Metrology method and apparatus for measuring periodic structures on a substrate

Abstract

A method of measuring a periodic structure on a substrate with an illuminating radiation having at least one wavelength, the periodic structure having at least one pitch, is disclosed. The method comprises configuring one or more of: an illumination aperture profile comprising one or more illumination regions in Fourier space, an orientation of the periodic structure for measurement, and a detection aperture profile comprising one or more separate detection regions in Fourier space, based on a ratio of the pitch to the wavelength. This configuration is such that: i) diffracted radiation of at least one pair of complementary diffraction orders is captured within the detection aperture profile, and ii) the diffracted radiation fills at least 80% of the one or more separate detection regions. The periodic structure is measured while applying the configured one or more of the illumination aperture profile, the detection aperture profile, and the orientation of the periodic structure.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims priority to European application 20154343.6 filed on January 29, 2020 and European application 20161488.0 filed on March 06, 2020 and European application 20186831.2 filed on July 21, 2020, the contents of which are incorporated by reference and as if fully set forth herein. TECHNICAL FIELD

[0003] The present invention relates to a metrology method and apparatus for determining a characteristic of a structure on a substrate. BACKGROUND

[0004] A lithography apparatus is a machine constructed to apply a desired pattern onto a substrate. The lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). The lithography apparatus can, for example, project a pattern (which can also be referred to as a “design layout” or “design”) at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).

[0005] To project a pattern on a substrate, a lithography apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. Typical wavelengths currently in use are 365 nm (g-line), 248 nm, 193 nm and 13.5 nm. Lithography apparatuses using extreme ultraviolet (EUV) radiation, having a wavelength within a range of 4-20 nm, for example 6.7 nm or 13.5 nm, can be used to form smaller features on a substrate than those formed using, for example, a lithography apparatus that uses radiation with a wavelength of 193 nm.

[0006] Low-ki lithography can be used to process features with dimensions smaller than the classical resolution limit of a lithographic apparatus, which is determined by the equation: CD = kixA / NA, where λ is the wavelength of radiation used by the lithographic apparatus, NA is the numerical aperture of the projection optics in the lithographic apparatus, CD is a "critical dimension" (generally, the smallest feature size that is typically a photoresist pattern after image development, but in this case a half pitch) and ki is an empirical resolution factor. In general, the smaller ki the more difficult it becomes to reproduce the shape and dimensions planned by a circuit designer in the substrate. To overcome these difficulties, sophisticated fine-tuning steps can be applied to the lithographic projection apparatus and / or the design layout. These include, for example, but not limited to, optimization of NA, customized illumination schemes, use of phase- shift patterning devices, various optimization of the design layout such as optical proximity correction (OPC, sometimes also referred to as "optical and process correction") in the design layout, or other methods generally defined as "resolution enhancement techniques" (RET). Alternatively, tight control loops of the stability of the lithographic apparatus can be used to improve the reproduction of patterns at low ki.

[0007] In lithographic processes, it will generally be desired to make measurements of the fabricated structure, for example to monitor and control the lithographic process. Various tools are known for making such measurements, including scanning electron microscopes or various forms of metrology apparatus, such as scatterometers. A general term that can be used to refer to such tools is metrology apparatus or inspection apparatus.

[0008] Metrology apparatus can apply computationally acquired aberration corrections to images captured by the metrology apparatus. Descriptions of such metrology apparatus refer to the use of coherent illumination and the acquisition of the phase of the field relating to the image as a basis for computationally performed correction methods. Coherent imaging has several challenges and it would therefore be desirable to use incoherent radiation (spatially) in such apparatus. SUMMARY

[0009] Embodiments of the application are disclosed in the claims and in the specific description.

[0010] In a first aspect of the application, there is provided a method of measuring a periodic structure on a substrate with illumination radiation having at least one wavelength, the periodic structure having at least one pitch, the method comprising: configuring one or more of an illumination aperture profile comprising one or more illumination regions in Fourier space, an orientation of the periodic structure for measurement, and a detection aperture profile comprising one or more separate detection regions in Fourier space, based on a ratio of the pitch to the wavelength; such that: i) at least one pair of complementary diffraction orders is captured within the detection aperture profile, and ii) the diffraction radiation fills at least 80% of the one or more separate detection regions; and measuring the periodic structure while applying the configured one or more of the illumination aperture profile, the detection aperture profile, and the orientation of the periodic structure.

[0011] In a second aspect of the application, there is provided a metrology apparatus for measuring a periodic structure on a substrate, the metrology apparatus comprising: a detection aperture profile comprising one or more separate detection regions in Fourier space; and an illumination aperture profile comprising one or more illumination regions in Fourier space; wherein one or more of the detection aperture profile, the illumination aperture profile, and a substrate orientation of a substrate comprising the periodic structure being measured, can be configured based on a ratio of at least one pitch of the periodic structure to at least one wavelength of illumination radiation used to measure the periodic structure, such that: i) at least one pair of complementary diffraction orders is captured within the detection aperture profile, and ii) radiation of the pair of complementary diffraction orders fills at least 80% of the one or more separate detection regions.

[0012] In another aspect, there is provided a metrology apparatus for measuring a periodic structure on a substrate and having at least one periodic pitch with illumination radiation having at least one wavelength, the metrology apparatus comprising: an illumination aperture profile; and a configurable detection aperture profile and / or substrate orientation, configurable for measurement based on the illumination aperture profile and a ratio of the pitch to the wavelength, such that at least one pair of complementary diffraction orders is captured within the detection aperture profile.

[0013] In another aspect, there is provided a metrology apparatus for measuring a periodic structure on a substrate and having at least one periodic pitch with illumination radiation having at least one wavelength, the metrology apparatus comprising: a substrate support for holding the substrate, the substrate support being rotatable about an optical axis thereof, the metrology apparatus being operable to optimize an illumination aperture profile by rotating the substrate about the optical axis in accordance with the ratio of pitch to wavelength. BRIEF DESCRIPTION OF DRAWINGS

[0014] Embodiments of the invention will now be described by way of example only, with reference to the accompanying illustrative drawings, in which:

[0015] - Figure 1 A schematic schematic diagram depicting a photolithography apparatus;

[0016] - Figure 2 A schematic schematic diagram depicting a photolithography unit;

[0017] - Figure 3 A schematic diagram depicting overall photolithography, illustrating the collaboration between three key technologies used to optimize semiconductor manufacturing;

[0018] - Figure 4 This is a schematic diagram of a scattering measurement device;

[0019] - Figure 5 Includes: (a) a schematic diagram of a dark-field scattering instrument for measuring a target using a first pair of irradiation apertures according to an embodiment of the invention; (b) details of the diffraction spectrum of a target grating for a given irradiation direction; (c) a second pair of irradiation apertures for providing other irradiation modes when using the scattering instrument for diffraction-based overlap (DBO) measurements; and (d) a third pair of irradiation apertures combining the first pair of apertures with the second pair of apertures.

[0020] - Figure 6 A schematic diagram including a measuring device for measuring a target according to an embodiment of the present invention;

[0021] - Figure 7 The figures show: (a) the outlines of the first illumination pupil and the detection pupil according to the first embodiment; (b) the outlines of the second illumination pupil and the detection pupil according to the second embodiment; and (c) the outlines of the third illumination pupil and the detection pupil according to the third embodiment.

[0022] - Figure 8 The illustration shows the contours of the illumination pupil and the detection pupil for two arrangements according to embodiments of the present invention, namely: (a) an arrangement without wafer rotation; and (b) an arrangement with wafer rotation having six consecutive λ / P ratios.

[0023] - Figure 9 This is a schematic illustration of an arrangement for obtaining illumination profiles for X and Y targets using different illumination conditions, according to an embodiment.

[0024] - Figure 10 (a) to Figure 10 (c) The illustration shows three proposed irradiation arrangements for implementing these overfilled detection NAs;

[0025] - Figure 11 The diagram illustrates an 8-part wedge design for individually imaging each captured diffraction order;

[0026] - Figure 12 Figure 8 shows another embodiment of the wedge design;

[0027] - Figure 13 The illustration shows specific irradiation NAs and detection NAs that can be used in embodiments of the present invention;

[0028] - Figure 14 The illustration shows another specific irradiation NA and detection NA that can be used in embodiments of the present invention;

[0029] - Figure 15 This is a schematic diagram of the arrangement for configuring both the irradiation and detection NA according to the first embodiment;

[0030] - Figure 16 It can be used as a substitute Figure 15 A schematic representation of the optical elements of a light wedge;

[0031] - Figure 17 It can be used as a substitute Figure 15 A schematic diagram of another optical element of the optical wedge;

[0032] - Figure 18 This is a schematic diagram of the arrangement for configuring both the irradiation and detection NA according to the second embodiment;

[0033] - Figure 19 This is a schematic diagram of the arrangement for configuring both the irradiation and detection NA according to the third embodiment; and

[0034] - Figure 20 A block diagram depicting a computer system used to control the systems and / or methods disclosed herein. Detailed Implementation

[0035] In this document, the terms “radiation” and “beam” are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having wavelengths in the range of about 5 nm to 100 nm).

[0036] As used herein, the terms “mask,” “mask,” or “patterning apparatus” can be broadly interpreted to refer to a general patterning apparatus that can be used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to a pattern to be generated in a target portion of a substrate. In such contexts, the term “optical valve” may also be used. Examples of other such patterning apparatuses besides classical masks (transmission or reflection, binary, phase-shift, hybrid, etc.) include programmable mirror arrays and programmable LCD arrays.

[0037] Figure 1 A lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also referred to as an irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a mask support (e.g., a mask stage) MT configured to support a patterning apparatus (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning apparatus MA according to certain parameters; a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the patterning apparatus MA to the radiation beam B onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0038] In operation, the irradiation system IL receives a radiation beam from the radiation source SO, for example, via a beam delivery system BD. The irradiation system IL may include various types of optical components for guiding, shaping, and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof. The irradiator IL can be used to adjust the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the pattern forming apparatus MA.

[0039] The term “projection system” PS as used herein should be broadly interpreted to encompass various types of projection systems suitable for the exposure radiation used and / or for other factors such as immersion in liquids or vacuum, including refractive, reflective, reflective-refractive, distorting, magnetic, electromagnetic, and / or electrostatic optical systems or any combination thereof. Any use of the term “projection lens” herein may be considered synonymous with the more general term “projection system” PS.

[0040] Photolithography equipment (LA) can fall into the category of systems in which at least a portion of the substrate can be covered by a liquid (e.g., water) having a relatively high refractive index to fill the space between the projection system (PS) and the substrate (W) – this is also known as immersion lithography. Further information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0041] Photolithography equipment (LA) can also be of the type with two or more substrate supports (WT) (also known as "dual platforms"). In such a "multi-platform" machine, substrate supports (WT) can be used in parallel, and / or a subsequent exposure step for preparing substrate W on one substrate support (WT) can be performed, while another substrate W on another substrate support (WT) is used to expose a pattern on the other substrate W.

[0042] In addition to the substrate support WT, the lithography apparatus LA may also include a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning devices. Sensors may be arranged to measure the properties of the projection system PS or the radiation beam B. The measurement platform holds multiple sensors. Cleaning devices may be arranged to clean parts of the lithography apparatus, such as parts of the projection system PS or parts of the system providing immersion liquid. The measurement platform can move below the projection system PS as the substrate support WT moves away from the projection system PS.

[0043] In operation, a radiation beam B is incident on a pattern forming apparatus (e.g., a mask) MA held on a mask support MT and patterned by a pattern (design layout) present on the pattern forming apparatus MA. Having traversed the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example, to position different target portions C in the path of the radiation beam B at a focused and aligned location. Similarly, a first positioner PM and possibly another position sensor (which is not in...) Figure 1 The pattern forming apparatus MA (as clearly depicted) can be used to accurately position itself relative to the path of the radiation beam B. The pattern forming apparatus MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2, as illustrated, occupy dedicated target portions, the marks can be located in the space between the target portions. When the substrate alignment marks P1, P2 are located between the target portions C, these substrate alignment marks are called scribing alignment marks.

[0044] like Figure 2As shown, the lithography apparatus LA can form part of a lithography unit LC (sometimes also referred to as a lithography cell or lithography cluster), which typically also includes equipment for performing pre-exposure and post-exposure processes on the substrate W. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chiller CH for regulating the temperature of the substrate W (e.g., for regulating the solvent in the resist layer), and a baking plate BK. A substrate transport device or robot RO picks up the substrate W from input / output ports I / O1, I / O2, moves the substrate W between different process units, and transfers the substrate W to the feed stage LB of the lithography apparatus LA. The devices in the lithography unit, generally referred to as the track or coating / developing system, are typically under the control of a track or coating / developing system control unit TCU, which itself can be controlled by a management control system SCS, which can also control the lithography apparatus LA, for example, via a lithography control unit LACU.

[0045] To ensure correct and consistent exposure of the substrate W exposed by the lithography unit LA, it is desirable to inspect the substrate to measure properties of the patterned structure, such as overlap error between subsequent layers, line thickness, critical dimension (CD), etc. For this purpose, inspection tools (not shown) can be included in the lithography unit LC. If errors are detected, adjustments can be made, for example, to the exposure of subsequent substrates or other processing steps to be performed on the substrate W, especially when inspection is performed before other substrates W in the same batch or leg are exposed or processed.

[0046] An inspection device, also known as a metrology device, is used to determine the properties of a substrate W, and specifically, to determine how the properties of different substrates W vary or how the properties associated with different layers of the same substrate W vary between layers. The inspection device is alternatively configured to identify defects on the substrate W and may be, for example, part of a photolithography unit LC, or may be integrated into a photolithography apparatus LA, or may even be a standalone device. The inspection device can measure the properties of a latent image (an image in a resist layer after exposure), or a semi-latent image (an image in a resist layer after a post-exposure baking step PEB), or the properties of a developed resist image (where the exposed or unexposed portions of the resist have been removed), or even the properties of an etched image (after a pattern transfer step such as etching).

[0047] Typically, the patterning process in photolithography (LA) equipment is one of the most critical steps in the process, requiring high accuracy in the dimensional calibration and placement of the structures on the substrate W. To ensure this high accuracy, three systems can be combined in a so-called "holistic" control environment, such as... Figure 3The diagram illustrates this schematically. One of these systems is a lithography apparatus LA, which is (in fact) connected to a metrology tool MT (the second system) and a computer system CL (the third system). The key to this “holistic” environment is optimizing the collaboration between these three systems to enhance the overall process window and provide a tight control loop, thereby ensuring that the patterning performed by the lithography apparatus LA remains within the process window. The process window defines a range of process parameters (e.g., dose, focal length, overlap) within which a specific manufacturing process yields a defined result (e.g., a functional semiconductor device)—typically, within this range, process parameters during the lithography or patterning process are allowed to vary.

[0048] The computer system CL can use the design layout (partial) to be patterned to predict which resolution enhancement technique to use and perform computational lithography simulations and calculations to determine which mask layout and lithography equipment settings will enable the patterning process within the maximum overall process window (in). Figure 3 (Depicted by double arrows in the first scale SC1). Typically, resolution enhancement techniques are arranged to match the patterning possibilities of the lithography equipment LA. The computer system CL can also be used to detect where the lithography equipment LA is currently operating within the process window (e.g., using input from the metrology tool MT) in order to predict whether defects may exist due to, for example, suboptimal processing (in...). Figure 3 (This is depicted by the arrow pointing to "0" in the second ruler SC2).

[0049] The measurement tool MET can provide input to the computer system CL for accurate simulation and prediction, and can provide feedback to the lithography equipment LA to identify possible drifts in, for example, the calibration status of the lithography equipment LA. Figure 3 (The middle part is depicted by multiple arrows in the third ruler SC3).

[0050] During photolithography, it is desirable to frequently measure the created structure, for example, for process control and verification. Various tools for performing such measurements are well-known, including scanning electron microscopes or various forms of metrology equipment (such as scatterometers). Examples of known scatterometers often rely on the provision of a dedicated measurement target, such as an underfilled target (in the form of a simple grating or a stacked grating in different layers, large enough that the measurement beam produces a spot smaller than the grating) or an overfilled target (thus illuminating a spot that partially or completely contains the target). Furthermore, metrology tools using angle-resolved scatterometers, for example, illuminating an underfilled target (such as a grating), allow for the use of so-called reconstruction methods, where the properties of the grating can be calculated by simulating the interaction of scattered radiation with a mathematical model of the target structure and comparing the simulation results with the measured results. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0051] A scatterometer is a multifunctional instrument that allows for the measurement of parameters of a photolithography process by means of a sensor located in the pupil or a plane conjugate to the pupil of the scatterometer's objective lens; such measurements are typically referred to as pupil-based measurements. Alternatively, parameters can be measured by means of a sensor located in the image plane or a plane conjugate to the image plane; in this case, the measurements are typically referred to as image- or field-based measurements. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, which are incorporated herein by reference in their entirety. The aforementioned scatterometers can measure multiple targets from multiple gratings within a single image using light from soft X-rays and the visible to near-IR wavelength range.

[0052] exist Figure 4 The image depicts a measurement device such as a scattering instrument. It includes a broadband (white light) radiation projector 2 that projects radiation 5 onto a substrate W. Reflected or scattered radiation 10 is transmitted to a spectrometer detector 4, which measures the spectrum 6 of the specularly reflected radiation 10 (i.e., the intensity I as a function of wavelength λ). Based on this data, the structure or profile 8 of the detected spectrum can be reconstructed by a processing unit PU, for example, through rigorous coupled-wave analysis and nonlinear regression or by comparison with a simulated spectral library. Typically, for reconstruction, the general form of the structure is known, and some parameters are assumed based on knowledge of the process used to manufacture the structure, leaving only a few parameters of the structure to be determined from the scattering measurement data. Such a scattering instrument can be configured as a normal-incident scattering instrument or an oblique-incident scattering instrument.

[0053] In the first embodiment, the scatterer MT is an angle-resolved scatterer. In such a scatterer, a reconstruction method can be applied to the measured signal to reconstruct or calculate the properties of the grating. This reconstruction can, for example, be caused by simulating the interaction between the scattered radiation and the target structure using a mathematical model and comparing the simulation results with the measured results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0054] In the second embodiment, the scatterer MT is a spectroscopic scatterer MT. In such a spectroscopic scatterer MT, radiation emitted by a radiation source is directed to the target, and reflected or scattered radiation from the target is directed to a spectroscopic detector, which measures the spectrum of the specularly reflected radiation (i.e., a measurement of intensity as a function of wavelength). Based on this data, the structure or profile of the target that generated the detected spectrum can be reconstructed, for example, by rigorous coupled-wave analysis and nonlinear regression or by comparison with a simulated spectral library.

[0055] In the third embodiment, the scatterer MT is an elliptic measurement scatterer. An elliptic measurement scatterer allows the determination of parameters of the photolithography process by measuring the scattered radiation for each polarization state. Such a metrology device emits polarized light (such as linear, annular, or elliptical) by using, for example, a suitable polarization filter in the illumination section of the metrology device. A source suitable for the metrology device can also provide polarized radiation. Various embodiments of existing elliptic measurement scatterers are described in U.S. patent applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110, and 13 / 891,410, which are incorporated herein by reference in their entirety.

[0056] In one embodiment of a scattering instrument (MT), the scattering instrument MT is adapted to measure the overlap of two misaligned gratings or periodic structures by measuring the reflectance spectrum and / or detecting an asymmetry in the configuration (the asymmetry relating to the extent of overlap). Two (typically stacked) grating structures can be applied to two different layers (not necessarily consecutive layers) and can be formed at substantially the same location on a wafer. The scattering instrument can have a symmetrical detection configuration, such as described, for example, in the commonly owned patent application EP1,628,164A, so that any asymmetry can be clearly identified. This provides a direct method for measuring misalignment in gratings. Further examples of measuring overlap error between two layers containing a periodic structure as a target via the asymmetry of said periodic structure can be found in PCT patent application publication number WO2011 / 012624 or U.S. patent application number US 20160161863, which are incorporated herein by reference in their entirety.

[0057] Other parameters of interest may be focal length and dose. Focal length and dose can be determined simultaneously by scattering measurements (or alternatively by scanning electron microscopy) as described in U.S. patent application US2011-0249244, which is incorporated herein by reference in its entirety. A single structure with a unique combination of critical dimensions and sidewall angle measurements for each point in the focal length energy matrix (FEM—also known as the focal length exposure matrix) can be used. If these unique combinations of critical dimensions and sidewall angles are available, the focal length and dose can be uniquely determined based on these measurements.

[0058] The measurement target can be the entirety of a composite grating formed primarily in a resist during a photolithography process and also, for example, after an etching process. Typically, the spacing and linewidth of the structures within the grating are highly dependent on the measurement optics (especially the NA of the optics) to capture the diffraction order from the measurement target. As previously indicated, the diffraction signal can be used to determine the shift (also known as “overlap”) between two layers or to reconstruct at least a portion of the original grating, such as that produced by the photolithography process. This reconstruction can provide quality guidance for the photolithography process and can be used to control at least a portion of the photolithography process. The target can have smaller subsegments configured to mimic the dimensions of functional portions of a design layout within the target. Due to these subsegments, the target will behave more similarly to the functional portions of the design layout, making the overall process parameter measurements preferably similar to the functional portions of the design layout. The target can be measured in underfill or overfill modes. In underfill mode, the measurement beam produces a spot smaller than the overall target. In overfill mode, the measurement beam produces a spot larger than the overall target. In such an overfill mode, different targets may also be measured simultaneously, thus determining different processing parameters simultaneously.

[0059] The overall measurement quality of lithography parameters performed for a specific target is determined at least in part by the measurement scheme used to measure such lithography parameters. The term "substrate measurement scheme" can include measuring one or more parameters of itself, one or more parameters of one or more patterns being measured, or both. For example, if the measurement used in the substrate measurement scheme is a diffraction-based optical measurement, one or more of the measured parameters can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. One of the criteria for selecting a measurement scheme can be, for example, the sensitivity of one of the measurement parameters to handling variations. Further examples are described in U.S. Patent Application US2016-0161863, which is incorporated herein by reference in its entirety, and in published U.S. Patent Application US2016 / 0370717A1.

[0060] Figure 5 (a) An embodiment of the measurement device, and more specifically a dark field scattering instrument. Figure 5 (b) illustrates the target T and the diffracted rays of the measurement radiation used to illuminate the target in more detail. The illustrated measurement device belongs to the type known as a dark-field measurement device. The measurement device can be a standalone device or incorporated into a lithography device LA or lithography unit LC at a measurement station, for example. The optical axis having several branches throughout the device is indicated by the dotted line O. In such a device, light emitted by source 11 (e.g., a xenon lamp) is guided onto the substrate W by an optical system including lenses 12, 14 and objective lens 16 via beam splitter 15. These lenses are arranged in a double sequence arranged in 4F. Different lens arrangements can be used, provided that the lens arrangements still provide an image of the substrate to the detector and simultaneously allow access to the intermediate pupil plane for spatial frequency filtering. Thus, the range of angles at which radiation is incident on the substrate can be selected by defining the spatial intensity distribution in a plane that presents the spatial spectrum of the substrate plane (here referred to as the (conjugate) pupil plane). Specifically, this selection can be made by inserting a suitable aperture plate 13 between lenses 12 and 14 in the plane of the back-projected image of the objective lens pupil plane. In the illustrated example, the aperture plate 13 has different forms (labeled 13N and 13S), thus allowing for the selection of different illumination modes. The illumination system in this example forms an off-axis illumination mode. In the first illumination mode, aperture plate 13N provides off-axis illumination from a direction designated "north" for descriptive purposes only. In the second illumination mode, aperture plate 13S is used to provide similar illumination, but from the opposite direction, labeled "south". Other illumination modes are possible by using different apertures. The remainder of the pupil plane is desiccated because any unwanted light outside the desired illumination mode would interfere with the desired measurement signal.

[0061] like Figure 5As shown in (b), the target T is positioned with the substrate W perpendicular to the optical axis O of the objective lens 16. The substrate W can be supported by a support (not shown). The ray I of the measurement radiation, irradiated at an angle to axis O onto the target structure T, produces a zero-order ray (solid line 0) and two first-order rays (dotted line +1 and double-dotted line -1). It should be remembered that, in the case of using an overfilled small target, these rays are merely one of many parallel rays covering the substrate area including the measurement target T and other features. Due to the limited width of the aperture in plate 13 (necessary for receiving a useful amount of light), the incident ray I will actually occupy an angular range, and the diffracted rays 0 and +1 / -1 will be slightly dispersed. Depending on the point spread function of the small target, each order +1 and -1 will be further dispersed over the angular range, rather than a single ideal ray as shown. It should be noted that the grating spacing and illumination angle of the target structure can be designed or adjusted so that the first-order ray entering the objective lens is closely aligned with the central optical axis. Figure 5 (a) and Figure 3 The rays illustrated in (b) are shown slightly off-axis so that they can be distinguished more easily in the figure.

[0062] At least one of the first orders of diffraction from the target T on the substrate W is collected by objective lens 16 and returned and guided through beam splitter 15. Return to Figure 5 (a) The first and second illumination modes are illustrated by indicating completely opposite apertures labeled North (N) and South (S). When the incident ray I for measuring radiation comes from the north side of the optical axis, i.e., when the first illumination mode is applied using aperture plate 13N, the +1 diffraction ray, labeled +1 (N), enters the objective lens 16. In contrast, when the second illumination mode is applied using aperture plate 13S, the -1 diffraction ray (labeled -1 (S)) is the diffraction ray entering the lens 16.

[0063] The second beam splitter 17 divides the diffracted beam into two measurement branches. In the first measurement branch, the optical system 18 uses the zeroth-order and first-order diffracted beams to form the diffraction spectrum (pupil plane image) of the target structure on the first sensor 19 (e.g., a CCD or CMOS sensor). Each diffraction order strikes a different point on the sensor, allowing image processing to compare and contrast several orders. The pupil plane image captured by the sensor 19 can be used for focusing measurement devices and / or to normalize the intensity measurements of the first-order beam. The pupil plane image can also be used for many measurement purposes such as reconstruction.

[0064] In the second measurement branch, optical systems 20 and 22 form an image of the target T on sensor 23 (e.g., a CCD or CMOS sensor). In this second measurement branch, a second aperture stop 21 is provided in a plane conjugate to the pupil plane. Aperture stop 21 blocks the zero-order diffraction beam, ensuring that the image of the target formed on sensor 23 is formed only by the -1 or +1 order beam. The image captured by sensors 19 and 23 is output to a processor PU that processes the image; the functionality of the processor PU will depend on the specific type of measurement being performed. It should be noted that the term "image" is used in a broad sense. Thus, if only one of the -1 and +1 orders is present, an image of the grating lines will not be formed.

[0065] Figure 5 The specific forms of the aperture plate 13 and field stop 21 shown are merely examples. In another embodiment of the invention, coaxial illumination of the target is used, and an aperture stop with an off-axis aperture is used to transmit approximately only one first-order diffracted beam to the sensor. In yet another embodiment, instead of a first-order beam or in addition to a first-order beam, second-order, third-order, and higher-order beams may also be used in the measurement. Figure 5 (Not shown in the image).

[0066] To accommodate these different types of measurements, the orifice plate 13 may include a number of aperture patterns formed around a disk, which is rotated to position the desired pattern. It should be noted that the orifice plate 13N or 13S may be used only to measure gratings oriented in one direction (X or Y, depending on the setup). For measuring orthogonal gratings, target rotations of up to 90° and 270° can be implemented. Figure 5 (c) and Figure 5 Different orifice plates are shown in (d). The use of these orifice plates and many other variations and applications of the equipment are described in the previously published applications mentioned above.

[0067] The metrology tools just described require low aberrations (e.g., for good machine-to-machine matching) and a wide wavelength range (e.g., to support a wide range of applications). Machine-to-machine matching (at least in part) depends on sufficiently small aberration variations in the (microscope) objectives, a challenging requirement that doesn't always need to be met. This also implies that it's virtually impossible to extend the wavelength range without compromising optical aberrations. Furthermore, item cost, tool volume, and / or weight largely limit the possibility of increasing wafer sampling density (more points per wafer, more wafers per batch) through parallelization achieved by providing multiple sensors to simultaneously measure the same wafer.

[0068] To address at least some of these problems, a measurement apparatus employing a computational imaging / phase acquisition method is described in U.S. Patent Publication US2019 / 0107781, which is incorporated herein by reference. Such a measurement apparatus can use relatively simple sensor optics with ordinary or even relatively mediocre aberration performance. This allows the sensor optics to have aberrations, and thus produces relatively aberrated images. Of course, simply allowing large aberrations within the sensor optics will have an unacceptable impact on image quality unless something is done to compensate for the effects of these optical aberrations. Therefore, computational imaging techniques are used to compensate for the negative impact of the relaxation of aberration performance within the sensor optics.

[0069] In this method, the intensity and phase of the target are obtained from one or more intensity measurements. Phase acquisition can use prior information about the measured target (e.g., to be included in the loss function used to derive / design the phase acquisition algorithm). Alternatively, or in combination with prior information, diversity measurements can be performed. To achieve diversity, the imaging system is slightly modified between the measurements. An example of diversity measurement is cross-focal stepping, i.e., obtaining measurements at different focal positions. Alternative methods for introducing diversity include, for example, using different illumination wavelengths or different wavelength ranges, adjusting the illumination, or changing the incident angle of the illumination on the target between measurements. Phase acquisition itself can be based on what is described in the aforementioned US2019 / 0107781 or patent application EP3480554 (also incorporated herein by reference). This description determines the corresponding phase acquisition from the intensity measurements such that the interaction between the target and the illumination radiation is described based on the target's electric field or composite field (“composite” here means both amplitude and phase information are present). The intensity measurements can be of lower quality than those used in conventional measurements and therefore can be defocused as described. The described interactions may include a representation of the electric and / or magnetic fields directly above the target. In this embodiment, an image of the irradiated target's electric and / or magnetic field is modeled as an equivalent source description by means of infinitesimal current and / or magnetohydrodynamic dipoles on a surface in a plane (e.g., two-dimensional) parallel to the target. This plane may be, for example, a plane directly above the target, such as a plane focused according to the Rayleigh criterion, but the location of the model plane is not critical: once the amplitude and phase at one plane are known, they can be computationally propagated to any other plane (focused, defocused, or even the pupil plane). Alternatively, the description may include a composite transmission of the target or its two-dimensional equivalent.

[0070] Phase acquisition may include modeling the effect of the interaction between the irradiation radiation and the target on the diffracted radiation to obtain a modeled intensity pattern; and optimizing the phase and amplitude of the electric field within the model to minimize the difference between the modeled intensity pattern and the detected intensity pattern. More specifically, during measurement acquisition, an image (e.g., an image of the target) is captured on a detector (at the detection plane), and its intensity is measured. A phase acquisition algorithm is used to determine the amplitude and phase of the electric field at a plane, for example, parallel to the target (e.g., directly above the target). The phase acquisition algorithm computationally images the target using a forward model of the sensor (e.g., considering aberrations) to obtain modeled values ​​of the intensity and phase of the field at the detection plane. A target model is not required. The difference between the modeled intensity value and the detected intensity value is minimized (e.g., iteratively) in terms of phase and amplitude, and the resulting corresponding modeled phase value is considered the acquired phase. Specific methods for using composite fields in measurement applications are also described in PCT application PCT / EP2019 / 052658, which is also incorporated herein by reference.

[0071] However, measurement sensors based on illumination computational imaging, such as those described in the aforementioned publication, are primarily designed for use with spatially coherent or partially spatially coherent radiation. This leads to the following disadvantages:

[0072] Optical crosstalk performance is significantly affected by the fact that the (partially) coherent point spread function is substantially larger than the (nearly) incoherent point spread function. This limits performance for process variations due to the influence of variations in adjacent customer structures on the asymmetry of the measured intensity of the target (e.g., inferring overlap or focal length from it). Also note that for a given identical detection NA, the incoherent resolution (limitation) is good and twice as good as the coherent resolution (limitation), which (from a different but relevant perspective) also contributes to reducing optical crosstalk.

[0073] • Phase acquisition requires (iterative) phase acquisition, which demands significant computational hardware, increasing the overall cost of the measurement sensor. Phase acquisition is also based on multiple diversity measurements to provide the necessary information for obtaining phase. It is estimated that, practically, 2 to 10 diversity measurements are required, increasing sensor acquisition time and / or complexity. For example, diversity can be obtained by performing measurements sequentially at multiple focus levels. Therefore, obtaining progressively defocused images is slow, resulting in slower measurement speeds and lower throughput. A simple calculation illustrates this. Assuming five transfocal (i.e., defocused) images are acquired for each combination of four (angular) directions and five (sequentially captured) wavelengths, and each image acquisition takes 1 ms, measuring each target would take approximately 100 ms. This does not include the time spent moving the platform and switching wavelengths. Furthermore, phase acquisition computation (which is typically iterative) itself can be computationally intensive and take a long time to converge to a solution.

[0074] Because for measurement sensors based on computational imaging under coherent illumination, the detection NA (numerical aperture) is larger than the illumination NA, a switchable illuminator is required that allows sequential measurements of the +1 and -1 diffraction orders for both x and y targets (and thus the ability to switch between four illumination modes). In particular, dark-field imaging requires such a switchable illuminator because images of the +1 and -1 diffraction orders can ultimately be positioned on top of each other, i.e., superimposed, for a specific λ / P ratio range. An alternative with one (low NA) coherent illuminator and four (large NA) detection pupils (which would not require a switchable illuminator) is not suitable for the desired λ / P ratio range in k-space / pupil space / Fourier space / solid angle space (the terms can be used synonymously). This increases the volume, cost, and complexity of the illuminated object, which is a disadvantage if it is desirable to operate multiple sensors in parallel to increase wafer sampling density. An additional disadvantage of this sequential measurement of the +1 and -1 diffraction orders is that the sensor is insensitive to (spatially averaged) temporal dose variations of the illumination source.

[0075] To address these issues, a measurement sensor based on computational imaging of spatially incoherent or closely approximated (or at least multimode) illumination is proposed. Such a measurement sensor could be, for example, a dark-field measurement sensor used for measuring asymmetry and parameters derived therefrom, such as overlap and focal length. For the remainder of the description, the term "incoherent illumination" will be used to describe spatially incoherent illumination or its closely approximation.

[0076] There are two conditions / assumptions under which monochrome image formation can be assumed to be spatially incoherent; these two conditions / assumptions are:

[0077]

[0078]

[0079] Where k x k y These are the x and y parameters in the pupil space (k-space). The angular spectrum of the electric field function O(x, y) of an indicator object (a scalar) is given by λ, where λ is the wavelength. dk x dk y Indicates the integral on the Kohler-type illumination pupil Furthermore, δ indicates the Dirac variable function, i.e., the Dirac Δ function. It should be noted that, in practice, the spatial coherence length of the illumination (e.g., expressed as near the target or near the detector) will be greater than zero; that is, the illuminator is not of the ideal Kohler type, but the above assumption still holds true / makes a computational model of (near)spatial incoherent image form produced even in this case. It should be noted that in the case of non-monochromatic illumination, this formalization of incoherent imaging, i.e., the extension of the formation mechanism, is possible under the third assumption that the target response does not (significantly) depend on the wavelength.

[0080] To facilitate the implementation of spatially incoherent illumination, while suppressing optical crosstalk from structures (with different periodic spacings) near overlapping and / or focused targets (e.g.), an optimized illumination arrangement is proposed, wherein the position of the illumination pupil is selected based on the ratio of the illumination wavelength λ (where λ equals the center wavelength, e.g., in the case of a not small illumination bandwidth) to the target spacing P, so as to ensure that a pair of complementary higher-order diffractions (e.g., +1 and -1) in the pupil space (k-space) coincides with (e.g., a fixed) detection aperture profile. In embodiments, the illumination NA is set to be equal to or (e.g., slightly) greater than the detection NA. For example, slightly greater could be greater than 5%, greater than 10%, greater than 15%, or greater than 20%. In alternative embodiments, the pupil space can be shared by two pairs of diffraction orders (and therefore two incident illumination angle directions), with one pair in each direction enabling simultaneous detection in X and Y. It should be noted that while the teachings in this paper are particularly applicable to incoherent systems (due to the larger illumination NA of these systems), they are not limited thereto, and the concepts disclosed herein are applicable to coherent and partially or nearly coherent systems.

[0081] Maintaining a fixed detection aperture profile simplifies optical design. However, alternative implementations may include fixing the illumination aperture profile and configuring the detection aperture profile according to the same requirements. Furthermore, both the illumination and detection aperture profiles can be configurable to adjust both the illumination and detection pupil locations to maintain consistency / matching between the diffraction order and the location of the detection pupil.

[0082] In the context of this disclosure, a pair of complementary diffraction orders can include, for example, any higher (i.e., non-zero) order pair of diffraction orders having the same order (e.g., +1 and -1). The pair of complementary diffraction orders can originate from two separate illuminations from substantially different directions (e.g., opposite directions), such as a -1 diffraction order from illumination from a first illumination direction and a +1 diffraction order from illumination from a second illumination direction. Alternatively, the pair of complementary diffraction orders can originate from a single illumination beam, such that the orientation of the illumination aperture profile and / or periodic structure configured according to the detection aperture profile and wavelength / spacing combination captures both the -1 and +1 diffraction orders originating from such a single illumination beam.

[0083] An additional benefit of using spatially incoherent irradiation (or closely approximating it) is that it enables the use of extended sources, for example, with limited bandwidth; the use of laser-like sources is not mandatory because, in practice, they will be used for spatially coherent irradiation.

[0084] Measuring the +1 and -1 diffraction orders simultaneously for either the X or Y target (or both) has the following advantages: the effects of intensity noise and wavelength noise (e.g., mode transitions) are more easily suppressed and are extremely likely to be suppressed better.

[0085] Figure 6 This is a schematic illustration of such a measuring tool according to an embodiment. It should be noted that this is a simplified representation, and the disclosed concepts can be implemented, for example, in applications such as... Figure 5 The measurement tools shown in the diagram (also for simplification) are among those illustrated.

[0086] An illumination source SO, which can be an extended and / or multi-wavelength source, provides source illumination to SI (e.g., via multimode fiber MF). An optical system, such as that represented here by lenses L1, L2, and objective lens OL, includes a spatial filter or mask SF, which is positioned in the pupil plane (Fourier plane) of the objective lens OL (or provided to such pupil plane for a channel or access for filtering). The optical system then filters the source illumination to SI. F The light is projected and focused onto the target T on the substrate S. This provides a configurable illumination profile, such that the illumination pupil NA and its position are defined by the filter SF. Diffraction radiation +1, -1 is guided by the detection mirror DM and lens L3 to the camera / detector DET (which may include one camera per diffraction order, or a single camera or any other arrangement). Thus, the detection pupil NA and its position are defined by the area and position of the detection mirror DM.

[0087] In this arrangement, the detection mirror and therefore the detection pupil may have a fixed size (NA) and position (because this is more practical in practice). Thus, it is proposed that the illumination pupil profile is configurable according to the wavelength-to-spacing ratio λ / P of a specific target spacing (or strictly and relatively, when the illumination wavelength can vary). The configurability of the illumination profile allows the diffraction radiation (e.g., +1 and -1 diffraction orders) to be aligned with and substantially captured by the detection mirror (e.g., one order per mirror); that is, the positions of the +1 and -1 diffraction orders correspond to and are aligned with the detection pupil defined by the detection mirror in the pupil space.

[0088] In one embodiment, the overlay / alignment of +1 and -1 orders can be such that the entirety of one of the plurality of orders overlaps with one of the detection pupils defined by one or more, or two or more separate detection areas (e.g., and captured by the detection mirror or other detection optics). In other embodiments, it can be: at least 95%, at least 90%, at least 80%, or at least 70% overlap of +1 and -1 orders, or filling the detection pupil defined by one or more, or two or more separate detection areas (e.g., and captured by the detection mirror). In other arrangements, the relevant range is >= 1% or >= 10%. Assuming the objective lens NA is 1, and using a nearly fully open illumination profile (see... Figure 7 (c)) , then 1% would correspond to a detection NA of approximately 0.10 [sine angle]. Of particular relevance is that each detection region within the detection region is largely filled with the corresponding diffraction order (assuming an infinitely large target, such that the diffraction order forms a Dirac Δ function in angular space (i.e., in the detection pupil space). This is analogous to the summation of the Kohler illuminators in the equation above. It is expected that all angles that can propagate exist. Since the angular space is limited to 1 [sine angle] (i.e., 90 degrees), it is impossible to add from -∞ to +∞ (which would be ideal from a mathematical (spatial coherence) perspective).

[0089] Thus, the method can provide an orientation for configuring the illumination aperture profile and / or the periodic structure based on a wavelength / spacing combination, such that radiation from at least one pair of complementary diffraction orders fills at least 80%, 85%, 90%, or 95% of one or more separate detection regions. In an embodiment, this configuration can cause radiation from at least one pair of complementary diffraction orders to fill at least 100% of the one or more separate detection regions.

[0090] It should be understood that the detection aperture profile and the illumination aperture profile do not necessarily need to be formed as solid holes in the illumination pupil plane and the detection pupil plane, respectively. The holes can also be located at other locations such that when these holes are propagated to the illumination pupil plane and the detection pupil plane, they respectively provide the detection aperture profile and the illumination aperture profile.

[0091] Each of the multiple individual illumination zones may correspond to a corresponding detection zone in the one or more detection zones. Each illumination zone may be the same size or larger than its corresponding detection zone; for example, each illumination zone may be up to 30% larger than its corresponding detection zone. A single illumination zone may include available Fourier space other than the Fourier space used for the detection aperture profile and the boundary between the illumination aperture profile and the detection aperture profile.

[0092] The configurability of the illumination pupil profile can be achieved by selecting a specific spatial filter (SF) as appropriate. For example, the filter can be manually inserted or mounted to a filter wheel. Other filtering options include using a spatial light modulator (SLM) or a digital micromirror device (DMD) instead of the spatial filter (SF), or even using a spatially configurable light source where its illumination profile can be directly configured. Any such method or any other method for obtaining and / or configuring the desired illumination profile can be used. The illumination aperture profile may include one or more illumination zones in Fourier space; for example, two illumination zones for illuminating the periodic structure in two substantially different angular directions (e.g., two opposite directions), or four illumination zones for illuminating the periodic structure in two substantially different angular directions (e.g., two opposite directions) for each target direction.

[0093] Figure 7 (a) The configuration shown in Figure 1, wherein the detection pupil DP comprises four detection pupil regions DPR (e.g., defined by four detection mirrors), which can be configured to simultaneously measure positive and negative diffraction order information for both X and Y targets. Thus, the illumination pupil IP comprises four illumination regions ILR for illuminating the target in two opposite (angular) orientations according to the X and Y orientations, and configured according to the λ / P ratio such that the resulting four first diffraction orders (i.e., +1, -1 orders in each direction, one order captured by each illumination region ILR) each first diffraction order coincides with the corresponding detection pupil region DPR in k-space (also known as Fourier space or angular space), and is therefore captured by the corresponding detection mirror. As is known, the illumination pupil region should not overlap with the detection pupil region in the pupil space (i.e., the pupil is divided into exclusive illumination and detection regions, although some spaces may not be both). Figure 7In the alternative embodiment illustrated in (b), the detection pupil DP has only two detection pupil regions DPR (e.g., two detection mirrors), which has the benefit of allowing for an increased detection NA (which reduces optical crosstalk). Thus, the illumination profile also has two illumination regions ILR to illuminate the target in two opposite (angular) directions. However, this would imply separate measurements in the X and Y directions.

[0094] With the help of a specific example, both the detection NA and the illumination NA can include (e.g., in) Figure 7 (In the example of (a)): 4 × NA = 0.18 to 0.23. For example, the detection NA and the irradiation NA can each include 4 × NA = 0.21. It should be noted that in each case, the irradiation NA can be equal to, or (e.g., slightly) greater than the detection NA. Figure 7 (b) In the example, the detection NA can be, for example, 2 × NA = 0.23 to 0.27 (e.g., 2 × NA = 0.25), which utilizes a correspondingly larger illumination NA (e.g., it can still be larger, e.g., 2 × NA = 0.3). The illumination NA can cause it to overfill the detection NA for the +1, -1 detection order. Overfilling in this context means that for a target of infinite size, the diffraction order forms a Dirac delta pulse in the detection pupil plane. In practice, of course, the target must have a finite size (e.g., 10 μm × 10 μm), so the energy of the diffraction order expands outward in the pupil space. For this reason, increasing the illuminator to have a larger NA than the detection NA can have the advantage that it can help the imaging get closer to the incoherent extremum. In this respect, it should be noted that the equations described above for which monochromatic imaging can be assumed to be spatially incoherent; that is, where the spatially mutually coherent functions collapse to the Dirac delta function, thereby allowing image formation to be computed without the need for phase information of the target.

[0095] Figure 7 (c) An alternative illumination arrangement is illustrated, excluding the need for a configurable / programmable illuminator. In this embodiment, the illumination area ILR comprises most of the available k-space; for example, all space except for the detection pupil area DPR and the boundary M therebetween, to avoid optical crosstalk from specular reflections (zero-order) from the target and / or surrounding structures. To better illustrate this boundary, the figure shows the IP+DP of the overlapping illumination pupil and detection pupil. In such a particular example, this boundary has a width equal to a sine angle of 0.08, but can be, for example, in the range of 0.05 to 0.12, 0.05 to 0.1, or 0.07 to 0.09. This filled illumination profile can have an NA greater than 0.9, or, for example, greater than 0.92. This filled illumination profile can be used with a unidirectional detection pupil (two detection pupil areas), such as... Figure 7As shown in (b).

[0096] This configuration, where both the illumination NA and the detection NA are of fixed size and position, while still providing optimized illumination for different λ / p ratios, enables smaller sensor volume, mass, and item cost. This is important when using multiple of these sensors in parallel to increase measurement speed and / or wafer sampling density (i.e., to measure all / more wafers from a batch, and / or more measurement targets per wafer).

[0097] An illumination NA equal to or slightly larger than the detection NA can be shown to be sufficient from a practical point of view to make the resulting imaging formation approximate spatially incoherent imaging formation; for example, to the extent that the detected camera image can be accurately calculated / predicted computationally using an incoherent imaging model. Relevant discussions can be found, for example, in Chapter 7.2 and Equations 7.2-61 of J. Goodman's book "Statistical Optics" (ISBN 1119009456, 9781119009450), which are incorporated herein by reference. The ability to calculate / predict the detected camera image in this way allows for the correction of detection optics aberrations via deconvolution (e.g., Wiener-like), which has the advantage of computational inexpensiveness. In this way, the complete vector problem can be decomposed into two scalar problems. If the aberrations result in zeros in the MTF (modulation transfer function), these zeros can be addressed using regularization (such as L1 total variation regularization). These regularizations are described in EP3480554 above.

[0098] For incoherent sensors, the modulation transfer function (MTF) is skewed, meaning the signal-to-noise ratio (S / N ratio) of the measured information depends on the spatial frequencies constituting the target. To maximize the S / N ratio derived from the overlap (and / or focal length) inference, it is preferable not to over-amplify spatial frequency components with poor S / N ratios. Therefore, the proposed deconvolution operation should not flatten the effective MTF again, as that would result in a suboptimal overlap S / N ratio. An optimal balance between the S / N ratio and the deconvolution gain (for each spatial frequency component) yields a Wiener filter (as is precisely the case); and thus, a "Wiener"-like deconvolution.

[0099] Once captured, the camera image can be processed to infer parameters of interest, such as overlap. Some processing operations or operations performed on the image may include one or more of the following: edge detection, intensity estimation, periodic fitting (if present in the image). All of these operations or operations can be (partially) written as convolution operations (or subsequent cascades of multiple convolutions), such as a kernel for the region of interest weighting pixels for intensity estimation. Correction kernels can be combined with all of these operations or operations. This approach also makes it possible to formulate aberration correction operations or operations that are field-dependent. This allows for the correction of not only field aberrations but also pupil aberrations.

[0100] For clear image I clean and the original measurement results I raw An example of the operation process is as follows:

[0101] I clean =I raw *K

[0102] Where K indicates the correction kernel, and * indicates the convolution operator. Where the region of interest kernel (ROI kernel) R is used to process the sharp and original image, then:

[0103] I clean *R=I raw *(K*R)

[0104] For example, the convolution of the calibration kernel (K) and other mathematical operation kernels (e.g., ROI kernel R) can be calculated outside the critical measurement path range at the start of the measurement operation. This is also general for all measurements, thus requiring only one operation per mathematical operation. A more efficient approach would be to convolve the calibration kernel over each acquired image.

[0105] In embodiments, corrective convolutional kernels can be combined with convolutional neural networks. For example, a convolutional neural network comprising one or more layers can be used to perform the evaluation of the convolution (or its functionality) (e.g., aberration correction, PSF reshaping, and ROI selection convolution). This means that a convolution with a large coverage kernel can be decomposed into multiple convolutions with kernels having smaller occupancy sizes. In this way, the field dependence of aberrations can be implemented / covered by the neural network.

[0106] An additional possibility is to include (a form of) wavefront coding to increase (for example) the usable focal range and / or to optimize one or more other aspects of performance. This covers the intentional introduction of (designed) aberrations into sensor optics that can be corrected by computational aberration correction. This reduces sensitivity to focus variations and thus effectively increases the usable focal range. For example, the following references, which include more details and are incorporated herein by reference, are cited: Dowski Jr., Edward R., and Kenneth S. Kubala, “Modeling of wavefront-coded imaging systems”, in Visual Information Processing XI, International Society for Optics and Photonics, Vol. 4736, pp. 116-126, 2002.

[0107] Additional possibilities may include reshaping the (near)incoherent point spread function (PSF) shape using apodization (which can be implemented in hardware, software, or a hybrid thereof). An aberration sensor produces an aberrated PSF. By means of aberration correction, the PSF can be reshaped to the PSF with an ideal / aberration-free sensor. Furthermore, optical crosstalk can be further reduced by suppressing the sidelobes of the resulting PSF by applying apodization. As a specific example, computational apodization can be applied such that the resulting PSF approximates the shape of a (radial) Hanning window function.

[0108] Another image correction technique (e.g., used for aberration correction) can be based on residual errors. Several methods exist to correct this error, such as:

[0109] A portion of the residual error can be determined by measuring the target at 0 and 180 degrees of rotation. This captures the imbalance of the optics, but not entirely effects such as crosstalk.

[0110] • Residual errors of field-dependent components can be captured by imaging targets under different XY shifts.

[0111] Crosstalk error can be captured by measuring test targets in different environments.

[0112] These residual error corrections can be determined for a finite set of targets to reduce the impact on measurement time.

[0113] For some diffraction-based overlap techniques, the target can include different spacings in each of its multiple layers. In such cases, the detection NA should be large enough that a single illumination ray / position can achieve a balance between detecting and capturing the spacing (here, coherent interference between the two spacings at the detector / camera level).

[0114] It is also proposed to include (e.g., programmable) rotation of the wafer around the optical axis of the sensor (or at least rotation of the target around the optical axis of the sensor). This can be used to increase / maximize the illumination and / or detection NA, and / or increase the λ / P ratio that can be supported (by freeing up other available k space). Alternatively or additionally, this rotational capability can be used to further suppress crosstalk from adjacent structures, since it will create four (or two) illumination pupils relative to different locations of one of the detection pupils.

[0115] In this embodiment, it is therefore proposed to use an illumination and detection pupil geometry optimized in combination with wafer rotation, wherein one or both of the illumination geometry (e.g., as described) and wafer rotation depend on the λ / P ratio.

[0116] Figure 8 Examples are shown of how such wafer rotation can be used to increase the detection (and illumination) NA and / or increase the range of available λ / P ratios. Figure 8 (a) shows an arrangement without wafer rotation (i.e., it is) Figure 7 (a) Overlaid illumination and detection profiles. It should be noted that the principles described in this section apply equally to... Figure 7 Irradiation and detection contours (e.g., Figure 7 (b) or Figure 7 (c)) any of the arrangements or any other arrangement within the scope of this disclosure. Without wafer rotation, for a fixed detection position DPR, the illumination position ILR moves along the arrows relative to the increasing λ / P ratio. This means that, without significantly limiting the λ / P that can be used for illuminating and detecting the NA stack in other ways, the detection and illumination of the NAs will not be larger than those illustrated (as shown by the boxes). Specifically, many intermediate ratios (e.g., corresponding to the middle portions of each path indicated by the arrows, where each illumination position ILR is close to the nearest detection region DPR) will be unavailable.

[0117] Figure 8 (b) shows six consecutive illumination profiles ((λ / P)1-(λ / P)6) for increasing the λ / P ratio respectively, wherein the illumination profile optimization involves wafer rotation about the optical axis (it should be noted that it appears as if the sensor is rotating, not the wafer in the figure). It can be seen that the illumination and detection NA (for the same given overall NA) in...Figure 8 (b) is larger, where the size comparison is shown at the top of the figure, while illumination and detection remain separated across the entire λ / P ratio range. The rotation can be used only for some λ / P ratios, for example, to increase the range of a given NA / detection profile.

[0118] It should also be understood that, taking into account the periodic spacing of the surrounding structures (e.g., to reduce the contribution of these surrounding structures to the parameters of interest (such as intensity asymmetry, overlap, focusing, etc.)) in order to optimize the illumination profile and / or λ / P ratio range, this concept of rotating the wafer according to the λ / P ratio can be used in metrology apparatuses independently of any other conception disclosed herein and for many different illumination and detection profiles and arrangements from those indicated.

[0119] In an embodiment, the rotation may be performed to optimize, for example... Figure 7 (c) shows the boundary M between the irradiation and detection pupils in the large irradiator embodiment; for example, to reduce leakage of specularly reflected light that does not carry information but contributes to photon pulse noise.

[0120] Other options for maximizing the permissible range of the detection NA and / or λ / P ratio may include:

[0121] • Rotate the wafer around its (local) normal.

[0122] • Rotate the sensor around its optical central axis.

[0123] • Rotate the target (periodic pattern) orientation on the wafer.

[0124] • Split the x-target and y-target measurements from two separate sensors.

[0125] • The +1 and -1 diffraction order measurements were split between two separate sensors.

[0126] • By splitting the wavelength range, the λ / P ratio range can be divided on two or more sensors.

[0127] • By splitting the spacing range, the λ / P ratio range on two or more sensors can be divided.

[0128] • Use solid / liquid immersion lenses to increase the available k-space.

[0129] • Any of the above mixtures / replacements / combinations (including splitting on more than two separate sensors).

[0130] As described, many embodiments described above use separate illumination and detection pupils for each of the complementary diffraction order pairs of the X and Y targets. The optimal illumination conditions (e.g., polarization conditions) may differ for the X and Y targets. For example, the X target may require horizontally polarized light, while the Y target may require vertically polarized light. For measurement devices (such as...) Figure 5 As illustrated in the diagram, the same settings are typically used during a single acquisition (e.g., for X and Y). Alternatively, to obtain optimal conditions, multiple acquisitions (e.g., two) can be performed. This results in a decrease in speed.

[0131] Arrangements that allow for the parallel (and simultaneous in both directions) measurement of different sets of targets (more specifically, for target X relative to target Y) using different illumination conditions will now be described. In the example, the different illumination conditions may include variations in one or more of the following: polarization state, wavelength, intensity, and duration (i.e., the integration time on the detector). In this way, twice the acquisition time (i.e., half the time) is possible for the same measurement quality.

[0132] Figure 9 The illustration shows a possible implementation for enabling separate polarization settings for X and Y. It shows an X-ray pupil with horizontal polarization XH and a Y-ray pupil with vertical polarization YV. These pupils are combined using suitable optical elements such as a polarizing beamsplitter (PBS) to obtain a combined illumination pupil XH+YV, which can then be used for measurement. The illustrated arrangement can only be adapted when the varying illumination conditions are conditions other than polarization. Thus, the polarizing beamsplitter (PBS) can be replaced with another suitable beam-combining element for combining illumination pupils of different wavelengths or durations. This arrangement can be adapted to situations where the illumination paths differ for X and Y illumination; many different methods exist to provide these different illumination paths, as will be apparent to those skilled in the art.

[0133] In alternative arrangements, for example, where the pupil is programmable, a polarizer (or other element dependent on illumination conditions) can be placed in the path of each respective pupil. Programmable pupils can be implemented, for example, in devices including embedded programmable digital micromirrors or similar devices, via modular illumination. Any suitable optical element that modifies the illumination conditions can be positioned in the pupil plane of the tool to operate on multiple individual zones of the pupil plane.

[0134] In many of the embodiments described herein, the illumination is configured to overfill the detection NA (separated detection region in the pupil space). Overfilling of the separated detection region means that the diffraction illumination of the desired diffraction order (e.g., a +1, -1 complementary order pair from the target in one or two orientations) fills 100% of the pupil space (Fourier space) defined by the separated detection region.

[0135] Figure 10 The illustrations show three proposed methods for implementing these overfilled detection NAs. In each case, only one isolated detection region (DPR) is shown, but in more common configurations there may be two or four. Figure 10 (a) illustrates a fully programmable arrangement in which the illumination regions ILR, ILR', ILR" are moved to maintain a diffractive radiation DIFF in the same spot on the detection region DPR for different λ / p combinations (each illumination region ILR, ILR', ILR" corresponds to a different λ / p combination). In this way, the detection region DPR is maintained overfilled by the diffractive radiation DIFF. Control of the illumination profile can be achieved by any of the methods disclosed herein (e.g., spatial filters, SLMs, DMDs, or spatially configurable light sources).

[0136] Figure 10 (b) and Figure 10 (c) The illustration shows a pre-configured irradiation zone covering a range of different λ / p combinations. Figure 10 In (b), an extended irradiation region EILR is used (e.g., fixed) to encompass different λ / p combinations that define a range extending from a first combination corresponding to a first extremum in the left figure to a second combination corresponding to a second extremum in the right figure. Within this range, diffraction radiation DIFF, DIFF;' always overfills the detection region DPR. Figure 10 (c) A similar arrangement is shown, but using a full illumination profile FILR, which covers the entire Fourier space except for the detection zone DPR and the safety boundary (the space in the full illumination profile FILR is provided for the second detection zone). Figure 10 (a) and Figure 10 In (b), a corresponding irradiation region is required for another diffraction order; this is not... Figure 10 (c) The case of complete illumination profile FILR.

[0137] In such Figure 5In the (e.g., dark-field) scatterometer measurement apparatus illustrated, it is known to illuminate overlapping targets (e.g., overlapping μDBO targets based on microdiffraction) using a quadrature illumination mask that defines an illumination NA comprising two diagonally opposed quadratures. Two other diagonally opposed quadratures are used for detection and define the detection NA. The scattered radiation is divided into +1, -1, and (optionally) zero diffraction orders using a four-part wedge. This arrangement enables simultaneous imaging of +1, -1, and zero orders. In the detected image, the X and Y pads are arranged adjacent to each other. If aberrations are present, XY crosstalk will exist between these pads, which will adversely affect the overlap acquisition results.

[0138] Instead of this arrangement, a number of specific Fourier plane arrangements will be described for simultaneous spatially incoherent (or partially incoherent) imaging of multiple diffraction orders. Each of these can be used in the embodiments disclosed herein (i.e., in an arrangement in which diffraction radiation of at least a pair of complementary diffraction orders is captured within the detection aperture and fills at least 80% of one or more separated detection regions).

[0139] Figure 11 The arrangement shown in the first figure uses an optical element that includes eight wedges instead of four wedges to allow the X pad and Y pad to be imaged separately.

[0140] The eight-part wedge can be located at the detection pupil plane and includes an optical element with eight parts, each having a wedge-shaped cross-section (in a plane perpendicular to and passing through the center of the pupil plane), thereby refracting light in the corresponding parts of the pupil plane toward different locations at the image / detector plane.

[0141] For the required functionality, fewer than eight segments may be necessary. For example, a 45-degree rotation (relative to the currently used orientation) of a four-part wedge may be sufficient to separate the + / - X / Y orders. Two additional sections can be provided to separate and capture the 0 order for, for example, dose correction or monitoring of the lithography process defining the target.

[0142] Therefore, this embodiment can use an optical element (or mirror or other optical element) comprising at least four wedges, which separates different parts / regions (specifically + / - X / Y order) of the detection aperture profile.

[0143] exist Figure 11 In (a), overlapping illumination and detection pupils IP+DP are shown, divided into 8 segments (dashed lines). The illumination may include a four-part illumination profile ILR, as in the case of a 4-wedge mask. As can be seen, each diffraction order DIFF +x DIFF - x、DIFF +y DIFF-x It is consistent with / matches the corresponding dedicated wedge or wedge part. Figure 11 (b) shows that, depending on the λ / p ratio of the pad, the illumination profile ILR' may need to be truncated into, for example, an hourglass profile, such that the diffraction order DIFF' +x ,DIFF' -x ,DIFF' +y ,DIFF' -x It remains separated by eight wedges.

[0144] Figure 11 (c) shows the image obtained at the image / detector plane. For the corresponding different IM levels... +x IM -x IM +y IM -x The images of IM0 are located at multiple separate locations on this image plane. Therefore, using this scheme, the use of the detection NA space is maximized (i.e., the imaging resolution is maximized) while the X and Y diffraction steps remain separated (i.e., the X and Y pads are imaged separately).

[0145] Because the X and Y pad diffraction orders pass through different parts of the detection pupil, they are affected by different parts of the aberration function. In the current 4-part wedge configuration, it is impossible to apply aberration correction separately to the X and Y pads (the problem is that due to XY crosstalk due to aberrations, it is impossible to spatially separate the diffraction from the pads and apply aberration correction separately). In the 8-part wedge configuration, aberration correction can be applied separately to the X and Y pads to reduce blurring and XX and YY crosstalk. To effectively apply computational image correction, it is assumed that image formation can be approximated as completely incoherent. In this case, image formation is described by simple convolution, and image correction can be achieved by simple deconvolution. Complete incoherence can be achieved (approximately) using any of the methods described, and / or by illuminating the sample from all angles with mutually incoherent plane waves, i.e., the illumination pupil is completely filled with mutually incoherent point sources. If the detection pupil is overfilled, there is no difference between the illumination pupil being completely filled (i.e., completely incoherent) or partially coherent (i.e., partially coherent).

[0146] It should be understood that Figure 11The arrangement shown is a specific arrangement for separating multiple diffraction orders, which can be summarized as follows: the detection is split into eight parts such that four parts capture +1 and -1 diffraction orders for each of the two target directions, and the other four parts can be used to capture any arrangement of zero-order diffraction. These parts can have any shape. Rotationally symmetric arrangements are advantageous for optical and mechanical fabrication, but are not necessary. The illumination profile can be configured relative to the detection NA to ensure that there is no crosstalk between the X and Y diffraction orders detected for the largest possible wavelength / spacing range. This can be achieved by any of the methods described. The detection and illumination masks can be (co-)optimized for incoherent wavelength / spacing ranges, cDBO spacing differences, illumination efficiency, number of available apertures, etc.

[0147] Figure 12 Another embodiment is illustrated, which achieves a high level of incoherence by overfilling the detection over a very large wavelength / spacing range (to allow for good performance in computational image correction) and simultaneously by supporting continuous DBO (cDBO) applications with limited illumination efficiency loss. Briefly, cDBO measurement may include measuring cDBO targets comprising: (e.g., per direction) a type A target or a pair of type A targets having a grating with a first spacing p1 located on top of a grating with a second spacing p2; and a type B target or a pair of type B targets, wherein these gratings are interchanged such that the second spacing p2 grating is located on top of the first spacing p1 grating. In this manner, and in contrast to μDBO target arrangement, the target bias varies continuously along each target. The overlap signal is encoded in a moiré pattern from (e.g., a dark field) image.

[0148] exist Figure 12 In the example illustrated, the illumination and detection masks are designed around two parameters:

[0149] • Kr: XY constraint (NA radius or central radial numerical aperture size) for the main portion of the irradiated ILR. This can be chosen relatively freely, in which case Kr = 0.4 (sin(α) element);

[0150] • D: The safe distance for the detection zone DPR. Typical values ​​can be between 0.03 and 0.15, or between 0.04 and 0.1, for example, 0.05 (sin(α) unit).

[0151] It should be noted that the detection pupil DP only shows the first-order detection area, but the corresponding area of ​​the illumination area ILR (or a subset thereof) (with the safety distance removed) can be used for zero-order detection.

[0152] Figure 13 Another Fourier plane arrangement is shown, in which the diffraction radiation DIFF from the target structure is shown. +x DIFF -x DIFF +y DIFF -x The corresponding detection area DPR is overfilled, but other wells are not overfilled. The figure also shows the corresponding irradiation profile ILR.

[0153] Figure 14 Another Fourier planar arrangement is shown, in which the diffraction radiation DIFF from the target structure is displayed. +x DIFF -x DIFF +y DIFF -x Each of each order is captured twice in two separate (e.g., overfilled) detection regions. The corresponding illumination profile ILR is also shown. This arrangement enables correction for low-order sensor artifacts (e.g., coma and / or astigmatism). This arrangement is also compatible with cDBO.

[0154] In all of the above arrangements, an optical element or wedge arrangement (e.g., multiple individual wedges for each diffraction order, such as multipart wedges, e.g., 4, 6, 8 part wedges) can be used to separate the diffraction order images on the camera.

[0155] In many arrangements where multiple individual detection zones are individually captured for corresponding orders, it can be understood that for each detection zone, the imaging is incoherent, and all scattered radiation will have produced the same aberrations. These aberrations can be corrected according to the following equation, where I is the captured image, |E| 2 It is the target intensity, and the PSF is the point spread function resulting from the NA and aberrations:

[0156]

[0157] It can be shown that deconvolution, which assumes incoherent imaging, can be used to adequately correct for 10 μm defocus (e.g., 5λZ4 aberration) in an image to obtain a good overlap value, which would be impossible with conventional imaging.

[0158] In the above text, based on the detection hole profile and The ratio is used to configure the irradiation aperture profile and / or orientation of the periodic structure used for measurement. This is to ensure sufficient coverage. If the value is (e.g., at least 1.3), then the detection pupil should be located at a high NA.

[0159] In an alternative embodiment, it is proposed to provide a programmable or configurable detection aperture profile, such that for lower... The center of the detection aperture can be positioned at a lower NA (Near Field of Atmosphere). This offers several additional advantages:

[0160] • Lens aberrations are typically lower with lower NA (lens aberration).

[0161] For thicker stacks, it is preferable to use smaller spacing for overlapping targets, employ a small illumination aperture, and maintain the illumination beam and the first-order detection beam close to the normal of the target to minimize parallax and distortion. This is achieved by a programmable detection aperture.

[0162] • If the imaging is operated in a manner close to the so-called Littrow condition, the effects of pupil aberration can be suppressed, where the illumination and the first order have the same angle of incidence; this is achieved by a programmable detection aperture.

[0163] For example, both the illumination pupil profile (illumination aperture profile) and the detection pupil profile (illumination aperture profile) can be programmable or configurable. A desired implementation may include positioning each center of the illumination and detection apertures at a distance from an axis perpendicular to the grating pitch direction. Location, or near A device for achieving, or at least approximating, the Littrow condition;

[0164] Several methods exist for implementing a configurable detection aperture profile to achieve these desired features. A first proposal may include applying programmable displacement of the illumination and detection apertures within the pupil profile. This method may use one or more optical elements to translate or shift the trajectories of both the illumination and detection beams in the pupil plane.

[0165] In an embodiment, the center of the illumination pupil is located at a distance from the relevant axis that is the same as or nearly the same as the center of the detection pupil, wherein the direction of the distance between the relevant axis and the target is orthogonal.

[0166] Figure 15This is a simplified schematic diagram of this arrangement. The arrangement is based on a pair of prisms, or multiple optical wedges, or multiple wedges W1, W2, located at the pupil plane. The wedges can be oriented in opposite directions such that they together shift the illumination and detection beams in the pupil plane without substantially changing their orientation (i.e., such that there is no directional change between the beam input and output of the optical system defined by the pair of wedges, wherein the directional change imposed by the first wedge W1 is canceled out by the opposite directional change imposed by the second wedge W2). The figure also shows the objective lens OL and the substrate S. Initial illumination is defined by a fixed pupil (as shown in plane AA'). However, the optical wedges W1, W2 can be configured to simultaneously change the illumination and detection beams. Detection of the optical pupil. In the illustrated embodiment, the optical wedges W1 and W2 can be configured via a configurable or variable distance between opposing planes AA' and BB' by moving one or both of the wedges W1 and W2 along the direction of the beam. The figure shows the wedge (or more specifically, wedge W2) in three positions (the center position is shown with a solid line, and the two positions on either side are shown with dashed lines). The illumination and first-order diffraction radiation paths corresponding to each of these positions are also shown (in addition, for the path corresponding to the dashed wedge W2 position, the path is drawn as a dashed line).

[0167] Prisms W1 and W2 simultaneously translate the illumination and first-order diffracted radiation in the same direction to the same magnitude in the pupil plane, depending on their spacing, as shown in plane BB'. As illustrated, alternatively, complementary illumination and diffracted light can be shifted in opposite directions using wedges oriented in opposite directions on the other side of the optical axis O.

[0168] As an alternative to wedges with variable separation distances, other arrangements may include wedges with programmable or configurable opening angles, i.e., aperture angles. For example, one or both wedges W1, W2 may be tunable wedges based on liquid lens technology (e.g., liquid lens optics).

[0169] Ideally, the illumination and detection apertures should be at the same distance from the optical y-axis (for an x-grating). However, as shown in the figure, this is not necessary.

[0170] The mechanical movement of the prism should be rapid to allow for short switching times. It can be demonstrated that switching times on the order of 1 ms should be feasible.

[0171] As an alternative to a prism with configurable separation distance or shape, the optical element may include optical plates (e.g., tiltable or rotatable optical plates), one on each side of the y-axis, to shift the beam. Figure 16 This schematically illustrates a rotating optical plate OP, where the displacement D depends on the incident angle θ.

[0172] In an embodiment, a beam splitter / combiner unit can be provided to the prism-based arrangement just described. The beam splitter / combiner unit can be positioned directly above the prism (or in another pupil plane). This unit separates the illumination beam from the diffracted beam.

[0173] Such a beam splitter / combiner unit may include, for example, a pair of small mirrors placed in each illumination path to guide the illumination rather than the diffracted radiation (e.g., the mirrors may act as partial pupil stops), such that the diffracted radiation travels only toward the detector. Alternatively, the mirrors may be positioned to guide the diffracted radiation rather than the illumination.

[0174] A pair of beam splitters (e.g., small beam-splitting squares) can be used in a similar manner, positioned in the paths of both illumination and diffraction radiation, but configured to deflect only one of them. The beam splitters can be combined with wedges for guiding orthogonal and complementary diffraction orders to different portions of the detector, where a single lens is used to transmit or relay the image on the detector (e.g., similar to the four-part wedge arrangement described).

[0175] The arrangement described above enables detection in only one grating direction (e.g., X or Y). Figure 17 Another embodiment is illustrated, in which a tapered (or axial pyramidal) wedge W2' and a corresponding dished wedge W1' (the latter shown in cross-section) can be used in both the X and Y directions to make the illumination and detection aperture profiles configurable. These wedges are replaceable. Figure 15 W1 and W2. Alternatively, a four-quadrant wedge can be used instead. Figure 15 The diagram illustrates two halves for parallel acquisition in X and Y, albeit at the cost of a lower λ / spacing range that can be supported. Continuous detection in X and Y can be achieved by rotating the wedge element between both X and Y measurements.

[0176] Another alternative for programming / configuring the illumination and detection pupil is to use a zoom lens (instead of an axonal pyramid and disc lens arrangement) to produce a magnified or reduced image of the pupil in the (intermediate) pupil plane.

[0177] Figure 18Another embodiment is illustrated, comprising a mirror TM (e.g., a galvanometer scanning mirror) with a tunable or variable angle in the (intermediate) field plane. Changing the tilt angle of the mirror YM in the field plane results in a corresponding translation of the pupil plane. The figure also shows the objective lens OL, the substrate S, and the lens systems L1, L2. The two halves of the pupil are separated, for example, using wedges W1 in the first pupil plane. In the field plane above these wedges, each half of the pupil plane will correspond to a shifted image (similar to the wedges in the detection branches currently used in some metrology tools, as described). In this plane, the tiltable mirror TM is used to change the angular orientation of the illumination ILL and diffraction DIFF beams, which in turn corresponds to a shift or displacement in subsequent pupil planning. It should be noted that the mirror TM can be placed at any nominal angle about other axes, causing the remaining optics to tilt off the plane. This can help achieve a large tilt range. This idea can be easily extended to include both X and Y gratings. This mirror-based embodiment can be used to achieve very short switching times of less than 0.5 ms.

[0178] Figure 19 Another embodiment is illustrated, employing a switchable configuration of the illumination and detection pupils instead of a continuously programmable configuration. In this embodiment, the imaging mode element or imaging mode turret IMW is placed in or around the pupil plane of the system and positioned at an angle such that the diffracted radiation DIFF is deflected away from the direction of the objective lens OL. The imaging mode turret IMW may include reflective and transmissive regions, such as a tilting mirror M and an aperture H. In the figures, two positions of the turret are shown, each with a different portion of the aperture H and mirror M in the pupil plane, wherein the aperture defines the contour of the illumination aperture and the mirror M defines the contour of the detection aperture, or vice versa.

[0179] The rotating disk IMW can include many rotational positions, each corresponding to a λ / spacing ratio. For each rotational position, the location and tilt angle of the mirrors M and / or the aperture H will be different, allowing them to be moved to the desired location to define the required illumination and detection aperture profile for a given λ / spacing ratio.

[0180] By providing appropriately different tilt angles for the reflector M section, the imaging mode turret IMW also provides some of the wedge functionality previously described in the current system (i.e., separating orthogonal and complementary orders in the image plane). An illumination mode selector can be used to coordinate with... Figure 5 The illumination is provided in a similar manner as described. However, this results in light loss because the entire NA must be illuminated, and most of it is subsequently blocked by the illumination aperture. To avoid this light loss, this embodiment can be combined with a tiltable reflector in the field plane, as discussed regarding...Figure 18 The method described involves coupling a programmable pupil portion to a fixed small NA illumination beam, thereby avoiding light loss.

[0181] The described arrangement is merely an example, and those skilled in the art of optical design will know how to implement differentiated illumination conditions for subsets of the illumination area in alternative ways.

[0182] It should be noted that the arrangement described above is merely an example of how such a system can be implemented, and different hardware setups are possible. For example, illumination and detection may not even have to pass through the same lens.

[0183] During measurement acquisition, components of the measurement system vary relative to preferred or optimal measurement conditions (e.g., XYZ positioning, illumination / detection aperture profile, center wavelength, bandwidth, intensity, etc.). When such variations with respect to optimal conditions are known (e.g., via direct measurement or prediction), the acquired image can be corrected for these variations, for example, via deconvolution.

[0184] As the throughput of the measurement system increases, placing components after (rapid) movements (e.g., XY traverses of a wafer platform) takes more time. For a measurement sequence, the measurement system is programmed for specific setpoints at the acquisition location. Each scanned component will have its own trajectory during this sequence. Optimizations can be performed to collectively optimize all scanned components and other system limitations. As described above, corrections for component variations during acquisition can then be used to correct for all known variations.

[0185] Measurements can also be collected before and after the ideal acquisition time. These results will be of lower quality due to poorer measurement conditions, but can still be used to obtain relevant information. The measurement results can be weighted using quality KPIs based on the deviation from optimal measurement conditions.

[0186] In all the embodiments described above, the illumination can be temporally modulated (e.g., using modulation within the integral time of measuring a target). This modulation can help increase the number of (spatial) incoherent modes and thus suppress coherence. To implement such modulation, a modulation element, such as a rapidly rotating frosted glass plate, can be implemented within the illumination branch to provide a (temporal) summation of multiple speckle modes.

[0187] Figure 20This is a block diagram illustrating a computer system 1000 that can assist in implementing the methods and processes disclosed herein. The computer system 1000 includes a bus 1002 or other communication mechanism for communicating information, and a processor 1004 (or multiple processors 1004 and 1005) coupled to the bus 1002 for processing information. The computer system 1000 also includes a main memory 1006, such as random access memory (RAM) or other dynamic storage, coupled to the bus 1002 for storing information and instructions to be executed by the processor 1004. The main memory 1006 may also be used to store temporary variables or other intermediate information during the execution of instructions to be executed by the processor 1004. The computer system 1000 also includes a read-only memory (ROM) 1008 or other static storage device coupled to the bus 1002 for storing static information and instructions for the processor 1004. A storage device 1010, such as a magnetic disk or optical disk, is provided and coupled to the bus 1002 for storing information and instructions.

[0188] Computer system 1000 can be coupled via bus 1002 to a display 1012 for displaying information to a computer user, such as a cathode ray tube (CRT), flat panel display, or touch panel display. An input device 1014, including alphanumeric keys and other keys, is coupled to bus 1002 for communicating information and command selections to processor 1004. Another type of user input device is a cursor controller 1016, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to processor 1004 and for controlling cursor movement on display 1012. Such input devices typically have two degrees of freedom on two axes (a first axis (e.g., x) and a second axis (e.g., y)), allowing the device to specify a position in a plane. Touch panel (screen) displays can also be used as input devices.

[0189] One or more of the methods described herein can be executed by computer system 1000 in response to processor 1004 executing one or more sequences of one or more instructions contained in main memory 1006. These instructions can be read into main memory 1006 from another computer-readable medium, such as storage device 1010. Execution of the sequence of instructions contained in main memory 1006 causes processor 1004 to perform the process steps described herein. One or more processors in a multiprocessor arrangement can also be used to execute the sequence of instructions contained in main memory 1006. In alternative embodiments, hardwired circuitry can be used instead of or in combination with software instructions. Therefore, the description herein is not limited to any particular combination of hardware circuitry and software.

[0190] As used herein, the term "computer-readable medium" refers to any medium that participates in providing instructions to processor 1004 for execution. Such media can take many forms, including (but not limited to) non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical discs or magnetic disks, such as storage device 1010. Volatile media include volatile memory, such as main memory 1006. Transmission media include coaxial cables, copper wires, and optical fibers, including wires containing bus 1002. Transmission media can also take the form of sound waves or light waves, such as sound waves or light waves generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, floppy disks, hard disks, magnetic tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, punched cards, paper tapes, any other physical media with a perforated pattern, RAM, PROMs and EPROMs, FLASH-EPROMs, any other memory chips or cartridges, carrier waves as described below, or any other media that can be read by a computer.

[0191] Various forms of computer-readable media may be involved when carrying one or more sequences of instructions to processor 1004 for execution. For example, the instructions may initially be carried on the disk of a remote computer. The remote computer may load the instructions into its volatile memory and transmit the instructions via a telephone line using a modem. A modem local to computer system 1000 may receive data over the telephone line and convert the data into an infrared signal using an infrared transmitter. An infrared detector coupled to bus 1002 may receive the data carried in the infrared signal and place the data on bus 1002. Bus 1002 carries the data to main memory 1006, from which processor 1004 fetches and executes the instructions. The instructions received by main memory 1006 may optionally be stored on storage device 1010 before or after execution by processor 1004.

[0192] Computer system 1000 also preferably includes a communication interface 1018 coupled to bus 1002. Communication interface 1018 provides bidirectional data communication coupled to network link 1020 connected to local area network 1022. For example, communication interface 1018 may be an Integrated Services Digital Network (ISDN) card or modem to provide data communication connectivity to a corresponding type of telephone line. As another example, communication interface 1018 may be a local area network (LAN) card to provide data communication connectivity to a compatible LAN. A wireless link may also be implemented. In any such implementation, communication interface 1018 transmits and receives electrical, electromagnetic, or optical signals carrying digital data streams representing various types of information.

[0193] Network link 1020 typically provides data communication to other data devices via one or more networks. For example, network link 1020 may provide a connection from local area network 1022 to host computer 1024 or to data equipment operated by Internet service provider (ISP) 1026. ISP 1026, in turn, provides data communication services via a global packet data communication network (now commonly referred to as the "Internet") 1028. Both local area network 1022 and Internet 1028 use electrical, electromagnetic, or optical signals that carry digital data streams. Signals via various networks and signals on network link 1020 and via communication interface 1018 (which carry digital data to and from computer system 1000) are exemplary forms of carriers for transmitting information.

[0194] Computer system 1000 can send messages and receive data (including program code) via a network, network link 1020, and communication interface 1018. In an Internet example, server 1030 may transmit requested code for an application via Internet 1028, ISP 1026, local area network 1022, and communication interface 1018. For example, such a downloaded application may provide one or more of the techniques described herein. The received code may be executed by processor 1004 upon receipt and / or stored in storage device 1010 or other non-volatile storage for later execution. In this way, computer system 1000 can obtain application code in carrier form.

[0195] Further embodiments are disclosed in the following enumeration of the numbering:

[0196] 1. A method for measuring a periodic structure on a substrate using illumination radiation having at least one wavelength, the periodic structure having at least one spacing, the method comprising:

[0197] - Configured as one or more of the following based on the ratio of the spacing to the wavelength:

[0198] Irradiation aperture profile, the illumination aperture profile including one or more illumination areas in Fourier space;

[0199] The orientation of the periodic structure used for measurement; and

[0200] The detection aperture profile includes one or more separate detection regions in Fourier space;

[0201] Such that: i) at least one pair of complementary diffraction orders are captured within the detection aperture profile, and ii) the diffraction radiation fills at least 80% of the one or more separate detection regions; and

[0202] - The periodic structure is measured while applying one or more of the configured orientations of the illumination aperture profile, the detection aperture profile, and the periodic structure.

[0203] 2. The method according to aspect 1, wherein the illumination aperture profile includes one or more illumination regions in Fourier space for illuminating the periodic structure from at least two substantially different (e.g., opposite) angular directions, and the detection aperture profile includes at least two separate detection regions in Fourier space for capturing a corresponding diffraction order of the pair of complementary diffraction orders.

[0204] 3. The method according to aspect 2, wherein the illumination aperture profile includes four groups in Fourier space for illuminating one or more illumination regions of the periodic structure from two substantially different (e.g., opposite) angular directions for each of the two periodic orientations of the substructure included within the periodic structure, and the detection aperture profile includes four detection regions in Fourier space for capturing a corresponding diffraction order of the pair of complementary diffraction orders for each of the periodic orientations.

[0205] 4. The method according to aspect 2 or 3, wherein each individual irradiation area in the one or more irradiation areas corresponds to a corresponding detection area in each detection area, and wherein each irradiation area is the same size or larger than its corresponding detection area.

[0206] 5. The method according to aspect 4, wherein each irradiation area is at most 10% larger than its corresponding detection area, or optionally, at most 20% larger, or optionally, at most 30% larger.

[0207] 6. The method according to aspect 2 or 3, wherein the one or more irradiation zones comprise only a single irradiation zone.

[0208] 7. The method according to aspect 6, wherein the single irradiation area includes available Fourier space other than the Fourier space for the detection aperture profile and the boundary portion between the irradiation aperture profile and the detection aperture profile.

[0209] 8. The method according to any one of aspects 2 to 7, wherein each detection zone in the detection zone defines a numerical aperture of not more than 0.4.

[0210] 9. The method according to any of the foregoing aspects, wherein the configuration of the illumination aperture profile includes spatially filtering the illumination radiation in the pupil plane or intermediate plane of the objective lens, or its equivalent plane, to apply the illumination profile.

[0211] 10. The method according to any of the foregoing aspects includes applying different irradiation conditions to at least two different irradiation zones and / or detection zones.

[0212] 11. The method according to any of the foregoing aspects, wherein the irradiation radiation comprises multimode radiation; or temporally and / or spatially incoherent radiation or an approximation thereof.

[0213] 12. The method according to aspect 11, comprising time-modulating the irradiation radiation using modulation within the integral time of the measurement.

[0214] 13. The method according to aspect 12, wherein the modulation is performed by rotating the frosted glass plate sufficiently rapidly within the irradiation radiation to provide a temporal summation of multiple speckle patterns.

[0215] 14. The method according to aspect 11, 12 or 13, including correcting the image of the periodic structure obtained during the measurement.

[0216] 15. The method according to aspect 14, wherein the correction includes correcting the image for aberrations in the sensor optics used to perform the measurement.

[0217] 16. The method according to aspect 15, wherein the correction of the image for aberrations is performed as a correction depending on the image position.

[0218] 17. The method according to aspect 15 or 16, wherein the correction includes performing a convolution of the original image and a correction kernel, wherein the correction kernel is position-dependent.

[0219] 18. The method according to aspect 17, wherein the correction further includes convolution for each of one or more image processing operations.

[0220] 19. The method according to aspects 15, 16, 17 or 18, wherein the correction is applied using a convolutional neural network.

[0221] 20. The method according to any one of aspects 15 to 19, wherein the method comprises: correcting the image to reshape the point spread function for aberrations in the point spread function caused by the sensor optics used to perform the measurement.

[0222] 21. The method according to any one of aspects 15 to 20, wherein the correction comprises reducing crosstalk in the image by computational apodization or similar shaping techniques.

[0223] 22. The method according to any one of aspects 15 to 21 further includes correcting the image for any deviation from optimal measurement conditions.

[0224] 23. The method according to any one of aspects 15 to 22, wherein the aberration includes intentional wavefront modulation aberration, and the method includes correcting for the wavefront modulation aberration in order to increase the usable focusing range and / or field of view depth of the sensor optics.

[0225] 24. The method according to any one of aspects 14 to 23, wherein the correction is based on residual errors determined by one or more of the following: performing measurements on the periodic structure under two opposite rotations to determine residual errors that may be caused by the measurement optics, and imaging the periodic structure under different positioning shifts in the substrate plane to capture the residual errors for field-dependent components.

[0226] 25. The method according to any of the foregoing aspects, wherein the irradiation radiation comprises a wavelength band spanning multiple wavelengths, and the at least one wavelength includes the center wavelength.

[0227] 26. The method according to any of the foregoing aspects, wherein the configuration of the orientation of the periodic structure includes rotating the periodic structure about an optical axis according to the ratio of the spacing to the wavelength.

[0228] 27. The method according to aspect 26, wherein the rotation of the periodic structure is performed by rotating the substrate about the optical axis or by rotating at least a portion of the sensor about the optical axis.

[0229] 28. The method according to aspect 26 or 27, wherein the rotation of the periodic structure enables: an increased region of the detection aperture profile and / or illumination aperture profile; and / or measurability of the increased range of the spacing compared to no rotation, and / or the increased range of the wavelength; and / or better suppression of crosstalk from surrounding structures.

[0230] 29. The method according to any of the foregoing aspects, wherein the illumination aperture profile includes a plurality of illumination zones in Fourier space, the plurality of illumination zones being used to illuminate the periodic structure from at least two substantially different (e.g., opposite) angular directions, and a subset of the illumination zones includes different illumination conditions.

[0231] 30. The method according to aspect 29, wherein the different irradiation conditions include one or more of the following: polarization state, intensity, wavelength, and integration time.

[0232] 31. The method according to aspect 29 or 30, wherein the plurality of irradiation zones comprises two pairs of irradiation zones, each pair comprising the different irradiation conditions.

[0233] 32. The method according to aspect 31, comprising combining the two pairs of irradiation zones using a beam combining device.

[0234] 33. The method according to aspect 32, wherein the beam combining device is a polarization beam splitter.

[0235] 34. The method according to aspect 31, wherein one or more optical elements are placed in the path of one or both of the illumination regions in each pair of illumination regions in the Fourier space to provide the different illumination conditions.

[0236] 35. The method according to any of the foregoing aspects, wherein the diffraction radiation fills at least 80% of the one or more separate detection regions.

[0237] 36. The method according to any of the foregoing aspects, wherein the diffraction radiation from each captured diffraction order is individually imaged in the image plane.

[0238] 37. The method according to any of the foregoing aspects, wherein the diffraction radiation from each captured diffraction order is imaged twice.

[0239] 38. The method according to any of the foregoing aspects includes simultaneously configuring both the illumination aperture profile and the detection aperture profile.

[0240] 39. The method according to aspect 38, wherein the simultaneous configuration step comprises altering one or more optical elements of the paths of at least one pair of the diffraction beams of the diffraction radiation and at least one pair of the illumination beams of the illumination radiation, such that the trajectories of the diffraction beams and the illumination beams are translated and / or shifted in the Fourier space.

[0241] 40. The method according to aspect 39, wherein the one or more optical elements cause them to shift the diffraction beam and the illumination beam in the Fourier space without substantially changing the orientation of the diffraction beam and the illumination beam.

[0242] 41. The method according to aspect 39 or 40, wherein the one or more optical elements comprise a pair of optical wedge elements having a similar configuration for each pair of illumination and diffraction beams but oriented in opposite directions.

[0243] 42. The method according to aspect 39 or 40, wherein the one or more optical elements comprise: an axial pyramidal or conical element and a corresponding disc-shaped element; or

[0244] A zoom lens device, operable to produce a magnified or reduced image in the Fourier space in the (intermediate) pupil plane.

[0245] 43. The method according to any one of aspects 39 to 42, wherein the change to one or more optical elements comprises changing the separation distance between a pair of optical elements.

[0246] 44. The method according to any one of aspects 39 to 42, wherein the change to one or more optical elements comprises changing the aperture angle of the one or more optical elements, wherein the optical elements comprise liquid lens optical elements.

[0247] 45. The method according to aspect 39 or 40, wherein the change to one or more optical elements comprises changing the angle of at least one pair of optical plates.

[0248] 46. ​​The method according to any one of aspects 39 to 45, wherein the one or more optical elements are included within the pupil plane.

[0249] 47. The method according to aspect 39 or 40, wherein the change to one or more optical elements comprises changing the angle of at least one pair of optical mirrors in the field plane or intermediate field plane.

[0250] 48. The method according to any one of aspects 39 to 47, comprising other optical elements for separating the irradiation beam from the diffraction beam prior to detection of the diffraction beam.

[0251] 49. The method according to aspect 38, wherein the change to one or more optical elements comprises positioning reflective and transmissive regions of different configurations in the pupil plane.

[0252] 50. The method according to aspect 49, wherein the positioning of one or more reflective zones and one or more transmissive zones of different configurations in the pupil plane includes changing the orientation and / or position of the imaging mode element comprising the reflective and transmissive zones.

[0253] 51. The method according to any of the foregoing aspects, wherein configuring the irradiation aperture profile includes configuring a central radial aperture size that will only include irradiation radiation.

[0254] 52. The method according to aspect 51 further includes configuring a safety boundary portion for each of the one or more separate detection zones relative to the irradiation aperture profile.

[0255] 53. A measuring device capable of operating to perform the method according to any one of aspects 1 to 52.

[0256] 54. A measuring apparatus for measuring periodic structures on a substrate, the measuring apparatus comprising:

[0257] A detection aperture profile, the detection aperture profile comprising one or more separate detection regions in Fourier space; and

[0258] Irradiation aperture profile, the illumination aperture profile including one or more illumination areas in Fourier space;

[0259] The detection aperture profile, the illumination aperture profile, and the substrate orientation of the substrate including the periodic structure being measured can be configured based on the ratio of at least one spacing of the periodic structure to at least one wavelength of the illumination radiation used to measure the periodic structure, such that:

[0260] i) Capture at least one pair of complementary diffraction steps within the detection aperture profile, and

[0261] ii) The radiation from the pair of complementary diffraction orders fills at least 80% of the one or more separate detection regions.

[0262] 55. The measuring apparatus according to aspect 54, wherein the illumination aperture profile includes one or more illumination regions in Fourier space for illuminating the periodic structure from at least two substantially different (e.g., opposite) angular directions, and the detection aperture profile includes at least two separate detection regions in Fourier space for capturing a corresponding diffraction order of the pair of complementary diffraction orders.

[0263] 56. The measuring apparatus according to aspect 54, wherein the illumination aperture profile includes one or more illumination regions in Fourier space, the one or more illumination regions being used to illuminate the periodic structure from two sets of two substantially different (e.g., opposite) angular directions for each of the two periodic orientations of the substructure included within the periodic structure, and the detection aperture profile includes four separate detection regions in Fourier space, the four separate detection regions being used to capture a corresponding diffraction order of the pair of complementary diffraction orders for each of the periodic orientations.

[0264] 57. The measuring apparatus according to aspect 55 or 56 includes separate irradiation areas corresponding to a corresponding detection area in each detection area, wherein each irradiation area is the same size or larger than its corresponding detection area.

[0265] 58. The measuring device according to aspect 57, wherein each irradiation area is at most 10% larger than its corresponding detection area, or optionally, at most 20% larger, or optionally, at most 30% larger.

[0266] 59. The measuring apparatus according to aspect 55 or 56, wherein the one or more irradiation zones comprise only a single irradiation zone.

[0267] 60. The measuring apparatus according to aspect 59, wherein the single irradiation area includes a Fourier space for the detection aperture profile and an available Fourier space outside the boundary portion between the irradiation aperture profile and the detection aperture profile.

[0268] 61. The measuring apparatus according to any one of aspects 55 to 60, wherein each detection zone in the detection zone defines a numerical aperture not greater than 0.4.

[0269] 62. The measuring apparatus according to any one of aspects 55 to 61, comprising a detection mirror or other optical element, wherein each of the detection mirror or other optical element defines the position and aperture of a corresponding detection area in the detection area.

[0270] 63. The measuring apparatus according to any one of aspects 54 to 62 further includes a spatial filter for applying the illumination aperture profile by filtering the illumination radiation in the pupil plane or intermediate plane of the objective lens, or its equivalent plane.

[0271] 64. The measuring device according to aspect 63, wherein the spatial filter can be physically replaced depending on the ratio of spacing to wavelength.

[0272] 65. The measuring apparatus according to aspect 64, wherein a plurality of spatial filters are mounted on a filter turntable.

[0273] 66. The measuring apparatus according to aspect 63, wherein the spatial filter includes a programmable spatial light modulator.

[0274] 67. The measuring apparatus according to any one of aspects 54 to 62, comprising an irradiation source having a configurable irradiation profile to apply the irradiation aperture profile.

[0275] 68. The measuring device according to any one of aspects 54 to 67, wherein the measuring device is operable to apply different irradiation conditions to at least two different irradiation zones and / or detection zones.

[0276] 69. The measuring apparatus according to any one of aspects 54 to 68, wherein the irradiation radiation comprises multimode radiation; or incoherent radiation or an approximation thereof.

[0277] 70. The measuring apparatus according to aspect 69, comprising a modulation element for time-modulating the irradiation radiation using modulation within the integral time of the measurement.

[0278] 71. The measuring apparatus according to aspect 70, wherein the modulation element comprises a rotatable frosted glass plate.

[0279] 72. The measuring apparatus according to any one of aspects 54 to 71, comprising a processor configured to correct an image of the periodic structure acquired during the measurement.

[0280] 73. The measuring apparatus according to aspect 72, wherein the processor is operable to correct the image for aberrations in the sensor optics used to perform the measurement.

[0281] 74. The measuring apparatus according to aspect 73, wherein the processor is operable to correct the image for aberrations, the correction being a correction dependent on the image position.

[0282] 75. The measurement apparatus according to aspect 73 or 74, wherein the processor is operable to perform the correction via convolution of the original image and a correction kernel, wherein the correction kernel is position-dependent.

[0283] 76. The measurement apparatus according to aspect 75, wherein the processor is operable to perform the correction as a convolution for each of one or more image processing operations.

[0284] 77. The measuring apparatus according to any one of aspects 73 to 76, wherein the processor is configured to perform the correction using a convolutional neural network.

[0285] 78. The measuring apparatus according to any one of aspects 73 to 77, wherein the processor is further operable to correct the image to reshape the point spread function for aberrations in the point spread function caused by the sensor optics used to perform the measurement.

[0286] 79. The measuring apparatus according to any one of aspects 73 to 78, wherein the processor is further operable to correct the image for any deviation from optimal measurement conditions.

[0287] 80. The measuring apparatus according to any one of aspects 73 to 79, wherein the aberration includes intentional wavefront modulation aberration, and the processor is further configured to correct for the wavefront modulation aberration in order to increase the usable focusing range and / or field of view depth of the sensor.

[0288] 81. The measuring apparatus according to any one of aspects 72 to 80, wherein the processor is operable to reduce crosstalk in the image by computational apodization or similar shaping techniques.

[0289] 82. The measuring apparatus according to any one of aspects 72 to 81, wherein the measuring apparatus is operable to perform the correction based on residual errors determined by one or more of the following: performing measurements on a periodic structure in two opposite rotations to determine residual errors that may be caused by measuring optics, and imaging the periodic structure under different positioning shifts in the substrate plane to capture the residual errors for field-dependent components.

[0290] 83. The measuring apparatus according to any one of aspects 54 to 82, wherein the irradiation radiation comprises a wavelength band spanning multiple wavelengths, and the at least one wavelength includes the center wavelength.

[0291] 84. The measuring apparatus according to any one of aspects 54 to 83, comprising a substrate support for holding the substrate, the substrate support being rotatable about its optical axis, the measuring apparatus being operable to configure the substrate orientation at least in part by rotating the substrate about the optical axis according to the ratio of the spacing to the wavelength or by rotating at least a portion of the sensor about the optical axis.

[0292] 85. The measuring apparatus according to aspect 84, wherein the rotation of the substrate enables the measurement of: an increased region of the detection aperture profile and / or the illumination aperture profile; and / or the measurability of the increased range of the spacing compared to no rotation, and / or the increased range of the wavelength.

[0293] 86. The measuring apparatus according to any one of aspects 54 to 85, comprising an irradiation source for providing the irradiation radiation.

[0294] 87. The measuring apparatus according to any of the foregoing aspects, wherein the illumination aperture profile includes a plurality of illumination zones in Fourier space, the plurality of illumination zones being used to illuminate the periodic structure from at least two substantially opposite angular directions, and a subset of the illumination zones including different illumination conditions.

[0295] 88. The measuring apparatus according to aspect 87, wherein the different irradiation conditions include one or more of the following: polarization state, intensity, wavelength, and integration time.

[0296] 89. The measuring device according to aspect 87 or 88, wherein the plurality of irradiation zones comprises two pairs of irradiation zones, each pair comprising the different irradiation conditions.

[0297] 90. The measuring apparatus according to aspect 89, comprising a beam combining device operable to combine the two pairs of irradiation zones.

[0298] 91. The measuring device according to aspect 90, wherein the beam combining device is a polarization beam splitter.

[0299] 92. The measuring device according to aspect 89, comprising one or more optical elements in the path of one or both of the illumination regions in each pair of illumination regions in the Fourier space for providing the different illumination conditions.

[0300] 93. The measuring apparatus according to any one of aspects 54 to 92, wherein the diffraction radiation fills 100% of the one or more separate detection regions.

[0301] 94. The measuring apparatus according to any one of aspects 54 to 93, comprising an optical element operable such that diffraction radiation from each captured diffraction order is individually imaged in an image plane.

[0302] 95. The measuring apparatus according to any one of aspects 54 to 94, wherein the measuring apparatus is operable such that the diffraction radiation from each captured diffraction order is imaged twice.

[0303] 96. The measuring device according to any one of aspects 54 to 95, wherein the measuring device is arranged for simultaneous measurement of both the irradiation aperture profile and the detection aperture profile.

[0304] 97. The measuring apparatus according to aspect 96, wherein the optical element comprising one or more optical elements in the paths of at least one pair of diffraction beams of the diffraction radiation and at least one pair of illumination beams of the illumination radiation, the one or more optical elements being variable such that the trajectories of the diffraction beams and the illumination beams are translated and / or shifted in the Fourier space.

[0305] 98. The measuring apparatus according to aspect 97, wherein the one or more optical elements together cause the diffraction beam and the illumination beam to be shifted in the Fourier space without substantially changing the orientation of the diffraction beam and the illumination beam.

[0306] 99. The measuring apparatus according to aspect 97 or 98, wherein the one or more optical elements comprise a pair of optical wedge elements having a similar configuration for each pair of illumination and diffraction beams but oriented in opposite directions.

[0307] 100. The measuring apparatus according to aspect 97 or 98, wherein the one or more optical elements comprise: an axial pyramid or conical element and a corresponding disc element; or a zoom lens device operable to produce a magnified or reduced image of the Fourier space in the (intermediate) pupil plane.

[0308] 101. The measuring apparatus according to any one of aspects 97 to 100, wherein the one or more optical elements include a variable separation distance between a pair of optical elements, the variation of the variable separation distance simultaneously configuring both the illumination aperture profile and the detection aperture profile.

[0309] 102. The measuring apparatus according to any one of aspects 97 to 100, wherein the optical element comprises a liquid lens optical element, and at least one of the one or more optical elements comprises a variable aperture angle, the variation of which simultaneously configures both the illumination aperture profile and the detection aperture profile.

[0310] 103. The measuring apparatus according to aspect 97 or 98, wherein the one or more optical elements comprise at least one pair of optical plates, wherein a change in the angle of each of the at least one pair of optical plates simultaneously configures both the illumination aperture profile and the detection aperture profile.

[0311] 104. The measuring apparatus according to any one of aspects 97 to 103, wherein the one or more optical elements are included within the pupil plane of the measuring apparatus.

[0312] 105. The measuring apparatus according to aspect 97 or 98, wherein the one or more optical elements comprise at least a pair of optical mirrors in the field plane or intermediate field plane of the measuring apparatus, wherein a change in the angle of each of the at least one pair of optical mirrors simultaneously configures both the illumination aperture profile and the detection aperture profile.

[0313] 106. The measuring apparatus according to any one of aspects 97 to 105, comprising other optical elements for separating the irradiation beam from the diffraction beam prior to detection of the diffraction beam.

[0314] 107. The measuring apparatus according to aspect 96, comprising an imaging mode element in the pupil plane of the measuring apparatus, the imaging mode element comprising one or more reflective regions and one or more transmissive regions, the imaging mode element being arranged such that changing its orientation and / or position simultaneously configures both the illumination aperture profile and the detection aperture profile.

[0315] 108. The measuring apparatus according to any one of aspects 54 to 107, wherein the irradiation aperture profile can be configured to define a central radial numerical aperture size that will only include irradiation radiation.

[0316] 109. The measuring device according to aspect 108 further includes a configurable safety boundary portion of each of the one or more separate detection zones relative to the contour of the irradiation aperture.

[0317] 110. A measuring apparatus for measuring a periodic structure located on a substrate and having at least one periodic spacing using illumination radiation having at least one wavelength, the measuring apparatus comprising:

[0318] A substrate support for holding the substrate, the substrate support being rotatable about its optical axis, and the measuring device being operable to optimize the irradiation aperture profile by rotating the substrate about the optical axis according to the ratio of spacing to wavelength.

[0319] 111. The measuring apparatus according to aspect 109, wherein the rotation of the substrate enables the measurement of: an increased region of the detection aperture profile and / or the illumination aperture profile; and / or the measurability of an increased range of the spacing compared to no rotation, and / or an increased range of the wavelength.

[0320] While specific references can be made to the use of lithography equipment in IC manufacturing within this document, it should be understood that the lithography equipment described herein can have other applications. Possible other applications include manufacturing integrated optical systems, guiding and testing for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, and so on.

[0321] While specific reference may be made herein to embodiments of the invention in the context of inspection or measurement equipment, embodiments of the invention can be used in other equipment. Embodiments of the invention can form part of a mask inspection apparatus, a lithography apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning apparatuses). The term "measurement equipment" can also refer to inspection equipment or inspection systems. For example, an inspection apparatus including embodiments of the invention can be used to detect defects in a substrate or defects in a structure on a substrate. In such embodiments, the characteristics of interest regarding the structure on the substrate may relate to defects in the structure, the absence of a specific portion of the structure, or the presence of an unwanted structure on the substrate.

[0322] While specifically referring to "measuring equipment / tools / systems" or "inspection equipment / tools / systems," these terms can refer to the same or similar types of tools, equipment, or systems. For example, inspection or measuring equipment including embodiments of the present invention can be used to determine the characteristics of a structure on a substrate or on a wafer. For example, inspection or measuring equipment including embodiments of the present invention can be used to detect defects in the substrate or defects in a structure on the substrate or on a wafer. In such embodiments, the characteristics of interest concerning the structure on the substrate may relate to defects in the structure, the absence of a specific portion of the structure, or the presence of unwanted structures on the substrate or on the wafer.

[0323] While the foregoing may have specifically referenced the use of embodiments of the invention in the context of optical lithography, it should be understood that the invention is not limited to optical lithography and can be used in other applications (e.g., imprint lithography) where circumstances permit.

[0324] While the targets or target structures described above (more generally, structures on a substrate) are measurement target structures specifically designed and formed for measurement purposes, in other embodiments, properties of interest can be measured on one or more structures of a functional portion of a device formed on a substrate. Many devices have regular grating-like structures. As used herein, the terms structure, target grating, and target structure do not require that the structure be specifically provided for the measurement being performed. Furthermore, the spacing P of the measurement targets can be close to or possibly smaller than the resolution limit of the scatterer's optical system, but can be much larger than the dimensions of a typical product feature fabricated by a photolithography process in the target portion C. In practice, the lines and / or spaces of overlapping gratings within the target structure can be comprised of smaller structures that are similar in size to product features.

[0325] While specific embodiments of the invention have been described above, it will be understood that the invention can be practiced in other ways than those described. The description above is intended to be illustrative and not restrictive. Therefore, those skilled in the art will understand that modifications can be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A method for measuring a periodic structure on a substrate using illumination radiation having at least one wavelength, the periodic structure having at least one spacing, the method comprising: - Configure one or more of the following items based on the ratio of the spacing to the wavelength: Irradiation aperture profile, the illumination aperture profile including one or more illumination areas in Fourier space; The orientation of the periodic structure used for measurement; and The detection aperture profile includes one or more separate detection regions in Fourier space; Such that: i) at least one pair of complementary diffraction orders are captured within the detection aperture profile, and ii) the diffraction radiation fills at least 80% of the one or more separate detection regions; and -Measuring the periodic structure while simultaneously applying one or more of the configured orientations of the illumination aperture profile, the detection aperture profile, and the periodic structure. The one or more irradiation areas are separated from the one or more separate detection areas in the Fourier space; and The one or more irradiated areas are larger than the one or more separate detection areas.

2. The method according to claim 1, wherein, The illumination aperture profile includes one or more illumination regions in Fourier space for illuminating the periodic structure from at least two substantially different angular directions, and the detection aperture profile includes at least two separate detection regions in Fourier space for capturing a corresponding diffraction order of the pair of complementary diffraction orders.

3. The method according to claim 2, wherein, The illumination aperture profile includes two sets of illumination regions in Fourier space for illuminating the one or more illumination regions of the periodic structure from two substantially different angular directions for each of the two periodic orientations of the substructure included within the periodic structure, and the detection aperture profile includes four detection regions in Fourier space for capturing a corresponding diffraction order of the pair of complementary diffraction orders for each of the periodic orientations.

4. The method according to claim 2 or 3, wherein, Each individual irradiation zone in the one or more irradiation zones corresponds to a corresponding detection zone in each detection zone, and each irradiation zone is the same size or larger than its corresponding detection zone.

5. The method according to claim 4, wherein, Each irradiated area is up to 10% larger than its corresponding detection area.

6. The method according to claim 2 or 3, wherein, The one or more irradiation zones include only a single irradiation zone.

7. The method according to claim 6, wherein, The single irradiation area includes the available Fourier space other than the Fourier space used for the detection aperture profile and the boundary portion between the irradiation aperture profile and the detection aperture profile.

8. The method according to claim 2, wherein, Each detection zone in the detection zone is defined with a numerical aperture not greater than 0.

4.

9. The method according to claim 1, wherein, The configuration of the illumination aperture profile includes spatially filtering the illumination radiation in the pupil plane or intermediate plane of the objective lens, or its equivalent plane, to apply the illumination aperture profile.

10. The method of claim 1, further comprising applying different irradiation conditions to at least two different irradiation zones and / or detection zones.

11. The method according to claim 1, wherein, The irradiation includes multimode radiation; or temporally and / or spatially incoherent radiation or its approximations.

12. The method of claim 11, further comprising time-modulating the irradiation radiation using modulation within the integral time of the measurement.

13. The method according to claim 12, wherein, The modulation is performed by rotating the frosted glass plate sufficiently quickly within the irradiation to provide a temporal summation of multiple speckle patterns.

14. The method of claim 11, 12 or 13, further comprising correcting an image of the periodic structure obtained during the measurement.

15. The method according to claim 14, wherein, The correction includes correcting the image for aberrations in the sensor optics used to perform the measurement.

16. The method according to claim 15, wherein, The correction of the image for aberrations is performed based on the image position.

17. The method according to claim 15, wherein, The correction involves performing a convolution on the original image and a correction kernel, wherein the correction kernel is location-dependent.

18. The method according to claim 17, wherein, The correction also includes convolution for each of one or more image processing operations.

19. The method according to claim 15, wherein, The correction is applied using a convolutional neural network.

20. The method of claim 15, wherein, The method includes: correcting the image to reshape the point spread function for aberrations caused by the sensor optics used to perform the measurement.

21. The method according to claim 15, wherein, The correction includes reducing crosstalk in the image by computational apodization or similar shaping techniques.

22. The method of claim 15, further comprising correcting the image for any deviation from optimal measurement conditions.

23. The method according to claim 15, wherein, The aberrations include intentional wavefront modulation aberrations, and the method includes correcting for the wavefront modulation aberrations in order to increase the usable focusing range and / or field of view of the sensor optics.

24. The method according to claim 14, wherein, The correction is based on residual errors determined by one or more of the following: performing measurements on the periodic structure under two opposite rotations to determine residual errors that may be caused by the measurement optics, and imaging the periodic structure under different positioning shifts in the substrate plane to capture the residual errors for field-dependent components.

25. The method according to claim 1, wherein, The irradiation includes a wavelength band spanning multiple wavelengths, and the at least one wavelength includes a center wavelength.

26. The method according to claim 1, wherein, The configuration of the orientation of the periodic structure includes rotating the periodic structure about the optical axis according to the ratio of the spacing to the wavelength.

27. The method according to claim 15, wherein, The configuration of the orientation of the periodic structure includes rotating the periodic structure about the optical axis according to the ratio of the spacing to the wavelength.

28. The method according to claim 26, wherein, The rotation of the periodic structure is performed by rotating the substrate around the optical axis.

29. The method according to claim 27, wherein, The rotation of the periodic structure is performed by rotating at least a portion of the sensor optics about the optical axis.

30. The method according to any one of claims 26 to 29, wherein, The rotation of the periodic structure enables: an increased area of ​​the detection aperture profile and / or illumination aperture profile; and / or measurability of the increased range of the spacing compared to no rotation, and / or the increased range of the wavelength; and / or better suppression of crosstalk from surrounding structures.

31. The method according to claim 1, wherein, The aperture profile includes multiple illumination zones in Fourier space, which are used to illuminate the periodic structure from at least two substantially different angular directions, and a subset of the illumination zones includes different illumination conditions.

32. The method according to claim 31, wherein, The different irradiation conditions include one or more of the following: polarization state, intensity, wavelength, and integration time.

33. The method according to claim 31 or 32, wherein, The plurality of irradiation zones includes two pairs of irradiation zones, each pair including the different irradiation conditions.

34. The method of claim 33, further comprising combining the two pairs of irradiation zones using a beam combining device.

35. The method according to claim 34, wherein, The beam combining device is a polarization beam splitter.

36. The method according to claim 33, wherein, One or more optical elements are placed in the path of one or both of the illumination zones in each pair of illumination zones in the Fourier space to provide the different illumination conditions.

37. The method according to claim 1, wherein, The diffraction radiation fills at least 80% of the one or more separate detection regions.

38. The method according to claim 1, wherein, The diffraction radiation from each captured diffraction order is imaged individually in the image plane.

39. The method according to claim 1, wherein, The diffraction radiation from each captured diffraction order is imaged twice.

40. The method of claim 1, further comprising simultaneously configuring both the illumination aperture profile and the detection aperture profile.

41. The method according to claim 40, wherein, The simultaneous configuration step includes altering one or more optical elements of the paths of at least one pair of diffraction beams of the diffraction radiation and at least one pair of illumination beams of the illumination radiation, such that the trajectories of the diffraction beams and the illumination beams are translated and / or shifted in the Fourier space.

42. The method according to claim 41, wherein, The one or more optical elements cause them to shift the diffraction beam and the illumination beam in the Fourier space without substantially changing the orientation of the diffraction beam and the illumination beam.

43. The method according to claim 41 or 42, wherein, The one or more optical elements include a pair of optical wedge elements, which have a similar configuration for each pair of illumination and diffraction beams but are oriented in opposite directions.

44. The method according to claim 41 or 42, wherein, The one or more optical elements include: an axial pyramid or conical element and a corresponding disc element; or A zoom lens device, operable to produce a magnified or reduced image in the Fourier space in the pupil plane.

45. The method according to claim 41, wherein, The change to one or more optical elements includes changing the separation distance between a pair of optical elements.

46. ​​The method according to claim 41, wherein, The change to one or more optical elements includes changing the aperture angle of the one or more optical elements, wherein the optical elements include liquid lens optical elements.

47. The method according to claim 41 or 42, wherein, The change to one or more optical elements includes changing the angle of at least one pair of optical plates.

48. The method according to claim 41, wherein, The one or more optical elements are included within the pupil plane.

49. The method according to claim 41 or 42, wherein, The change to one or more optical elements includes changing the angle of at least one pair of optical mirrors in the field plane or intermediate field plane.

50. The method of claim 41, further comprising other optical elements for separating the illumination beam from the diffraction beam prior to detection of the diffraction beam.

51. The method according to claim 41, wherein, The changes to one or more optical elements include positioning reflective and transmissive regions with different configurations in the pupil plane.

52. The method according to claim 51, wherein, The positioning of one or more reflective zones and one or more transmissive zones in the pupil plane with different configurations includes changing the orientation and / or position of the imaging mode element containing the reflective and transmissive zones.

53. The method according to claim 1, wherein, The configuration of the irradiation aperture profile includes configuring the center radial aperture size that will only include the irradiation radiation.

54. The method of claim 53, further comprising configuring a safety boundary portion relative to the irradiation aperture profile for each of the one or more separate detection zones.

55. A measuring device capable of operating to perform the method according to any one of claims 1 to 54.

56. A measuring apparatus for measuring periodic structures on a substrate, the measuring apparatus comprising: One or more optical elements are configured to provide a detection aperture profile, the detection aperture profile comprising one or more separate detection regions in Fourier space; An illumination source is configured to provide an illumination aperture profile, the illumination aperture profile comprising one or more illumination regions in Fourier space; and A substrate support is configured to orient a substrate including a periodic structure. The detection aperture profile, the illumination aperture profile, and the substrate orientation of the substrate including the periodic structure being measured can be configured based on the ratio of at least one spacing of the periodic structure to at least one wavelength of the illumination radiation used to measure the periodic structure, such that: i) Capture at least one pair of complementary diffraction steps within the detection aperture profile, and ii) The radiation from the pair of complementary diffraction orders fills at least 80% of the one or more separate detection regions. The one or more irradiation areas are separated from the one or more separate detection areas in the Fourier space; and The one or more irradiated areas are larger than the one or more separate detection areas.

57. The measuring device according to claim 56, wherein, The illumination aperture profile includes one or more illumination regions in Fourier space for illuminating the periodic structure from at least two substantially different angular directions, and the detection aperture profile includes at least two separate detection regions in Fourier space for capturing a corresponding diffraction order of the pair of complementary diffraction orders.

58. The measuring device according to claim 57, wherein, The illumination aperture profile includes one or more illumination regions in Fourier space, the one or more illumination regions being used to illuminate the periodic structure from two sets of two substantially different angular directions for each of two periodic orientations of the substructure included within the periodic structure, and the detection aperture profile includes four separate detection regions in Fourier space, the four separate detection regions being used to capture a corresponding diffraction order of the pair of complementary diffraction orders for each of the periodic orientations.

59. The measuring apparatus according to claim 57 or 58, comprising a separate irradiation area corresponding to a corresponding detection area in each detection area, and wherein, Each irradiated area is the same size or larger than its corresponding detection area.

60. The measuring device according to claim 59, wherein, Each irradiated area is up to 10% larger than its corresponding detection area.

61. The measuring device according to claim 57 or 58, wherein, The one or more irradiation zones include only a single irradiation zone.

62. The measuring device according to claim 61, wherein, The single irradiation area includes the Fourier space for the detection aperture profile and the available Fourier space outside the boundary between the irradiation aperture profile and the detection aperture profile.

63. The measuring device according to claim 57, wherein, Each detection zone in the detection zone is defined with a numerical aperture not greater than 0.

4.

64. The measuring apparatus of claim 57, comprising a detection mirror or other optical element, wherein each of the detection mirror or other optical element defines the position and aperture of a corresponding detection area in the detection area.

65. The measuring apparatus of claim 56 further includes a spatial filter for applying the illumination aperture profile by filtering the illumination radiation in the pupil plane or intermediate plane of the objective lens, or its equivalent plane.

66. The measuring device according to claim 65, wherein, The spatial filter can be physically replaced depending on the ratio of spacing to wavelength.

67. The measuring device according to claim 66, wherein, Multiple spatial filters are mounted on a filter turntable.

68. The measuring device according to claim 65, wherein, The spatial filter includes a programmable spatial light modulator.

69. The measuring apparatus of claim 56, comprising an irradiation source having a configurable irradiation profile to apply the irradiation aperture profile.

70. The measuring device according to claim 56, wherein the measuring device is operable to apply different irradiation conditions to at least two different irradiation zones and / or detection zones.

71. The measuring device according to claim 56, wherein, The irradiation includes multimode radiation; or incoherent radiation or its approximations.

72. The measuring apparatus of claim 71, comprising a modulation element for time-modulating the irradiation radiation using modulation within the integral time of the measurement.

73. The measuring device according to claim 72, wherein, The modulation element includes a rotatable frosted glass plate.

74. The measuring apparatus of claim 56, comprising a processor configured to correct an image of the periodic structure acquired during the measurement.

75. The measuring device according to claim 74, wherein, The processor is operable to correct the image for aberrations in the sensor optics used to perform the measurement.

76. The measuring device according to claim 75, wherein, The processor is operable to correct the image for aberrations, the correction being position-dependent.

77. The measuring device according to claim 75 or 76, wherein, The processor is operable to perform the correction via convolution of the original image and a correction kernel, wherein the correction kernel is location-dependent.

78. The measuring device according to claim 77, wherein, The processor is operable to perform the correction as a convolution for each of one or more image processing operations.

79. The measuring device according to claim 75, wherein, The processor is configured to perform the correction using a convolutional neural network.

80. The measuring device according to claim 75, wherein, The processor is also operable to correct the image to reshape the point spread function in response to aberrations in the point spread function caused by the sensor optics used to perform the measurement.

81. The measuring device according to claim 75, wherein, The processor is also capable of operating to correct the image for any deviation from optimal measurement conditions.

82. The measuring device according to claim 75, wherein, The aberrations include intentional wavefront modulation aberrations, and the processor is also configured to correct for the wavefront modulation aberrations in order to increase the usable focusing range and / or field of view of the sensor optics.

83. The measuring device according to claim 74, wherein, The processor is capable of operating to reduce crosstalk in the image by computational apodization or similar shaping techniques.

84. The measurement apparatus of claim 74, wherein the measurement apparatus is operable to perform the correction based on residual errors determined by one or more of the following: performing measurements on the periodic structure in two opposite rotations to determine residual errors that may be caused by the measurement optics, and imaging the periodic structure under different positioning shifts in the substrate plane to capture the residual errors for field-dependent components.

85. The measuring device according to claim 56, wherein, The irradiation includes a wavelength band spanning multiple wavelengths, and the at least one wavelength includes a center wavelength.

86. The measurement apparatus of claim 56, comprising a substrate support for holding the substrate, the substrate support being rotatable about its optical axis, the measurement apparatus being operable to configure the substrate orientation at least in part by rotating the substrate about the optical axis according to the ratio of the spacing to the wavelength.

87. The measurement apparatus of claim 75, comprising a substrate support for holding the substrate, the substrate support being rotatable about its optical axis, the measurement apparatus being operable to configure the substrate orientation at least partially by rotating at least a portion of the sensor optics about the optical axis according to the ratio of the spacing to the wavelength.

88. The measuring device according to claim 86 or 87, wherein, The rotation of the substrate enables the following: an increased area of ​​the detection aperture profile and / or illumination aperture profile; and / or measurability of the increased range of the spacing compared to no rotation; and / or the increased range of the wavelength.

89. The measuring apparatus according to any one of claims 56 to 88, comprising an irradiation source for providing the irradiation radiation.

90. The measuring device according to claim 56, wherein, The aperture profile includes multiple illumination zones in Fourier space, which are used to illuminate the periodic structure from at least two substantially opposite angular directions, and a subset of the illumination zones includes different illumination conditions.

91. The measuring device according to claim 90, wherein, The different irradiation conditions include one or more of the following: polarization state, intensity, wavelength, and integration time.

92. The measuring device according to claim 90 or 91, wherein, The plurality of irradiation zones includes two pairs of irradiation zones, each pair including the different irradiation conditions.

93. The measuring apparatus of claim 92, further comprising a beam combining device operable to combine the two pairs of irradiation zones.

94. The measuring device according to claim 93, wherein, The beam combining device is a polarization beam splitter.

95. The measuring apparatus of claim 92, comprising one or more optical elements in the path of one or both of the illumination regions in each pair of illumination regions in the Fourier space for providing the different illumination conditions.

96. The measuring apparatus of claim 56, wherein the diffraction radiation fills 100% of the one or more separate detection zones.

97. The measuring apparatus of claim 56, comprising an optical element operable such that diffraction radiation from each captured diffraction order is individually imaged in an image plane.

98. The measuring apparatus of claim 56, wherein the measuring apparatus is operable such that the diffraction radiation from each captured diffraction order is imaged twice.

99. The measuring device according to claim 56, wherein the measuring device is arranged for simultaneous measurement of both the irradiation aperture profile and the detection aperture profile.

100. The measuring device according to claim 99, wherein, The optical elements included simultaneously in the paths of at least one pair of diffraction beams of the diffraction radiation and at least one pair of illumination beams of the illumination radiation, wherein the one or more optical elements are variable such that the trajectories of the diffraction beams and the illumination beams are translated and / or shifted in the Fourier space.

101. The measuring device according to claim 100, wherein, The one or more optical elements together cause the diffraction beam and the illumination beam to shift in the Fourier space without substantially changing the orientation of the diffraction beam and the illumination beam.

102. The measuring device according to claim 100 or 101, wherein, The one or more optical elements include a pair of optical wedge elements, which have a similar configuration for each pair of illumination and diffraction beams but are oriented in opposite directions.

103. The measuring device according to claim 100 or 101, wherein, The one or more optical elements include: an axial pyramid or conical element and a corresponding disc element; or A zoom lens device, operable to produce a magnified or reduced image in the Fourier space in the pupil plane.

104. The measuring device according to claim 100, wherein, The one or more optical elements include a variable separation distance between a pair of optical elements, the variation of which simultaneously configures both the illumination aperture profile and the detection aperture profile.

105. The measuring device according to claim 100, wherein, The optical element includes a liquid lens optical element, and at least one of the one or more optical elements includes a variable aperture angle, the variation of which simultaneously configures both the illumination aperture profile and the detection aperture profile.

106. The measuring device according to claim 100 or 101, wherein, The one or more optical elements include at least one pair of optical plates, wherein the angle variation of each of the at least one pair of optical plates simultaneously configures both the illumination aperture profile and the detection aperture profile.

107. The measuring device according to claim 100, wherein, The one or more optical elements are included within the pupil plane of the measuring device.

108. The measuring device according to claim 100 or 101, wherein, The one or more optical elements include at least one pair of optical mirrors in the field plane or intermediate field plane of the measuring device, wherein the angle of each of the at least one pair of optical mirrors simultaneously configures both the illumination aperture profile and the detection aperture profile.

109. The measuring apparatus of claim 100, further comprising other optical elements for separating the illumination beam from the diffraction beam prior to detection of the diffraction beam.

110. The measuring apparatus of claim 99, comprising an imaging mode element in the pupil plane of the measuring apparatus, the imaging mode element comprising one or more reflective regions and one or more transmissive regions, the imaging mode element being arranged such that changing its orientation and / or position simultaneously configures both the illumination aperture profile and the detection aperture profile.

111. The measuring device according to claim 56, wherein, The aperture profile can be configured to define a central radial numerical aperture size that includes only the irradiated radiation.

112. The measuring apparatus of claim 111, further comprising a configurable safety boundary portion of each of the one or more separate detection zones relative to the irradiation aperture profile.

113. A measuring apparatus for measuring a periodic structure located on a substrate and having at least one periodic spacing using illumination radiation having at least one wavelength, the measuring apparatus comprising: A substrate support for holding the substrate, the substrate support being rotatable about its optical axis, and the measuring device being operable to optimize the irradiation aperture profile by rotating the substrate about the optical axis according to the ratio of spacing to wavelength.

114. The measuring device according to claim 112, wherein, The substrate is rotated to enable: an increased area of ​​the detection aperture profile and / or illumination aperture profile; and / or measurability of the increased range of the spacing compared to no rotation, and / or the increased range of the wavelength.

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