Measurement system based on multimode optical fiber imaging and photoetching equipment

Abstract

An inspection system includes a radiation source, a multimode optical fiber, an optical structure, a two-dimensional detector array, and a computing device. The radiation source irradiates a target to generate scattered radiation from the target. The scattered radiation includes diffraction order pairs. The multimode fiber receives scattered radiation and outputs a mixture of diffraction order pairs based on propagating properties of the multimode fiber. The optical structure combines the diffractive order pair on the input side of the multimode fiber. The two-dimensional detector array receives a mixture of the pairs of diffractive orders and generates a measurement signal corresponding to the mixture of the pairs of diffractive orders. The computing device analyzes the measurement signal based on the propagating property and discriminates an intensity of the diffracted order pair based on the analysis.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application No. 63 / 435,707, filed on December 28, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to metrology systems, eg, inspection systems, for measuring mark asymmetry in lithographic apparatus and systems. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate (typically onto a target portion of the substrate). For example, a lithographic apparatus can be used in the manufacture of integrated circuits (ICs). In this case, a patterning device, which can be a mask or reticle, is used to generate the circuit pattern to be formed on a single layer of the IC. This pattern can be transferred to a target portion (e.g., comprising a portion of a die, one or several dies) on a substrate (e.g., a silicon wafer). Typically, this transfer is performed by imaging the pattern onto a layer of radiation-sensitive material (photoresist, or simply "resist") provided on the substrate. Often, a single substrate will contain a grid of adjacent target portions that are patterned sequentially. Known lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by simultaneously scanning the radiation beam across the target portion in a given direction (the "scanning" direction) while the radiation beam scans the pattern in parallel or antiparallel to this scan direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0005] During a lithography operation, different processing steps can necessitate the sequential formation of different layers on the substrate. Therefore, it may be necessary to position the substrate with high accuracy relative to a previous pattern formed on the substrate. Typically, alignment marks are placed on the substrate to allow alignment and positioning relative to a second object. A lithographic apparatus may use an alignment device to detect the position of the alignment marks and use them to align the substrate to ensure accurate exposure from the mask. Misalignment between alignment marks at two different layers is measured as overlay error.

[0006] To monitor the photolithography process, parameters of the patterned substrate are measured. These parameters may include, for example, the overlay error between successive layers formed in or on the patterned substrate and the critical linewidth of the developed photoresist. These measurements can be performed on production substrates and / or on specialized metrology targets. Various techniques exist for measuring the microstructures formed during photolithography, including the use of scanning electron microscopes and specialized tools. A rapid and non-invasive form of specialized inspection tool is a scatterometer: a radiation beam is directed onto a target on the surface of the substrate, and the properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after reflection or scattering by the substrate, the properties of the substrate can be determined. This can be accomplished, for example, by comparing the reflected beam with data stored in a library of known measurements of known properties. Spectral 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 specific narrow angular range. In contrast, angle-resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

[0007] Such optical scatterometers can be used to measure parameters such as the critical dimension of a developed photoresist or the overlay error (OV) between two layers formed in or on a patterned substrate. Properties of the substrate can be determined by comparing the properties of an illumination beam before and after it is reflected or scattered by the substrate.

[0008] The printing accuracy of a lithography system depends heavily on the precision of the inspection tools it uses. Summary of the Invention

[0009] Therefore, it is desirable to improve metrology techniques to achieve higher measurement accuracy. For example, optical inspection processes can be performed more accurately based on the apparatus and methods disclosed herein.

[0010] In some aspects, an inspection system may include a radiation source, a multimode optical fiber, an optical structure, a two-dimensional detector array, and a computing device. The radiation source may be configured to irradiate a target to generate scattered radiation. The scattered radiation may include diffraction order pairs. The multimode optical fiber may be configured to receive the scattered radiation and output a mixture of the diffraction order pairs based on the propagation properties of the multimode optical fiber. The optical structure may be configured to combine the diffraction order pairs at the input side of the multimode optical fiber. The two-dimensional detector array may be configured to receive the mixture of the diffraction order pairs and generate a measurement signal corresponding to the mixture of the diffraction order pairs. The computing device may be configured to analyze the measurement signal based on the propagation properties and to discern the intensity of the diffraction order pairs based on the analysis.

[0011] In some aspects, a lithographic apparatus may include an illumination system, a projection system, and an inspection system. The illumination system may be configured to illuminate a pattern of a pattern forming device. The projection system may be configured to project an image of the pattern onto a substrate. The inspection system may include a radiation source, a multimode optical fiber, an optical structure, a two-dimensional detector array, and a computing device. The radiation source may be configured to irradiate a target on the substrate to generate scattered radiation from the target. The scattered radiation may include diffraction order pairs. The multimode optical fiber may be configured to receive the scattered radiation and output a mixture of the diffraction order pairs based on the propagation properties of the multimode optical fiber. The optical structure may be configured to combine the diffraction order pairs at the input side of the multimode optical fiber. The two-dimensional detector array may be configured to receive the mixture of the diffraction order pairs and generate a measurement signal corresponding to the mixture of the diffraction order pairs. The computing device may be configured to analyze the measurement signal based on the propagation properties and to discern the intensities of the diffraction order pairs based on the analysis.

[0012] In some aspects, a method may include one or more of the following operations. The method may include generating scattered radiation including a first diffraction beam and a second diffraction beam by irradiating a lithography target. The method may also include splitting the scattered radiation to produce a first portion of the first diffraction beam, a first portion of the second diffraction beam, a second portion of the first diffraction beam, and a second portion of the second diffraction beam. The method may also include generating a first measurement signal based on the first portion received at a first two-dimensional detector array. The method may also include receiving a second portion at an input side of a multimode optical fiber to mix the second portion of the first diffraction beam and the second portion of the second diffraction beam based on propagation properties of the multimode optical fiber. The method may also include generating a second measurement signal based on the mixed second portion received at a second two-dimensional detector array. The method may also include quantifying the propagation properties of the multimode optical fiber based on analyzing the first measurement signal and the second measurement signal to compare the first portion and the mixed second portion.

[0013] The following describes in detail the additional features of various aspects of the present disclosure with reference to the accompanying drawings. Note that the present disclosure is not limited to the specific aspects described herein. These aspects are presented herein for illustrative purposes only. Based on the teachings contained in this invention, those skilled in the relevant art will understand additional aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate the disclosure and, together with the description, further serve to explain the principles of the disclosure and enable one skilled in the relevant art to make and use the aspects described herein.

[0015] Figure 1AA reflective lithographic apparatus according to some aspects is shown.

[0016] Figure 1B A transmissive lithographic apparatus according to some aspects is shown.

[0017] Figure 2 More details of a reflective lithographic apparatus according to some aspects are shown.

[0018] Figure 3 A lithographic cell according to some aspects is shown.

[0019] Figure 4A and Figure 4B An inspection apparatus according to some aspects is shown.

[0020] Figure 5 A portion of an inspection device 500 is shown in accordance with some aspects.

[0021] Figure 6 A calibration system for calibrating a multimode optical fiber to be used in an inspection system is shown in accordance with some aspects.

[0022] Figure 7 Methods for characterizing and using the transfer function of a multimode optical fiber according to some aspects are presented.

[0023] Features of the present disclosure will become apparent from the detailed description set forth below in conjunction with the accompanying drawings, in which like reference numerals identify corresponding elements throughout. In the drawings, similar reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit of a reference numeral identifies the drawing in which the reference numeral first appears. Unless otherwise indicated, the drawings provided throughout this disclosure should not be construed as being to scale. DETAILED DESCRIPTION

[0024] The embodiments described herein and references to "one aspect," "an aspect," "an exemplary aspect," and the like in the specification indicate that the described aspects may include specific features, structures, or characteristics, but each aspect may not necessarily include the specific features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same aspects. In addition, when specific features, structures, or characteristics are described in conjunction with aspects, it should be understood that, whether or not explicitly described, it is within the knowledge of those skilled in the art to achieve such features, structures, or characteristics in conjunction with other aspects.

[0025] For ease of description, spatially relative terms, such as "below," "beneath," "below," "above," "on," and the like, may be used herein to describe the relationship of one element or feature to another element or feature as illustrated in the accompanying drawings. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the drawings. The device may be otherwise oriented (rotated 90 degrees or in other orientations) and the spatially relative descriptors used herein should be interpreted accordingly.

[0026] The terms "about," "approximately," and the like may be used herein to indicate a value for a given quantity that may vary based on a particular technology. Based on the particular technology, the terms "about," "approximately," and the like may indicate a value for a given quantity that varies, for example, within 10% to 30% above or below the stated value (e.g., ±10%, ±20%, or ±30% of the stated value).

[0027] Aspects of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Aspects of the present disclosure may also be implemented as instructions stored on a computer-readable medium that can be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, machine-readable magnetic storage media may include: read-only memory (ROM); random-access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), etc. Furthermore, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be understood that such description is merely for convenience, and that these actions are performed by a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc. The term "machine-readable medium" may be used interchangeably with similar terms such as "computer program product," "computer-readable medium," "non-transitory computer-readable medium," etc. The term "non-transitory" may be used herein to refer to one or more forms of computer-readable media other than transitory propagated signals.

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

[0029] Exemplary lithography systems

[0030] Figure 1A and Figure 1BA lithographic apparatus 100 and a lithographic apparatus 100 ′ are shown, respectively, in which aspects of the present disclosure may be implemented. Each of the lithographic apparatuses 100 and 100 ′ includes the following components: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask, reticle, or dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and a substrate table (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. The lithographic apparatuses 100 and 100 ′ also have a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion (e.g., comprising one or more dies) C of the substrate W. In the lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In the lithographic apparatus 100', the patterning device MA and the projection system PS are transmissive.

[0031] The illumination system IL may 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 guiding, shaping or controlling the radiation beam B.

[0032] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to a reference frame, the design of at least one of the lithographic apparatuses 100 and 100', and other conditions (e.g., whether 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 stage, for example, which can be fixed or movable. Using sensors, the support structure MT can ensure that the patterning device MA is in a desired position, for example, relative to the projection system PS.

[0033] The term “patterning device” MA is to 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 so as to create a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer of a device to be created in the target portion C to form an integrated circuit.

[0034] The patterning device MA may be of the transmissive type (e.g. Figure 1B lithographic apparatus 100 ′) or reflective (as in Figure 1Alithographic apparatus 100). 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 masks, alternating phase-shift masks, or attenuated phase-shift masks, as well as various hybrid mask types. One example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam B that is reflected by the matrix of small mirrors.

[0035] The term "projection system" PS as used herein includes 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 used or other factors such as the use of an immersion liquid or the use of a vacuum on the substrate W. A vacuum environment may be used for EUV or electron beam radiation, as other gases may absorb too much radiation or electrons. A vacuum environment may therefore be provided to the entire beam path by means of vacuum walls and a vacuum pump.

[0036] The lithographic apparatus 100 and / or the lithographic apparatus 100' may be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a "multi-stage" machine, the additional substrate tables WT may be used in parallel, or preparatory steps may be performed on one or more tables while one or more other substrate tables WT are being used for exposure. In some cases, the additional tables may not be substrate tables WT.

[0037] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered with a liquid having a relatively high refractive index, such as water, to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces within the lithographic apparatus, such as 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 necessarily mean that structures such as the substrate are submerged in the liquid. For example, during exposure, the liquid may be located between the projection system and the substrate.

[0038] refer to Figure 1A and Figure 1B , the illuminator IL receives a radiation beam from a radiation source SO. When the source SO is an excimer laser, the source SO and the lithographic apparatus 100, 100' may be separate physical entities. In this case, the source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam is delivered to the lithographic apparatus 100 or 100' by means of a beam delivery system BD (in the embodiment of FIG. 1 ) comprising, for example, suitable directing mirrors and / or a beam expander. Figure 1BThe radiation system may comprise the source SO, the illuminator IL and / or the beam delivery system BD.

[0039] The illuminator IL may comprise an adjuster AD (at Figure 1B Typically, at least the outer radial extent and / or the inner radial extent (commonly referred to as "σ-outer" and "σ-inner", respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. Furthermore, the illuminator IL may include various other components (in Figure 1B ), such as an integrator IN and a condenser CO. The illuminator IL may be used to condition the radiation beam B so as to have a desired uniformity and intensity distribution in its cross-section.

[0040] refer to Figure 1A The radiation beam B is incident on and patterned by the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT. In the lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., mask) MA. After reflecting from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g., an interferometer arrangement, a linear encoder, a 2D encoder, or a capacitive sensor), the substrate table WT can be accurately moved (e.g., to position a different target portion C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. The patterning device (eg, mask) MA and substrate W may be aligned using mask alignment marks M1 , M2 and substrate alignment marks P1 , P2 .

[0041] refer to Figure 1BThe radiation beam B is incident on and patterned by the patterning device (e.g., mask MA), which is held on the support structure (e.g., mask table MT). 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 PPU that is conjugate with the illumination system pupil IPU. Portions of the radiation originate from the intensity distribution at the illumination system pupil IPU and traverse the mask pattern unaffected by diffraction at the mask pattern, producing an image of the intensity distribution at the illumination system pupil IPU.

[0042] The projection system PS projects an image of the marking pattern MP onto a photoresist layer coated on the substrate W, wherein the image is formed by a diffraction beam generated from the marking pattern MP by radiation from the intensity distribution. For example, the mask pattern MP may comprise an array of lines and spaces. Diffraction of radiation other than the zeroth-order diffraction at the array generates a deflected diffraction beam having a change in direction perpendicular to the lines. The undiffracted beam (i.e., the so-called zeroth-order diffraction beam) traverses the pattern without any change in propagation direction. The zeroth-order diffraction beam passes through an upper lens or upper lens group of the projection system PS (located upstream of the conjugate pupil PPU of the projection system PS) to reach the conjugate pupil PPU. The portion of the intensity distribution associated with the zeroth-order diffraction beam in the plane of the conjugate pupil PPU is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture arrangement PD is, for example, disposed at or approximately located in a plane including the conjugate pupil PPU of the projection system PS.

[0043] The projection system PS is arranged (e.g., using a lens or lens group L) to capture a zeroth-order diffraction beam, a first-order diffraction beam, and / or higher-order diffraction beams (not shown). In some aspects, dipole illumination can be used to image a line pattern extending perpendicular to the line to exploit the resolution-enhancing effect of dipole illumination. For example, the first-order diffraction beam interferes with the corresponding zeroth-order diffraction beam at the level of the wafer W to produce an image of the line pattern MP with the highest possible resolution and process window (i.e., the available depth of focus combined with the tolerable exposure dose deviation). In some aspects, astigmatic aberrations can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Furthermore, in some aspects, astigmatic aberrations can be reduced by blocking the zeroth-order beam associated with the radiation pole in the opposite quadrant in the conjugate pupil PPU of the projection system. This is described in more detail in US Pat. No. 7,511,799 B2, issued Mar. 31, 2009, which is incorporated herein by reference in its entirety.

[0044] With the help of a second positioner PW and a position sensor IFD (e.g. an interferometer arrangement, a linear encoder, a 2D encoder or a capacitive sensor), the substrate table WT can be accurately moved (e.g. to position a different target portion C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not in use) can be moved (e.g. after mechanical retrieval from a mask library or during a scan). Figure 1B ) is used to accurately position the mask MA relative to the path of the radiation beam B.

[0045] Typically, movement of the mask table MT may 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 may 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 may be connected to a short-stroke actuator, or may be fixed. The mask MA and substrate W may be aligned using mask alignment marks M1, M2, and substrate alignment marks P1, P2. Although the substrate alignment marks shown in the figure occupy dedicated target portions, they may be located in the spaces between multiple target portions (these are called scribe line alignment marks). Similarly, where more than one die is provided on the mask MA, the patterning device alignment marks may be located between these dies.

[0046] The mask table MT and patterning device MA can be located within a vacuum chamber, where an in-vacuum robot (IVR) can be used to move the patterning device (such as a mask or reticle) into and out of the vacuum chamber. Alternatively, when the mask table MT and patterning device MA are outside the vacuum chamber, an out-of-vacuum robot can be used for various transport operations similar to the in-vacuum robot (IVR). Both the in-vacuum and out-of-vacuum robots should be calibrated to smoothly transfer any payload (e.g., a mask) to the fixed kinematic mount of the transfer station.

[0047] The lithographic apparatus 100 and 100 may be used in at least one of the following modes:

[0048] 1. In step mode, the support structure (e.g., mask table) MT and substrate table WT remain essentially stationary while an entire pattern imparted to the radiation beam is projected at once onto a target portion C (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.

[0049] 2. In scan mode, the support structure (e.g., mask table) MT and substrate table WT are scanned synchronously while a pattern imparted to the radiation beam 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 (e.g., mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0050] 3. In another mode, the support structure (e.g., mask table) MT holding the programmable patterning device is held substantially stationary 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 may be employed, and the programmable patterning device updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography using a programmable patterning device, such as a programmable mirror array.

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

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

[0053] In some aspects, the lithographic apparatus 100 includes a deep ultraviolet (DUV) source configured to generate a DUV radiation beam for DUV lithography. Typically, 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.

[0054] Figure 2 The lithographic apparatus 100 is shown in greater detail and includes the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged to maintain a vacuum environment within an enclosure 220 of the source collector apparatus SO. A plasma 210 emitting EUV radiation can be formed by a discharge-generated plasma source. EUV radiation can be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor) in which the EUV radiation-emitting plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. For example, the EUV radiation-emitting plasma 210 is generated by a discharge that causes an at least partially ionized plasma. For efficient radiation generation, Xe, Li, Sn vapor, or any other suitable gas or vapor, for example, at a partial pressure of 10 Pa, can be used. In some aspects, an excited tin (Sn) plasma (e.g., via laser excitation) is provided to generate the EUV radiation.

[0055] Radiation emitted by EUV radiation emitting plasma 210 is transferred from source chamber 211 to collector chamber 212 via an optional gas barrier or contaminant trap 230 (also referred to in some cases as a contaminant barrier or fin trap) positioned in or behind an opening in source chamber 211. The contaminant trap 230 can include a channel structure. The contaminant 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, as otherwise referred to herein, includes at least a channel structure.

[0056] The collector chamber 211 may include a radiation collector CO which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the collector CO may be reflected out to be focused at a virtual source point INIF. The virtual source point is often referred to as an intermediate focus INTF, and the source collector apparatus is arranged such that the intermediate focus INTF is located at or near an opening 219 in the enclosure structure 220. The virtual source point INTF is an image of the EUV radiation emitting plasma 210. A grating spectral filter 240 is used, in particular, to suppress infrared (IR) radiation.

[0057] The radiation then traverses the illumination system IL, which may include a faceted field mirror arrangement 222 and a faceted pupil mirror arrangement 224 arranged to provide a desired angular distribution of the radiation beam 221 at the patterning device MA, and a desired uniformity of radiation intensity at the patterning device MA. When the radiation beam 221 is reflected at the patterning device MA, which is 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 a wafer stage or substrate table WT.

[0058] There may typically be more elements than shown in the illumination optics unit IL and projection system PS. A grating spectral filter 240 may optionally be present, depending on the type of lithographic apparatus. Additionally, there may be more than Figure 2 More reflectors, such as those shown in Figure 2 Compared to the situation shown in FIG, there may be one to six additional reflective elements in the projection system PS.

[0059] Collector optics CO (such as Figure 2 As an example only of a collector (or collector mirror), a nested collector is depicted (illustrated in FIG) as having grazing incidence reflectors 253, 254, and 255. The grazing incidence reflectors 253, 254, and 255 are arranged axially symmetrically around the optical axis O, and this type of collector optics CO is preferably used in conjunction with a discharge produced plasma source (often referred to as a DPP source).

[0060] Exemplary Lithography Cell

[0061] Figure 3A lithography cell 300, sometimes also referred to as a lithocell or cluster, is shown according to some aspects. The lithography apparatus 100 or 100' may form part of the lithography cell 300. The lithography cell 300 may also include one or more devices for performing pre-exposure and post-exposure processes on a substrate. Typically, these devices include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH, and a bake plate BK. A substrate transport device or robot RO picks up substrates from input / output ports I / O1 and I / O2, moves them between various process devices, and delivers them to a loading station LB of the lithography apparatus 100 or 100'. These devices are generally referred to as a coating and developing system and are controlled by a coating and developing system control unit TCU, which is itself controlled by a supervisory control system SCS, which in turn controls the lithography apparatus via a lithography control unit LACU. Thus, the various devices can be operated to maximize throughput and processing efficiency.

[0062] Exemplary inspection equipment

[0063] To control the lithography process and accurately place device features on the substrate, alignment marks are typically placed on the substrate, and the lithography apparatus includes one or more inspection devices to accurately position the marks on the substrate. These alignment devices are effectively position measurement devices. Different types of marks and alignment devices and / or systems are known from different times and by different manufacturers. One type of system widely used in current lithography apparatus is based on a self-referencing interferometer, as described in U.S. Patent No. 6,961,116 (den Boef et al.). Typically, the marks are measured separately to obtain the X and Y positions. However, combined X and Y measurements can be performed using the techniques described in U.S. Publication No. 2009 / 195768 A (Bijnen et al.). The entire contents of both patents are incorporated herein by reference.

[0064] Figure 4A A cross-sectional view of an inspection apparatus 400 is shown, according to some aspects. The metrology system 400 can be implemented as part of a lithographic apparatus 100 or 100'. In some aspects, the inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) relative to a patterning device (e.g., patterning device MA). The inspection apparatus 400 can also be configured to detect the positions of alignment marks on the substrate and use the detected positions of the alignment marks to align the substrate relative to the patterning device or other components of the lithographic apparatus 100 or 100'. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0065] The terms "inspection equipment", "measurement system", etc. may be used herein to refer to, for example, a device for measuring properties of a structure (e.g., an overlay sensor, a critical dimension sensor, etc.), or a device used in a lithography device to check the alignment of a wafer (alignment sensor), etc.

[0066] In some aspects, inspection apparatus 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and a computational processor 432. Illumination system 412 may be configured to provide an electromagnetic narrowband radiation beam 413 having one or more passbands. In one example, the one or more passbands may be within a spectrum of wavelengths between approximately 500 nm and approximately 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a spectrum of wavelengths between approximately 500 nm and approximately 900 nm. Illumination system 412 may also be configured to provide one or more passbands having a substantially constant center wavelength (CWL) value over an extended period of time (e.g., over the lifetime of illumination system 412). As discussed above, in current alignment systems, this configuration of illumination system 412 may help prevent actual CWL values from drifting from desired CWL values. And, therefore, using a constant CWL value may improve the long-term stability and accuracy or precision of an alignment system (eg, inspection apparatus 400 ) compared to current alignment apparatuses.

[0067] 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. Figure 4A. The beam splitter 414 can also be configured to direct a radiation sub-beam 415 onto a substrate 420 placed on a platform 422. In one example, the platform 422 can be moved along a direction 424. The radiation sub-beam 415 can be configured to illuminate an alignment mark or target 418 located on the substrate 420. The alignment mark or target 418 can be coated with a radiation-sensitive film. In some aspects, the alignment mark or target 418 can have a one hundred eighty degree (i.e., 180°) symmetry. That is, when the alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to the plane of the alignment mark or target 418, the rotated alignment mark or target 418 can be substantially identical to the unrotated alignment mark or target 418. The target 418 on substrate 420 can be: (a) a resist layer grating comprising bars formed from 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. Such patterns are sensitive to chromatic aberrations and illumination symmetry in the lithographic projection apparatus (particularly the projection system PL), and the presence of such aberrations will manifest themselves as variations in the printed grating. One in-line method for measuring line width, pitch, and critical dimensions in device fabrication utilizes a technique known as scatterometry. Scatterometry methods are described in Raymond et al., "Multiparameter Grating Metrology Using SPIE 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), both of which are incorporated herein by reference in their entirety. In scatterometry, light is reflected by periodic structures in the target, and the reflection spectrum at a given angle is detected. The structure that produced the reflection spectrum is reconstructed, for example, using rigorous coupled wave analysis (RCWA) or by comparison with a library of simulated patterns. Thus, scatterometry data of the printed grating is used to reconstruct the grating. The parameters of the grating, such as line width and line shape, can be input into the reconstruction process, which is performed by the processing unit PU based on knowledge of the printing process and / or other scatterometry processes.

[0068] In some aspects, according to one aspect, the beam splitter 414 can also be configured to receive the diffracted radiation beam 419 and split the diffracted radiation beam 419 into at least two radiation sub-beams. The radiation beam 419 can be split into radiation sub-beams 429 and 439, as shown in FIG. Figure 4AAs shown in .

[0069] It should be noted that even though beam splitter 414 is shown as directing radiation sub-beam 415 toward alignment mark or target 418 and directing diffracted radiation sub-beam 429 toward interferometer 426, the present disclosure is not limited thereto. Other optical arrangements may be used to obtain similar results of illuminating alignment mark or target 418 onto substrate 420 and detecting an image of alignment mark or target 418.

[0070] like Figure 4A , the interferometer 426 can be configured to receive the radiation sub-beam 417 and the diffracted radiation sub-beam 429 via the beam splitter 414. In an exemplary aspect, the diffracted radiation sub-beam 429 can be at least a portion of the radiation sub-beam 415 that can be reflected from the alignment mark or target 418. In examples of this aspect, the interferometer 426 includes any suitable set of optical elements, such as a prism combination, which can be configured to form two images of the alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be understood that good quality images need not be formed. Resolving features of the alignment mark 418 may be sufficient. The interferometer 426 can also be configured to rotate one of the two images by 180° relative to the other of the two images and interferometrically recombine the rotated image and the unrotated image.

[0071] In some aspects, detector 428 can be configured to receive the recombined image via interferometer signal 427 when alignment axis 421 of inspection apparatus 400 passes through the center of symmetry (not shown) of alignment mark or target 418, and detect interference resulting from the recombined image. According to example aspects, this interference may be due to the 180° symmetry of alignment mark or target 418, and according to example embodiments, the recombined image interferes constructively or destructively. Based on the detected interference, detector 428 can also be configured to determine the position of the center of symmetry of alignment mark or target 418 and, therefore, the position of substrate 420. This determination can be made, for example, by an onboard processor of the detector or another processor or computing device (e.g., processor 432). According to an example, alignment axis 421 can be aligned with an optical beam perpendicular to substrate 420 and passing through the center of image rotation interferometer 426. Detector 428 can also be configured to estimate the position of alignment mark or target 418 by implementing sensor characteristics and interacting with wafer marking process variations.

[0072] In further aspects, the detector 428 determines the location of the center of symmetry of the alignment mark or target 418 by performing one or more of the following measurements:

[0073] 1. Measure the position change (position shift between colors) for each wavelength;

[0074] 2. Measuring the positional variation for each order (the positional shift between diffraction orders); and

[0075] 3. Measure the position change for each polarization (the position shift between the polarizations).

[0076] This data can be obtained using any type of alignment sensor, such as: a SMASH (Smart Alignment Sensor Hybrid) sensor, as described in U.S. Patent No. 6,961,116, which uses a self-referencing interferometer with a single detector and four different wavelengths and extracts the alignment signal in software; or Athena (Advanced Technology using High-Order Enhanced Alignment), as described in U.S. Patent No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector, both of which are incorporated herein by reference in their entirety.

[0077] In some aspects, beam analyzer 430 can be configured to receive and determine the optical state of diffracted radiation sub-beam 439. The optical state can be a measure of the beam wavelength, polarization, or beam profile. Beam analyzer 430 can also be configured to determine the position of platform 422 and correlate the position of platform 422 with the position of the center of symmetry of alignment mark or target 418. In this way, the position of alignment mark or target 418 relative to alignment platform 422, and therefore the position of substrate 420 relative to alignment platform 422, can be accurately known. Alternatively, beam analyzer 430 can be configured to determine the position of inspection device 400 or any other reference element, so that the center of symmetry of alignment mark or target 418 can be known relative to inspection device 400 or any other reference element. Beam analyzer 430 can be a point or imaging polarimeter with some form of wavelength band selectivity. In some aspects, according to other aspects, beam analyzer 430 can be directly integrated into inspection device 400 or connected via several types of optical fiber: polarization-maintaining single-mode, multimode, or imaging.

[0078] In some aspects, beam analyzer 430 may also be configured to determine overlay data between two patterns on substrate 420. One of these patterns may be a reference pattern on a reference layer. The other pattern may be an exposure pattern on an exposure layer. The reference layer may be an existing etching layer on substrate 420. The reference layer may be generated by exposing a reference pattern on the substrate using lithography apparatus 100 and / or 100'. The exposure layer may be an exposed resist layer adjacent to the reference layer. The exposure layer may be generated using an exposure pattern on substrate 420 exposed by lithography apparatus 100 or 100'. The exposure pattern on substrate 420 may correspond to movement of substrate 420 caused by stage 422. In some aspects, the measured overlay data may also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data may be used as calibration data to calibrate the exposure pattern exposed by lithography apparatus 100 or 100', such that, after calibration, the offset between the exposure layer and the reference layer is minimized.

[0079] In some aspects, the beam analyzer 430 can also be configured to determine a model of the product stack profile of the substrate 420 and can be configured to measure the overlay, critical dimension, and focus of the target 418 in a single measurement. The product stack profile contains information about the stack product, such as alignment marks, the target 418, or the substrate 420, and can include optical signature measurements caused by marking process variations, which are a function of illumination variations. The product stack profile can also include product raster profile, mark stack profile, and mark asymmetry information. An example of a beam analyzer 430 is the Yieldstar manufactured by ASML of Veldhoven, The Netherlands. TM , as described in U.S. Patent No. 8,706,442, which is incorporated herein by reference in its entirety. The beam analyzer 430 can also be configured to process information related to specific properties of the exposure pattern in the layer. For example, the beam analyzer 430 can process: overlay parameters (indicating the accuracy of positioning of the layer relative to the previous layer on the substrate, or the accuracy of positioning of the first layer relative to a mark on the substrate), focus parameters, and / or critical dimension parameters of the drawn image in the layer (e.g., line width and its variation). Other parameters are image parameters related to the quality of the image of the drawn exposure pattern.

[0080] In some aspects, a detector array (not shown) can be connected to the beam analyzer 430 and allow the possibility of accurate stack profile detection, as discussed below. For example, the detector 428 can be a detector array. For the detector array, there are several options: multimode fiber bundles, discrete PIN detectors per channel, or CCD or CMOS (linear) arrays. For stability reasons, the use of a multimode fiber bundle allows any dissipative elements to be remotely located. Discrete PIN detectors can provide a larger dynamic range, but each requires a separate preamplifier. Therefore, the number of elements is limited. CCD linear arrays provide many elements that can be read at high speed and are particularly noteworthy when phase-stepped detection is used.

[0081] In some aspects, the second beam analyzer 430' can be configured to receive and determine the optical state of the diffracted radiation sub-beam 429, such as Figure 4B . The optical state can be a measure of the 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 functions of beam analyzer 430, such as determining the position of platform 422 and correlating the position of platform 422 with the position of the center of symmetry of alignment mark or target 418. In this way, the position of alignment mark or target 418 relative to alignment platform 422, and therefore the position of substrate 420 relative to alignment platform 422, can be accurately known. Alternatively, beam analyzer 430 can be configured to determine the position of inspection device 400 or any other reference element, so that the center of symmetry of alignment mark or target 418 can be known relative to inspection device 400 or any other reference element. Second beam analyzer 430' can also be configured to determine overlay data between two patterns and a model of the product stack profile of substrate 420. Second beam analyzer 430' can also be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement.

[0082] In some aspects, according to other aspects, second beam analyzer 430' can be directly integrated into inspection device 400, or it can be connected via several types of optical fibers: polarization-maintaining single-mode fiber, multimode fiber, or imaging fiber. Alternatively, second beam analyzer 430' and beam analyzer 430 can be combined to form a single analyzer (not shown) that is configured to receive and determine the optical state of diffracted radiation sub-beams 429 and 439.

[0083] In some aspects, processor 432 receives information from detector 428 and beam analyzer 430. For example, processor 432 may be an overlay calculation processor. The information may include a model of the product stack profile constructed by beam analyzer 430. Alternatively, processor 432 may use the received information about product markings to construct a model of the product marking profile. In either case, processor 432 uses or combines the model of the product marking profile to construct a model of the stacked product and overlay marking profile. The overlay model is then used to determine the overlay offset and minimize spectral effects on the overlay offset measurement. Processor 432 may generate 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, alignment signals, associated position estimates, and optical states in pupil, image, and other planes. The pupil plane is a plane where the radial position of the radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Processor 432 may utilize the basic correction algorithm to characterize the inspection apparatus 400 with reference to wafer marks and / or alignment marks 418.

[0084] In some aspects, the processor 432 can also be configured to determine, for each mark, a printed pattern position offset error relative to the sensor estimate based on information received from the detector 428 and the beam analyzer 430. The information includes, but is not limited to, the product stack profile, overlay, critical dimension, and focus measurements for each alignment mark or target 418 on the substrate 420. The processor 432 can utilize a clustering algorithm to group marks into sets of similar constant offset errors and generate an alignment error offset correction table based on the information.

[0085] In some aspects, the processor 432 may determine a correction for each mark and feed the correction back to the lithographic apparatus 100 or 100 ′, for example, by feeding the correction into the inspection apparatus 400 , for use in correcting errors in alignment / overlay.

[0086] Example Diffraction Order Characterization Using Multimode Fiber

[0087] Trends in the photolithographic fabrication of integrated circuits (ICs) indicate a desire for high accuracy in pattern transfer (e.g., sub-nanometer precision photolithography). Consequently, the chip manufacturing industry is seeking more accurate metrology tools for monitoring the photolithographic process.

[0088] In some respects, similar to Figure 4A and Figure 4BInspection systems such as those in

[0014] can be used to align substrates for accurate layering of different lithographic patterns (e.g., where it is desired to place a new layer on top of an existing layer on a substrate with sub-nanometer accuracy). However, error offsets in the measured positions may arise from defects introduced by the lithographic operation or even imperfections in the optics of the inspection system. Error offsets may be caused, for example, by damage to alignment marks after repeated lithographic layering, asymmetry in the diffraction order pairs used in the measurement (e.g., asymmetric intensities between the +1 and -1 beams of the diffracted radiation sub-beam 429), signal contamination from higher diffraction orders, and the like. Therefore, the inspection system may include one or more devices and methods for determining correction terms to account for the error offsets.

[0089] As previously referenced Figure 4A and Figure 4B As explained, the interference of diffraction order pairs (e.g., +1 and -1) can be used to extract a highly accurate position of an inspection target (e.g., an alignment mark). In some aspects, a correction term can be determined by measuring the asymmetry of the diffraction order pairs (e.g., measuring how much the intensity of the +1 diffraction order differs from the intensity of the -1 diffraction order). To achieve this, a portion of the diffracted radiation 419 can be separated (e.g., using a beam splitter) and routed to a detector, analyzer, and / or processor that can quantify the intensity of each component of the diffraction order pair. Based on the quantized intensities, a correction term can be determined for the measured position of the inspection target. However, if other, unrelated diffraction orders are mixed into the diffracted radiation 419, the resulting correction term may be less accurate.

[0090] Therefore, in some aspects, contributions from extraneous diffraction orders can be taken into account. In a non-limiting example, the extraneous diffraction orders can be blocked. To perform the blocking, inspection apparatus 400 can include a mechatronic device (not shown) located at a pupil plane of inspection apparatus 400 for moving into position to block the undesired diffraction orders. As a non-limiting example, the mechatronic blocking element can be positioned in the path of diffracted radiation beam 419 (other locations can be used). However, such motorized components can be difficult to implement due to mechanical complexity, severe space constraints within inspection apparatus 400, moving parts that risk contaminating the clean lithography environment, high cost, and the like.

[0091] In some aspects, extraneous diffraction orders can be taken into account by quantifying the additional contributing diffraction orders and then subtracting their contributions from the combined signal. One or more aspects of the present disclosure relate to using a two-dimensional array detector and multimode fiber to address the issue of extraneous diffraction orders while avoiding the issues mentioned above when using mechatronic devices.

[0092] Figure 5FIG. 5 shows a portion of an inspection device 500 according to some aspects. In some aspects, the inspection device 500 can implement the inspection device 400 ( Figure 4A and Figure 4B ) describes the capabilities, devices and functions.

[0093] In some aspects, inspection system 500 can include a multimode optical fiber 502, a two-dimensional detector array 504, and an optical structure 506. Optical structure 506 can be an optical objective (eg, including one or more lenses 508). Inspection system 500 can also optionally include an aperture stop 510.

[0094] In some aspects, a radiation source can irradiate a target 512 on a substrate 514 to generate scattered radiation 516. Scattered radiation 516 can include a pair of diffraction orders (e.g., +1 order and -1 order). Scattered radiation 516 can also include a pair of irrelevant diffraction orders (+3 order and -3 order). It will be understood that designating +3 order and -3 order as irrelevant diffraction orders is a non-limiting example. Which diffraction orders are used by a measurement and which diffraction orders are irrelevant can vary depending on the type of information sought for a given measurement. In some aspects, an aperture stop 510 can be used to block the 0th order. Additional irrelevant diffraction orders beyond + / - 3 orders can be used.

[0095] In some aspects, the optical structure 506 can combine pairs of diffraction orders of scattered radiation 516 at the input side of the multimode optical fiber 502. The multimode optical fiber 502 can propagate the illumination from the input side to the output side. The propagation of the illumination within the multimode optical fiber 502 can be characterized according to the propagation properties of the multimode optical fiber 502. A non-limiting example of a propagation property can be a mixing / homogenizing effect due to internal reflections within the core of the optical fiber (other propagation properties, such as dispersion, are also contemplated). To illustrate the mixing / homogenizing effect, Figure 5 , an image of distinguishable diffraction orders 518 is shown. Distinguishable diffraction orders 518 may exist at pupil plane 520 of inspection system 500. The diffraction orders may be mixed / averaged by multimode fiber 502 and then output to two-dimensional detector array 504. The image detected by two-dimensional detector array 504 may be shown as speckle pattern 522. Therefore, it may be impossible or impractical to invert speckle pattern 522 into its diffraction order components using optical hardware. Scattered radiation 516 may be coherent radiation (e.g., from a laser).

[0096] However, in some aspects, the speckle pattern 522 can be deconstructed into its diffraction order components by measuring and quantifying the propagation behavior of the multimode optical fiber 502 and then applying the quantified behavior (a so-called transfer function) to the output of the optical fiber (i.e., the image detected at the two-dimensional detector array 504). The transfer function allows the output of the multimode optical fiber 502 to be mapped to the input of the multimode optical fiber 502.

[0097] In some aspects, the input / output behavior of the multimode optical fiber 502 can be represented by the matrix equation (also called transfer function) characterization, where is the transfer matrix, is a vector describing the radiation at the input of the fiber, and is a vector describing the output speckle pattern 522. In other words, the transfer matrix Acting on input To generate output . Transfer matrix is a function of the material and construction of the multimode optical fiber 502 and may vary based on uncertainties in the preparation of the multimode optical fiber 502. For any given configuration of the multimode optical fiber 502, the transfer matrix may be determined via calibration measurements (e.g., performed at the factory or in the field during an inspection of the system 500). .

[0098] In some aspects, a well-defined image of the target 512 and the modal distribution can be used as input. In a first-order approximation, the scattering properties of the target 512 can be known to a high degree of accuracy (e.g., using a calibrated grating target). The homogenized output of the multimode optical fiber 502 can then be recorded. A computing device (e.g., processor 432) can analyze the input and output to determine the transfer matrix associated with the multimode waveguide 502. The computing device can also perform its analysis based on the known scattering properties of the calibration grating target (e.g., the diffraction angle varies predictably depending on the structure of the target 512). Once the transfer matrix is determined The inspection system 500 can be considered calibrated and can be used to inspect the target. Characterization of the transfer matrix is disclosed in WO 2022 / 012927 A1 published on January 20, 2022, and in L. Amitonova and JF de Boer, "Endo-microscopy beyond the Abbe and Nyquist limits", Light: Science & Applications 9: 81 (2020). , the contents of which are incorporated herein by reference in their entirety. It will be understood that the concept of characterizing the propagation properties of the multimode optical fiber 502 may refer to the matrix equation Quantization, transfer matrix Quantification of elements, etc.

[0099] In some aspects, an algorithm can be programmed to reconstruct or predict the input to multimode fiber 502. Reconstruction of the input need not be limited to generating an image. The reconstructed information can be, for example, a digital representation of the intensity cross-section of the radiation impinging at the input of multimode fiber 502. Due to the focusing properties of optical structure 506, the surface at the input of multimode fiber 502 can be a plane conjugate to pupil plane 520. Therefore, the computing device can also be configured to perform a conjugate-based transform calculation (e.g., a Fourier transform) of the radiation at the output of multimode fiber 502 (e.g., the output detected by two-dimensional detector array 504). The conjugate-based transform calculation can produce reconstructed diffraction orders 524, which can be represented as an image or intensity information (e.g., intensity values at a given location in the pupil plane).

[0100] In some aspects, the distinguishable diffraction orders 518 can be distributed along a line (one dimension). However, the aspects disclosed herein are not limited in this regard. In some aspects, for example, by implementing a two-dimensional diffraction structure for the target 512, the diffraction orders can be distributed along a plane (two dimensions). An example of a two-dimensional diffraction pattern is shown as distinguishable diffraction orders 518′.

[0101] In some aspects, Figure 5 The technique illustrated in FIG. 5 can be used to avoid the need to use mechanical structures to selectively block diffraction orders for distinguishing between them. Multimode fiber 502 and reconstruction algorithms can extract the same intensity information while avoiding the problems associated with mechanized components. As a result, better correction values can be determined for measurements performed by inspection system 500 without complicating the structure of inspection system 500, which has complex mechatronic devices.

[0102] The functionality of the inspection system 500 can be expressed as follows. In some aspects, a radiation source can be configured to illuminate a target 512 to generate scattered radiation 516. The scattered radiation 516 can include a pair of diffraction orders (e.g., a first diffraction beam (+1st order) and a second diffraction beam (-1st order)). The scattered radiation 516 can also include another pair of diffraction orders (e.g., a third diffraction beam (+2nd order, +3rd order, etc.) and a fourth diffraction beam (-2nd order, -3rd order, etc.). The multimode optical fiber can be configured to receive the scattered radiation and output a mixture of the diffraction order pairs based on the propagation properties of the multimode optical fiber 502. The optical structure 506 can be configured to combine the diffraction order pairs at the input side of the multimode optical fiber 502. The two-dimensional detector array 504 can be configured to receive the mixture of the diffraction order pairs and generate a measurement signal corresponding to an image of the mixture of the diffraction order pairs. A computing device (e.g., processor 432 ( FIG. 4 )) can be configured to analyze the measurement signal based on the propagation properties and, based on the analysis, discern the intensities of the first diffraction beam and the second diffraction beam.

[0103] In some aspects, the inspection system 500 can also be configured to determine a value corresponding to a property of the target (e.g., alignment position). The computing device can also be configured to determine a correction to the value based on the identified intensity of the diffraction order pair. The computing device can also be configured to identify the intensity of another diffraction order pair based on analysis of the measurement signal. The computing device can also be configured to perform the correction determination further based on the identified intensity of the other diffraction order pair. The inspection system 500 can be configured to propagate the diffraction order pair through the pupil plane 520 such that a first diffracted beam in the diffraction order pair is disposed at a first position in the pupil plane 520, and a second diffracted beam in the diffraction order pair is located at a second position in the pupil plane 520 that is different from the first position.

[0104] In some aspects, the computing device may also be configured to determine the intensity asymmetry of the first diffraction beam and the second diffraction beam based on an analysis of the measurement signal. The computing device may also be configured to perform a Fourier transform of the data in the measurement signal and determine image information of the diffraction order pairs at the pupil plane 520. The computing device may also be configured to execute an algorithm to perform determination of the intensities of the diffraction order pairs. The algorithm may be configured via machine learning training using a training data set to determine the propagation properties of the multimode optical fiber. More details on the use of machine learning can be found in “Image reconstruction through a multimode fiber with a simple neural network architecture” by Zhu, C. et al., Scientific Reports 11, 896 (2021) and “High-fidelity imaging through multimode fibers via deep learning” by Jun Zhao et al., J. Phys. Photonics 3, 015003 (2021), the contents of which are incorporated herein by reference in their entirety. The inspection system 500 may be implemented as a lithography apparatus (e.g., the lithography apparatus 100 or 100′ ( Figure 1A 、 Figure 1B and Figure 2 ) part.

[0105] In some aspects, enumerable adjectives (e.g., "first," "second," "third," etc.) can be used to distinguish similar elements without establishing an order, hierarchy, quantity, or permanent numerical assignment (unless otherwise specified). For example, the terms "first diffraction beam" and "second diffraction beam" can be used in a manner similar to "i-th diffraction beam" and "j-th diffraction beam" to distinguish two diffraction beams without specifying a particular order, hierarchy, quantity, or immutable numerical correspondence.

[0106] Figure 6 A calibration system 600 is shown for calibrating a multimode optical fiber 602 to be used in an inspection system according to some aspects. In some aspects, the multimode optical fiber 602 can be used as the multimode optical fiber 502 ( Figure 5 ) is incorporated into the inspection system 500. The calibration system 600 can be used to characterize the propagation properties of the multimode optical fiber 602 (eg, determine the transfer function ).

[0107] In some aspects, calibration system 600 may include a radiation source 604, a radiation deflector 606 (e.g., a beam splitter), a telescope and / or filter structure 608, a beam splitter 610, a two-dimensional detector array 612 (e.g., a first camera), a two-dimensional detector array 614 (e.g., a second camera), one or more lenses or objectives 616 (lenses 616-a through 616-d are specifically shown here, but fewer or more lenses may be used), and a target 618. Multimode fiber 602 may be implemented as a series of two or more multimode optical fibers (as a non-limiting example, a series of multimode optical fibers 602-a and 602-b is shown). Each lens 616 may be a single lens or a lens system.

[0108] In some aspects, one or more lenses 616 can be used to focus radiation at multiple locations in the optical path. Lens 616-a can be positioned between the radiation source 604 and the radiation deflector 606. Lens 616-b can be positioned between the radiation deflector 606 and the target 618. Lens 616-c can be positioned between the beam splitter 610 and the multimode optical fiber 602. Lens 616-d can be positioned between the multimode optical fiber 602 and the two-dimensional detector array 614.

[0109] In some aspects, telescope and / or filter structure 608 can be used to optically align numerous optical structures in calibration system 600. The spatial filter portion of filter structure 608 can be used to perform calibration measurements with a portion of the pupil blocked (e.g., at pupil plane 620). Using the spatial filter, characterization measurements can be performed by allowing positive (+) orders to pass while blocking negative (-) orders (and vice versa).

[0110] In some aspects, the target 618 can include a reticle having multiple diffractive structures. Each diffractive structure can generate a different configuration of diffraction order pairs to help characterize the propagation behavior in the multimode optical fiber 602 based on different configurations and arrangements of the diffraction order pairs (e.g., + order blocked, - order blocked, no order blocked, etc.).

[0111] In some aspects, radiation can be sent from a radiation source 604 to a target 618 to generate scattered radiation having a pair of diffraction orders. A beam splitter 610 can split a portion of the scattered radiation and send the split portion to a two-dimensional detector array 612. The radiation detected at the two-dimensional detector array 612 can be used to determine the state of the scattered radiation at the input end 622 of the multimode optical fiber 602. That is, the transfer function can be determined by analyzing the measurement signal generated by the two-dimensional detector array 612. The input part .

[0112] In some aspects, due to the propagation properties of the multimode optical fiber 602, a portion of the scattered radiation launched into the multimode optical fiber 602 may become mixed. The output end 624 of the multimode optical fiber 602 may output mixed diffraction order pairs. The mixed diffraction order pairs may be received at the two-dimensional detector array 614. The radiation detected at the two-dimensional detector array 614 may be used to determine the state of the scattered radiation at the output end 624 of the multimode optical fiber 602. That is, the transfer function may be determined by analyzing the measurement signal generated by the two-dimensional detector array 614. The output part From the measurements performed using the two-dimensional detector arrays 612 and 614, the transfer matrix can be determined (e.g., using a computing device with an algorithm that analyzes the measurement signals from the two-dimensional detector arrays 612 and 614). The process can be repeated until various target structures and diffraction order configurations have been measured to determine the transfer matrix or even optimize the elements of the transfer matrix T by averaging repeated measurements with different parameter variations.

[0113] In some aspects, the algorithm can be a machine learning algorithm (e.g., a deep learning algorithm). The algorithm can be trained using various target structures and diffraction order configurations as a training data set. Once trained, the algorithm can be combined with the inspection system 500 ( Figure 5 ) to execute the algorithm. When inspection system 500 measures target 512 using multimode fiber 602, the computing device can execute the trained algorithm to determine the output from multimode fiber 602 associated with target 518 (as captured by two-dimensional detector array 504). The algorithm can then reconstruct the input of multimode fiber 602 associated with target 518. Furthermore, because two-dimensional detector array 612 can receive pairs of diffraction orders in their distinguishable arrangement (separated diffracted beams), the computing device can be trained to directly reconstruct the intensity distribution of the diffracted beam at pupil plane 620 (e.g., without performing a Fourier transform).

[0114] Figure 7 1 shows a transfer function ( 100 ) for characterizing and using a multimode optical fiber 502 / 602 according to some aspects. Figure 5 and Figure 6 In some aspects, at step S702, a lithography target (eg, target 618 ( Figure 6)) to generate scattered radiation from the lithography target. The scattered radiation may include a first diffracted beam and a second diffracted beam (e.g., a +1 and -1 diffraction order pair). At step S704, the scattered radiation may be split into a first portion and a second portion (e.g., a first portion of the first diffracted beam, a first portion of the second diffracted beam, a second portion of the first diffracted beam, and a second portion of the second diffracted beam).

[0115] In some aspects, at step S706, a first measurement signal may be generated based on the first portion received at the first two-dimensional detector array. At step S708, a first measurement signal may be generated on the multimode optical fiber 602 ( Figure 6 ) receives the second portion at an input side of a multimode optical fiber. The second portion of the first diffracted beam and the second portion of the second diffracted beam may be mixed based on propagation properties of the multimode optical fiber. At step S710, a second measurement signal may be generated based on the mixed second portion received at the second two-dimensional detector array. At step S712, the propagation properties of the multimode optical fiber may be quantified by analyzing the first measurement signal and the second measurement signal to compare the first portion and the mixed second portion.

[0116] In some aspects, one or more operations of method 700 may be iterated using various different diffractive structures, and the multimode optical fiber 602 ( Figure 6 The resulting input and output of the training dataset can be used as a training data set for a machine learning algorithm. The trained algorithm can be used in an inspection device that uses the multimode optical fiber used to generate the training data set.

[0117] Can be executed in any possible order Figure 7 In addition, the method steps described above do not necessarily require execution of all method steps. Figure 7 The method steps of FIG. 1 only reflect examples of these steps and are not restrictive. Figure 6 The described aspects contemplate additional method steps and functions.

[0118] These embodiments can be further described using the following aspects:

[0119] 1. An inspection system comprising:

[0120] a radiation source configured to irradiate a target to generate scattered radiation from the target, wherein the scattered radiation comprises a pair of diffraction orders;

[0121] a multimode optical fiber configured to receive the scattered radiation and output a mixture of the diffraction order pairs based on propagation properties of the multimode optical fiber;

[0122] an optical structure configured to combine the pairs of diffraction orders at an input side of the multimode optical fiber;

[0123] a two-dimensional detector array configured to receive the mixture of the diffraction order pairs and to generate a measurement signal corresponding to the mixture of the diffraction order pairs; and

[0124] A computing device is configured to analyze the measurement signal based on the propagation properties and to identify the intensities of the diffraction order pairs based on the analysis.

[0125] 2. The inspection system according to aspect 1, wherein:

[0126] The inspection system is further configured to determine a value corresponding to a property of the target; and

[0127] The computing device is further configured to determine a correction to the value based on the discerned intensities of the diffraction order pairs.

[0128] 3. The inspection system according to aspect 1, wherein:

[0129] said scattered radiation comprises another pair of diffraction orders; and

[0130] The computing device is further configured to:

[0131] identifying an intensity of the other pair of diffraction orders based on the analyzing; and

[0132] The determining of the correction is performed further based on the discerned intensity of the further pair of diffraction orders.

[0133] 4. An inspection system according to aspect 1, wherein the inspection system is configured to: cause the diffraction order pair to propagate through a pupil plane of the inspection system so that a first diffraction beam in the diffraction order pair is set at a first position at the pupil plane, and a second diffraction beam in the diffraction order pair is located at a second position at the pupil plane that is different from the first position.

[0134] 5. The inspection system of aspect 4, wherein the computing device is further configured to determine an intensity asymmetry of the first diffracted beam and the second diffracted beam based on the analysis.

[0135] 6. The inspection system of aspect 4, wherein the computing device is further configured to perform a Fourier transform on the data in the measurement signal and to determine image information for the diffraction order pair at the pupil plane.

[0136] 7. An inspection system according to aspect 1, wherein the computing device is further configured to execute an algorithm to perform the determination of the intensities of the diffraction order pairs, the algorithm having been configured to determine the propagation properties of the multimode optical fiber via machine learning training using a training data set.

[0137] 8. A lithographic apparatus comprising:

[0138] an illumination system configured to illuminate the patterning device;

[0139] a projection system configured to project an image of the pattern onto a substrate; and

[0140] An inspection system, comprising:

[0141] a radiation source configured to irradiate a target on the substrate to generate scattered radiation from the target, wherein the scattered radiation includes a pair of diffraction orders;

[0142] a multimode optical fiber configured to receive the scattered radiation and output a mixture of the diffraction order pairs based on propagation properties of the multimode optical fiber;

[0143] an optical structure configured to combine the pairs of diffraction orders at an input side of the multimode optical fiber;

[0144] a two-dimensional detector array configured to receive the mixture of the diffraction order pairs and to generate a measurement signal corresponding to the mixture of the diffraction order pairs; and

[0145] A computing device is configured to analyze the measurement signal based on the propagation properties and to identify the intensities of the diffraction order pairs based on the analysis.

[0146] 9. The inspection system according to aspect 1, wherein:

[0147] The inspection system is further configured to determine a value corresponding to a property of the target; and

[0148] The computing device is further configured to determine a correction to the value based on the discerned intensities of the diffraction order pairs.

[0149] 10. The lithographic apparatus of clause 8, wherein:

[0150] said scattered radiation comprises another pair of diffraction orders; and

[0151] The computing device is further configured to:

[0152] discerning an intensity of the other pair of diffraction orders based on the analyzing; and

[0153] The determining of the correction is performed further based on the discerned intensity of the further pair of diffraction orders.

[0154] 11. A lithographic device according to aspect 8, wherein the inspection system is configured to: cause the diffraction order pair to propagate through a pupil plane of the inspection system, so that a first diffraction beam in the diffraction order pair is set at a first position at the pupil plane, and a second diffraction beam in the diffraction order pair is located at a second position at the pupil plane that is different from the first position.

[0155] 12. The lithographic apparatus of clause 11, wherein the computing device is further configured to determine an intensity asymmetry of the first and second diffracted beams based on the analysis.

[0156] 13. The lithographic apparatus of clause 11, wherein the computing device is further configured to perform a Fourier transform on the data in the measurement signal and to determine image information for the diffraction order pair at the pupil plane.

[0157] 14. A lithographic apparatus according to aspect 8, wherein the computing device is further configured to execute an algorithm to perform the determination of the intensities of the diffraction order pairs, the algorithm having been configured to determine the propagation properties of the multimode optical fiber via machine learning training using a training data set.

[0158] 15. A method comprising:

[0159] generating scattered radiation comprising a first diffracted beam and a second diffracted beam by irradiating a lithographic target;

[0160] splitting the scattered radiation to produce a first portion of the first diffracted beam, a first portion of the second diffracted beam, a second portion of the first diffracted beam, and a second portion of the second diffracted beam;

[0161] generating a first measurement signal based on the first portion received at a first two-dimensional detector array;

[0162] receiving the second portion at an input side of a multimode optical fiber to mix the second portion of the first diffracted beam and the second portion of the second diffracted beam based on propagation properties of the multimode optical fiber;

[0163] generating a second measurement signal based on the mixed second portion received at a second two-dimensional detector array; and

[0164] The propagation property of the multimode optical fiber is quantified based on analyzing the first measurement signal and the second measurement signal to compare the first portion and the mixed second portion.

[0165] 16. The method of clause 15, wherein the quantification of the propagation property comprises determining a transfer function corresponding to a relationship between an input and an output of the multimode optical fiber.

[0166] 17. The method of clause 15, wherein the lithography target comprises a plurality of diffraction structures, and the method further comprises generating a plurality of diffraction order pairs corresponding to the plurality of diffraction order structures.

[0167] 18. The method of clause 17, wherein the quantification of the propagation property comprises analyzing the plurality of diffraction order pairs using a machine learning algorithm.

[0168] 19. The method of clause 18, further comprising determining an intensity of each of the first diffracted beam and the second diffracted beam based on the quantification and using the machine learning algorithm.

[0169] 20. The method of clause 18, further comprising generating data for image reconstruction of the first diffraction beam and the second diffraction beam, wherein the first diffraction beam and the second diffraction beam are disposed at different positions in the image reconstruction.

[0170] The terms "radiation," "beam," "light," "irradiation," and the like may be used herein to refer to one or more types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength λ of 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV or soft X-ray) radiation (e.g., having a wavelength in the range of 5 nm to 20 nm, such as, for example, 13.5 nm), or hard X-rays operating at less than 5 nm, and particle beams (such as ion beams or electron beams). Generally, radiation having wavelengths between about 400 nm and about 700 nm is considered visible radiation; radiation having wavelengths between about 780 nm and 3000 nm (or greater) is considered IR radiation. UV refers to radiation having wavelengths between about 100 nm and 400 nm. In photolithography, the term "UV" also applies to the following wavelengths, which can be produced by mercury discharge lamps: G-line 436 nm; H-line 405 nm; and / or I-line 365 nm. Vacuum UV or VUV (i.e., UV absorbed by gases) refers to radiation having a wavelength of approximately 100 nm to 200 nm. Deep UV (DUV) generally refers to radiation having a wavelength ranging from 126 nm to 428 nm, and in some aspects, excimer lasers can generate DUV radiation for use within lithographic equipment. Radiation having a wavelength in the range of, for example, 5 nm to 20 nm should be understood to refer to radiation having a wavelength band at least partially within the range of 5 nm to 20 nm.

[0171] While some aspects of the present disclosure are described in the context of lithographic apparatus used in IC manufacturing, it should be understood that the lithographic apparatus described herein can be used in other applications, such as fabricating integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal displays (LCDs), thin-film magnetic heads, and the like. 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 specific examples of the more general terms "substrate" or "target portion," respectively. The substrate can be processed before or after exposure, for example, in a coater / developer unit (a tool that typically applies a resist layer to the 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, to produce a multi-layer IC, so that the term substrate as used herein can also refer to a substrate that already contains multiple processed layers.

[0172] Furthermore, while 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, the topography in a patterning device defines the pattern produced on a substrate. The topography of the patterning device can be imprinted into a resist layer supplied to the substrate, whereupon the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist, leaving a pattern therein.

[0173] It will be understood that the phraseology or terminology herein is for the purpose of description and not limitation, so that the phraseology or terminology in this specification will be interpreted by those skilled in the relevant art in accordance with the teachings herein.

[0174] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation methods of the specified functions and their mutual relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined in this article. As long as the specified functions and their relationships are properly performed, alternative boundaries can be defined. The foregoing description of specific aspects will fully reveal the general nature of the present disclosure so that others can easily modify and / or adapt to various applications of these specific aspects by applying knowledge within the scope of the art without departing from the overall concept of the present disclosure and without excessive experimentation. Therefore, based on the teachings and guidance proposed herein, such adaptations and modifications are intended to fall within the meaning and scope of equivalents of the disclosed aspects.

[0175] It will be understood that the Detailed Description section, rather than the Summary and Abstract sections, is intended to be used to interpret the claims. As contemplated by the inventors, the Summary and Abstract sections may illustrate one or more, but not necessarily all, aspects of the present disclosure, and therefore 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 aspects described above, but rather by the appended claims and their equivalents.

Claims

1. An inspection system comprising: a radiation source configured to irradiate a target to generate scattered radiation from the target, wherein the scattered radiation comprises a pair of diffraction orders; a multimode optical fiber configured to receive the scattered radiation and output a mixture of the diffraction order pairs based on propagation properties of the multimode optical fiber; an optical structure configured to combine the pairs of diffraction orders at an input side of the multimode optical fiber; a two-dimensional detector array configured to receive the mixture of the diffraction order pairs and to generate a measurement signal corresponding to the mixture of the diffraction order pairs; as well as A computing device is configured to analyze the measurement signal based on the propagation properties and to discern the intensities of the diffraction order pairs based on the analysis.

2. The inspection system according to claim 1, wherein: The inspection system is further configured to determine a value corresponding to a property of the target; and The computing device is further configured to determine a correction to the value based on the discerned intensities of the diffraction order pairs.

3. The inspection system according to claim 1, wherein: said scattered radiation comprises another pair of diffraction orders; and The computing device is further configured to: discerning an intensity of the other pair of diffraction orders based on the analyzing; and The determining of the correction is performed further based on the discerned intensity of the further pair of diffraction orders.

4. The inspection system according to claim 1, wherein: The inspection system is configured to propagate the diffraction order pair through a pupil plane of the inspection system such that a first diffraction beam in the diffraction order pair is disposed at a first position at the pupil plane and a second diffraction beam in the diffraction order pair is located at a second position at the pupil plane that is different from the first position.

5. The inspection system according to claim 4, wherein: The computing device is further configured to determine an intensity asymmetry of the first and second diffracted beams based on the analysis.

6. The inspection system according to claim 4, wherein: The computing device is further configured to perform a Fourier transform of the data in the measurement signal and to determine image information of the diffraction order pair at the pupil plane.

7. The inspection system according to claim 1, wherein: The computing device is further configured to execute an algorithm to perform the determination of the intensities of the diffraction order pairs, the algorithm having been configured to determine the propagation properties of the multimode optical fiber via machine learning training using a training data set.

8. A lithographic apparatus comprising: an illumination system configured to illuminate the patterning device; a projection system configured to project an image of the pattern onto a substrate; as well as An inspection system, comprising: a radiation source configured to irradiate a target on the substrate to generate scattered radiation from the target, wherein the scattered radiation includes a pair of diffraction orders; a multimode optical fiber configured to receive the scattered radiation and output a mixture of the diffraction order pairs based on propagation properties of the multimode optical fiber; an optical structure configured to combine the pairs of diffraction orders at an input side of the multimode optical fiber; a two-dimensional detector array configured to receive the mixture of the diffraction order pairs and to generate a measurement signal corresponding to the mixture of the diffraction order pairs; and A computing device is configured to analyze the measurement signal based on the propagation properties and to identify the intensities of the diffraction order pairs based on the analysis.

9. The inspection system of claim 1 , wherein: The inspection system is further configured to determine a value corresponding to a property of the target; and The computing device is further configured to determine a correction to the value based on the discerned intensities of the diffraction order pairs.

10. The lithographic apparatus according to claim 8, wherein: said scattered radiation comprises another pair of diffraction orders; and The computing device is further configured to: discerning an intensity of the other pair of diffraction orders based on the analyzing; and The determining of the correction is performed further based on the discerned intensity of the further pair of diffraction orders.

11. The lithographic apparatus according to claim 8, wherein The inspection system is configured to propagate the diffraction order pair through a pupil plane of the inspection system such that a first diffraction beam in the diffraction order pair is disposed at a first position at the pupil plane and a second diffraction beam in the diffraction order pair is located at a second position at the pupil plane that is different from the first position.

12. The lithographic apparatus according to claim 11, wherein The computing device is further configured to determine an intensity asymmetry of the first and second diffracted beams based on the analysis.

13. The lithographic apparatus according to claim 11, wherein: The computing device is further configured to perform a Fourier transform of the data in the measurement signal and to determine image information of the diffraction order pair at the pupil plane.

14. The lithographic apparatus according to claim 8, wherein: The computing device is further configured to execute an algorithm to perform the determination of the intensities of the diffraction order pairs, the algorithm having been configured to determine the propagation properties of the multimode optical fiber via machine learning training using a training data set.

15. A method comprising: generating scattered radiation comprising a first diffracted beam and a second diffracted beam by irradiating a lithographic target; splitting the scattered radiation to produce a first portion of the first diffracted beam, a first portion of the second diffracted beam, a second portion of the first diffracted beam, and a second portion of the second diffracted beam; generating a first measurement signal based on the first portion received at a first two-dimensional detector array; receiving the second portion at an input side of a multimode optical fiber to mix the second portion of the first diffracted beam and the second portion of the second diffracted beam based on propagation properties of the multimode optical fiber; generating a second measurement signal based on the mixed second portion received at a second two-dimensional detector array; as well as The propagation property of the multimode optical fiber is quantified based on analyzing the first measurement signal and the second measurement signal to compare the first portion and the mixed second portion.

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