Method and assembly for wavelength calibration

Abstract

An assembly and method for wavelength calibration of radiation. The assembly includes one or more spectrometers configured to measure a first radiation spectrum of the radiation. The assembly then measures a second radiation spectrum when a gas is present in the propagation path of the radiation. The gas has an absorption line overlapping at least one wavelength of the radiation. The assembly optionally also includes a processor configured to determine a wavelength calibration of the one or more spectrometers based on a difference between the second radiation spectrum and the first radiation spectrum.

Description

Methods and components for wavelength calibration

[0001] Cross-references to related applications

[0002] This application claims priority to European application 23201419.1, filed October 3, 2023; European application 23210087.5, filed November 15, 2023; European application 24150712.8, filed January 8, 2024; and European application 24166360.8, filed March 26, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to methods and components for wavelength calibration of one or more spectrometers in a measuring apparatus. In particular, it relates to absolute wavelength calibration using gas absorption lines for short-wavelength applications. Background Technology

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

[0005] To project a pattern onto a substrate, photolithography equipment can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the feature that can be formed on the substrate. Typical wavelengths currently used are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Compared to photolithography equipment using radiation with a wavelength of, for example, 193 nm, photolithography equipment using extreme ultraviolet (EUV) radiation with wavelengths in the range of 4 nm to 20 nm (e.g., 6.7 nm or 13.5 nm) can be used to form smaller features on the substrate.

[0006] Low-k1 lithography can be used to process features smaller than the classical resolution limit of lithography equipment. In such a process, the resolution can be expressed as CD = k1 × λ / NA, where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection optics in the lithography equipment, CD is the "critical size" (typically the smallest feature size printed, but in this case, half a pitch), and k1 is an empirical resolution factor. Generally, the smaller k1 is, the more difficult it is to reproduce patterns on the substrate that resemble the shape and size planned by the circuit designer to achieve specific electrical functionality and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithography projection equipment and / or design layout. These steps include, for example, but not limited to, optimization of NA, custom illumination schemes, use of phase-shifting patterning apparatus, various optimizations of the design layout such as optical proximity correction (OPC, sometimes also called "optical and process correction"), or other methods generally defined as "resolution enhancement techniques" (RET). Alternatively, a tight control loop used to control the stability of the lithography equipment can be used to improve pattern reproduction at low k1.

[0007] In photolithography and other manufacturing processes, it is desirable to frequently measure the resulting structures, for example, for process control and verification. Various tools are known for performing these measurements, including scanning electron microscopes, often used to measure critical dimensions (CD), and specialized tools for measuring overlap (the alignment accuracy of two layers in a device). Recently, various forms of scattering instruments have been developed for use in the field of photolithography.

[0008] The manufacturing process can be, for example, photolithography, etching, deposition, chemical mechanical planarization, oxidation, ion implantation, diffusion, or a combination of two or more of these.

[0009] Examples of known scatterers often rely on the provision of a dedicated measurement target. For instance, the method might require a target in the form of a simple grating, large enough that the measurement beam produces a spot smaller than the grating (i.e., grating underfill). In so-called reconstruction methods, the properties of the grating can be calculated by simulating the interaction between the scattered radiation and a mathematical model of the target structure. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0010] Besides measuring feature shapes via reconstruction, such devices can also be used to measure diffraction-based overlap, as described in published patent application US2006066855A1. Diffraction-based overlap measurement using dark-field imaging of diffraction orders enables overlap measurements of smaller targets. These targets can be smaller than the illumination spot and can be surrounded by product structures on a wafer. Examples of dark-field imaging measurements can be found, for example, in numerous published patent applications such as US2011102753A1 and US20120044470A. Multiple gratings can be measured in a single image using composite grating targets. Scattermeters are known to tend to use light in the visible or near-infrared (IR) wavelength range, which requires the grating pitch to be much coarser than the actual product structure whose properties are actually attributable to the object of interest. Such product features can be defined using deep ultraviolet (DUV), extreme ultraviolet (EUV), or X-ray radiation with much shorter wavelengths. Unfortunately, such wavelengths are generally unavailable or unsuitable for measurement.

[0011] On the other hand, the size of modern product structures is so small that they cannot be imaged using optical metrology techniques. Small features include, for example, those formed through multiple patterning processes and / or pitch multiplication. Therefore, targets used for high-volume metrology often use features much larger than the overlap error or critical size of the product for which the property of interest is. Measurement results are only indirectly related to the size of the actual product structure and may be inaccurate because the measured target does not suffer the same distortion under optical projection in a lithography apparatus and / or different treatments in other steps of the manufacturing process. While scanning electron microscopy (SEM) can directly resolve these modern product structures, SEM is much more time-consuming than optical measurements. Furthermore, electrons cannot penetrate thick process layers, making them less suitable for metrology applications. Other techniques, such as using contact pads to measure electrical properties, are also known, but they only provide indirect evidence of the actual product structure.

[0012] By reducing the wavelength of the radiation used during measurement, smaller structures can be resolved, thereby increasing sensitivity to structural changes and / or further penetration into the product structure. One such method for generating appropriate high-frequency radiation (e.g., hard X-rays, soft X-rays, and / or EUV radiation) can use pump radiation (e.g., infrared IR radiation) to excite the generating medium, thereby producing emitted radiation, optionally including the generation of higher-order harmonics of the high-frequency radiation.

[0013] In short-wavelength measurements, the target can be illuminated by broadband radiation, and the scattered radiation (e.g., from diffraction orders) can be detected by one or more detectors. The detected radiation can be analyzed, for example, to reconstruct relevant parameters of the target. In some measurement applications, multiple parameters can be reconstructed simultaneously based on the same detected scattered radiation. This can be referred to as profilometry. In such applications, accurate calibration of the detectors capturing the scattered radiation is crucial for obtaining accurate profilometry results. Summary of the Invention

[0014] According to an aspect of this disclosure, an assembly for wavelength calibration of radiation is provided. The assembly includes one or more spectrometers configured to measure a first radiation spectrum of the radiation. The one or more spectrometers are further configured to measure a second radiation spectrum while krypton is present in the propagation path of the radiation. The krypton has an absorption line superimposed on at least one wavelength of the radiation. The assembly also includes a processor configured to determine wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0015] Optionally, the difference may be the ratio of the second radiation spectrum to the first radiation spectrum. Optionally, the difference may be the subtraction of the second radiation spectrum from the first radiation spectrum.

[0016] Optionally, the radiation may include one or more wavelengths in the range of 1 nm to 100 nm, or 1 nm to 10 nm, or 10 nm to 20 nm, or 0.1 nm to 10 nm.

[0017] Optionally, the component may include a plurality of spectrometers. The component may be configured to determine the wavelength calibration of each of the plurality of spectrometers.

[0018] Optionally, the processor may be configured to determine the wavelength calibration for each of the one or more spectrometers, identifying the position of the krypton absorption line on the spectrometer based on the difference between the second radiation spectrum and the first radiation spectrum. The processor may also be configured to calibrate the wavelength corresponding to the krypton absorption line to the position of the absorption line.

[0019] Alternatively, the absorption line of krypton can be associated with photon energies in the range of 90 eV to 95 eV, such as with a wavelength of 13.5 nm.

[0020] Optionally, the one or more spectrometers may be configured to be disposed inside the measurement or inspection container. The radiation may be configured to propagate inside the measurement or inspection container. The krypton gas may be configured to be added to the measurement or inspection container.

[0021] Optionally, the component may also include a gas module configured to add krypton gas inside the measuring or inspection container at a pressure ranging from 0.0001 mbar to 1 mbar, such as 0.01 mbar.

[0022] Optionally, the propagation length of the radiation inside the measuring or inspection device can be in the range of 10 cm to 5 m, such as in the range of 50 cm to 70 cm.

[0023] Optionally, the component may further include a gas chamber. The krypton gas can be configured to be added to the gas chamber.

[0024] Optionally, the gas chamber may include an inlet pipe for the entry and exit of the krypton gas, and two outlet pipes. The outlet pipes may be configured to serve as the input and output of the gas chamber for the radiation.

[0025] Optionally, the propagation length of the radiation in the air chamber can be in the range of 5 mm to 20 cm, such as 10 cm.

[0026] Optionally, measuring the first and second radiation spectra may include performing lock detection.

[0027] Optionally, the one or more spectrometers may be included in the reference arm of the measurement or inspection device.

[0028] Optionally, the one or more spectrometers may be included in the measuring arm of the measurement or inspection device.

[0029] According to another aspect of this disclosure, a component is provided. The component includes: a radiation input device configured to receive emitted radiation; and an irradiation system arranged to irradiate at least a portion of the emitted radiation onto a structure to generate one or more scattered radiations. The component further includes a plurality of detectors. At least a portion of the plurality of detectors is arranged to detect at least a portion of the one or more scattered radiations or at least a portion of the emitted radiation. The component further includes a gas supply system configured to supply gas to absorb a portion of the emitted radiation, thereby generating an absorption line in the spectrum of the one or more scattered radiations and the at least a portion of the emitted radiation. Optionally, the plurality of detectors are configured to simultaneously measure the absorption line.

[0030] According to another aspect of this disclosure, a method for wavelength calibration of radiation is provided. The method includes measuring a first radiation spectrum of the radiation using one or more spectrometers. The method also includes measuring a second radiation spectrum using the one or more spectrometers while krypton is present in the propagation path of the radiation. The krypton has an absorption line superimposed on at least one wavelength of the radiation. The method further includes determining wavelength calibration of the one or more spectrometers by a processor based on the difference between the second radiation spectrum and the first radiation spectrum.

[0031] According to another aspect of this disclosure, an assembly for wavelength calibration of radiation is provided. The assembly includes one or more spectrometers configured to measure a first radiation spectrum of the radiation and a second radiation spectrum while helium is present in the propagation path of the radiation. The helium has an absorption line superimposed on at least one wavelength of the radiation. The assembly further includes a processor configured to determine wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0032] According to another aspect of this disclosure, an assembly for wavelength calibration of radiation is provided. The assembly includes one or more spectrometers configured to measure a first radiation spectrum of the radiation and a second radiation spectrum while a wavelength-selective filter is present in the propagation path of the radiation. The wavelength-selective filter has an absorption line superimposed on at least one wavelength of the radiation. The assembly further includes a processor configured to determine wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0033] Optionally, the wavelength-selective filter may be a solid-state thin-film filter.

[0034] Optionally, the wavelength-selective filter may be a transmission filter.

[0035] Optionally, the wavelength selective filter may be a multi-cavity filter.

[0036] Optionally, the wavelength-selective filter may be a reflective filter.

[0037] Optionally, the wavelength-selective filter may be a multilayer mirror.

[0038] Optionally, the incident angle of the radiation on the reflective filter can be selected to fine-tune the reflected wavelength.

[0039] According to another aspect of this disclosure, an assembly for wavelength calibration of radiation is provided. The assembly includes one or more spectrometers configured to measure a first radiation spectrum of the radiation and a second radiation spectrum while a first wavelength selection element and a second wavelength selection element are present in the propagation path of the radiation. The first wavelength selection element has a first absorption line superimposed on at least a first wavelength of the radiation. The second wavelength selection element has a second absorption line superimposed on at least a second wavelength of the radiation. The first wavelength and the second wavelength are different. The assembly further includes a processor configured to determine wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0040] Optionally, the first wavelength selection element may be one of a solid thin film, krypton, helium, a transmission filter, or a reflection filter. Optionally, instead of a wavelength selection element, a first wavelength diffraction element may be provided, such as, for example, a metamaterial structure.

[0041] Optionally, the second wavelength-selective element may be different from the first wavelength-selective element. The second wavelength-selective element may be one of a solid thin film, krypton, helium, a transmission filter, or a reflection filter. Optionally, instead of the wavelength-selective element, a second wavelength-diffraction element, such as, for example, a metamaterial structure, may be provided.

[0042] According to another aspect of this disclosure, an assembly for wavelength calibration of radiation is provided. The assembly may include one or more spectrometers configured to measure a first spectrum of the radiation. The one or more spectrometers may measure a second spectrum of the radiation while a wavelength diffraction element is present in the propagation path of the radiation. The wavelength diffraction element may include a grating configured to spatially separate different wavelengths of the radiation to different locations on the spectrometer. The assembly further includes a processor configured to determine wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0043] Optionally, the wavelength diffraction element may include a three-dimensional metamaterial structure.

[0044] According to another aspect of this disclosure, a method for measuring the spectrum of broadband radiation, wherein the broadband radiation has a propagation direction. The broadband radiation may include multiple wavelengths. The method includes diffracting the broadband radiation into multiple diffraction orders using a transmission grating. A detector at a first location is used to measure at least one of the multiple diffraction orders to obtain a first measurement signal, wherein the measurement includes a wavelength-resolved measurement of the position of the radiation on the detector. The detector is moved from the first location to a second location along the propagation direction, defined as the movement of the detector having a non-zero component along the propagation direction, and optionally also having a component not parallel to the propagation direction. The angle between the movement of the detector and the propagation direction may be known for calibrating the spectral measurement. The detector at the second location is used to measure at least one of the multiple diffraction orders to obtain a second measurement signal. The spectrum of the broadband radiation is determined based on the difference between the first location and the second location and the difference between the first measurement signal and the second measurement signal.

[0045] Optionally, the detector may include a spectrometer.

[0046] Optionally, the at least one diffraction order may include a non-zero diffraction order.

[0047] Optionally, the at least one diffraction order may include one or both of a negative one (-1) diffraction order and a positive one (+1) diffraction order.

[0048] Optionally, moving the detector may also include moving the detector in a direction perpendicular to the propagation direction.

[0049] Optionally, the broadband radiation may include multiple wavelengths in the range of 1 nm to 100 nm, or 1 nm to 10 nm, or 10 nm to 20 nm, or 8 nm to 18 nm, or 0.1 nm to 10 nm.

[0050] Optionally, the wavelength resolution measurement may include combining measurement data measured by the detector to obtain wavelength information.

[0051] Optionally, the first measurement signal may include a plurality of wavelengths at first positions on the detector, and the second measurement signal may include the plurality of wavelengths at second positions on the detector. The spectrum may be determined based on a comparison between the difference between the first and second positions on the detector and the difference between the first and second portions of the plurality of wavelengths on the detector.

[0052] Optionally, the method may further include: moving the detector from the second location to the third location along the propagation direction; and using the detector at the third location to measure at least one of the plurality of diffraction radiation orders to obtain a third measurement signal. The determination of the spectrum of the broadband radiation may be based on the difference between the first location, the second location, and the third location, and the difference between the first measurement signal, the second measurement signal, and the third measurement signal.

[0053] Optionally, the detector may be positioned along the measurement branch of the measuring device. The broadband radiation may include the measurement radiation.

[0054] Optionally, the broadband radiation can propagate from the transmission grating to the detector without passing through the optical components.

[0055] Optionally, the method may further include: moving the detector to a plurality of locations in a set pattern; and using the detector at each of the plurality of locations to measure at least one of the plurality of diffraction orders.

[0056] Optionally, the pattern of the part may include: movement along the propagation direction of the radiation; and movement along a direction perpendicular to the propagation direction. Movement along a direction perpendicular to the propagation direction is defined as movement with a non-zero component along a direction perpendicular to the propagation direction, and optionally multiple movements with a non-zero component along a direction perpendicular to the propagation direction.

[0057] Optionally, the determined spectrum can be used for radiation calibration.

[0058] According to another aspect of this disclosure, an assembly for measuring the spectrum of broadband radiation is provided. The assembly includes: a transmission grating configured to diffract the broadband radiation into a plurality of diffraction orders; a detector configured to measure at least one of the plurality of diffraction orders; and a processor configured to control the assembly to perform the method described above. The assembly may include a platform configured to move the detector according to the method described herein. The platform may, for example, be configured to move the detector to a first location, a second location, etc., to obtain different measurements.

[0059] According to another aspect of this disclosure, a measuring device is provided, including the components as described above.

[0060] According to another aspect of this disclosure, an inspection device is provided, including the components as described above.

[0061] According to another aspect of this disclosure, a photolithography apparatus is provided, including the components as described above.

[0062] According to another aspect of this disclosure, a photolithography unit is provided, including the apparatus as described above. Attached Figure Description

[0063] Embodiments will now be described with reference to the accompanying illustrative drawings, which are by way of example only, in which:

[0064] Figure 1 depicts a schematic schematic diagram of a photolithography apparatus;

[0065] Figure 2 is a schematic schematic diagram of a photolithography unit;

[0066] Figure 3 depicts a schematic representation of overall photolithography, illustrating the collaboration between three key technologies used to optimize semiconductor manufacturing;

[0067] Figure 4 schematically illustrates the scattering measurement equipment;

[0068] Figure 5 schematically illustrates the transmission scattering measurement equipment;

[0069] Figure 6 depicts a schematic representation of the measurement equipment using EUV and / or SXR radiation;

[0070] Figure 7 depicts a simplified schematic diagram of the irradiation source;

[0071] Figure 8 depicts a schematic representation of the components used for wavelength calibration;

[0072] Figure 9 depicts a schematic representation of a gas cell to be included in a component for wavelength calibration;

[0073] Figure 10 illustrates a flowchart of the steps in the method for wavelength calibration;

[0074] Figure 11 depicts a schematic representation of the components used for wavelength calibration;

[0075] Figure 12 depicts a schematic diagram of transmission varying with wavelength by a transmission filter;

[0076] Figure 13 depicts a model curve of the reflectivity of a multilayer mirror for different incident angles;

[0077] Figure 14 depicts a schematic representation of a component used for diffraction radiation from a metamaterial structure;

[0078] Figure 15 depicts a schematic representation of the components used to measure the spectrum of broadband radiation using a movable detector;

[0079] Figure 16 illustrates a flowchart of the steps in a method for measuring the spectrum of broadband radiation using a movable detector; and

[0080] Figure 17 depicts a schematic representation of a component used to measure the spectrum of broadband radiation using radiation with known wavelengths. Detailed Implementation

[0081] In this document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic and particle radiation, including ultraviolet radiation (e.g., having wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), extreme ultraviolet radiation (EUV, e.g., having wavelengths in the range of about 5 nm to 100 nm), X-ray radiation, electron beam radiation, and other particle radiation.

[0082] 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-shifting, hybrid, etc.) include programmable mirror arrays and programmable LCD arrays.

[0083] Figure 1 schematically depicts a lithography apparatus LA. 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, EUV radiation, or X-ray radiation); a mask support (e.g., a mask stage) T 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.

[0084] 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, diffractive, 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.

[0085] As used herein, the term "projection system" PS 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.

[0086] Photolithography equipment (LA) can fall into a category where at least a portion of the substrate can be covered by a liquid with a relatively high refractive index, such as water, to fill the space between the projection system (PS) and the substrate (W) – this is also known as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference in its entirety.

[0087] Photolithography equipment (LA) can also be of the type with two or more substrate supports (WT) (also known as "dual-platform"). 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.

[0088] 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. The sensors may be arranged to measure the properties of the projection system PS or the properties of the radiation beam B. The measurement platform may hold multiple sensors. The 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 when the substrate support WT is away from the projection system PS.

[0089] In operation, a radiation beam B is incident on a pattern forming apparatus (e.g., a mask) MA held on a mask support T 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. The substrate support WT can be accurately moved, for example, to position different target portions C in the focused and aligned position along the path of the radiation beam B, by means of a second locator PW and a position measurement system IF. Similarly, a first locator PM and possibly another position sensor (not explicitly depicted in Figure 1) can be used to accurately position the pattern forming apparatus MA relative to the path of the radiation beam B. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the pattern forming apparatus MA and the substrate W. 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 substrate alignment marks P1 and P2 are located between target portions C, these substrate alignment marks P1 and P2 are called scribing alignment marks.

[0090] As shown in Figure 2, the lithography apparatus LA can form part of a lithography unit LC (sometimes also referred to as a lithography cell or (lithography) cluster), which often also includes equipment for performing pre-exposure and post-exposure processes on the substrate W. Typically, this equipment includes a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, and, for example, a chiller CH and a baking plate BK for regulating the temperature of the substrate W (e.g., for regulating the solvent in the resist layer). 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, often collectively referred to as the track or coating / developing system, can be controlled by a track or coating / developing system control unit TCU, which may itself be controlled by a management control system SCS, which may also control the lithography apparatus LA, for example, via a lithography control unit LACU.

[0091] During photolithography, it is desirable to perform frequent measurements on the resulting structure, for example, for process control and verification. The tools used to perform these measurements can be referred to as measurement tools (MTs). Different types of measurement devices (MTs) for performing such measurements are known, including scanning electron microscopes or various forms of scatterometer measurement tools (MTs). A scatterometer is a multifunctional instrument that allows the measurement of parameters of the photolithography process by means of a sensor located in or near the pupil or a plane conjugate to the pupil of the scatterometer's objective lens; these measurements are typically referred to as pupil-based measurements. Alternatively, the measurement of parameters of the photolithography process can be performed by means of a sensor located in or near the image plane or a plane conjugate to the image plane; in this case, the measurement is typically referred to as image- or field-based measurements. Such scatterometers and associated measurement techniques are further described by reference in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A. The aforementioned scattering instrument can use light from hard X-rays (HXR), soft X-rays (SXR), extreme ultraviolet (EUV), visible to near-infrared (IR), and the IR wavelength range to measure the grating. In the case of radiation being hard X-rays or soft X-rays, the aforementioned scattering instrument can optionally be a small-angle X-ray scattering measurement tool.

[0092] To ensure accurate 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), and shape of the structure. For this purpose, inspection tools and / or measurement 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.

[0093] Inspection equipment, also known as metrology equipment, is used to determine the properties of a substrate W, and in particular, how the properties of different substrates W vary or how the properties associated with different layers of the same substrate W vary between different layers. Inspection equipment 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 separate device. Inspection equipment can measure the properties on 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 on a developed resist image (where the exposed or unexposed portions of the resist have been removed), or even the properties on an etched image (after a pattern transfer step such as etching).

[0094] 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.

[0095] In a 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 a target, and reflected, transmitted, or scattered radiation from the target is directed to a spectroscopic detector that measures the spectrum of specularly reflected radiation (i.e., a measurement of intensity varying with wavelength). From this data, the structure or profile of the target that produces the detected spectrum can be reconstructed, for example, through rigorous coupled-wave analysis and nonlinear regression or by comparison with a simulated spectral library. It should be understood that a spectrum can be understood as spectral correlation parameters, and determining the spectrum of radiation can be understood as obtaining spectral correlation parameters. In one embodiment, only a portion of the spectrum, rather than the complete spectrum, is determined.

[0096] In the third embodiment, the scatterer MT is an elliptic scatterer. An elliptic scatterer allows the determination of parameters of the photolithography process by measuring the scattered or transmitted radiation for each polarization state. Such a metrology device emits polarized light (such as linear, circular, 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 scatterers are described herein by reference 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.

[0097] In one embodiment of the 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 asymmetry in the configuration, the asymmetry being related to the degree of overlap. Two (stackable) grating structures can be applied to two different layers (not necessarily consecutive layers), and the two grating structures can be formed at substantially the same location on the wafer. The scattering instrument can have a symmetrical detection configuration, such as described, for example, in the commonly owned patent application EP1,628,164A, such that any asymmetry is clearly distinguishable. This provides a straightforward way to measure misalignment in gratings. Further examples of measuring overlap error between two layers of a periodic structure by means of asymmetry of the targeted periodic structure can be found in PCT patent application publication WO 2011 / 012624 or U.S. patent application US 20160161863, which are incorporated herein by reference in their entirety.

[0098] Other parameters of interest may be focus and dose. Focus 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 focus and dose values ​​can be uniquely determined based on these measurements.

[0099] The measurement target can be an assembly of composite gratings formed primarily in a resist by a photolithography process and also after other manufacturing processes, such as etching. The pitch and linewidth of the structures in the gratings can be largely dependent on the measurement optics (especially the NA of the optics) to be able 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 be used to 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 sub-segments configured to mimic the dimensions of functional portions of the design layout in the target. Due to these sub-segments, the target will behave more similarly to the functional portions of the design layout, such that overall process parameter measurements are preferably similar to the functional portions of the design layout. The target can be measured in an underfilled mode or an overfilled mode. In the underfilled mode, the measurement beam produces a spot smaller than the overall target. In the overfilled mode, the measurement beam produces a spot larger than the overall target. In such an overfilled mode, different targets may be measured simultaneously, thus determining different processing parameters at the same time.

[0100] 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 used to select the 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 and U.S. Patent Application US2016 / 0370717A1, which are incorporated herein by reference in their entirety.

[0101] The patterning process in a lithography apparatus (LA) can be one of the most critical steps in the process, requiring high accuracy in determining and placing the dimensions of the structure on the substrate W. To ensure this high accuracy, three systems can be combined in a so-called “holistic” control environment, schematically depicted in Figure 3. One of these systems is the lithography apparatus (LA), which is (in effect) connected to a metrology tool (MT) (the second system) and to 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 particular manufacturing process produces a defined result (e.g., a functional semiconductor device)—potentially, within which process parameters in the lithography or patterning process are allowed to vary.

[0102] The computer system CL can use the design layout (partially) 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 setup will enable the maximum overall process window for the patterning process (described by the double arrows in the first scale SC1 in Figure 3). Resolution enhancement techniques can be 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 MET) in order to predict whether defects may exist due to, for example, suboptimal processing (described by the arrows pointing to "0" in the second scale SC2 in Figure 3).

[0103] The measurement tool MT 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 the calibration state of the lithography equipment LA (described by multiple arrows in the third scale SC3 in Figure 3).

[0104] Many different types of measurement tools (MTs) are available for measuring structures produced using photolithographic patterning equipment. A measurement tool (MT) can interrogate a structure using electromagnetic radiation. The properties of the radiation (e.g., wavelength, bandwidth, power) can affect different measurement characteristics of the tool, with shorter wavelengths generally allowing for improved resolution. The radiation wavelength influences the achievable resolution of the measurement tool. Therefore, a measurement tool (MT) with a short-wavelength radiation source is preferred to enable the measurement of structures using features with small dimensions.

[0105] Another way radiation wavelength can affect measurement characteristics is through-penetration depth and the transparency / opacity of the material being inspected at that wavelength. Depending on opacity and / or through-penetration depth, radiation can be used for either transmissive or reflective measurements. The type of measurement can affect whether information about the surface and / or bulk interior of a structure / substrate is obtained. Therefore, through-penetration depth and opacity are other factors to consider when selecting the radiation wavelength for a measurement tool.

[0106] To achieve higher resolution measurements of photolithographically patterned structures, measurement tools (MTs) with short wavelengths are preferred. This can include wavelengths shorter than the visible wavelength, for example, in the UV, EUV, and X-ray portions of the electromagnetic spectrum. Hard X-ray methods, such as transmission small-angle X-ray scattering (TSAXS), utilize the high resolution and high penetration depth of hard X-rays and can therefore operate in transmission. On the other hand, soft X-rays and EUV do not penetrate as far as the target but can elicit rich optical responses in the material being probed. This can be attributed to the optical properties of many semiconductor materials and to the fact that the size of the structure can be comparable to the probe wavelength. As a result, EUV and / or soft X-ray measurement tools (MTs) can operate in reflection, for example, by imaging or by analyzing diffraction patterns from photolithographically patterned structures.

[0107] For hard X-rays, soft X-rays, and EUV radiation, the lack of available high-brightness sources at the desired wavelengths limits their application in high-volume manufacturing (HVM) applications. In the case of hard X-rays, commonly used sources in industrial applications include X-ray tubes. X-ray tubes, including advanced X-ray tubes (e.g., those based on liquid metal anodes or rotating anodes), can be relatively affordable and compact, but may lack the brightness required for HVM applications. High-brightness X-ray sources such as synchrotron light sources (SLS) and X-ray free-electron lasers (XFELs) exist, but their size (>100 m) and high cost (over €100 million) make them excessively large and expensive for metrology applications. Similarly, there is a lack of sufficiently bright EUV and soft X-ray sources available.

[0108] Figure 4 depicts an example of a measurement device, such as a scatterer. The scatterer may include a broadband (e.g., white light) radiation projector 2 that projects radiation 5 onto a substrate W. Reflected or scattered radiation 10 is passed to a spectrometer detector 4, which measures the spectrum 6 of the specularly reflected radiation (i.e., the intensity I as a function of wavelength λ). From 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 shown at the bottom of Figure 4. Typically, for reconstruction, the general form of the structure is known, and some parameters are assumed based on knowledge of the processes used to manufacture the structure, leaving only a few parameters of the structure to be determined from the scattering measurement data. Such a scatterer can be configured as a normal-incident scatterer or an oblique-incident scatterer.

[0109] Figure 5 depicts an example transmission version of the measuring device, such as the scatterer shown in Figure 4. Transmitted radiation 11 is passed to a spectrometer detector 4, which measures the spectrum 6 as discussed with respect to Figure 4. This scatterer can be configured as a normal-incident scatterer or an oblique-incident scatterer. Optionally, a transmission version using hard X-ray radiation with wavelengths <1 nm, optionally <0.1 nm, and optionally <0.01 nm is used.

[0110] As an alternative to optical measurement methods, the use of hard X-rays, soft X-rays, or EUV radiation, such as radiation having at least one of the following wavelength ranges: < 0.01 nm, < 0.1 nm, < 1 nm, between 0.01 nm and 100 nm, between 0.01 nm and 50 nm, between 1 nm and 50 nm, between 1 nm and 20 nm, between 5 nm and 20 nm, and between 10 nm and 20 nm. An example of a measurement instrument operating within one of the wavelength ranges presented above is transmitted small-angle X-ray scattering (as described in its entirety in US 2007224518A, T-SAXS). Lemaillet et al. discuss the use of T-SAXS for profile (CD) measurements in “Intercomparison between optical and X-ray scatterometry measurements of FinFET structures” (Proc. of SPIE, 2013, 8681). It should be noted that the use of laser-generated plasma (LPP) X-ray sources is described in its entirety in U.S. Patent Publication Nos. 2019 / 003988A1 and 2019 / 215940A1, which are incorporated herein by reference. Reflectance measurement techniques using X-rays (GI-XRS) and extreme ultraviolet (EUV) radiation under grazing incidence can be used to measure the properties of films and stacked layers on a substrate. Within the general field of reflectance measurement, goniometric and / or spectroscopic techniques can be applied. In goniometrics, the variation of the reflected beam at different incident angles can be measured. On the other hand, spectroscopic reflectance measurement measures the spectrum of wavelengths reflected at a given angle (using broadband radiation). For example, EUV reflectance measurement has been used for the inspection of mask blanks before the fabrication of masks (patterning apparatuses) for EUV lithography.

[0111] It is possible that the scope of application makes the use of wavelengths in, for example, hard X-ray, soft X-ray, or EUV domains insufficient. Published patent applications US 20130304424A1 and US2014019097A1 (Bakeman et al. / KLA) describe hybrid metrology techniques in which measurements using X-rays are combined with optical measurements utilizing wavelengths in the range of 120 nm to 2000 nm to obtain measurements of parameters such as CD. CD measurements are obtained by coupling X-ray mathematical models and optical mathematical models via one or more common components. The full contents of the listed U.S. patent applications are incorporated herein by reference.

[0112] Figure 6 illustrates a schematic representation of a measurement device 302 in which the aforementioned radiation can be used to measure parameters of a structure on a substrate. The measurement device 302 shown in Figure 6 is applicable to the hard X-ray, soft X-ray, and / or EUV domains.

[0113] Figure 6 illustrates a schematic physical arrangement of a measurement apparatus 302 including a spectroscopic scatterer using optional grazing-incidence hard X-rays, soft X-rays, and / or EUV radiation, and is by way of example only. An alternative form of the inspection apparatus may be provided as an angle-resolved scatterer, which, similar to a conventional scatterer operating at longer wavelengths, can use normally or near-normally incident radiation, and may also use radiation having an angle greater than 1° or 2° with respect to a direction parallel to the substrate. An alternative form of the inspection apparatus may be provided as a transmission scatterer, the configuration of which is applied in Figure 5.

[0114] The inspection device 302 includes a radiation source or so-called irradiation source 310, an irradiation system 312, a substrate support 316, detection systems 318 and 398, and a measurement processing unit (MPU) 320.

[0115] In this example, the irradiation source 310 is used to generate EUV, hard X-ray, or soft X-ray radiation. The irradiation source 310 can be based on the high-order harmonic generation (HHG) technology shown in Figure 6, and it can also be other types of irradiation sources, such as liquid metal jet sources, inverse Compton scattering (ICS) sources, plasma channel sources, magnetic undulator sources, free electron laser (FEL) sources, tight storage ring sources, discharge-generated plasma sources, soft X-ray laser sources, rotating anode sources, solid anode sources, particle accelerator sources, micro-focal sources, or laser-generated plasma sources.

[0116] HHG sources can be gas jet / nozzle sources, capillary / fiber sources, or gas chamber sources.

[0117] For an example of an HHG source, as shown in Figure 6, the main components of the radiation source are a pump radiation source 330 operable to emit pump radiation and a gas delivery system 332. Optionally, the pump radiation source 330 is a laser, and optionally, the pump radiation source 330 is a pulsed high-power infrared or optical laser. The pump radiation source 330 can be, for example, a fiber-based laser with an optical amplifier, thereby generating pulses of infrared radiation that can last for, for example, less than 1 nanosecond (1 ns) per pulse, wherein the pulse repetition rate can be as high as several megahertz as needed. The wavelength of the infrared radiation can be in the range of 200 nm to 10 μm, for example, about 1 micrometer (1 μm). Optionally, the laser pulse is delivered to the gas delivery system 332 as a first pump radiation 340, wherein in the gas, a portion of the radiation is converted to a higher frequency than the first radiation to become emitted radiation 342. A gas supply 334 supplies a suitable gas to the gas delivery system 332, wherein the suitable gas is optionally ionized by a power source 336. The gas delivery system 332 can be a cutting tube.

[0118] The gas provided by the gas delivery system 332 defines a gas target, which can be a gas flow or a static volume. The gas can be, for example, air, neon (Ne), helium (He), nitrogen (N2), oxygen (O2), argon (Ar), krypton (Kr), xenon (Xe), carbon dioxide, and combinations thereof. These gases can be selectable options within the same device. The emitted radiation can include multiple wavelengths. If the emitted radiation is monochromatic, measurement calculations (e.g., reconstruction) can be simplified, but it is easier to generate radiation with a certain number of wavelengths. The emission divergence angle of the emitted radiation can be wavelength-dependent. Different wavelengths will, for example, provide different levels of contrast when imaging structures of different materials. For example, to inspect metallic or silicon structures, different wavelengths can be selected to characterize (carbon-based) resists or to detect contamination in these different materials. One or more filter devices 344 can be provided. For example, filters such as aluminum (Al) or zirconium (Zr) thin films can be used to cut off the basic IR radiation from further transmission into the inspection device. A grating (not shown) can be provided to select one or more specific wavelengths from the generated wavelengths. Optionally, the irradiation source includes a space configured to be evacuated and a gas delivery system configured to provide a gaseous target within said space. Optionally, some or all of the nanobeam path can be contained within a vacuum environment; it should be noted that SXR and / or EUV radiation is absorbed when traveling in air. Various components of the radiation source 310 and the irradiation optics 312 can be adjustable to implement different measurement “configurations” within the same device. For example, different wavelengths and / or polarizations can be selected.

[0119] Depending on the material of the structure being inspected, different wavelengths can provide the desired degree of penetration into the underlying layers. Short wavelengths are often preferred for distinguishing minimum device features and defects within them. For example, one or more wavelengths in the range of 0.01 nm to 20 nm, or optionally between 1 nm and 10 nm, or optionally between 10 nm and 20 nm, can be selected. Wavelengths shorter than 5 nm can suffer very low critical angles when reflected from the material of interest in semiconductor manufacturing. Therefore, selecting wavelengths greater than 5 nm can provide a stronger signal at higher incident angles. On the other hand, if the inspection task is to detect the presence of a material, such as to detect contamination, wavelengths up to 50 nm can be useful.

[0120] The filtered beam 342 can enter the inspection chamber 350 from the radiation source 310, in which the substrate W, including the structure of interest, is held by the substrate support 316 for inspection at the measurement location. The structure of interest is designated T. Optionally, the gas atmosphere within the inspection chamber 350 can be maintained to near vacuum by a vacuum pump 352, allowing SXR and / or EUV radiation to pass through the gas atmosphere without undue attenuation. The irradiation system 312 has the function of focusing the radiation into a focused beam 356 and may include, for example, a two-dimensional curved mirror or a series of one-dimensional curved mirrors, as described in the published U.S. patent application US2017 / 0184981A1 (the entire contents of which are incorporated herein by reference). Focusing is performed to achieve a circular or elliptical spot S with a diameter of less than 10 μm when projected onto the structure of interest. The substrate support 316 includes, for example, an XY translation platform and a rotation platform, by which any portion of the substrate W can be directed to the focal point of the beam in a desired orientation. Thus, a radiation spot S is formed on the structure of interest. Alternatively or additionally, the substrate support 316 includes, for example, a tilting platform that can tilt the substrate W at a certain angle to control the incident angle of the focused beam on the structure of interest T.

[0121] Optionally, the illumination system 312 provides a reference radiation beam to a reference detector 314, which can be configured to measure the spectrum and / or intensity of different wavelengths in the filtered beam 342. The reference detector 314 can be configured to generate a signal 315 provided to the processor 320, and the filter can include information about the spectrum of the filtered beam 342 and / or the intensity of different wavelengths in the filtered beam.

[0122] The reflected radiation 360 is captured by detector 318 and the spectrum is provided to processor 320 for calculating the properties of the target structure T. The irradiation system 312 and detection system 318 thus form an inspection apparatus. Such an inspection apparatus may include hard X-ray, soft X-ray, and / or EUV spectroreflectometers of the kind whose contents are incorporated herein by reference in their entirety.

[0123] If the target Ta has a periodicity, the radiation from the focused beam 356 can also be partially diffracted. The diffracted radiation 397 follows another path at a clearly defined angle relative to the incident angle and then relative to the reflected radiation 360. In Figure 6, the absorbed diffracted radiation 397 is schematically absorbed, and the diffracted radiation 397 can follow many other paths besides the absorption path. The inspection device 302 may also include additional detection systems 398 for detecting at least a portion of the diffracted radiation 397 and / or imaging at least a portion of the diffracted radiation 397. In Figure 6, a single additional detection system 398 is depicted, but embodiments of the inspection device 302 may also include more than one additional detection system 398 arranged at different locations to detect and / or image the diffracted radiation 397 in multiple diffraction directions. In other words, the (higher) diffraction order of the focused radiation beam irradiating the target Ta is detected and / or imaged by one or more additional detection systems 398. The one or more detection systems 398 generate a signal 399, which is provided to the measurement processor 320. The signal 399 may include information about the diffracted light 397 and / or may include an image obtained from the diffracted light 397. Both reflected radiation and diffracted radiation can be referred to as scattered radiation.

[0124] To aid in the alignment and focusing of spot S with the desired product structure, inspection device 302 may also provide auxiliary optics using auxiliary radiation under the control of measurement processor 320. Measurement processor 320 may also communicate with position controller 372, which operates translation, rotation, and / or tilting platforms. Processor 320 receives highly accurate feedback regarding the position and orientation of the substrate via sensors. Sensor 374 may include, for example, an interferometer, which can provide an accuracy of approximately several picometers. During operation of inspection device 302, spectral data 382 captured by detection system 318 is transmitted to measurement processing unit 320.

[0125] As mentioned, alternative forms of inspection equipment use hard X-rays, soft X-rays, and / or EUV radiation at normal or near-normal incidence, for example, to perform diffraction-based asymmetry measurements. Another alternative form of inspection equipment uses hard X-rays, soft X-rays, and / or EUV radiation with an angle greater than 1° or 2° to a direction parallel to the substrate. Both types of inspection equipment can be provided in hybrid metrology systems. The performance parameters to be measured can include overlap (OVL), critical size (CD), focusing of the lithography apparatus when the target structure is printed, coherent diffraction imaging (CDI), and overlap-by-resolution (ARO) measurements. Hard X-rays, soft X-rays, and / or EUV radiation can, for example, have wavelengths less than 100 nm, such as radiation in the range of 5 nm to 30 nm, optionally in the range of 10 nm to 20 nm. The radiation can be narrow-band or broadband in characteristics. The radiation can have discrete peaks in a specific wavelength band or can have more continuous characteristics.

[0126] Similar to optical scattering instruments used in today's manufacturing facilities, inspection device 302 can be used to measure structures within resist materials processed within a lithography unit (post-development inspection or ADI), and / or to measure said structures after they have been formed in a harder material (post-etching inspection or AEI). For example, inspection device 302 can be used to inspect said substrate after it has been processed by developing equipment, etching equipment, annealing equipment, and / or other equipment.

[0127] Measurement tools (MTs), including but not limited to the scattering instruments mentioned above, can use radiation from a radiation source to perform measurements. The radiation used by the measurement tool MT can be electromagnetic radiation. The radiation can be optical radiation, such as radiation in the infrared, visible, and / or ultraviolet portions of the electromagnetic spectrum. The measurement tool MT can use radiation to measure or inspect the properties and aspects of a substrate, such as a photolithographic pattern on a semiconductor substrate. The type and quality of the measurement can depend on a number of properties of the radiation used by the measurement tool MT. For example, the resolution of an electromagnetic measurement can depend on the wavelength of the radiation, where, for example, due to diffraction limitations, shorter wavelengths can measure smaller features. To measure features with small dimensions, radiation with short wavelengths, such as EUV, hard X-rays (HXR), and / or soft X-rays (SXR), is preferably used to perform the measurement. To perform measurements at a specific wavelength or wavelength range, the measurement tool MT needs access to a source that provides radiation at said / those wavelengths. Different types of sources exist for providing radiation at different wavelengths. Depending on the wavelength provided by the source, different types of radiation generation methods can be used. For extreme ultraviolet (EUV) radiation (e.g., 1 nm to 100 nm) and / or soft X-ray (SXR) radiation (e.g., 0.1 nm to 10 nm), the source can use higher-order harmonic generation (HHG) or any other type of source mentioned above to obtain radiation at the desired wavelength.

[0128] Figure 7 shows a simplified schematic diagram of embodiment 600 of the illumination source 310, which may be an illumination source for high-order harmonic generation (HHG). One or more features of the illumination source in the measurement tool described in Figure 6 may also be present in the illumination source 600 where appropriate. The illumination source 600 includes a chamber 601 and is configured to receive pump radiation 611 having a propagation direction indicated by the arrow. The pump radiation 611 shown in this example is an example of pump radiation 340 from pump radiation source 330, as shown in Figure 6. The pump radiation 611 may be directed into the chamber 601 by a radiation input device 605, which may be an observation area optionally made of molten silica or a similar material. The pump radiation 611 may have a Gaussian or hollow (e.g., annular) transverse cross-sectional profile and may be incident (optionally focused) on an airflow 615 within the chamber 601 having a flow direction indicated by the second arrow. The gas flow 615 comprises a small volume of a specific gas (e.g., air, neon (Ne), helium (He), nitrogen (N2), oxygen (O2), argon (Ar), krypton (Kr), xenon (Xe), carbon dioxide, and combinations thereof) with a pressure higher than a certain value, said small volume being referred to as the gas volume or gas target (e.g., several cubic mm). The gas flow 615 can be a steady flow. Other media, such as metallic plasma (e.g., aluminum plasma), can also be used.

[0129] The gas delivery system of the irradiation source 600 is configured to provide an airflow 615. The irradiation source 600 is configured to place pump radiation 611 in the airflow 615 to drive the generation of emitted radiation 613. The region in which at least a majority of the emitted radiation 613 is generated is referred to as the interaction region. The interaction region can vary from tens of micrometers (for tightly focused pump radiation) to several millimeters or centimeters (for moderately focused pump radiation) or even up to several meters (for very loosely focused pump radiation). The gas delivery system is configured to provide the gas target for generating emitted radiation at the interaction region of the gas target, and optionally, the irradiation source is configured to receive the pump radiation and provide the pump radiation at the interaction region. Optionally, the airflow 615 is provided by the gas delivery system to an evacuated or nearly evacuated space. The gas delivery system may include a gas nozzle 609, as shown in FIG. 6, the gas nozzle including an opening 617 in the ejection plane of the gas nozzle 609. The airflow 615 is provided from the opening 617. The gas trap is used to confine the gas flow 615 within a volume by extracting residual gas flow and maintaining a vacuum or near-vacuum atmosphere inside chamber 601. Optionally, the gas nozzle 609 may be made of thick-walled tube and / or a material with high thermal conductivity to avoid thermal deformation due to high-power pump radiation 611.

[0130] The size of the gas nozzle 609 can conceivably also be used in scaled-up or scaled-down versions ranging from micrometer-sized nozzles to meter-sized nozzles. This wide range of sizes is determined by the fact that the arrangement should be scaled so that the intensity of the pump radiation at the gas flow is ultimately within a specific range that is beneficial to the emitted radiation. This requires different sizes for different pump radiation energies, which may be pulsed lasers, and the pulse energy can vary from tens of microjoules to several joules. Optionally, the gas nozzle 609 has thicker walls to reduce nozzle deformation caused by thermal expansion effects that can be detected, for example, by a camera. A gas nozzle with thicker walls can produce a stable gas volume with reduced variation. Optionally, the irradiation source includes a gas trap located near the gas nozzle to maintain the pressure in chamber 601.

[0131] Due to the interaction between the pump radiation 611 and the gas atoms of the gas flow 615, the gas flow 615 will convert a portion of the pump radiation 611 into emitted radiation 613, which may be an example of emitted radiation 342 shown in FIG. 6. The central axis of the emitted radiation 613 may be collinear with the central axis of the incident pump radiation 611. The emitted radiation 613 may have a wavelength in the X-ray or EUV range, wherein the wavelength is in the range of 0.01 nm to 100 nm, optionally from 0.1 nm to 100 nm, optionally from 1 nm to 100 nm, optionally from 1 nm to 50 nm, or optionally from 10 nm to 20 nm.

[0132] In operation, the emitted radiation beam 613 can pass through the radiation output 607 and can subsequently be manipulated and directed by the irradiation system 603 to a substrate to be inspected for measurement purposes; the irradiation system 603 can be an example of the irradiation system 312 in FIG. 6. The emitted radiation 613 can be directed (optionally focused) onto a structure on the substrate.

[0133] Because air (and virtually any gas) largely absorbs SXR or EUV radiation, the volume between the airflow 615 and the wafer to be inspected can be evacuated or nearly evacuated. Since the central axis of the emitted radiation 613 can be collinear with the central axis of the incident pump radiation 611, the pump radiation 611 may need to be blocked to prevent it from passing through the radiation output 607 and entering the irradiation system 603. This can be done by incorporating the filter device 344 shown in FIG. 6 into the radiation output 607, which is positioned in the path of the emitted beam and is opaque or nearly opaque to the pump radiation (e.g., opaque or nearly opaque to infrared or visible light) but at least partially transparent to the emitted radiation beam. The filter can be fabricated using zirconium or a combination of materials in multiple layers. When the pump radiation 611 has a hollow (optionally annular) transverse cross-sectional profile, the filter can be a hollow (optionally annular) bulk. Optionally, the filter is neither perpendicular nor parallel to the propagation direction of the emitted radiation beam to achieve efficient pump radiation filtering. Optionally, the filter device 344 includes a hollow bulk and a thin-film filter such as an aluminum (Al) or zirconium (Zr) film filter. Optionally, the filter device 344 may also include a mirror that effectively reflects the emitted radiation but poorly reflects the pump radiation, or a metal mesh that effectively transmits the emitted radiation but poorly transmits the pump radiation.

[0134] This document describes methods, apparatus, and components for obtaining emitted radiation optionally at the higher harmonic frequencies of the pump radiation. The radiation generated by a process (optionally using nonlinear effects to generate an HHG of radiation optionally at the harmonic frequencies of the provided pump radiation) can be set as radiation in a metrology tool MT for substrate inspection and / or measurement. If the pump radiation comprises short pulses (i.e., several cycles), the generated radiation need not be precisely at the harmonic frequency of the pump radiation. The substrate may be a photolithographically patterned substrate. The radiation obtained by the process can also be set in a photolithography apparatus LA and / or a photolithography unit LC. The pump radiation may be pulsed radiation, which can provide high peak intensity within a short burst.

[0135] Pump radiation 611 may include radiation having one or more wavelengths higher than the emitted radiation. Pump radiation may include infrared radiation. Pump radiation may include radiation having wavelengths in the range of 500 nm to 1500 nm. Pump radiation may include radiation having wavelengths in the range of 800 nm to 1300 nm. Pump radiation may include radiation having wavelengths in the range of 900 nm to 1300 nm. Pump radiation may be pulsed radiation. Pulsed pump radiation may include pulses having a duration in the femtosecond range.

[0136] In some embodiments, the emitted radiation (optionally higher-order harmonic radiation) may include one or more harmonics having a pump radiation wavelength. The emitted radiation may include wavelengths in the extreme ultraviolet, soft X-ray, and / or hard X-ray portions of the electromagnetic spectrum. The emitted radiation 613 may include wavelengths in one or more of the following ranges: less than 1 nm, less than 0.1 nm, less than 0.01 nm, 0.01 nm to 100 nm, 0.1 nm to 100 nm, 0.1 nm to 50 nm, 1 nm to 50 nm, and 10 nm to 20 nm.

[0137] Radiation such as the higher-order harmonic radiation described above can be used as source radiation in a metrology tool (MT). The metrology tool MT can use the source radiation to perform measurements on a substrate exposed by a photolithography apparatus. The measurements can be used to determine one or more parameters of the structure on the substrate. Compared to using longer wavelengths (e.g., visible light radiation, infrared radiation), using radiation at shorter wavelengths (e.g., EUV, SXR, and / or HXR wavelengths included in the wavelength range described above) allows for the resolution of smaller features of the structure by the metrology tool. Radiation with shorter wavelengths, such as EUV, SXR, and / or HXR radiation, can also penetrate deeper into materials such as patterned substrates, meaning that measurements of deeper layers on the substrate are possible. These deeper layers may not be reachable by radiation with longer wavelengths.

[0138] In a metrology tool (MT), source radiation can be emitted from a radiation source and directed onto a target structure (or other structure) on a substrate. The source radiation may include EUV, SXR, and / or HXR radiation. The target structure may reflect, transmit, and / or diffract the source radiation incident on it. The metrology tool (MT) may include one or more sensors for detecting diffracted radiation. For example, the metrology tool (MT) may include detectors for detecting the +1st and -1st diffraction orders. The metrology tool (MT) may also measure specular reflection or transmission radiation (0th-order diffraction radiation). Additional sensors for measurement may be present in the metrology tool (MT), for example, to measure other diffraction orders (e.g., higher diffraction orders).

[0139] In example photolithography applications, an optical column, which may be referred to as an irradiator, can be used to focus HHG-generated radiation onto a target on a substrate, transferring the radiation from the HHG source to the target. The HHG radiation can then be reflected from the target, detected, and processed, for example, to measure and / or infer the properties of the target.

[0140] Gas-targeted HHG configurations can be broadly categorized into three separate types: gas jets, gas chambers, and gas capillaries. Figure 7 depicts an example gas jet configuration where a gas volume is introduced into the driving radiation laser beam. In the gas jet configuration, the interaction between the driving radiation and the solid component is kept to a minimum. The gas volume can, for example, comprise a gas flow perpendicular to the driving radiation beam, with the gas volume enclosed within a gas chamber. In the gas capillary arrangement, the dimensions of the capillary structure containing the gas are very small in the lateral direction, significantly affecting the propagation of the driving radiation laser beam. The capillary structure can, for example, be a hollow-core optical fiber, with the hollow core configured to hold and contain the gas.

[0141] The gas jet HHG configuration offers relative degrees of freedom for shaping the spatial profile of the driving radiation beam in the far field, as it is not constrained by the limitations imposed by the gas capillary structure. The gas jet configuration can also have less stringent alignment tolerances. On the other hand, the gas capillary can provide increased interaction partitioning between the driving radiation and the gaseous medium, which can optimize the HHG process.

[0142] To use HHG radiation, for example in measurement applications, the HHG radiation is separated from the driving radiation downstream of the gas target. The separation of HHG radiation from the driving radiation may differ for gas jet and gas capillary configurations. In both cases, the driving radiation rejection scheme may include a metallic transmission-type filter for filtering out any remaining driving radiation from the short-wavelength radiation. However, before such a filter can be used, the intensity of the driving radiation should be significantly reduced from its intensity at the gas target to avoid damaging the filter. Methods for this intensity reduction may differ for gas jet and capillary configurations. For gas jet HHG, due to the relative degrees of freedom in the shape and spatial profile (which may also be referred to as spatial distribution and / or spatial frequency) of the driving radiation beam focused onto the gas target, this can be engineered to have low intensity in the far field along the direction of propagation of the short-wavelength radiation. This spatial separation in the far field means that an aperture or diaphragm can be used to block the driving radiation and reduce its intensity.

[0143] In contrast, in a gas capillary structure, the spatial profile of the bundle as it passes through the gaseous medium can be primarily defined by the capillary. The spatial profile of the driving radiation can be determined by the shape and material of the capillary structure. For example, when a hollow-core fiber is used as the capillary structure, the shape and material of the fiber structure determine which driving radiation modes are supported to propagate through the fiber. For most standard fibers, the supported propagation modes produce a spatial profile in which the high intensity of the driving radiation superimposes with the high intensity of the HHG radiation. For example, the driving radiation intensity can be centered on a Gaussian or near-Gaussian profile in the far field.

[0144] While specific references are made to HHG, it should be understood that the invention can be practiced using any radiation source where circumstances permit. In one embodiment, the radiation source is a laser-generated plasma (LPP) source as mentioned above for hard X-rays, soft X-rays, EUV, DUV, and visible irradiation. In one embodiment, the radiation source is one of the following: a liquid metal jet source, an inverse Compton scattering (ICS) source, a plasma channel source, a magnetic undulator source, a free electron laser (FEL) source, a tight storage ring source, a discharge-generated plasma source, a rotating anode source, a solid anode source, a particle accelerator source, and a micro-focal source.

[0145] The HHG radiation described herein can be used in inspection and / or measurement equipment. The inspection / measurement equipment can be used for the inspection / measurement of photolithographic substrates. Measurement can, for example, perform measurements to determine one or more parameters of a photolithographically patterned structure on the substrate. In one embodiment, the substrate is a patterning apparatus (e.g., a mask). In another embodiment, the substrate is a semiconductor wafer. Because the structure can be small in size, the inspection / measurement equipment can use short-wavelength radiation. The inspection / measurement equipment can include the detection of short-wavelength radiation scattered from a target structure. The scattered radiation can include diffracted radiation (zero and / or non-zero diffraction order). The diffracted radiation can be measured by one or more detectors, such as a spectrometer. The detected wavelength can, for example, be used for the reconstruction of the target structure and / or the measurement of parameters of interest. To achieve accurate measurements, the detectors can be calibrated to measure the radiation. For the reconstruction of the target structure, a calibrated wavelength may be required. Calibration can be specific to the radiation and / or inspection / measurement settings used in a particular inspection / measurement equipment. Achieving accurate calibration in short-wavelength settings can be challenging.

[0146] The target structure can diffract different wavelengths to different locations on the detector. For example, the target structure can diffract each different wavelength to a different spot on the detector. As a result, the intensity of the radiation detected at each location can inherit / represent the properties of the incident diffracted wavelength. Therefore, wavelength information can be used to deconvolve the target structure response from the radiation beam properties and ultimately, for example, to reconstruct the target structure. A challenge in using this information is that the short-wavelength radiation beam profile can be sensitive to small aberrations present in the driving laser used to generate HHG radiation. Short-wavelength beam measurements can help optimize the wavefront of the driving laser to a high quality, which can reduce the occurrence of aberrations.

[0147] Although the embodiments apply to both measuring and inspection devices, the following embodiments will only mention measuring devices as examples.

[0148] In an example implementation, calibration can be performed using a measurement device positioned outside the radiation path during the use of the measurement setup. A disadvantage of using this setup is that it requires adjustment of the measurement setup compared to when measurements are being performed. Consequently, such calibration may not be possible in real time. Real-time calibration can be desirable, especially for HVM applications. An example implementation may perform calibration of the radiation beam in a separate branch, separate from the radiation measurement branch. This separate branch may be referred to as a reference branch.

[0149] In the example, wavelength calibration of the spectrometer can be performed by reconstructing its geometry using measurement data from the spectrometer and approximate knowledge of the characteristics of the HHG radiation source providing the radiation. However, this alone may not be sufficient, as there may be too many unknowns / assumptions in the process. To further assist calibration, additional measurements can be performed using the absorption characteristics of one or more materials. For this to work, the wavelength at which absorption occurs should be superimposed on the wavelength of the radiation.

[0150] Aluminum filters can be used in radiation beams (before they strike the spectrometer). Aluminum exhibits a very significant drop in transmission at wavelengths around 17 nm. This drop in transmission can be referred to as the aluminum edge. Using this drop in transmission near a known wavelength in the spectrum can help anchor, i.e., fix, the spectrum. The aluminum edge filtering method can have drawbacks, resulting in insufficient accuracy for precise calibration. The exact location of the aluminum edge (or generally, any absorption edge) can vary depending on the chemical environment. Processes such as oxidation or carbon growth on the aluminum filter can also alter the location of the edge. Furthermore, the aluminum edge can have limited usefulness if it lies within a portion of the spectrum of a low-intensity radiation source. For example, in a source using a zirconium filter (used to reject infrared radiation), the wavelength around 17 nm may be low because zirconium already suppresses transmission near that wavelength. Any subsequent suppression of transmission at around 17 nm by the aluminum filter may have a limited / hard-to-detect effect. These drawbacks make using aluminum filters for absolute calibration difficult and less precise. Other materials, such as zirconium and / or silicon, can be used to filter radiation. However, they come with their own challenges. It may be desirable to reduce the amount of silicon in the device because it absorbs a significant portion of the short-wavelength spectrum. Zirconium may lack sharp absorption lines in the desired short-wavelength range.

[0151] Using the absorption characteristics of a material to calibrate radiation can be difficult because the absorption characteristics need to be superimposed with the intensity peaks of the harmonic signals of the short-wavelength radiation. Furthermore, for the energy access of the detector to be calibrated, two (or more) points with known energies should ideally be known along the axis. Another challenge can arise because the uncertainty / aberration of the geometric configuration of the diffraction structure (e.g., a toroidal grating) relative to the diffracted radiation beam can introduce additional uncertainties. This paper provides methods and components for improving the accuracy of wavelength calibration in measurement settings.

[0152] Figure 8 depicts a component 800 for wavelength calibration of radiation that can be used in a measurement or inspection apparatus. The component may be disposed within the measurement or inspection apparatus (e.g., forming part of the measurement or inspection apparatus). Optionally, the component is used to measure parameters of a structure (or target structure) on a substrate. Optionally, the component is used to inspect defects on a substrate, optionally the substrate is a substrate exposed by a photolithography apparatus, and optionally the substrate is a mask for exposing a pattern onto another substrate. The component includes one or more spectrometers or detectors 802(a) to 802(b), wherein the radiation to be calibrated relative to the wavelength of the measured radiation is calibrated by the spectrometers 802(a) to 802(b). In one embodiment, the component includes multiple spectrometers or detectors 802(a) to 802(b). The one or more spectrometers 802(a) to 802(b) may include one or more of the detectors (or detector systems) 314, 318, and 398 in Figure 6. One or more spectrometers 802(a) to 802(b) are configured to measure a first radiation spectrum of the radiation. Once the first radiation spectrum has been measured, a gas, optionally an inert gas, optionally krypton, or helium, is added to the propagation path. A gas supply system, which may include a gas supply module 804, may be added to the component to control the krypton supply. The gas supply system is configured to provide gas to absorb a portion of the radiation (e.g., the emitted radiation) to produce absorption lines on at least a portion of the spectrum of one or more scattered radiations and / or emitted radiations. The spectrum may be different on multiple detectors. In one embodiment, at least a portion of the multiple detectors are arranged to detect at least a portion of one or more scattered radiations to measure parameters. Optionally, the parameter is a profile measurement parameter. Optionally, the parameter is an overlap parameter. Optionally, the parameter is a critical size (CD) parameter. The krypton has an absorption line superimposed on at least one wavelength of the radiation. While the krypton is present in the propagation path of the radiation, one or more spectrometers 802(a) to 802(b) measure a second radiation spectrum of the radiation. Wavelength calibration for one or more spectrometers is determined based on the difference between the second radiation spectrum and the first radiation spectrum. In one embodiment, the absorption line is used to measure the spectrum of at least a portion of one or more scattered and / or emitted radiation.

[0153] The radiation to be wavelength-calibrated may include short-wavelength radiation, such as (EUV) radiation (e.g., 1 nm to 100 nm) and / or soft X-ray (SXR) radiation (e.g., 0.1 nm to 10 nm). The radiation may include, for example, wavelengths in the range of 1 nm to 100 nm, 1 nm to 10 nm, 10 nm to 20 nm, 0.1 nm to 10 nm, or 1 nm to 7.5 nm.

[0154] The advantage of the component described above regarding Figure 8 is that it allows for absolute calibration of the radiation. This is likely because one of the multiple absorption lines of krypton appears at a photon energy of approximately 92 eV (e.g., in the range of 90 to 95 eV), where the photon energy and wavelength have the following relationship: E = h*c / λ (E = photon energy; h = Planck's constant; c = speed of light; λ = wavelength). The absorption peak of krypton can appear at a photon energy of 91.2 eV. The absorption line can have a full width at half maximum (FWHM) of approximately 0.02 nm. Such an absorption line can correspond to a wavelength of approximately 13.5 nm.

[0155] Using known fitting and data manipulation techniques, it may be possible to determine the center of an absorption line with greater accuracy than the width of the absorption line. Example fitting and data manipulation techniques may involve, for example, appropriate fitting functions (e.g., Gaussian fitting, Lorentz fitting) or centroid methods, where the intensity of adjacent pixels is used as weights to calculate a weighted average position. For example, the center of a krypton absorption line may be determined with an accuracy greater than three times the line width (i.e., approximately 0.006 nm). This level of accuracy can be considered the desired accuracy for wavelength calibration of a metrology device. The desired accuracy may be related to the size of the structure to be measured by the metrology device. This accuracy is higher than previously known calibration methods or components that do not require moving parts of the metrology setup. The result of improved calibration accuracy can be improved inferences about the properties of the measurement target based on measurements obtained from a calibrated detector. These measurements may be derived from diffraction patterns of the measurement target detected by one or more spectrometers. Therefore, accurate wavelength calibration as described herein can lead to higher accuracy and precision measurements by the metrology device. This, in turn, can lead to improved reproduction by the metrology device.

[0156] The use of krypton is particularly relevant for short-wavelength radiation with wavelengths of approximately 13.5 nm. This may be the case, for example, for radiation harmonics generated by higher-order harmonics. For short-wavelength radiation, materials with absorption lines in the correct portion of the spectrum can be rare, while krypton provides a transmission window with narrow absorption lines in the EUV / SXR range of the spectrum. Helium is an alternative to krypton for short-wavelength ranges in some cases. Another advantage of using a gas for calibration is that it allows for calibration without moving parts of the measurement equipment. Therefore, this calibration method can be faster than alternatives, such as those using far-field spectrometers.

[0157] For the measurement setup described herein, the calibration accuracy of the spectrometer can be more than an order of magnitude smaller than the wavelength, for example, 0.1 nm, 0.01 nm, or smaller for a wavelength of 13.5 nm. In such cases, the spectrometer can be understood as a sensor capable of separately observing different wavelengths. In some cases, the spectrometer can mean a sensor that disperses a radiation beam through a periodic (e.g., in one direction) known structure and then images the beam onto a camera.

[0158] Figure 8 further illustrates a radiation input device 806 for receiving radiation to be calibrated, which may be emitted radiation 342 as shown in Figure 6. This radiation input device may, for example, be connected to an HHG or LPP source, optionally for providing short-wavelength radiation. Components may be housed within the measurement apparatus for measuring a substrate located on a substrate stage 812. A number of components 810 for guiding the radiation (which may be an illumination system 312 as shown in Figure 6) may be present within the measurement apparatus. In one embodiment, the illumination system irradiates at least a portion of the emitted radiation on the structure to generate one or more scattered radiations, such as reflected radiation 360 and diffracted radiation 397. Such components may, for example, include a toroidal mirror for guiding the radiation to the target substrate to be measured. A toroidal grating may be present on the mirror. Any components of the calibration assembly 800 may need to be provided to fit around existing components 810 of the measurement apparatus. In one embodiment, at least one or a portion of a plurality of detectors are arranged to detect at least a portion of one or more scattered radiations or at least a portion of (emitted) radiation.

[0159] The component 800 may further include a processing unit (which may also be referred to as a processor) for performing data processing and calculations to determine the calibration. The processing unit may include one or more processors and a memory. The processing unit may receive data collected by one or more spectrometers. The data may represent a first radiation spectrum and a second radiation spectrum. The processing unit may perform other processing on the received data, such as noise reduction. The processing unit may receive other data related to the radiation spectrum, such as the time, date, pressure, temperature, etc., of the component when the radiation spectrum was obtained. In some embodiments, the processing unit may be located at a component for a measurement device, and the calibration may be determined at that device. In alternative embodiments, some processing and determination may be performed remotely by transmitting the first and second radiation spectrum data and any associated data to the processing unit, which may be remotely connected to the component, for example, via a wired and / or wireless connection.

[0160] Determining the difference between the calibrated second radiation spectrum and the first radiation spectrum can include a ratio or subtraction of the second radiation spectrum to the first radiation spectrum. This could, for example, involve dividing an image of the radiation spectrum obtained in the presence of krypton by an image of the radiation spectrum obtained in the absence of krypton. This can reveal the absorption spectrum of krypton without the distortion effect of the inherent spectral shape of the radiation source. For example, a Gaussian or Lorentz function can be used to fit to the peaks in the absorption spectrum to provide the position of the absorption peaks relative to the detector grid of the spectrometer with high accuracy. Those wavelength-to-pixel absolutely calibrated mappings can then be used to further analyze the spectra recorded using the detector. Absolute wavelength calibration is possible because the wavelengths of the krypton absorption lines are narrow and absolutely known.

[0161] Further calibration of the spectrometer can be performed, for example, using one or more known calibration methods. The absolute calibration of the spectrometer described herein, along with other calibration methods, can fix the spectrum relative to the wavelength axis. This can mean that it is no longer necessary to fit geometric parameters with associated uncertainties, such as detector position and grating alignment. An additional advantage of using the methods described herein is that if multiple spectrometer detectors exist, these detectors can be intrinsically calibrated to each other.

[0162] The resulting mapping can be unique for each individual detector. Therefore, the calibration of the spectrometer using the method described herein can be based on the radiation spectrum measured by the same spectrometer.

[0163] In some implementations, multiple spectrometers may be present in the assembly. Each spectrometer may require calibration. Each spectrometer may be calibrated based on the radiation spectrum measured by the spectrometer. Each spectrometer may be calibrated simultaneously using the same krypton gas. In an example implementation, the measurement device may include two spectrometers requiring wavelength calibration: a first spectrometer and a second spectrometer. A first portion of the radiation may be directed to the first spectrometer, and a second portion of the radiation may be directed to the second spectrometer. The first spectrometer may measure a first radiation spectrum of the radiation, and the second spectrometer may also measure a first radiation spectrum of the radiation, both without krypton gas being supplied to the assembly. Once the first radiation spectrum has been measured, krypton gas may be added to the propagation paths of both the first and second portions of the radiation. The gas may be present in a portion of the propagation path before the first and second portions are separated, and / or the gas may be present in a portion of the radiation propagation path where the first and second portions of the radiation are combined in the same radiation beam. The first spectrometer may measure the second radiation spectrum in the presence of krypton gas, and the second spectrometer may also measure the second radiation spectrum in the presence of krypton gas. The component can determine the wavelength calibration of the first spectrometer based on the difference between a first radiation spectrum and a second radiation spectrum measured by the first spectrometer. The component can determine the wavelength calibration of the second spectrometer based on the difference between a first radiation spectrum and a second radiation spectrum measured by the second spectrometer. The method described above for two spectrometers can be extended to three, four, or any other number of spectrometers.

[0164] The wavelength calibration of the spectrometer described herein may include identifying the location of the krypton absorption line (e.g., for a wavelength of approximately 13.5 nm) on the spectrometer. This location can be determined based on the difference between a first radiation spectrum in which the radiating wavelength is present and a second radiation spectrum in which the wavelengths absorbed by krypton have been significantly removed. The location on the spectrometer where this difference between the first and second spectra occurs can be associated with the corresponding absorption line of krypton. Once this location has been calibrated to the krypton absorption line, the location of the remaining portion of the radiating wavelength on the spectrometer can be determined relative to this calibrated wavelength.

[0165] A spectrometer can be incorporated into the measurement apparatus, for example, to monitor source fluctuations. The spectrometer can be incorporated into a reference arm of the measurement apparatus. Alternatively, the spectrometer can be incorporated into a measurement arm of the measurement apparatus. In an example embodiment, the spectrometer can be positioned to detect first-order diffracted radiation from a component in the measurement setup. The component can be, for example, a focusing mirror comprising a variable-pitch grating. The received spectrum can be a reference spectrum obtained for monitoring source fluctuations. It can be calibrated to the radiation focused on the target substrate to be measured. The reference spectrum captured by the detector of the spectrometer can be compared with the spectrum obtained after interaction with the target substrate.

[0166] One or more spectrometers for the measurement apparatus may be located inside a measurement container. The measurement container may be a chamber within the measurement apparatus containing the spectrometers. The chamber may also be configured to include a target substrate to be measured by the measurement apparatus, and components for controlling the radiation used for measurement. Radiation can propagate through the chamber. The substrate to be measured may be located inside the chamber. Other components of the measurement apparatus (e.g., optics, actuators) may also be present inside the chamber. During use, the measurement chamber may be maintained under vacuum conditions. During normal operation, when no krypton gas has been added, the measurement chamber may be maintained at approximately 1 × 10⁻⁶. -5 The order of millibars or 1×10 -4 millibars to 1×10 -6 Vacuum pressure in the range of millibars. The pressure inside the container can increase when krypton is added to the chamber. If krypton is added to the entire container, the pressure can increase from 1 × 10⁻⁶. -3 millibars to 1×10 -2 Within the millibar range. If a gas chamber is provided, the gas is configured to be added to said gas chamber, as discussed in more detail below. When krypton is added, the increase in container pressure may be small, for example, at 1 × 10⁻⁶. -5 millibars to 1×10 -4 Within the range of millibars.

[0167] In some embodiments, krypton gas can be added to a chamber, which can then be used as a container for holding the krypton gas. The chamber may include one or more gas inlets and one or more gas outlets for adding and removing krypton gas, respectively. The gas outlets may include a vacuum pump of a vacuum system. Krypton gas can be added to the container at pressures ranging from 0.0001 mbar to 1 mbar. Inside the container / chamber, the pressure of the krypton gas can be, for example, 0.01 mbar. Adding krypton gas to the container may take approximately several seconds (e.g., 1 s to 10 s). Removing the krypton gas and restoring the pressure to its previous level may take approximately one minute or several minutes. When using a gas chamber, removing krypton gas from the container may be faster (e.g., approximately tens of seconds to one minute or several minutes) compared to adding the gas to the entire container. These pressures can be managed by the vacuum pump system of the measurement device. The pressure mentioned may be the pressure used when measuring a second radiation spectrum. The pressure can be gradually increased to this value by the host before measurement and can be gradually reduced to a lower pressure after measurement.

[0168] The pressure of the krypton can be selected such that the amount of krypton is large enough to have a significant effect on the radiation spectrum (making absorption lines observable). The amount of krypton can be low enough that the gas's effect on the radiation spectrum is limited to the wavelength of radiation absorbing the absorption lines, without having a relative effect on other wavelengths. Those skilled in the art will understand that the pressure range of the krypton for observing the desired absorption behavior can depend on the propagation length of the radiation through the krypton. The amount of interaction between the radiation and the krypton can depend on both the pressure of the krypton and the propagation length of the radiation through the gas. When krypton is added to the measuring container, the interaction length between the radiation and the krypton can be equal to the propagation length of the radiation through the measuring container. The radiation can have a propagation length through the measuring container in the range of 10 cm to 5 m, for example, in the range of 50 cm to 150 cm, or 60 cm to 150 cm, or 50 cm to 150 cm. When a gas chamber is used, the propagation length inside the gas chamber can be in the range of 5 cm to 15 cm. The gas chamber can include an inlet and an outlet for the radiation to pass through. In one embodiment, the propagation length of radiation in the air chamber is in the range of 5 mm to 20 cm, such as 10 cm.

[0169] The advantage of adding krypton directly into the chamber of the device is that it is a simple solution that does not require a large amount of space or additional components or structures inside the measuring device.

[0170] In some embodiments, a gas chamber may be provided within a cavity. The gas chamber may sometimes be referred to as a flushing box. The propagation path of radiation may pass through the gas chamber. A gas supply system may include the gas chamber. Figure 9 depicts a schematic representation of a gas chamber 900. In one embodiment, the gas supply system includes a gas nozzle, such as gas nozzle 609 in Figure 7. The gas chamber may have a gas inlet 902 and one or more gas outlets 904(a) to 904(b). The gas inlet 902 may be an inlet pipe attached to the gas chamber body 906. The gas outlets 904(a) to 904(b) may be two outlet pipes. The outlet pipes may be positioned such that the propagation path of the radiation is transmitted along the channel formed by the outlet pipes 904(a) and 904(b). Thus, the outlet pipes may serve as an input for radiation 908 input to the gas chamber and an output for radiation 910 output from the gas chamber 900. Other chamber shapes can be used, such as a chamber body in which the inlet and / or outlet are not tubes / pipes, or a T-tube in which the base can be used as an inlet and the two arms can be used as an outlet.

[0171] The advantages of using a gas chamber are: it allows for a lower krypton flow rate compared to directly inserting krypton into the chamber serving as a container, because the area to be filled with gas is smaller. It also allows the chamber to remain at a lower pressure compared to injecting gas into the entire chamber serving as a container. The gas chamber should be positioned within the radiation propagation path, which may already be in a confined area with limited space for additional components.

[0172] Inside outlet pipes 904(a) to 904(b), the gas can achieve laminar flow rather than turbulent flow due to the pressure mechanism present in the measuring device. This laminar flow can be advantageous because turbulence can lead to local pressure differences that change over time and can make the total interaction between radiation and krypton less constant.

[0173] The propagation length of radiation within the gas chamber can range from 5 mm to 20 cm, such as 10 cm. The propagation length of radiation within the gas chamber 900 can be at least 10 cm, or within the range of 10 cm to 20 cm. The propagation length inside the gas chamber can include the lengths of the two outlet tubes. The propagation length can be used to determine the interaction length between the radiation and the krypton gas. When determining the interaction length, the tube lengths can be weighted using a weighting factor. This is because the gas pressure inside the tube can decrease towards the ends of the tube. This may result in a reduction in the interaction between the radiation and the gas.

[0174] Similar to when the gas is supplied directly into the chamber serving as a container, the amount of krypton needs to be sufficient to make the absorption of radiation at the krypton absorption line noticeable (measurable), but not so high that other wavelengths of the radiation are substantially affected. Since the gas is supplied only along a portion of the radiation's propagation length, achieving this may require a higher krypton pressure inside the chamber than the pressure within the chamber itself. The actual pressure required can depend on the length of the interaction between the radiation and the krypton.

[0175] The size of the chamber body 906 of the gas chamber can also affect the amount of airflow / gas pressure required. A larger gas chamber may require lower gas pressure and lower airflow to achieve the same amount of radiation-gas interaction compared to a smaller gas chamber. Based on the propagation length range of radiation within the gas chamber, which is in the range of 5 mm to 20 cm or 1 cm to 20 cm as described above, the gas pressure inside the gas chamber can range from 0.1 mbar to 2 mbar. The gas pressure can be considered as the pressure within the chamber body 906 of the gas chamber. The gas pressure can vary towards the outlet ends 904(a) to 904(b) of the gas chamber 900.

[0176] In some embodiments, the gas chamber may include one or more components of the measuring device, such as one or more optical components for guiding the radiation within the measuring device. The gas chamber may, for example, be positioned around a focusing mirror. This can have the additional advantage that the gas chamber 900 can be used as a rinsing chamber for components.

[0177] In some cases, the above method may encounter problems if the visibility of the absorption peaks of the calibration gas in the second radiation spectrum is poor. This can occur, for example, when the spectral change between the presence and absence of the gas is less than the noise level of the detector. In such cases, lock-in detection can be used to improve the visibility of the peaks. Lock-in detection can be performed using a calibration assembly including, for example, the gas chamber described with respect to Figure 9. The lock-in technique involves modulating the gas pressure at a known frequency while a time series of the image is captured by a spectrometer. Gas pressure modulation can be implemented, for example, using a pulsed gas valve. The pulsed gas valve can be piezoelectrically controlled. Subsequently, the time series of the image is analyzed, and signal components that do not vary at the same frequency as the applied pulsed pressure are filtered out from the image of the spectrum. The remainder of the spectrum is a component of the radiation spectrum that varies at the same frequency as the pulsed pressure, which may be the absorption peaks of the gas.

[0178] The advantage of using lock-in detection is that it allows for the use of lower gas pressures, ensuring that the difference between the radiation spectra with and without gas pressure is less than the noise level of the spectrometer being calibrated. This means that less gas is required for calibration, and that the pressure inside the measurement device can be kept low.

[0179] While the methods and components for using krypton have been described above, krypton can be a particularly relevant gas for radiation with wavelengths ranging from 1 nm to 20 nm, but other gases can be used to implement the same methods. The suitability of a gas can depend on several factors, including the wavelength at which the absorption line appears and the thickness of the absorption line. Helium is a suitable example gas, possessing the same inert gas advantages as krypton. Helium also has an absorption peak in the 1 nm to 20 nm range. Other applicable gases include phosphorus-based gases (e.g., phosphine PH3), silicon-based gases (e.g., silane SiH4), sulfur-based gases (e.g., sulfur dioxide SO2), and boron-based gases (e.g., boron trichloride BCl3).

[0180] When the absorption peak of a gas falls within the trough of the radiation spectral comb, the absorption effect by the gas becomes difficult to observe. To overcome this challenge, one or more parameters of the radiation source can be varied to alter the spectrum output by the source. Examples of parameters to be varied include the driving laser wavelength (which shifts the peak), the pulse length of a pulsed driving laser (shorter pulse lengths broaden the peak), and the absence of a second harmonic in the driving laser, which adds more peaks in the even harmonics. The pressure within the generating medium of the driving laser can be altered, which can induce a wavelength shift in the resulting harmonics. Changing these parameters may require significant changes to the measurement / source setup. Changing the parameters can, for example, cause a spectral shift such that the absorption line overlaps with a peak in the radiation spectrum. Alternatively, changing the parameters may cause spectral broadening such that the absorption line falls within a broadened peak in the spectrum.

[0181] Figure 10 illustrates a flowchart of a method 1000 for wavelength calibration or radiation of one or more spectrometers in a measurement apparatus, as described herein. In step 1002, one or more spectrometers measure a first radiation spectrum of the radiation. Once the first radiation spectrum has been measured, a measured amount of krypton (or helium, or other suitable) gas is added 1004 to the propagation path of the radiation in the measurement apparatus. The gas has an absorption line superimposed on at least one wavelength of the radiation. While the gas is present in the propagation path, one or more spectrometers measure 1006 a second radiation spectrum. Then, wavelength calibration of one or more spectrometers is determined 1008 based on the difference between the second radiation spectrum and the first radiation spectrum.

[0182] The foregoing describes components and methods for calibrating the radiation wavelength of a spectrometer in a measuring apparatus by adding a gas to the propagation path of the radiation, wherein the gas has an absorption line superimposed on the wavelength of the radiation. Instead of adding a gas, other wavelength-selective elements having known absorption lines can be added to the propagation path of the radiation.

[0183] Figure 11 depicts a schematic representation of a component 1100 for wavelength calibration of radiation in a measurement device. The measurement device includes one or more spectrometers 1102(a), 1102(b) to be calibrated. The measurement device may have the properties described above with respect to Figure 8, but instead of a gas, a wavelength-selective filter 1104 is added to the radiation propagation path. The wavelength-selective filter 1104 may have an absorption line superimposed on at least one wavelength of the radiation. Similar to the radiation input device 806 described above, the radiation input device 1106 can provide radiation to the component 1100. One or more optical components 1110 may be provided to interact with the radiation. A substrate stage 1112, configured to hold the target substrate to be measured, may also be disposed within the chamber of the measurement device.

[0184] The advantage of using a wavelength-selective filter is that it can be designed to select the desired wavelength for transmission / reflection. Therefore, the wavelength can be fine-tuned for the specific radiation spectrum to be calibrated. This contrasts with adding a gas, where absorption lines are a property of the material. Introducing the filter into the measurement device is also simpler than adding a gas.

[0185] Wavelength-selective filters can be solid-state thin-film filters. Thin-film filters can be made of suitable silicon-based materials, such as silicon nitride or pure silicon. Thin-film filters can be designed by selecting the thickness of one or more filter layers to select light with a specific bandwidth. Thin-film filters can also be designed by selecting materials and their associated wavelength properties. The filter can be a transmission-type filter. The transmission-type filter can include multiple filters. The filter can be a multi-cavity filter. In a multi-cavity filter, multiple thin-film bandpass filters can be included, as illustrated in Figure 12. Figure 12 depicts a schematic graph of transmittance T (in the range of 0% to 100%) varying with wavelength λ. The filter can have high transmittance for multiple peaks 1202, for which the transmittance is high. The filter can have well-defined spectral properties, for example, measured using a radiation source with well-defined wavelength properties. By placing the transmission-type filter in the path of the radiation before it reaches the spectrometer, the resulting measured spectrum can involve radiation convolved with the filter. The spectrometer can be calibrated based on the measured spectrum (with and without the filter) and knowledge of the transmission-type filter.

[0186] In some implementations, the filter can be a reflective filter, such as a multilayer mirror. The reflector is designed to reflect only certain wavelengths, which can be achieved, for example, by adding multiple layers of coating to the mirror to reflect only the selected wavelengths. Layer thickness and material selection can be used to design the wavelength reflection properties of the mirror. In addition to the layers of the multilayer mirror, the angle of incidence of the radiation onto the mirror can also be used to select which wavelengths will be reflected (because the angle of incidence changes the propagation length of the radiation through multiple layers). By changing the angle of incidence, the mirror can be fine-tuned by several nanometers depending on the exact angle of incidence.

[0187] Figure 13 illustrates model curves (1300) depicting the reflection properties of example mirrors for different incident angles. The x-axis represents the wavelength of the radiation, and the y-axis represents the reflectivity. Curve 1302 shows an example reflectivity curve for an incident angle of 60°. Curve 1304 shows an example reflectivity curve for an incident angle of 70°. Curve 1306 shows an example reflectivity curve for an incident angle of 80°. The mirror can be a Si / Mo multilayer mirror comprising 40 layers. Each layer can have a thickness of 6.9 nm. This model curve is provided as an example only, and other mirror designs and incident angles can be used.

[0188] Multilayer mirrors, acting as reflective filters, can be positioned in front of a toroidal grating to filter out specific wavelengths within the radiation spectrum. These wavelengths can then be used to calibrate the spectrum on the detector with higher accuracy. Different configurations of the mirrors can be used to reflect radiation onto the toroidal grating. In an example configuration, two mirrors can laterally displace the beam onto the toroidal grating. This may cause the radiation reaching the detector and the grating to also shift, which can complicate the calibration. In another example configuration, four mirrors can be positioned in front of the grating. With the mirrors correctly positioned relative to each other, the radiation beam should not shift, and no additional difficulty is imposed on the calibration.

[0189] In some configurations, the mirror can be placed on an actuation platform (e.g., a rotating platform). By actuating, the angle of incidence can be fine-tuned, for example, to achieve the angle of incidence fine-tuning described with respect to Figure 13. Fine-tuning the reflected wavelength can affect the spectrum of radiation reaching the detector. By rotating the mirror, different wavelengths can experience the highest reflectivity. Although the design of the mirror (material, number of layers and coatings) cannot be changed once it is manufactured, rotating the angle can be used to produce a change in the reflected spectrum.

[0190] While adding wavelength-selective filters allows for wavelength calibration of the spectrometer, having two points for calibration can be advantageous. Having two well-defined points allows the energy axis to be constructed as a separate calibration method, independent of other parameters or inputs. In the example, one wavelength can be used to calibrate the spectrometer, and the spacing between the harmonics of the radiation can then be used to reconstruct the entire energy axis. This spacing can be highly dependent on the wavelength of the fundamental (pump) laser pulse in the interaction region (e.g., a gas jet), potentially requiring its own separate calibration. Furthermore, the geometry and incident angle of the toroidal mirror, including the grating, can be identified / calibrated, allowing the entire energy axis to be reconstructed using a single point.

[0191] As described above, gas and / or other wavelength-selective filters with narrow absorption lines superimposed on the wavelength of radiation of interest can be used for calibration of short-wavelength radiation settings. An alternative to providing wavelength-selective elements is to provide wavelength-diffraction elements. Instead of selecting some wavelengths and excluding others, the wavelength-diffraction elements diffract different wavelengths in different directions. Wavelength-diffraction elements can be, for example, crystalline structures, optionally three-dimensional (3D) crystalline structures. Crystalline structures can be, for example, crystalline materials, optionally three-dimensional (3D) crystalline materials. Wavelength-diffraction elements can be, for example, metamaterial structures. The metamaterial structure can be a three-dimensional (3D) metamaterial structure. 3D metamaterials can be, for example, transmissive metamaterials. 3D metamaterials can be, for example, reflective metamaterials. 3D metamaterials / crystalline structures can be 3D gratings located in the propagation path of the radiation beam. Metamaterials can be designed to mimic the crystalline structure of atoms. The size of the metamaterial unit cell can be designed to correspond to the wavelength of the radiation to be calibrated. The resulting interaction with the radiation can mimic the interaction of hard or soft X-rays with atoms for calibration.

[0192] Metamaterials can be materials comprising repeating units, which can be referred to as unit cells. Different unit cell designs can be provided, such as cubic, quadrilateral, orthorhombic, monoclinic, triclinic, hexagonal, and rhombic. These unit cells can mimic unit cell designs found in atomic crystalline structures. Details regarding different types of crystalline structures are known in the art. However, any metamaterial structure can be designed, regardless of whether the structure exists in naturally occurring materials. Metamaterial structures can be referred to as 3D gratings or 3D lattice superstructures. Lattice superstructures can be designed with dimensions and angles to improve interaction with radiation. The design can be specific to the wavelength range of radiation of interest. In some embodiments, cubic unit cells can be chosen for 3D metamaterial structures. The advantages of cubic unit cells include their simple, repeatable design, which allows for easier fabrication. They can also lead to easier analysis of interactions with incident radiation.

[0193] Metamaterial structures can be designed to be symmetrical about a specific, chosen axis. The advantage of this symmetry is that the orientation of the material relative to the radiation beam is insignificant compared to the structure's symmetry. For example, due to its symmetry, how the meta-lattice is positioned within the radiation beam to be diffracted may be irrelevant. The diffraction pattern produced when the meta-lattice is rotated can ultimately always show minimum and maximum values. These minimum / maximum locations can be wavelength-dependent using 3D metamaterial parameters.

[0194] Figure 14 depicts a schematic representation of a portion of example component 1400, wherein a metamaterial structure and / or crystalline structure 1406 diffracts radiation. The metamaterial / crystalline structure may be a 3D metamaterial / crystalline structure. A short-wavelength radiation source 1402 may provide a radiation beam 1404 comprising multiple short wavelengths. In this example, the multiple short wavelengths may be included in a soft X-ray wavelength spectrum. In this example, the multiple short wavelengths may be included in a hard X-ray wavelength spectrum. The radiation beam 1404 may be incident on the 3D metamaterial / crystalline structure 1406. The radiation beam 1404 may be a soft X-ray beam. The 3D metamaterial / crystalline structure 1406 may diffract the radiation into multiple diffracted radiation beams 1408. The diffracted radiation 1408 may be incident on a detector 1410 configured to measure the properties of said radiation. When the short-wavelength radiation interacts with the 3D crystalline structure, the resulting diffraction pattern may be correlated with the properties of the crystalline structure. When the short-wavelength radiation interacts with the 3D metamaterial, the resulting diffraction pattern may be correlated with the metamaterial design. Metamaterial structures can be placed in the path of radiation propagation in components, which are provided, for example, in measuring or inspection devices as described herein.

[0195] By knowing the detailed properties of the metamaterial design (lattice structure, dimensions, angles, etc.), the properties of short-wavelength radiation can be inferred based on diffraction patterns captured by one or more spectrometers. The 3D metamaterial structure can be provided individually for wavelength calibration, or as one or more elements in a plurality of calibration components. The 3D metamaterial structure can be (at least partially) transparent to the range of short-wavelength radiation of interest. Different short-wavelength radiation wavelengths can be separated within the 3D metamaterial structure. Properties at different wavelengths, such as (e.g.) intensity recorded by a detector, can be measured. This information can be used to calibrate the radiation.

[0196] A component for wavelength calibration of radiation in a measurement device comprising one or more spectrometers can be provided. The component can be configured to have the one or more spectrometers measure a first radiation spectrum of the radiation. After the first radiation spectrum has been measured, a first wavelength selection element and a second wavelength selection element can be added to the propagation path of the radiation in the measurement device. The first wavelength selection element may have a first absorption line superimposed on at least a first wavelength of the radiation. The second wavelength selection element may have a second absorption line superimposed on at least a second wavelength of the radiation. The first wavelength and the second wavelength are different. Although the wavelength selection elements are present in the propagation path of the radiation, one or more spectrometers each measure a second radiation spectrum. Wavelength calibration for one or more spectrometers can be determined based on the difference between the second radiation spectrum and the first radiation spectrum. In one embodiment, the wavelength calibration is determined for one spectrometer. In one embodiment, multiple detectors are configured to simultaneously measure the absorption line. In one embodiment, wavelength calibration is determined simultaneously for more than one spectrometer.

[0197] If two calibration points are used, any combination of two gas, solid-film, transmissive, and reflective filters can be used. For example, a gas and a transmissive filter, or a first gas and a second gas, or a transmissive filter and a reflective filter, etc.

[0198] As stated above, obtaining absolute calibration of broadband radiation incident on a spectrometer setup can be challenging. Calibration can rely on approximations and / or assumptions about the geometry of the measurement setup. Short-wavelength spectra, as described herein, can be measured and calibrated, for example, by a far-field spectrometer or a transmission grating spectrometer. Far-field spectrometers can use diffraction structures such as toroidal mirrors comprising variable-pitch gratings to obtain diffraction spectra in which wavelengths can be spatially separated. Based on the positional information of the radiation incident on the detector, the wavelength can be determined based on the spatial separation of the diffraction structure and knowledge (e.g., using grating equations). Divergence information can also be obtained, for example, based on an axis on the detector perpendicular to the axis along which the spatial separation produced by diffraction is observable. However, any measured spatial separation can depend on the alignment of the radiation with the grating (e.g., the angle of incidence) and the distance between the grating and the detector. Schemes using krypton, wavelength-selective elements, etc., as described herein, can be used to obtain absolute calibration. Further schemes for obtaining calibration of radiation that reduce reliance on assumptions or approximations will be described below. These methods may also be used in addition to or as alternatives to the calibration methods and components described above.

[0199] The example component can use a detector that can move along the propagation direction of the radiation beam to be calibrated to acquire multiple spectral images at several different locations. The detector can be placed on a platform within the component with precise position control. Due to the precise position control of the platform, the location along the propagation direction (which may be referred to as the Z-location along the Z-direction) can be precisely known. Moving the detector that measures the diffracted radiation (having a non-zero order, allowing for the observation of wavelength-based separation) along the propagation direction of the radiation will result in a change in the position of the diffracted radiation on the detector. The movement of the detector along the propagation direction is defined as having a non-zero component along the propagation direction, and optionally also having a component that is not parallel to the propagation direction. In the case where the diffraction pattern is separated by wavelength along a single direction (e.g., by diffraction achieved by a line grating), this direction may be referred to as the X-direction. The location on the detector along the X-direction may be referred to as the X-position.

[0200] By measuring the X position of the diffraction spectrum at different Z locations, the changes of these lateral X positions with respect to the Z locations can be compared without knowing the absolute positions of X or Z.

[0201] Figure 15 illustrates a schematic representation of a component 1500 for measuring a spectrum using a detector 1508 on a movable platform 1516. Broadband radiation 1502 can be incident on a transmission diffraction structure 1504 (e.g., a transmission grating). The diffraction structure can diffract the broadband radiation into multiple diffraction orders 1506. These diffraction orders can include zero diffraction orders (i.e., mirror transmission) and non-zero diffraction orders, such as a positive-1 diffraction order (+1), a negative-1 diffraction order (-1), etc. One or more diffraction orders (including at least one non-zero diffraction order) are incident on the detector 1508. The platform 1516 can move the detector between different locations, and the detector can obtain measurements of the diffracted radiation incident on it at each location. The platform can move the detector along a Z-direction 1510, which can be parallel to the propagation direction of the broadband radiation 1502. The difference 1512 between the Z-regions can be compared with the difference 1514 between the regions of diffraction radiation (along the X-direction) on the detector to determine the radiation spectrum without knowing the absolute position of the platform 1516 relative to the diffraction structure 1504. Alternatively, in some embodiments, movement of the platform along the X-direction can be performed, as described in more detail below.

[0202] Figure 16 illustrates a flowchart of the steps in a method 1600 for measuring the spectrum of broadband radiation 1502. The broadband radiation may have a propagation direction 1510. The broadband radiation beam 1602 is diffracted into multiple diffraction orders using a transmission diffraction structure (such as a transmission grating). A detector at a first location is used to measure at least one of the multiple diffraction orders 1604 to obtain a first measurement signal. The measurement includes a wavelength-resolved measurement of the position of the radiation on the detector. The detector is moved 1606 along the propagation direction from the first location to a second location. A detector at the second location is used to measure at least one of the multiple diffraction orders 1608 to obtain a second measurement signal. The spectrum of the broadband radiation 1610 is determined based on the difference 1512 between the first and second locations and the difference between the first and second measurement signals. The difference between the first and second measurement signals may include the difference in the lateral position of the wavelength-resolved radiation data on the detector.

[0203] In one embodiment, no optical elements are placed in the optical path of the plurality of diffraction orders 1506 between the transmission grating 1504 and the detector 1508. This has the advantage that the presence of any optical element could alter the wavelength and affect the spectral measurement. In another embodiment, one or more of a focusing lens, a steering mirror, and an order classification filter can be placed in the optical path of the plurality of diffraction orders 1506 between the transmission grating 1504 and the detector 1508, and the plurality of diffraction orders 1506 can be focused at multiple locations on the detector 1508.

[0204] The detector may be a spectrometer. The spectrometer may have any of the properties of a spectrometer as described herein. The spectrometer may be positioned in the path of diffracted radiation from the transmission grating to capture at least one diffraction order. The at least one diffraction order may include a non-zero diffraction order. For example, the detector may detect a negative-1 diffraction order (i.e., -1) and / or a positive-1 diffraction order (i.e., +1). Filters or other types of blocking features may be used to (at least partially) block the zero-order incident radiation onto the detector. This may be due, for example, to the high intensity of radiation present in the zero-order diffraction order compared to the non-zero diffraction order.

[0205] The transmission diffraction structure may include a diffraction grating, such as a line grating. The diffraction structure can be a transmission structure because a reflection grating may not work well. The reflection properties of a grating are not always understood in as much detail as their transmission properties. Therefore, for a transmission grating, the absolute effect of the grating on radiation can be obtained in more detail.

[0206] Platform 1516 can place a detector in a first measurement location. Once the detector is positioned, it can measure a first measurement signal. The signal can detect the intensity of radiation incident on the detector. The signal can be wavelength-resolved, meaning the detected signal includes data on the wavelengths of the radiation already detected in the signal. Wavelength-resolved data can be obtained, for example, by combining the measured data from the detector. The detector can also be position-resolved, meaning the detected signal includes data on the location on the detector where the radiation was detected. The detected signal can include data representing the intensity distribution of one or more wavelengths of radiation incident across different locations on the detector. One or more processors can be provided as part of a component to receive and process the measurement signal and perform steps for measuring and calibrating spectra and spectrometers as described herein.

[0207] In the case of an online grating, different wavelengths can be diffracted at different angles. Therefore, for broadband radiation incident on a transmission grating, the resulting diffraction pattern can be expected to include a distribution of different wavelengths of radiation along a direction which may be referred to herein as the lateral direction or the X-direction.

[0208] Once the detector has performed the first measurement, the platform 1516 can move the detector to the second location. This movement can be along the propagation direction 1510 of broadband radiation, for example, the propagation direction of broadband radiation incident on the transmission grating. The platform can have precise position control, meaning that the distance the detector has moved (i.e., the difference between the first and second locations) can be known with high accuracy.

[0209] At the second location, the detector can acquire a second measurement signal. The process of acquiring the second measurement signal can be as described above regarding the first measurement signal. The second measurement signal can measure the diffraction order, which is the same as the first measurement signal but located at a different location. Once the first and second measurement signals have been acquired, they can be compared. Since the position pointers of the wavelength-resolved signals for both the first and second signals on the detector are known, as part of the comparison, the positional difference (i.e., shift) between the first and second signals for each wavelength can be determined. This difference in the position of the wavelengths on the detector can be compared to the difference in the location of the detector. Based on this information, the calibration of the spectrum on the detector can be determined without knowing the exact location of the detector relative to the transmission grating. This has the advantage of making the measurement less dependent on assumptions about the geometry of the measurement setup.

[0210] Although the determination of the spectrum as described above is based on measuring signals at two separate locations, it is understood that the process can be repeated for a third detector location, a fourth detector location, and so on. In such a case, the detector can be moved to a third location, a third measurement signal can be obtained, and the third signal and the third measurement signal can be included in the determination of the spectrum as described herein.

[0211] The detector can be positioned within a measurement apparatus as described above regarding other aspects. The detector can be positioned within a measurement branch of the measurement apparatus. The broadband radiation may include the measured radiation. The detector can be used with one or more other spectrometers to determine the calibration of the radiation as described herein. Measurements obtained in the moving detector setup described herein can be combined, for example, with measurements obtained from different detectors in a reference branch of the measurement setup. Spectra obtained from different detectors can be coupled together. Combining multiple different spectral calibration results can be used for, for example, verification, error control, in-situ drift control, and relative measurements.

[0212] The broadband radiation to be measured can propagate from the transmission grating to the detector without passing through the optical components. This is because placing additional optical components between the grating and the detector can change the wavelength and / or direction of the diffracted radiation beam (e.g., due to dispersion).

[0213] Depending on the quality of the detector, multiple wavelengths can be incident on a single pixel. Alternatively or additionally, it may be desirable to obtain a determination of the location of radiation on the detector with a resolution better than the pixel size of the detector. To achieve sub-pixel resolution along the X-direction of the diffracted radiation for determining the spectrum, the platform can be moved in both the propagating Z-direction 1510 and the lateral direction (X-direction) 1518. In one embodiment, to achieve sub-pixel resolution along the X-direction of the diffracted radiation for determining the spectrum, the platform can be moved in both the propagating Z-direction 1510 and two (or more) different lateral directions (X-directions) 1518. The platform can move in a set pattern in the X and Z directions, with the x-axis and z-axis shown in Figure 15 for the X and Z directions. At each point, the spectrum can be measured by the detector. The wavelength can be determined from the image set by fitting the results to the image set. In one embodiment, the set pattern of the location includes movement with a non-zero component along the propagation direction of radiation and movement with a non-zero component along a direction perpendicular to the propagation direction. Optionally, a movement with a non-zero component along a direction perpendicular to the propagation direction includes multiple movements with a non-zero component along a direction perpendicular to the propagation direction.

[0214] The detector can move in a predetermined pattern to multiple locations and can measure a signal at each location. Using a predetermined pattern means that measurements taken at different time points can be compared (e.g., to determine relative drift). For each movement within the predetermined pattern, the detector can move at least along the Z-direction. As described above, in some cases, the detector can move along both the Z and X directions for each movement.

[0215] In another embodiment, in some cases, the spectrum of radiation on the detector can be determined by using an additional radiation source (e.g., for detector calibration). The radiation source may have a known wavelength with a narrow linewidth, such that measurements of radiation from such a source have a known wavelength and diffraction behavior with respect to a known diffraction grating pitch. Measurements for the known radiation can be obtained, after which broadband radiation can be measured. The known wavelength may differ from the wavelength of the broadband radiation (i.e., it does not overlap with the wavelength of the broadband radiation). The segmented grating can be configured with different grating pitches to accommodate both the known wavelength and the broadband radiation wavelength.

[0216] Figure 17 depicts a schematic representation of component 1700 for measuring the spectrum of broadband radiation 1702 on detector 1708. An additional source is provided, providing radiation 1703 at a known wavelength. A segmented grating 1704 may be provided, which may relate to a segmented version of the transmission structure described in Figure 15. The segmented grating may, for example, be a grating comprising different segments with different pitches, the different segments being configured to diffract the broadband radiation wavelength and the known wavelength, respectively. Detector 1708 may be configured to obtain a measurement signal as described with respect to Figure 15. The detector may obtain separate measurement signals for the diffracted known radiation 1707 and the diffracted broadband radiation 1706. The detector may be movable in both the Z-direction 1710 of the propagation of the broadband radiation and the X-direction 1718 along the diffraction direction of the broadband radiation. The known radiation becomes parallel to the broadband after incident on the segmented grating. The features described with respect to Figure 15 may also be combined with the components of Figure 17.

[0217] The components of Figure 17 can be used to perform a method for measuring the spectrum of broadband radiation. The method may include receiving a calibration radiation beam having a known wavelength. The calibration radiation beam may be diffracted into multiple diffraction orders using a segmented grating. A detector may be used to measure at least one of the multiple diffraction orders to obtain a calibration measurement. The measurement may include wavelength-resolved measurements of one or more locations of the radiation on the detector. The distance from the segmented grating to the detector may be determined based on the calibration measurement and the known wavelength of the calibration radiation. A broadband radiation beam may be received on the segmented grating and diffracted into multiple diffraction orders using the segmented grating. The detector may be used to measure at least one of the multiple diffraction orders. The spectrum of the broadband radiation may be determined based on the difference between a first location and a second location and the difference between a first measurement signal and a second measurement signal. The broadband radiation and calibration radiation beams may have parallel propagation directions when incident on the grating. The broadband radiation and calibration radiation may have at least partial spatial overlap.

[0218] The components may be the inspection or measurement devices described herein. The radiation may be short-wavelength radiation, such as EUV and / or SXR radiation. For example, broadband radiation may include multiple wavelengths in the range of 1 nm to 100 nm, or 1 nm to 10 nm, or 10 nm to 20 nm, or 0.1 nm to 10 nm.

[0219] It is understood that the methods and components described herein with respect to movable detectors can be combined with features described with respect to other embodiments. In particular, these components can be incorporated into measurement or lithography setup and calibration applications as described herein. The components and methods can be used at wavelengths and wavelength ranges as described above.

[0220] Embodiments may include a computer program comprising one or more sequences of machine-readable instructions describing methods of optical metrology and / or methods of analyzing measurements to obtain information about a lithography process. Embodiments may include computer program code containing one or more sequences of machine-readable instructions or data describing the methods. Such a computer program or program code may be executed, for example, within a unit MPU in the device of FIG. 6 and / or a control unit CL of FIG. 3. A data storage medium (e.g., semiconductor memory, disk, or optical disk, etc.) in which such a computer program or program code is stored may also be provided. Where existing metrology devices of the type shown in FIG. 6 are already in production and / or in use, embodiments of the invention may be implemented by providing an updated computer program product that causes a processor to execute one or more of the methods described herein. The computer program or program code may optionally be arranged to control optical systems, substrate supports, etc., to perform methods of measuring parameters of a lithography process with respect to suitable plurality of targets. The computer program or program code may update lithography and / or metrology options for measurements on additional substrates. Computer programs or program code can be arranged to control (directly or indirectly) photolithography equipment for patterning and processing of additional substrates.

[0221] The irradiation source can be placed in, for example, a measurement device (MT), an inspection device, a lithography device (LA), and / or a lithography unit (LC).

[0222] The properties of the emitted radiation used to perform the measurement can affect the quality of the obtained measurement. For example, the shape and size of the transverse beam profile (cross section) of the radiation beam, the intensity of the radiation, and the power spectral density of the radiation can all affect the measurement performed by radiation. Therefore, it is beneficial to have a source that provides radiation with properties that induce high-quality measurements.

[0223] Further embodiments are disclosed in the following numbered aspects:

[0224] 1. A component for wavelength calibration of radiation, wherein the component comprises:

[0225] One or more spectrometers, said one or more spectrometers being configured to:

[0226] Measure the first radiation spectrum of the radiation;

[0227] A second radiation spectrum is measured while krypton is present in the propagation path of the radiation, wherein the krypton has an absorption line superimposed on at least one wavelength of the radiation; and

[0228] A processor configured to determine the wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0229] 2. The component according to any of the foregoing aspects, wherein the difference is the ratio of the second radiation spectrum to the first radiation spectrum.

[0230] 3. The component according to any of the foregoing aspects, wherein the radiation includes one or more wavelengths in the range of 1 nm to 100 nm, or 1 nm to 10 nm, or 10 nm to 20 nm, or 0.1 nm to 10 nm.

[0231] 4. The component according to any of the foregoing aspects, wherein the component comprises a plurality of spectrometers, and wherein the component is configured to determine wavelength calibration for each of the plurality of spectrometers.

[0232] 5. The component according to any of the foregoing aspects, wherein the processor is configured to:

[0233] The position of the krypton absorption line on each of the one or more spectrometers is identified based on the difference between the second radiation spectrum and the first radiation spectrum; and

[0234] The wavelength corresponding to the absorption line of krypton is calibrated to the position of the absorption line.

[0235] To determine the wavelength calibration for each spectrometer.

[0236] 6. The component according to any of the foregoing aspects, wherein the absorption line of krypton is associated with a photon energy in the range of 90 eV to 95 eV, such as with a wavelength of 13.5 nm.

[0237] 7. The component according to any of the foregoing aspects, wherein the one or more spectrometers are configured to be disposed inside a measurement or inspection container, wherein the radiation is configured to propagate inside the measurement or inspection container, and wherein the krypton gas is configured to be added to the measurement or inspection container.

[0238] 8. The component according to aspect 7, wherein the component further comprises a gas module configured to add krypton gas inside the measuring or checking container at a pressure in the range of 0.0001 mbar to 1 mbar, such as 0.01 mbar.

[0239] 9. The component according to any one of aspects 7 to 8, wherein the propagation length of the radiation within the measuring or inspecting device is in the range of 10 cm to 5 m, such as in the range of 60 cm to 150 cm or 50 cm to 70 cm.

[0240] 10. The component according to any one of aspects 1 to 6, wherein the component further includes a gas chamber, and wherein the krypton gas is configured to be added to the gas chamber.

[0241] 11. The component according to aspect 10, wherein the gas chamber includes an inlet pipe and two outlet pipes, wherein the outlet pipes are further configured to serve as an input end and an output end of the gas chamber for the radiation.

[0242] 12. The component according to any one of aspects 10 to 11, wherein the propagation length of the radiation in the air chamber is in the range of 5 mm to 20 cm, such as 10 cm.

[0243] 13. The component according to any of the foregoing aspects, wherein measuring the first radiation spectrum and the second radiation spectrum includes performing lock detection.

[0244] 14. The component according to any of the foregoing aspects, wherein the one or more spectrometers are included in the reference arm of the measuring or inspection device.

[0245] 15. The component according to any of the foregoing aspects, wherein the one or more spectrometers are included in the measuring arm of the measuring or inspection device.

[0246] 16. A method for wavelength calibration of radiation, the method comprising:

[0247] The first radiation spectrum of the radiation is measured by one or more spectrometers;

[0248] A second radiation spectrum is measured by one or more spectrometers while krypton is present in the propagation path of the radiation, wherein the krypton has an absorption line superimposed on at least one wavelength of the radiation; and

[0249] The processor determines the wavelength calibration of one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0250] 17. A component for wavelength calibration of radiation, wherein the component comprises:

[0251] One or more spectrometers, said one or more spectrometers being configured to:

[0252] Measure the first radiation spectrum of the radiation;

[0253] A second radiation spectrum is measured while helium is present in the propagation path of the radiation, wherein the helium has an absorption line superimposed on at least one wavelength of the radiation; and

[0254] A processor configured to determine the wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0255] 18. A component for wavelength calibration of radiation, wherein the component comprises:

[0256] One or more spectrometers, said one or more spectrometers being configured to:

[0257] Measure the first radiation spectrum of the radiation;

[0258] A second radiation spectrum is measured while a wavelength-selective filter is present in the propagation path of the radiation, wherein the wavelength-selective filter instrument has an absorption line superimposed on at least one wavelength of the radiation; and

[0259] A processor configured to determine the wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0260] 19. The component according to aspect 18, wherein the wavelength selective filter is a solid-state thin-film filter.

[0261] 20. The component according to any one of aspects 18 to 19, wherein the wavelength selective filter is a transmission filter.

[0262] 21. The component according to any one of aspects 19 to 20, wherein the wavelength selective filter is a multi-cavity filter.

[0263] 22. The component according to any one of aspects 18 to 19, wherein the wavelength selective filter is a reflective filter.

[0264] 23. The component according to aspect 22, wherein the wavelength selective filter is a multilayer mirror.

[0265] 24. The component according to any one of aspects 22 to 23, wherein the incident angle of the radiation on the reflective filter is selected to fine-tune the reflected wavelength.

[0266] 25. A component for wavelength calibration of radiation, wherein the component comprises:

[0267] One or more spectrometers, said one or more spectrometers being configured to:

[0268] Measure the first radiation spectrum of the radiation;

[0269] A second radiation spectrum is measured while a first wavelength selection element and a second wavelength selection element are present in the propagation path of the radiation, wherein the first wavelength selection element has a first absorption line superimposed on at least a first wavelength of the radiation, and the second wavelength selection element has a second absorption line superimposed on at least a second wavelength of the radiation, and wherein the first wavelength is different from the second wavelength; and

[0270] A processor configured to determine the wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0271] 26. The component according to aspect 25, wherein the first wavelength selection element is one of a solid thin film, krypton, helium, a transmission filter, or a reflection filter.

[0272] 27. The component according to any one of aspects 25 to 26, wherein the second wavelength selection element is different from the first wavelength selection element, and the second wavelength selection element is one of a solid thin film, krypton, helium, a transmission filter, or a reflection filter.

[0273] 28. A component for wavelength calibration of radiation, wherein the component comprises:

[0274] One or more spectrometers, said one or more spectrometers being configured to:

[0275] Measure the first radiation spectrum of the radiation;

[0276] The second radiation spectrum of the radiation is measured while the wavelength diffraction element is present in the propagation path of the radiation;

[0277] The wavelength diffraction element includes a grating configured to spatially separate different wavelengths of the radiation to different locations on the spectrometer; and

[0278] A processor configured to determine the wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

[0279] 29. The component according to aspect 28, wherein the wavelength diffraction element comprises a three-dimensional metamaterial structure or a three-dimensional crystalline structure.

[0280] 30. A measuring device comprising components according to any one of aspects 1 to 15 and 17 to 29.

[0281] 31. An inspection device comprising the components described in any one of aspects 1 to 15 and 17 to 29.

[0282] 32. A photolithography apparatus comprising the components described in any one of aspects 1 to 15 and 17 to 29.

[0283] 33. A photolithography unit comprising the apparatus according to any one of aspects 30 to 32.

[0284] 34. A component comprising:

[0285] A radiation input device configured to receive emitted radiation;

[0286] An illumination system, the illumination system being arranged to illuminate at least a portion of the emitted radiation onto the structure to produce one or more scattered radiations;

[0287] A plurality of detectors, wherein at least a portion of the plurality of detectors is arranged to detect at least a portion of the one or more scattered radiations or at least a portion of the emitted radiation; and

[0288] A gas supply system configured to supply gas to absorb a portion of the emitted radiation, thereby generating absorption lines on the spectrum of the one or more scattered radiations and at least a portion of the emitted radiation;

[0289] The plurality of detectors are configured to simultaneously measure the absorption line.

[0290] 35. The component according to aspect 34, wherein the gas is an inert gas.

[0291] 36. The component according to aspect 35, wherein the inert gas is krypton.

[0292] 37. The component according to any one of aspects 34 to 36, wherein the absorption line is used to measure the spectrum of at least a portion of the one or more scattered radiations and / or the emitted radiations.

[0293] 38. The component according to any one of aspects 34 to 37, wherein the spectrum is different on the plurality of detectors.

[0294] 39. The component according to any one of aspects 34 to 38, wherein the component is used to measure parameters of a structure on a substrate, and the at least portion of the plurality of detectors is arranged to detect the at least portion of the one or more scattered radiations to measure the parameters.

[0295] 40. The component according to aspect 39, wherein the parameter is a contour measurement parameter.

[0296] 41. The component according to any one of aspects 34 to 40, wherein the emitted radiation includes one or more wavelengths in the range of 1 nm to 100 nm, or 1 nm to 10 nm, or 10 nm to 20 nm, or 0.1 nm to 10 nm.

[0297] 42. The component according to any one of aspects 34 to 41, wherein the component further includes a gas chamber, and wherein the gas is configured to be added to the gas chamber.

[0298] 43. The component according to aspect 42, wherein the gas chamber includes an inlet and an outlet for the emitted radiation.

[0299] 44. The component according to aspect 43, wherein the propagation length of the radiation in the air chamber is in the range of 5 mm to 20 cm, such as 10 cm.

[0300] 45. The component according to any one of aspects 34 to 44, wherein the radiation input device is connected to a high-order harmonic generation (HHG) source or a laser-generated plasma (LPP) source.

[0301] 46. ​​An inspection device comprising the components described in any one of aspects 34 to 45.

[0302] 47. A measuring device comprising the components described in any one of aspects 34 to 45.

[0303] 48. A method for measuring the spectrum of broadband radiation, wherein the broadband radiation has a propagation direction, the method comprising:

[0304] The broadband radiation is diffracted into multiple diffraction radiation orders using a transmission grating;

[0305] A first measurement signal is obtained by measuring at least one of the plurality of diffraction orders using a detector at the first location, wherein the measurement includes a wavelength-resolved measurement of the position of the radiation on the detector.

[0306] The detector is moved from the first location to the second location, wherein the movement of the detector has a non-zero component along the propagation direction;

[0307] The detector at the second location is used to measure at least one of the plurality of diffraction orders to obtain a second measurement signal; and

[0308] The spectrum of the broadband radiation is determined based on the difference between the first location and the second location and the difference between the first measurement signal and the second measurement signal.

[0309] 49. The method according to aspect 48, wherein the detector comprises a spectrometer.

[0310] 50. The method according to any one of aspects 48 to 49, wherein the at least one diffraction order includes a non-zero diffraction order.

[0311] 51. The method according to aspect 50, wherein the at least one diffraction order comprises one or both of a negative-1 (-1) diffraction order and a positive-1 (+1) diffraction order.

[0312] 52. The method according to any one of aspects 48 to 51, wherein moving the detector further comprises moving the detector in a direction perpendicular to the propagation direction.

[0313] 53. The method according to any one of aspects 48 to 52, wherein the broadband radiation includes a plurality of wavelengths in the range of 1 nm to 100 nm, or 1 nm to 10 nm, or 10 nm to 20 nm, or 0.1 nm to 10 nm.

[0314] 54. The method according to any one of aspects 48 to 53, wherein the wavelength resolution measurement includes combining measurement data measured by the detector to obtain wavelength information.

[0315] 55. The method according to any one of aspects 48 to 54, wherein the first measurement signal includes a plurality of wavelengths at first positions on the detector, and the second measurement signal includes the plurality of wavelengths at second positions on the detector; and

[0316] The spectrum is determined based on a comparison between the difference between the first and second portions of the detector and the difference between the first and second positions of the plurality of wavelengths on the detector.

[0317] 56. The method according to any one of aspects 48 to 55, wherein the method further comprises:

[0318] The detector is moved from the second location to the third location in a manner that has a non-zero displacement component along the propagation direction; and

[0319] The detector at the third location is used to measure at least one of the plurality of diffraction orders to obtain a third measurement signal; and

[0320] The spectrum of the broadband radiation is determined based on the difference between the first part, the second part, and the third part, and the difference between the first measurement signal, the second measurement signal, and the third measurement signal.

[0321] 57. The method according to any one of aspects 48 to 56, wherein the detector is positioned along a measurement branch of the measuring device, and wherein the broadband radiation includes the measurement radiation.

[0322] 58. The method according to any one of aspects 48 to 57, wherein the broadband radiation propagates from the transmission grating to the detector without passing through the optical components.

[0323] 59. The method according to any one of aspects 48 to 58, wherein the method comprises: moving the detector to a plurality of locations in a set pattern; and using the detector at each of the plurality of locations to measure at least one diffraction order of the plurality of diffraction orders.

[0324] 60. The method according to aspect 59, wherein the setting pattern of the part includes: movement with a non-zero component along the propagation direction of the radiation; and movement with a non-zero component along a direction perpendicular to the propagation direction, optionally multiple movements with a non-zero component along a direction perpendicular to the propagation direction.

[0325] 61. The method according to any one of aspects 48 to 60, wherein the determined spectrum is used for radiation calibration.

[0326] 62. The method according to any one of aspects 48 to 61, wherein no optical elements are placed in the optical path of the plurality of diffraction radiation orders between the transmission grating and the detector.

[0327] 63. An assembly for measuring the spectrum of broadband radiation, comprising:

[0328] A transmission grating, configured to diffract the broadband radiation into multiple diffraction radiation orders;

[0329] A detector configured to measure at least one of the plurality of diffraction orders; and

[0330] A processor configured to control the components to perform the method according to any one of aspects 48 to 62.

[0331] 64. A component for wavelength calibration of radiation, wherein the component comprises:

[0332] One or more spectrometers, said one or more spectrometers being configured to:

[0333] The radiation spectrum is measured while the wavelength diffraction element is present in the propagation path of the radiation;

[0334] The wavelength diffraction element includes a grating configured to spatially separate different wavelengths of the radiation to different locations on the spectrometer; and

[0335] A processor configured to determine the wavelength calibration of one or more spectrometers based on the radiation spectrum and the properties of the metamaterial design.

[0336] 65. The component according to aspect 64, wherein the wavelength diffraction element comprises a three-dimensional metamaterial structure or a three-dimensional crystalline structure.

[0337] 66. The component according to any one of aspects 28, 29, 64 and 65, wherein the radiation is broadband radiation.

[0338] 67. The component according to any one of aspects 64 to 66, wherein the radiation is measured after the wavelength diffraction element.

[0339] 68. The component according to any one of aspects 64 to 67, wherein the properties of the metamaterial design include one or more of lattice structure, size, and angle.

[0340] 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 may have other applications. Possible other applications include manufacturing integrated optical systems, patterning for guiding and detecting magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0341] While specific references may be made herein to embodiments within the context of photolithography equipment, these embodiments can be used in other equipment. The embodiments may form part of mask inspection equipment, metrology equipment, or any equipment that measures or processes objects such as wafers (or other substrates) or masks (or other patterning apparatus). These devices are generally referred to as photolithography tools. Such photolithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0342] While specific reference may be made herein to embodiments in the context of inspection or measurement equipment, these embodiments can be used in other equipment. Embodiments may form part of a mask inspection apparatus, a lithography apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning apparatuses). The term "measurement equipment" (or "inspection equipment") may also refer to an inspection apparatus or inspection system (or a measurement apparatus or measurement system). For example, an inspection apparatus including embodiments may be used to detect defects in a substrate or defects in a structure on a substrate. In such embodiments, the characteristics of interest in the structure on the substrate may involve defects in the structure, the absence of a specific portion of the structure, or the presence of an undesired structure on the substrate.

[0343] While reference may be made specifically to the use of the embodiments in the context of optical lithography, it should be understood that the invention is not limited to optical lithography and may be used in other applications (such as imprint lithography) where circumstances permit.

[0344] 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 may be measured for 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 pitch of the measurement target may be close to or smaller than the resolution limit of the scatterer's optical system, but may be much larger than the size of a typical non-target structure (optionally a product structure) formed by a photolithography process in the target portion C. In practice, the lines and / or spaces of overlapping gratings within the target structure may be comprised of smaller structures that are similar in size to non-target structures.

[0345] While specific embodiments have been described above, it should be understood that the invention can be practiced in other ways than those described. The above description 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.

[0346] While specifically referring to "measuring equipment / tools / systems" or "inspection equipment / tools / systems," these terms may refer to tools, equipment, or systems of the same or similar type. For example, inspection or measuring equipment including embodiments of the present invention can be used to determine the characteristics of structures on a substrate or wafer. For example, inspection or measuring equipment including embodiments of the present invention can be used to detect defects in a substrate or defects in structures on a substrate or wafer. In such embodiments, the characteristics of interest in the structure on the substrate may involve defects in the structure, the absence of a specific portion of the structure, or the presence of undesired structures on the substrate or wafer.

[0347] While specific references are made to HXR, SXR, and EUV electromagnetic radiation, it should be understood that the invention can be practiced with all electromagnetic radiation, including radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays, where circumstances permit.

[0348] Additional objectives, advantages, and features of the invention are set forth in this specification and will, in part, become apparent to those skilled in the art upon review of the following, or may be learned by practice of the invention. The invention disclosed in this application is not limited to any particular set or combination of objectives, advantages, and features. It will be understood that various combinations of the stated objectives, advantages, and features constitute the invention disclosed in this application.

Claims

1. A component comprising: A radiation input device configured to receive emitted radiation; An illumination system, the illumination system being arranged to illuminate at least a portion of the emitted radiation onto the structure to produce one or more scattered radiations; A plurality of detectors, wherein at least a portion of the plurality of detectors is arranged to detect at least a portion of the one or more scattered radiations or at least a portion of the emitted radiations; and a gas supply system configured to supply gas to absorb a portion of the emitted radiation, thereby generating an absorption line on the spectrum of the one or more scattered radiations and at least a portion of the emitted radiation; wherein the plurality of detectors are configured to simultaneously measure the absorption line.

2. The component according to claim 1, wherein, The gas is an inert gas.

3. The component according to claim 2, wherein, The inert gas is krypton.

4. The component according to any one of the preceding claims, wherein, The absorption line is used to measure the spectrum of at least a portion of the one or more scattered radiations and / or the emitted radiations.

5. The component according to any one of the preceding claims, wherein, The spectrum is different on the multiple detectors.

6. The component according to any one of the preceding claims, wherein, The component is used to measure parameters of a structure on a substrate, and at least a portion of the plurality of detectors is arranged to detect at least a portion of the one or more scattered radiations to measure the parameters.

7. The component according to claim 6, wherein, The parameters are contour measurement parameters.

8. The component according to any one of the preceding claims, wherein, The emitted radiation includes one or more wavelengths in the range of 1 nm to 100 nm, or 1 nm to 10 nm, or 10 nm to 20 nm, or 0.1 nm to 10 nm.

9. The component according to any one of the preceding claims, wherein, The component also includes a gas chamber, wherein the gas is configured to be added to the gas chamber.

10. The component of claim 9, wherein, The gas chamber includes an inlet and an outlet for the emitted radiation.

11. The component of claim 10, wherein, The propagation length of the radiation in the air chamber is in the range of 5 mm to 20 cm, such as 10 cm.

12. The component according to any one of the preceding claims, wherein, The radiation input device is connected to a high-order harmonic generation (HHG) source or a laser-generated plasma (LPP) source.

13. A component for wavelength calibration of radiation, wherein, The component includes: one or more spectrometers configured to: measure a first radiation spectrum of the radiation; measure a second radiation spectrum while krypton is present in the propagation path of the radiation, wherein the krypton has an absorption line superimposed on at least one wavelength of the radiation; and a processor configured to determine wavelength calibration of the one or more spectrometers based on the difference between the second radiation spectrum and the first radiation spectrum.

14. An inspection device comprising the components according to any one of claims 1 to 13.

15. A measuring device comprising the components according to any one of claims 1 to 13.

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