Substrate parameter measurement

Abstract

A method of measuring a parameter of a structure of a substrate includes directing a beam of emitting radiation onto the structure and thereby generating diffracted radiation due to diffraction by the structure. The emitted radiation has a spectrum comprising a plurality of peaks. The method further includes detecting the diffracted radiation using an imaging sensor; obtaining an estimate of diffraction efficiency as a function of wavelength using knowledge about the spectrum and a priori of diffraction efficiency; and measuring the parameter of the structure using the estimated diffraction efficiency.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to European application 23195434.8, filed on 5 September 2023, and European application 24182209.7, filed on 14 June 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a method for measuring the structural parameters of a substrate. Background Technology

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

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

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

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

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

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

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

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

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

[0013] The radiation used during measurement can have a broadband spectrum, such as a spectrum extending beyond 10 nm or greater. In this case, a given location on the detector can receive diffracted radiation with different wavelengths and different diffraction orders. This can introduce inaccuracies into the analysis of structures using diffracted radiation. Summary of the Invention

[0014] According to a first aspect of the present invention, a method for measuring parameters of a structure of a substrate is provided, the method comprising: directing a beam of radiation onto the structure, the radiation having a spectrum including a plurality of peaks; using an imaging sensor to detect radiation diffracted from the structure; identifying peaks in the detected diffracted radiation; identifying, based on knowledge of the spectrum and knowledge of the pitch of the structure, a peak comprising a composite peak having two different wavelengths; and using the remaining peaks to measure the parameters of the structure.

[0015] According to a second aspect of the invention, a method is provided for determining the properties of a structure on a substrate based on measured data, wherein the measured data is obtained based on measurements of scattered radiation scattered by the structure, wherein the scattered radiation is generated by irradiating the structure with incident radiation, wherein the incident radiation is generated by irradiating a target medium with pump radiation, wherein the determination is based on knowledge of the properties of the pump radiation.

[0016] Advantageously, embodiments of the invention are able to eliminate ambiguity regarding the wavelength of the peak intensity measured by the detector. This allows for more accurate parameter measurements.

[0017] The remaining peaks can be single-wavelength peaks consisting of a single wavelength, or single-wavelength peaks consisting of a single wavelength and a negligible number of second wavelengths.

[0018] The radiated beam can have an acute angle of incidence on the structure.

[0019] The structure can be periodic.

[0020] The periodic structure can be a grating.

[0021] The parameters of the structure can be measured by constructing a model of the structure.

[0022] The method can use the second, third, and fourth diffraction orders.

[0023] According to a third aspect of the invention, a measurement system configured to measure parameters of a structure of a substrate is provided, the measurement system comprising: pump radiation and a target medium, the pump radiation being configured to direct a pump radiation beam into the target medium and thereby cause the target medium to emit radiation having a spectrum including multiple peaks; an optical device configured to direct the beam of radiation onto the structure; an imaging sensor configured to detect radiation diffracted from the structure; and a processor configured to: identify peaks in the detected diffracted radiation; identify, based on knowledge of the spectrum and knowledge of the pitch of the structure, a peak comprising a composite peak of radiation having two different wavelengths; and use the remaining peaks to measure the parameters of the structure.

[0024] Advantageously, embodiments of the invention are able to eliminate ambiguity regarding the wavelength of the peak intensity measured by the detector. This allows for more accurate parameter measurements.

[0025] The processor can also be configured to add the inserted peak to the remaining peaks before measuring the parameters of the substrate.

[0026] The remaining peaks can be single-wavelength peaks consisting of a single wavelength, or single-wavelength peaks consisting of a single wavelength and a negligible number of second wavelengths.

[0027] The optical device is configured to guide the radiated beam onto the structure at an acute angle of incidence.

[0028] The processor can be configured to measure the parameters of the structure by constructing a model of the structure.

[0029] The processor can use a second diffraction order, a third diffraction order, and a fourth diffraction order.

[0030] According to a fourth aspect of the invention, a method for measuring parameters of a structure of a substrate is provided, the method comprising: directing a beam of emitted radiation onto the structure and thereby generating diffracted radiation attributable to diffraction by the structure, wherein the emitted radiation has a spectrum comprising a plurality of peaks; detecting the diffracted radiation using an imaging sensor; obtaining an estimate of the diffraction efficiency as a function of wavelength using knowledge of the spectrum and prior knowledge of the diffraction efficiency; and measuring the parameters of the structure using the estimated diffraction efficiency.

[0031] Optionally, the method also includes using knowledge related to the fuzziness of the emitted radiation beam to obtain the estimate of the diffraction efficiency as a function of wavelength.

[0032] Optionally, the prior of the diffraction efficiency is the prior of the second derivative of the diffraction efficiency as a function of wavelength.

[0033] Optionally, the method also includes generating the estimate of the diffraction radiation incident on the imaging sensor.

[0034] Optionally, the method includes minimizing the difference between the estimated diffracted radiation incident on the imaging sensor and the detected diffracted radiation to obtain the estimate of the diffraction efficiency as a function of wavelength.

[0035] Optionally, the structure is a periodic structure with a pitch.

[0036] Optionally, the method includes using knowledge about the pitch of the periodic structure to obtain the estimate of the diffraction efficiency as a function of wavelength.

[0037] Optionally, the step of using the estimated diffraction efficiency to measure the parameters of the structure includes using the estimated diffraction efficiency as input to the simulation.

[0038] Optionally, the emitted radiation is broadband radiation.

[0039] Optionally, the diffraction radiation incident on the imaging sensor includes at least partially superimposed diffraction steps on the surface of the imaging sensor.

[0040] According to a fifth aspect of the invention, a method for estimating the diffraction efficiency of a substrate structure is provided, the method comprising: directing a beam of emitted radiation onto the structure and thereby generating diffracted radiation attributable to diffraction by the structure, wherein the emitted radiation has a spectrum comprising a plurality of peaks, and wherein the diffracted illumination comprises a plurality of diffraction steps; detecting the diffracted radiation using an imaging sensor, wherein the diffracted radiation incident on the imaging sensor comprises at least partially superimposed diffraction steps on a surface of the imaging sensor; and separating the at least partially superimposed steps using knowledge of the spectrum and a priori knowledge of the diffraction efficiency.

[0041] Optionally, the emitted radiation is broadband radiation.

[0042] Optionally, the structure is a periodic structure.

[0043] The method can also utilize the prior knowledge of the diffraction efficiency.

[0044] The radiation emitted by the target medium can be broadband radiation.

[0045] The diffraction radiation incident on the sensor may include at least partially superimposed diffraction orders.

[0046] According to a sixth aspect of the invention, a method is provided for measuring the illumination spectrum of an illumination beam used by a measurement system, the method comprising: directing a pump radiation beam into a target medium and thereby causing the target medium to emit radiation, the emitted radiation having a spectrum comprising a plurality of peaks, and the measurement system serving as an illumination beam having an illumination spectrum; directing the illumination beam onto a grating having a known diffraction efficiency and thereby generating diffracted radiation; using an imaging sensor to detect the diffracted radiation as a spectral power function; representing the spectral power function according to a wavelength multiplied by a diffraction order, the spectral power function being the product of the illumination spectrum and the known diffraction efficiency; and determining the illumination spectrum using the represented spectral power function and the measured spectral power function.

[0047] The effects of focusing error and / or diffraction-limited spot size can be removed from the measured spectral power function, or the influence of focusing error and / or diffraction-limited spot size on the spectral power function can be reduced.

[0048] Removing or reducing the effects of focusing errors and / or diffraction-limited spot size can include applying deconvolution and / or integral transforms.

[0049] When removing or reducing the effects of focusing error and / or diffraction-limited spot size from the spectral power function, the prior probability of the smoothness of the illumination spectrum can be used.

[0050] The illumination spectrum can be represented based on the signal response of the imaging sensor.

[0051] According to a seventh aspect of the invention, a non-transitory computer program product is provided, comprising machine-readable instructions therein, which, when executed by a computer system, are configured to cause the computer system to perform at least any of the methods mentioned above.

[0052] Different aspects of the present invention can be combined together. Attached Figure Description

[0053] Embodiments will now be described by way of example only, with reference to the accompanying illustrative drawings, in which:

[0054] - Figure 1 A schematic schematic diagram depicting a photolithography apparatus;

[0055] - Figure 2 A schematic schematic diagram depicting a photolithography unit;

[0056] - Figure 3 A schematic representation of monolithography illustrates the collaboration between three key technologies used to optimize semiconductor manufacturing.

[0057] - Figure 4A schematic diagram of a scattering measurement device;

[0058] - Figure 5 A schematic diagram of a transmission-type scattering measurement device;

[0059] - Figure 6 A schematic representation of the measurement equipment used in this process, employing EUV and / or SXR radiation;

[0060] - Figure 7 A simplified schematic diagram depicting the irradiation source;

[0061] - Figure 8 A schematic depiction of the soft X-ray spectrum output by the scattering measurement device;

[0062] - Figure 9 The different diffraction orders produced by the grating when broadband spectral radiation is incident on it are schematically depicted.

[0063] - Figure 10 The intensity of different diffraction orders is schematically depicted for a broadband spectrum including a series of peaks incident on the detector of a scattering measurement device.

[0064] - Figure 11 A method for selecting peaks of diffraction radiation for analysis according to embodiments of the present disclosure is schematically depicted.

[0065] - Figure 12 A flowchart including the steps in a method for reconstructing a grating according to embodiments of the present disclosure;

[0066] - Figure 13 A series of graphs illustrating the operation of the method according to embodiments of the present invention; and

[0067] - Figure 14 A series of graphs are used to demonstrate the operation of the same method with incident broadband spectral radiation including a certain divergence.

[0068] - Figure 15 A schematic depiction of an apparatus for measuring the spectrum of a radiation beam; and

[0069] - Figure 16 A series of graphs illustrating the operation of the method according to embodiments of the present invention. Detailed Implementation

[0070] In this document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic and particle radiation, including ultraviolet radiation (e.g., having wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), EUV (extreme ultraviolet radiation, e.g., having wavelengths in the range of about 5 nm to 100 nm), X-ray radiation, electron beam radiation, and other particle radiation.

[0071] As used herein, the terms "mask," "mask," or "patterning apparatus" can be broadly interpreted to refer to a general patterning apparatus that can be used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to a pattern to be generated in a target portion of a substrate. The term "optical valve" may also be used in this context. Examples of these patterning apparatuses, in addition to classic masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), include programmable mirror arrays and programmable LCD arrays.

[0072] Figure 1 A lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also referred to as an irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation, DUV radiation, EUV radiation, or X-ray radiation); a mask support (e.g., a mask stage) T configured to support a pattern forming apparatus (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the pattern forming apparatus MA according to certain parameters; a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the pattern forming apparatus MA to the radiation beam B onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0073] In operation, the irradiation system IL receives a radiation beam from the radiation source SO, for example, via a beam delivery system BD. The irradiation system IL may include various types of optical elements for guiding, shaping, and / or controlling the radiation, such as refractive, reflective, diffractive, magnetic, electromagnetic, electrostatic, and / or other types of optical elements, or any combination thereof. The irradiator IL can be used to adjust the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the pattern forming apparatus MA.

[0074] The term "projection system" PS as used herein should be broadly interpreted to encompass various types of projection systems suitable for the exposure radiation used and / or for other factors such as immersion in liquids or vacuum, including refractive, reflective, diffractive, reflective-refractive, distorting, magnetic, electromagnetic, and / or electrostatic optical systems or any combination thereof. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0075] Photolithography equipment (LA) can fall into the following categories: at least a portion of the substrate can be covered by a liquid (e.g., water) with 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 techniques is given in US6952253, which is incorporated herein by reference in its entirety.

[0076] Photolithography equipment (LA) can also be of the type with two or more substrate supports (WT) (also known as "dual platforms"). In such a "multi-platform" machine, substrate supports (WT) can be used in parallel, and / or a subsequent exposure step to prepare substrate W can be performed on a substrate W located on one of the substrate supports (WT), while another substrate W on another substrate support (WT) is used to expose a pattern on the other substrate W.

[0077] In addition to the substrate support WT, the lithography apparatus LA may also include a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning devices. The sensors may be arranged to measure the properties of the projection system PS or the properties of the radiation beam B. The measurement platform may hold multiple sensors. The cleaning devices may be arranged to clean parts of the lithography apparatus, such as a part of the projection system PS or a system providing immersion liquid. The measurement platform may move below the projection system PS as the substrate support WT moves away from the projection system PS.

[0078] In operation, a radiation beam B is incident on a pattern forming apparatus (e.g., a mask) MA held on a mask support T and patterned by a pattern (design layout) present on the pattern forming apparatus MA. Having traversed the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example, to position different target portions C in a focused and aligned position within the path of the radiation beam B. Similarly, a first positioner PM and possibly another position sensor (the other position sensor is not in...) Figure 1(As clearly depicted in the diagram) can be used to accurately position the patterning apparatus MA relative to the path of the radiation beam B. The patterning 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 occupy dedicated target portions as illustrated, they can also be located in the space between target portions. When the substrate alignment marks P1, P2 are located between target portions C, these substrate alignment marks P1, P2 are referred to as scribing alignment marks.

[0079] like Figure 2 As shown, the lithography apparatus LA can form part of a lithography unit LC (sometimes also referred to as a lithography cell or (lithography) cluster), which often also includes equipment for performing pre-exposure and post-exposure processes on a substrate W. Conventionally, these devices include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, and, for example, a chiller CH and a baking plate BK for regulating the temperature of the substrate W (e.g., for regulating the solvent in the resist layer). A substrate transport device or robot RO picks up the substrate W from input / output ports I / O1, I / O2, moves the substrate between different process units, and transfers the substrate W to the feed stage LB of the lithography apparatus LA. The devices in the lithography unit, often collectively referred to as a track or coating / developing system, can be under the control of a track or coating / developing system control unit TCU, which itself may be controlled by a management control system SCS, which may also control the lithography apparatus LA, for example, via a lithography control unit LACU.

[0080] During photolithography, it is desirable to frequently measure the resulting structure, for example, for process control and verification. The tools used to perform these measurements are called metrology tools (MTs). Different types of metrology tools (MTs) used for these measurements are well-known, including scanning electron microscopes (SEMs) or various forms of scatterometer metrology tools (MTs). A scatterometer is a multi-functional instrument that allows the measurement of parameters of the photolithography process by means of a sensor located in or near the pupil of the scatterometer's objective lens; these measurements are typically referred to as pupil-based measurements. Alternatively, the measurement of parameters of the photolithography process can be performed by means of a sensor located in or near the image plane of the objective lens; in this case, the measurement is typically referred to as image- or field-based measurements. These scattering instruments and associated measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, which are incorporated herein by reference in their entirety. The aforementioned 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 instruments can optionally be small-angle X-ray scattering measurement tools.

[0081] To ensure accurate and consistent exposure of the substrate W exposed by the lithography unit LA, it is desirable to inspect the substrate to measure properties of the patterned structure, such as overlap error between subsequent layers, line thickness, critical dimension (CD), and shape of the structure. For this purpose, inspection tools and / or measurement tools (not shown) can be included in the lithography unit LC. Especially when inspection is performed before other substrates W in the same batch or leg are still awaiting exposure or processing, if errors are detected, adjustments can be made, for example, to the exposure of subsequent substrates or other processing steps to be performed on the substrate W.

[0082] Inspection equipment, also known as metrology equipment, is used to determine the properties of a substrate W, and in particular, to determine how the properties of different substrates W vary or how the properties associated with different layers of the same substrate W vary between different layers. Inspection equipment may alternatively be configured to identify defects on the substrate W and may be, for example, part of a photolithography unit LC, or integrated into a photolithography apparatus LA, or even a separate device. Inspection equipment can measure the properties on a latent image (an image in a resist layer after exposure), or a semi-latent image (an image in a resist layer after a post-exposure baking step PEB), or the properties on a developed resist image (where the exposed or unexposed portions of the resist have been removed), or even the properties on an etched image (after a pattern transfer step such as etching).

[0083] In the first embodiment, the scatterer MT is an angle-resolved scatterer. In such a scatterer, a reconstruction method can be applied to the measured signal to reconstruct or calculate the properties of the grating. This reconstruction can, for example, be caused by simulating the interaction between the scattered radiation and the target structure using a mathematical model and comparing the simulation results with the measured results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0084] In the second embodiment, the scatterer MT is a spectroscopic scatterer MT. In such a spectroscopic scatterer MT, radiation emitted by a radiation source is directed 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 its intensity as a function of wavelength). Based on this data, the structure or profile of the target that generated the detected spectrum can be reconstructed, for example, through rigorous coupled-wave analysis and nonlinear regression or by comparison with a simulated spectral library.

[0085] In the third embodiment, the scatterer MT is an elliptic scatterer. An elliptic scatterer allows the determination of parameters of the photolithography process by measuring the scattered or transmitted radiation for each polarization state. This measurement device emits polarized light (such as linear, circular, or elliptical) by using, for example, a suitable polarization filter in the illumination section of the measurement device. A source suitable for the measurement device can also provide polarized radiation. Various embodiments of existing elliptic scatterers are described in U.S. Patent Applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110, and 13 / 891,410, which are incorporated herein by reference in their entirety.

[0086] In one embodiment of the scattering instrument MT, the scattering instrument MT is adapted to measure the overlap of two misaligned gratings or periodic structures by measuring the reflectance spectrum and / or detecting asymmetry in the configuration, the asymmetry being related to the extent of the overlap. Two (potentially partially stacked) grating structures can be applied to two different layers (not necessarily consecutive layers), and the two grating structures can be formed approximately at the same location on the wafer. The scattering instrument can have a symmetrical detection configuration, such as described, for example, in the commonly owned patent application EP1,628,164A, making any asymmetry clearly distinguishable. This provides a direct method for measuring misalignment in gratings. Further examples including the overlap error between two layers of a periodic structure as a target for measurement by asymmetry of the periodic structure can be found in PCT patent application publication WO 2011 / 012624 or U.S. patent application US 20160161863, which are incorporated herein by reference in their entirety.

[0087] Other parameters of interest may be focus and dose. Focus and dose can be determined simultaneously by scattering measurements as described in U.S. Patent Application US2011-0249244, which is incorporated herein by reference in its entirety. A single structure with a unique combination of critical size and sidewall angle measurements for each point in the focal length energy matrix (FEM—also known as the focal length exposure matrix) can be used. If these unique combinations of critical size and sidewall angle are available, the focus and dose values ​​can be uniquely determined based on these measurements.

[0088] The measurement target can be an assembly of composite gratings formed primarily in a resist by a photolithography process and also after other fabrication processes such as etching. The pitch and linewidth of the structures in the grating can be largely dependent on the measurement optics (specifically, the NA of the optics) to capture the diffraction order from the measurement target. As previously indicated, the diffraction signal can be used to determine the shift (also known as “overlap”) between two layers or can be used to reconstruct at least a portion of the original grating, such as that produced by the photolithography process. This reconstruction can be used to guide 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 subsegments configured to mimic the dimensions of functional portions of a design layout in the target. Due to these subsegments, the target will behave more similarly to the functional portions of the design layout, making the overall process parameter measurements better resemble the functional portions of the design layout. The target can be measured in an underfilled mode or an overfilled mode. In the underfilled mode, the measurement beam produces a spot smaller than the overall target. In the overfilled mode, the measurement beam produces a spot larger than the overall target. In such an overfilled mode, different targets may be measured simultaneously, thus determining different processing parameters at the same time.

[0089] The overall measurement quality of lithography parameters for a specific target is determined at least in part by the measurement scheme used to measure such lithography parameters. The term "substrate measurement scheme" can include measuring one or more parameters of itself, one or more parameters of one or more patterns being measured, or both. For example, if the measurement used in the substrate measurement scheme is a diffraction-based optical measurement, one or more of the measured parameters can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. One of the criteria used to select the measurement scheme can be, for example, the sensitivity of one of the measurement parameters to handling variations. Further examples are described in U.S. Patent Application US2016-0161863 and U.S. Patent Application US2016 / 0370717A1, which are incorporated herein by reference in their entirety.

[0090] The patterning process in lithography equipment (LA) can be one of the most critical steps in the process requiring high accuracy in the dimensional calibration and placement of structures on the substrate (W). To ensure this high accuracy, three systems can be combined in a so-called "holistic" control environment, such as... Figure 3 The diagram illustrates this schematically. One of these systems is a lithography apparatus LA, which is (in effect) connected to a metrology tool MT (the second system) and a computer system CL (the third system). The key to this “holistic” environment is optimizing the collaboration between these three systems to enhance the overall process window and provide a tight control loop 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, focus, overlap) within which a particular manufacturing process produces a defined result (e.g., a functional semiconductor device)—possibly allowing for variations in process parameters during the lithography or patterning process within this range.

[0091] The computer system CL can use the design layout (partially) to be patterned to predict which resolution enhancement techniques to use and perform computational lithography simulations and calculations to determine which mask layouts and lithography equipment settings will enable the patterning process within the maximum overall process window (in [the specified area]). 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 equipment LA. The computer system CL can also be used (e.g., using input from the metrology tool MET) to detect where the lithography equipment LA is currently operating within the process window to predict whether defects might exist due to, for example, suboptimal processing. Figure 3 The middle section is depicted by an arrow pointing to "0" in the second scale SC2.

[0092] The measurement tool MT can provide input to the computer system CL for accurate simulation and prediction, and can provide feedback to the lithography equipment LA to identify possible drifts in, for example, the calibration status of the lithography equipment LA. Figure 3 (The middle section is depicted by multiple arrows in the third scale SC3).

[0093] Many different types of measurement tools (MTs) are available for measuring structures produced using photolithographic patterning equipment. MTs can use electromagnetic radiation to query structures. The properties of the radiation (e.g., wavelength, bandwidth, power) can affect the different measurement characteristics of the tool, with shorter wavelengths generally allowing for increased resolution. The radiation wavelength influences the resolution achievable by the measurement tool. Therefore, MTs with shorter wavelength radiation sources are preferred for measuring structures with features of small size.

[0094] Another way radiation wavelength can affect measurement characteristics is through-penetration depth and the transparency / opacity of the material being inspected at that wavelength. Depending on opacity and / or through-penetration depth, radiation can be used for either transmissive or reflective measurements. The type of measurement can affect whether information about the surface and / or bulk interior of a structure / substrate is obtained. Therefore, through-penetration depth and opacity are other factors to consider when selecting the radiation wavelength for a measurement tool.

[0095] To achieve higher resolution measurements of photolithographically patterned structures, measurement tools (MTs) with shorter wavelengths are preferred. This can include wavelengths shorter than the visible wavelength, for example, in the UV, EUV, and X-ray portions of the electromagnetic spectrum. Hard X-ray methods, such as transmission-at-small-angle X-ray scattering (TSAXS), utilize the high resolution and deep penetration 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 elicit rich optical responses in the material being probed. This can be attributed to the optical properties of many semiconductor materials and to the size of the structure being comparable to the detection wavelength. Therefore, EUV and / or soft X-ray measurement tools (MTs) can operate in reflection, for example, by imaging or by analyzing diffraction patterns from photolithographically patterned structures.

[0096] For hard X-rays, soft X-rays, and EUV radiation, the limited availability of high-brightness radiation sources at the desired wavelengths in high-volume manufacturing (HVM) applications can be attributed to this. In the case of hard X-rays, commonly used sources in industrial applications include X-ray tubes. X-ray tubes, including advanced ones based on liquid metal anodes or rotating anodes, can be relatively affordable and compact, but may lack the brightness required for HVM applications. High-brightness X-ray sources such as synchrotron light sources (SLS) and X-ray free-electron lasers (XFELs) exist, but their size (>100m) and high cost (over €100 million) make them excessively large and expensive for metrology applications. Similarly, there is a lack of sufficiently bright EUV and soft X-ray radiation sources available.

[0097] Figure 4 An example of a measurement device, such as a scatterer, is depicted. The measurement device may include a broadband (e.g., white light) radiation projector 2, which includes optics that project radiation 5 onto a 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., the intensity I as a function of wavelength λ). Based on this data, the measurement is performed, for example, through rigorous coupled-wave analysis and nonlinear regression, or through... Figure 4 The comparison of the simulated spectral library shown at the bottom can be used to reconstruct the structure or profile of the detected spectrum through the processing unit PU. Typically, for reconstruction, the general form of the structure is well-known, and some parameters are assumed from knowledge of the processes upon which the structure is manufactured, leaving only a few parameters of the structure to be determined from the scattering measurement data. Such a scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0098] Figure 5 The transmission version of the example measuring device depicted in the text, such as Figure 4 The scatterer is shown in the image. Transmitted radiation 11 is passed to the spectrometer detector 4, which measures as directed... Figure 4 The spectrum discussed is 6. Such a scatterer can be configured as a normal incidence scatterer or an oblique incidence scatterer. Optionally, a transmission version of hard X-ray radiation with wavelengths less than 1 nm, optionally less than 0.1 nm, and optionally less than 0.01 nm can be used.

[0099] As an alternative to optical measurement methods, the use of hard X-rays, soft X-rays, or EUV radiation, for example, radiation having at least one of the following wavelength ranges: less than 0.01 nm, less than 0.1 nm, less than 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 X-ray scattering at a small angle of transmission (such as T-SAXS in US 2007224518A, the contents of which are incorporated herein by reference in their entirety). Lemaillet et al., in “Intercomparison between optical and X-ray scatterometry measurements of FinFET structures,” Proc. of SPIE, 2013, 8681, discuss the use of T-SAXS profile (CD) measurements. 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, which are incorporated herein by reference in their entirety. Reflectance measurement techniques using X-rays (GI-XRS) and extreme ultraviolet (EUV) radiation at grazing incidence can be used to measure the properties of films and stacked layers on a substrate. Within the general field of reflectance measurement, goniometric and / or spectroscopic techniques can be applied. In goniometrics, the variation of the reflected beam at different incident angles can be measured. On the other hand, spectroscopic reflectance measurement (using broadband radiation) measures the spectrum of wavelengths reflected at a given angle. For example, EUV reflectance measurement has been used to inspect mask components before the fabrication of masks (patterning apparatuses) used in EUV lithography.

[0100] The scope of application may render the use of wavelengths in, for example, hard X-rays, soft X-rays, or the EUV domain insufficient. Publicated patent applications US20130304424A1 and US2014019097A1 (Bakeman et al. / KLA) describe hybrid metrology techniques that combine measurements using X-rays with optical measurements utilizing wavelengths in the 120 nm to 2000 nm range to obtain measurements of parameters such as CD. CD measurements are obtained by coupling X-ray mathematical models and optical mathematical models via one or more common components. The contents of the listed U.S. patent applications are incorporated herein by reference in their entirety.

[0101] Figure 6 A schematic representation of a measuring device 302 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 used in the hard X-ray, soft X-ray, and / or EUV domains.

[0102] Figure 6 The illustration is a schematic physical arrangement of a measurement apparatus 302, using only an example of a spectroscopic scattering instrument that optionally uses hard X-rays, soft X-rays, and / or EUV radiation at grazing incidence. An alternative form of the inspection apparatus may be provided as an angle-resolved scattering instrument, similar to a conventional scattering instrument operating at longer wavelengths, which can use radiation at normal or near-normal incidence, and which can also use radiation having an angle greater than 1° or 2° with respect to a direction parallel to the substrate. An alternative form of the inspection apparatus may be provided as a transmission scattering instrument. Figure 5 The configuration in [the configuration] is applied to the transmission scattering instrument.

[0103] The inspection device 302 includes a radiation source or so-called irradiation source 310, an irradiation system 312, a substrate support 316, detection systems 318 and 398, and a measurement processing unit (MPU) 320.

[0104] 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, for example... Figure 6 The HHG technology shown in the figure 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, micro-focusing sources, or laser-generated plasma sources.

[0105] HHG sources and other types of sources can have a gas target and can be a gas jet / nozzle source, capillary / fiber source, or gas chamber source. HHG sources and other types of sources can have a solid or liquid target. Although HHG sources with gas targets are described below, it will be understood that the invention is not limited to HHG sources with gas targets and can be used in HHG sources with solid or liquid targets and in other types of sources with any target. Gas targets, solid targets, and liquid targets can be referred to as generation / target media.

[0106] For example, HHG source, 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, the pump radiation source 330 is a pulsed high-power infrared or optical laser. The pump radiation source 330 can be, for example, a fiber-based laser with an optical amplifier, thereby generating pulses of infrared radiation that can last for, for example, less than 1 ns (1 nanosecond), wherein the pulse repetition rate can reach several megahertz as needed. The wavelength of the infrared radiation can be in the range of 200 nm to 10 µm, for example, about 1 μm (1 micrometer). Optionally, the laser pulse is delivered to the gas delivery system 332 as a first pump radiation 340, wherein in the gas, a portion of the radiation is converted to a higher frequency than the first radiation to become emitted radiation 342. A gas supply 334 supplies a suitable gas to the gas delivery system 332, in which the suitable gas is optionally ionized by a power source 336. The gas delivery system 332 can be a cut-off tube.

[0107] The gas provided by the gas delivery system 332 defines a gas target, which can be a gas flow or a static volume. The gas can be, for example, air, neon (Ne), helium (He), nitrogen (N2), oxygen (O2), argon (Ar), krypton (Kr), xenon (Xe), carbon dioxide, and combinations thereof. These gases can be optional options within the same device. The emitted radiation can include multiple wavelengths. The emission divergence angle of the emitted radiation can be wavelength-dependent. Different wavelengths will, for example, provide different levels of contrast when imaging structures of different materials. For example, to inspect metallic or silicon structures, different wavelengths can be selected for characterizing (carbon-based) resists or for detecting contamination in these different materials. One or more filters 344 can be provided. For example, filters such as thin films of aluminum (Al) or zirconium (Zr) can be used to cut off the underlying IR radiation to prevent further propagation into the inspection device. A grating (not shown) can be provided to select one or more specific wavelengths from the generated wavelengths. Optionally, the irradiation source includes a space configured to be evacuated, and the gas delivery system is configured to provide the gas target in said space. Optionally, some or all of the beam path can be included in a vacuum environment; it should be noted that SXR and / or EUV radiation is absorbed when traveling in air. The various elements of the radiation source 310 and the irradiation optics 312 can be adjustable to implement different measurement “configurations” within the same apparatus. For example, different wavelengths and / or polarizations can be optional.

[0108] Depending on the material of the structure being inspected, different wavelengths can provide the desired level of penetration into the underlying layers. Short wavelengths are often preferred for distinguishing minimum device features and defects within them. For example, one or more wavelengths in the range of 0.01 nm to 20 nm, or optionally between 1 nm and 10 nm, or optionally between 10 nm and 20 nm, can be selected. Wavelengths shorter than 5 nm can suffer very low critical angles when reflected from the material of interest in semiconductor manufacturing. Therefore, selecting wavelengths greater than 5 nm can provide stronger signals at higher incident angles. On the other hand, if the inspection task is to detect the presence of a material, such as to detect contamination, wavelengths up to 50 nm can be useful.

[0109] A filtered beam 342 can enter an inspection chamber 350 from a radiation source 310, in which a substrate W, including the structure of interest, is held by a substrate support 316 for inspection at a measurement location. The structure of interest is designated S. Optionally, the atmosphere within the inspection chamber 350 can be maintained to near-vacuum by a vacuum pump 352, allowing SXR and / or EUV radiation to pass through the atmosphere without excessive attenuation. The irradiation system 312 has the function of focusing radiation into a focused beam 356 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 (the contents of US2017 / 0184981A1 are incorporated herein by reference in their entirety) mentioned above. Focusing is performed to achieve a circular or elliptical spot S with a diameter of less than 10 μm when projected onto the structure of interest. The substrate support 316 includes, for example, an XY translation platform and a rotation platform, which allow any portion of the substrate W to reach the focal point of the beam in a desired orientation. Thus, a radiation spot S is formed on the structure of interest. Alternatively or additionally, the substrate support 316 includes, for example, a tilting platform that allows the substrate W to be tilted at an angle to control the incident angle of the focused beam on the structure of interest, Ta.

[0110] Optionally, the illumination system 312 provides a reference radiation beam to a reference detector 314, which can be configured to measure the spectrum and / or intensity of different wavelengths in the filtered beam 342. The reference detector 314 can be configured to generate a signal 315 provided to the processor 320, and the filter can include information about the spectrum of the filtered beam 342 and / or the intensity of different wavelengths in the filtered beam.

[0111] 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 Ta. Irradiation system 312 and detection system 318 thus form an inspection apparatus. Such an inspection apparatus may include hard X-ray, soft X-ray, and / or EUV spectroreflectometers of the kind whose contents are incorporated herein by reference in their entirety as described in US2016282282A1.

[0112] If the target Ta has a certain periodicity, the radiation from the focused beam 356 can also be partially diffracted. The diffracted radiation 397 follows another path at a clearly defined angle relative to the incident angle and then relative to the reflected radiation 360. Figure 6 In the diagram, the diffraction radiation 397 is drawn schematically, and the diffraction radiation 397 may follow many other paths besides the drawn path. The inspection device 302 may also include an additional detection system 398 for detecting at least a portion of the diffraction radiation 397 and / or imaging at least a portion of the diffraction radiation 397. Figure 6 In this embodiment, a single additional detection system 398 is used, but embodiments of the inspection device 302 may also include more than one additional detection system 398, which are arranged at different locations to detect diffracted radiation 397 in multiple diffraction directions and / or image the diffracted radiation 397. In other words, the (higher) diffraction order of the focused radiation beam illuminating the target Ta is detected and / or imaged by one or more additional detection systems 398. One or more detection systems 398 generate signals 399 that are provided to the measurement processor 320. Signals 399 may include information about the diffracted light 397 and / or may include an image obtained from the diffracted light 397.

[0113] To aid in the alignment and focusing of spot S with the desired product structure, inspection device 302 may also provide auxiliary optics using auxiliary radiation under the control of measurement processor 320. Measurement processor 320 may also communicate with position controller 372, which operates translation, rotation, and / or tilting platforms. Processor 320 receives highly accurate feedback regarding the position and orientation of the substrate via sensors. Sensor 374 may include, for example, an interferometer, which can provide an accuracy of approximately several picometers. During operation of inspection device 302, spectral data 382 captured by detection system 318 is transmitted to measurement processing unit 320.

[0114] As mentioned, alternative forms of inspection equipment use hard X-rays, soft X-rays, and / or EUV radiation, optionally at normal or near-normal incidence, for example, to perform diffraction-based asymmetry measurements. Another alternative form of inspection equipment uses hard X-rays, soft X-rays, and / or EUV radiation with an angle greater than 1° or 2° to the direction parallel to the substrate. Both types of inspection equipment can be incorporated into a hybrid metrology system. The performance parameters to be measured can include overlap (OVL), critical size (CD), focal length of the lithography apparatus when the target structure is printed on the lithography apparatus, coherent diffraction imaging (CDI), and overlap at resolution (ARO) measurements. Hard X-rays, soft X-rays, and / or EUV radiation can, for example, have wavelengths less than 100 nm, such as radiation in the range of 5 nm to 30 nm, optionally in the range of 10 nm to 20 nm. The radiation can be narrowband or broadband in characteristics. The radiation can have discrete peaks in a specific wavelength band or can have more continuous characteristics.

[0115] Similar to optical scattering instruments used in today's manufacturing facilities, inspection device 302 can be used to measure structures within resist materials processed within a lithography unit (post-development inspection or ADI), and / or to measure structures after they have been formed in a harder material (post-etching inspection or AEI). For example, inspection device 302 can be used to inspect a substrate after it has been processed by developing equipment, etching equipment, annealing equipment, and / or other equipment.

[0116] Measurement tools (MTs), including but not limited to the scattering instruments mentioned above, can use radiation from a radiation source to perform measurements. The radiation used by the measurement tool MT can be electromagnetic radiation. The radiation can be optical radiation, such as radiation in the infrared, visible, and / or ultraviolet portions of the electromagnetic spectrum. The measurement tool MT can use radiation to measure or inspect the properties and aspects of a substrate, such as a photolithographically exposed pattern on a semiconductor substrate. The type and quality of the measurement can depend on a number of properties of the radiation used by the measurement tool MT. For example, the resolution of an electromagnetic measurement can depend on the wavelength of the radiation, where, for example, due to diffraction limitations, shorter wavelengths can measure smaller features. To measure features with small dimensions, radiation with short wavelengths, such as EUV, hard X-rays (HXR), and / or soft X-rays (SXR), can preferably be used to perform the measurement. To perform measurements at a specific wavelength or wavelength range, the measurement tool MT needs access to a source that provides radiation at said / those wavelengths. Different types of sources exist for providing radiation at different wavelengths. Depending on the wavelength(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 be an HHG or any other type of source mentioned above to obtain radiation at the desired wavelength(s).

[0117] Figure 7 A simplified schematic diagram of embodiment 600 of the irradiation source 310 is shown, which may be an irradiation source for HHG. Regarding Figure 6 One or more features of the irradiation source in the described measuring instrument may also be present in the irradiation source 600 where appropriate. The irradiation source 600 includes a chamber 601 and is configured to receive pump radiation 611 having a propagation direction indicated by the arrow. The pump radiation 611 shown here is an example of pump radiation 340 from pump radiation source 330, such as... Figure 6As shown in the diagram. Pump radiation 611 can be directed into chamber 601 through radiation input 605, which may be an observation port optionally made of molten silica or a similar material. Pump radiation 611 may have a Gaussian or hollow (e.g., annular) transverse cross-sectional profile and may be incident (optionally focused) onto gas flow 615 within chamber 601, which has 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) with a gas pressure above a certain value, referred to as the gas volume or gas target (e.g., a few cubic millimeters). Gas flow 615 may be a steady flow. Other media such as metallic plasma (e.g., aluminum plasma) may also be used.

[0118] The gas delivery system of the irradiation source 600 is configured to provide an airflow 615. The irradiation source 600 is configured to provide pump radiation 611 in the airflow 615 to drive the generation of emitted radiation 613. The region in which at least a majority of the emitted radiation 613 is generated is referred to as the interaction region. The interaction region can vary from tens of micrometers (for tightly focused pump radiation) to several millimeters or centimeters (for moderately focused pump radiation) or even up to several meters (for very loosely focused pump radiation). The gas delivery system is configured to provide 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 airflow 615 is provided via 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, the gas nozzle 609 includes an opening 617 in the exit plane of the gas nozzle 609. A gas flow 615 is supplied from the opening 617. A gas trap is used to confine the gas flow 615 within a volume by extracting residual gas flow and maintaining a vacuum or near-vacuum atmosphere inside the chamber 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 attributable to the high-power pump radiation 611.

[0119] The size of the gas nozzle 609 can conceivably also be used in scaled-up or scaled-down versions of nozzles ranging from micrometers to meters. This wide range of size specifications stems from the fact that the settings can be scaled so that the intensity of the pump radiation at the gas flow ultimately falls within a specific range that is beneficial to the emitted radiation. This requires different size specifications for different pump radiation energies, which may be pulsed lasers, and the pulse energy can vary from tens of microjoules to several joules. Optionally, the gas nozzle 609 has thicker walls to reduce nozzle deformation caused by thermal expansion effects that can be detected, for example, by a camera. A gas nozzle with thicker walls can produce a stable gas volume with reduced variation. Optionally, the irradiation source includes a gas trap near the gas nozzle to maintain the pressure in chamber 601.

[0120] Due to the interaction between the pump radiation 611 and the gas atoms of the gas flow 615, the gas flow 615 will convert a portion of the pump radiation 611 into emitted radiation 613, which may be... Figure 6 An 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 from 0.1 nm to 100 nm, optionally from 1 nm to 100 nm, optionally from 1 nm to 50 nm, or optionally from 10 nm to 20 nm.

[0121] In operation, the emitted radiation beam 613 can pass through the radiation output terminal 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 may be... Figure 6 An example of the irradiation system 312. The emitted radiation 613 can be directed (optionally focused) onto the structure on the substrate.

[0122] Because air (and virtually any gas) absorbs a large amount of SXR or EUV radiation, the volume between the airflow 615 and the wafer to be inspected can be evacuated or nearly evacuated. Since the central axis of the emitted radiation 613 can be collinear with the central axis of the incident pump radiation 611, the pump radiation 611 may need to be blocked to prevent it from passing through the radiation output terminal 607 and entering the irradiation system 603. This can be achieved by... Figure 6The filter 344 shown is incorporated into the radiation output terminal 607, which is positioned in the path of the emitted beam and is opaque or nearly opaque to the pump radiation (e.g., opaque or nearly opaque to infrared or visible light) but at least partially transparent to the emitted radiation beam. The filter can be fabricated using zirconium or a combination of materials in multiple layers. When the pump radiation 611 has a hollow (optionally annular) cross-sectional profile, the filter can be a hollow (optionally annular) bulk. Optionally, the filter is neither perpendicular nor parallel to the propagation direction of the emitted radiation beam to achieve efficient pump radiation filtering. Optionally, the filter 344 comprises a hollow bulk and a thin-film filter such as an aluminum (Al) or zirconium (Zr) 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.

[0123] This document describes methods, apparatus, and components for obtaining emitted radiation, optionally at higher harmonic frequencies of the pump radiation. The radiation generated by the process (optionally using nonlinear effects to generate HHG of radiation optionally at the harmonic frequencies of the provided pump radiation) can be set as radiation in a metrology tool (MT) for substrate inspection and / or measurement. If the pump radiation comprises short pulses (i.e., a few cycles), the generated radiation need not be precisely at the harmonics of the pump radiation frequency. The substrate can be a photolithographically patterned substrate. The radiation obtained by the process can also be set in a photolithography apparatus (LA) and / or a photolithography cell (LC). The pump radiation can be pulsed radiation capable of providing peak intensity over a short time.

[0124] Pump radiation 611 may include radiation having one or more wavelengths higher than the emitted radiation. Pump radiation may include infrared radiation. Pump radiation may include radiation having multiple wavelengths in the range of 500 nm to 1500 nm. Pump radiation may include radiation having multiple wavelengths in the range of 800 nm to 1300 nm. Pump radiation may include radiation having multiple wavelengths in the range of 900 nm to 1300 nm. Pump radiation may be pulsed radiation. Pulsed pump radiation may include pulses having a duration in the femtosecond range.

[0125] In some embodiments, the emitted radiation (optionally higher-order harmonic radiation) may include one or more harmonics having pump radiation wavelengths(s). The emitted radiation may include wavelengths in the extreme ultraviolet, soft X-ray, and / or hard X-ray portions of the electromagnetic spectrum. 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.

[0126] Radiation such as higher-order harmonic radiation described above can be used as source radiation in a metrology tool (MT). The metrology tool MT can use the source radiation to perform measurements on a substrate exposed by a photolithography apparatus. These measurements can be used to determine one or more parameters of the structure on the substrate. Compared to using longer wavelengths (e.g., visible light, infrared radiation), using radiation at shorter wavelengths (e.g., within the wavelength range described above, including EUV, SXR, and / or HXR wavelengths) allows for the resolution of smaller features of the structure by the metrology tool. Radiation with shorter wavelengths (such as EUV, SXR, and / or HXR radiation) can also penetrate deeper into materials such as patterned substrates, meaning that measurements of deeper layers on the substrate are possible. These deeper layers may not be accessible by radiation with longer wavelengths.

[0127] In a metrology tool (MT), source radiation can be emitted from a radiation source and directed onto a target structure (or other structure) on a substrate. Source radiation can include EUV, SXR, and / or HXR radiation. The target structure can reflect, transmit, and / or diffract the source radiation incident on it. The metrology tool (MT) can include one or more sensors for detecting diffracted radiation. For example, the metrology tool (MT) can include detectors for detecting positive (+1) and negative (-1) diffraction orders. The metrology tool (MT) can also measure specular reflection or transmission radiation (0th-order diffraction radiation). Additional sensors for measurement can be present in the metrology tool (MT), for example, to measure other diffraction orders (e.g., higher diffraction orders).

[0128] In exemplary photolithography applications, an optical column can be used to focus radiation generated by an HHG source onto a target on a substrate. This optical column can be referred to as an irradiator that transfers radiation from the HHG source to the target. The HHG radiation can then be reflected from the target, detected, and processed, for example, to measure and / or infer the properties of the target.

[0129] Gas target HHG configurations can be broadly categorized into three separate types: gas jet, gas chamber, and gas capillary. Figure 7An exemplary gas jet configuration is depicted, in which a gas volume is introduced into a driving radiation laser beam. In this gas jet configuration, the interaction between the driving radiation and the solid portion is minimized. The gas volume may, for example, comprise a gas flow perpendicular to the driving radiation beam, wherein the gas volume is confined within a gas chamber. In a gas capillary arrangement, the dimensions of the capillary structure containing the gas are small in the lateral direction, such that the capillary structure significantly affects the propagation of the driving radiation laser beam. The capillary structure may, for example, be a hollow-core optical fiber, wherein the hollow core is configured to contain the gas.

[0130] The gas jet HHG configuration can provide relative degrees of freedom to shape the spatial profile of the driving radiation beam in the far field because it is not constrained by the limitations imposed by the gas capillary structure. The gas jet configuration can also have less stringent alignment tolerances. On the other hand, the gas capillary can provide increased interaction partitioning between the driving radiation and the gaseous medium, which can optimize the HHG process.

[0131] To use HHG radiation, for example in measurement applications, the HHG radiation is separated from the driving radiation downstream of the gas target. The separation of HHG radiation from the driving radiation may differ for gas jet and gas capillary configurations. In both cases, the driving radiation suppression scheme may include a metallic transmission filter to filter out any remaining driving radiation from the short-wavelength radiation. However, before such a filter can be used, the intensity of the driving radiation should be significantly reduced from its intensity at the gas target to avoid damaging the filter. The methods that can be used for this intensity reduction differ for gas jet and capillary configurations. For gas jet HHG, due to the relative degrees of freedom of the shape and spatial profile (which may also be referred to as spatial distribution and / or spatial frequency) of the driving radiation beam focused onto the gas target, this can be designed such that, in the far field, the driving radiation beam has a lower intensity in the direction of propagation of 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.

[0132] In contrast, in gas capillary structures, the spatial profile of the bundle as it passes through the gaseous / solid medium can be primarily defined by the capillary. The spatial profile of the driving radiation can be determined by the shape and material of the capillary structure. For example, in the case of using a hollow-core fiber as the capillary structure, the shape and material of the fiber structure determine which driving radiation modes are supported to propagate through the fiber. For most standard fibers, the supported propagation modes result in a spatial profile in which the higher intensities of the driving radiation superimpose with the higher intensities of the HHG radiation. For example, the driving radiation intensity can be centered in a Gaussian or near-Gaussian profile in the far field.

[0133] While specific reference is made to HHG, it will be understood that the invention can be practiced using any radiation source where circumstances permit. In one embodiment, the radiation source is a laser-generated plasma (LPP) source as mentioned above for hard X-ray, soft X-ray, EUV, DUV, and visible light irradiation. In another 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 microfocusing source.

[0134] As further explained above, when the HHG process is used to generate a radiation beam for use by a measurement system (e.g., Figure 4 When depicting the radiation beam (5), the beam consists of harmonics of the pump radiation wavelength. In one example, the pump radiation wavelength is 1030 nm. The spectrum λ of the radiation beam generated by the higher-order harmonic process... h It can have peaks at the following wavelengths:

[0135] Equation 1

[0136] Where λ0 is the wavelength of the pump radiation, and h is the number of harmonics and can be an odd integer. Typically, h can be a sequence, for example, h = 51, 53, 55, ..., 103. In the case of a 1030 nm pump beam, the radiation beam provided by the HHG can have wavelengths of 10 nm, 10.20 nm, 10.40 nm, ..., 20.20 nm. These wavelengths together form a spectrum, where the wavelengths at either end of the spectrum have the lowest intensity, and the wavelengths at the center of the spectrum have the highest intensity. Between each wavelength of the spectrum, there are portions with zero or negligible intensity, and thus the spectrum consists of a series of peaks.

[0137] Figure 8 The spectrum of an exemplary radiation beam generated by an HHG and used by a measuring instrument is schematically depicted. The spectrum comprises a series of peaks having wavelengths determined according to procedure 1 above. The horizontal axis represents the wavelength, and Figure 8 The vertical axis represents the normalized intensity. In the schematically depicted spectrum, the intensity drops to zero between adjacent peaks.

[0138] Figure 9 The diffraction order produced by the broadband radiation beam when it is incident on a diffraction grating is schematically depicted. Figure 9 In this case, the incident broadband radiation beam is not composed of peaks, but instead has a continuous series of wavelengths. Figure 9The horizontal axis is sin(θ) relative to the incident radiation (which is perpendicular to the diffraction grating). Figure 9 The vertical axis represents the diffraction efficiency. Although combined Figure 9 While normal incidence is mentioned, embodiments of the invention operate with an acute angle of incidence (normal incidence is used here for ease of explanation). Embodiments of the invention may, for example, use an angle of incidence of 30˚ (+ / - 10˚).

[0139] Figure 9 The angular positions of the diffraction peaks observed are determined by the following diffraction equation:

[0140] Equation 2

[0141] Where p is the pitch of the diffraction grating and m is the diffraction order.

[0142] exist Figure 9 In the diagram, the solid line indicates the second diffraction order m=2, the dashed line indicates the third diffraction order m=3, and the dotted line indicates the fourth diffraction order m=4. As can be seen, in... Figure 9 In the model, the second diffraction order m=2 begins with a small sin(θ) value, while the third and fourth diffraction orders begin with larger sin(θ) values. However, there is considerable overlap between the diffraction orders. (The remaining text appears to be incomplete and requires further context.) Figure 9 Understandably, because when using broadband radiation, different diffraction orders are superimposed on each other, so it is problematic to determine which diffraction order contributes to the measured intensity at a given sin(θ) value.

[0143] refer to Figure 4 The detector 4 of the measuring instrument detects the broadband radiation diffracted by the grating on the substrate W. The position of the diffracted radiation incident on the detector 4 is determined by the diffraction angle θ. For relatively small angles, such as in the case of the measuring instrument, Sin(θ) can be directly mapped to the position on the detector 4. Therefore, Figure 9 The horizontal axis can be considered as a linear position (with arbitrary units) on detector 4. As mentioned above, diffraction orders are superimposed on each other. Therefore, detector 4 cannot distinguish, for example, the second diffraction order from the third diffraction order at locations where both orders on the detector have significant intensity. This limits the measurements that can be achieved using this method. At least some embodiments of the present invention address this problem.

[0144] One embodiment of the invention is a method for determining properties, optionally wavelength-dependent properties of a structure / target on a substrate, such as a target response. Optionally, the target response is a target diffraction efficiency spectrum. The determination method can be based on measured data, such as intensity measured by a detector. The determination method can use properties of pump radiation, such as the source spectrum of pump radiation. Optionally, the determination method can also use properties of the structure, such as the pitch of the structure. The measured data can be obtained based on measurements of scattered radiation scattered by the structure, generated by irradiating the structure with incident radiation, and optionally, the incident radiation can be generated by irradiating the target medium with pump radiation, optionally via an HHG process.

[0145] Figure 10 The diffraction order is schematically depicted by the broadband radiation generated using HHG. (As described above...) Figure 8 As mentioned, the spectrum of the incident radiation beam consists of a series of peaks that are separated from each other. Therefore, when incident on detector 4 (see...) Figure 4 The diffraction radiation at that point also includes a series of peaks. (Similar to...) Figure 9 The second diffraction order m=2 is depicted using solid lines, the third diffraction order m=3 using dashed lines, and the fourth diffraction order m=4 using dotted lines. Figure 10 In this context, assuming constant diffraction efficiency (independent of wavelength), the vertical axis represents the illumination (or source) spectrum. The unit will be intensity (e.g., ...). Figure 11 (In the case of [the previous scenario]), but the vertical axis has been scaled to set 1.0 as the maximum value for each diffraction order to allow the peaks to be more easily observed. The horizontal axis is sin(θ) or the equivalent linear position on the detector with arbitrary units. For each diffraction order, Figure 10 The shortest wavelength is shown on the left-hand side, where the wavelength is oriented towards... Figure 10 The number gradually increases on the right side.

[0146] Figure 10 The first few peaks in the spectrum originate from the second diffraction order m=2. Figure 10 Only the longer wavelengths of the second diffraction order are shown (shorter wavelengths would have smaller sin(θ) and are not depicted). The peak intensity of the continuous peaks of the second diffraction order decreases as the wavelength becomes longer (corresponding to larger sin(θ)).

[0147] The initial peak of the third diffraction order m=3 has a low peak intensity at shorter wavelengths, gradually increasing to a maximum peak intensity, and then decreasing again. As schematically depicted, the shorter wavelengths of the third diffraction order m=3 overlap with the longer wavelengths of the second diffraction order m=2. As schematically depicted, for some wavelengths, the peaks of the second and third diffraction orders overlap considerably, while for other wavelengths, the peaks of the second and third diffraction orders do not overlap at all or have negligible overlap.

[0148] Figure 10 The fourth diffraction order, m=4, is also shown. The initial peak of the fourth diffraction order has a low peak intensity at shorter wavelengths, gradually increasing to a maximum peak intensity. For larger sin(θ) values, the intensity of the fourth diffraction order peak will decrease, but this is not shown here. As schematically depicted, for some wavelengths, the peaks of the third and fourth diffraction orders overlap considerably, while for other wavelengths, the peaks of the third and fourth diffraction orders do not overlap at all or have negligible overlap.

[0149] Figure 10 The horizontal axis can be considered as detector 4 (see Figure 4 A linear position with arbitrary units on ). Figure 10 The left and right ends of the detector can correspond to the left and right ends of the detector 4. Peaks of different diffraction orders are incident on different linear positions on the detector 4. In some cases, the intensity peaks consist of two diffraction order peaks that are quite overlapping. This can be called a composite peak. In other cases, the intensity peaks consist of a single diffraction order peak (or a single diffraction order plus a negligible contribution from another diffraction order). This can be called a single-wavelength peak.

[0150] Figure 11 A schematic depiction of when multiplied by Figure 9 diffraction efficiency Figure 10 The intensity of the radiation seen by detector 4 when the diffracted broadband radiation is incident on the detector. Figure 11 The vertical axis represents the intensity of the radiation incident on the detector, and the horizontal axis represents the linear position (in arbitrary units) on the detector. When two peaks corresponding to two different diffraction orders have significant overlap, this produces a composite peak, i.e., a peak formed by the combination of two different diffraction orders. Four such composite peaks, 700, 702, 704, and 706, are depicted on [the graph]. Figure 11 middle.

[0151] A disk-shaped peak identifies the radiation peak on the detector composed of the second diffraction order m=2 and negligible contributions from the third and fourth diffraction orders. An upward-pointing triangle identifies the radiation peak on the detector composed of the third diffraction order m=3 and negligible contributions from the second and fourth diffraction orders. A downward-pointing triangle identifies the fourth diffraction order peak m=4 and negligible contributions from the second and third diffraction orders. These peaks can be referred to as single-wavelength peaks.

[0152] As from Figure 11As can be seen, multiple peaks are identified for each of the second, third, and fourth diffraction orders, with negligible contributions from the other diffraction orders. In other words, multiple single-wavelength peaks are identified. This resolves the problem of at least partially superimposed diffraction orders, as further explained above.

[0153] The measurement tool can be configured to omit composite peaks when performing analysis of the detected diffraction spectrum. Alternatively, the measurement tool can be configured to use only single-wavelength peaks when performing analysis of the detected diffraction spectrum.

[0154] The measurement tool can be configured to interpolate between the measured single-wavelength peaks and add any missed peaks. The resulting diffraction spectrum, including the interpolated peaks, can then be used to analyze the substrate grating that generated the diffraction pattern.

[0155] In one example, the so-called reconstruction method is used to reconstruct the properties of the grating that produces the detected diffraction. As further explained above, in the reconstruction method, the properties of the grating are calculated by simulating the interaction between the scattered radiation and a mathematical model of the grating structure. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern (including inserted peaks) similar to that observed from a real grating. The reconstruction method can utilize knowledge of the properties of the measurement instrument, such as the spectrum (watts / nm) of the broadband radiation beam, the exposure time (i.e., the amount of time during which radiation is detected), and the position of the detector (which could be an imaging detector). The properties of the measurement instrument can be measured using a calibration process. This is a modeling approach based on physical phenomena.

[0156] In machine learning methods, a model for generating an SXR tool is created. The model of a target structure with repeating structures of size and / or optical properties can be modified. Using a model of the target structure with an electromagnetic (EM) solver (e.g., strictly coupled-wave analysis (RCWA)), a person skilled in the art can simulate a series of target responses R(m,λ) for a given target structure pitch (or pitch in two directions). Using a series of target responses in the SXR tool model, a person skilled in the art can predict a corresponding series of measured intensities I(κ) for a typical source spectrum S(λ). Given a source spectrum S(λ), measured intensities I(κ), and (multiple) target pitches, the series of measured intensities and the corresponding annotated target responses can then be used to train a neural network or other machine learning model to infer the target response R(m,λ).

[0157] Advantageously, embodiments of the invention can provide grating reconstruction with an accuracy previously unattainable using existing methods. In particular, embodiments of the invention can be used to remove ambiguity regarding the wavelength of peaks of intensity measured by a detector.

[0158] The method of the present invention can be used for gratings. The grating can be a simple 1-D grating (i.e., having parallel lines). The grating can be a 2-D grating (i.e., having repeating unit cells in both the x and y directions). 2-D gratings can have a checkerboard configuration. The grating can be formed from a periodic product structure. More than one grating can be provided, for example, in different layers of a substrate, thereby allowing overlapping measurements (overlapping measurements) to be performed. The grating is an example of a target structure that can be used by embodiments of the present invention. Other forms of target structures with periodic structures can be used. The method of the present invention can be used for non-periodic structures.

[0159] The wavelength of the peak in the broadband radiation produced by an HHG source depends on the properties of the HHG source, such as the gas supplied and the form of the source's capillary structure. These properties do not change, and therefore the wavelength of the peak is known when a measurement is performed. If necessary, a spectrometer can be used periodically to measure the wavelength of the peak.

[0160] Measurement methods can be used to measure grating properties such as critical size and overlap. Critical size can cause variations in grating properties; overlap can cause variations in the position of the grating relative to different layers of the substrate. However, the pitch of the grating itself can be expected to be approximately as designed. Therefore, the pitch of a grating illuminated by broadband radiation is well known. Prior knowledge of the radiation spectrum provided by the HHG source and, optionally, the pitch of the target allows for the calculation of the expected positions of diffraction peaks. This prior knowledge also allows for the identification of single-wavelength peaks of the detected radiation to be used for analysis, and the identification of composite peaks not used for analysis (such as...). Figure 11 (Illustrated schematically in Chinese).

[0161] Figure 12 A method according to an embodiment of the present invention is schematically depicted. In a first step 800, broadband radiation is directed at a target grating, and the intensity of the diffracted radiation incident on the imaging detector as a function of position is measured.

[0162] In the second step 802, the positions of the intensity peaks are identified. Identifiers are assigned to each peak, for example, i = 0, 1, 2...

[0163] In the third step 804, for each peak, the diffraction order m and the number of harmonics h are identified using knowledge of the spectrum of broadband radiation and optionally knowledge of the grating pitch (HHG is used as an example here). If a single diffraction order and harmonic number are identified (the peak is a single-wavelength peak), the wavelength of the peak is calculated. This provides data points that can be used for measurement. In one embodiment, if multiple diffraction orders and harmonic numbers apply to a given peak (the peak is a composite peak), the peak is not used for measurement.

[0164] In step 806, the missing data points (i.e., the missing single-wavelength peaks) are inserted and added to the data.

[0165] In step 808, the data is used to reconstruct the grating.

[0166] In the depicted embodiments, there is a portion with zero intensity between each wavelength peak in the spectrum. In some embodiments, the portion between each wavelength peak may have a non-zero but negligible intensity. In these cases, the non-zero intensity may have a negligible effect on the accuracy of the measurement method. In some embodiments, the non-zero intensity between wavelength peaks may be non-negligible. The measurement method can still be used, but the non-zero intensity between wavelength peaks may reduce the accuracy of the measurement method.

[0167] The operation of the HHG irradiation source 310 can be modified to minimize the intensity of radiation between wavelength peaks. For example, narrowing the spectrum of the pump radiation 330, 611 (e.g., by providing a longer pump radiation pulse) can reduce the intensity of radiation between wavelength peaks. This can reduce the total power of the broadband radiation beam while still providing an increase in the accuracy of the measurement method. The width of the wavelength peaks can be affected by adding some chirp to the pump radiation pulse. This can also reduce the total power of the broadband radiation beam.

[0168] In some cases, the number of harmonics h may not be a precise integer. However, the method works in the same way.

[0169] The advantage of embodiments of the present invention is that once a single-wavelength diffraction peak has been identified and any missed peaks have been inserted, the resulting diffraction spectrum is independent of the parameters of the measurement tool. Therefore, reconstructing the grating using the diffraction spectrum does not require including the measurement tool parameters.

[0170] Another advantage of embodiments of the present invention is that the reconstruction of the grating using diffraction spectroscopy can be performed using analysis based on physical phenomena (based on autocorrelation functions). Examples of this are described in US20230040124A1, the contents of which are incorporated herein by reference in their entirety. This avoids incorrect results that might otherwise be attributable to interfering parameters in cases where analysis based on non-physical phenomena is used.

[0171] In some cases, the broadband radiation beam incident on the target may exhibit a certain degree of divergence. This divergence will tend to obscure the signal received at detector 4. (Reference) Figure 11 As an example, the peak is broadened by blurring due to the divergence of the broadband radiation beam. Users of the measurement system may not receive information about the grating on the lithographic substrate being measured. These problems can make it difficult to implement the machine learning methods described further above to reconstruct the properties of the grating. Alternative methods are now described.

[0172] Alternative methods use the spectrum of broadband radiation beams. (spectrum This can be referred to as the illumination spectrum. The knowledge of fuzzy B can be used, and optionally, the knowledge of fuzzy B can be used to estimate the diffraction efficiency R. Fuzzy B and the spectrum can be obtained using sensors present in the measurement system. This kind of knowledge.

[0173] spectrum It can originate from higher-order harmonic generation processes and can include odd harmonics of the pump laser wavelength (as in Equation 1), or spectral components. It can include both odd harmonics and even harmonics.

[0174] In one example, the estimation of diffraction efficiency R also uses two priors (the priors are assumed probability distributions for the parameters). The first prior states the fact that, as wavelength R... λ The diffraction efficiency of the function is smooth, meaning that the diffraction efficiency has a relatively low second derivative; a non-smooth function R... λ It has a lower probability than the smoothing function. The second prior represents the following fact: R λ Close to the reasonable value R (0) For example, at a wavelength of 10 nm that constitutes a broadband radiation beam. -4 Or 10 -3 The pitch of the target being measured can also be known. In some embodiments, it can be done without a first prior (i.e., with R). λ Estimation is performed under the condition of prior knowledge related to the second derivative.

[0175] The signal measured by detector 4 can be referred to as the spectral flux. The spectral flux on the detector plane can be mapped to the pupil space. If the target is at the origin and the detector pixel is at coordinates (x, y, z), where (x, y) is in the plane of the target, then the pupil coordinates of the pixel are (x / r, y / r), where... Spectral flux can be considered as a pupil spatial displacement. Strength of the function In this context, pupil spatial displacement means the offset between the pupil coordinates of 0th-order diffraction and the coordinates of the observed intensity. For a given diffraction order m, we have ,in The pitch (period) of the target pattern.

[0176] The spectral flux of a known spectrum as a broadband radiation source can be expressed as: This can be converted into a pupil space, which is the signal that will be seen at detector 4 for perfect diffraction by the target without ambiguity, as shown below:

[0177] (Equation 3)

[0178] diffraction efficiency for the target The signal that will be seen at detector 4 is:

[0179] (Equation 4)

[0180] in Let be the fuzzy kernel and * be the convolution operator. The fuzzy kernel is determined based on the fuzziness measured by a measurement system. In some cases (such as when the ambiguity is small enough that it will not significantly affect the measurement output), the ambiguity can be ignored.

[0181] In one example The estimation of can be a minimization problem. Let This is the right-hand side of equation 4. Next,

[0182] Equation 5

[0183] in and It is a regularization parameter used to adjust the relative importance of the corresponding terms, and

[0184] Equation 6

[0185] The integral is taken within the relevant range of x. Figure 13 This demonstrates how the above methods work (via simulation). Figure 13 The topmost drawing schematically depicts the diffraction order at detector 4 caused by broadband radiation generated using an HHG. As mentioned above, the spectrum of the incident radiation beam consists of a series of peaks separated from each other. The diffraction radiation at detector 4 also includes a series of peaks. Each of the second diffraction order m=2, the third diffraction order m=3, and the fourth diffraction order m=4 is labeled. As can be seen, each diffraction order includes a series of peaks. The third diffraction order is superimposed on the second and fourth diffraction orders.

[0186] The intermediate plot depicts the simulated intensity of radiation incident on detector 4 after diffraction by the target, in this example, where the target is a grating with a pitch of 100 nm.

[0187] The bottom plot depicts the estimated diffraction efficiency for each of the three diffraction orders. Solid lines for the second diffraction order, dashed lines for the third, and dotted lines for the fourth are used to indicate the estimated diffraction efficiency determined using the above method. Because Figure 13 For simulation purposes, the actual diffraction efficiency known from the simulation is well-known. The actual diffraction efficiency for each order is plotted using dotted lines. It can be seen that the estimated diffraction efficiency closely follows the actual diffraction efficiency.

[0188] Figure 14 Showing with Figure 13 The three plots are identical: the spectrum of radiation at the detector (top plot), the intensity of radiation at the detector (middle plot), and the estimated diffraction efficiency (bottom plot). Figure 14 In the simulation, the incident radiation beam has a beam divergence of 2 mrad at a pitch of 100 nm, while... Figure 13 In the simulation, the incident radiation beam does not diverge.

[0189] exist Figure 14 In the bottom plot, solid lines for the second diffraction order, dashed lines for the third diffraction order, and dotted lines for the fourth diffraction order are used to indicate the estimated diffraction efficiency. The actual diffraction efficiency for each order is depicted using dotted lines. Although ambiguity exists in the incident radiation beam, the estimated diffraction efficiency closely follows the actual diffraction efficiency. This demonstrates that the above method works well even in the presence of ambiguity caused by diverging incident radiation.

[0190] The implementation details of an embodiment of the method will now be described. For each diffraction order, a "reasonable" value... It can take different values. Figure 13 and Figure 14 In this context, the inferred value (i.e. the value estimated using the method) is taken as the value located at the edge of the range.

[0191] The implementation method can be achieved through Reparameterize. That is, S, I, and R are all expressed as The function. This is convenient because the subsequent minimization algorithm does not need to know the target's pitch, whereas general algorithms do not need to rely on... To parameterize the spectrum. For example, according to Doing it this way will be simple. It can be equivalently expressed as m.λ.

[0192] For the regularization parameter in Equation 5 It can be small, such that as long as a large intensity I exists, included in Equation 5 The terms are negligible. It can be large enough that the peak of the illumination spectrum does not begin to appear in the inferred diffraction efficiency R.

[0193] Given a large (sparse) matrix, standard library routines can be used to perform least-squares optimization for matrix-vector equations of x. Perform a least-squares solution. Optimization can be efficient. If signal I is represented by N points and there are M diffraction orders, then vector x will have NM (for each diffraction order, in...) The diffraction efficiency R at N values), matrix A will have a shape ,in And b will be a vector with K elements.

[0194] Each column in matrix A will represent an equation, where the corresponding element of b serves as the right-hand side of the equation.

[0195] The set of N columns in matrix A represents Equation 2. If there is no ambiguity, each of these columns has M non-zero values ​​representing the illumination value; the corresponding elements in b are the corresponding observed signal values. If ambiguity exists, there will be more non-zero values ​​to couple the column to nearby wavelengths. value).

[0196] in addition Columns represent each discrete Equation of value The second derivative is approximated as:

[0197] Equation 7

[0198] in for The step size in the middle.

[0199] Additionally, the NM column represents the equation. More columns can be added to matrix A to represent additional equations.

[0200] When solving matrix equations, the x vector can include The estimated / inferred diffraction efficiency spectrum in the domain can be converted into a representation in wavelength for further analysis.

[0201] The above method relates to a diffraction grating target having a pitch extending in one direction. This can be referred to as a 1D periodic target. The method can also be used for targets having pitches extending in two directions (these targets can be referred to as 2D periodic targets). For a pitch of x... and y-pitch The 2D periodic target, characterized by diffraction order, was identified as (m x , m y The algorithm is applied to groups of diffraction orders with potential confusion, such as the group {(2, -1), (4, -2), (6, -4)} or more generally, orders ( , ) groups, where And in this example, , .

[0202] The effective pitch is then:

[0203] Equation 8

[0204] Even when using a noisy signal as input to the method, the above method can still provide a diffraction efficiency value.

[0205] Optionally, the smoothness parameter can be adjusted. As The function. Because the target response tends to be in 1 / λ rather than in λ or λ. The wavelength is quasi-periodic, so this is beneficial. Near wavelengths where the target response is known to be less smooth, the target response can be reduced. This can be achieved at approximately... It was carried out at that location, in approximately The optical properties of silicon suddenly change.

[0206] The above-described method can utilize methods known in the field of machine learning. However, because the training involved is not present, the embodiments of the methods described herein are not strictly machine learning. A small number of simulations (e.g., once or twice) can be performed to obtain two regularization parameters. and The value of . and It can be estimated based on prior knowledge.

[0207] The above methods can utilize machine learning techniques, such as using training data (simulated measurements) to optimize parameters. , , Compared to the case where a neural network will generate an SXR tool, far less training data will be required (as further described above).

[0208] At least a portion of the steps described above in the method can be used to estimate the diffraction efficiency of a substrate structure. In one embodiment, there is a method for estimating diffraction efficiency, the method comprising directing a beam of emitted radiation onto the structure and thereby generating diffracted radiation attributable to the structure. Optionally, the emitted radiation has a spectrum comprising multiple peaks, and optionally the diffracted illumination comprises multiple diffraction steps. The method for estimating diffraction efficiency further comprises using an imaging sensor to detect the diffracted radiation. Optionally, the diffracted radiation incident on the imaging sensor comprises at least partially superimposed diffraction steps on the surface of the imaging sensor. The method for estimating diffraction efficiency further comprises using knowledge of the spectrum and prior knowledge of diffraction efficiency to separate the at least partially superimposed steps.

[0209] Optionally, the step of using the estimated diffraction efficiency to measure the parameters of the structure described above includes using the estimated diffraction efficiency as input to the simulation. Optionally, the simulation is based on model reconstruction.

[0210] The above method allows the use of the complete measured signal instead of just the non-overlapping order (which can be called the composite order) to calculate the target autocorrelation function.

[0211] The above methods are robust. The above methods do not separate the processing of zero values ​​in the illumination spectrum. The above methods do not exhibit Fourier transform-related artifacts near the edges of the signal.

[0212] The term "broadband radiation" can be interpreted as radiation with a spectrum in which the ratio of the longest wavelength to the shortest wavelength exceeds 1.4. The spectrum can include a series of peaks.

[0213] As further explained above, embodiments of the present invention can utilize the spectrum of the incident radiation beam. (Spectrum of the incident radiation beam) This can be referred to as the illumination spectrum. This knowledge can be used to represent the illumination spectrum based on wavelength or wavenumber (the number of wavelengths per unit distance).

[0214] Figure 15 An example of a portion of the measuring device according to this disclosure is schematically depicted. Figure 15 The portion of the measuring device shown in the figure can correspond to Figure 6 The diagram illustrates a portion of the scatterer. A radiation beam 901 is incident on a measurement target on a substrate W (e.g., a wafer). The radiation beam 901 can be, for example, broadband radiation and can include radiation in the hard X-ray (HXR), soft X-ray (SXR), extreme ultraviolet (EUV), visible to near-infrared (IR), and / or IR wavelength ranges. It can be generated by, for example... Figure 6The radiation source SO, 310, illustrated in the figure and further described above, produces a radiation beam 901. This radiation beam may be referred to as an irradiation beam.

[0215] The diffraction from the measurement target on the substrate W to the detector 905 (e.g., array sensor 905) is captured. The diffraction efficiency of the target for various wavelength components can be measured and the diffraction efficiency can be converted into estimates of parameters of interest, such as the overlap and critical dimensions of the substrate W.

[0216] like Figure 15 As shown, the illumination beam 901 can be guided toward the substrate W via a reflector 902 (e.g., a ring reflector). An imaging sensor 903 (e.g., the imaging sensor 903 may be referred to as an illumination monitoring sensor) can be used to monitor the illumination beam 901 for measurement. For example, a portion of the illumination beam 901 (the illumination beam 901 may be referred to as the measurement illumination) can be diffracted onto the illumination monitoring sensor 903 by a transmission diffraction grating 904. The diffraction efficiency of the transmission diffraction grating 904 can be known (e.g., via calibration measurement). The output from the illumination monitoring sensor 903 can be used to determine the spectrum of the illumination beam using the methods further described below. (Spectrum of the irradiation beam) This can be referred to as the illumination spectrum. ).

[0217] In an alternative arrangement (not shown), the illumination beam 901 can be reflected from a reference diffraction grating onto an imaging sensor 905 configured to perform a measurement. The diffraction efficiency of the reference diffraction grating (e.g., via calibration measurement) can be known. The output from the imaging sensor 905 can be used (e.g., using the methods described below) to determine the illumination spectrum. Other types of gratings can be used to measure the illumination spectrum.

[0218] With measurement of irradiation spectrum The associated problem is that the illumination spectrum can include wavelength components that extend beyond octaves (i.e., a factor of more than 2 between the longest and shortest wavelengths). For example, the illumination spectrum can range from 8 nm to 22 nm. The positions of the illumination beam 901, the transmission diffraction grating 904, and the illumination monitoring sensor 903 can be accurately known. However, a fundamental problem exists: the second diffraction order at a given wavelength λ will superimpose with the first diffraction order at wavelength 2λ. For example, the second order at 10 nm and the first order at 20 nm superimpose on the illumination monitoring sensor 903. Because of this superposition, it means that the illumination spectrum cannot be measured in a simple manner using the illumination monitoring sensor 903. Therefore, this is problematic.

[0219] This problem is solved by embodiments of the present invention. The method uses... , where m is the diffraction order number (m=1, 2, ...) and λ is the wavelength. This refers to the same item used in conjunction with other methods mentioned above.

[0220] As mentioned above, there is superposition at the irradiation monitoring sensor 903 at different diffraction orders, which means that the output signal from the irradiation monitoring sensor 903 is not the irradiation spectrum. The measurement results. The measured content can be alternatively referred to as the spectral power function. And it includes contributions from superimposed diffraction orders. The spectral power function is measured using the illumination monitoring sensor 903. It can be expressed in units of ADU nm -1 s -1 Let ADU stand for "Analog-Digital Unit" (the unit of sensor output, regardless of the sensor's wavelength-dependent sensitivity). The output signal from the illumination monitoring sensor 903 can be converted into a spectral power function using knowledge of the pitch of the transmission diffraction grating 904 and the spacing between the grating and the illumination monitoring sensor. .

[0221] The diffraction efficiency of the transmission diffraction grating 904 is well-known (this can be determined in advance using calibration methods). The spectral power function has been measured using the illumination monitoring sensor 903. Taken together, these can be used to calculate the illumination spectrum S(λ).

[0222] Let the true incident spectrum (i.e., the illumination spectrum) be Also in ADU nm -1 s -1 The unit is . This spectrum is not yet widely known. Let the diffraction efficiency of transmission diffraction grating 904 be . , It depends on the wavelength and the number of discrete diffraction orders. This is dimensionless. The value is between zero and one. The diffraction efficiency of the transmission diffraction grating 904 is well known.

[0223] Let the point spread function (“kernel”) be , to represent, for example, focusing error and the size of the diffraction-limited spot on the illumination monitoring sensor 903.

[0224] Spectral power function Described by the following equation:

[0225] Equation 9

[0226] Among them, * indicates targeting The convolution operator.

[0227] In some cases, This can be similar to the Dirac delta function. In this case, equation 9 can be omitted. Items. The remaining ones have different The value at which the unknown is located A system of equations for the value of . For example, if the wavelength range of S is known to be between 8 nm and 22 nm, and If captured in a step size of 0.01 nm (1400 points) within the range of 8 nm to 22 nm, then there will be 1400 equations with 1400 unknowns. Other step sizes can be used. Other wavelength ranges can be used. The measured spectral power function can be used. and known diffraction efficiency Solve these equations to obtain the irradiation spectrum. .

[0228] Typically, an extremely sparse system with N equations and N unknowns can be used to obtain the illumination spectrum S(λ).

[0229] In some cases, nuclear It can be fixed (and not a Dirac delta function). That is, for For all values ​​of and for each diffraction order m, the kernel can be the same. In this case, deconvolution can be used to eliminate K. One deconvolution method that can be used is Wiener deconvolution, which applies an optimized low-pass filter to P before performing deconvolution. The remaining values ​​are those with different values. The value at which the unknown is located A system of equations for the value of . Solve these equations to obtain the irradiation spectrum. .

[0230] In some cases, different nuclei can exist for each diffraction order m. ,For example (That is, the nucleus of second-order diffraction can be different from that of first-order diffraction.) In these cases, an assumed illumination spectrum can be used. The smoothness prior. In one example, the entire right-hand side of Equation 9 is written as 1400 equations with 1400 unknowns. The smoothness prior can be described using 1398 equations that favor continuous and generally smooth solutions (i.e., assuming a prior probability of smoothness). If Discretized into Then those equations (one equation for each j) will take the following form:

[0231] Equation 10

[0232] in It is a regularization parameter that can be tuned based on the signal-to-noise ratio. The overdetermined equations (Equations 9 and 10) are preserved, and the illumination spectrum can be obtained using least-squares fitting (or other fitting methods). Alternatively, it can be based on knowledge of what a typical spectrum looks like. Depends on j (e.g., can make (The peaks in the spectrum are smaller near the expected locations). Typically, the prior probability of spectral smoothness can be used when deconvolving K.

[0233] The number of equations mentioned above is merely an example, and other numbers of equations can be used. Each measured value is represented as an equation on the right-hand side of Equation 9. It is assumed that the smoothness equation is related to the nearest neighboring equation. If the differences between values ​​are correlated, then the number of smoothness equations (such as Equation 10 or its equivalent) can be reduced by two. Typically, there can be N equations according to Equation 9 and N-2 equations (or different representations of the smoothness prior) according to Equation 10. In this example, the smoothness prior replaces Wiener deconvolution.

[0234] In some cases, a universal integral kernel may exist. In these cases, a smoothness prior can be used in the manner described above.

[0235] Smoothness priors can be used in the kernel The case where it is fixed. Smoothness priors can be used in its kernel. This is the case for the Dirac delta function.

[0236] When using a smoothness prior, 2N-2 overdetermined equations and N unknowns are obtained. Least squares fitting methods (or other fitting methods) can be used to obtain the illumination spectrum using these overdetermined equations. .

[0237] In some cases, for certain order-wavelength combinations, the diffraction efficiency It can be zero or close to zero. For these combinations, Any value of will be equivalent in Equation 9. To produce a better-behaving function S, the equation takes the following form:

[0238] Equation 11

[0239] It can be added, among which This is another regularization parameter. This regularization will benefit those with smaller... The solution to the value of .

[0240] If the point spread function is If the convolution in Equation 9 is not constant, then the convolution can be expressed by having the form Discretized into The kernel is replaced by a discretized integral transform (where j can be negative). Equation It will have the following form:

[0241] Equation 12

[0242] Typically, the effects of focusing errors and / or diffraction-limited spot size, as represented by the kernel, can be removed from or reduced from the spectral power function. Deconvolution and integral transform can be considered examples of removing (or reducing) the effects of focusing errors and diffraction-limited spot size from the spectral power function. The use of smoothness priors can also be considered an example of removing (or reducing) the effects of focusing errors and diffraction-limited spot size from the spectral power function.

[0243] Figure 16 An example (generated via simulation) illustrating the operation of the above method is depicted. The depicted example uses a fictitious diffraction efficiency of the transmission diffraction grating 904 instead of the measured diffraction efficiency to demonstrate the method. Figure 16 The first graph in the figure is an example of the signal observed at the illumination monitoring sensor 903 (i.e., the spectral power function measured by the illumination monitoring sensor). ). Figure 16 The second graph shows the irradiation spectrum calculated using the method described above, starting from the measured spectral power function. The second graph includes the error value, and it can be seen that the error is relatively small.

[0244] Irradiation spectrum can be used during measurement. Irradiation spectrum It can change over time. Therefore, the irradiation spectrum can be calculated on a continuous basis using measurements taken by the irradiation monitoring sensor 903. Alternatively, the irradiation spectrum can be calculated periodically using measurements taken by the irradiation monitoring sensor 903.

[0245] The third graph shows the data used to calculate the illumination spectrum. The diffraction efficiency of the transmission grating 904 is given. As mentioned above, this is a hypothetical scenario for simulation. However, the diffraction efficiency of the transmission grating 904 can be measured via calibration measurements. As further mentioned above, other types of gratings can be used.

[0246] Calculated irradiation spectrum With ADU nm -1 s-1 The units are those of the sensor output, without considering the sensor's wavelength-dependent sensitivity. Since the superimposed wavelengths are already in the calculated illumination spectrum... The illumination spectrum is distinguished, so the spectrum can be divided by the sensor sensitivity spectrum (a wavelength-dependent value in ADU / J – measured via calibration) to obtain the spectrum in W / nm.

[0247] If used to measure the illumination monitoring sensors 903 and 905 after diffraction from substrate W (see...) Figure 15 Since both sensors 903 and 905 have the same sensitivity spectrum, the calculated irradiation spectrum can be kept in ADU-based units. That is, because the responses for both sensors 903 and 905 are identical, converting to W / nm is redundant. The irradiation spectrum can be expressed in other units, such as charge or electron count, instead of ADU.

[0248] Calculate the irradiation spectrum The method can be executed by the controller.

[0249] Embodiments may include a computer program comprising one or more machine-readable instruction sequences describing methods for optical measurement and / or methods for analyzing measurement results to obtain information about a photolithography process. Embodiments may include computer code containing one or more sequences of machine-readable instructions or data describing the methods. This can be, for example, in... Figure 6 Unit MPU and / or Figure 3 The computer program or code is executed within the control unit CL. A data storage medium (e.g., semiconductor memory, disk, or optical disk) in which such a computer program or code is stored may also be provided. In existing measurement equipment (e.g., Figure 6 If the types shown are already in production and / or use, embodiments of the invention can be implemented by providing an updated computer program product that causes a processor to perform one or more of the methods described herein. The computer program or code may optionally be arranged to control optical systems, substrate supports, etc., to perform methods for measuring parameters of a lithography process with respect to suitable plurality of targets. The computer program or code may update lithography and / or metrology options for measuring additional substrates. The computer program or code may be arranged to (directly or indirectly) control lithography equipment for patterning and processing additional substrates.

[0250] The irradiation source can be placed in, for example, a measurement device (MT), an inspection device, a lithography device (LA), and / or a lithography unit (LC).

[0251] The properties of the emitted radiation used to perform the measurement can affect the quality of the obtained measurement. For example, the shape and size of the transverse beam profile (cross section) of the radiation beam, the intensity of the radiation, and the power spectral density of the radiation can affect the measurement performed by radiation. Therefore, it is beneficial to have a source that provides radiation with properties that induce high-quality measurements.

[0252] Further embodiments are disclosed in the following numbered aspects:

[0253] 1. A method for measuring structural parameters of a substrate, the method comprising:

[0254] A beam of radiation is directed onto the structure, wherein the radiation has a spectrum comprising multiple peaks;

[0255] An imaging sensor is used to detect radiation diffracted from the structure;

[0256] Identify the peaks in the detected diffraction radiation;

[0257] Based on knowledge of the spectrum and the pitch of the structure, peaks are identified as composite peaks comprising radiation with two different wavelengths; and

[0258] The remaining peaks are used to measure the parameters of the structure.

[0259] 2. The method according to aspect 1 further includes adding the inserted peak to the remaining peaks before measuring the parameters of the substrate.

[0260] 3. The method according to aspect 1 or aspect 2, wherein the remaining peaks are single-wavelength peaks comprising a single wavelength, or single-wavelength peaks comprising a single wavelength and a negligible number of second wavelengths.

[0261] 4. The method according to any of the foregoing aspects, wherein the radiated beam has an acute angle of incidence on the structure.

[0262] 5. The method according to any of the foregoing aspects, wherein the structure is periodic.

[0263] 6. The method according to aspect 5, wherein the periodic structure is a grating.

[0264] 7. The method according to any of the foregoing aspects, wherein the parameters of the structure are measured by constructing a model of the structure.

[0265] 8. The method according to any of the foregoing aspects, wherein the method uses a second diffraction order, a third diffraction order, and a fourth diffraction order.

[0266] 9. A measurement system configured to measure parameters of a substrate structure, the measurement system comprising:

[0267] A source, the source being used to emit radiation having a spectrum including multiple peaks;

[0268] An optical device configured to direct the beam of radiation toward the structure;

[0269] An imaging sensor, configured to detect radiation diffracted from the structure; and

[0270] Processor, the processor being configured to:

[0271] Identify the peaks in the detected diffraction radiation;

[0272] Based on knowledge of the spectrum and the pitch of the structure, peaks are identified as composite peaks comprising radiation with two different wavelengths; and

[0273] The remaining peaks are used to measure the parameters of the structure.

[0274] 10. The measurement system according to aspect 9, wherein the processor is further configured to add the inserted peak to the remaining peaks before measuring the parameters of the substrate.

[0275] 11. The measurement system according to aspect 9 or aspect 10, wherein the remaining peaks are single-wavelength peaks comprising a single wavelength, or single-wavelength peaks comprising a single wavelength and a negligible number of second wavelengths.

[0276] 12. The measurement system according to any one of aspects 9 to 11, wherein the optical device is configured to guide the radiated beam onto the structure at an acute angle of incidence.

[0277] 13. The measurement system according to any one of aspects 9 to 12, wherein the processor is configured to measure the parameters of the structure by constructing a model of the structure.

[0278] 14. The measurement system according to any one of aspects 9 to 13, wherein the processor uses a second diffraction order, a third diffraction order, and a fourth diffraction order.

[0279] 15. A method for determining the properties of a structure on a substrate based on measured data, wherein the measured data is obtained based on measurements of scattered radiation scattered by the structure, wherein the scattered radiation is generated by irradiating the structure with incident radiation, wherein the incident radiation is generated by irradiating a target medium with pump radiation, wherein the determination is based on knowledge of the properties of the pump radiation.

[0280] 16. The method according to aspect 15, wherein the incident radiation is generated by irradiating the target medium with the pump radiation via a nonlinear process.

[0281] 17. The method according to aspect 16, wherein the nonlinear process is a higher-order harmonic generation.

[0282] 18. The method according to any one of aspects 15 to 17, wherein the property of the pump radiation is wavelength.

[0283] 19. The method according to any one of aspects 15 to 18, wherein the scattered radiation is broadband radiation.

[0284] 20. The method according to any one of aspects 15 to 19, wherein the scattered radiation has a wavelength in the wavelength range of 10 nm to 20 nm.

[0285] 21. The method according to any one of aspects 15 to 20, wherein the property of the structure is wavelength-dependent.

[0286] 22. The method according to any one of aspects 15 to 21, wherein the structure is a periodic structure with a pitch, and the measured data is obtained based on the measurement result of the diffracted radiation diffracted by the structure.

[0287] 23. The method according to aspect 22, wherein the wavelength-dependent property is related to the diffraction efficiency.

[0288] 24. The method according to any one of aspects 15 to 23, wherein the incident radiation has a spectrum comprising multiple peaks.

[0289] 25. The method according to aspect 24, the method further comprising: identifying peaks in the scattered radiation.

[0290] 26. The method according to aspect 24 or 25 further includes: identifying, based on knowledge of the spectrum, a peak comprising a composite peak having two different wavelengths of radiation.

[0291] 27. The method according to aspect 25 or 26 of reference 22, wherein the identification of a peak as a composite peak comprising radiation having two different wavelengths is based on knowledge of the pitch of the structure.

[0292] 28. A method for measuring parameters of a substrate structure, the method comprising:

[0293] A beam of emitted radiation is directed onto the structure and thus diffracted radiation is generated by diffraction performed by the structure, wherein the emitted radiation has a spectrum comprising multiple peaks;

[0294] The diffracted radiation is detected using an imaging sensor;

[0295] Using knowledge of the spectrum and prior knowledge of diffraction efficiency, an estimate of the diffraction efficiency as a function of wavelength is obtained; and

[0296] The estimated diffraction efficiency is used to measure the parameters of the structure.

[0297] 29. The method according to aspect 28, wherein the method comprises: using knowledge relating to the ambiguity of the emitted radiation beam to obtain the estimate of the diffraction efficiency as a function of wavelength.

[0298] 30. The method according to aspect 28 or 29, wherein the prior of the diffraction efficiency is the prior of the second derivative of the diffraction efficiency as a function of wavelength.

[0299] 31. The method according to any one of aspects 28 to 30, wherein the method comprises: generating the estimate of the diffraction radiation incident on the imaging sensor.

[0300] 32. The method according to any one of aspects 28 to 31, wherein the method comprises: minimizing the difference between the estimated diffracted radiation incident on the imaging sensor and the detected diffracted radiation to obtain the estimate of diffraction efficiency as a function of wavelength.

[0301] 33. The method according to any one of aspects 28 to 32, wherein the structure is a periodic structure having a pitch.

[0302] 34. The method according to aspect 33, wherein the method comprises: using knowledge about the pitch of the periodic structure to obtain the estimate of the diffraction efficiency as a function of wavelength.

[0303] 35. The method according to any one of aspects 28 to 34, wherein the step of measuring the parameter of the structure using the estimated diffraction efficiency comprises: using the estimated diffraction efficiency as input to the simulation.

[0304] 36. The method according to any one of aspects 28 to 35, wherein the emitted radiation is broadband radiation.

[0305] 37. The method according to any one of aspects 28 to 36, wherein the diffraction radiation incident on the imaging sensor comprises at least partially superimposed diffraction steps on the surface of the imaging sensor.

[0306] 38. A method for estimating the diffraction efficiency of a substrate structure, the method comprising:

[0307] A beam of emitted radiation is directed onto the structure and thus diffracted radiation is generated by diffraction performed by the structure, wherein the emitted radiation has a spectrum comprising multiple peaks, and wherein the diffraction irradiation comprises multiple diffraction orders.

[0308] An imaging sensor is used to detect the diffracted radiation, wherein the diffracted radiation incident on the imaging sensor includes: at least partially superimposed diffraction patterns on the surface of the imaging sensor; and

[0309] The at least partially superimposed orders are separated using knowledge about the spectrum and prior knowledge of the diffraction efficiency.

[0310] 39. The method according to aspect 38, wherein the emitted radiation is broadband radiation.

[0311] 40. The method according to aspect 38 or 39, wherein the structure is a periodic structure.

[0312] 41. A method for measuring the illumination spectrum of an illumination beam used by a measurement system, the method comprising:

[0313] The pump radiation beam is directed into the target medium, thereby causing the target medium to emit radiation, the emitted radiation having a spectrum including multiple peaks, and the emitted radiation is used by the measurement system as an irradiation beam having an irradiation spectrum;

[0314] The irradiation beam is directed onto a grating with a known diffraction efficiency, thereby generating diffraction radiation.

[0315] An imaging sensor is used to detect the diffracted radiation as a spectral power function;

[0316] The spectral power function is expressed as the wavelength multiplied by the diffraction order, and the spectral power function is the product of the illumination spectrum and the known diffraction efficiency; and

[0317] The irradiation spectrum is determined using the expressed spectral power function and the measured spectral power function.

[0318] 42. The method according to aspect 41, wherein the influence of focusing error and / or diffraction-limited spot size is removed from the measured spectral power function, or the influence of focusing error and / or diffraction-limited spot size on the spectral power function is reduced.

[0319] 43. The method according to aspect 42, wherein removing or reducing the effects of focusing error and / or diffraction-limited spot size includes applying deconvolution and / or integral transform.

[0320] 44. The method according to aspect 42, wherein the prior probability of the smoothness of the illumination spectrum is used when removing or reducing the influence of focusing error and / or diffraction-limited spot size from the spectral power function.

[0321] 45. The method according to any one of aspects 41 to 44, wherein the illumination spectrum is represented based on the signal response of the imaging sensor.

[0322] 46. ​​A measuring device including a controller, wherein the controller is configured to cause the execution of the method according to any one of aspects 1 to 8 and 15 to 45.

[0323] 47. A non-transitory computer program product comprising machine-readable instructions that, when executed by a computer system, are configured to cause the computer system to perform at least any one of aspects 1 to 8 and 15 to 45 of the method.

[0324] While specific references can be made to the use of lithography equipment in IC manufacturing within this document, it should be understood that the lithography equipment described herein can have other applications. Possible other applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0325] While specific references may be made herein to embodiments within the context of photolithography equipment, these embodiments can be used in other equipment. Embodiments may form part of mask inspection equipment, metrology equipment, or any equipment that measures or processes objects such as wafers (or other substrates) or masks (or other patterning apparatus). These devices may generally be referred to as photolithography tools. Such photolithography tools can be used in vacuum conditions or ambient (non-vacuum) conditions.

[0326] While specific reference may be made herein to embodiments in the context of inspection or measurement equipment, these embodiments can be used in other equipment. Embodiments may form part of a mask inspection apparatus, a lithography apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning apparatuses). The term "measurement equipment" (or "inspection equipment") may also refer to an inspection apparatus or inspection system (or a measurement apparatus or measurement system). For example, an inspection apparatus including embodiments may be used to detect defects in a substrate or defects in a structure on a substrate. In such embodiments, the characteristics of interest in the structure on the substrate may be related to defects in the structure, the absence of a specific portion of the structure, or the presence of an unwanted structure on the substrate.

[0327] While specific reference has been made to the use of the embodiments in the context of optical lithography, it will be understood that the invention is not limited to optical lithography and can be used in other applications (such as imprint lithography) where circumstances permit.

[0328] While the targets or target structures described above (more generally, structures on a substrate) are measurement target structures specifically designed and formed for measurement purposes, in other embodiments, properties of interest may be measured for one or more structures of a functional portion of a device formed on a substrate. Many devices have regular grating-like structures. The terms “structure,” “target grating,” and “target structure” as used herein do not require that the structure has been specifically provided for the measurement being performed. Furthermore, the pitch of the measurement target may be close to or smaller than the resolution limit of the scatterer’s optical system, but may be much larger than the size of a typical non-target structure (optionally a product structure) formed by a photolithography process in the target portion C. In practice, the lines and / or spaces of overlapping gratings within the target structure may be comprised of smaller structures that are similar in size to non-target structures.

[0329] While specific embodiments have been described above, it will be understood that the invention can be practiced in other ways than those described. The above description is intended to be illustrative and not restrictive. Therefore, those skilled in the art will understand that modifications can be made to the described invention without departing from the scope of the claims set forth below.

[0330] While specifically referring to "measuring equipment / tools / systems" or "inspection equipment / tools / systems," these terms may refer to tools, equipment, or systems of the same or similar type. For example, inspection or measuring equipment including embodiments of the present invention can be used to determine the characteristics of structures on a substrate or wafer. For example, inspection or measuring equipment including embodiments of the present invention can be used to detect defects in a substrate or defects in structures on a substrate or wafer. In such embodiments, the characteristics of interest in the structure on the substrate may be related to defects in the structure, the absence of a specific portion of the structure, or the presence of unwanted structures on the substrate or wafer.

[0331] While specific reference is made to HXR, SXR, and EUV electromagnetic radiation, it will be understood that the invention can be practiced with all electromagnetic radiation, including radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays, where circumstances permit.

[0332] Additional objectives, advantages, and features of the invention are set forth in this specification, and will be apparent in part to those skilled in the art upon review of the following, or may be learned through practice of the invention. The invention disclosed in this application is not limited to any particular set or combination of objectives, advantages, and features. Various combinations of the stated objectives, advantages, and features are considered to constitute the invention disclosed in this application.

Claims

1. A method of measuring a parameter of a structure of a substrate, the method comprising: directing a beam of emitted radiation onto the structure and thereby generating diffracted radiation due to diffraction by the structure, wherein the emitted radiation has a spectrum comprising a plurality of peaks; detecting the diffracted radiation using an imaging sensor; using knowledge about the spectrum and a priori of diffraction efficiency to obtain an estimate of diffraction efficiency as a function of wavelength; and using the estimated diffraction efficiency to measure the parameter of the structure.

2. The method of claim 1, wherein, The method comprises using knowledge about blurring of the beam of emitted radiation to obtain the estimate of diffraction efficiency as a function of wavelength.

3. The method of claim 1 or 2, wherein, The a priori of the diffraction efficiency is a priori of a second derivative of the diffraction efficiency as a function of wavelength.

4. The method of any preceding claim, wherein, The method comprises generating the estimate of the diffracted radiation incident at the imaging sensor.

5. The method of any preceding claim, wherein, The method comprises minimizing a difference between the estimated diffracted radiation and the detected diffracted radiation incident at the imaging sensor to obtain the estimate of diffraction efficiency as a function of wavelength.

6. The method of any preceding claim, wherein, The structure is a periodic structure having a pitch.

7. The method of claim 6, wherein, The method comprises using knowledge about the pitch of the periodic structure to obtain the estimate of diffraction efficiency as a function of wavelength.

8. The method of any preceding claim, wherein, The step of using the estimated diffraction efficiency to measure the parameter of the structure comprises using the estimated diffraction efficiency as input to a simulation.

9. The method of any preceding claim, wherein, The emitted radiation is broadband radiation.

10. The method of any preceding claim, wherein, The diffracted radiation incident at the imaging sensor comprises at least partially overlapping diffraction orders on a surface of the imaging sensor.

11. A method for estimating a diffraction efficiency of a structure of a substrate, the method comprising: directing a beam of emitted radiation onto the structure and thereby generating diffracted radiation due to diffraction by the structure, wherein the emitted radiation has a spectrum comprising a plurality of peaks, and wherein diffracted illumination comprises a plurality of diffraction orders; detecting the diffracted radiation using an imaging sensor, wherein the diffracted radiation incident at the imaging sensor comprises at least partially overlapping diffraction orders on a surface of the imaging sensor; and using knowledge about the spectrum and a priori of the diffraction efficiency to separate the at least partially overlapping orders.

12. The method of claim 11, wherein, The emitted radiation is broadband radiation.

13. The method of claim 11 or 12, wherein, The structure is a periodic structure.

14. A metrology apparatus comprising a controller, wherein, The controller is configured to cause performance of the method of any of claims 1 to 13.

15. A non-transitory computer program product comprising machine readable instructions embodied therein, the machine readable instructions being configured to cause a computer system, when executed by the computer system, to at least cause performance of the method of any of claims 1 to 13.

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