. Detection system 506 can consistently capture intensity data, even if the location of the pupil image and the field image may change within the field of view. Therefore, detection system 506 can flexibly accommodate any pitch grating without moving parts, as compared to existing systems which may use a reference grating that can only be tuned to one specific pitch.

[0101] In some aspects, detection system 506 can include any commercially available two-dimensional light detector device such as, for example, an image sensor (e.g., a camera), a spatial light modulator, and/or a masked detector. For example, detection system 506 can include a complementary metal oxide semiconductor (CMOS) active -pixel sensor having a photodiode and a CMOS transistor switch for each pixel, allowing pixel signals to be amplified individually. In another example, detection system 506 can include a spatial light modulator configured to modulate at least one of the intensity, phase, or polarization of received light in a spatially varying manner, and capture the modified light with a built- in detector. In this example configuration, the spatial light modulator could modulate the polarization of the received light, thereby allowing for repeat measurements with a different polarization state to acquire more data at the cost of throughput. In some aspects, detection system 506 can include a masked detector configured to capture multiple images by shifting bit values in quick succession. In this example configuration, the masked detector can acquire multiple images from one measurement of a target mark 514, thereby improving the amount of image captured within a shorter duration of time.

[0102] In some aspects, detection system 506 can capture the pupil image and field image as a single color or shade. For example, detection system 506 can include a wavelength-dependent filter wheel configured for particular wavelengths, for example, with the use of spectral coatings. In this example configuration, the wavelength-dependent filter wheel can tune the received light to permit only predetermined wavelengths to transmit toward a detector within detection system 506. The wavelengthdependent filter wheel may be adjusted to selectively transmit a certain wavelength from a variety of wavelength options. In some aspects, detection system 506 can be configured to capture multiwavelength measurements simultaneously of the pupil image and the field image. In this example configuration, detection system 506 can obtain multiple wavelength measurements by using optical color wedges and shifting the pupil image and/or the field image. In some aspects, the range of wavelengths can be visible light wavelengths from about 380 nm to about 750 nm.

[0103] In some aspects, image processor 508 can be configured to manipulate the image data of the pupil image and the field image received at detection system 506. In some aspects, image processor 508 can apply a region of interest to the pupil image and the field image to determine a pupil plane and an image plane. In this configuration, a portion of the field of view of detection system 506 can be selectively filtered for computational operations. Therefore, image processor 508 can obtain the pupil image and field image as inputs for the computational operations even if detection system 506 does not provide precise geometrical positioning. As a result, image processor 508 can be insensitive to the above-mentioned problems caused by wedge resist for existing systems using self-referencing interferometers.

[0104] In some aspects, image processor 508 can apply a phase retrieval algorithm to computationally determine a phase of the pupil sub-beams 530a, 530b and field sub-beams 532a, 532b produced from higher-order diffracted beams 521a, 521b scattered from target mark 514 at a target plane. In this configuration, image processor 508 can computationally extract the phase of the alignment signal. In some aspects, image processor 508 can use phase retrieval algorithms including, for example, the Gerchberg-Saxton algorithm or the hybrid input-output algorithm.

[0105] In one example, the Gerchberg-Saxton algorithm is an iterative phase retrieval algorithm for retrieving the phase of a complex-valued wavefront from two intensity measurements acquired in two different planes. Within the context of alignment system 500, the image processor can use the two intensity (e.g., amplitude) measurements, obtained by detection system 506, of the pupil image at the pupil plane and the field image at the field plane as inputs. The wavefront propagation between the pupil plane and the field plane is given by a Fourier transform such that the pupil image and the field image are Fourier transforms of each other. Image processor 508 can iteratively estimate the phase and tailor the computed phase to the ground truth of the measurement performed by alignment system 500, and then adapt the phase retrieval algorithm accordingly.

[0106] Other phase retrieval algorithms can be used, as would become apparent to persons skilled in the art. For example, a ptychographic phase retrieval algorithm can be used to process multiple sets of diffraction pattern images.

[0107] In the context of wafer alignment and metrology, optical module 504 can manipulate image measurements of diffraction spots to form simultaneous pupil images and field images at detection system 506, and then image processor 508 can apply a phase retrieval algorithm to obtain the phase difference between the higher-order diffracted beams 521a, 521b scattered from target mark 514 at a target plane. This information can be used to determine positioning of a target mark 514 as stage 518 moves under an alignment sensor and/or if a target mark 514 has been printed with asymmetry. The combination of measurements and computations can be used to calibrate out errors in the metrology process.

[0108] In some aspects, image processor 508 can be used upon performing pupil metrology processes. For example, pupil metrology processes can be used to correct alignment signal errors caused by crosstalk. Crosstalk can occur when an alignment mark is improperly illuminated such that signal leakage from neighboring structures interferes with the alignment signal. Wafer processing and the presence of stacks above substrate 516 can affect the spot profile of the pupil image and the field image. The presence of stacks can produce a shift in the spot profile and can lead to a reweighting of the diffraction spot (e.g., producing a non-Gaussian spot that can cause process inaccuracies). For example, the variability of the stacks, in combination with aberrations in optical module 504 can cause a degraded accuracy in the alignment signal of about a few nanometers.

[0109] In some aspects, image processor 508 can monitor the spot profile intensities of the pupil image and field image at detection system 506, which conveys information about plus and minus orders of diffracted light such as, for example, higher-order diffracted beams 521a, 521b. By capturing the spot in the pupil image, image processor 508 can mitigate the effects of crosstalk by using a spot shift and spot profile calibration. For example, alignment system 500 can compensate for crosstalk effects by calibrating for a change in a wavefront sample due to stack variations. Accordingly, alignment system 500 can use pupil metrology to determine characteristics of the stack above a target mark 514 and calibrate out the error with control system 510 to improve accuracy of measurements.

[0110] Persons skilled in the art would understand that image processor 508 can be used upon performing overlay metrology processes as well.

[0111] In some aspects, control system 510 can be configured to adjust a position of substrate 516 based on the phase determined by image processor 508. For example, the determined phase can be indicative of a position of a target mark 514. Accordingly, control system 510 can actuate stage 518 based on the determined phase to adjust a position of substrate 516 to align a target mark 514 into a desired position. [0112] FIG. 6 shows a detection system view 650 corresponding to detection system 506 of alignment system 500, according to some aspects. In some aspects, detection system view 650 can be a detailed view of an image captured by a detector within detection system 506. In some aspects, detection system view 650 can represent an aperture of detection system 506. Accordingly, detection system view 650 can represent a aperture that is sufficiently broad to collect a desired range of pitches for target marks 514. For example, the aperture represented by detection system view 650 can be equivalent in size to a size of an objective pupil. In one example, if an objective pupil is 18 mm, then detection system view 650 can correspond to a detection system 506 having an 18 mm aperture.

[0113] In some aspects, detection system view 650 can include a pupil image 634 and a field image 636. In some aspects, detection system view 650 can be an image of pupil image 634 and field image 636 captured simultaneously. Pupil image 634 can be two spots located near the edges of detection system view 650. A pitch of a target mark 514 can affect how far apart the spots of pupil image 634 are located on detection system view 650. Field image 636 can be a single spot located near the center of detection system view 650. Pupil image 634 and field image 636 can be inspected by image processor 508 for intensity and spot profile characteristics for use in at least one of wafer alignment metrology, pupil metrology, or overlay metrology.

[0114] FIG. 7 shows an alignment system 700 configured to alter a magnification of an image, according to some aspects. The above discussion of alignment system 500 shown in FIG. 5 applies to alignment system 700 shown in FIG. 7. The aspects of alignment system 500 shown in FIG. 5, for example, and the aspects of alignment system 700 shown in FIG. 7 may be similar. Similar reference numbers are used to indicate features of the aspects of alignment system 500 shown in FIG. 5 and the similar features of the aspects of alignment system 700 shown in FIG. 7.

[0115] In some aspects, optical module 704 can include at least one focusing element 728 configured to modify a magnification of at least one of the pupil image or the field image. In the example aspect shown in FIG. 7, optical module 704 includes three focusing elements 728a-728c to alter a magnification of a field image produced by field sub-beams 732a, 732b. Focusing element 728a can be configured to direct field sub-beams 732a, 732b to a certain point on a mirror 726, from which field sub-beams 732a, 732b overlap and focusing elements 728b, 728c can adjust the size of the field image spot produced by the overlapping field sub-beams 732a, 732b.

[0116] In some aspects, a pitch of a target mark 714 can produce beam spots that use up a certain amount of space on a field of view of detection system 706. To prevent overlapping beam spots, it is beneficial for optical module to use one or more focusing elements 728 to control the size of a beam spot for either the pupil image or field image, or both. A person skilled in the art would recognize that focusing elements 728 can change not only size of a pupil image or field image, but also positioning of a pupil image or a field image within a field of view of detection system 706.

[0117] FIG. 8 shows a detection system view 850 corresponding to detection system 706 of alignment system 700, according to some aspects. In some aspects, detection system view 850 can be a detailed view of an image captured by a detector within detection system 706. The above discussion of detection system view 650 shown in FIG. 6 applies to detection system view 850 shown in FIG. 8. The aspects of detection system view 650 shown in FIG. 6, for example, and the aspects of detection system view 850 shown in FIG. 8 may be similar. Similar reference numbers are used to indicate features of the aspects of detection system view 650 shown in FIG. 6 and the similar features of the aspects of detection system view 850 shown in FIG. 8.

[0118] In some aspects, detection system view 850 can include a pupil image 834 and an modified field image 838. In some aspects, detection system view 850 can be an image of pupil image 834 and field image 838 captured simultaneously. In the example aspect shown in FIG. 8, modified field image 838 can be a larger magnified spot in comparison to field image 636 shown in FIG. 6. A person skilled in the art would recognize that focusing elements 728 can modify not only size of modified field image 838, but also positioning of modified field image 838 within detection system view 850. A person skilled in the art would recognize that focusing elements 728 can also be used to modify the size and/or positioning of pupil image 834 within detection system view 850.

[0119] FIG. 9 shows an alignment system 900 configured to use two detectors 940a, 940b, according to some aspects. The above discussion of alignment systems 500 and 700 shown in FIGS. 5 and 7 applies to alignment system 900 shown in FIG. 9. The aspects of alignment systems 500 and 700 shown in FIGS. 5 and 7, for example, and the aspects of alignment system 900 shown in FIG. 9 may be similar. Similar reference numbers are used to indicate features of the aspects of alignment systems 500 and 700 shown in FIGS. 5 and 7 and the similar features of the aspects of alignment system 900 shown in FIG. 9.

[0120] In some aspects, detection system 906 can include two detectors 940a, 940b. In some aspects, detector 940a can be configured to receive a pupil image produced by pupil sub-beams 930a, 930b and detector 940b can be configured to receive a field image produced by field sub-beams 532a, 532b. In this configuration, alignment system 900 can use optical module 904 that is a more simplified design compared to optical modules 504 and 704 because optical module 904 uses less optical elements, such as having one mirror 926 and one focusing element 928. It would be apparent to a person skilled in the relevant art that other optical arrangements may be used to obtain a similar result.

[0121] FIG. 10 shows detector views corresponding to the alignment system 900 of FIG. 9, according to some aspects. In some aspects, the detector views can include a pupil image detector view 1060 and a field image detector view 1070. The above discussion of detection system views 650 and 850 shown in FIGS. 6 and 8 applies to pupil image detector view 1060 and field image detector view 1070 shown in FIG. 10. The aspects of detection system views 650 and 850 shown in FIGS. 6 and 8, for example, and the aspects of pupil image detector view 1060 and field image detector view 1070 shown in FIG. 10 may be similar. Similar reference numbers are used to indicate features of the aspects of detection system views 650 and 850 shown in FIGS. 6 and 8 and the similar features of the aspects of pupil image detector view 1060 and field image detector view 1070 shown in FIG. 10. [0122] In some aspects, pupil image detector view 1060 and field image detector view 1070 can be detailed views of images captured by detectors 940a, 940b within detection system 906. For example, pupil image detector view 1060 can be a first independent image of pupil image 1034 captured by detector 940a and field image detector view 1070 can be a second independent image of field image 1036 captured by detector 940b. In some aspects, pupil image detector view 1060 and field image detector view 1070 can be captured simultaneously by detectors 940a, 940b.

[0123] Example Methods

[0124] FIG. 11 shows a method 1100 for extracting a phase of an alignment signal, according to some aspects. In some aspects, at step 1102, an illumination source (e.g., an illumination source 502) can direct a beam (e.g., illumination beam 512) toward a target mark (e.g., target mark 514) disposed on a substrate (e.g., substrate 516).

[0125] In some aspects, at step 1104, an optical module (e.g., optical module 504) can split one or more diffracted beams (e.g., higher-order diffracted beams 521a, 521b) from the target mark into a pupil image (e.g., pupil image 634 produced by pupil sub-beams 530a, 530b) and a field image (e.g., field image 636 produced by field sub-beams 532a, 532b). In some aspects, the splitting the one or more diffracted beams can include splitting the one or more diffracted beams with the optical module comprising at least one of a beam splitter, a mirror, a prism, a focusing element, or a Fresnel lens.

[0126] In some aspects, at step 1106, the pupil image and the field image from the optical module can be received at a detection system (e.g., detection system 506). In some aspects, the receiving the pupil image and the field image can include receiving simultaneously the pupil image and the field image at the detection system. In some aspects, the receiving the pupil image and the field image can include receiving the pupil image at a first detector of the detection system and receiving the field image at a second detector of the detection system. In some aspects, the receiving the pupil image and the field image can include receiving the pupil image and the field image at the detection system comprising at least one of a camera, a spatial light modulator, or a masked detector.

[0127] In some aspects, at step 1108, an image processor (e.g., image processor 508) can apply a region of interest to the pupil image and the field image to determine a pupil plane and an image plane.

[0128] In some aspects, at step 1110, the image processor can apply a phase retrieval algorithm to computationally determine a phase of the one or more diffracted beams from the target mark at a target plane. In some aspects, the applying the phase retrieval algorithm can include applying the phase retrieval algorithm comprising at least one of the Gerchberg-Saxton algorithm or the hybrid inputoutput algorithm. In some aspects, the applying the phase retrieval algorithm can include applying the phase retrieval algorithm comprising a ptychographic phase retrieval algorithm.

[0129] In some aspects, at step 1112, a position of the substrate can be adjusted based on the determined phase.

[0130] In some aspects, method 1100 can further include modifying a magnification of at least one of the pupil image or the field image with the optical module comprising at least one focusing element. [0131] In some aspects, method 1100 can further include transmitting, with a wavelength-dependent filter disposed in front of the detection system, predetermined wavelengths of the pupil image and the field image toward the detection system.

[0132] The method steps of FIG. 11 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 11 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. 1A-10.

[0133] FIG. 12 shows a method 1200 for performing pupil metrology with an alignment signal, according to some aspects. In some aspects, at step 1202, an illumination source (e.g., an illumination source 502) can direct a beam (e.g., illumination beam 512) toward a target mark (e.g., target mark 514) disposed on a substrate (e.g., substrate 516).

[0134] In some aspects, at step 1204, an optical module (e.g., optical module 504) can split one or more diffracted beams (e.g., higher-order diffracted beams 521a, 521b) from the target mark into a pupil image (e.g., pupil image 634 produced by pupil sub-beams 530a, 530b) and a field image (e.g., field image 636 produced by field sub-beams 532a, 532b). In some aspects, the splitting the one or more diffracted beams can include splitting the one or more diffracted beams with the optical module comprising at least one of a beam splitter, a mirror, a prism, a focusing element, or a Fresnel lens.

[0135] In some aspects, at step 1206, the pupil image and the field image from the optical module can be received at a detection system (e.g., detection system 506). In some aspects, the receiving the pupil image and the field image can include receiving simultaneously the pupil image and the field image at the detection system. In some aspects, the receiving the pupil image and the field image can include receiving the pupil image at a first detector of the detection system and receiving the field image at a second detector of the detection system. In some aspects, the receiving the pupil image and the field image can include receiving the pupil image and the field image at the detection system comprising at least one of a camera, a spatial light modulator, or a masked detector.

[0136] In some aspects, at step 1208, an image processor (e.g., image processor 508) can apply a region of interest to the pupil image and the field image to determine a pupil plane and an image plane.

[0137] In some aspects, at step 1210, the image processor can apply a phase retrieval algorithm to computationally determine a beam spot profile of the one or more diffracted beams from the target mark at a target plane. In some aspects, the applying the phase retrieval algorithm can include applying the phase retrieval algorithm comprising at least one of the Gerchberg-Saxton algorithm or the hybrid inputoutput algorithm. In some aspects, the applying the phase retrieval algorithm can include applying the phase retrieval algorithm comprising a ptychographic phase retrieval algorithm.

[0138] In some aspects, at step 1212, a position of the substrate can be adjusted based on the determined beam spot profile.

[0139] In some aspects, method 1200 can further include modifying a magnification of at least one of the pupil image or the field image with the optical module comprising at least one focusing element. [0140] In some aspects, method 1200 can further include transmitting, with a wavelength-dependent filter disposed in front of the detection system, predetermined wavelengths of the pupil image and the field image toward the detection system.

[0141] In some aspects, method 1200 can further include calibrating a measurement apparatus based on the determined beam spot profile.

[0142] The method steps of FIG. 12 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 12 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. 1A-10.

[0143] The embodiments may further be described using the following clauses:

1. An alignment system comprising: an illumination source configured to direct a beam toward a target mark disposed on a substrate; an optical module configured to split one or more diffracted beams from the target mark into a pupil image and a field image; a detection system configured to receive the pupil image and the field image from the optical module; an image processor configured to: apply a region of interest to the pupil image and the field image to determine a pupil plane and an image plane, and apply a phase retrieval algorithm to computationally determine a phase of the one or more diffracted beams from the target mark at a target plane; and a control system configured to adjust a position of the substrate based on the determined phase.

2. The alignment system of clause 1 , wherein the optical module comprises at least one of a beam splitter, a mirror, a prism, a focusing element, or a Fresnel lens.

3. The alignment system of clause 1, wherein the optical module comprises at least one focusing element configured to modify a magnification of at least one of the pupil image or the field image.

4. The alignment system of clause 1 , wherein the detection system is configured to simultaneously receive the pupil image and the field image.

5. The alignment system of clause 1, wherein the detection system comprises a first detector configured to receive the pupil image and a second detector configured to receive the field image.

6. The alignment system of clause 1, wherein the detection system comprises at least one of a camera, a spatial light modulator, or a masked detector.

7. The alignment system of clause 1, further comprising a wavelength-dependent filter disposed in front of the detection system, the wavelength-dependent filter configured to transmit predetermined wavelengths of the pupil image and the field image toward the detection system.

8. The alignment system of clause 1, wherein the phase retrieval algorithm comprises at least one of the Gerchberg-Saxton algorithm or the hybrid input-output algorithm. 9. The alignment system of clause 1, wherein the phase retrieval algorithm comprises a ptychographic phase retrieval algorithm.

10. A method comprising: directing a beam with an illumination source toward a target mark disposed on a substrate; splitting, with an optical module, one or more diffracted beams from the target mark into a pupil image and a field image; receiving the pupil image and the field image from the optical module at a detection system; applying, with an image processor, a region of interest to the pupil image and the field image to determine a pupil plane and an image plane; applying, with the image processor, a phase retrieval algorithm to computationally determine a phase of the one or more diffracted beams from the target mark at a target plane; and adjusting a position of the substrate based on the determined phase.

11. The method of clause 10, wherein the splitting the one or more diffracted beams comprises splitting the one or more diffracted beams with the optical module comprising at least one of a beam splitter, a mirror, a prism, a focusing element, or a Fresnel lens.

12. The method of clause 10, further comprising modifying a magnification of at least one of the pupil image or the field image with the optical module comprising at least one focusing element.

13. The method of clause 10, wherein the receiving the pupil image and the field image comprises receiving simultaneously the pupil image and the field image at the detection system.

14. The method of clause 10, wherein the receiving the pupil image and the field image comprises receiving the pupil image at a first detector of the detection system and receiving the field image at a second detector of the detection system.

15. The method of clause 10, wherein the receiving the pupil image and the field image comprises receiving the pupil image and the field image at the detection system comprising at least one of a camera, a spatial light modulator, or a masked detector.

16. The method of clause 10, further comprising transmitting, with a wavelength-dependent filter disposed in front of the detection system, predetermined wavelengths of the pupil image and the field image toward the detection system.

17. The method of clause 10, wherein the applying the phase retrieval algorithm comprises applying the phase retrieval algorithm comprising at least one of the Gerchberg-Saxton algorithm or the hybrid input-output algorithm.

18. The method of clause 10, wherein the applying the phase retrieval algorithm comprises applying the phase retrieval algorithm comprising a ptychographic phase retrieval algorithm.

19. A pupil metrology method comprising: directing a beam with an illumination source toward a target mark disposed on a substrate; splitting, with an optical module, one or more diffracted beams from the target mark into a pupil image and a field image; receiving the pupil image and the field image from the optical module at a detection system; applying, with an image processor, a region of interest to the pupil image and the field image to determine a pupil plane and an image plane; applying, with the image processor, a phase retrieval algorithm to computationally determine a beam spot profile of the one or more diffracted beams from the target mark at a target plane; and adjusting a position of the substrate based on the determined beam spot profile.

20. The pupil metrology method of clause 19, further comprising calibrating a measurement apparatus based on the determined beam spot profile.

[0144] 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 I 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 5-100 nm such as, for example, 13.5 nm), or hard X-ray working at less than 5 nm, as well as particle beams, such as ion beams or electron beams. 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 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, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.

[0145] 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, LCDs, thin-film 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.

[0146] Furthermore, although some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, 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.

[0147] 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.

[0148] 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.

[0149] 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. The breadth 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

2. The alignment system of claim 1 , wherein the optical module comprises at least one of a beam splitter, a mirror, a prism, a focusing element, or a Fresnel lens.

3. The alignment system of claim 1, wherein the optical module comprises at least one focusing element configured to modify a magnification of at least one of the pupil image or the field image.

4. The alignment system of claim 1 , wherein the detection system is configured to simultaneously receive the pupil image and the field image.

5. The alignment system of claim 1, wherein the detection system comprises a first detector configured to receive the pupil image and a second detector configured to receive the field image.

6. The alignment system of claim 1, wherein the detection system comprises at least one of a camera, a spatial light modulator, or a masked detector.

7. The alignment system of claim 1 , further comprising a wavelength-dependent filter disposed in front of the detection system, the wavelength-dependent filter configured to transmit predetermined wavelengths of the pupil image and the field image toward the detection system.

8. The alignment system of claim 1, wherein the phase retrieval algorithm comprises at least one of the Gerchberg-Saxton algorithm or the hybrid input-output algorithm.

9. The alignment system of claim 1, wherein the phase retrieval algorithm comprises a ptychographic phase retrieval algorithm.

11. The method of claim 10, wherein the splitting the one or more diffracted beams comprises splitting the one or more diffracted beams with the optical module comprising at least one of a beam splitter, a mirror, a prism, a focusing element, or a Fresnel lens.

12. The method of claim 10, further comprising modifying a magnification of at least one of the pupil image or the field image with the optical module comprising at least one focusing element.

13. The method of claim 10, wherein the receiving the pupil image and the field image comprises receiving simultaneously the pupil image and the field image at the detection system.

14. The method of claim 10, wherein the receiving the pupil image and the field image comprises receiving the pupil image at a first detector of the detection system and receiving the field image at a second detector of the detection system.

15. The method of claim 10, wherein the receiving the pupil image and the field image comprises receiving the pupil image and the field image at the detection system comprising at least one of a camera, a spatial light modulator, or a masked detector.