Assembly for wavelength calibration

Abstract

A component for calibrating the wavelength of radiation. This component can be provided in a measuring device. The component includes an input configured to receive radiation. The component also includes a diffraction element for diffracting the radiation. The diffraction element includes a bottom layer having a transverse periodic structure and a top layer having a lower surface adjacent to the periodic structure, the transverse periodic structure being used to diffract radiation at an upper surface of the bottom layer, and wherein the top layer has a flat top surface. The diffraction element is arranged to receive radiation on the upper surface of the top layer and reflectively diffract the radiation such that the radiation exits the diffraction element via the upper surface of the top layer. The component also includes a detector configured to detect the diffracted radiation.

Description

Cross-reference to related applications

[0001] This application claims priority to European application 23212376.0, filed on 27 November 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to an assembly for calibrating the wavelength of radiation. In particular, it relates to an assembly having a diffraction element comprising a bottom layer having a diffraction structure and a top layer having a flat surface through which radiation enters and is present in the diffraction element. Background Technology

[0003] A lithography apparatus is a machine configured to apply a desired pattern onto a substrate. For example, a lithography apparatus can be used to manufacture integrated circuits (ICs). For example, a lithography apparatus can project a pattern (also often referred to as a “design layout” or “design”) on a patterning apparatus (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).

[0004] To project a pattern onto a substrate, a photolithography apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the feature that can be formed on the substrate. Commonly used wavelengths are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Photolithography apparatuses using extreme ultraviolet (EUV) radiation, with wavelengths ranging from 4 nm to 20 nm, such as 6.7 nm or 13.5 nm, can be used to form even smaller features on the substrate compared to photolithography apparatuses using, for example, radiation with a wavelength of 193 nm.

[0005] Low Photolithography can be used to process features smaller than the classical resolution limitations of photolithography devices. In this process, the resolution formula can be expressed as: ,in It refers to the wavelength of the radiation used. It is the numerical aperture of projection optics in a photolithography apparatus. It is the "critical size" (usually referring to the minimum feature size for printing, but in this case it refers to half a pitch). It is the empirical resolution factor. Typically, The smaller the substrate, the more difficult it becomes to reproduce patterns on it that are similar in shape and size to those planned by circuit designers to achieve specific electrical functions and performance. To overcome these difficulties, precise fine-tuning steps can be applied to the photolithography projection apparatus and / or design layout. These steps include, but are not limited to, optimization. Customized illumination schemes, the use of phase-shifting patterning apparatuses, and various optimizations to 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 compact control loop for controlling the stability of the lithography apparatus can be used to improve low-resolution imaging. The reproduction of the pattern below.

[0006] In photolithography and other manufacturing processes, frequent measurements of the created structures are desirable, for example, for process control and verification. Various tools are known for performing such measurements, including scanning electron microscopes commonly used to measure critical dimensions (CD), and specialized tools for measuring overlay (the accuracy of alignment between two layers in a device). Recently, various types of scatterometers have been developed for use in photolithography.

[0007] These manufacturing processes can be, for example, photolithography, etching, deposition, chemical mechanical planarization, oxidation, ion implantation, diffusion, or a combination of two or more of these.

[0008] Examples of known scatterers typically rely on providing a dedicated measurement target. For instance, one approach 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 characteristics of the grating are calculated by simulating the interaction between the scattered radiation and a mathematical model of the target structure. The model's parameters are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0009] In addition to reconstructing the shape of the measurement feature, such a device can be used to measure diffraction-based overlay, as described in published patent application US2006066855A1. Diffraction-based overlay measurements using dark-field imaging of diffraction orders enable overlay measurements on smaller targets. These targets can be smaller than the illumination spot and can be surrounded by the product structure on the wafer. Examples of dark-field imaging measurements can be found in several published patent applications, such as US2011102753A1 and US20120044470A, for example. Multiple gratings can be measured in a single image using a composite grating target. Known scatterometers tend to use light in the visible or near-infrared range, which requires the grating pitch to be much coarser than the actual product structure, the very features of which are of interest. Such product features can be defined using much shorter wavelengths of deep ultraviolet (DUX), extreme ultraviolet (EUV), or X-ray radiation. Unfortunately, such wavelengths are often unavailable or unsuitable for measurement.

[0010] On the other hand, the dimensions of modern product structures are 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 typically use features much larger than those of interest to products where overlay errors or critical dimensions are of interest. Measurement results are only indirectly related to the dimensions of the actual product structure and may be inaccurate because the measured target does not exhibit the same distortion issues under the optical projection of the lithography apparatus, and / or there may be different processing issues at other steps in the manufacturing process. While scanning electron microscopy (SEM) can directly resolve these modern product structures, SEM is far more time-consuming than optical measurements. Moreover, electrons cannot penetrate thick process layers, making it unsuitable for metrology applications. Other techniques, such as measuring electrical properties using contact pads, are also known, but they only provide indirect evidence of the actual product structure.

[0011] By reducing the wavelength of the radiation (including the radiation beam) used during measurement, it is possible to resolve smaller structures, thereby increasing sensitivity to structural changes and / or penetrating deeper 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 radiation) to excite the generating / targeting medium, thereby generating emitted radiation, optionally including high-harmonic generation (HHG) of high-frequency radiation.

[0012] One method for measuring patterned structures on a substrate uses diffraction-based measurements. Diffraction-based measurements can be performed by irradiating a target diffractive structure (e.g., a grating) on ​​the substrate and capturing the diffracted radiation beam. The captured diffracted radiation can be analyzed to infer parameters of interest. For parameter inference to work, the characteristics of the radiation beam and the target structure should be known. Understanding the diffraction characteristics of the diffraction structure can be accomplished through modeling or calibration. Modeling requires a complete understanding of the target geometry of the diffraction structure. Calibration requires the grating to remain stable over time. Since these variations may occur over time, it may be necessary to periodically repeat modeling or calibration to account for such variations. Modeling the diffraction structure can require detailed knowledge of the exact properties of the grating, which can be difficult to achieve accurately in practice.

[0013] The measurement setup can exist within a vacuum chamber. A well-known problem is that contaminants can deposit over time on the surfaces of elements present in the vacuum chamber. For example, contaminants can deposit on diffraction structures. This can result in a thin layer of contaminants on the surfaces of elements inside the chamber, which can degrade the performance of these elements. This can affect the stability and efficiency of the elements and cause reduced performance of the measurement device. The embodiments described herein provide a solution to the challenge of contaminants degrading the performance of diffraction elements. Summary of the Invention

[0014] According to an aspect of this disclosure, an assembly for calibrating the wavelength of radiation is provided. The assembly includes an input configured to receive radiation. The assembly also includes a diffraction element for diffracting the radiation. The diffraction element includes a bottom layer having a transverse periodic structure for diffracting radiation on an upper surface of the bottom layer; and a top layer having a lower surface adjacent to the periodic structure and a flat upper surface. The diffraction element is arranged to receive radiation on the upper surface of the top layer and reflectively diffract the radiation such that the radiation exits the diffraction element via the upper surface of the top layer. The assembly also includes a detector configured to detect the diffracted radiation.

[0015] Optionally, the top layer may have a height that extends beyond the height of the lateral periodic structure.

[0016] Optionally, the top layer can have the same height as the horizontal periodic structure.

[0017] Optionally, the detector may include a spatially resolved sensor.

[0018] Optionally, the radiation may include multiple wavelengths in the range of 1 nm to 20 nm, 1 nm to 10 nm, 10 nm to 20 nm, and 9 nm to 18 nm.

[0019] Optionally, the periodic structure may include a periodic grating.

[0020] Optionally, the bottom layer may include a first material and the top layer may include a second material, wherein the first material and the second material may have different refractive indices for the wavelength of radiation.

[0021] Optionally, the second material may include at least one of the following: oxide, nitride, or carbon-based material.

[0022] Optionally, the periodic structure has a height difference in the range of 1 nm to 10 nm or in the range of 1 nm to 7.5 nm in a direction perpendicular to the flat surface of the top layer.

[0023] Optionally, the top layer has a thickness of at least 1 nm or at least 2 nm.

[0024] Optionally, the periodic structure can have a pitch in the range of 1 nm to 100 nm.

[0025] Alternatively, two or more different periodic structures can be combined in the diffraction element.

[0026] Alternatively, the diffraction element can be provided on the substrate support.

[0027] Alternatively, the diffraction element can be provided on a component of the irradiation system.

[0028] Alternatively, a component of the irradiation system may be a ring mirror.

[0029] According to another aspect of this disclosure, a measuring device is provided, which includes the components described above.

[0030] According to another aspect of this disclosure, an inspection tool is provided, which includes the components described above.

[0031] According to another aspect of this disclosure, a photolithography apparatus is provided, which includes the components described above.

[0032] According to another aspect of this disclosure, a photolithography unit is provided, which includes the apparatus described above.

[0033] According to another aspect of this disclosure, a reflector is provided that includes the components described above. Optionally, the reflector includes a curved reflective surface. Optionally, the reflector is a ring mirror. Attached Figure Description

[0034] The embodiments will now be described by way of example only, with reference to the accompanying schematic diagrams, wherein: - Figure 1 A schematic overview of the photolithography apparatus is depicted; - Figure 2 A schematic overview of the photolithography unit is depicted; - Figure 3 A schematic representation of overall photolithography is depicted, illustrating the synergy between three key technologies to optimize semiconductor manufacturing; - Figure 4 The scattering measurement device is illustrated schematically. - Figure 5 The schematic diagram illustrates a transmission scattering measurement device; - Figure 6 A schematic representation of a measurement apparatus using EUV and / or SXR radiation is depicted; - Figure 7 A simplified schematic diagram of the irradiation source is depicted; - Figure 8 A schematic representation of the components used to calibrate the wavelength of radiation is depicted; - Figures 9(a) and 9(b) depict schematic representations of diffraction elements; - Figure 10(a) depicts example graphs of diffraction efficiency according to wavelength for different diffraction element configurations; and - Figure 10(b) depicts an example graph showing the relative diffraction efficiency variation for exposed and buried gratings. Detailed Implementation

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

[0036] As used herein, the terms “mask,” “mask,” or “patterning apparatus” can be broadly interpreted to refer to a general patterning apparatus used to impart a cross-section of an incident radiation beam pattern corresponding to a pattern to be created in a target portion of a substrate. The term “optical valve” may also be used in this context. Examples of other such patterning apparatuses, besides classic masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), include programmable mirror arrays and programmable LCD arrays.

[0037] Figure 1 A lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also called an irradiator) IL configured to adjust 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 transmitted from the patterning apparatus MA to the radiation beam B onto a target portion C (e.g., comprising one or more dies) of the substrate W.

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

[0039] As used herein, the term "projection system" (PS) should be interpreted broadly to encompass all types of projection systems, including refractive, reflective, diffractive, catadioptric, anamorphic, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof, to suit the exposure radiation used and / or other factors, such as the use of immersion or vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" (PS).

[0040] The lithography apparatus LA can be of the type in which at least a portion of the substrate can be covered by a liquid (e.g., water) having a relatively high refractive index to fill the space between the projection system PS and the substrate W—this is also known as immersion lithography. More information on immersion technology is given in US6952253, the entire contents of which are incorporated herein by reference.

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

[0042] In addition to the substrate support WT, the lithography apparatus LA may include a measurement stage. This measurement stage is arranged to carry sensors and / or cleaning devices. The sensors may be arranged to measure characteristics of the projection system PS or the radiation beam B. The measurement stage may carry multiple sensors. The cleaning devices may be arranged to clean part of the lithography apparatus, such as part of the projection system PS or part of a system providing immersion solution. When the substrate support WT is moved away from the projection system PS, the measurement stage may be moved below the projection system PS.

[0043] In operation, a radiation beam B is incident on a pattern forming apparatus (e.g., a mask) MA supported by a mask support T, and patterned by a pattern (design layout) present on the pattern forming apparatus MA. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be moved precisely, for example, to position the different target portions C in the path of the radiation beam B, in a focused and aligned position. Similarly, a first positioner PM and possibly another position sensor (not shown in the image)... Figure 1(As explicitly depicted in the diagram) can be used to accurately position the pattern forming apparatus MA with respect to the path of the radiation beam B. The pattern forming apparatus MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2, as illustrated, occupy dedicated target portions, they can be located in the space between the target portions. When the substrate alignment marks P1, P2 are located between the target portions C, they are referred to as scribing alignment marks.

[0044] like Figure 2 As shown, the lithography apparatus LA can form part of the lithography unit LC, sometimes referred to as a lithography unit or (lithography) cluster, which typically also includes devices for performing pre- and post-exposure processes on the substrate W. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a cooling plate CH, and a baking plate BK (e.g., for adjusting the temperature of the substrate W, such as for adjusting 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 them between different process units, and delivers the substrate W to the feed stage LB of the lithography apparatus LA. The devices in the lithography unit, often collectively referred to as tracks, can be controlled by a track control unit TCU, which itself can be controlled by a management control system SCS, which can also control the lithography apparatus LA, for example, via the lithography control unit LACU.

[0045] In photolithography, frequent measurements of the created structure are desirable, for example, for process control and verification. The tools used to perform these measurements are called metrology tools (MTs). Different types of MTs are known for such measurements, including scanning electron microscopes (SEMs) or various forms of scatterometer MTs. A scatterometer is a versatile instrument that allows the measurement of photolithography parameters via sensors located in or near the pupil of the scatterometer objective, or in a plane conjugate to the pupil. These measurements are typically referred to as pupil-based measurements. Alternatively, the measurement of photolithography parameters via sensors located in or near the image plane, or in a plane conjugate to the image plane, is typically referred to as image-based or field-based measurements. Such scattering instruments and associated measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, the entire contents of which are incorporated herein by reference. The aforementioned scattering instruments can measure gratings using light from hard X-rays (HXR), soft X-rays (SXR), extreme ultraviolet (EUV), visible to near-infrared (IR), and the IR wavelength range. In the case of hard or soft X-ray radiation, the aforementioned scattering instrument may optionally be a small-angle X-ray scattering measurement tool.

[0046] To ensure that the substrate W exposed by the lithography unit LA is correctly and consistently exposed, it is desirable to inspect the substrate to measure characteristics of the patterned structure, such as overlay errors between subsequent layers, line thickness, critical dimensions (CD), and the 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 process steps to be performed on the substrate W, especially if the inspection has been completed before other substrates W in the same batch or lot are still awaiting exposure or processing.

[0047] An inspection apparatus, also known as a measurement apparatus, is used to determine the characteristics of a substrate W, particularly how the characteristics of different substrates W vary, or how the characteristics associated with different layers of the same substrate W vary layer by layer. The inspection apparatus may alternatively be configured to identify defects on the substrate W, and may be, for example, part of a photolithography unit LC, integrated into a photolithography apparatus LA, or even a stand-alone device. The inspection apparatus can measure characteristics on a latent image (the image in the resist layer after exposure), or a semi-latent image (the image in the resist layer after the post-exposure baking step PEB), or a developed resist image (where the exposed or unexposed portions of the resist have been removed), or even an etched image (after a pattern transfer step such as etching).

[0048] In the first embodiment, the scatterer MT is an angle-resolved scatterer. In such a scatterer, reconstruction methods can be applied to the measured signal to reconstruct or calculate the characteristics of the grating. For example, this reconstruction can be caused by simulating the interaction between the scattered radiation and a mathematical model of the target structure, and comparing the simulation results with those measured. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0049] In the second embodiment, the scatterer MT is a spectroscopic scatterer MT. In this spectroscopic scatterer MT, radiation emitted by a radiation source is directed onto a target, and reflected, transmitted, or scattered radiation from the target is directed to a spectroscopic detector that measures the spectrum of the specularly reflected radiation (i.e., a measurement of intensity as a function of wavelength). Based on this data, the structure or profile of the target that causes the detected spectrum can be reconstructed, for example, through rigorous coupled-wave analysis and nonlinear regression, or through comparison with a simulated spectral library.

[0050] In the third embodiment, the scatterer MT is an elliptically polarized scatterer. An elliptically polarized scatterer allows for the determination of parameters of a photolithography process by measuring the scattered or transmitted radiation for each polarization state. Such a measurement device emits polarized light (such as linearly polarized, circularly polarized, or elliptically polarized light) by using a suitable polarizing filter, for example, in the illumination portion of the measurement device. A source suitable for the measurement device can also provide polarized radiation. Various embodiments of existing elliptically polarized scatterers are described in U.S. Patent Applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110, and 13 / 891,410, the entire contents of which are incorporated herein by reference.

[0051] In one embodiment of a scattering instrument (MT), the MT is adapted to measure the overlay 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 overlay. These two (potentially overlapping) grating structures can be applied to two different layers (not necessarily consecutive layers) and can be substantially formed at the same location on the wafer. The scattering instrument can have a symmetrical detection configuration, such as described in the co-owned patent application EP1,628,164A, such that any asymmetry can be clearly distinguished. This provides a direct way to measure grating misalignment. Further examples of overlay errors between two layers containing the target periodic structure, measured by asymmetry of the periodic structure, can be found in PCT patent application publication WO 2011 / 012624 or U.S. patent application US 20160161863, the entire contents of which are incorporated herein by reference.

[0052] Other parameters of interest may be focal length and dose. Focal length and dose can be determined simultaneously by scattering measurements (or alternatively by scanning electron microscopy), as described in its entirety in U.S. Patent Application US2011-0249244, which is incorporated herein by reference. A single structure can be used, having 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). If these unique combinations of critical dimensions and sidewall angles are available, the focal length and dose values ​​can be uniquely determined from these measurements.

[0053] The measurement target can be an assembly of composite gratings formed by photolithography, primarily in the resist, but also after other manufacturing processes, such as etching. The pitch and linewidth of the structures in the grating can be strongly dependent on the measurement optics (particularly the NA of the optics) to capture the diffraction order from the measurement target. As previously indicated, the diffraction signal can be used to determine the offset between two layers (also known as "overlap"), or it can be used to reconstruct at least a portion of the original grating produced by the photolithography process. Reconstruction can be used to provide guidance on the quality of 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 this sub-segmentation, the target will behave more similarly to the functional portions of the design layout, making the overall process parameter measurements more similar to the functional portions of the design layout. The target can be measured in underfill or overfill modes. In underfill mode, the measurement beam generates a spot smaller than the entire target. In overfill mode, the measurement beam generates a spot larger than the entire target. In this overfill mode, different targets may also be measured simultaneously, thus determining different process parameters simultaneously.

[0054] The overall measurement quality of lithography parameters for a specific target is determined at least in part by the measurement configuration used to measure those parameters. The term "substrate measurement configuration" can include one or more parameters of the measurement itself, one or more parameters of one or more measured patterns, or both. For example, if the measurement used in the substrate measurement configuration 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 criterion for selecting a measurement configuration can be, for example, the sensitivity of one of the measurement parameters to process variations. Further examples are described in U.S. Patent Application US2016-0161863 and published U.S. Patent Application US2016 / 0370717A1, the entire contents of which are incorporated herein by reference.

[0055] Patterning in a photolithography (LA) apparatus is arguably one of the most critical steps in the process, demanding high precision in the size and placement of the structures on the substrate. To ensure this precision, three systems can be combined in a so-called "holistic" control environment, such as... Figure 3 The diagram illustrates this schematically. One of these systems is the lithography apparatus LA, which is (virtually) connected to the metrology tool MT (second system) and the computer system CL (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 to ensure 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, overlay) within which a particular manufacturing process produces a defined result (e.g., a functional semiconductor device)—which can be a range that allows for variations in process parameters during the lithography or patterning process.

[0056] The computer system CL can use the (partial) design layout to be patterned to predict which resolution enhancement techniques to use, and perform computational lithography simulations and calculations to determine which mask layout and lithography setup achieves the maximum overall process window (in) of the patterning process. Figure 3 (Depicted by double arrows in the first scale SC1). Resolution enhancement techniques can be arranged to match the patterning possibilities of the lithography apparatus LA. The computer system CL can also be used to detect where the lithography apparatus LA is currently operating within the process window (e.g., using input from the metrology tool MET) to predict whether defects might exist due to, for example, suboptimal processing (in... Figure 3 (This is depicted by the arrow pointing to "0" in the second scale SC2).

[0057] The measurement tool MT can provide input to the computer system CL for accurate simulation and prediction, and can provide feedback to the lithography apparatus LA to identify possible drift, for example, during the calibration state of the lithography apparatus LA. Figure 3 (Depicted by multiple arrows in the third scale SC3).

[0058] Many different types of measurement tools (MTs) are available for measuring structures created using photolithographic patterning apparatuses. MTs can probe structures using electromagnetic radiation. The characteristics of the radiation (e.g., wavelength, bandwidth, power) can affect different measurement features of the tool, with shorter wavelengths generally allowing for increased resolution. The radiation wavelength influences the resolution achievable by the measurement tool. Therefore, for the purpose of measuring structures with small-sized features, MTs with short-wavelength radiation sources are preferred.

[0059] Another way radiation wavelength can affect measurement characteristics is through penetration depth, and the transparency / opacity of the material under inspection at that wavelength. Depending on opacity and / or penetration depth, radiation can be used for measurements in transmission or reflection. The type of measurement can affect whether information about the surface and / or internal structure / substrate is obtained. Therefore, penetration depth and opacity are another factor to consider when selecting a radiation wavelength for a measurement tool.

[0060] To achieve higher resolution measurements of lithographically patterned structures, measurement tools (MTs) with short wavelengths are preferred. This can include wavelengths shorter than visible light, such as 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. Soft X-rays and EUV, on the other hand, do not penetrate the target very deeply but can induce rich optical responses in the material being probed. This is likely due to the optical properties of many semiconductor materials, and because the size of the structure is comparable to the probe wavelength. Therefore, EUV and / or soft X-ray measurement tools (MTs) can operate in reflection, for example, by imaging the lithographically patterned structure or by analyzing the diffraction patterns from the lithographically patterned structure.

[0061] For hard X-rays, soft X-rays, and EUV radiation, their application in high-volume manufacturing (HVM) applications may be limited due to the lack of high-brightness sources available at the required wavelengths. For hard X-rays, commonly used sources in industrial applications include X-ray tubes. X-ray tubes, including advanced X-ray tubes such as 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) currently exist, but their size (>100 meters) and high cost (hundreds of millions of euros) make them too large and expensive for metrology applications. Similarly, sufficiently bright EUV and soft X-ray sources are also lacking.

[0062] An example of a measuring device, such as a scatterometer, is... Figure 4 The image is depicted in the image. It may include a broadband (e.g., white light) radiation projector 2 that projects radiation 5 onto the substrate W. The reflected or scattered radiation 10 is passed to a spectrometer detector 4, which measures the spectrum 6 of the specular reflected radiation (i.e., a measurement of intensity I as a function of wavelength λ). Based on this data, the structure or profile 8 that produces 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, such as... Figure 4 As shown at the bottom. Typically, for reconstruction, the overall form of the structure is known, and some parameters are assumed based on the technological knowledge of manufacturing the structure, leaving only a few parameters of the structure to be determined from the scattering measurement data. This scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0063] Figure 5 The measuring device (such as) is described Figure 4 The scatterer shown is a transmission version. Transmitted radiation 11 is passed to spectrometer detector 4, which measures spectrum 6, as shown for... Figure 4 The scatterer discussed here can be configured as a normal incidence scatterer or an oblique incidence scatterer. Optionally, a transmission version of hard X-ray radiation with wavelengths <1 nm, optionally <0.1 nm, or optionally <0.01 nm can be used.

[0064] As alternatives to optical measurement methods, 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 (such as T-SAXS in US 2007224518A, the entire contents of which are incorporated herein by reference). Lemaillet et al., in “Intercomparison between optical and X-ray scatterometry measurements of FinFET structures,” Proc. of SPIE, 2013, 8681, discuss profile (CD) measurements using T-SAXS. Note that the use of laser-generated plasma (LPP) X-ray sources is described in U.S. Patent Publication Nos. 2019 / 003988A1 and 2019 / 215940A1, the entire contents of which are incorporated herein by reference. Reflectance measurement techniques using grazing-incidence X-rays (GI-XRS) and grazing-incidence extreme ultraviolet (EUV) radiation can be used to measure the properties of films and stacks on substrates. In the general field of reflectance measurement, goniometric and / or spectroscopic techniques can be applied. In goniometric methods, the variation of the reflected beam with different incident angles can be measured. On the other hand, spectroscopic reflectance measurements measure the wavelength spectrum of the reflected light at a given angle (using broadband radiation). For example, EUV reflectance measurement has been used to inspect mask substrates before fabricating masks (patterning apparatus) for EUV lithography.

[0065] The application scope may limit the use of wavelengths in fields such as hard X-rays, soft X-rays, or EUV. Published patent applications US 20130304424A1 and US 2014019097A1 (Bakeman et al. / KLA) describe hybrid metrology techniques in which measurements using X-rays are combined with optical measurements in the wavelength range of 120 nm and 2000 nm to obtain measurements of parameters such as CD. CD measurements are obtained by coupling X-ray mathematical models and optical mathematical models through one or more common methods. The entire contents of the cited U.S. patent applications are incorporated herein by reference.

[0066] Figure 6A schematic representation of the measuring device 302 is depicted, in which the aforementioned radiation can be used to measure parameters of a structure on a substrate. Figure 6 The measurement device 302 presented herein can be applied to the fields of hard X-ray, soft X-ray and / or EUV.

[0067] Figure 6 The illustration shows a schematic physical arrangement of a measurement device 302, which includes a spectroscopic scatterer using hard X-rays, soft X-rays, and / or EUV radiation (optionally grazing incidence). This is only an example. An alternative form of the inspection device can be provided as an angle-resolved scatterer that can use normal or near-normal incidence radiation similar to that of a conventional scatterer operating at longer wavelengths, and can also use radiation whose direction is greater than 1° or 2° to the direction parallel to the substrate. An alternative form of the inspection device can be provided as a transmission scatterer. Figure 5 The configuration is applied to this transmission scattering instrument.

[0068] The inspection device 302 includes a radiation source or irradiation source 310, an irradiation system 312, a substrate support 316, detection systems 318 and 398, and a measurement processing unit (MPU) 320.

[0069] 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 higher harmonic generation (HHG) techniques, such as... Figure 6 As shown, 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, compact storage ring sources, discharge-generated plasma sources, soft X-ray laser sources, rotating anode sources, solid anode sources, particle accelerator sources, microfocus sources, or laser-generated plasma sources.

[0070] HHG sources and other types of sources can have a gas target and are gas jet / nozzle sources, capillary / fiber sources, or gas chamber sources. HHG sources and other types of sources can have solid or liquid targets. Although HGG sources with gas targets are described below, it should be understood that the invention is not limited to HGG sources with gas targets and can be used with HGG sources with solid or liquid targets as well as other types of sources with any target. Gas targets, solid targets, and liquid targets can be referred to as generation media / target media.

[0071] Examples for HHG sources, such as Figure 6As shown, 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, it 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, generating infrared radiation pulses, each pulse having a duration of, for example, less than 1 ns (1 nanosecond), and a pulse repetition rate of, if desired, up to several megahertz. The wavelength of the infrared radiation can be in the range of 200 nm to 10 µm, for example, around 1 µm (1 micrometer). Optionally, the laser pulse is delivered to the gas delivery system 332 as a first pump radiation 340, wherein a portion of the radiation in the gas is converted into emitted radiation 342 at a higher frequency than the first radiation. A gas supplier 334 supplies appropriate gas to the gas delivery system 332, where the gas is optionally ionized by a power source 336. The gas delivery system 332 can be a cut tube.

[0072] 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 can be optional options within the same apparatus. The emitted radiation can contain multiple wavelengths. If the emitted radiation is monochromatic, measurement calculations (e.g., reconstruction) can be simplified, but generating radiation with multiple wavelengths is easier. The emission divergence angle of the emitted radiation can be wavelength-dependent. For example, different wavelengths will provide different levels of contrast when imaging structures of different materials. For example, for the inspection of metallic or silicon structures, a different wavelength can be selected than that used to image (carbon-based) resist features, or a different wavelength can be selected than that used to detect contamination in such different materials. One or more filtering devices 344 can be provided. For example, filters such as thin films of aluminum (Al) or zirconium (Zr) can be used to cut off the fundamental frequency IR radiation, preventing it from further penetrating the inspection apparatus. 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 is configured to provide a gas target within that space. Optionally, some or all of the beam path may be contained within a vacuum environment, taking into account the absorption of SXR and / or EUV radiation as it propagates in air. Various components of the radiation source 310 and the irradiation optics 312 may be adjustable to achieve different measurement “configurations” within the same apparatus. For example, different wavelengths and / or polarizations may be selectable.

[0073] Depending on the material of the structure to be inspected, different wavelengths can provide the necessary penetration level to reach the underlying layer. Short wavelengths may be preferred to distinguish the smallest device features and defects within those features. For example, one or more wavelengths in the range of 0.01 nm to 20 nm, optionally in the range of 1 nm to 10 nm, or optionally in the range of 10 nm to 20 nm can be selected. Wavelengths shorter than 5 nm may present a problem of 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 certain material, such as detecting contamination, wavelengths up to 50 nm can be useful.

[0074] From radiation source 310, a filtered beam 342 can enter inspection chamber 350, which includes a substrate W containing the structure of interest supported by substrate support 316 at a measurement position for inspection. This structure of interest is designated T. Optionally, the gaseous environment within inspection chamber 350 can be maintained near vacuum by vacuum pump 352, allowing SXR and / or EUV radiation to pass through the gaseous environment without excessive attenuation. The function of irradiation system 312 is to focus the radiation into a focused beam 356, which is a measurement beam, and may include, for example, two-dimensional curved mirrors, or a series of one-dimensional curved mirrors, as described in the published U.S. patent application US2017 / 0184981A1 mentioned above (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. Note that the focusing function is optional, and when irradiation system 312 is not focused, the measurement beam 356 is not focused. The substrate support 316 includes, for example, an XY translation stage and a rotary stage, by which any portion of the substrate W can be brought 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 stage, which can tilt the substrate W at a certain angle to control the incident angle of the focused beam on the structure of interest T.

[0075] 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, which is 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.

[0076] 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. Therefore, the irradiation system 312 and the detection system 318 form an inspection apparatus. This inspection apparatus may include hard X-ray, soft X-ray, and / or EUV spectral reflectors, as described in US2016282282A1, the entire contents of which are incorporated herein by reference.

[0077] If the target Ta has some periodicity, the radiation from the focused beam 356 can also be partially diffracted. The diffracted radiation 397 follows another path with a well-defined angle about the angle of incidence, followed by the path of the reflected radiation 360. Figure 6 In the diagram, the diffraction radiation 397 is drawn schematically, and the diffraction radiation 397 may follow many other paths than those drawn. The inspection device 302 may also include a further detection system 398 that detects and / or images at least a portion of the diffraction radiation 397. Figure 6 A single additional detection system 398 is also depicted, but embodiments of the inspection apparatus 302 may also include more than one additional detection system 398, which are 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 striking the target Ta is detected and / or imaged by one or more additional detection systems 398. 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.

[0078] To aid in the alignment and focusing of the light spot S with the desired product structure, the inspection apparatus 302 may also provide auxiliary optics that utilize auxiliary radiation under the control of the measurement processor 320. The measurement processor 320 may also communicate with a position controller 372, which operates translation, rotation, and / or tilt stages. The processor 320 receives highly accurate feedback regarding the substrate position and orientation via sensors. Sensors 374 may include, for example, interferometers, which can provide picometer-level accuracy. During the operation of the inspection apparatus 302, spectral data 382 captured by the detection system 318 is transmitted to the measurement processing unit 320.

[0079] As previously mentioned, alternative inspection devices utilize hard X-rays, soft X-rays, and / or EUV radiation, optionally in a perpendicular or near-perpendicular manner, for example, to perform diffraction-based asymmetry measurements. Other alternative forms of inspection devices utilize hard X-rays, soft X-rays, and / or EUV radiation in a direction 1° or 2° greater than the direction parallel to the substrate. Both types of inspection devices can be provided in hybrid metrology systems. The performance parameters to be measured can include overlay accuracy (OVL), critical dimension (CD), focal length of the lithography apparatus when printing the target structure, coherent diffraction imaging (CDI), and overlay at resolution (ARO) measurements. The wavelength of the hard X-rays, soft X-rays, and / or EUV radiation can, for example, be less than 100 nm, e.g., radiation in the range of 5 nm to 30 nm, or optionally in the range of 10 nm to 20 nm. This radiation can be narrowband or broadband. The radiation can have discrete peaks within a specific wavelength band, or it can have a more continuous characteristic.

[0080] Similar to optical scattering instruments used in modern 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 structures formed in harder materials (post-etching inspection or AEI). For example, inspection device 302 can be used to inspect substrates after they have been processed by developing, etching, annealing, and / or other means.

[0081] Measurement instruments (MTs), including but not limited to the scatterer mentioned above, can perform measurements using radiation from a radiation source. The radiation used by a measurement instrument MT can be electromagnetic radiation. This radiation can be optical radiation, such as radiation in the infrared, visible, and / or ultraviolet portions of the electromagnetic spectrum. A measurement instrument MT can use radiation to measure or inspect properties and aspects of a substrate, such as photolithographic patterns on a semiconductor substrate. The type and quality of the measurement can depend on several characteristics of the radiation used by the measurement instrument MT. For example, the resolution of an electromagnetic measurement can depend on the wavelength of the radiation, where smaller wavelengths can measure smaller features, for example, due to diffraction limits. To measure features with small dimensions, it is preferable to use radiation with short wavelengths, such as EUV, hard X-rays (HXR), and / or soft X-rays (SXR). To perform measurements at a specific wavelength or wavelength range, the measurement instrument MT needs access to a source that provides that / these wavelengths of radiation. Different types of sources exist to provide radiation at different wavelengths. Depending on the wavelength(s) provided by the source(s), 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 HHG or any other type of source mentioned above to obtain radiation of the desired (multiple) wavelengths.

[0082] Figure 7 A simplified schematic diagram of embodiment 600 of the irradiation source 310 is shown, which can be an irradiation source for HHG. Regarding Figure 6 One or more features of the irradiation source in the described measurement tool may also suitably be present in the irradiation source 600. The irradiation source 600 includes a cavity 601 and is configured to receive pump radiation 611 having a propagation direction indicated by an arrow. The pump radiation 611 shown here is an example of pump radiation 340 from pump radiation source 330, as... Figure 6 As shown. Pump radiation 611 can be directed into cavity 601 via radiation input 605, which can be an observation port and optionally made of fused silica or a similar material. Pump radiation 611 can have a Gaussian or hollow (e.g., annular) transverse cross-sectional profile and can be incident, optionally focused, onto a gas flow 615 within cavity 601, having a flow direction indicated by a second arrow. 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), referred to as a gas volume or gas target (e.g., a few cubic millimeters), with a pressure above a certain value. Gas flow 615 can be a steady flow. Other media, such as metallic plasma (e.g., aluminum plasma), can also be used.

[0083] The gas delivery system of the irradiation source 600 is configured to provide a gas flow 615. The irradiation source 600 is configured to provide pump radiation 611 in the gas flow 615 to drive the generation of emitted radiation 613. The region in which at least most of the emitted radiation 613 is generated is called 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 extremely loosely focused pump radiation). The gas delivery system is configured to provide a gas target for generating emitted radiation at the interaction region of the gas target, and optionally, the irradiation source is configured to receive pump radiation and provide pump radiation at the interaction region. Optionally, the gas flow 615 is provided by the gas delivery system to a evacuated or nearly evacuated space. The gas delivery system may include a gas nozzle 609, such as... Figure 6 As shown, it includes an opening 617 in the outlet plane of the gas nozzle 609. A gas flow 615 is supplied from the opening 617. The gas trap is used to confine the gas flow 615 within a specific volume by evacuating residual gas flow and maintaining a vacuum or near-vacuum environment inside the cavity 601. Optionally, the gas nozzle 609 may be made of a thick-walled tube and / or a material with high thermal conductivity to avoid thermal deformation due to high-power pump radiation 611.

[0084] The size of the gas nozzle 609 can conceivably also be used in scaled-down or enlarged versions, ranging from micrometer-sized nozzles to meter-sized nozzles. This wide range of sizes stems from the fact that the setup can be scaled so that the pump radiation intensity at the gas flow ultimately falls within a specific range that may be beneficial for emitted radiation, requiring different size settings for different pump radiation energies (which can be pulsed lasers and the pulse energy can vary from tens of microjoules to joules). Optionally, the gas nozzle 609 has thicker walls to reduce gas nozzle deformation caused by thermal expansion effects, which 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 near the gas nozzle to maintain the pressure in cavity 601.

[0085] Due to the interaction between the pump radiation 611 and the gas atoms of the gas flow 615, the gas flow 615 will convert part of the pump radiation 611 into emitted radiation 613, which can be... Figure 6An example of emitted radiation 342 is shown. The central axis of emitted radiation 613 may be collinear with the central axis of incident pump radiation 611. 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 in the range of 0.1 nm to 100 nm, optionally in the range of 1 nm to 100 nm, optionally in the range of 1 nm to 50 nm, or optionally in the range of 10 nm to 20 nm.

[0086] In operation, the emitted radiation beam 613 can pass through the radiation output 607 and can subsequently be manipulated and guided by the irradiation system 603 to the substrate to be inspected for measurement purposes. The irradiation system 603 can be... Figure 6 An example of an illumination system 312. The emitted radiation 613 can be guided, and optionally focused, onto a structure on a substrate.

[0087] Because air (and indeed any gas) strongly absorbs SXR or EUV radiation, the volume between the gas flow 615 and the wafer under inspection 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, it may be necessary to block the pump radiation 611 to prevent it from passing through the radiation output 607 and entering the irradiation system 603. This can be achieved by... Figure 6 The filter 344 shown is integrated into the radiation output 607, 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 multiple materials combined in a multilayer. The filter can be a hollow, optionally annular, bulk material, when the pump radiation 611 has a hollow (optionally annular) transverse cross-sectional profile. 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 344 comprises a hollow bulk material and a thin-film filter, such as an aluminum (Al) or zirconium (Zr) thin-film filter. Optionally, the filter 344 may also include a mirror that effectively reflects the emitted radiation but poorly reflects the pump radiation, or a wire mesh that effectively transmits the emitted radiation but poorly transmits the pump radiation.

[0088] This document describes methods, apparatus, and components for obtaining emitted radiation (optionally at the high harmonic frequency of the pump radiation). The radiation generated by this process, optionally using nonlinear effects to generate the HHG (optionally at the harmonic frequency of the provided pump radiation), can be provided as radiation in a metrology tool MT for substrate inspection and / or measurement. If the pump radiation comprises short pulses (i.e., few periods), the generated radiation may not necessarily be precisely at the harmonic frequency of the pump radiation. The substrate may be a photolithographically patterned substrate. The radiation obtained by this process can also be provided in a photolithography apparatus LA, and / or a photolithography cell LC. The pump radiation can be pulsed radiation, which can provide high peak intensity within a short burst time.

[0089] Pump radiation 611 may include radiation having one or more wavelengths, which are higher than one or more wavelengths of the emitted radiation. Pump radiation may include infrared radiation. Pump radiation may include (multiple) radiation with wavelengths in the range of 500 nm to 1500 nm. Pump radiation may include (multiple) radiation with wavelengths in the range of 800 nm to 1300 nm. Pump radiation may include (multiple) radiation with wavelengths in the range of 900 nm to 1300 nm. Pump radiation may be pulsed radiation. Pulsed pump radiation may include pulses with durations in the femtosecond range.

[0090] In some embodiments, the emitted radiation, optionally higher harmonic radiation, may include one or more harmonics of the pump radiation wavelength(s). The emitted radiation may include wavelengths of 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.

[0091] Radiation, such as the higher harmonic radiation described above, can be provided as source radiation in a metrology tool (MT). The metrology tool MT can use this 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. Using shorter wavelengths of radiation, such as EUV, SXR, and / or HXR wavelengths included in the aforementioned wavelength range, compared to using longer wavelengths (e.g., visible radiation, infrared radiation), allows the metrology tool to resolve smaller features of the structure. 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 accessible by radiation with longer wavelengths.

[0092] In a measurement 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 can include EUV XR and / or HXR radiation. The target structure can reflect, transmit, and / or diffract the source radiation incident on it. The MT can include one or more sensors for detecting diffracted radiation. For example, the MT can include detectors for detecting the positive and negative first-order diffraction orders. The MT can also measure specular reflection or transmission radiation (zero-order diffraction). Further sensors may be present in the MT for measurement, such as for measuring further diffraction orders (e.g., higher diffraction orders).

[0093] In exemplary photolithography applications, an array of optics, which can be referred to as an irradiator, can be used to focus the radiation generated by the HHG source onto a target on a substrate. The HHG radiation can then be reflected from the target, detected, and processed, for example, to measure and / or infer the characteristics of the target.

[0094] Gas target HHG configurations can be broadly categorized into three separate types: gas jet streams, gas chambers, and gas capillaries. Figure 7 An example gas jet configuration is depicted, in which 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 minimized. The gas volume may, for example, comprise a gas flow perpendicular to the driving radiation beam, and this gas volume is enclosed within a gas chamber. In a gas capillary arrangement, the dimensions of the capillary structure containing the gas are very small in the transverse direction, such that they significantly affect the propagation of the driving radiation laser beam. The capillary structure may, for example, be a hollow fiber, in which the hollow core is configured to contain the gas.

[0095] The gas jet HHG configuration offers relative degrees of freedom to shape 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 an increased interaction region between the driving radiation and the gaseous medium, which can optimize the HHG process.

[0096] To utilize HHG radiation, such as in metrological applications, it must be separated from the driving radiation downstream of the gas target. The separation of HHG and driving radiation can differ for gas jet and gas capillary configurations. In both cases, driving radiation suppression schemes may include metallic transmission filters to filter out any remaining driving radiation from the short-wavelength radiation. However, before using such a filter, the intensity of the driving radiation should be significantly reduced from its intensity when it is on the gas target to avoid damaging the filter. Methods for this intensity reduction can differ for gas jet and capillary configurations. For gas jet HHG, due to the relative degrees of freedom in the shape and spatial profile (also referred to as spatial distribution and / or spatial frequency) of the driving radiation beam focused onto the gas target, this can be configured such that it has low intensity in the far field in the direction of propagation along the short-wavelength radiation. This spatial separation in the far field means that an aperture can be used to block the driving radiation and reduce its intensity.

[0097] In contrast, in a gas capillary structure, the spatial profile of the beam as it passes through the gaseous medium can be primarily determined by the capillary itself. The spatial profile of the driving radiation can be determined by the shape and material of the capillary structure. For example, when using hollow-core fiber as the capillary structure, the shape and material of the fiber structure determine which driving radiation modes are supported for propagation through the fiber. For most standard fibers, the supported propagation modes result in a spatial profile where the high intensity of the driving radiation overlaps with the high intensity of the HHG radiation. For example, the driving radiation intensity in the far field can be centered on a Gaussian or near-Gaussian profile.

[0098] Although specific references are made to HHG, it should be understood that the invention can be practiced using any radiation source where the context permits. In one embodiment, the radiation source is a laser-generated plasma (LPP) source as described above for generating hard X-rays, soft X-rays, EUV, DUV, and visible light 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 compact storage ring source, a discharge-generated plasma source, a rotating anode source, a solid anode source, a particle accelerator source, and a microfocus source.

[0099] Challenges can arise in photolithography applications: Calibration of sensors and detectors can be difficult due to the small scale of the structures used in the setup and / or the short wavelengths of the radiation. The types of components available for controlling radiation may be limited due to the material interaction properties at short wavelengths. Measurement devices can use short-wavelength radiation comprising multiple different wavelengths. To determine the characteristics in the measurement setup, diffraction can be used to directionally separate the different wavelengths. This directional wavelength-based separation can lead to spatial separation in the far field. This can be used to calibrate, for example, one or more wavelengths of radiation, or wavelength-sensitive detectors. The diffractive element used to separate the radiation spectrally into different wavelength components can be called a spectral dispersive element, which can include, for example, a diffraction grating.

[0100] Diffraction-based measurements can be important methods, for example, for overlay and / or profilometry. Promising variants of diffraction-based measurements use narrow-beam, short-wavelength radiation to irradiate a target diffracted structure. The diffraction radiation order can be captured by a detector. To convert the diffraction signal in the reflection and infer the parameters of interest, the spectral intensity of the radiation beam can be calibrated. If the radiation beam is calibrated and its characteristics are known, the effects of the radiation characteristics can be separated from the effects of the irradiated structure in the analysis of the measured radiation signal. The calibration of the radiation can be monitored over time to identify any changes to the calibration settings. Changes to the calibration settings can occur, for example, due to contaminants affecting the performance of the calibration settings.

[0101] In some implementations, determining the spectrum and intensity of the radiation used for calibration can be achieved by separating a portion of the measurement radiation beam into a separate branch. This separate branch may be referred to as a reference branch. In other example implementations, a spectral-resolved detector can be placed along the radiation path. In both options, a diffraction grating can be used to achieve spectral decomposition of the radiation. In another exemplary implementation, the diffraction grating can be placed on a substrate support, in which case the same detector used to capture the substrate signal can be used to calibrate the radiation beam.

[0102] High-resolution, short-wavelength measurements are typically performed in a vacuum. This can be, for example, to protect the target structure and / or measurement components. However, even under vacuum conditions, contaminants can be present in the environment. These contaminants can deposit on surfaces inside the measurement setup, particularly in areas of high radiation intensity, such as areas of the radiation incident on components. This can include, for example, diffraction structures used for wavelength calibration. An associated challenge is that the presence of contaminants can affect the properties of the diffraction structure. Therefore, within a vacuum chamber, the properties of the diffraction structure can change over time, meaning that calibration accuracy degrades over time. Recalibration requires knowledge of the new diffraction properties of the contaminated structure, either through modeling or recalibration. Modeling may require a complete understanding of the target's geometry and composition. Calibration may require the grating to remain stable. Obtaining modeling information is not straightforward, meaning that contamination of the diffraction structure can negatively impact the performance and accuracy of the measurement setup.

[0103] Contaminants within a vacuum cavity can include carbon or carbon-containing materials. Optical elements within the vacuum cavity can be contaminated by a thin layer of carbon or carbon-containing material, which can be deposited, for example, under the influence of short-wavelength radiation. The amount of carbon contaminant deposited can increase over time. This can affect the stability of the diffraction efficiency of the diffraction element. While it is possible to model the deposited contaminant layer, this requires a detailed understanding of the growth mechanism, such as whether it is a conformal deposition process. It may also require details about the deposition around the corners of the diffraction structure. This paper presents components to address the challenges associated with contaminant deposition on diffraction structures.

[0104] Figure 8 A schematic representation of a component 800 for calibrating the wavelength of radiation is depicted. This component can be provided in a measurement apparatus. The component includes an input 804 configured to receive radiation 802. Optionally, radiation 802 is an embodiment of emitted radiation 342. Optionally, radiation 802 is an embodiment of a focused beam 356. Optionally, radiation 802 is an embodiment of reflected radiation 360. In one embodiment, radiation 802 is equivalent to emitted radiation 342. In another embodiment, radiation 802 is equivalent to a focused beam 356. In yet another embodiment, radiation 802 is equivalent to reflected radiation 360. The component includes a diffraction element 806 for diffracting radiation. The diffraction element includes a bottom layer with a transverse periodic structure for diffracting radiation at its upper surface. The diffraction element also includes a top layer having a lower surface with a periodic structure immediately adjacent to the bottom layer and a flat upper surface. The transverse periodic structure in the bottom layer covered by the top layer can be referred to as a buried transverse periodic structure. The diffraction element is arranged to receive radiation on the upper surface of the top layer. The diffraction element reflectively diffracts radiation, causing the radiation to pass through the top surface of the top layer of the diffraction element. The assembly also includes a detector 808 configured to detect at least some of the diffracted radiation.

[0105] about Figure 8 The advantage of the described component is that any contaminants are deposited on a flat surface, and therefore have a significantly reduced / substantially negligible effect on the diffraction characteristics of the diffraction element. Diffraction in the short wavelength domain can be dominated by a single scattering. Therefore, short-wavelength diffraction may be most sensitive to variations in the patterned layer of the transverse periodic structure. In the described component, the periodic structure is buried beneath a layer of other material. The upper layer of this material is flat, for example, achieved by depositing a planarizing material on top of the periodic structure. If a contaminant layer is deposited on a diffraction element with a planarized top layer, it can form a uniform, unpatterned layer on top of the top layer material. Therefore, the diffraction of radiation by the periodic structure is not affected by the uniform, flat contaminant layer deposition. The contaminant layer may only significantly affect the second-order reflection of scattered light at the contaminant layer interface. The second-order reflection can have a small impact on the overall diffraction efficiency.

[0106] Figure 9(a) depicts the... Figure 8 A schematic representation of a first embodiment of the described diffraction element 906. The diffraction element 906 includes a base layer 910. A lateral periodic structure 912 may be present on the upper surface of the base layer 910. In the embodiment of FIG. 9(a), the lateral periodic structure 912 includes a structure that is periodically repeated in a plane of the surface of the base layer 910 or in any other direction parallel to the plane of the surface of the base layer 910. The lateral periodic structure may include a grating. The diffraction element 906 may include a top layer 914, wherein the top layer may be adjacent to the upper surface of the base layer 910. The upper surface of the top layer may be flat. A flat surface may also be referred to as a planar surface, which can be understood as a two-dimensional surface. When the diffraction element is used in a measuring device, a contaminant layer 916 may be deposited on top of the top surface. The contaminant layer 916 is optional.

[0107] Figure 9(b) depicts the... Figure 8 A schematic representation of a second embodiment of the described diffraction element 906. The diffraction element 906 includes a bottom layer 910. A transverse periodic structure 912 may exist on the upper surface of the bottom layer 910. The transverse periodic structure may include a grating. The diffraction element 906 may include a top layer 915, wherein the top layer 915 may be adjacent to the upper surface of the bottom layer 910. The top layer may be used to fill the gaps in the transverse periodic structure 912 such that the height of the top layer is the same as the height of the transverse periodic structure. The upper surface of the top layer may reach the same height as the transverse periodic structure of the bottom layer. The upper surface of the resulting diffraction element 906 may be flat / planar, formed by the combination of the upper surface of the top layer and the upper surface of the bottom layer. Therefore, the resulting diffraction element may have a height consistent with the height of the transverse periodic structure to form a planar surface. Although the top layer is described as a single layer, in some instances, the top layer may be formed from multiple unconnected material portions.

[0108] The described embodiments allow for the avoidance of contaminant direct deposition on the diffraction structure and further avoid performance degradation. The described embodiments allow for the avoidance of stability and efficiency drift and further avoid performance degradation of the metrology device. The embodiments described herein can provide a solution to the challenge of contaminants degrading the performance of diffraction elements.

[0109] For some embodiments, the embodiment of FIG9(a) is superior to the embodiment of FIG9(b) for manufacturing reasons. Manufacturing can be easier when the top surface consists of a single material. Patterned layers or surfaces with more than one material may be difficult to planarize / flatten because different materials have different chemical mechanical polishing (CMP) rates.

[0110] The bottom layer 910 of the diffractive element 906 may include a first material. The first material may, for example, include polycrystalline silicon or amorphous silicon. The first material may, for example, include a metal, metal oxide, silicon, silicon dioxide, and / or silicon nitride. The top layer may include a second material. Optionally, the first and second materials may have different refractive indices. Specifically, the refractive indices of the first and second materials may differ for the radiation wavelength interacting with the diffractive element (e.g., in the range of 1 nm to 20 nm). The second material may include at least one of the following: oxide, nitride, or carbon-based material. The carbon-based material may have planarization properties that contribute to the planarization of the top surface, such as, for example, spin-coated carbon. The second material may be selected to have the greatest possible optical contrast with the first material. The second material may be further selected to be compatible with semiconductor processes.

[0111] Radiation 802 may include multiple wavelengths. The radiation may include multiple wavelengths in the range of 1 nm to 20 nm, 1 nm to 10 nm, 10 nm to 20 nm, or 9 nm to 18 nm. Calibration radiation 802 can be understood as including the spectrum of the calibration radiation. Calibration radiation 802 may include determining the wavelength and / or intensity of the captured radiation. The radiation to be calibrated includes a spatially resolved sensor. The spatially resolved sensor may be a spectrometer. Diffraction structure 806 may diffract different wavelengths in different directions. Wavelengths propagating in different directions may be captured at different locations on the spatially resolved sensor, thereby resolving the wavelengths. The spatially resolved sensor may be, for example, a CCD (charge-coupled device) array or a CMOS (complementary metal-oxide-semiconductor) sensor.

[0112] One advantage of using spatially resolved sensors with diffractive structures is that they enable calibration of short-wavelength radiation, such as in the wavelength range described above. For radiation in and / or near the visible wavelength range, more optical components are available that can be used for calibration. Optical components operating in transmission, such as prisms, can be used for spectral separation of radiation in the visible portion of the spectrum. However, at the sorter wavelength, the absorption of radiation by the material is significantly higher, making it impossible or challenging to produce prisms and other components. The diffractive elements described herein can operate in reflection.

[0113] The diffractive element layer can be a planar layer, and the lateral periodic structure can include a periodic repeating structure in a direction perpendicular to the plane of the layer. In another embodiment, the lateral periodic structure can include a periodic repeating structure in a direction within the plane of the layer. The lateral periodic structure can include features that are not parallel to the direction of incident radiation propagation. The periodic structure can have a height difference in a direction relative to the plane of the layer. The height difference can be at least 1 nm. The requirement for the structure height can be wavelength-dependent. The height can be shorter than half the longest wavelength in the radiation to be calibrated, or preferably shorter than one-third of the shortest wavelength to be calibrated. If the height of the periodic structure is too low, the diffraction effect will be too small. If the height of the periodic structure is too high, an interference effect can occur. The height can be set in a range between these two effects. For example, the lateral periodic structure can include a height difference in the range of 1 nm to 10 nm, or in the range of 1 nm to 7.5 nm. The top layer can have a thickness of at least 1 nm, or at least 2 nm. As described with respect to FIG9(b), in some cases, the top layer can have a thickness of 0 nm in some regions above the portion of the lateral periodic structure protruding from the underlying substrate. This allows the height of the top layer to be level with the highest part of the horizontal periodic structure at the bottom.

[0114] The transverse periodic structure may include a periodic grating. Optionally, the periodic grating is periodic in one direction. Optionally, the periodic grating is periodic in two perpendicular directions. The periodic structure may have a pitch in the range of 1 nm to 100 nm, or in the range of 30 nm to 300 nm. The minimum pitch may be half of the shortest wavelength to be diffracted, or preferably at least half of the longest wavelength to be diffracted.

[0115] The periodic structure may include multiple periodic structures. In a first embodiment, the multiple periodic structures may include multiple gratings with different pitches. The multiple gratings may exist on the same portion of the substrate. These multiple periodic structures with different pitches may have similar lateral heights. In some embodiments, the multiple periodic structures may include multiple structures from different substrates. These different structures may have different layer heights and optionally different pitches.

[0116] The diffraction element can be provided on a substrate support present in the measurement apparatus. This substrate support can be configured to hold the substrate to be measured. Therefore, the diffraction element can be located in close proximity to the substrate being measured by the measurement apparatus. Alternatively or additionally, the diffraction element can be provided on a component of the illumination system of the measurement apparatus. The component of the illumination system can be, for example, a mirror, optionally a mirror with a curved reflective surface, and optionally a ring mirror.

[0117] Figure 10(a) depicts an example graph 1000 illustrating the variation of diffraction efficiency DE with wavelength λ. Graphs 1002 and 1004 depict the diffraction efficiency of an “exposed” grating not buried beneath a flat top layer. Graph 1002 shows a grating without carbon deposition, and graph 1004 shows a grating with a 1 nm carbon deposition layer on top. These graphs clearly show the observable effect of the 1 nm carbon deposition layer on the diffraction efficiency of the exposed, unburied grating. Graphs 1006 and 1008 depict the diffraction efficiency for a grating buried beneath a top layer, as described with respect to Figures 9(a) and 9(b). Graph 1006 shows a grating without carbon deposition, and curve 1008 shows a grating with a 1 nm carbon deposition layer on top. These graphs show the effect of the 1 nm carbon deposition layer on the significant reduction in diffraction efficiency of the buried grating.

[0118] Figure 10(b) depicts an example graph 1050 illustrating the relative variation of diffraction efficiency R with wavelength. This variation can be between a grating without carbon deposition and a grating with a 1 nm carbon layer deposition. Graph 1052 depicts an example relative variation for an exposed, unburied grating. For an exposed grating, the relative variation in diffraction efficiency reaches 30%. Graph 1054 depicts an example relative variation for a buried grating. The maximum observed relative variation in diffraction efficiency decreases to 3.3%. Compared to an exposed grating, this likely corresponds to an approximately 9-fold performance improvement for the buried grating.

[0119] Figures 10(a) and 10(b) illustrate how burying the structure beneath the planar layer can significantly reduce the adverse effects of contaminant deposition on the diffraction structure. This can have the advantage of increasing the lifetime of the diffraction element, as the diffraction element can withstand a larger amount of contaminant deposition while maintaining its function.

[0120] While the buried gratings and diffraction elements described above are for applications in reflection, alternative implementations that function in transmission are also possible. To achieve this, different types of diffraction elements that function in transmission can be provided in the assembly. A diffraction element comprising a periodic structure for diffracting radiation can be provided. This diffraction element can function in transmission and may include a metal layer. The periodic structure can be etched into the metal layer. The etching removes all metal material, and the resulting etched area includes an opening penetrating the entire metal layer. The periodic structure may include a periodic grating, which can be a periodic transmission grating. The periodic structure can receive radiation on a first side of the metal layer. A portion of the received radiation can be transmitted through the metal layer and can be diffracted on a second side of the metal layer, opposite to the first side. The radiation can be short-wavelength radiation as described above.

[0121] One embodiment is a diffractive element that functions in transmission, which may be referred to as a transmission diffractive element. The transmission diffractive element may include a laterally periodic structure having a top interface and a bottom interface. The transmission diffractive element may have the same features as the periodic structure 912 described with respect to Figures 9(a) to 9(b), unless these features specifically relate to reflection and are incompatible in transmission. The transmission diffractive element may include a capping layer, optionally having the same features as the top layer 914 in Figure 9(b). In one embodiment, the capping layer covers both the top and bottom interfaces of the laterally periodic structure and has two surfaces, namely a top surface and a bottom surface. As mentioned in embodiment 906 of Figure 9, the surface of the capping layer may be flat. The contaminant layer 916 shown in Figure 9 may be deposited on one or both surfaces of the capping layer. Optionally, the space between the laterally periodic structures is filled with the material of the capping layer.

[0122] In another embodiment, the capping layer covers the top interface of the transverse periodic structure, while the bottom interface of the transverse periodic structure is not covered but is planarized by the material of the capping layer. This other embodiment may have two distinct surfaces: a surface of the capping layer and a surface of the planarized interface. The surface of the planarized interface may include both the material of the capping layer and the material of the transverse periodic structure. Optionally, a contaminant layer 916 is deposited on both the surface of the capping layer and the surface of the planarized interface. Optionally, the contaminant layer 916 is deposited on the surface of the capping layer but not on the surface of the planarized interface. Optionally, the contaminant layer 916 is deposited on the surface of the planarized interface but not on the surface of the capping layer.

[0123] For embodiments including transmission diffraction elements, a capping layer prevents deposition on the transmission diffraction elements, particularly on the sidewalls of transversely periodic structures, which can affect the stability of the diffraction efficiency of the transmission diffraction elements. This can have the advantage of increasing the lifetime of the diffraction elements because it allows for a larger amount of contaminant deposition while maintaining functionality.

[0124] exist Figure 6 In this process, reflected radiation 360 is captured by detector 318, and the spectrum is provided to processor 320 to measure the spectrum of the zero-order beam reflected from the wafer. This radiation branch can be referred to as the mirror branch (SB). After being reflected from the wafer, reflected radiation 360 can be diffracted from a diffraction element, such as a grating on a ring mirror, to generate a diffraction order falling on the SB detector 318. Therefore, the SB needs to be calibrated using a known target, or a reference target. As mentioned above, this reference target can be integrated on a substrate support WT or 316.

[0125] There are various challenges in SB calibration: • The reflectivity of the material required for accuracy is unknown within the spectral range. • Calibration of the SB takes a long time because most of the available reference targets have poor reflectivity. • When the spectrum is broadband, it is difficult to find targets with a flat reflectance spectrum across the broadband wavelength range. Often, the reflectance of certain parts of the spectrum is very poor (1000 times lower than the average reflectance of the spectrum), and this increases acquisition (and calibration) time. In one example, when using a Ru target with a thickness of 15 nm, the reflectance at 11 nm to 12 nm is approximately 1000 times worse than the reflectance in the 13 nm to 20 nm range.

[0126] In one embodiment, multiple (optionally two) reference targets with a single varying target parameter are used. Optionally, each reference target in the reference target package includes a flat layer of metallic material (i.e., a metal film), and these different metal films have different thicknesses, ranging from 5 nm to 100 nm, and optionally from 5 nm to 20 nm, due to the different spectral ranges of differential reflectance for reference targets with different thicknesses. Optionally, the metallic material is ruthenium, because ruthenium has good reflectivity in the SXR / EUV spectral range. Optionally, the metal film is located on a silicon substrate.

[0127] By utilizing two or more targets, the problem caused by spectral regions with differential reflectivity can be addressed. Instead of increasing the integration time of the mirror detector to capture the range of reflectivity differences, two or more measurements can be used. In these measurements, the material remains constant (e.g., Ru), and only the thickness of the metal film varies. This allows for SB calibration within a shorter timeframe.

[0128] Having multiple targets, optionally more than two, can be useful, especially when material properties are unknown. Multiple measurements of targets with different thicknesses allow for floating of the real and imaginary parts of the refractive index with a single variable (layer thickness).

[0129] One embodiment is a measurement component, optionally a measurement device, such as... Figure 4 or Figure 6 The diagram illustrates a measurement apparatus for measuring parameters of a structure on a substrate related to a manufacturing process. The measurement apparatus includes a source, optionally an HHG source or optionally an LPP source, configured to provide measurement radiation for radiating the structure; a substrate support configured to support, optionally and move, the substrate; and one or more detectors configured to detect scattered measurement radiation from the structure to measure the parameters of the structure. Optionally, the substrate support may include one or more metal films. Optionally, the one or more detectors include mirror detectors configured to detect reflected measurement radiation from the one or more metal films for calibrating the spectrum of the reflected measurement radiation. Optionally, the measurement radiation is broadband radiation, and optionally, the wavelength of the broadband radiation includes soft X-rays and / or extreme ultraviolet (EUV) wavelength ranges. Optionally, the one or more metal films have different thicknesses. Optionally, the one or more metal films are ruthenium films with different thicknesses.

[0130] One embodiment is a substrate support configured to hold a substrate, the substrate support comprising one or more metal films of different thicknesses, optionally ruthenium films. Optionally, the one or more metal films are used to calibrate the spectrum of reflected radiation for measurement.

[0131] One embodiment is a substrate support configured to hold a substrate. The substrate support includes a diffraction element for diffracting radiation. The diffraction element includes: a bottom layer having a transverse periodic structure for diffracting radiation at an upper surface of the bottom layer; and a top layer having a lower surface immediately adjacent to the periodic structure. The top layer has a flat upper surface. The diffraction element is arranged to receive radiation on the upper surface of the top layer and reflectively diffract the radiation such that the radiation exits the diffraction element via the upper surface of the top layer. Optionally, the substrate support also includes one or more metal films of different thicknesses, optionally ruthenium films. Optionally, the one or more metal films are used to calibrate the spectrum of the reflected radiation for measurement.

[0132] It is desirable to be able to correct the propagation direction of diffracted radiation. This can be applied to implementations involving reflection and / or transmission. To achieve this, one or more mirrors can be placed in the path of the diffracted radiation. The mirrors can reflect the diffracted radiation in a direction different from the original direction. This can be advantageous, for example, if the diffracted radiation is directed towards a location unsuitable for placing a detector.

[0133] The components described herein can be provided in settings that utilize radiation, such as measurement or inspection devices. An apparatus that includes one or more components as described herein may include one or more processors for controlling the components (e.g., controlling and receiving data from the detectors, controlling radiation, etc.).

[0134] An embodiment may include a computer program comprising one or more machine-readable instruction sequences describing optical metrology methods and / or analytical measurements to obtain information about a photolithography process. An embodiment may include computer code containing one or more machine-readable instruction sequences or data describing the method. The computer program or code may, for example, be in... Figure 6 The unit MPU and / or Figure 3 The operation is performed within the control unit CL. A data storage medium (e.g., semiconductor memory, disk, or optical disk) may also be provided, in which such a computer program or code is stored. If existing measuring devices, such as... Figure 6 The types shown, already in production and / or use, can be implemented by providing updated computer program products for causing a processor to execute one or more of the methods described herein. This computer program or code may optionally be arranged to control optical systems, substrate supports, etc., and similarly perform methods for measuring lithography process parameters on suitable plurality of targets. The computer program or code may update the configuration for measuring lithography and / or metrology on other substrates. The computer program or code may be arranged to (directly or indirectly) control lithography apparatus for patterning and processing other substrates.

[0135] The irradiation source can be provided in, for example, a measurement device (MT), an inspection device, a lithography device (LA), and / or a lithography unit (LC).

[0136] The characteristics of the emitted radiation used to perform a measurement can affect the quality of the resulting measurement. For example, the shape and size of the transverse beam profile (cross-section), the intensity of the radiation, and the power spectral density of the radiation can all influence the measurement performed by that radiation. Therefore, it is beneficial to have a source that provides radiation with characteristics that produce high-quality measurements.

[0137] Further embodiments are disclosed in the following numbered clauses: 1. A component for calibrating the wavelength of radiation, the component comprising: Input, which is configured to receive radiation; A diffraction element, used for diffracting the radiation, comprising: A bottom layer having a transverse periodic structure for diffracting the radiation at its upper surface; and The top layer has a lower surface immediately adjacent to the periodic structure; And the top layer has a flat upper surface; The diffraction element is arranged to receive the radiation on the upper surface of the top layer and reflectively diffract the radiation such that the radiation exits the diffraction element via the upper surface of the top layer; and A detector configured to detect the diffracted radiation. 2. The component according to Clause 1, wherein the top layer has a height extending beyond the height of the lateral periodic structure. 3. The component according to Clause 1, wherein the top layer has a height consistent with the height of the lateral periodic structure. 4. The component according to any of the preceding clauses, wherein the detector comprises a spatially resolved sensor. 5. The component according to any of the preceding clauses, wherein the radiation includes multiple wavelengths in the range of 1 nm to 20 nm, 1 nm to 10 nm, 10 nm to 20 nm, and 9 nm to 18 nm. 6. The component according to any of the preceding clauses, wherein the periodic structure comprises a periodic grating. 7. The component according to any of the preceding clauses, wherein the bottom layer comprises a first material and the top layer comprises a second material, wherein optionally, the first material and the second material have different refractive indices for the wavelength of the radiation. 8. The component according to Clause 7, wherein the second material comprises at least one of the following: an oxide, a nitride, or a carbon-based material. 9. The component according to any of the preceding clauses, wherein the periodic structure has a height difference in the range of 1 nm to 10 nm or in the range of 1 nm to 7.5 nm in a direction perpendicular to the flat surface of the top layer. 10. The component according to any of the preceding clauses, wherein the top layer has a thickness of at least 1 nm or at least 2 nm. 11. The component according to any of the preceding clauses, wherein the periodic structure has a pitch in the range of 1 nm to 100 nm. 12. The component according to any of the preceding clauses, wherein two or more different periodic structures are combined in the diffraction element. 13. The component according to any of the preceding clauses, wherein the diffraction element is provided on a substrate support. 14. The component according to any one of clauses 1 to 12, wherein the diffraction element is provided on a component of the irradiation system. 15. The component according to Clause 12, wherein the component of the irradiation system is a ring mirror. 16. A measuring device comprising any one of the components according to Clauses 1 to 15. 17. An inspection tool comprising any one of the components pursuant to Clauses 1 to 15. 18. A photolithography apparatus comprising any one of the components according to Clauses 1 to 15. 19. A photolithography unit comprising means according to any one of clauses 16 to 18. 20. A reflector comprising any one of the components according to clauses 1 to 15. 21. The reflector as described in Clause 20, wherein the reflector includes a curved reflective surface. 22. The reflector as described in Clause 21, wherein the reflector is a ring mirror. 23. A substrate support configured to hold a substrate, comprising any one of the components according to clauses 1 to 14. 22. A substrate support configured to hold a substrate, the substrate support comprising: Diffraction element, the diffraction element being used for diffraction radiation, wherein the diffraction element comprises: A bottom layer having a transverse periodic structure for diffracting the radiation at its upper surface; and The top layer has a lower surface adjacent to the periodic structure; And the top layer has a flat upper surface; The diffraction element is arranged to receive the radiation on the upper surface of the top layer and reflectively diffract the radiation such that the radiation exits the diffraction element via the upper surface of the top layer. 25. The substrate support according to Clause 24, wherein the substrate is patterned by a photolithography apparatus and placed on the substrate support for a measurement apparatus. 26. The substrate support according to clause 24 or 25, wherein the substrate support is a substrate support for a measuring device. 27. A measuring apparatus for measuring parameters of a structure on a substrate, said parameters being related to a manufacturing process, said measuring apparatus comprising: The source is configured to provide measurement radiation for radiating the structure; A substrate support is configured to support and move the substrate. The substrate support includes one or more metal films; and One or more detectors are configured to detect the scattered radiation from the structure to measure parameters of the structure. The one or more detectors include a mirror detector configured to detect the measured radiation reflected from the one or more metal films to calibrate the spectrum of the measured radiation reflected. 28. The measuring apparatus according to Clause 27, wherein the measuring radiation is broadband radiation. 29. The measuring apparatus according to Clause 28, wherein the broadband radiation has wavelengths including soft X-rays and / or extreme ultraviolet (EUV) wavelength ranges. 30. The measuring device according to any one of clauses 27 to 29, wherein the one or more metal films have different thicknesses. 31. The measuring apparatus according to Clause 30, wherein the one or more metal films are ruthenium films of different thicknesses. 32. A substrate support configured to hold a substrate, the substrate support comprising one or more ruthenium films of different thicknesses. 33. The substrate support according to any one of clauses 23 to 26, wherein the substrate support comprises one or more ruthenium films of different thicknesses.

[0138] While this article specifically references the use of photolithography apparatuses in IC manufacturing, it should be understood that the photolithography apparatuses described herein can have other applications. Possible other applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0139] While specific examples in the context of photolithography apparatus may be referenced herein, these examples can be used in other apparatuses. Examples may form part of a mask inspection apparatus, a measurement apparatus, or any apparatus for measuring or processing an object, such as a wafer (or other substrate) or a mask (or other patterning apparatus). These apparatuses are generally referred to as photolithography tools. Such photolithography tools may use vacuum conditions or (non-vacuum) conditions of the surrounding environment.

[0140] While specific examples in the context of a photolithography apparatus may be referenced herein, these examples can be used in other apparatuses. Examples may form part of a mask inspection apparatus, a photolithography apparatus, or any apparatus for measuring or processing an object, such as a wafer (or other substrate) or a mask (or other patterning apparatus). The term "measuring apparatus" (or "inspection apparatus") may also refer to an inspection apparatus or inspection system (or a measuring apparatus or measurement system). For example, an inspection apparatus including examples may be used to detect defects in a substrate or defects in a structure on a substrate. In such embodiments, features of interest in a structure on a substrate may relate to defects in the structure, the absence of a specific portion of the structure, or the presence of an undesirable structure on the substrate.

[0141] Although the embodiments described above have been specifically referenced in the context of optical lithography, it should be understood that, where the context permits, the invention is not limited to optical lithography and can be used in other applications, such as imprint lithography.

[0142] While the aforementioned target or target structure (more generally, a structure on a substrate) is a measurement target structure specifically designed and formed for measurement purposes, in other embodiments, the characteristics of interest can be measured on one or more structures of a functional portion of a device formed on a substrate. Many devices have regular, grating-like structures. The terms structure, target grating, and target structure used herein do not require that the structure be provided specifically for the measurement being performed. Furthermore, the pitch of the measurement target can be close to or smaller than the resolution limit of the scatterometer's optical system, but can be much larger than the size of a typical non-target structure, optionally a product structure, optionally fabricated in the target portion C by a photolithography process. In practice, the lines and / or gaps of the overlaid grating within the target structure can be fabricated to include smaller structures with dimensions similar to non-target structures.

[0143] While specific embodiments have been described above, it should be understood that the invention may be practiced in ways other than those described. The above description is intended to be illustrative and not restrictive. Therefore, modifications to the described invention may be made without departing from the scope of the claims set forth below, as will be apparent to those skilled in the art.

[0144] Although the terms "measuring apparatus / tool / system" or "inspection apparatus / tool / system" are specifically used, these terms can refer to tools, apparatus, or systems of the same or similar type. For example, an inspection apparatus or measuring apparatus including embodiments of the present invention can be used to determine the characteristics of a structure on a substrate or wafer. For example, an inspection apparatus or measuring apparatus including embodiments of the present invention can be used to detect defects in a substrate or defects in a structure on a substrate or wafer. In such embodiments, the characteristics of interest in a structure on a substrate may relate to defects in the structure, the absence of a specific portion of the structure, or the presence of an undesirable structure on the substrate or wafer.

[0145] Although HXR, SXR and EUV electromagnetic radiation are specifically referenced, it should be understood that the invention can be practiced using all electromagnetic radiation, including radio waves, microwaves, infrared, (visible) light, ultraviolet light, X-rays and gamma rays, where the context permits.

[0146] Additional objects, 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 description, 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 objects, advantages, and features. It is contemplated that various combinations of the stated objects, advantages, and features constitute the invention disclosed in this application.

Claims

1. A component for calibrating the wavelength of radiation, the component comprising: Input, which is configured to receive radiation; A diffraction element, used for diffracting the radiation, comprising: A bottom layer having a transverse periodic structure for diffracting the radiation at its upper surface; and The top layer has a lower surface immediately adjacent to the periodic structure; And the top layer has a flat upper surface; The diffraction element is arranged to receive the radiation on the upper surface of the top layer and reflectively diffract the radiation such that the radiation exits the diffraction element via the upper surface of the top layer; and A detector configured to detect the diffracted radiation.

2. The component of claim 1, wherein the top layer has a height extending beyond the height of the lateral periodic structure.

3. The component of claim 1, wherein the top layer has a height consistent with the height of the transverse periodic structure.

4. The component according to any of the preceding claims, wherein the detector comprises a spatially resolved sensor.

5. The component according to any of the preceding claims, wherein the bottom layer comprises a first material and the top layer comprises a second material.

6. The component of claim 5, wherein the first material and the second material have different refractive indices for the wavelength of the radiation.

7. The component according to claim 5 or 6, wherein the second material comprises at least one of the following: an oxide, a nitride, or a carbon-based material.

8. The component according to any of the preceding claims, wherein the periodic structure has a height difference in the range of 1 nm to 10 nm or in the range of 1 nm to 7.5 nm in a direction perpendicular to the flat surface of the top layer.

9. The component according to any of the preceding claims, wherein the periodic structure has a pitch in the range of 1 nm to 100 nm.

10. The component according to any of the preceding claims, wherein two or more different periodic structures are combined in the diffraction element.

11. The component according to any of the preceding claims, wherein the diffraction element is provided on a substrate support.

12. The component according to any one of claims 1 to 10, wherein the diffraction element is provided on a component of the irradiation system.

13. The component of claim 12, wherein the component of the irradiation system is a ring mirror.

14. A measuring or inspection device comprising the components according to any one of claims 1 to 13.

15. A reflector having a curved reflective surface, comprising the components according to any one of claims 1 to 12.

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