Method for aligning an illumination-detection system of a measuring device and associated measuring device

Abstract

The invention relates to a method for determining an illumination-detection system alignment of an illumination-detection system, said illumination-detection system alignment describing an alignment of at least one detector of a measurement device and / or a measurement illumination in accordance with two or more illumination-detection system alignment parameters, each illumination-detection system alignment parameter is related to a respective degree of freedom for aligning the detector and / or the measurement illumination. The method comprises: obtaining a diffraction pattern associated with diffraction of broadband radiation from the structure; transforming each of one or more diffraction orders of the diffraction pattern to a respective regional coordinate system, each regional coordinate system comprising a first axis and a second axis, each regional coordinate system such that the first axis is aligned with respect to a direction of an intensity metric for each transformed diffraction order; and determining an illumination-detection system alignment parameter value for the illumination-detection system alignment parameter.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to European application No. 22176957.3 filed on June 2, 2022 and European application No. 22180144.2 filed on June 21, 2022, which are hereby incorporated by reference in their entirety. Technical Field

[0003] The present invention relates to metrology applications in integrated circuit manufacturing. Background Art

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

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

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

[0007] During photolithography, as well as other manufacturing processes, it is often necessary to make measurements of the resulting structures, for example for process control and verification. Various tools are known for making such measurements, including scanning electron microscopes, which are commonly used to measure critical dimensions (CD), and specialized tools for measuring the overlay, alignment accuracy of two layers in a device. More recently, various forms of scatterometers have been developed for use in the field of photolithography.

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

[0009] Examples of known scatterometers generally rely on providing a dedicated measurement target. For example, a method may require a target in the form of a simple grating that is large enough so that the measurement beam produces a spot that is smaller than the grating (i.e., the grating is not filled). In a so-called reconstruction method, the properties of the grating can be calculated by simulating the interaction of the scattered radiation with a mathematical model of the target structure. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to the diffraction pattern observed from a real target.

[0010] In addition to measuring feature shapes by reconstruction, diffraction-based overlay can also be measured using such a device, as described in published patent application US2006066855A1. Diffraction-based overlay measurement using dark field imaging of diffraction orders enables overlay measurement of smaller targets. These targets can be smaller than the irradiation spot and can be surrounded by product structures on the wafer. Examples of dark field imaging measurements can be found in many published patent applications, such as, for example, US2011102753A1 and US20120044470A. Using a composite grating target, multiple gratings can be measured in one image. Known scatterometers tend to use light in the visible or near infrared (IR) wave range, which requires the pitch of the grating to be much coarser than the actual product structure with the properties of actual interest. Such product features can be defined using deep ultraviolet (DUV), extreme ultraviolet (EUV), or X-ray radiation with much shorter wavelengths. Unfortunately, such wavelengths are generally not available or cannot be used for measurement.

[0011] On the other hand, the size of modern product structures is so small that modern product structures cannot be imaged by optical measurement techniques. Smaller features include, for example, those formed by multiple patterning processes and / or pitch multiplication. Therefore, targets for high-volume measurement usually use features that are much larger than products whose overlay error or critical dimensions are the properties of interest. The measurement results are only indirectly related to the size of the actual product structure and may be inaccurate because the measurement target does not undergo the same distortion under optical projection in the lithography equipment and / or different treatments in other steps of the manufacturing process. Although scanning electron microscopes (SEMs) can directly resolve these modern product structures, SEMs are too time-consuming than optical measurements. In addition, electrons cannot penetrate thick process layers, which makes electrons less suitable for measurement applications. Other techniques, such as measuring electrical properties using contact pads, are also known, but measuring electrical properties using contact pads only provides indirect evidence of the true product structure.

[0012] By reducing the wavelength of the radiation used during metrology, smaller structures can be resolved to increase sensitivity to structural changes in structures and / or to penetrate further into the product structure. One such method of appropriately generating high frequency radiation (e.g., hard X-rays, soft X-rays, and / or EUV radiation) may be to use pump radiation (e.g., infrared IR radiation) to excite a generating medium, thereby generating emitted radiation, optionally including high harmonic generation of the high frequency radiation.

[0013] In order to perform metrology using broadband SXR radiation, it is necessary to determine the alignment of the illumination-detection system of the metrology device; for example the alignment of the detector of the metrology device and / or the measurement illumination relative to the target. The diffraction pattern may comprise curves with a curvature that depends on the alignment of the detector. The diffraction orders are spectrally dispersed on these curves, wherein for each point on the curve the wavelength is initially unknown.

[0014] It would be desirable to improve current detector alignment methods. Summary of the invention

[0015] In a first aspect of the present invention, a method for determining an illumination-detection system alignment of an illumination-detection system is provided, wherein the illumination-detection system alignment describes the alignment of at least one detector and / or measurement illumination of a measurement device according to two or more illumination-detection system alignment parameters, each illumination-detection system alignment parameter being associated with a corresponding degree of freedom for aligning the detector and / or the measurement illumination; the method comprising: obtaining a diffraction pattern associated with diffraction of broadband radiation from a structure; transforming each of one or more diffraction orders of the diffraction pattern into a corresponding regional coordinate system, each regional coordinate system comprising a first axis and a second axis, each regional coordinate system being aligned such that the first axis is aligned relative to the direction of an intensity measurement of each transformed diffraction order; and determining illumination-detection system alignment parameter values ​​for the illumination-detection system alignment parameters such that the position of the intensity measurement of each of the diffraction patterns substantially corresponds to an expected configuration in the regional coordinate system.

[0016] The above and other aspects of the present invention will be understood through a consideration of the embodiments described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0018] Figure 1 A schematic overview of a lithographic apparatus is depicted;

[0019] Figure 2 A schematic overview of a lithography unit is depicted;

[0020] Figure 3 A schematic diagram of overall lithography is shown, representing the collaboration between the three key technologies to optimize semiconductor manufacturing;

[0021] Figure 4 A scatterometry device is schematically shown;

[0022] Figure 5 shows a schematic diagram of a metrology apparatus in which EUV and / or SXR radiation is used;

[0023] Figure 6 A simplified schematic diagram of an illumination source is shown, which may be used for example Figure 5 The irradiation source of the high harmonic generation of the measurement equipment shown;

[0024] Figure 7comprising (a) a schematic diagram of a dark field scatterometer for use in measuring a target using a first pair of illumination apertures according to an embodiment of the present invention, (b) details of a diffraction spectrum of a target grating for a given illumination direction, (c) a second pair of illumination apertures providing an additional illumination pattern in the scatterometer for use for diffraction-based overlay measurements, and (d) a third pair of illumination apertures combining the first pair of apertures and the second pair of apertures;

[0025] Figure 8 is a schematic diagram of a measuring device of known construction; and

[0026] Fig. 9 You can use Figure 8 An illustration of a two-dimensional (2D) diffraction pattern obtained by the metrology apparatus shown;

[0027] Fig.10 is a graphical representation of the 2D diffraction pattern transformed into pupil coordinates;

[0028] Fig.11 is a flowchart describing a method according to an embodiment;

[0029] Fig.12 It shows that Fig.11 Assigning a region of interest to a single diffraction order as performed in the method of;

[0030] Fig.13 is a 4D graph of the two-dimensional pupil space relative to the two-dimensional area space corresponding to the region of interest, with the peak intensities of the diffraction orders plotted thereon; and

[0031] Fig.14 It is a graph of the peak intensity and its partial derivatives in a two-dimensional region space. DETAILED DESCRIPTION

[0032] In this document, the terms "radiation" and "beam" are used to include all types of electromagnetic radiation and particle radiation, including ultraviolet radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of approximately 5 nm to 100 nm), X-ray radiation, electron beam radiation, and other particle radiation.

[0033] The terms "reticle", "mask", or "patterning device" as used herein may be broadly interpreted as referring to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam that corresponds to the pattern to be formed in a target portion of the substrate. The term "light valve" may also be used in this context. In addition to conventional masks (transmissive or reflective, binary, phase-shift, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0034] Figure 1 A lithographic apparatus LA is schematically shown. The lithographic apparatus LA comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, EUV radiation, or X-ray radiation), a mask support (e.g., a mask stage) T configured to support a patterning device (e.g., a mask) MA and connected to a first positioning device PM configured to precisely position the patterning device MA according to specific parameters, a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioning device PW configured to precisely position the substrate support according to specific parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0035] In operation, the illumination system IL receives a radiation beam from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components for directing, shaping, and / or controlling the radiation, such as refractive, reflective, diffractive, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof. The illuminator IL may be used to adjust the radiation beam B to have a desired spatial and angular intensity distribution in a cross section of the radiation beam B at the plane of the pattern forming device MA. The term "projection system" PS used herein should be broadly interpreted to include various types of projection systems, including refractive, reflective, diffractive, reflective-refractive, anamorphic, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation used, and / or for other factors such as the use of an immersion liquid or the use of a vacuum. The term "projection lens" used arbitrarily herein may be considered synonymous with the more general term "projection system" PS.

[0036] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g. water) so as to fill the space between the projection system PS and the substrate W, which is also known as immersion lithography. More information on immersion technology is given in US6952253, the entire contents of which are incorporated herein by reference.

[0037] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as a "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or steps preparing for subsequent exposure of the substrate W may be performed on a substrate W on one substrate support WT while another substrate W on another substrate support WT is being used to expose a pattern on another substrate W.

[0038] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measurement platform may hold a plurality of sensors. The cleaning means may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS or a part of the system for providing immersion liquid. The measurement platform may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0039] In operation, a radiation beam B is incident on a patterning device (e.g. a mask) MA held on a mask support T and is patterned by a pattern (design layout) present on the patterning device MA. After having passed through the mask MA, the radiation beam B passes through a projection system PS which focuses the radiation beam onto a target portion C of the substrate W. With the aid of a second positioning device PW and a position measurement system IF, the substrate support WT can be precisely moved, for example in order to position different target portions C in the path of the radiation beam B at focused and aligned positions. Similarly, the first positioning device PM and possibly another position sensor ( Figure 1 The other position sensor (not explicitly shown) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. The mask alignment marks M1, M2 and the substrate alignment marks P1, P2 can be used to align the patterning device MA and the substrate W. Although the substrate alignment marks P1, P2 are shown occupying dedicated target portions, the substrate alignment marks P1, P2 shown can be located in the space between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribe line alignment marks.

[0040] like Figure 2As shown, the lithography apparatus LA may form part of a lithography cell LC, which is sometimes also referred to as a lithography cell or (lithography) cluster, and which typically also includes equipment for performing pre-exposure and post-exposure processing on a substrate W. Conventionally, these equipment include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a cooling plate CH, and a baking plate BK, which are used, for example, to regulate the temperature of the substrate W, for example, for regulating the solvent in the resist layer. A substrate handler or robot RO picks up the substrate W from the input / output ports I / O1, I / O2, moves the substrate W between the different processing equipment, and delivers the substrate W to a loading bay LB of the lithography apparatus LA. The devices in the lithography cell, which are also generally referred to as tracks or coating and developing systems, may be under the control of a track control unit TCU, which itself may be controlled by a supervisory control system SCS, which may also control the lithography apparatus LA, for example, via a lithography control unit LACU. During the lithography process, it is desirable to frequently measure the resulting structure, for example for process control and verification. The tool for performing such measurements may be referred to as a metrology tool MT. Different types of metrology tools MT for performing such measurements are known, including scanning electron microscopes or various forms of scatterometer metrology tools MT. A scatterometer is a general purpose instrument that allows the measurement of parameters of a lithography process by arranging a sensor in the pupil of an objective of the scatterometer or in a plane conjugated to the pupil of the objective of the scatterometer or near the pupil or plane, which measurement is generally referred to as pupil-based measurement, or by arranging a sensor in or near an image plane or a plane conjugated to the image plane, in which case the measurement is generally referred to as image- or field-based measurement. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, which are incorporated herein by reference in their entirety. The scatterometer can measure gratings using light from the hard X-ray (HXR), soft X-ray (SXR), extreme ultraviolet (EUV), visible to near infrared (IR) and IR wavelength ranges. In the case where the radiation is hard X-ray or soft X-ray, the scatterometer can optionally be a small angle X-ray scattering measurement tool.

[0041] In order for substrates W exposed by the lithographic apparatus LA to be correctly and consistently exposed, it is desirable to inspect the substrates to measure properties of the patterned structures, such as overlay errors between successive layers, line widths, critical dimensions (CD), shapes of structures, etc. Inspection tools and / or metrology tools (not shown) may be included in the lithography cell LC for this purpose. If errors are detected, especially if the inspection is done before other substrates W of the same batch or lot are still to be exposed or processed, for example, adjustments may be made to the exposure of subsequent substrates or to other processing steps to be performed on the substrates W.

[0042] The inspection apparatus, which may also be referred to as a metrology apparatus, is used to determine properties of a substrate W, and in particular, to determine how properties of different substrates W vary or how properties relating to different layers of the same substrate W vary from layer to layer. The inspection apparatus may alternatively be configured to identify defects on the substrate W, and may for example be part of the lithography cell LC, or may be integrated into the lithography apparatus LA, or may even be a stand-alone device. The inspection apparatus may measure properties on a latent image (the image in the resist layer after exposure) or a semi-latent image (the image in the resist layer after a post-exposure bake step PEB) or a developed resist image (wherein exposed or unexposed parts of the resist have been removed) or even an etched image (after a pattern transfer step such as etching).

[0043] In a first embodiment, the scatterometer MT is an angle-resolved scatterometer. In such a scatterometer, reconstruction methods can be applied to the measured signals to reconstruct or calculate the properties of the grating. Such a reconstruction can be obtained, for example, by simulating the interaction of the scattered radiation with a mathematical model of the target structure 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 the diffraction pattern observed from a real target.

[0044] In a second embodiment, the scatterometer MT is a spectroscopic scatterometer MT. In such a spectroscopic scatterometer 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 spectrometer detector which measures the spectrum of the specularly reflected radiation (i.e. a measure of intensity as a function of wavelength). From this data, the structure or profile of the target which produced the detected spectrum can be reconstructed, for example by rigorous coupled wave analysis and nonlinear regression or by comparison with a library of simulated spectra.

[0045] In a third embodiment, the scatterometer MT is an ellipsometric scatterometer. An ellipsometric scatterometer allows parameters of a lithographic process to be determined by measuring scattered radiation of each polarization state, which may be diffracted, reflected, or transmitted radiation. Such a measurement device emits polarized light (such as linearly polarized light, circularly polarized light, or elliptically polarized light) by using, for example, an appropriate polarization filter in the illumination portion of the measurement device. A source suitable for the measurement device may also provide polarized radiation. Various embodiments of existing ellipsometric scatterometers are described in U.S. patent applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110, and 13 / 891,410, the entire contents of which are hereby incorporated herein by reference.

[0046] In one embodiment of the scatterometer MT, the scatterometer MT is adapted to measure the overlap of two misaligned gratings or periodic structures by measuring the reflection spectrum and / or an asymmetry in the detection configuration, the asymmetry being related to the degree of overlap. The two (possibly overlapping) grating structures may be applied in two different layers (not necessarily consecutive layers) and may be formed substantially at the same position on the wafer. The scatterometer may have a symmetrical detection configuration, such as described in co-owned patent application EP1,628,164A, so that any asymmetry is clearly distinguishable. This provides a straightforward way to measure misalignment in the gratings. Other examples of measuring the overlay error between two layers containing a periodic structure as a target by the asymmetry of the periodic structure may be found in PCT patent application publication number WO2011 / 012624 or in US patent application US 20160161863, the entire contents of which are incorporated herein by reference.

[0047] Other parameters of interest may be focus and dose. Focus and dose may be determined simultaneously by scatterometry (or by scanning electron microscopy), as described in U.S. Patent Application US2011-0249244, which is incorporated herein by reference in its entirety. A single structure may be used that has a unique combination of critical dimension and sidewall angle measurements for each point in a focus or focus energy matrix (FEM—also referred to as a focus or focal exposure matrix). If these unique combinations of critical dimensions and sidewall angles are available, focus and dose values ​​may be uniquely determined from these measurements.

[0048] The metrology target may be a collection of composite gratings formed primarily in resist by a lithography process but also after other manufacturing processes such as an etching process. The pitch and line width of the structures in the grating may depend primarily on the measurement optics (particularly the NA of the optics) to be able to capture the diffraction orders from the metrology target. As previously described, the diffraction signal may be used to determine the offset (also called "overlap") between two layers, or may be used to reconstruct at least a portion of the original grating produced by the lithography process. This reconstruction may be used to provide guidance on the quality of the lithography process and may be used to control at least a portion of the lithography process. The target may have smaller subdivisions configured to simulate the size of a functional portion of a design layout in the target. Due to this subdivision, the target may behave more similarly to a functional portion of the design layout, so that the overall process parameter measurement result better resembles the functional portion of the design layout. The target may be measured in an underfill mode or in an overfill mode. In the underfill mode, the measurement beam produces a spot that is smaller than the entire target. In the overfill mode, the measurement beam produces a spot that is larger than the entire target. In this overfill mode, different targets may also be measured simultaneously, thereby determining different process parameters simultaneously.

[0049] The overall measurement quality of the lithography parameters using a specific target is at least partially determined by the measurement configuration scheme used to measure this lithography parameter. The term "substrate measurement configuration scheme" may include one or more parameters of the measurement itself, one or more parameters of the one or more patterns measured, or one or more parameters of the measurement itself and one or more parameters of the one or more patterns measured. For example, if the measurement used in the substrate measurement configuration scheme is an optical measurement based on diffraction, one or more parameters in the measured parameters may include the wavelength of the radiation, the polarization of the radiation, the incident angle of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. One of the criteria for selecting the measurement configuration scheme may be, for example, the sensitivity of one of the measurement parameters to process changes in the measurement parameters. More examples are described in U.S. Patent Application US 2016-0161863 and published U.S. Patent Application US 2016 / 0370717A1, and the entire contents of US 2016-0161863 and US 2016 / 0370717A1 are incorporated herein by reference.

[0050] The patterning process in the lithographic apparatus LA may be one of the most critical steps in the process requiring a high degree of precision in the dimensioning and positioning of structures on the substrate W. In order to ensure this high degree of precision, the patterning process may be performed in a manner such as Figure 3. One of these systems is a lithography apparatus LA that is (virtually) connected to a metrology tool MT (a second system) and a computer system CL (a third system). The key to this "holistic" environment is to optimize the collaboration between these three systems to enhance the overall process window and to provide a tight control loop to ensure that the patterning operations performed by the lithography apparatus LA remain within the process window. The process window defines the 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) and within which variations in process parameters in the lithography process or the patterning process may be allowed.

[0051] The computer system CL can use the (partial) design layout to be patterned to predict which resolution enhancement technique to use and perform computational lithography simulations and calculations to determine which mask layout and lithography equipment settings achieve the maximum overall process window for the patterning process (in Figure 3 The resolution enhancement technique may be arranged to match the probability of pattern formation of the lithographic apparatus LA. The computer system CL may also be used (e.g. using input from a metrology tool MET) to detect where within the process window the lithographic apparatus LA is currently operating to predict whether there are defects (e.g. due to suboptimal processing) Figure 3 ), as indicated by the arrow pointing to “0” in the second measuring disk SC2.

[0052] The metrology tool MT may provide input to the computer system CL to enable accurate simulations and predictions, and may provide feedback to the lithographic apparatus LA to identify possible drifts, such as drifts in the calibration state of the lithographic apparatus LA (in Figure 3 ), as indicated by the multiple arrows in the third measuring disk SC3.

[0053] Many different forms of metrology tools MT for measuring structures produced using lithographic patterning equipment may be provided. The metrology tool MT may use electromagnetic radiation to probe the structure. The characteristics of the radiation (e.g. wavelength, bandwidth, power) may affect different measurement characteristics of the tool, with shorter wavelengths typically allowing an increase in resolution. The wavelength of the radiation has an influence on the resolution that can be achieved by the metrology tool. Therefore, in order to be able to measure structures with features of smaller size, a metrology tool MT with a radiation source of shorter wavelength is preferred.

[0054] Another way that the wavelength of the radiation can affect the measurement characteristics is the penetration depth, and the transparency / opacity of the material to be inspected at the wavelength of the radiation. Depending on the opacity and / or penetration depth, the radiation can be used for measurements of transmission or reflection. The type of measurement can affect whether information about the surface of the structure / substrate and / or the interior of the body is obtained. Therefore, penetration depth and opacity are another factor to consider when selecting a radiation wavelength for a metrology tool.

[0055] In order to achieve higher resolution for measurement of lithographically patterned structures, a metrology tool MT with a shorter wavelength is preferred. This can include wavelengths shorter than the visible wavelength, such as wavelengths in the UV, EUV, and X-ray parts of the electromagnetic spectrum. Hard X-ray methods, such as transmission small angle X-ray scattering (TSAXS), take advantage of the high resolution and long penetration depth of hard X-rays and can therefore operate in transmission. On the other hand, soft X-rays and EUV cannot penetrate as deeply into the target, but can induce a rich optical response in the material to be probed. This may be due to the optical properties of many semiconductor materials, and to the fact that the structures are comparable in size to the detection wavelength. As a result, the EUV and / or soft X-ray metrology tool MT can operate in reflection, for example by imaging, or by analyzing diffraction patterns from lithographically patterned structures.

[0056] For hard X-rays, soft X-rays, and EUV radiation, application in high volume manufacturing (HVM) applications may be limited due to the lack of high brightness radiation sources available at the required wavelengths. In the case of hard X-rays, sources commonly used in industrial applications include X-ray tubes. X-ray tubes, including, for example, advanced X-ray tubes based on liquid metal anodes or rotating anodes, may be relatively low cost and compact, but may lack the brightness required for HVM applications. Currently there are high brightness X-ray sources, such as synchrotron light sources (SLS) and X-ray free electron lasers (XFELs), but their size (>100m) and high cost (hundreds of millions of euros) make them too large and expensive for metrology applications. Similarly, there is a lack of available sufficiently bright EUV and soft X-ray radiation sources.

[0057] During lithography, it is frequently desirable to measure the generated structures, for example for process control and verification. Various tools for making such measurements are known, including scanning electron microscopes or various forms of metrology equipment, such as scatterometers. Examples of known scatterometers typically rely on providing a dedicated metrology target, such as an underfilled target (a target in the form of a simple grating or overlapping gratings in different layers, which is large enough that the measurement beam generates a spot smaller than the grating) or an overfilled target (whereby the illumination spot partially or completely encompasses the target). Furthermore, the use of a metrology tool, such as an angle-resolved scatterometer, which illuminates a target such as an underfilled target (e.g., a grating), allows the use of so-called reconstruction methods, in which the properties of the grating can be calculated by simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulated results with the measured results. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to the diffraction pattern observed from a real target.

[0058] Scatterometers are general instruments that allow measuring parameters of a lithography process by providing a sensor in the pupil of the objective of the scatterometer or in a plane conjugate to the pupil of the objective of the scatterometer (this measurement is usually referred to as pupil-based measurement), or by providing a sensor in the image plane or in a plane conjugate to the image plane (in this case, the measurement is usually referred to as image-based or field-based measurement). Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, which are incorporated herein by reference in their entirety. The above-mentioned scatterometers can measure multiple targets from multiple gratings in one image using light from soft x-rays, extreme ultraviolet, and visible to near IR wave ranges.

[0059] exist Figure 4 An example of a metrology device (e.g. a scatterometer) is shown in FIG. The metrology device may comprise a broadband (e.g. white light) radiation projector 2 which projects 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 specularly reflected radiation (i.e. a measure of the intensity I as a function of the wavelength λ). From this data, the structure or profile 8 which gave rise to the detected spectrum may be reconstructed by a processing unit PU, e.g. by rigorous coupled wave analysis and nonlinear regression or by comparing the structure or profile 8 with the spectrometer detector 4 as in Figure 4 The simulated spectral library shown at the bottom is used for comparison reconstruction. Typically, for reconstruction, the general form of the structure is known and some parameters are assumed based on knowledge of the process by which the structure was made, leaving only some parameters of the structure to be determined from the scatterometer data. Such a scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0060] Another embodiment is a transmission version of the measurement device, e.g. Figure 4 The transmitted radiation is passed to a spectrometer detector such as Figure 4 The spectrum is measured as discussed above. Such a scatterometer may be configured as a normal incidence scatterometer or an oblique incidence scatterometer. Optionally, the transmission form uses hard X-ray radiation having a wavelength of less than 1 nm, optionally less than 0.1 nm, optionally less than 0.01 nm.

[0061] As an alternative to optical metrology methods, the use of hard X-rays, soft X-rays, or EUV radiation has also been considered, such as 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 20 nm, between 5 nm and 20 nm, and between 10 nm and 20 nm. An example of a metrology tool that functions in one of the above wavelength ranges is transmission small angle X-ray scattering (such as T-SAXS in US 2007224518A, the contents of which are incorporated herein by reference in their entirety). Lemaillet et al. discuss profile (CD) measurements using T-SAXS in the paper "Intercomparison between optical and X-ray scatterometry measurements of FinFET structures", Proc. of SPIE, 2013, 8681. Note that the use of a laser produced plasma (LPP) x-ray source is described in U.S. Patent Publication No. 2019 / 003988A1 and U.S. Patent Publication No. 2019 / 215940A1, the entire contents of which are incorporated herein by reference. Reflectometry techniques using grazing incidence X-rays (GI-XRS) and extreme ultraviolet (EUV) radiation can be used to measure the properties of films and stacks on substrates. Within the general field of reflectometry, goniometric and / or spectroscopic techniques can be applied. In goniometric methods, the change in the reflected beam with different angles of incidence can be measured. On the other hand, a spectroscopic reflectometer (using broadband radiation) measures the spectrum of wavelengths reflected at a given angle. For example, EUV reflectometry has been used to inspect mask blanks prior to manufacturing reticles (patterning devices) for EUV lithography.

[0062] It may be that the range of applications is such that the use of wavelengths in, for example, hard X-rays, soft X-rays, or the EUV domain is insufficient. Published patent applications US 20130304424A1 and US2014019097A1 (Bakeman et al. / KLA) describe hybrid metrology techniques in which measurements using X-rays and optical measurements at wavelengths in the range of 120 nm and 2000 nm are combined to obtain measurements of parameters such as CD. X-ray mathematical models and optical mathematical models are coupled through one or more common parts to obtain CD measurements. The contents of the cited US patent applications are incorporated herein by reference in their entirety.

[0063] Figure 5 A schematic diagram of a metrology device 302 is shown, wherein the above-mentioned radiation can be used to measure parameters of structures on a substrate. Figure 5 The metrology device 302 shown in FIG. 3 may be applicable to hard X-ray, soft X-ray, and / or EUV domains.

[0064] Figure 5 A schematic physical arrangement of a metrology apparatus 302 including a spectroscopic scatterometer using hard X-ray, soft X-ray, and / or EUV radiation, optionally at grazing incidence, is shown by way of example only. An alternative form of inspection apparatus may be provided in the form of an angle resolved scatterometer, which may use radiation at normal or near normal incidence similar to conventional scatterometers operating at longer wavelengths, and which may also use radiation at a direction greater than 1° or 2° from parallel to the substrate. An alternative form of inspection apparatus may be provided in the form of a transmission scatterometer.

[0065] The inspection apparatus 302 includes a radiation source or so-called illumination source 310 , an illumination system 312 , a substrate support 316 , detection systems 318 , 398 , and a metrology processing unit (MPU) 320 .

[0066] In this example, the radiation source 310 is used to generate EUV, hard X-ray, or soft X-ray radiation. The radiation source 310 can be based on Figure 6 The high harmonic generation (HHG) technology shown, and the irradiation source 310 can also be other types of irradiation sources, such as a liquid metal jet source, an inverse Compton scattering (ICS) source, a plasma channel source, a magnetic corrugator source, a free electron laser (FEL) source, a compact storage ring source, a discharge-generated plasma source, a soft X-ray laser source, a rotating anode source, a solid-state anode source, a particle accelerator source, a microfocus source, or a laser-generated plasma source.

[0067] The HHG source can be a gas jet / nozzle source, a capillary / fiber source, or a gas chamber source.

[0068] For example, a HHG source such as Figure 6 As 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, which produces pulses of infrared radiation, which can last, for example, less than 1 ns (1 nanosecond) / pulse, with a pulse repetition rate of up to several megahertz as required. The wavelength of the infrared radiation can be in the range of 200nm to 10μm, for example in the range of 1μm (1 micrometer). Optionally, the laser pulse is delivered to the gas delivery system 332 as the first pump radiation 340, wherein a portion of the radiation is converted to have a higher frequency than the first radiation and becomes the emission radiation 342. The gas source 334 supplies a suitable gas to the gas delivery system 332, wherein, optionally, the gas is ionized by the power supply 336. The gas delivery system 332 can be a cutting tube.

[0069] The gas provided by the gas delivery system 332 defines a gas target, which can be a gas flow or a static volume. The gas can be, for example, air, neon (Ne), helium (He), nitrogen (N2), oxygen (O2), argon (Ar), krypton (Kr), xenon (Xe), carbon dioxide, and combinations thereof. These gases can be selectable options within the same device. The emitted radiation can contain multiple wavelengths. If the emitted radiation is monochromatic, the measurement calculation (e.g., reconstruction) can be simplified, but it is easier to generate radiation with multiple wavelengths. The emission divergence angle of the emitted radiation can be wavelength-dependent. For example, when imaging structures of different materials, different wavelengths can provide different contrast levels. For example, in order to inspect metal structures or silicon structures, different wavelengths can be selected as wavelengths for imaging features of (carbon-based) resists, or for detecting contamination of these different materials. One or more filtering devices 344 can be provided. For example, filters such as thin films of aluminum (Al) or zirconium (Zr) can be used to prevent basic IR radiation from further entering the inspection device. A grating (not shown) can be provided to select one or more specific wavelengths from the generated wavelengths. Optionally, the illumination source includes a space configured to be evacuated, and the gas delivery system is configured to provide a gas target in the space. Optionally, given that SXR and / or EUV radiation is absorbed when traveling in air, some or all of the beam path may be contained within a vacuum environment. Various components of the radiation source 310 and illumination optics 312 may be adjustable to implement different measurement "configurations" within the same device. For example, different wavelengths and / or polarizations may be implemented as selectable.

[0070] Depending on the material of the structure being inspected, different wavelengths can provide the desired level of penetration into the underlying layers. In order to address the smallest device features and defects in the smallest device features, short wavelengths may be preferred. For example, one or more wavelengths in the range of 0.01 nm to 20 nm, or alternatively in the range of 1 nm to 10 nm, or optionally in the range of 10 nm to 20 nm, can be selected. Wavelengths shorter than 5 nm may suffer from very low critical angles when reflecting off the material of interest in semiconductor manufacturing. Therefore, selecting a wavelength greater than 5 nm can provide a stronger signal at higher angles of incidence. On the other hand, if the inspection task is to detect the presence of a certain material, such as detecting contamination, wavelengths up to 50 nm may be useful.

[0071] The filtered beam 342 may pass from the radiation source 310 into an inspection chamber 350 in which a substrate W including a structure of interest is held in a measurement position by a substrate support 316 for inspection. The structure of interest is labeled T. Optionally, the gas environment within the inspection chamber 350 may be maintained near vacuum by a vacuum pump 352 so that SXR and / or EUV radiation may pass through the gas environment without undue attenuation. The illumination system 312 has the function of focusing the radiation into a focused beam 356, and may include, for example, a two-dimensional curved mirror, or a series of one-dimensional curved mirrors, as described in the above-mentioned published U.S. patent application US2017 / 0184981A1 (the contents of US2017 / 0184981A1 are incorporated herein by reference in their entirety). Focusing is performed to achieve a circular or elliptical spot S having a diameter of less than 10 μm when projected onto the structure of interest. The substrate support 316 includes, for example, an XY translation stage and a rotation stage, by which any part of the substrate W can be brought to the focus of the beam to be in a desired orientation. Thus, a radiation spot S is formed on the structure of interest. Alternatively, or additionally, the substrate support 316 includes, for example, a tilting stage, which can tilt the substrate W at a certain angle to control the incident angle of the focal beam on the structure of interest T.

[0072] 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 that is provided to the processor 320, and the filter can include information about the spectrum of the filtered beam 342 and / or the intensity of different wavelengths in the filtered beam.

[0073] The reflected radiation 360 is captured by the detector 318, and the spectrum is provided to the processor 320 for calculating the properties of the target structure T. The illumination system 312 and the detection system 318 then form an inspection device. The inspection device may include a hard X-ray, soft X-ray, and / or EUV spectroscopic reflectometer of the type described in US2016282282A1, the contents of which are incorporated herein by reference in their entirety.

[0074] If the target Ta has a certain periodicity, the radiation of the focal beam 356 may also be partially diffracted. The diffracted radiation 397 follows another path at a well-defined angle relative to the angle of incidence, followed by the reflected radiation 360. Figure 5 In FIG. 3 , the diffracted radiation 397 is drawn in a schematic manner, and the diffracted radiation 397 may follow many other paths than the drawn path. The inspection device 302 may also include an additional detection system 398 for detecting and / or imaging at least a portion of the diffracted radiation 397. Figure 5 , a single further detection system 398 is depicted, but embodiments of the inspection device 302 may also include more than one further detection system 398 arranged at different positions to detect and / or image the diffracted radiation 397 in multiple diffraction directions. In other words, the (higher) diffraction orders of the focused radiation beam impinging on the target Ta are detected and / or imaged by one or more further detection systems 398. The one or more detection systems 398 generate a signal 399 which is provided to the metrology processor 320. The signal 399 may include information of the diffracted light 397 and / or may include an image obtained from the diffracted light 397.

[0075] To help align the spot S with the desired product structure and focus, the inspection device 302 can also use auxiliary radiation to provide auxiliary optical devices under the control of the measurement processor 320. The measurement processor 320 can also communicate with a position controller 372 that operates a translation platform, a rotation and / or a tilt platform. The processor 320 receives highly accurate feedback about the position and orientation of the substrate through sensors. The sensor 374 may include, for example, an interferometer that can provide an accuracy in the range of picometers. In the operation of the inspection device 302, the spectral data 382 captured by the detection system 318 is transmitted to the measurement processing unit 320.

[0076] As described above, alternative forms of inspection equipment use hard X-rays, soft X-rays, and / or EUV radiation, optionally at normal incidence 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 a direction greater than 1° or 2° from a direction parallel to the substrate. Both types of inspection equipment can be provided in a hybrid measurement system. The performance parameters to be measured may include overlay (OVL), critical dimension (CD), focal length of the lithography device when the lithography device prints the target structure, coherent diffraction imaging (CDI), and resolution overlay (ARO) measurements. The hard X-rays, soft X-rays, and / or EUV radiation may have a wavelength, for example, in the range of 0.01 nm to 100 nm, optionally 0.1 nm to 100 nm, optionally 1 nm to 100 nm, optionally 1 nm to 50 nm, or optionally 10 nm to 20 nm. The radiation may be narrowband or broadband in nature. The radiation may have discrete peaks in a particular wavelength band, or may have a more continuous character.

[0077] Like optical scatterometers used in today's production facilities, inspection device 302 can be used to measure structures in resist materials processed in a lithography unit (after development inspection or ADI), and / or to measure structures in harder materials after they have been formed (after etching inspection or AEI). For example, inspection device 302 can be used to inspect a substrate after it has been processed by a development device, an etching device, an annealing device, and / or other devices.

[0078] The measurement tool MT, including but not limited to the above-mentioned scatterometer, 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 parts of the electromagnetic spectrum. The measurement tool MT can use radiation to measure or inspect the properties and aspects of the substrate, such as a lithography exposure pattern on a semiconductor substrate. The type and quality of the measurement can depend on multiple properties of the radiation used by the measurement tool MT. For example, the resolution of the electromagnetic measurement can depend on the wavelength of the radiation, where, for example, due to the diffraction limit, smaller wavelengths can measure smaller features. In order to measure features with smaller sizes, it is preferred to use radiation with shorter wavelengths, such as EUV, hard X-ray (HXR), and / or soft X-ray (SXR) radiation, to perform the measurement. In order to perform measurements at a specific wavelength or wavelength range, the measurement tool MT needs to access a source that provides radiation at that / those (multiple) wavelengths. There are different types of sources for providing radiation of different wavelengths. Depending on the (multiple) wavelengths provided by the source, different types of radiation generation methods can be used. For extreme ultraviolet (EUV) radiation (e.g., 1 nm to 100 nm) and / or soft X-ray (SXR) radiation (e.g., 0.1 nm to 10 nm), the source can use high harmonic generation (HHG) or any other type of source described above to obtain radiation at the desired wavelength(s).

[0079] Figure 6 A simplified schematic diagram of an embodiment 600 of an illumination source 310 is shown, which may be an illumination source for high harmonic generation (HHG). In the illumination source 600, there may also be a suitable Figure 5 One or more of the features of the illumination source in the described metrology tool. Illumination source 600 includes cavity 601 and is configured to receive pump radiation 611 having a propagation direction indicated by an arrow. Pump radiation 611 shown here is an example of pump radiation 340 from pump radiation source 330, such as Figure 5As shown. Pump radiation 611 can be directed into cavity 601 through radiation input end 605, which can be a window, which can be optionally made of fused silica or similar material. Pump radiation 611 can have a Gaussian or hollow, for example, annular, transverse cross-sectional profile, and can be incident, optionally focused, on a gas flow 615 located within chamber 601 with a flow direction indicated by a second arrow. Gas flow 615 includes 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) called a gas volume or gas target (e.g., a few cubic millimeters), wherein the gas pressure is above a certain value. Gas flow 615 can be a steady gas flow. Other media can also be used, such as metal plasma (e.g., aluminum plasma).

[0080] The gas delivery system of the irradiation source 600 is configured to provide a gas flow 615. The irradiation source 600 is configured to provide pump radiation 611 in the gas flow 615 to drive the generation of emitted radiation 613. The area where at least most of the emitted radiation 613 is generated is called the interaction area. The interaction area can be from tens of microns (for tightly focused pump radiation) to several millimeters or centimeters (for moderately focused pump radiation) or even up to several meters (for extremely loosely focused pump radiation). The gas delivery system is configured to provide a gas target for generating emitted radiation at the interaction area of ​​the gas target, and optionally, the irradiation source is configured to receive the pump radiation and provide the pump radiation at the interaction area. Optionally, the gas flow 615 is provided by the gas delivery system into a space that is evacuated or nearly evacuated. The gas delivery system may include, for example, Figure 6 , the gas nozzle 609 may include an opening 617 in the outlet plane of the gas nozzle 609. The gas flow 615 is provided from the opening 617. The gas trap is used to confine the gas flow 615 within a certain volume by extracting the residual gas flow and maintaining a vacuum or near-vacuum gas environment inside the chamber 601. Optionally, the gas nozzle 609 can be made of a thick-walled tube and / or a high thermal conductivity material to avoid thermal deformation due to the high-power pump radiation 611.

[0081] It is conceivable that the dimensions of the gas nozzle 609 can also be used in scaled-up or scaled-down form for a range from micron-sized nozzles to meter-sized nozzles. This wider range of dimensioning comes from the fact that the device can be scaled so that the intensity of the pump radiation at the gas flow ends up in a specific range that may be beneficial for the emitted radiation, which requires different dimensioning for different pump radiation energies, which can be pulsed lasers and the pulse energy can vary from tens of microjoules to tens of joules. Optionally, the gas nozzle 609 has thicker walls to reduce nozzle deformation caused by thermal expansion effects, which can be detected by, for example, 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 close to the gas nozzle to maintain the pressure of the chamber 601.

[0082] Due to the interaction of the pump radiation 611 with the gas atoms of the gas flow 615, the gas flow 615 converts a portion of the pump radiation 611 into emitted radiation 613, which may be Figure 5 342. The central axis of the emitted radiation 613 may be co-linear with the central axis of the incident pump radiation 611. The emitted radiation 613 may have a wavelength in the X-ray or EUV range, wherein the wavelength is in the range from 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.

[0083] In operation, the emitted radiation beam 613 may pass through the radiation output port 607, such as an aperture or window, and may then be output by a Figure 5 The illumination system 603 of the example of the illumination system 312 in FIG. 6 is manipulated and directed to a substrate to be inspected for metrology measurements. The emitted radiation 613 can be directed, and optionally focused, to structures located on the substrate.

[0084] Because air (and indeed any gas) absorbs SXR or EUV radiation significantly, the volume between the gas flow 615 and the wafer to be inspected may be evacuated or nearly evacuated. Since the central axis of the emitted radiation 613 may be collinear with the central axis of the incident pump radiation 611, the pump radiation 611 may need to be blocked to prevent the pump radiation 611 from passing through the radiation output 607 and entering the illumination system 603. This may be accomplished by placing Figure 6The filter device 344 shown in is incorporated into the radiation output end 607, which is placed in the emission beam path and is opaque or almost opaque to the pump radiation (for example, opaque or almost opaque to infrared or visible light), but is at least partially transparent to the emitted radiation beam. The filter can be made of zirconium or a plurality of materials combined in multiple layers. When the pump radiation 611 has a hollow, optionally annular transverse cross-sectional profile, the filter can be a hollow, optionally annular block. Optionally, the filter is not perpendicular to and is not parallel to the propagation direction of the emitted radiation beam to have efficient pump radiation filtering. Optionally, the filter device 344 includes a hollow block and a thin film filter, such as an aluminum (Al) or zirconium (Zr) film filter. Optionally, the filter device 344 may also include a reflector that effectively reflects the emitted radiation but poorly reflects the pump radiation, or includes a metal wire mesh that effectively transmits the emitted radiation but poorly transmits the pump radiation.

[0085] Methods, devices, and assemblies for obtaining emitted radiation optionally at a high harmonic frequency of a pump radiation are described herein. The radiation produced by the process, optionally utilizing nonlinear effects to produce HHG of radiation optionally at a harmonic frequency of the provided pump radiation, can be provided as radiation in a metrology tool MT for inspecting and / or measuring a substrate. If the pump radiation comprises short pulses (i.e., a few cycles), the radiation produced is not necessarily exactly at a harmonic of the pump radiation frequency. The substrate can be a lithographically patterned substrate. The radiation obtained by the process can also be provided in a lithographic apparatus LA and / or a lithographic cell LC. The pump radiation can be a pulsed radiation that can provide a high peak intensity for a short burst time.

[0086] The pump radiation 611 may include radiation having one or more wavelengths higher than one or more wavelengths of the emitted radiation. The pump radiation may include infrared radiation. The pump radiation may include radiation having a wavelength(s) in the range of 500 nm to 1500 nm. The pump radiation may include radiation having a wavelength(s) in the range of 800 nm to 1300 nm. The pump radiation may include radiation having a wavelength(s) in the range of 900 nm to 1300 nm. The pump radiation may be pulsed radiation. The pulsed pump radiation may include pulses having a duration in the femtosecond range.

[0087] For some embodiments, the emitted radiation (optionally high harmonic radiation) may include one or more harmonics of the pump radiation wavelength(s). The emitted radiation may include wavelengths in the extreme ultraviolet, soft x-ray, and / or hard x-ray portions of the electromagnetic spectrum. The emitted radiation 613 may include wavelengths in one or more of the 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.

[0088] Radiation, such as the above-mentioned high harmonic radiation, can be provided as source radiation in the measurement tool MT. The measurement tool MT can use the source radiation to perform measurements on the substrate exposed by the lithographic equipment. The measurement can be used to determine one or more parameters of the structure on the substrate. Compared with the use of longer wavelengths (e.g., visible light radiation, infrared radiation), the use of radiation at shorter wavelengths (e.g., EUV, SXR, and / or HXR wavelengths included in the above-mentioned wavelength range) can allow the measurement tool to resolve smaller features of the structure. Radiation with shorter wavelengths, such as EUVSXR and / or HXR radiation, can also penetrate deeper into materials such as patterned substrates, which means that measurement of deeper layers on the substrate is possible. These deeper layers may not be reached by radiation with longer wavelengths.

[0089] In the measurement tool MT, source radiation can be emitted from a radiation source and directed onto a target structure (or other structure) on a substrate. The source radiation may include EUVSXR and / or HXR radiation. The target structure may reflect, transmit, and / or diffract the source radiation incident on the target structure. The measurement tool MT may include one or more sensors for detecting diffracted radiation. For example, the measurement tool MT may include detectors for detecting positive (+1st) and negative (-1st) first diffraction orders. The measurement tool MT can also measure specularly reflected or transmitted radiation (0th order diffracted radiation). Additional sensors for measurement may be present in the measurement tool MT, for example to measure additional diffraction orders (e.g., higher diffraction orders).

[0090] In an exemplary lithography metrology application, HHG generated radiation can be focused onto a target on a substrate using an optical train, which can be referred to as an illuminator that transmits 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 properties of the target.

[0091] Gas-targeted HHG configurations can be broadly divided into three separate categories: gas injectors, gas chambers, and gas capillaries. Figure 6An exemplary gas jet configuration is depicted, wherein a gas volume is introduced into the driving radiation laser beam. In the gas jet configuration, the interaction of the driving radiation with the solid part is kept to a minimum. The gas volume may, for example, include a gas flow perpendicular to the driving radiation beam, wherein the gas volume is enclosed inside a gas chamber. In a gas capillary device, the size of the capillary structure holding the gas is smaller in the lateral direction, so that the capillary structure significantly affects the propagation of the driving radiation laser beam. The capillary structure may, for example, be a hollow fiber, wherein the hollow core is configured to hold the gas.

[0092] Because the gas jet HHG configuration is not limited by the constraints imposed by the gas capillary structure, the gas jet HHG configuration can provide relative freedom to shape the spatial profile of the drive radiation beam in the far field. The gas jet configuration can also have less stringent alignment tolerances. On the other hand, the gas capillary can provide an increased interaction area of ​​the drive radiation and the gaseous medium, which can optimize the HHG process.

[0093] In order 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 and driving radiation can be different for gas jet and gas capillary configurations. In both cases, the driving radiation suppression scheme can include a metal transmission filter for filtering out any remaining driving radiation from the short wavelength radiation. However, before such a filter can be used, the intensity of the driving radiation can be significantly reduced from the intensity of the driving radiation at the gas target in order to avoid damage to the filter. The methods that can be used for this intensity reduction are different for gas jet and capillary configurations. For gas jet HHG, due to the relative freedom of the shape and spatial profile (the shape and spatial profile can also be referred to as spatial distribution and / or spatial frequency) of the driving radiation beam focused on the gas target, this can be designed so that the driving radiation beam has a lower intensity in the far field along the direction of propagation of the short wavelength radiation. This spatial separation in the far field means that holes can be used to block the driving radiation and reduce the intensity of the driving radiation.

[0094] In contrast, in a gas capillary structure, the spatial distribution of the beam can be determined primarily by the capillary as the beam passes through the gas medium. The spatial distribution of the driving radiation can be determined by the shape and material of the capillary structure. For example, in the case where a hollow core fiber is used as the capillary structure, the shape and material of the fiber structure determine which modes of driving radiation are supported to propagate through the fiber. For most standard optical fibers, the supported propagation modes result in a spatial distribution in which higher intensities of the driving radiation overlap with higher intensities of the HHG radiation. For example, the driving radiation intensity can be centered in the far field with a Gaussian or near-Gaussian distribution.

[0095] Embodiments may include a computer program comprising a sequence of one or more machine-readable instructions describing a method of optical metrology and / or a method of analyzing measurement results to obtain information about a lithography process. Embodiments may include a computer code comprising a sequence of one or more machine-readable instructions or a sequence of data describing the method. The computer program or code may be implemented in, for example, Figure 6 The unit MPU and / or Figure 3 A data storage medium (e.g., a semiconductor memory, a magnetic disk, or an optical disk, etc.) in which such a computer program or code is stored may also be provided. Figure 6 Where existing measurement equipment of the type shown is already in production and / or in use, embodiments of the present invention may be implemented by providing an updated computer program product for causing a processor to perform one or more of the methods described herein. The computer program or code may optionally be arranged to control an optical system, a substrate support, etc. to perform a method of measuring parameters of a lithography process on a suitable plurality of targets. The computer program or code may update a lithography and / or measurement configuration scheme for measuring additional substrates. The computer program or code may be arranged to (directly or indirectly) control a lithography apparatus for patterning and processing of additional substrates.

[0096] The illumination source may be arranged, for example, in the metrology apparatus MT, the inspection apparatus, the lithographic apparatus LA, and / or the lithocell LC.

[0097] The properties of the emitted radiation used to perform the measurements may affect the quality of the measurements obtained. For example, the shape and size of the lateral beam profile (cross-section) of the radiation beam, the intensity of the radiation, the power spectral density of the radiation, etc. may affect the measurements performed by the radiation. Therefore, it is beneficial to have a source that provides radiation with properties that result in high quality measurements.

[0098] Figure 7 (a) shows another metrology device suitable for use with embodiments of the present invention. Note that this is only one example of a suitable metrology device. Alternative suitable metrology devices may use EUV radiation, such as disclosed in WO2017 / 186483A1. Figure 7(b) shows in more detail the target structure T and the diffracted rays of the measurement radiation used to illuminate the target structure. The type of measurement device shown is called a dark field measurement device. The measurement device can be a stand-alone device, or can be incorporated in the lithography device LA (for example, at the measurement station), or incorporated in the lithography unit LC. The optical axis running through the device and having multiple branches is represented by the dotted line O. In the device, the light emitted by the source 11 (for example, a xenon lamp) is guided to the substrate W via a beam splitter 15 through an optical system including lenses 12, 14 and an objective lens 16. These lenses are arranged in a double sequence of a 4F arrangement. Different lens arrangements can be used as long as they still provide the substrate image to the detector and at the same time allow access to the intermediate pupil plane for spatial frequency filtering. Therefore, the angle range of radiation incident on the substrate can be selected by defining the spatial intensity distribution in the plane (here called the (conjugate) pupil plane) that presents the spatial spectrum of the substrate plane. In particular, this can be done by inserting an aperture plate 13 of suitable form between lenses 12 and 14 in the plane which is the back-projected image of the objective pupil plane. In the example shown, the aperture plate 13 has different forms, marked 13N and 13S, which allow different illumination modes to be selected. The illumination system in this example forms an off-axis illumination mode. In a first illumination mode, the aperture plate 13N provides off-axis from a direction designated as "North" for description purposes only. In a second illumination mode, the aperture plate 13S is used to provide similar illumination but from an opposite direction marked as "South". By using different apertures, other modes of illumination are possible. Because any unnecessary light outside the desired illumination mode may interfere with the desired measurement signal, the rest of the pupil plane is desirably dark.

[0099] like Figure 7 As shown in (b), the target structure T is placed perpendicular to the optical axis O of the objective lens 16 together with the substrate W. The substrate W can be supported by a support (not shown). The rays of the measurement illumination I (e.g., including the SXR wavelength) irradiated onto the target structure T from an angle offset from the axis O produce a zero-order ray (solid line 0) and two first-order rays (dotted line +1 and double-dotted line -1). It should be remembered that with the overfilled smaller target structure, these rays are only one of many parallel rays covering the area of ​​the substrate including the measurement target structure T and other features. Since the hole in the plate 13 has a finite width (needed to allow a useful amount of light, the incident ray I will actually occupy a certain angle range, and the diffracted rays 0 and +1 / -1 will be slightly spread out. According to the point spread function of the smaller target, each order +1 and -1 will be further spread out over a certain angle range, rather than a single ideal ray as shown. Note that the illumination angle and the grating pitch of the target structure can be designed or adjusted so that the first-order rays entering the objective lens are closely aligned with the central optical axis. Figure 7The rays shown in (a) and 7(b) are slightly off-axis purely to make them easier to distinguish in the figures.

[0100] At least the 0th and +1st diffraction orders diffracted by the target structure T on the substrate W are collected by the objective lens 16 and directed back through the beam splitter 15. Figure 7 (a) shows the first and second illumination modes by designating diametrically opposed apertures labeled as north (N) and south (S). When the incident ray I of the measurement illumination comes from the north side of the optical axis, that is, when the first illumination mode is applied using aperture plate 13N, the +1 diffracted ray labeled as +1 (N) enters the objective lens 16. Conversely, when the second illumination mode is applied using aperture plate 13S, the -1 diffracted ray (labeled as -1 (S)) is the diffracted ray that enters the lens 16.

[0101] The second beam splitter 17 splits the diffracted beam into two measurement branches. In the first measurement branch, the optical system 18 forms a diffraction spectrum (pupil plane image) of the target structure on a first sensor 19 (e.g., a CCD or CMOS sensor) using the zeroth order and the first order diffracted beams. Each diffraction order impinges on a different point on the sensor so that image processing can compare and contrast the orders. The pupil plane image captured by the sensor 19 can be used to focus the measurement device and / or normalize the intensity measurement of the first order beam. The pupil plane image can also be used for many measurement purposes, such as reconstruction.

[0102] In the second measurement branch, the optical systems 20, 22 form an image of the target structure T on a sensor 23 (e.g., a CCD or CMOS sensor). In the second measurement branch, an aperture stop 21 is arranged in a plane conjugate to the pupil plane. The aperture stop 21 is used to block the zeroth order diffraction beam so that the image of the target formed on the sensor 23 is formed only by the -1 or +1 order beam. The image captured by the sensors 19 and 23 is output to a processor PU for processing the image, the function of which will depend on the specific type of measurement being performed. Note that the term "image" is used here in a broad sense. If only one of the -1 and +1 diffraction orders is present, no image of such grating lines will be formed.

[0103] Figure 8 is to use, for example Figure 5Schematic diagram of an exemplary measurement of an SXR metrology device shown. In an SXR measurement, a structure or target T (in a structure plane or a target plane) may be illuminated with a beam of SXR radiation ILL (e.g. in a wavelength range of 10 nm to 20 nm). The diffraction pattern DIFF is captured by (at least one) detector DET, which may be an image sensor, such as a CCD or CMOS image sensor. The target T coordinate system is labeled x, y, z (where x and y describe the structure plane / target plane), while the detector coordinate system is labeled x', y', z'. The illumination incident angle is labeled θ and the illumination azimuth is labeled φ. The illumination polarization vector PV has a polarization angle γ. The detector DET may actually include two or more detectors that are not necessarily coplanar.

[0104] Fig. 9 is an exemplary two-dimensional (2D) diffraction image that can be captured on the detector DET. In this particular example, the x and y axes are labeled per pixel (e.g., a 1024×1024 pixel detector). The details of the detector are of course purely an example. It can be seen that the multiple diffraction orders comprise curves whose curvature depends on the orientation and position of the detector DET. In particular, it is desired to find the wavelength value for each detector position (pixel). To this end, the actual position of the detector in space should be determined.

[0105] For some physics-based parameter inference methods (as opposed to data-driven methods), it is necessary to map pixel coordinates to wavelengths. If the pixel coordinates (x ', y ') can be transformed into Figure 8 The target coordinates (x, y, z) are shown, and the target pitch (p x , p y ) is known, such mapping is possible. Due to manufacturing tolerances and possible drifts, the alignment of the detector relative to the pupil plane of the system is not known with sufficient accuracy. In order to perform the mapping, such alignment is required. There are 6 mapping degrees of freedom (i.e., 6 detector alignment degrees of freedom). These degrees of freedom include the three directions of the detector coordinate system x', y', z' and the rotation R around each of these directions x’ , R y’ , R z’ The alignment of the SXR radiation beam ILL can lead to two additional degrees of freedom, the illumination alignment degrees of freedom: the illumination azimuth angle φ and the illumination incidence angle θ. Thus, a total of up to 8 degrees of freedom are possible for the combined illumination-detection system.

[0106] In a known example, it is known that by centering on the zeroth order (located at Fig. 9), two degrees of freedom of the mapping can be eliminated. However, this only works if the zeroth order and higher orders of diffraction are captured on the same sensor (which may not be desirable since the sensor will not allow the measurement of the spectrum of the zeroth order radiation) and without saturating the detector. For targets with 2D periodic diffraction elements (e.g. Figure 8 target T), there is typically not enough dynamic range to capture higher orders and an unsaturated zeroth order. In addition, the approach eliminates only six degrees of freedom for detector alignment and two of the eight degrees of freedom for illumination-detection system alignment. "1D" and "2D" in this article refer to the direction of periodicity: that is, a one-dimensional (1D) periodic structure is periodic (repeating) in one direction, and a 2D periodic structure is periodic (repeating) in two dimensions. Thus, a 1D periodic structure may include a line pattern (e.g., a line-space grating), and a 2D periodic structure may include a bulk pattern.

[0107] Another known method for performing this mapping uses a dedicated fiducial target (not on the wafer) to calibrate the sensor position. However, the fact that the fiducial is not on the same wafer as the metrology target being measured introduces a new calibration problem: alignment of the fiducial relative to the customer target.

[0108] Even for data-driven methods, the first preprocessing step may typically include mapping the signal (image data f(x,y)) into an antisymmetric component A(x,y) and a symmetric component S(x,y), for example:

[0109]

[0110] where x0 is the target center in the x direction. Most of the overlap response tends to be in the antisymmetric component A(x,y); if the target center x0 is not precisely known, the overlap signal may be overwhelmed by the alignment error signal.

[0111] A method for determining illumination-detection system alignment (e.g., relative to a pupil plane of a metrology tool) based on at least a subset of applicable degrees of freedom will be disclosed; for example, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, or at least 8 of the possible degrees of freedom for illumination-detection system alignment, or at least 2, at least 3, at least 4, at least 5, at least 6 of the detector alignment degrees of freedom. In the case where there is more than one detector without a fixed relationship between the detectors, a subset of degrees of freedom associated with detector position may be determined for each detector (e.g., there may be 6 possible detector position degrees of freedom for each detector), such that describing the subset as including three detector position degrees of freedom may be understood as describing the same three detector position degrees of freedom for each detector.

[0112] The proposed method can robustly and quickly fit at least three degrees of freedom (R z’ , x', y'). These are the more important degrees of freedom for mapping pixel coordinates into target coordinates. With a large enough NA, more degrees of freedom can be fitted, i.e. (R x’ , R y’ , z'), and / or optionally the illumination alignment degrees of freedom: one or more of the illumination azimuth angle φ and the illumination incidence angle θ.

[0113] The method may comprise fitting illumination-detection system alignment parameters (each illumination-detection system alignment parameter corresponding to one of said degrees of freedom) until the peaks of the diffraction pattern correspond to the expected positions of the diffraction orders, or more generally until the position of an intensity metric (such as the peak intensity of each of said diffraction patterns) substantially corresponds to the expected configuration. This will be fairly straightforward if the (e.g. SXR) source radiation is monochromatic. In this case, each diffraction order produces a known diffraction order (m x , m y ) of discrete light spots; the 6-parameter model for calculating the positions of these light spots can then be used to describe the light spot positions as x'[m x , m y ], y'[m x , m y ].

[0114] However, the concepts described herein involve broadband (e.g., SXR) radiation rather than monochromatic radiation. Fig. 9 The curvature of the line depends on the detector alignment. The diffraction orders are spectrally dispersed on these curves. Therefore, each point on these curves is now parameterized by the wavelength λ, that is, each point can be calculated as x'(m x ,m y , λ), y' (m x , m y , λ). However, for each point on the curve, the wavelength λ is initially unknown.

[0115] In one embodiment, the method may include eliminating the unknown wavelength and converting the fitting problem into a i , Y i Fit to the function Y=F(X), where F depends on the illumination-detection system alignment parameters. In this way, the parameter fit can be transformed into a least squares fit.

[0116] In one embodiment, the method may use a transformation from detector space to pupil space (kx , k y ). These are the x and y components of the unit vector of the ray emitted by the target, where x, y, z are in target coordinates, i.e. attached to the target unit cell. The detector position can be described by the rotation matrix Q and the position vector r0 in target coordinates; the relationship of the vector to the position r' in detector coordinates and the vector r in target coordinates is given by the transformation:

[0117] (Formula 1)

[0118] The rotation matrix Q can be written as the product of rotation matrices:

[0119] (Formula 2)

[0120] Where Q0 is the rotation matrix of the nominal detector position, Q' x , Q' y , Q' z is the rotation matrix for small angle rotations (e.g., a few milliradians) along the detector x', y', z' axes (representing alignment errors), and Q z Represents the target rotation, for example, a rotation along the target z-axis that is a multiple of 90 degrees. Matrix Q' x , Q' y , Q' z (hereinafter referred to as the abbreviation Q' xyz (denoted by) is the identity matrix without alignment error. Matrix Q' x , Q' y , Q' z The order is arbitrary; if the alignment errors are small (miradian or less), the choice of order may have only a small effect.

[0121] Compute the intersection of a ray with unit vector k (emitted from the origin) with the detector plane (given Q and r).

[0122] Fig.10 is an example of a 2D diffraction pattern in pupil coordinates. Given a target pitch (p x , p y ), diffraction order (m x , m y ) and wavelength λ, the pupil coordinates can be calculated as:

[0123] (Formula 3)

[0124] Among them, (k 0x , k 0y) is the pupil coordinate of the illumination (or equivalently, the zeroth order diffraction / specular reflection). If the unit cell of the target is not a rectangle, but a parallelogram, then there will be primitive translation vectors p1, p2 and Eq. 3 will need to be modified.

[0125] Additionally, the transformation from wavelength and diffraction order to pupil coordinate vector can be defined as:

[0126] (Formula 4)

[0127] Fig.11 1 is a flow chart describing a method for implementing the concepts disclosed herein. The method may determine two or more illumination-detection system alignment parameters from eight illumination-detection system alignment parameters. The eight illumination-detection system alignment parameters may include six detector alignment parameters (e.g., for each detector where appropriate) and two illumination alignment parameters (illumination azimuth angle φ and illumination incidence angle θ), wherein the detector alignment parameters include three parameters for the detector position r0 (i.e., its x, y, and z components) and a generated rotation matrix Q' xyz The three rotation angles α x , α y , α z The steps are as follows:

[0128] At step 1100, a wavelength having an approximately known wavelength range λ is used. a <λ<λ b The SXR source obtains the diffraction pattern as an image in the detector coordinates , the diffraction pattern is similar to that with a known pitch (p x , p y ) is related to the target (eg, obtained by measurement). Optionally, the wavelength λ b can be chosen to be an integer multiple of the longest wavelength in the SXR source; for example, twice the longest wavelength. This prevents having to accommodate overlapping diffraction orders, such as from Fig.10 It can be appreciated that the region of interest for diffraction order (2,0) is an extension of diffraction order (1,0).

[0129] At step 1110, at least for detecting alignment parameters r0 and α xyz Initial estimates (nominal values) of are defined (eg, up to six values ​​in total; angles may be assumed to have a nominal value of zero). Initial estimates (nominal values) may also be defined for the illumination alignment parameters illumination azimuth angle φ and illumination incidence angle θ.

[0130] At step 1120, using these parameters, the image can be transformed to pupil coordinates, yielding the function g(k x ,k y ), such as Fig.10 Note that Fig.10 In , the diffraction orders are essentially straight, which would indicate that the mapping is accurate and the detector positions have been well defined. It is possible that in the first iteration of the method, these diffraction orders may not be as straight as shown here.

[0131] At step 1130, the pupil space (k x , k y The region of interest (e.g., a rectangular region of interest) is allocated in a space such that a corresponding region of interest is allocated to each of the one or more transformed diffraction orders. The region of interest may be defined using Equation 3 above. The region of interest may be large enough so that the diffraction intensity of the corresponding diffraction order of the region of interest is completely contained within the region (e.g., a rectangle); the amount of additional space or margin may depend on the SXR beam divergence and the expected alignment error. Fig.12 A single diffraction order (1, 0) and a respective exemplary region of interest (ROI) for the single diffraction order are shown.

[0132] This step may be performed for all imaged diffraction orders or a subset of these diffraction orders (e.g., one or more, two or more, three or more, four or more, six or more, or eight or more diffraction orders). In the case where only a subset is selected, the subset may include the strongest (highest intensity) of the imaged orders. Thus, in one embodiment, the selected orders may include four orders (±1, 0) and (0, ±1) (i.e., in Fig.10 at least any three of the marked orders on .

[0133] At step 1140, a regional coordinate system XY is defined for each region of interest. The regional coordinate system can be such that an intensity metric such as peak intensity (peak diffraction intensity) is located on the X-axis, that is, if the alignment parameters (e.g., Q and r0) are correct, the intensity metric is located at Y=0. More generally, the X-axis or first axis can be aligned relative to the direction of the intensity metric (e.g., parallel to the direction of the intensity metric or aligned in the direction of the intensity metric). Although it is convenient to define the X-axis so that the intensity metric is located on this axis, the X-axis can alternatively be aligned on the edge of the rectangular region rather than at the center. This will require only slight modifications to the method. In any case, this step may include assigning g(k x ,k y ) is mapped to a new function h(X, Y).

[0134] The coordinates of multiple diffraction peaks can be obtained (X i , Y iIn one embodiment, this may include, for example, by preselecting X i and evaluate the following formula and convert h(X i , Y) is converted to value Y i (e.g. as a weighted average (centroid) along Y):

[0135]

[0136] Among them, the integral limit covers the interior of the region. Fig.13 is k showing this transformation x , k y and a graph of X, Y. Then you can combine each region X i , Y i ; for example, if each of the four regions has 100 X i The sampling is done at the value, then i=1, …, 400. Fig.13 There are 7 Xs in i Value. X combined over all regions i The total number of values ​​is usually not less than the number of alignment parameters.

[0137] It is understandable that h(X i , Y) describes the mapping within a region only; the full mapping of the pupil can be obtained by h(m x , m y , X, Y) to describe, where m x , m y is a pair of integers used to identify the region. Therefore, instead of mapping each region individually and then combining, we can preselect X i and evaluate the following formula to achieve this mapping:

[0138]

[0139] Optionally, at this step, the standard error σ i Assign to each Y i Values, for example:

[0140]

[0141] (Only the ratio of standard errors can be used; the normalization factor is omitted here).

[0142] There are alternatives to mapping as a weighted average along Y. These include mapping as:

[0143] - median along Y;

[0144] - Mode along Y (peak position);

[0145] - Values ​​obtained by fitting to a function describing the known peak shape T(Y), e.g., a least squares fit to b×T(Y -Yi) with b, Yi as fitting parameters. This may be useful if the beam profile is known to be asymmetric, i.e., T(Y) ≠ T(-Y). The function T may be chosen based on the diffraction order, i.e., T(mx, my, Y). The function T may be chosen based on the X coordinate, i.e., T(mx, my, X, Y).

[0146] In general, a mapping can be represented as:

[0147]

[0148] where F is implicitly dependent on the total diffraction pattern f(x', y') and the target pitch p x , p y function. Each X i The values ​​are accompanied by the diffraction order m xi and m yi The function may be constructed using, for example, interpolation similar to that described below in step 1150 .

[0149] At step 1150, the Jacobian matrix J describing the partial derivatives of Y with respect to each alignment parameter is ij Can be constructed as:

[0150]

[0151] where the components of the vector a are the detector alignment parameters: for example, the three components of r0 and the three angles α xyz and optionally irradiating alignment parameters, or a subset of these six or eight parameters (j=1 to m, where m is the number of alignment parameters being optimized). For example, the Jacobian matrix can be constructed by applying Equation 4 above. A practical implementation of this step may include generating different sets of X values ​​for a range of wavelengths, computing partial derivatives using finite differences, and interpolating to obtain the values ​​from step 1140 for X. i Value, for Y i The value of .

[0152] At step 1160, Δa may be estimated by solving a least squares method for the correction Δa for the detector alignment parameters:

[0153]

[0154] Optionally, the standard error σ described in step 1030 i can be used to perform weighted least squares. Steps 1150 and 1160 are performed by Fig.14A graph of Y versus X is shown schematically.

[0155] Then, the new detector alignment parameter estimate can be determined as:

[0156]

[0157] At step 1170, it may be determined whether convergence has been reached, and if not, the method may return to step 1120 and perform further iterations of steps 1120 to 1170 using new detector alignment parameter estimates. If convergence is reached, the method stops and the final alignment parameter estimates are used to define detector positions for any mapping. Such convergence may result in the position of the intensity metric of each of the diffraction patterns substantially corresponding to an expected configuration or configuration in the zone coordinate system (e.g., aligned on or aligned with (e.g., parallel to) the X-axis).

[0158] Steps 1150 to 1170 describe a method of fitting up to six detector alignment parameters and optionally one or two additional illumination alignment parameters in an a-vector. The method is a specific implementation of a least squares fit that minimizes the sum of squares:

[0159]

[0160] Standard error σ i You can take a constant (for example, all σ i =1) or can be estimated as optionally described in step 1140. There are many well-known algorithms for performing this minimization; for example: the Levenberg-Marquardt algorithm, the Nelder-Mead method, and the Gauss-Newton algorithm. Steps 1150 to 1170 actually describe a variant of the Gauss-Newton algorithm.

[0161] Because the least squares algorithm (i.e., minimizing S above) is fast, it is usually used. There are metrics other than "sum of squares" for minimizing (close to zero), and the metrics can be used in the methods disclosed herein. For example, if there is prior knowledge of the probability distribution of vector a, a Bayesian approach can be used. In particular, if the least squares fit of all six degrees of freedom in a leads to unrealizable results, Bayesian inference can be used (optionally using a Gaussian prior on a).

[0162] A more conventional notation for least squares curve fitting is minimization:

[0163]

[0164] Here, the superscript symbol "'" in F' indicates that F' is a different function from F above. This can also be used to find a, but the entire step-by-step process will need to be modified as follows:

[0165] - Obtain f(x', y') [as before].

[0166] -Start with an initial assumed value for a; the initial assumed value for a is called a0.

[0167] -Use a0 to transform f(x', y') into g(k x , k y ).

[0168] - Allocate the region of interest in k-space [as described above].

[0169] - Construct the function F'(a0, a, X, m x , m y ); function F'(a0, a, X, m x , m y ) is the Y value that would be obtained if a were the true calibration parameter vector and a0 were used to generate the g function. For a = a0, we have F' = 0. This function can be used as Fig.11 Interpolation in the described method.

[0170] - Perform a least squares minimization, ie, curve fitting, to find the best fitting parameter vector a (eg, according to the equation at the top of this paragraph). Use any standard algorithm for curve fitting (eg, Levenberg-Marquardt).

[0171] Bayesian methods can also be used in this embodiment.

[0172] When the three degrees of freedom (r0 and α z When optimizing the x and y components of a θ ( ), it has been shown that convergence using the methods described herein can be achieved very quickly, for example, the fitted position can be stabilized to less than 10 nm and the angle can be stabilized to less than 10 μrad after only two iterations.

[0173] As already explained, there may be more than one detector for detecting the diffraction pattern. If so, and the relative positions of the two or more detectors are fixed and known, the concepts disclosed herein are directly applicable. If the relative positions are not precisely known, the method can be applied to each detector independently.

[0174] Understandably, Fig.10The pupil representation and corresponding transformation method shown in may also be useful in the context of data-driven parameter inference methods in addition to physics-based methods. For example, if the tool alignment drifts, the representation can be used to remove the effect of this drift from the signal.

[0175] Further embodiments are disclosed in the following sequentially numbered aspects:

[0176] 1. A method for determining an illumination-detection system alignment of an illumination-detection system, the illumination-detection system alignment describing the alignment of at least one detector and / or a measurement radiation of a metrology device in accordance with two or more illumination-detection system alignment parameters, each illumination-detection system alignment parameter being associated with a respective degree of freedom for aligning the detector and / or the measurement radiation; the method comprising:

[0177] obtaining a diffraction pattern associated with diffraction of broadband radiation from the structure;

[0178] transforming each of the one or more diffraction orders of the diffraction pattern into a respective regional coordinate system, each regional coordinate system comprising a first axis and a second axis, each regional coordinate system having the first axis aligned relative to a direction of an intensity measure of each transformed diffraction order; and

[0179] An illumination-detection system alignment parameter value of the illumination-detection system alignment parameter is determined such that a position of the intensity metric of each of the diffraction patterns substantially corresponds to an expected configuration in the zone coordinate system.

[0180] 2. The method of clause 1, wherein the diffraction pattern comprises a two-dimensional diffraction pattern and the structure comprises a two-dimensional periodic structure for performing metrology in two dimensions of a plane of the structure.

[0181] 3. A method according to aspect 1 or 2, wherein the method comprises fitting three or more illumination-detection system alignment parameters.

[0182] 4. A method according to aspects 1 or 2, wherein the method comprises fitting six or more illumination-detection system alignment parameters.

[0183] 5. The method according to any of the preceding aspects, wherein the degrees of freedom for aligning the detector and / or measuring the illumination comprise six detector alignment degrees of freedom: three directions of the detector coordinate system and rotations about each of these directions.

[0184] 6. The method according to any of the preceding aspects, wherein the degrees of freedom for aligning the detector and / or measuring the illumination comprise two degrees of freedom for illumination alignment: illumination azimuth and illumination incidence angle.

[0185] 7. A method according to any of the above aspects, wherein the intensity metric is the peak intensity of each diffraction order.

[0186] 8. A method according to any preceding aspect, wherein the expected configuration comprises a substantially straight line in the regional coordinate system.

[0187] 9. A method according to claim 8, wherein the straight line is aligned with the first axis of the regional coordinate system, and the step of determining the illumination-detection system alignment parameter value includes: minimizing the distance of the position of the intensity measurement within the regional coordinate system from the first axis.

[0188] 10. The method according to any one of the preceding aspects, wherein the step of transforming one or more diffraction orders of the diffraction pattern into a regional coordinate system comprises:

[0189] transforming the diffraction pattern from a detector coordinate system to a pupil coordinate system;

[0190] identifying a region of interest for each of the one or more diffraction orders, the region of interest comprising a corresponding diffraction order for the region of interest; and

[0191] A mapping is performed of a function describing each of the one or more diffraction orders in the pupil coordinate system to a function describing each of the one or more diffraction orders in the zone coordinate system.

[0192] 11. A method according to clause 10, wherein each region of interest is rectangular.

[0193] 12. The method according to aspect 10 or 11, wherein the mapping is performed as one of:

[0194] the average or weighted average along the second axis of the regional coordinate system,

[0195] a median value along a second axis of the regional coordinate system;

[0196] a mode along a second axis of the regional coordinate system;

[0197] Values ​​obtained by fitting to a function describing a known peak shape.

[0198] 13. The method according to any one of the above aspects, comprising:

[0199] determining coordinates of the intensity metric in the region coordinate system; and

[0200] Minimize the value of the secondary axis coordinate.

[0201] 14. A method according to clause 13, wherein the step of minimizing the value comprises constructing a Jacobian matrix of partial derivatives describing the sensitivity of the second axis coordinate to each alignment parameter.

[0202] 15. A method according to clause 13 or 14, wherein the step of minimizing the value is performed iteratively starting with an initial estimate of the alignment parameters and iteratively optimizing the alignment parameters until convergence.

[0203] 16. The method of any one of aspects 13 to 15, wherein the step of minimizing the value comprises Levenberg-Marquardt minimization, Nelder-Meider minimization, Gauss-Newton minimization, or other sum-of-squares minimization.

[0204] 17. A method according to any one of clauses 13 to 15, comprising: obtaining a priori knowledge of the probability distribution of the illumination-detection system alignment parameters; and wherein the step of minimizing the value comprises Bayesian inference minimization.

[0205] 18. A method according to any preceding aspect, wherein the one or more diffraction orders include one or more diffraction orders having a maximum intensity within the diffraction pattern.

[0206] 19. A method according to any preceding aspect, wherein the one or more diffraction orders include at least two first-order diffraction orders.

[0207] 20. A method according to any preceding aspect, wherein the one or more diffraction orders include at least three first order diffraction orders.

[0208] 21. A computer program comprising computer readable instructions operable to perform at least the processing and determining position steps of the method according to any one of aspects 1 to 20.

[0209] 22. A processor and associated storage medium, the storage medium comprising a computer program according to aspect 21, enabling the processor to be operable to perform a method according to any one of aspects 1 to 20.

[0210] 23. A measurement device operable to perform a method according to any one of aspects 1 to 20.

[0211] 24. The measurement device according to aspect 23, comprising a detector,

[0212] wherein the method is performed to determine an illumination-detection system alignment of the detector and / or measuring illumination;

[0213] Therein, the processor is further operable to determine a parameter of interest for a measurement performed using the metrology device based on the determined illumination-detection system alignment.

[0214] 25. A lithography cell comprising a metrology apparatus according to clause 23.

[0215] Although specific reference is made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0216] Although specific reference is made herein to embodiments in the context of lithographic apparatus, embodiments may be used in other apparatus. Embodiments may form part of mask inspection equipment, metrology equipment, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0217] Although specific reference may be made herein to embodiments in the context of inspection or measurement equipment, embodiments may be used in other equipment. Embodiments may form part of mask inspection equipment, lithography equipment, or any equipment for measuring or processing objects such as wafers (or other substrates) or masks (or other pattern forming devices). The term "measurement equipment" (or "inspection equipment") may also refer to inspection equipment or inspection systems (or measurement equipment or measurement systems). For example, inspection equipment including embodiments may be used to detect defects in a substrate or defects in a structure on a substrate. In such embodiments, the characteristic of interest in a structure on a substrate may relate to defects in the structure, the absence of a particular portion of the structure, or the presence of an unwanted structure on the substrate.

[0218] Although specific reference has been made above to the use of the embodiments in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography and may be used in other applications such as imprint lithography where the context permits.

[0219] Although the above-mentioned targets or target structures (more generally, structures on the substrate) are measurement target structures that are specifically designed and formed for measurement purposes, in other embodiments, the properties of interest may be measured on one or more structures that are functional parts of a device formed on the substrate. Many devices have regular, grating-like structures. The terms "structure", "target", "target grating" and "target structure" as used herein do not require that the structure has been specifically provided for the measurement being performed. In addition, the pitch of the measurement target can be close to the resolution limit of the optical system of the scatterometer, or can be smaller, but can be much larger than the size of a typical non-target structure, which can optionally be a product structure manufactured by a photolithography process in the target portion C.

[0220] Although specific embodiments have been described above, it should be understood that the present invention may be implemented in a manner other than that described. The above description is intended to be illustrative rather than restrictive. Therefore, it will be readily apparent to those skilled in the art that modifications may be made to the described invention without departing from the scope of the appended claims.

[0221] Although specific reference is made to "measurement equipment / tool / system" or "inspection equipment / tool / system," these terms may refer to the same or similar types of tools, equipment, or systems. For example, an inspection or measurement equipment including embodiments of the present invention may be used to determine characteristics of structures on a substrate or wafer. For example, an inspection equipment or measurement equipment including embodiments of the present invention may be used to detect defects in a substrate or defects in a structure on a substrate or wafer. In such embodiments, the characteristic of interest of the structure on the substrate may relate to a defect in the structure, the absence of a particular portion of the structure, or the presence of an undesirable structure on the substrate or wafer.

[0222] Although specific reference is made to HXR, SXR and EUV electromagnetic radiation, it will be appreciated that the invention may be practiced with all electromagnetic radiation including radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays, where the context permits.

[0223] Although specific embodiments have been described above, it will be appreciated that one or more features in one embodiment may also be present in a different embodiment, and features in two or more different embodiments may also be combined.

Claims

1. A method for determining an illumination-detection system alignment of an illumination-detection system, wherein the illumination-detection system alignment describes the alignment of at least one detector and / or a measurement radiation of a metrology device in accordance with two or more illumination-detection system alignment parameters, each illumination-detection system alignment parameter being associated with a respective degree of freedom for aligning the detector and / or the measurement radiation; the method comprising: obtaining a diffraction pattern associated with diffraction of broadband radiation from the structure; transforming each of the one or more diffraction orders of the diffraction pattern into a corresponding regional coordinate system, each regional coordinate system comprising a first axis and a second axis, each regional coordinate system having the first axis aligned relative to a direction of an intensity measure of each transformed diffraction order; as well as An illumination-detection system alignment parameter value of the illumination-detection system alignment parameter is determined such that a position of the intensity metric of each of the diffraction patterns substantially corresponds to an expected configuration in the zone coordinate system.

2. The method according to claim 1, wherein: The diffraction pattern comprises a two-dimensional diffraction pattern, and the structure comprises a two-dimensional periodic structure for performing metrology in two dimensions of a plane of the structure.

3. A method according to any preceding claim, wherein: The intensity measure is the peak intensity of each diffraction order.

4. A method according to any preceding claim, wherein: The expected configuration comprises a substantially straight line in the regional coordinate system.

5. The method according to claim 4, wherein: The straight line is aligned with the first axis of the regional coordinate system, and the step of determining a value of an illumination-detection system alignment parameter comprises minimizing a distance of a position of the intensity metric within the regional coordinate system from the first axis.

6. A method according to any preceding claim, wherein: The step of transforming one or more diffraction orders of the diffraction pattern into a regional coordinate system comprises: transforming the diffraction pattern from a detector coordinate system to a pupil coordinate system; identifying a region of interest for each of the transformed one or more diffraction orders, the region of interest including its corresponding diffraction order; and A mapping is performed of a function describing each of the one or more diffraction orders in the pupil coordinate system to a function describing each of the one or more diffraction orders in the zone coordinate system.

7. The method according to claim 6, wherein: The mapping is performed as one of the following: the average or weighted average along the second axis of the regional coordinate system, a median value along a second axis of the regional coordinate system; a mode along a second axis of the regional coordinate system; Values ​​obtained by fitting to a function describing a known peak shape.

8. A method according to any preceding claim, comprising: determining coordinates of the intensity metric in the region coordinate system; as well as Minimize the value of the second axis coordinate, Wherein, optionally, the step of minimizing the value comprises: constructing a Jacobian matrix of partial derivatives describing the sensitivity of the second axis coordinate to each alignment parameter.

9. The method according to claim 8, wherein: The step of minimizing the value is performed iteratively, starting with an initial estimate for the alignment parameters, and iteratively optimizing the alignment parameters until convergence.

10. The method according to any one of claims 8 and 9, comprising: obtaining a priori knowledge of the probability distribution of the illumination-detection system alignment parameters; and Wherein, the step of minimizing the value includes Bayesian inference minimization.

11. A method according to any preceding claim, wherein: The one or more diffraction orders include at least two first order diffraction orders.

12. A method for measuring a structure, comprising: Based on the knowledge that the diffraction pattern diffracted from the structure and captured by the detector of the illumination-detection system corresponds to an expected configuration according to the target, alignment parameters of the illumination-detection system related to corresponding degrees of freedom for aligning the detector of the illumination-detection system and / or measuring illumination are determined.

13. A computer program comprising computer readable instructions which, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 12.

14. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 12.

15. A metrology device comprising an illumination-detection system, wherein: An alignment of the at least one detector and / or a measuring illumination comprising the broadband radiation of the metrology device is determined by causing a diffraction pattern associated with diffraction of the broadband radiation of the metrology device from the structure and captured by the at least one detector of the metrology device to correspond to an expected configuration based on the known pitch of the structure having the known pitch.

Images