Metrology method for determining one or more parameters of a periodic target on an object and associated metrology apparatus

Abstract

A measurement method and associated measurement apparatus for determining one or more parameters of a periodic target on an object are disclosed. The periodic target is adjacent to a reference mark having a pitch equal to that of the periodic target. The method includes projecting radiation onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on the reference mark. The method also includes measuring at least one interference pattern formed by the contributions of both the first and second portions of the radiation to a single diffraction order. The method further includes determining one or more parameters depending on the at least one interference pattern.

Description

Cross-reference to related applications

[0001] This application claims priority to European application 24152530.2, filed on 18 January 2024, and European application 24155902.0, filed on 6 February 2024, which are incorporated herein by reference in their entirety. Technical Field

[0002] This invention relates to a novel measurement method for determining one or more parameters of a periodic target on an object. The invention also relates to an associated measurement apparatus for determining one or more parameters of a periodic target on an object. The novel method and apparatus can be applied to measurement tools used to inspect silicon wafers during the fabrication of integrated circuits using photolithography. In particular, the novel method and apparatus can be applied to such measurement apparatuses aimed at determining overlay accuracy (a measure of the alignment of two or more successively formed photolithographic layers). Background Technology

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

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

[0005] Low-k1 lithography can be used to process features with dimensions smaller than the classical resolution limit of a lithography apparatus. In such a process, the resolution formula can be expressed as CD = k1 × λ / NA, where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection optics in the lithography apparatus, CD is the "critical size" (typically the smallest feature size printed, but in this case, half a pitch), and k1 is an empirical resolution factor. Generally, the smaller k1 is, the more difficult it is to reproduce patterns on the substrate that are similar in shape and size to those planned by the circuit designer to achieve specific electrical functions and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithography projection apparatus and / or design layout. These include, for example, but not limited to, optimizing NA, customizing the illumination scheme, using phase-shifting patterning equipment, various optimizations of the design layout (such as optical proximity correction (OPC, sometimes also referred to as "optical and process correction")), or other methods generally defined as "resolution enhancement techniques" (RET). Alternatively, a tight control loop for controlling the stability of the lithography apparatus can be used to improve pattern reproduction at low k1.

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

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

[0008] Examples of known scatterers typically rely on providing a dedicated measurement target. For instance, a method might require a target in the form of a simple grating, large enough that the measurement beam generates a spot smaller than the grating (i.e., the grating is underfilled). In so-called reconstruction methods, the properties of the grating can be calculated by simulating the interaction between the scattered radiation and a mathematical model of the target structure. The parameters of the model are tuned until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0009] Besides measuring feature shapes through reconstruction, diffraction-based overlay accuracy can be measured using a device such as that described in published patent application US2006066855A1. Diffraction-based overlay accuracy measurement uses dark-field imaging of the diffraction order, enabling overlay accuracy measurements on small targets. These targets can be smaller than the illumination spot and can be surrounded by the product structure on the wafer. Examples of dark-field imaging measurements can be found in numerous published patent applications such as US2011102753A1 and US20120044470A. Multiple gratings can be measured in a single image using a composite grating target. Known scatterometers tend to use light in the visible or near-infrared (IR) wavelength range, requiring grating pitches much coarser than the actual product structure, the properties of which are of real 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 unsuitable or unavailable for measurement.

[0010] On the other hand, the size of modern product structures is so small that they cannot be imaged using optical metrology techniques. Small features include, for example, features formed through multiple patterning processes and / or pitch multiplication. Therefore, targets used for high-volume metrology typically use features much larger than the product itself, where the overlay accuracy error or critical dimension of the product is the property of interest. Measurement results are only indirectly related to the size of the actual product structure and may be inaccurate because the measured target does not suffer the same distortion under different treatments in the optical projection in the lithography apparatus and / or other steps of the manufacturing process. While scanning electron microscopy (SEM) can directly resolve these modern product structures, SEM is much more time-consuming than optical measurements. Furthermore, electrons cannot penetrate thick process layers, making them less suitable for metrology applications. Other techniques, such as using contact pads to measure electrical properties, are also known, but they only provide indirect evidence of the actual product structure.

[0011] By reducing the wavelength of the radiation used during measurement, smaller structures can be resolved, increasing sensitivity to structural changes and / or further penetration into the product structure. One such method for generating appropriate high-frequency radiation (e.g., hard X-rays, soft X-rays, and / or EUV radiation) can be to excite the generating / target medium using pump radiation (e.g., infrared IR radiation), thereby generating the emitted radiation, optionally including high-harmonic generation (HHG) of high-frequency radiation.

[0012] It may be desirable to provide new measurement methods and apparatus for determining one or more parameters of a periodic target (e.g., on a wafer), which at least partially solve one or more problems associated with a known arrangement, whether such problems are identified herein or otherwise. Summary of the Invention

[0013] According to a first aspect of this disclosure, a measurement method is provided for determining one or more parameters of a periodic target on an object, the periodic target being adjacent to a reference mark having a pitch equal to that of the periodic target. The method includes: projecting radiation onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on the reference mark; measuring at least one interference pattern formed by the contributions of both the first and second portions of the radiation to a single diffraction order; and determining one or more parameters based on the at least one interference pattern.

[0014] As discussed now, the method according to the first aspect is advantageous. Since the reference marker has a pitch equal to that of the periodic target, the two structures can produce a diffraction pattern comprising diffracted beams scattered at substantially the same angle. In the far field, each diffracted beam from the periodic target can generally overlap spatially with its corresponding diffracted beam from the reference marker. The corresponding diffracted beam pairs from the periodic target and the reference marker can be collectively referred to as an interference beam. Furthermore, in the far field, each interference beam in the interference beam can be spatially separated (at a sufficient distance from the object).

[0015] The method can be considered an interferometric method, which utilizes at least one pair of interfering beams (within each interfering beam). Based on the interference pattern and the profile of the radiation projected onto the target, the phase difference between the contributions from the reference marker and the periodic target can be determined. If the structure of the reference marker is known, the phase of the contribution from the reference marker to each diffraction beam can be determined. Furthermore, the phase of the contribution from the periodic target to each diffraction beam can thus be determined.

[0016] This method can be applied to metrology tools used to inspect silicon wafers during the fabrication of integrated circuits using photolithography. In particular, it can be applied to metrology apparatuses designed to determine overlay accuracy (a measure of the alignment of two or more sequentially formed photolithographic layers). One or more parameters determined by the method according to the first aspect may include any of the following: critical dimension (CD), overlay accuracy (i.e., the amount by which two or more process layers are misaligned), and / or the thickness of one or more process layers.

[0017] Some such metrological tools use soft X-ray (SXR) measurements, irradiating a periodic target on a wafer with radiation (e.g., including multiple discrete wavelength components) in a spectral range of approximately 10 nm–20 nm. The diffraction pattern is captured and analyzed spectrally. Various methods exist to extract these parameters from the scattering measurement data. For example, the target response spectrum can be obtained by measuring the diffraction efficiency. The form is captured, in which , It is a discrete integer diffraction order, and It is the wavelength. The data obtained in this way contains information about parameters of interest, such as overlay accuracy and critical dimensions.

[0018] However, using such known techniques, only the intensity of the diffracted light is captured.

[0019] In contrast, the method according to the first aspect allows for the measurement of the phase of diffracted radiation, which also contains useful information. Furthermore, it provides a relatively simple and cost-effective method for determining such phase information. For example, a known method for determining the phase response of a target would be using techniques such as digital holographic microscopy (DHM). However, several problems exist when applying such techniques with soft X-rays. First, it would require a beam splitter for soft X-rays, which is difficult. Second, it would require two beam paths stabilized on the interference to a path length difference of <<10 nm, which would be very expensive. Third, the fringe pattern on the image sensor would have a period of <100 nm, which would require an image sensor with impractically small pixels to resolve the fringes.

[0020] At least one interference pattern can be measured using any suitable detector array or camera.

[0021] Projecting radiation onto an object can include focusing the radiation onto the object (such that a first portion of the radiation is incident on a periodic target, and a second portion of the radiation is incident on a reference mark). That is, the object can be positioned at or near the waist of the radiation beam. In such an embodiment, at least one interference pattern can be measured in the far field. In particular, at least one interference pattern can be measured at a location not within the Rayleigh length of the radiation.

[0022] Determining one or more parameters based on at least one interference pattern may include: for each at least one interference pattern, determining the phase difference between the contributions of a first portion and a second portion of the radiation to the diffracted beam.

[0023] Determining one or more parameters based on at least one interference pattern may include: for each at least one interference pattern, determining the position of the interference pattern.

[0024] For example, each interference pattern is formed by the contributions of both the first and second portions of the radiation to a single diffraction order. Each diffraction beam can illuminate a spot region (e.g., circular or elliptical) on the detector in the far field. Each such spot region corresponds to the projection of the beam spot region (of the radiation projected onto the object) onto the detector.

[0025] Within each such spot region, if the contributions from the first and second portions of the radiation are in phase, the intensity distribution within the spot region can generally match the intensity distribution of the radiation projected onto the object (e.g., a Gaussian beam distribution). However, the inventors have realized that if the contributions from the first and second portions of the radiation are out of phase, dark fringes may appear in the intensity distribution within the spot region in the direction corresponding to the separation direction of the periodic target and the reference mark. For example, if the radiation projected onto the object has a Gaussian profile, it would be desirable for the intensity distribution within the spot region, in the direction corresponding to the separation direction of the periodic target and the reference mark, to have two independent peaks separated by dark fringes.

[0026] For example, if the periodic target and the reference mark are set at substantially the same x-position on the object but at different y-positions, the two peaks can be separated on the detector in the direction corresponding to the y-direction. By determining the position (in the separation direction of the periodic target and the reference mark) and / or relative intensity of the peaks of the interference pattern within the spot region, the relative phase of the contributions of the first and second portions of radiation to the diffracted beam can be inferred or determined.

[0027] Determining one or more parameters based on at least one interference pattern may include: fitting a desired distribution to an intensity distribution in a spot region corresponding to the diffraction beam in a direction corresponding to the separation direction of the periodic target and the reference mark; and determining one or more parameters of the periodic target from one or more parameters of the desired distribution.

[0028] The desired distribution can depend on the spatial intensity profile of the radiation projected onto the object.

[0029] In some embodiments, the radiation may include soft X-rays. It will be understood that the radiation includes sufficiently coherent radiation to produce at least one interference pattern.

[0030] Radiation can include radiation in the spectral range of 10 nm to 20 nm.

[0031] It will be understood that radiation included in the spectral range of 10 nm to 20 nm is intended to mean that the radiation includes at least one wavelength component (which may be monochromatic) in the spectral range of 10 nm to 20 nm. In some embodiments, the radiation includes radiation in the spectral range of 9 nm to 18 nm.

[0032] Radiation can include multiple discrete wavelength components.

[0033] For example, the spectrum of radiation may include multiple discrete peaks, each of which can be referred to as a discrete wavelength component. This can be described as a comb structure (but it is understood that each peak may have a non-zero bandwidth). The radiation may include radiation in the spectral range of 10 nm–20 nm. The multiple discrete peaks (or wavelength components) may have a typical spacing of about 0.5 nm. The radiation may include about 20 such wavelength components. The bandwidth of each peak (discrete wavelength component) in the spectrum may be about 0.1 nm or less.

[0034] The method may include: measuring at least one interference pattern for each of a plurality of discrete wavelength components, each interference pattern being formed by the contribution of both a first portion and a second portion of radiation to a single diffraction order of a single discrete wavelength component; and determining one or more parameters based on the at least one interference pattern for each of the plurality of discrete wavelength components.

[0035] Advantageously, this allows the phase response to be determined based on the wavelength.

[0036] The method may include: measuring multiple interference patterns, each interference pattern being formed by the contributions of both a first part and a second part of the radiation to a single diffraction order; and determining one or more parameters based on the multiple interference patterns.

[0037] For 1D patterns, the shearing direction of periodic targets and reference marks can be defined as a direction that is generally perpendicular to the lines of the pattern.

[0038] The shearing direction of each of the periodic target and the reference mark can be perpendicular to the separation direction of the periodic target and the reference mark.

[0039] Such an arrangement is advantageous if the radiation projected onto the object comprises multiple wavelength components. For diffraction orders above the 0th order, the different wavelength components can be separated in the shear direction in the far field, but the two peaks formed by the inverted first and second portions of the radiation can be separated in the separation direction. Therefore, if the shear direction is perpendicular to the separation direction, the relative phase of the first and second portions of the radiation can be more easily determined.

[0040] Alternatively, in some other embodiments, the shearing direction of the periodic target and the shearing direction of the reference mark may be parallel to the separation direction of the periodic target and the reference mark.

[0041] In some embodiments, the separation direction of the periodic target and the reference mark lies in the incident plane of the radiation. Using such an embodiment, for a typical diffraction order, there may be an optical path difference between the first and second portions of the radiation, and the radiation may have a coherence length greater than this optical path difference.

[0042] Alternatively, in some embodiments, the separation direction of the periodic target from the reference mark is perpendicular to the incident plane of the radiation. Such embodiments can allow for a shorter coherence length of the radiation.

[0043] Determining one or more parameters based on at least one interference pattern can be achieved in several ways. First, raw data comprising one or more images of the interference pattern from the detector can be determined. Second, one or more parameters can be determined or inferred from the raw data in one of several different ways. As mentioned above, one or more parameters may include information relating to the phase of the contribution of a first portion of the radiation (which is incident on a periodic target) to the (multiple) diffracted beams.

[0044] Determining one or more parameters may include using a trained machine learning model.

[0045] The method may also include using training data to train a machine learning model.

[0046] For example, multiple different known calibration targets (such as one or more parameters, like phase information, that are known to the calibration target) can be used to generate raw data. Machine learning models can then be trained using this raw data along with the known parameters.

[0047] Determining one or more parameters may include, for each at least one interferometric pattern: determining the phase response of the contribution from the reference marker to the interferometric pattern using model-based reconstruction of the reference marker; and combining the determined phase response with the interferometric pattern to determine the phase response of the contribution from the periodic target to the interferometric pattern.

[0048] A simple resist grating (which can be used as a reference marker) has very few unknown parameters. In principle, complex-valued diffraction efficiencies can be constructed for such a marker. This improves the diffraction efficiency. Depend on Provided.

[0049] Measurement methods may also include generating radiation.

[0050] Generating radiation may include generating a laser beam having a first wavelength and converting at least a portion of the laser beam into multiple different radiation components. The conversion of at least a portion of the laser beam into multiple different radiation components can be achieved using higher harmonic generation.

[0051] The measurement method may also include: projecting radiation onto an object such that it is incident on a periodic target; measuring at least one diffraction beam; and determining one or more parameters based on at least one diffraction beam.

[0052] Because the radiation is projected onto the object, it is incident only on the periodic target (rather than on both the periodic target and the reference marker), thus allowing the diffraction efficiency of the periodic target to be determined in any known manner. Furthermore, this can help determine phase information related to a periodic target based on at least one interference pattern.

[0053] The measurement method may also include: projecting radiation onto the object such that it is incident on a reference mark; measuring at least one reference diffraction beam; and determining one or more parameters based on at least one reference diffraction beam.

[0054] Because the radiation is projected onto the object, it is incident only on the reference marker (rather than on both the periodic target and the reference marker), thus allowing the diffraction efficiency of the reference marker to be determined in any known manner. Furthermore, this can help determine phase information related to a periodic target based on at least one interference pattern.

[0055] In some embodiments, the periodic target may be adjacent to a second reference mark having a pitch equal to that of the periodic target and a fixed, non-zero spatial phase shift relative to the reference mark. For such embodiments, the method may further include: projecting radiation onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on the second reference mark; measuring at least one second interference pattern formed by the contributions of both the first and second portions of the radiation to a single diffraction order; and determining one or more parameters based on the at least one second interference pattern.

[0056] This is particularly advantageous because interference patterns typically consist of only a single dark fringe, and therefore, the information derived from measurements using only a periodic target and a reference marker may be insufficiently constrained and may not uniquely determine the phase of the contribution from the periodic target relative to the reference marker. However, by using a second reference marker with a different spatial phase relative to the reference marker for repeated measurements, it is possible to measure both the phase and amplitude of the fringes, even if only some fringes are visible.

[0057] The spatial phase shift of the second reference marker relative to the reference marker can be approximately 90°. Using this phase shift, the fringe pattern observed with the second reference marker (which may be referred to as the second fringe pattern) is shifted relative to the fringe pattern observed with the reference marker (which may be referred to as the first fringe pattern). Therefore, if a portion of the first pattern is dark (bright), the corresponding portion of the second pattern can be bright (dark). It is understood that the spatial phase shift of the second reference marker relative to the reference marker does not need to be precisely 90°.

[0058] The measurement method may also include: projecting radiation onto an object such that it is incident on a second reference mark; measuring at least one second reference diffraction beam; and determining one or more parameters based on at least one second reference diffraction beam.

[0059] The multiple reference markers may include simple patterns. For example, the multiple reference markers may include a square grating with a 50% duty cycle. The multiple reference markers may include a grating structure formed in a photoresist layer on a substrate.

[0060] The pitch of periodic targets (and (multiple) reference markers) can typically range from 20 nm to 2000 nm, for example, from 40 nm to 400 nm. Periodic targets can include one-dimensional (1D) patterns or two-dimensional (2D) patterns.

[0061] According to a second aspect of this disclosure, a measuring apparatus is provided for determining one or more parameters of a periodic target on an object, the measuring apparatus comprising: an illumination optics arranged to project a radiation beam onto the object; a detector array arranged to receive a portion of a radiation beam scattered from the object, the radiation beam including at least one diffracted beam; and a controller operable to determine one or more parameters based on an interference pattern formed in at least one of a plurality of diffracted beams.

[0062] The apparatus according to the second aspect of this disclosure can be used to perform the method according to the first aspect. Additionally or alternatively, the apparatus according to the second aspect of this disclosure can be used to perform the method according to the fifth aspect.

[0063] At least one reference mark may be disposed on the object adjacent to the periodic target. Each of the plurality of diffraction beams may include a first portion of radiation scattered from the periodic target and a second portion of radiation scattered from the reference mark.

[0064] Irradiation optics can be arranged to focus a radiation beam onto an object.

[0065] In other words, the object can be positioned at or near the waist of the radiation beam. In such an embodiment, the detector array can be positioned in the far field. Specifically, the detector array can be positioned outside the Rayleigh length of the radiation from the object.

[0066] The detector array can be arranged such that it can distinguish between an interference pattern formed by a periodic target and an adjacent reference pattern. As described above, such an interference pattern may include a single dark fringe. To distinguish this fringe, the detector array can be positioned such that at least three sensing elements (pixels) of the detector array span the full width at half maximum (FWHM) of the spot region corresponding to the diffraction order that forms the interference pattern.

[0067] The controller can be operated to perform any step of the method according to the first aspect of this disclosure.

[0068] The measuring device may also include a radiation source operable to generate a radiation beam.

[0069] The radiation source may include a seed source (e.g., a laser) operable to generate seed radiation having a first wavelength. The radiation source may include a conversion module arranged to convert at least a portion of the seed radiation into multiple different radiation components. The conversion of at least a portion of the seed radiation into multiple different radiation components can be achieved using higher harmonic generation.

[0070] In some embodiments, the radiation may include soft X-rays. It will be understood that the radiation includes sufficiently coherent radiation to produce at least one interference pattern.

[0071] The radiation beam can include radiation in the spectral range of 10 nm to 20 nm.

[0072] It is understood that radiation including radiation in the spectral range of 10 nm to 20 nm is intended to mean that the radiation includes at least one wavelength component (which may be monochromatic) in the spectral range of 10 nm to 20 nm. In some embodiments, the radiation includes radiation in the spectral range of 9 nm to 18 nm.

[0073] Radiation can include multiple discrete wavelength components.

[0074] The measuring device may also include a support for supporting the object, such that the object can be positioned so that the irradiation optics can project a radiation beam onto the object.

[0075] Supports for supporting substrates may include substrate holders operable to hold the substrate in place. For example, a support may include a clamp for holding the substrate to the support. A support may also include a stage, such as a wafer stage.

[0076] The measuring device may also include a moving mechanism operable to cause relative movement between the support and the illumination optics.

[0077] This allows an object or substrate to be stepped or scanned through a beam-spotted area of ​​an optics. As used herein, scanning of an object refers to the continuous movement of the object. As used herein, stepping of an object refers to the movement of the object in multiple successive (temporally separated) steps.

[0078] According to a third aspect of this disclosure, a computer-readable medium is provided having instructions for performing the method of a second aspect of this disclosure.

[0079] The computer-readable medium may be a non-transitory computer-readable medium. When executed by a computer system, the instructions may cause the computer system to perform any of the methods of the first aspect of this disclosure.

[0080] According to a fourth aspect of this disclosure, a measurement target for determining one or more parameters of a manufacturing process is provided, the measurement target comprising: a periodic target; a first reference mark adjacent to the periodic target and having a pitch equal to that of the periodic target; and a second reference mark adjacent to the periodic target and having a pitch equal to that of the periodic target, the second reference mark having a fixed, non-zero spatial phase shift relative to the reference mark.

[0081] The measurement target according to the fourth aspect of this disclosure may include any feature of the periodic target and / or the features of the reference mark and / or the second reference mark of the measurement method according to the first aspect of this disclosure.

[0082] In some embodiments, one or more patterns may be formed on an object in a process layer that spatially overlaps with a reference mark and / or a second reference mark, wherein one or more patterns have a pitch different from the pitch of the reference mark and the pitch of the second reference mark.

[0083] One or more patterns may be referred to as lower-level patterns (because they may be formed below a reference mark and / or a second reference mark).

[0084] According to a fifth aspect of this disclosure, a measurement method is provided for determining one or more parameters of a periodic target on an object, the method comprising: projecting radiation onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on a first adjacent region of the object to generate a plurality of diffraction orders of the periodic target from the first portion of the radiation, the first adjacent region of the object such that at least one diffraction order of the periodic target exists in a measurement plane, the at least one diffraction order not being boarded or overlapping with the radiation from the second portion of the radiation; and measuring a first intensity distribution of the at least one diffraction order of the periodic target in the measurement plane. Radiation is projected onto an object such that a third portion of the radiation is incident on a periodic target and a fourth portion of the radiation is incident on a second adjacent region of the object, to generate multiple diffraction orders of the periodic target from the third portion of the radiation, the second adjacent region of the object such that at least one diffraction order of the periodic target exists in the measurement plane that does not intersect or overlap with the radiation from the fourth portion of the radiation; a second intensity distribution of at least one diffraction order of the periodic target is measured in the measurement plane; and one or more parameters are determined based on both: (a) a first intensity distribution determined from a first portion of the radiation; and (b) a second intensity distribution determined from the third portion of the radiation.

[0085] As is now being discussed, the approach according to the fifth aspect is advantageous.

[0086] If the first and second adjacent regions of the object are patterned using a pattern having substantially the same pitch and orientation as the periodic target, they will produce a diffraction pattern similar to that of the periodic target (i.e., the two structures can produce diffraction patterns comprising diffracted beams scattered at substantially the same angle). Therefore, in the near field, each diffraction order of the periodic target can intersect and be adjacent to the corresponding diffraction order formed by one of the first and second adjacent regions. If radiation is focused onto the object (i.e., the object is positioned at or near the waist of the radiation beam), then in the far field, each diffraction order of the periodic target can at least partially overlap spatially with the corresponding diffraction order formed by one of the first and second adjacent regions.

[0087] In contrast, the first adjacent region of the object ensures that at least one diffraction order of a periodic target exists in the measurement plane, and that at least one diffraction order does not intersect or overlap with radiation from the second portion of the radiation. In the measurement plane, at least one diffraction beam acts as if a hard mask has been provided, blocking the second portion of the radiation from reaching the measurement plane. Similarly, the second adjacent region of the object ensures that at least one diffraction order of a periodic target exists in the measurement plane, and that at least one diffraction order of the periodic target does not intersect or overlap with radiation from the fourth portion of the radiation. In the measurement plane, at least one diffraction beam acts as if a hard mask has been provided, blocking the fourth portion of the radiation from reaching the measurement plane. That is, for at least these diffraction beams, the first and second adjacent regions of the object produce an effect equivalent to providing a hard mask that blocks the portion of the incident radiation.

[0088] Furthermore, this constraint implies that the phase distribution of the diffracted beam in the measurement plane is related to the amplitude distribution of the diffracted beam in the measurement plane via the Kramers-Kronig relation. Advantageously, this means that both the amplitude and phase of at least one diffraction order can be determined.

[0089] The intensity distribution of radiation in the measurement plane (e.g., measured using a camera) is related to the square of the radiation amplitude. Therefore, the amplitude can be determined from this intensity distribution. That is, a first amplitude distribution can be determined from a first intensity distribution, and a second amplitude distribution can be determined from a second intensity distribution. Using the Kramers-Kleinich relation, a first phase distribution can be determined from the first amplitude distribution, and a second phase distribution can be determined from the second amplitude distribution. Finally, the phase distribution of the entire diffraction beam can be determined from the first and second phase distributions.

[0090] In some embodiments, the first adjacent portion and / or the second adjacent portion may not have a pattern.

[0091] Such a part or area of ​​an object can be called a patternless area.

[0092] In practice, such unpatterned areas on a wafer can adversely affect chemical processing in patterned areas adjacent to them. Therefore, in some embodiments, the first adjacent portion and / or the second adjacent portion are not necessarily unpatterned, but may also include patterns (e.g., grating structures).

[0093] In some embodiments, the first adjacent portion and / or the second adjacent portion may include a pattern having a pitch and / or orientation different from that of the periodic target.

[0094] The pitch and / or orientation of the patterns in the first and second parts can be selected such that most diffraction orders from these patterns do not intersect or overlap with the diffraction orders of the periodic target.

[0095] Projecting radiation onto an object such that a first portion of the radiation is incident on a periodic target and a second portion of the radiation is incident on a first adjacent region of the object can be accomplished such that the first portion includes half of the radiation and the second portion includes half of the radiation.

[0096] Projecting radiation onto an object such that a third portion of the radiation is incident on a periodic target and a fourth portion of the radiation is incident on a second adjacent region of the object can be accomplished such that the third portion includes half of the radiation and the fourth portion includes half of the radiation.

[0097] In some embodiments of the measurement method, determining one or more parameters may include: determining a first amplitude distribution from a first intensity distribution; determining a second amplitude distribution from a second intensity distribution; determining a first phase distribution from the first amplitude distribution using the Kramers-Clernig relation; determining a second phase distribution from the second amplitude distribution using the Kramers-Clernig relation; and determining the phase distribution of the entire diffraction beam from the first phase distribution and the second phase distribution.

[0098] Radiation can include radiation in the spectral range of 10 nm to 20 nm.

[0099] It is understood that radiation including radiation in the spectral range of 10 nm to 20 nm is intended to mean that the radiation includes at least one wavelength component (which may be monochromatic) in the spectral range of 10 nm to 20 nm. In some embodiments, the radiation includes radiation in the spectral range of 9 nm to 18 nm.

[0100] Radiation can include multiple discrete wavelength components.

[0101] For example, the spectrum of radiation may include multiple discrete peaks, each of which can be referred to as a discrete wavelength component. This can be described as a comb structure (but it is understood that each peak may have a non-zero bandwidth). The radiation may include radiation in the spectral range of 10 nm–20 nm. The multiple discrete peaks (or wavelength components) may have a typical spacing of about 0.5 nm. The radiation may include about 20 such wavelength components. The bandwidth of each peak (discrete wavelength component) in the spectrum may be about 0.1 nm or less.

[0102] Measurement methods may include using at least one diffraction beam to determine one or more parameters for each of a plurality of discrete wavelength components.

[0103] Measurement methods may also include generating radiation.

[0104] Generating radiation may include generating a laser beam having a first wavelength and converting at least a portion of the laser beam into multiple different radiation components. This conversion of at least a portion of the laser beam into multiple different radiation components can be achieved using higher harmonic generation.

[0105] According to a sixth aspect of this disclosure, a computer-readable medium is provided having instructions for performing the method of the fifth aspect.

[0106] The computer-readable medium may be a non-transitory computer-readable medium. When executed by a computer system, the instructions may cause the computer system to perform any of the methods of the first aspect of this disclosure. Attached Figure Description

[0107] The embodiments will now be described by way of example only with reference to the accompanying schematic diagrams, in which:

[0108] Figure 1 A schematic overview of a lithography system, including a lithography apparatus and a radiation source, is provided.

[0109] Figure 2 A schematic overview of the photolithography unit is described;

[0110] Figure 3 A schematic representation of monolithography is depicted, which represents the collaboration between three key technologies to optimize semiconductor manufacturing;

[0111] Figure 4 The scattering device is illustrated schematically.

[0112] Figure 5 The diagram illustrates a transmission scattering device.

[0113] Figure 6 A schematic representation of a measurement device using EUV and / or SXR radiation is depicted;

[0114] Figure 7 A simplified schematic diagram of the irradiation source is depicted;

[0115] Figure 8 A novel measurement method for determining one or more parameters of a periodic target on an object is illustrated schematically according to an embodiment of the present disclosure;

[0116] Figure 9 An example of an object is illustrated schematically, with a periodic target defined on the object and a reference marker applied to it. The object can correspond to... Figure 6 The substrate shown, and the periodic target 2100 can correspond to Figure 6 The target shown;

[0117] Figure 10 The diagram schematically illustrates radiation being projected onto an object, such that a first portion of the radiation is incident on a periodic target and a second portion of the radiation is incident on a reference mark.

[0118] Figure 11A A portion of the diffraction pattern that can be produced in the far field by irradiating a periodic target with a radiation beam comprising six discrete wavelength components is schematically shown.

[0119] Figure 11B This schematically illustrates a radiation beam comprising six discrete wavelength components, such as... Figure 10 The portion of the diffraction pattern that can be produced in the far field when the first part of the radiation is incident on a periodic target and the second part of the radiation is incident on an adjacent reference mark with the same pitch is shown.

[0120] Figure 11C This schematically illustrates a radiation beam that includes continuous wavelength components, such as... Figure 10 The portion of the diffraction pattern that can be produced in the far field when the first part of the radiation is incident on a periodic target and the second part of the radiation is incident on an adjacent reference mark with the same pitch is shown.

[0121] Figure 12A For cases where the periodic target and the reference mark are in phase, Figure 11B The spot intensity of one of the diffraction beams shown is illustrated as a contour plot;

[0122] Figure 12B There is a relationship between the periodic target and the reference mark. The phase difference situation will Figure 11B The spot intensity of one of the diffraction beams shown is illustrated as a contour plot;

[0123] Figure 13A against (i.e., a 50:50 power ratio) For and The four different phase differences between them ( - - and The intensity is indicated by the separation direction in the far field;

[0124] Figure 13B against (i.e., a power ratio of 80:20) For and The four different phase differences between them ( - - and The intensity is indicated by the separation direction in the far field;

[0125] Figure 14 Another example of an object is schematically shown, in which a periodic target is defined on the object and a reference mark and a second reference mark have been applied to the object, the second reference mark having a fixed, non-zero spatial phase shift relative to the reference mark;

[0126] Figure 15 Another example of an object is illustrated schematically, in which a periodic target is defined on the object and a reference mark has been applied to the object, wherein the portion of the process layer surrounding or adjacent to the periodic target also includes the mark (e.g., a grating structure).

[0127] Figure 16 This is a schematic diagram of a new measuring device for determining one or more parameters of a periodic target on an object, according to embodiments of the present disclosure;

[0128] Figure 17 This schematically illustrates another novel measurement method for determining one or more parameters of a periodic target on an object, according to an embodiment of the present disclosure;

[0129] Figure 18 This is a partial plan view of the substrate, showing: periodic targets, a first adjacent region of the substrate, a second adjacent region of the substrate, and... Figure 17 The locations of the beam spot regions at two different steps of the method are schematically shown in the diagram; and

[0130] Figure 19 It schematically shows that in Figure 17 The diagram illustrates the final step of the method, which consists of several sub-steps. Detailed Implementation

[0131] Before describing the embodiments of the present invention in detail, it is beneficial to present example environments in which the embodiments of the present invention can be implemented.

[0132] Figure 1 A lithography system is shown, comprising a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and supply the EUV radiation beam B to the lithography apparatus LA. The lithography apparatus LA includes an irradiation system IL, a support structure MT configured to support a patterning apparatus MA (e.g., a mask), a projection system PS, and a substrate stage WT configured to support a substrate W.

[0133] The irradiation system IL is configured to modulate the EUV radiation beam B before it is incident on the patterning apparatus MA. For this purpose, the irradiation system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. Together, the faceted field mirror device 10 and the faceted pupil mirror device 11 provide the EUV radiation beam B with the desired cross-sectional shape and the desired intensity distribution. In addition to the faceted field mirror device 10 and the faceted pupil mirror device 11, the irradiation system IL may also include other mirrors or devices, or replace the faceted field mirror device 10 and the faceted pupil mirror device 11.

[0134] After being adjusted in this way, the EUV radiation beam B interacts with the patterning apparatus MA. Due to this interaction, a patterned EUV radiation beam B' is generated. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. For this purpose, the projection system PS may include a plurality of mirrors 13, 14, which are configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate surface WT. The projection system PS can apply a reduction factor to the patterned EUV radiation beam B', thus forming an image with features that can be smaller than the corresponding features on the patterning apparatus MA. For example, a reduction factor of 4 or 8 can be applied. Although the projection system PS... Figure 1 The diagram shows only two reflectors 13 and 14, but the projection system PS can include a different number of reflectors (e.g., six or eight).

[0135] The substrate W may include a previously formed pattern. In this case, the photolithography apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the pattern previously formed on the substrate W.

[0136] A relative vacuum, i.e., a small amount of gas (e.g., hydrogen) at a pressure far below atmospheric pressure, can be provided in a radiation source SO, an irradiation system IL, and / or a projection system PS.

[0137] Figure 1The radiation source SO shown is, for example, of the type that can be referred to as a laser-generated plasma (LPP) source. A laser system 1 (which may include, for example, a CO2 laser) is arranged to deposit energy via a laser beam 2 onto a fuel such as tin (Sn) supplied by, for example, a fuel emitter 3. Although tin is mentioned in the following description, any suitable fuel can be used. The fuel may be, for example, in liquid form and may be, for example, a metal or alloy. The fuel emitter 3 may include a nozzle configured to guide tin, for example, in the form of microdroplets, along a trajectory toward the plasma-forming region 4. The laser beam 2 is incident on the tin at the plasma-forming region 4. The deposition of laser energy into the tin creates a tin plasma 7 at the plasma-forming region 4. During the de-excitation and recombination of electrons and ions in the plasma, radiation, including EUV radiation, is emitted from the plasma 7.

[0138] EUV radiation from the plasma is collected and focused by collector 5. Collector 5 includes, for example, a near-normal incident radiation collector 5 (sometimes more generally referred to as a normal incident radiation collector). Collector 5 may have a multi-layered mirror structure arranged to reflect EUV radiation (e.g., EUV radiation with a desired wavelength such as 13.5 nm). Collector 5 may have an elliptical configuration with two foci. The first foci may be located at plasma formation region 4, and the second foci may be located at intermediate foci 6, as discussed below.

[0139] Laser system 1 can be spatially separated from radiation source SO. In this case, laser beam 2 can be delivered from laser system 1 to radiation source SO by means of a beam delivery system (not shown), which includes, for example, suitable guiding mirrors and / or beam expanders and / or other optical devices. Laser system 1, radiation source SO, and beam delivery system can be considered together as a radiation system.

[0140] The radiation reflected by collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused at intermediate focus 6 to form an image of the plasma present in plasma formation region 4. The image at intermediate focus 6 acts as a virtual radiation source for the irradiation system IL. The radiation source SO is arranged such that intermediate focus 6 is located at or near opening 8 in the outer casing structure 9 of the radiation source SO.

[0141] although Figure 1 The radiation source SO is described as a laser-generated plasma (LPP) source, but any suitable source (such as a discharge-generated plasma (DPP) source, a high-harmonic generation (HHG) source, or a free-electron laser (FEL)) can be used to generate EUV radiation.

[0142] like Figure 2 As shown, the lithography apparatus LA can form part of the lithography unit LC, sometimes referred to as a lithography pool or (lithography) cluster. It typically also includes apparatus for performing pre-exposure and post-exposure processes on the substrate W. Conventionally, the apparatus includes a spin coater SC to deposit a resist layer, a developer DE to develop the exposed resist, a chiller CH, and a baking plate BK, for example, to regulate the temperature of the substrate W, or to regulate the solvent in the resist layer. A substrate processor or robot RO picks up the substrate W from input / output ports I / O1, I / O2, moves the substrate between different process units, and delivers the substrate W to the feed stage LB of the lithography apparatus LA. The equipment in the lithography pool, often collectively referred to as a track, is under the control of a track control unit TCU. The track control unit TCU itself can be controlled by a supervisory control system SCS, which can also control the lithography apparatus LA, for example, via a lithography control unit LACU.

[0143] In photolithography, frequent measurements of the created structure are desirable, for example, for process control and verification. The tools used to perform these measurements are called metrology tools (MTs). Different types of metrology tools (MTs) for such measurements are known, including scanning electron microscopes (SEMs) or various forms of scatterometer metrology tools (MTs). A scatterometer is a versatile instrument that allows measurement of photolithography parameters by placing a sensor in or near the pupil of the scatterometer's objective lens; this measurement is typically referred to as pupil-based measurement. Alternatively, photolithography parameters can be measured by placing the sensor in or near the image plane; in this case, the measurement is typically referred to as image- or field-based measurement. Such scattering instruments and associated measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, which are incorporated herein by reference in their entirety. The aforementioned scattering instruments can measure gratings using light from hard X-rays (HXR), soft X-rays (SXR), extreme ultraviolet (EUV), visible to near-infrared (IR), and the IR wavelength range. In the case of hard or soft X-ray radiation, the aforementioned scattering instrument may optionally be a small-angle X-ray scattering measurement tool.

[0144] To ensure correct and consistent exposure of the substrate W in the lithography apparatus LA, it is desirable to inspect the substrate to measure properties of the patterned structure, such as overlay accuracy errors between subsequent layers, line thickness, critical dimension (CD), and structural shape. For this purpose, inspection tools and / or measurement tools (not shown) may be included in the lithography pool LC. If errors are detected, particularly if the inspection is performed before other substrates W in the same batch or batch still need to be exposed or processed, adjustments can be made, for example, to the exposure of subsequent substrates or other processing steps to be performed on the substrate W.

[0145] An inspection apparatus, also known as a measurement apparatus, is used to determine the properties of a substrate W, and specifically to determine how the properties of different substrates W vary or how the properties associated with different layers of the same substrate W vary layer by layer. The inspection apparatus may alternatively be configured to identify defects on the substrate W and may be, for example, part of a photolithography cell (LC), or integrated into a photolithography apparatus (LA), or even a stand-alone device. The inspection apparatus can measure properties on latent images (images in the resist layer after exposure), or semi-latent images (images in the resist layer after a post-exposure baking (PEB) step), or developed resist images (where exposed or unexposed portions of the resist have been removed), or even etched images (after a pattern transfer step such as etching).

[0146] In the first embodiment, the scatterer MT is an angle-resolved scatterer. In such a scatterer, a reconstruction method can be applied to the measured signal to reconstruct or calculate the properties of the grating. Such reconstruction can, for example, be produced by simulating the interaction between the scattered radiation and a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0147] In the second embodiment, the scatterer MT is a spectroscopic scatterer MT. In such a spectroscopic scatterer MT, radiation emitted by a radiation source is directed onto a target, and radiation reflected, transmitted, or scattered from the target is directed to a spectroscopic detector, which measures the spectrum of the specularly reflected radiation (i.e., the intensity based on wavelength). Based on this data, the structure or profile of the target that generates the detected spectrum can be reconstructed, for example, through rigorous coupled-wave analysis and nonlinear regression, or by comparison with a simulated spectral library.

[0148] In the third embodiment, the scatterer MT is an elliptically polarized scatterer. An elliptically polarized scatterer allows for the determination of lithography process parameters by measuring the scattered or transmitted radiation for each polarization state. Such a measurement device emits polarized light (such as linear, circular, or elliptical) by, for example, using an appropriate polarization filter in the illumination section of the measurement device. A source suitable for the measurement device can also provide polarized radiation. Various embodiments of existing elliptically polarized scatterers are described in U.S. Patent Applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110, and 13 / 891,410, which are incorporated herein by reference in their entirety.

[0149] In one embodiment of the scattering instrument MT, the scattering instrument MT is adapted to measure the overlay accuracy of two misaligned gratings or periodic structures by measuring the reflectance spectrum and / or the asymmetry in the detection configuration, the asymmetry being related to the degree of overlay accuracy. Two (potentially overlapping) grating structures can be applied in two different layers (not necessarily consecutive layers) and can be formed substantially at the same location on the wafer. The scattering instrument can have a symmetrical detection configuration, for example, described in the co-owned patent application EP1,628,164A, such that any asymmetry can be clearly distinguished. This provides a simple method for measuring grating misalignment. Other examples of overlay accuracy errors between two layers of a periodic structure, when the target is measured by means of the asymmetry of the periodic structure, can be found in PCT patent application publication no. WO2011 / 012624 or U.S. patent application US 20160161863, both of which are incorporated herein by reference in their entirety.

[0150] Other parameters of interest may be focus and dose. As described in U.S. Patent Application US2011-0249244, focus and dose can be determined simultaneously by scattering measurements (or optionally by scanning electron microscopy), which is incorporated herein by reference in its entirety. A single structure can be used, having a unique combination of critical size and sidewall angle measurements for each point in the focus energy matrix (FEM, also known as the focus exposure matrix). If these unique combinations of critical size and sidewall angles are available, the focus and dose values ​​can be uniquely determined from these measurements.

[0151] The measurement target can be an assembly of composite gratings formed by photolithography, primarily in a resist, but can also be formed after other manufacturing processes (e.g., etching). The pitch and linewidth of the structures in the gratings may be strongly dependent on the measurement optics (particularly the NA of the optics) to capture the diffraction order from the measurement target. As previously mentioned, the diffraction signal can be used to determine the offset between two layers (also known as "overlay accuracy"), or it can be used to reconstruct at least a portion of the original grating produced by the photolithography process. This reconstruction can be used to provide guidance on the quality of the photolithography process and can be used to control at least a portion of the photolithography process. The target can have small sub-segments configured to mimic the dimensions of functional portions of the design layout in the target. Due to this sub-segmentation, the target's behavior will be more similar to the functional portions of the design layout, making the overall process parameter measurements closer to the functional portions of the design layout. The target can be measured in underfill or overfill modes. In underfill mode, the measurement beam generates a spot smaller than the overall target. In overfill mode, the measurement beam generates a spot larger than the overall target. In such overfill mode, different targets can also be measured simultaneously, thus determining different processing parameters simultaneously.

[0152] The overall measurement quality of a lithography parameter for a specific target is at least partially determined by the measurement scheme used to measure that lithography parameter. The term "substrate measurement scheme" can include one or more parameters of the measurement itself, one or more parameters of one or more patterns being measured, or both. For example, if the measurement used in the substrate measurement scheme is a diffraction-based optical measurement, the one or more parameters measured can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. One criterion for selecting a measurement scheme can be, for example, the sensitivity of one of the measurement parameters to handling variations. Further examples are described in U.S. Patent Application US2016-0161863 and published U.S. Patent Application US2016 / 0370717A1, both of which are incorporated herein by reference in their entirety.

[0153] The patterning process in photolithography (LA) is arguably one of the most critical steps in the process, requiring high-precision dimensional adjustments and placement of the structure on the substrate W. To ensure this high precision, three systems can be combined in a manner such as... Figure 3The diagram illustrates a so-called "holistic" control environment. One of these systems is a lithography apparatus (LA), which is (virtually) connected to a metrology tool (MT) (a second system) and a computer system (CL) (a third system). The key to such a "holistic" environment is optimizing the collaboration between these three systems to enhance the overall process window and provide a tight control loop, thereby ensuring that the patterning performed by the lithography apparatus (LA) remains within the process window. The process window defines a range of process parameters (e.g., dose, focus, overlay accuracy) within which a specific manufacturing process produces a defined result (e.g., a functional semiconductor device). This range of process parameters allows for variations in process parameters during either the lithography or patterning process.

[0154] Computer systems can use a portion of the design layout to be patterned to predict which resolution enhancement techniques will be used and perform computational lithography simulations and calculations to determine which mask layout and lithography setup will achieve the maximum overall process window for the patterning process (e.g., ...). Figure 3 (Depicted by the double arrows at the first scale SC1). Resolution enhancement techniques can be arranged to match the patterning possibilities of the lithography apparatus LA. The computer system CL can also be used to detect the current position of the lithography apparatus LA within the process window (e.g., using input from the metrology tool MET) to predict whether defects exist due to, for example, suboptimal processing (such as...). Figure 3 (Depicted by the arrow pointing to "0" in the second scale SC2).

[0155] The measurement tool MT can provide input to the computer system CL to enable accurate simulation and prediction, and can provide feedback to the lithography apparatus LA to, for example, identify possible drifts in the calibration state of the lithography apparatus LA (e.g., Figure 3 (Depicted by multiple heavy arrows at the third scale SC3).

[0156] Many different types of measurement tools (MTs) can be provided for measuring structures created using photolithographic patterning apparatuses. Measurement tools (MTs) can probe structures using electromagnetic radiation. The properties of the radiation (e.g., wavelength, bandwidth, power) can affect different measurement characteristics of the tool, with shorter wavelengths generally allowing for higher resolution. The radiation wavelength affects the resolution achievable by the measurement tool. Therefore, measurement tools (MTs) with short-wavelength radiation sources are preferred for measuring structures with small-sized features.

[0157] Another way radiation wavelength can affect measurement characteristics is through-penetration depth and the transparency / opacity of the material being inspected at that wavelength. Depending on opacity and / or through-penetration depth, radiation can be used for measurements in either transmission or reflection. The type of measurement can affect whether information relating to the surface and / or interior of the structure / substrate is obtained. Therefore, through-penetration depth and opacity are another factor to consider when selecting a radiation wavelength for a measurement tool.

[0158] To achieve high-resolution measurements of photolithographically patterned structures, measurement tools (MTs) with short wavelengths are preferred. This can include wavelengths shorter than visible wavelengths, such as those in the UV, EUV, and X-ray portions of the electromagnetic spectrum. Hard X-ray methods, such as transmission small-angle X-ray scattering (TSAXS), utilize the high resolution and high penetration depth of hard X-rays and can therefore operate in transmission. On the other hand, soft X-rays and EUV do not penetrate as far as the target, but can induce rich optical responses in the material being probed. This is likely due to the optical properties of many semiconductor materials, and because the structure is sized to match the probe wavelength. As a result, EUV and / or soft X-ray measurement tools (MTs) can operate in reflection, for example, by imaging or by analyzing the diffraction patterns from the photolithographically patterned structure.

[0159] For hard X-rays, soft X-rays, and EUV radiation, their application in high-volume manufacturing (HVM) applications may be limited due to the lack of available high-brightness sources at the required wavelengths. In the case of hard X-rays, commonly used sources in industrial applications include X-ray tubes. X-ray tubes include advanced X-ray tubes based on liquid metal anodes or rotating anodes. X-ray tubes may be relatively inexpensive and compact, but may lack the brightness required for HVM applications. High-brightness X-ray sources exist, such as synchrotron light sources (SLS) and X-ray free-electron lasers (XFELs), but their size (>100 meters) and high cost (hundreds of millions of euros) make them too large and expensive for metrology applications. Similarly, sufficiently bright EUV and soft X-ray radiation sources are also unavailable.

[0160] Figure 4 An example of a measurement device, such as a scatterer, is depicted. It may include a broadband (e.g., white light) radiation projector 2 that projects radiation 5 onto a substrate W. The reflected or scattered radiation 10 is transmitted to a spectrometer detector 4, which measures the spectrum 6 of the specularly reflected radiation (i.e., the intensity I according to wavelength λ). Based on this data, the structure or profile 8 of the detected spectrum can be generated by a processing unit PU, for example, through rigorous coupled-wave analysis and nonlinear regression, or through methods such as... Figure 4The bottom of the image shows a comparison with a simulated spectral library for reconstruction. Typically, for reconstruction, the overall form of the structure is known, and some parameters are assumed based on knowledge of the structure's manufacturing process, allowing only a small number of parameters to be determined using scattering measurement data. Such a scatterometer can be configured as a normal-incident scatterometer or an oblique-incident scatterometer.

[0161] Figure 5 The text describes measuring devices (such as...) Figure 4 The example shown is a transmission version of the scatterer. The transmitted radiation 11 is passed to the spectrometer detector 4, which measures the radiation as follows: Figure 4 The spectrum discussed is 6. Such a scatterer can be configured as a normal-incident scatterer or an oblique-incident scatterer. Optionally, the transmission version uses hard X-ray radiation with wavelengths of <1 nm, optionally <0.1 nm, and optionally <0.01 nm.

[0162] As alternatives to optical measurement methods, the use of hard X-rays, soft X-rays, or EUV radiation, such as radiation having at least one of the following wavelength ranges: <0.01 nm, <0.1 nm, <1 nm, between 0.01 nm and 100 nm, between 0.01 nm and 50 nm, between 1 nm and 50 nm, between 1 nm and 20 nm, between 5 nm and 20 nm, and between 10 nm and 20 nm. An example of a measurement instrument operating within one of the wavelength ranges given above is transmitted small-angle X-ray scattering (T-SAXS, 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 “Intercomparison between optical and X-ray scatterometry measurements of FinFET structures”, Proc. of SPIE, 2013, 8681. Note that the use of laser-generated plasma (LPP) X-ray sources is described in U.S. Patent Publication No. 2019 / 003988A1 and U.S. Patent Publication No. 2019 / 215940A1, which are incorporated herein by reference in their entirety. Reflectance measurement techniques using grazing incidence X-rays (GI-XRS) and extreme ultraviolet (EUV) radiation can be used to measure the properties of films and layer stacks on substrates. Within the general field of reflectance measurement, goniometric and / or spectroscopic techniques can be applied. In goniometrics, variations in reflected beams at different incident angles can be measured. On the other hand, spectroscopic reflectance measurement measures the spectrum of wavelengths reflected at a given angle (using broadband radiation). For example, EUV reflectance measurement has been used to inspect mask blanks before fabricating masks (patterning apparatus) for use in EUV lithography.

[0163] The scope of application may render the use of wavelengths in, for example, the hard X-ray, soft X-ray, or EUV domains insufficient. Published patent applications US 20130304424A1 and US 2014019097A1 (Bakeman et al / KLA) describe hybrid metrology techniques in which measurements using X-rays are combined with optical measurements utilizing wavelengths in the 120 nm to 2000 nm range to obtain measurements of parameters such as CD. CD measurements are obtained by coupling X-ray mathematical models and optical mathematical models through one or more common models. The contents of the cited US patent applications are incorporated herein by reference in their entirety.

[0164] Figure 6 A schematic representation of the measuring device 302 is depicted, wherein the aforementioned radiation can be used to measure parameters of a structure on a substrate. Figure 6 The measurement device 302 presented herein can be applied to the hard X-ray, soft X-ray and / or EUV domains.

[0165] Figure 6 The illustration shows a schematic physical arrangement of the measurement device 302, which includes a spectroradiometer. By way of example only, the spectroradiometer uses optional grazing-incidence hard X-rays, soft X-rays, and / or EUV radiation. Alternatively, the inspection device can be provided as an angle-resolved scatterometer, which can use radiation with normal or near-normal incidence similar to conventional scatterometers operating at longer wavelengths, and can also use radiation starting from a direction parallel to the substrate with a direction greater than 1° or 2°. Another alternative inspection device can be provided as a transmission scatterometer. Figure 5 The configuration in the document is applied to alternative forms of inspection devices.

[0166] The inspection device 302 includes a radiation source or so-called irradiation source 310, an irradiation system 312, a substrate support 316, detection systems 318 and 398, and a measurement processing unit (MPU) 320.

[0167] In this example, the irradiation source 310 is used to generate EUV, hard X-ray, or soft X-ray radiation. The irradiation source 310 can be based on, for example... Figure 6 The high harmonic generation (HHG) technology shown can also be other types of irradiation sources, such as liquid metal jet sources, inverse Compton scattering (ICS) sources, plasma channel sources, magnetic wave generator sources, free electron laser (FEL) sources, compact storage ring sources, discharge-generated plasma sources, soft X-ray laser sources, rotating anode sources, solid anode sources, particle accelerator sources, microfocus sources, or laser-generated plasma sources.

[0168] HHG sources and other types of sources can have a gas target and can be a gas jet / nozzle source, capillary / fiber source, or gas chamber source. HHG sources and other types of sources can also have a solid or liquid target. Although the following text describes an HHG source with a gas target, it should be understood that the invention is not limited to HHG sources with a gas target and can also be used in HHG sources with solid or liquid targets, as well as in other types of sources with any target. The gas target, solid target, and liquid target can be referred to as the generation / target medium.

[0169] For example, HHG source, such as Figure 6As shown, the main components of the radiation source are a pump radiation source 330 operable to emit pump radiation and a gas delivery system 332. Optionally, the pump radiation source 330 is a laser, and optionally, it is a pulsed high-power infrared or optical laser. The pump radiation source 330 can be, for example, a fiber-based laser with an optical amplifier, generating infrared radiation pulses with a duration of less than 1 ns (1 nanosecond) per pulse, as needed, wherein the pulse repetition rate is up to several megahertz. The wavelength of the infrared radiation can be in the range of 200 nm to 10 µm, for example, in the region of 1 μm (1 micrometer). Optionally, the laser pulse is delivered to the gas delivery system 332 as a first pump radiation 340, wherein a portion of the radiation is converted into emitted radiation 342 at a frequency higher than the first radiation. A gas supply device 334 supplies a suitable gas to the gas delivery system 332, wherein the gas is optionally ionized by a power source 336. The gas delivery system 332 can be a cutting tube.

[0170] The gas provided by the gas delivery system 332 defines a gas target, which can be a gas flow or a static volume. The gas can be, for example, air, neon (Ne), helium (He), nitrogen (N2), oxygen (O2), argon (Ar), krypton (Kr), xenon (Xe), carbon dioxide, and combinations thereof. These can be optional options within the same apparatus. The emitted radiation can contain multiple wavelengths. If the emitted radiation is monochromatic, measurement calculations (e.g., reconstruction) can be simplified, but it is easier to generate radiation with several wavelengths. The emission divergence angle of the emitted radiation may be wavelength-dependent. Different wavelengths can, for example, provide different levels of contrast when imaging structures of different materials. For the inspection of metallic or silicon structures, for example, different wavelengths can be selected for imaging the characteristics of (carbon-based) resists or for detecting contamination in such different materials. One or more filtering devices 344 can be provided. For example, a thin-film filter such as aluminum (Al) or zirconium (Zr) can be used to prevent the fundamental IR radiation from further propagating into the inspection apparatus. A grating (not shown) may be provided to select one or more specific wavelengths from the generated wavelengths. Optionally, the irradiation source includes a space configured to be emptied, and a gas delivery system is configured to provide a gaseous target within the space. Optionally, part or all of the beam path may be contained within a vacuum environment to account for absorption of SXR and / or EUV radiation as it travels in air. The various components of the radiation source 310 and the irradiation optics 312 may be adjusted to achieve different measurement “schemes” within the same apparatus. For example, different wavelengths and / or polarizations may be optional.

[0171] Depending on the material of the structure being inspected, different wavelengths can provide the desired level of penetration into the underlying layers. Shorter wavelengths may be preferred for distinguishing defects between minimum device features and minimum device features. For example, one or more wavelengths in the range of 0.01 nm to 20 nm, or optionally one or more wavelengths in the range of 1 nm to 10 nm, or optionally 10 nm to 20 nm, can be selected. Wavelengths shorter than 5 nm may suffer very low critical angles when reflected from the material of interest in semiconductor manufacturing. Therefore, selecting wavelengths greater than 5 nm can provide a stronger signal at higher incident angles. On the other hand, if the inspection task is to detect the presence of specific materials, such as contamination, wavelengths up to 50 nm may be useful.

[0172] From radiation source 310, a filtered beam 342 can enter inspection chamber 350, in which a substrate W, including the structure of interest, is held in a measurement position by substrate support 316 for inspection. The structure of interest is designated T. Optionally, the atmosphere within inspection chamber 350 can be maintained near vacuum by vacuum pump 352, allowing SXR and / or EUV radiation to pass through the atmosphere without excessive attenuation. As described in the published U.S. patent application US2017 / 0184981A1 (the contents of which are incorporated herein by reference in their entirety), irradiation system 312 has the function of focusing radiation into a focused beam 356 and may include, for example, two-dimensional curved mirrors or a series of one-dimensional curved mirrors. Focusing is performed to achieve a circular or elliptical spot S with a diameter less than 10 μm when projected onto the structure of interest. Substrate support 316 includes, for example, an XY translation platform and a rotation platform, any portion of the substrate W can be moved to the focal point of the beam in a desired orientation by means of the XY translation platform and the rotation platform. Therefore, the radiation spot S is formed on the structure of interest. Alternatively or additionally, the substrate support 316 includes, for example, a tilting platform that can tilt the substrate W at a specific angle to control the incident angle of the focused beam on the structure of interest T.

[0173] Optionally, the illumination system 312 provides a reference radiation beam to a reference detector 314, which can be configured to measure the spectrum and / or intensity of different wavelengths in the filtered beam 342. The reference detector 314 can be configured to generate a signal 315, which is provided to the processor 320, and the filter can include information related to the spectrum of the filtered beam 342 and / or the intensity of different wavelengths in the filtered beam.

[0174] The reflected radiation 360 is captured by detector 318, and the spectrum is provided to processor 320 for calculating the properties of the target structure T. The irradiation system 312 and detection system 318 thus form an inspection apparatus. This inspection apparatus may include hard X-ray, soft X-ray, and / or EUV spectroreflectometers of the type described in US2016282282A1, the contents of which are incorporated herein by reference in their entirety.

[0175] If the target T has a specific periodicity, the radiation from the focused beam 356 can also be partially diffracted. The diffracted radiation 397 follows another path at a defined angle relative to the angle of incidence, and then relative to the reflected radiation 360. Figure 6 In the diagram, the diffraction radiation 397 is drawn schematically, and the diffraction radiation 397 may follow many other paths besides the drawn path. The inspection device 302 may also include an additional detection system 398 that detects and / or images at least a portion of the diffraction radiation 397. Figure 6 A single additional detection system 398 is depicted in the diagram, but embodiments of the inspection apparatus 302 may also include more than one additional detection system 398 arranged at different locations to detect and / or image the diffracted radiation 397 at multiple diffraction directions. In other words, the (higher) diffraction order of the focused radiation beam striking the target T can be detected and / or imaged by one or more additional detection systems 398. One or more detection systems 398 generate a signal 399, which is provided to the measurement processor 320. The signal 399 may include information about the diffracted light 397 and / or may include an image obtained from the diffracted light 397.

[0176] To assist in aligning and focusing the spot S with the desired product structure, the inspection apparatus 302 may also provide auxiliary optics that utilize auxiliary radiation under the control of the measurement processor 320. The measurement processor 320 may also communicate with a position controller 372, which operates a translation platform, a rotation platform, and / or a tilting platform. The processor 320 receives high-precision feedback regarding the position and orientation of the substrate via a sensor 374. The sensor 374 may include an interferometer, for example, one capable of providing accuracy in the picometer range. During the operation of the inspection apparatus 302, spectral data 382 captured by the detection system 318 is delivered to the measurement processing unit 320.

[0177] As previously described, alternative forms of inspection apparatus may use hard X-rays, soft X-rays, and / or EUV radiation at normal or near-normal incidence, for example, to perform diffraction-based asymmetry measurements. Another alternative form of inspection apparatus uses hard X-rays, soft X-rays, and / or EUV radiation at an angle greater than 1° or 2° from the direction parallel to the substrate. Both types of inspection apparatus can be provided in a hybrid metrology system. The performance parameters to be measured may include overlay accuracy (OVL), critical dimension (CD), the focal point of the lithography apparatus when printing the target structure, coherent diffraction imaging (CDI), and resolution overlay accuracy (ARO) measurements. Hard X-rays, soft X-rays, and / or EUV radiation may, for example, have wavelengths less than 100 nm, such as radiation in the 5 nm–30 nm range, or optionally radiation in the 10 nm–20 nm range. The radiation may have narrow-band or broadband characteristics. The radiation may have discrete peaks in a specific wavelength band, or it may have more continuous characteristics.

[0178] Similar to optical scattering instruments used in modern manufacturing facilities, inspection device 302 can be used to measure structures within resist materials treated in a photolithography bath (after development inspection or ADI), and / or to measure structures after they have been formed in a harder material (after etching inspection or AEI). For example, substrates can be inspected using inspection device 302 after they have been treated by development, etching, annealing, and / or other means.

[0179] Measurement instruments (MTs), including but not limited to the aforementioned scatterers, can perform measurements using radiation from a radiation source. The radiation used by the measurement instrument MT can be electromagnetic radiation. The radiation can be optical radiation, such as radiation in the infrared, visible, and / or ultraviolet portions of the electromagnetic spectrum. The measurement instrument MT can use radiation to measure or inspect the properties and aspects of a substrate, such as a photolithographically exposed pattern on a semiconductor substrate. The type and quality of the measurement may depend on several properties of the radiation used by the measurement instrument MT. For example, the resolution of an electromagnetic measurement may depend on the wavelength of the radiation; for example, smaller wavelengths can measure smaller features due to diffraction limits. To measure features with small dimensions, it may be preferable to use short-wavelength radiation, such as EUV, hard X-rays (HXR), and / or soft X-rays (SXR). To perform measurements at a specific wavelength or wavelength range, the measurement instrument MT needs access to a source that provides radiation at that wavelength / these wavelengths. Different types of sources exist to provide radiation at different wavelengths. Depending on the wavelength(s) provided by the source(s), different types of radiation generation methods can be used. For extreme ultraviolet (EUV) radiation (e.g., 1 nm to 100 nm) and / or soft X-ray (SXR) radiation (e.g., 0.1 nm to 10 nm), the source can be HHG or any other type of source mentioned above to obtain radiation at (multiple) desired wavelengths.

[0180] Figure 7 A simplified schematic diagram of embodiment 600 of the irradiation source 310 is shown. The irradiation source 310 can be an irradiation source for HHG. Relative to Figure 6 One or more features of the irradiation source in the described measurement tool may also be present in the irradiation source 600 as needed. The irradiation source 600 includes a chamber 601 and is configured to receive pump radiation 611 having a propagation direction indicated by the arrow. (As...) Figure 6 As shown, the pump radiation 611 illustrated here is an example of pump radiation 340 from pump radiation source 330. Pump radiation 611 can be directed into chamber 601 via radiation input 605, which can be a viewport and optionally made of fused silica or a similar material. Pump radiation 611 can have a Gaussian or hollow cross-sectional profile, such as an annular transverse cross-sectional profile, and can be incident (optionally focused) onto a gas flow 615 within chamber 601, the gas flow 615 having a flow direction indicated by a second arrow. Gas flow 615 comprises a small volume of a specific gas (e.g., air, neon (Ne), helium (He), nitrogen (N2), oxygen (O2), argon (Ar), krypton (Kr), xenon (Xe), carbon dioxide, and combinations thereof) with a gas pressure above a certain value, the small volume referred to as a gas volume or gas target (e.g., several square millimeters). Gas flow 615 can be a steady-state flow. Other media, such as metallic plasma (e.g., aluminum plasma), can also be used.

[0181] The gas delivery system of the irradiation source 600 is configured to provide a gas flow 615. The irradiation source 600 is configured to provide pump radiation 611 in the gas flow 615 to drive the generation of emitted radiation 613. The region in which at least most of the emitted radiation 613 is generated is referred to as the interaction region. The interaction region can range from tens of micrometers (for compact focused pump radiation) to several millimeters or centimeters (for medium focused pump radiation), or even up to several meters (for extremely loosely focused pump radiation). The gas delivery system is configured to provide a gas target for generating emitted radiation at the interaction region of the gas target, and optionally, the irradiation source is configured to receive pump radiation and provide pump radiation at the interaction region. Optionally, the gas flow 615 is provided by the gas delivery system to a vented or nearly vented space. The gas delivery system may include, for example, Figure 6 The gas nozzle 609 shown includes an opening 617 in its outlet plane. A gas flow 615 is supplied from the opening 617. A gas trap is used to confine the gas flow 615 within a specific volume by extracting residual gas flow and maintaining a vacuum or near-vacuum environment within the chamber 601. Optionally, the gas nozzle 609 may be made of a thick-walled tube and / or a material with high thermal conductivity to avoid thermal deformation caused by high-power pump radiation 611.

[0182] The size of the gas nozzle 609 can also be used in scaled-up or scaled-down versions, ranging from micrometer-level nozzles to meter-level nozzles. This wide range of sizes stems from the fact that the setup can be scaled to ensure that the intensity of the pump radiation at the gas flow is within a specific range that is beneficial for emitted radiation. This requires different size designs for different pump radiation energies, which can be pulsed lasers and the pulse energy can vary from tens of microjoules to joules. Optionally, the gas nozzle 609 has a thicker wall to reduce nozzle deformation due to thermal expansion effects, which can be detected, for example, by a camera. A gas nozzle with a thicker wall can produce a stable gas volume with reduced deformation. Optionally, the irradiation source includes a gas trap located near the gas nozzle to maintain the pressure in chamber 601.

[0183] Due to the interaction between the pump radiation 611 and the gas atoms of the gas flow 615, the gas flow 615 can convert a portion of the pump radiation 611 into emitted radiation 613, which can be... Figure 6The example shown is the emitted radiation 342. The central axis of the emitted radiation 613 may be collinear with the central axis of the incident pump radiation 611. The emitted radiation 613 may have a wavelength in the X-ray or EUV range, wherein the wavelength is in the range of 0.01 nm to 100 nm, optionally in the range of 0.1 nm to 100 nm, optionally in the range of 1 nm to 100 nm, optionally in the range of 1 nm to 50 nm, or optionally in the range of 10 nm to 20 nm.

[0184] In operation, the emitted radiation beam 613 can be transmitted through radiation output 607 and can subsequently be manipulated and guided by irradiation system 603 to the substrate to be inspected for measurement purposes. Irradiation system 603 can be... Figure 6 An example of the irradiation system 312. The emitted radiation 613 can be guided, and optionally focused, onto the structure on the substrate.

[0185] Because air (and virtually any gas) heavily absorbs SXR or EUV radiation, the volume between the gas flow 615 and the wafer to be inspected can be emptied or nearly emptied. Since the central axis of the emitted radiation 613 can be collinear with the central axis of the incident pump radiation 611, the pump radiation 611 may need to be blocked to prevent it from passing through the radiation output 607 and entering the irradiation system 603. This can be achieved by... Figure 6 The filtering device 344 shown is incorporated into the radiation output 607. The filtering device 344 is positioned in the path of the emitted beam and is opaque or nearly opaque to the pump radiation (e.g., opaque or nearly opaque to infrared or visible light), but at least partially transparent to the emitted radiation beam. The filter can be fabricated using zirconium or a combination of materials in multiple layers. When the pump radiation 611 has a hollow, optional annular cross-sectional profile, the filter can be a hollow, optional annular block. Optionally, the filter is neither perpendicular nor parallel to the propagation direction of the emitted radiation beam to achieve efficient pump radiation filtering. Optionally, the filtering device 344 includes a hollow block and a thin-film filter, such as an aluminum (Al) or zirconium (Zr) film filter. Optionally, the filtering device 344 may also include a mirror that efficiently reflects the emitted radiation but poorly reflects the pump radiation, or a mesh that efficiently transmits the emitted radiation but poorly transmits the pump radiation.

[0186] This document describes methods, apparatus, and components for optionally obtaining emitted radiation at the high harmonic frequencies of the pump radiation. Radiation generated by a process, optionally using nonlinear effects to generate the high harmonic frequency (HHG) of the radiation at the harmonic frequencies 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., few cycles), the generated radiation is not necessarily exactly at the harmonics of the pump radiation frequency. The substrate can be a photolithographically patterned substrate. The radiation obtained by the process can also be provided in a photolithography apparatus (LA) and / or a photolithography cell (LC). The pump radiation can be pulsed radiation, which can provide high peak intensity within a short burst.

[0187] Pump radiation 611 may include radiation having one or more wavelengths higher than one or more wavelengths of emitted radiation. Pump radiation may include infrared radiation. Pump radiation may include radiation having multiple wavelengths in the range of 500 nm to 1500 nm. Pump radiation may include radiation having multiple wavelengths in the range of 800 nm to 1300 nm. Pump radiation may include radiation having multiple wavelengths in the range of 900 nm to 1300 nm. Pump radiation may be pulsed radiation. Pulsed pump radiation may include pulses having a duration in the femtosecond range.

[0188] In some embodiments, the emitted radiation, optionally higher harmonic radiation, may include one or more harmonics of the pump radiation wavelength(s). The emitted radiation may include wavelengths in the extreme ultraviolet, soft X-ray, and / or hard X-ray portions of the electromagnetic spectrum. The emitted radiation 613 may include wavelengths in one or more of the following ranges: less than 1 nm, less than 0.1 nm, less than 0.01 nm, 0.01 nm to 100 nm, 0.1 nm to 100 nm, 0.1 nm to 50 nm, 1 nm to 50 nm, and 10 nm to 20 nm.

[0189] Radiation, such as the aforementioned higher harmonic radiation, can be provided as source radiation in a metrology tool (MT). The metrology tool (MT) can use this source radiation to perform measurements on a substrate exposed by a photolithography apparatus. The measurements can be used to determine one or more parameters of the structure on the substrate. Using radiation at shorter wavelengths, such as EUV, SXR, and / or HXR wavelengths included in the aforementioned wavelength range, allows the metrology tool to resolve smaller features of the structure compared to using longer wavelengths (e.g., visible radiation, infrared radiation). Radiation with shorter wavelengths, such as EUV, SXR, and / or HXR radiation, can also penetrate deeper into materials such as patterned substrates, meaning that measurements of deeper layers on the substrate are possible. These deeper layers may not be reachable by radiation with longer wavelengths.

[0190] In a metrology tool (MT), source radiation can be emitted from a radiation source and directed onto a target structure (or other structure) on a substrate. Source radiation can include EUV, SXR, and / or HXR radiation. The target structure can reflect, transmit, and / or diffract the source radiation incident on it. The metrology tool (MT) can include one or more sensors for detecting diffracted radiation. For example, the metrology tool (MT) can include detectors for detecting the positive (+1) and negative (-1) first diffraction orders. The metrology tool (MT) can also measure specular reflection or transmitted radiation (0th-order diffraction). Other sensors for measurement can be present in the metrology tool (MT), for example, to measure other diffraction orders (e.g., higher diffraction orders).

[0191] In example photolithography applications, the radiation generated by HHG can be focused onto a target on a substrate using an optical column, which can be referred to as an irradiator, to transfer radiation from the HHG source to the target. The HHG radiation can then be reflected from the target, detected, and processed, for example, to measure and / or infer the properties of the target.

[0192] Gas target HHG configurations can be broadly classified into three separate categories: gas jet, gas pool, and gas capillary. Figure 7 An example gas jet configuration is depicted, in which a gas volume is introduced into the driving radiation laser beam. In the gas jet configuration, the interaction between the driving radiation and the solid component is kept to a minimum. The gas volume may, for example, comprise a gas flow perpendicular to the driving radiation beam, wherein the gas volume is surrounded within a gas pool. In a gas capillary arrangement, the dimensions of the capillary structure holding the gas are small in the transverse direction, such that it significantly affects the propagation of the driving radiation laser beam. The capillary structure may, for example, be a hollow fiber, wherein the hollow portion is configured to hold the gas.

[0193] Gas-jet HHG configurations offer relative freedom in shaping the spatial profile of the driving radiation beam in the far field, as they are not constrained by the gas capillary structure. Gas-jet configurations may also have less stringent alignment tolerances. On the other hand, the gas capillary can provide an increased interaction zone between the driving radiation and the gaseous medium, which can optimize the HHG process.

[0194] For example, in measurement applications, HHG radiation is separated from the driving radiation downstream of the gas target. The separation of the HHG from the driving radiation can differ for gas jet and gas capillary configurations. In both cases, driving radiation suppression schemes can include metallic transmission filters to filter out any remaining driving radiation from the short-wavelength radiation. However, before such a filter can be used, the intensity of the driving radiation should be significantly reduced from its intensity at the gas target to avoid damaging the filter. Methods for this intensity reduction can differ for gas jet and capillary configurations. For gas jet HHGs, due to the relative degrees of freedom in the shape and spatial profile (which may also be referred to as spatial distribution and / or spatial frequency) of the driving radiation beam focused onto the gas target, the relative degrees of freedom can be designed such that, in the far field, the driving radiation beam has low intensity along the direction of propagation of the short-wavelength radiation. This spatial separation in the far field means that the aperture can be used to block the driving radiation and reduce its intensity.

[0195] Conversely, in gas capillary structures, the spatial profile of the beam as it propagates through the gaseous medium is likely largely determined by the capillary. The spatial profile of the driving radiation can be determined by the shape and material of the capillary structure. For example, when hollow fibers are used as the capillary structure, the shape and material of the fiber structure determine which modes of the driving radiation are supported for propagation through the fiber. For most standard fibers, the supported propagation modes result in a spatial profile where the high intensity of the driving radiation overlaps with the high intensity of the HHG radiation. For example, the driving radiation intensity can be centered in the far field with a Gaussian or near-Gaussian profile.

[0196] Although HHG is specifically referenced, it will be understood that the invention can be practiced using any radiation source where the context permits. In one embodiment, the radiation source is a laser-generated plasma (LPP) source as described above, used for generating hard X-rays, soft X-rays, EUV, DUV, and visible light irradiation. In one embodiment, the radiation source is one of a liquid metal jet source, an inverse Compton scattering (ICS) source, a plasma channel source, a magnetic wave generator source, a free electron laser (FEL) source, a compact reservoir ring source, a discharge-generated plasma source, a rotating anode source, a solid anode source, a particle accelerator source, and a microfocus source.

[0197] As an alternative to the scattering instrument, the measurement device may include a holographic microscope, such as a digital holographic microscope (DHM) or a digital dark-field holographic microscope. Such devices are disclosed, for example, in US2019 / 0107781 and WO2021121733A1, both of which are incorporated herein by reference.

[0198] In scattering measurement tools, light can be used to create an image of a structure on a substrate (e.g., at one or both of the image plane and the pupil plane). Such tools can measure the intensity or amplitude of the detected light, for example, after it has been scattered by the structure (or related measurement parameters, such as diffraction efficiency), and use this intensity or amplitude to determine one or more parameters of interest related to the structure. In many cases, knowing the complex field (i.e., amplitude and phase) of the light scattered by the structure can be beneficial.

[0199] Several current methods exist that, in addition to measuring intensity / amplitude, enable the determination of phase. One such technique is the aforementioned DHM; however, holographic methods typically suffer from stringent stability requirements and / or very low acquisition times to suppress mechanical vibrations and / or drift, and thus require the necessary interference between the scattered radiation and the reference radiation at the detector.

[0200] Another known method involves performing multiple measurements under various conditions (e.g., different focal length levels) and using iterative algorithms to reconstruct the complex field of the scattered light (e.g., as described in WO2021 / 121733, which is incorporated herein by reference). However, such methods are computationally very demanding / expensive and can therefore be slow, particularly since the accuracy of the retrieved phase is required in metrology than in more conventional phase retrieval applications (such as microscopes where only image formation is required). Other techniques are also known, such as using masks with pinholes or similar apertures in the detection branch of the tool, which allow for interferometric measurements (e.g., as described in WO2020 / 254041, which is incorporated herein by reference).

[0201] Some embodiments of this disclosure relate to novel measurement methods for determining one or more parameters of a periodic target on an object. Example embodiments of such novel measurement methods 1000 are described below. Figure 8 It is shown schematically in the middle.

[0202] The new measurement method 1000 is used to determine one or more parameters of a periodic target on an object, the periodic target being adjacent to a reference mark having a pitch equal to that of the periodic target.

[0203] The new measurement method 1000 includes step 1100: projecting radiation onto an object such that a first portion of the radiation is incident on a periodic target and a second portion of the radiation is incident on a reference mark.

[0204] The new measurement method 1000 also includes step 1200: measuring at least one interference pattern formed by the contributions of both the first and second portions of radiation to a single diffraction order.

[0205] The new measurement method 1000 also includes step 1300: determining one or more parameters based on at least one interference pattern.

[0206] One or more parameters (in) Figure 8 The step 1300 of the method 1000 shown may include any of the following: critical dimension (CD), overlay accuracy (i.e., the amount by which two or more process layers are misaligned) and / or the thickness of one or more process layers.

[0207] Figure 9 An example of object 2000 is schematically shown, with periodic target 2100 defined on object 2000 and reference mark 2200 applied to object 2000. Object 2000 may correspond to Figure 6 The substrate W shown. Periodic target 2100 can correspond to... Figure 6 The target T is shown in the figure. In this example, object 2000 includes substrate 2300, on which one or more process layers 2310, 2320 have been formed. Each of the process layers 2310, 2320 includes periodic patterns 2312, 2322, each of which forms a portion of the periodic target 2100.

[0208] As used herein, the terms “mark” and “target” are synonymous and are intended to refer to a pattern formed on object 2000 that can be irradiated by radiation to cause radiation scattering or diffraction. Such objects are generally planar, meaning they have two dimensions (often referred to herein as the x-direction and y-direction) that are significantly larger than their third dimension (often referred to herein as the z-direction). As used herein, the terms “mark” and “target” are intended to refer to a pattern formed on object 2000 that is defined in the plane of the object (i.e., the region defined by the x-direction and y-direction). It is understood that such object 2000 has some non-zero thickness and can typically include multiple different layers. One or more of such layers can define a pattern (e.g., a periodic pattern). For example, one or more of such layers can define a diffraction grating structure, etc. In general, if two such patterns formed in different layers are set at substantially the same location in the xy-plane, they can contribute to the same mark or target (when radiation is incident on that region of the xy-plane, it can see the combination of patterns and can scatter from that combination). Therefore, in general, each mark or target on an object consists of multiple patterns formed in multiple different process layers.

[0209] Reference mark 2200 may include a simple pattern. For example, reference mark 2200 may include a square grating with a 50% duty cycle. Reference mark 2200 may include a grating structure formed in a photoresist layer 2400 on substrate 2300. In this embodiment, the grating structure is formed in the photoresist layer 2400 on substrate 2300: (a) above periodic patterns 2312, 2322 formed in process layers 2310, 2320, the periodic patterns 2312, 2322 forming portions of periodic targets 2100; (b) adjacent to these periodic patterns 2312, 2322. The portions of the grating structure formed in photoresist layer 2400 over the periodic patterns 2312, 2322 formed in process layers 2310, 2320 also form portions of periodic targets 2100.

[0210] The pitch of the periodic target 2100 (and reference mark 2200) can typically be in the range of 20 nm to 2000 nm, for example, in the range of 40 nm to 400 nm. The periodic target 2100 may include a one-dimensional (1D) pattern or a two-dimensional (2D) pattern.

[0211] Figure 10 The diagram schematically illustrates radiation 2500 projected onto object 2000, such that a first portion of the radiation is incident on a periodic target 2100 and a second portion is incident on a reference mark 2200 (e.g., at step 1100 of the new method 1000). Specifically, the radiation beam 2500 is focused onto object 2000. That is, object 2000 can be positioned at or near the waist of the radiation beam 2500. In such an embodiment, at least one interference pattern can be measured in the far field (at step 1300 of the new method 1000). Specifically, at least one interference pattern can be measured at a location not within the Rayleigh length of the radiation 2500.

[0212] like Figure 10 As shown, the first portion 2510 of radiation 2500 is incident on the periodic target 2100, and the second portion 2520 of radiation 2500 is incident on the reference mark 2200.

[0213] For ease of understanding, Figure 10 Only a single diffraction beam (with diffraction angle) is shown. It is understandable that, generally speaking, multiple diffraction beams can be generated using a periodic target 2100 and a reference marker 2200.

[0214] As is being discussed now, such as Figure 8The method 1000 shown is advantageous. Since the reference mark 2200 has a pitch equal to that of the periodic target 2100, the two structures can produce diffraction patterns comprising diffracted beams scattered at substantially the same angle. Therefore, as... Figure 10 As schematically shown, in the far field, each diffraction beam from the periodic target 2100 can generally overlap spatially with its corresponding diffraction beam from the reference marker 2200. The pair of corresponding diffraction beams from the periodic target 2100 and the reference marker 2200 can be collectively referred to as an interference beam. Furthermore, in the far field, each interference beam in the interference beam can be spatially separated (at a sufficient distance from the object 2000).

[0215] Figure 8 The method shown can be considered an interferometric method that utilizes at least one pair of interfering beams (within each interfering beam). Based on the interference pattern and the profile of the radiation 2500 projected onto the object 2000, the phase difference between the contributions from the reference mark 2200 and the periodic target 2100 can be determined. If the structure of the reference mark 2200 is known, the phase of the contribution from the reference mark 2200 to each diffraction beam can be determined. Furthermore, the phase of the contribution from the periodic target 2100 to each diffraction beam can thus be determined.

[0216] Figure 8 The method shown can be applied to metrology tools used to inspect silicon wafers W during the fabrication of integrated circuits using photolithography. Specifically, the method can be applied to metrology devices (e.g., as described above) designed to determine overlay accuracy (a measure of the alignment of two or more sequentially formed photolithographic layers). Figure 6 In the type of measuring device 302 shown.

[0217] Some such metrological tools use soft X-ray (SXR) measurements, irradiating a periodic target on a wafer with radiation (e.g., including multiple discrete wavelength components) in a spectral range of approximately 10 nm–20 nm. The diffraction pattern is captured and analyzed spectrally. Various methods exist to extract these parameters from the scattering data. For example, the target response spectrum can be obtained by measuring the diffraction efficiency. The form is captured, in which , It is a discrete integer diffraction order, and It is the wavelength. The data acquired in this way includes information related to parameters of interest, such as overlay accuracy and critical dimensions.

[0218] However, using such known techniques, only the intensity of the diffracted light is captured.

[0219] In comparison, Figure 8The method 1000 shown allows for the measurement of the phase of diffracted radiation, which also contains useful information. Furthermore, it provides a relatively simple and cost-effective method for determining such phase information. For example, a known method for determining the phase response of a target would be using techniques such as digital holographic microscopy (DHM). However, several problems exist when applying such techniques with soft X-rays. First, it would require a beam splitter for soft X-rays, which is difficult. Second, it would require two beam paths stabilized on the interference to a path length difference of <<10 nm, which would be very expensive. Third, the fringe pattern on the image sensor would have a period of <100 nm, which would require an image sensor with impractically small pixels to resolve the fringes.

[0220] At least one interference pattern can be measured using any suitable detector array or camera.

[0221] In some embodiments, the radiation (used at step 1100) may include soft X-rays. It will be understood that the radiation includes sufficiently coherent radiation to produce at least one interference pattern.

[0222] In some embodiments, the radiation (used at step 1100) may include radiation in the spectral range of 10 nm to 20 nm.

[0223] In some embodiments, the radiation (used at step 1100) may include multiple discrete wavelength components. For example, the spectrum of the radiation may include multiple discrete peaks, each of which may be referred to as a discrete wavelength component. This may be referred to as a comb structure (but it is understood that each peak will have a non-zero bandwidth). The radiation may include radiation in the spectral range of 10 nm to 20 nm. The multiple discrete peaks (or wavelength components) may have a typical spacing of about 0.5 nm. The radiation may include about 20 such wavelength components. The bandwidth of each peak (discrete wavelength component) of the spectrum may be about 0.1 nm or less.

[0224] In some embodiments, radiation (used at step 1100) may be generated by the methods described above and... Figure 7 The type of irradiation source 600 shown is used to generate it.

[0225] In some embodiments, step 1300 of determining one or more parameters based on at least one interference pattern may include: for each at least one interference pattern, determining the relative phase of the contributions of a first portion and a second portion of the radiation to the diffracted beam.

[0226] In some embodiments, step 1300 of determining one or more parameters based on at least one interference pattern may include: as now combined Figures 11A to 13BThe discussion focuses on determining the position of each interference pattern, for each at least one interference pattern.

[0227] Figure 11A A portion of a diffraction pattern 3000 can be schematically shown in the far field produced by illuminating a periodic target with a radiation beam comprising six discrete wavelength components. (As shown) Figure 11A As shown, the diffraction pattern 3000 includes a 0th-order diffraction beam 3100 (containing radiation from all six wavelength components) and six 1st-order diffraction beams 3200, 3202, 3204, 3206, 3208, and 3210 (each corresponding to a different wavelength component among the six wavelength components).

[0228] It is understandable that, generally speaking, many more diffraction orders can exist in such a diffraction pattern 3000. For example, there can be +1st order diffraction beams and -1st order diffraction beams. In addition, there can be higher order diffraction beams (±2nd order, ±3rd order, etc.). Furthermore, it will be understood that, generally speaking, the radiation beam can include different numbers (in addition to six) of discrete wavelength components. Figure 11A The example presented here is a simple one showing only two diffraction beams and six wavelength components for ease of understanding.

[0229] Figure 11B This schematically illustrates when... Figure 10 As shown, a radiation beam comprising six discrete wavelength components is projected such that a portion of a diffraction pattern 3300 can be produced in the far field when a first portion of the radiation is incident on a periodic target and a second portion of the radiation is incident on an adjacent reference mark having the same pitch.

[0230] Because the reference marker has a pitch equal to that of the periodic target, the two structures can produce diffraction patterns comprising diffraction beams scattered at substantially the same angle. Specifically, as... Figure 11B As shown, the diffraction pattern 3300 includes a 0th-order diffraction beam 3400 (containing radiation from all six wavelength components) and six 1st-order diffraction beams 3500, 3502, 3504, 3506, 3508, and 3510 (each corresponding to a different wavelength component among the six wavelength components). Figure 10 As schematically shown, in the far field, each diffraction beam from the periodic target 2100 can generally overlap spatially with its corresponding diffraction beam from the reference marker 2200. The pair of corresponding diffraction beams from the periodic target 2100 and the reference marker 2200 can be collectively referred to as an interference beam. Furthermore, in the far field, each interference beam within the interference beam can be spatially separated (at a sufficient distance from the object 2000). For example, the 0th-order diffraction beam 3400 is spatially separated from the 1st-order diffraction beams 3500, 3502, 3504, 3506, 3508, and 3510.

[0231] Furthermore, in this embodiment, since the radiation beam includes discrete wavelength components, such as Figure 11B As shown, in the far field (at a sufficient distance of 2000 from the object), each of the six first-order diffraction beams 3500, 3502, 3504, 3506, 3508, and 3510 (each corresponding to a different wavelength component among the six wavelength components) is spatially separated. However, this may not be the case in other embodiments, as described below relative to... Figure 11C This will be discussed separately.

[0232] Despite Figure 11B Not shown in the diagram, but due to the phase difference between the contributions from the periodic target and the reference marker, the 0th order diffraction beam 3400 can change shape (relative to) Figure 11A The 0th order diffraction beam 3100 is shown in the figure. However, since each wavelength component can generally cause different shape changes, the net effect is likely that the 0th order diffraction beam 3400 can be slightly elongated along the x-direction.

[0233] Each interference pattern is formed by the contributions of both the first and second portions of the radiation to a single diffraction order. Each diffraction beam can illuminate a spot region (e.g., circular, elliptical, or elongated region) on the detector in the far field. Each such spot region can correspond to the projection of the beam spot region (of the radiation projected onto the object) onto the detector.

[0234] In each such spot region, if the contributions from the first and second portions of the radiation are in phase, the intensity distribution in the spot region can generally match the intensity distribution of the radiation projected onto the object (e.g., a Gaussian beam distribution). Figure 11B The first-order diffraction beam 3500 shown in the diagram is an example of this.

[0235] However, the inventors have realized that if the contributions from the first and second portions of the radiation are out of phase, dark fringes may appear in the intensity distribution in the spot region in the direction corresponding to the separation direction between the periodic target 2100 and the reference mark 2200 (see first-order diffraction beams 3502-3510). For example, if the radiation projected onto the object has a Gaussian profile, one would expect the intensity distribution in the spot region in the direction corresponding to the separation direction between the periodic target 2100 and the reference mark 2200 to have two independent peaks separated by dark fringes.

[0236] For example, if periodic targets and reference markers are set at substantially the same y position but different x positions on an object (such as in...) Figure 10 (as illustrated in the diagram), then the two peaks can be separated on the detector in the direction corresponding to the x-direction (e.g., in...). Figure 11B (As shown in the figure). By determining the position (in the separation direction) and / or relative intensity of the peaks of the interference pattern within the spot region, the relative phase of the contributions of the first and second portions of radiation to the diffracted beam can be inferred or determined.

[0237] Consider a single diffraction order and a single wavelength Single diffraction order and single wavelength The incident light is separated in the x-direction (and is set at essentially the same y-position on the object, i.e., as in...). Figure 10 (Schematic illustration) On the periodic target 2100 and reference marker 2200. For this diffraction order, the periodic target and reference marker each have well-defined complex diffraction efficiencies. and (As defined at the reference point). The combined pattern is illuminated by focusing a Gaussian beam, which has an electric field amplitude. ,in x , y These are the coordinate axes in the plane of the wafer, with the origin at the reference point. Far-field amplitude. Then it can be obtained through Fourier transform: in Value or This depends on the location. Does it correspond to a periodic target or a reference marker? Fourier domain coordinates. , It is related to the diffraction angle (relative to the principal ray for that diffraction order), and is roughly as follows:

[0238] Figure 12A For cases where the periodic target and the reference marker are in phase, the spot intensity will be... It is shown as a contour map, and Figure 12B There is a phase difference between the periodic target and the reference mark. The situation will affect the intensity of the spots. This is shown as a contour map. (As shown from...) Figure 12B As can be seen, the phase difference between the periodic target and the reference mark causes a shift in the maximum value and the appearance of dark fringes within the diffraction order.

[0239] according to The intensity value (i.e., in the far field) x It can depend on and The ratio of phase difference and diffraction efficiency between them This is in Figure 13A and Figure 13B The image is shown in the middle. Figure 13A against (i.e., a 50:50 power ratio) For and Four different phase differences ( - , - -0 and ),according to The intensity is shown (i.e., in the far field). Figure 13B against (i.e., a power ratio of 80:20) For and Four different phase differences ( - , - -0 and ),according to The intensity is shown (i.e., in the far field).

[0240] For the beam focus split across the periodic target and reference mark, the fringe direction is ( ) for each wavelength component. Figure 11B The intensity profile in the y-direction (of the vector) can be obtained. Each such intensity profile can be... Figure 13A and Figure 13B The intensity profile shown is in form. Typically, if it can be observed as... Figure 13A and Figure 13B The phase difference and diffraction efficiency ratio can both be inferred from the line shape. Furthermore, the total diffraction energy (and...) The proportionate phase difference (proportional) can be inferred from the area under the curve. Therefore, by fitting the line shape, the phase difference between the periodic target and the reference marker can be determined for each intensity profile. Power ratio and total spectral diffraction intensity (In W / nm) can be inferred.

[0241] To understand the absolute phase and amplitude response of the reference marker (i.e., the complex-valued response), In the case of ), the phase of the target response It can be inferred that:

[0242] If the incident spectral intensity for the wavelength component Given that the target's diffraction efficiency is given by any of the following equations:

[0243] Equation (4) is likely preferred because it is for It performs well in terms of numerical values.

[0244] It is understandable that the above analysis ( Figures 11A to 13B (The discussion) is based on Gaussian beams. In practice, beams can be non-Gaussian and / or may have wavefront aberrations (such as astigmatism), and the intensity profile in the far field may differ from that of a pure Gaussian beam. Furthermore, in practice, the incident beam focus may not have a 50 / 50 energy split across the periodic target and reference markers. However, if the beam shape is known, a fitted shape can still be obtained for non-Gaussian beams to obtain the phase difference. and diffraction efficiency ratio The above method applies. The power split ratio (50 / 50 or other) can be used based on prior knowledge or can be included as a fitting parameter when the online shape is fitted.

[0245] As described above, in some embodiments, determining one or more parameters from at least one interference pattern (at step 1300) may include: (a) fitting a desired distribution to an intensity distribution in the spot region corresponding to the diffraction beam in a direction corresponding to the separation direction of the periodic target and the reference mark; and (b) determining one or more parameters of the periodic target from one or more parameters of the desired distribution.

[0246] Generally speaking, the desired distribution can depend on the spatial intensity profile of the radiation projected onto the object.

[0247] For embodiments in which the radiation includes multiple wavelength components, Figure 8 The method 1000 shown may include: measuring at least one interference pattern for each of a plurality of discrete wavelength components, each interference pattern being formed by contributions from both a first portion and a second portion of radiation to a single diffraction order for a single discrete wavelength component; and determining one or more parameters from the at least one interference pattern for each of the plurality of discrete wavelength components. Advantageously, this allows the phase response to be determined according to the wavelength.

[0248] Figure 11C This schematically illustrates when... Figure 10 As shown, a portion of a diffraction pattern 3600 can be produced in the far field when a radiation beam including continuous wavelength components is projected such that a first portion of the radiation is incident on a periodic target and a second portion of the radiation is incident on adjacent reference marks having the same pitch.

[0249] Because the reference marker has a pitch equal to that of the periodic target, the two structures can produce diffraction patterns comprising diffraction beams scattered at substantially the same angle. Specifically, as... Figure 11C As shown, the diffraction pattern 3600 includes a 0th-order diffraction beam 3700 (containing radiation from all six wavelength components) and a 1st-order diffraction beam 3800. Figure 11B In the embodiment shown, in the far field, each interference beam in the interference beam is spatially separated (at a sufficient distance of 2000 from the object). For example, the 0th order diffraction beam 3700 is spatially separated from the 1st order diffraction beam 3800.

[0250] In this embodiment, since the radiation beam includes continuous wavelength components, such as Figure 11C As shown, in the far field, first-order diffraction beams from different wavelengths at least partially overlap to produce a single first-order diffraction beam 380°. (As in...) Figure 11C As schematically illustrated, if the contributions from the first and second portions of the radiation are out of phase, a dark fringe 3802 may appear in the intensity distribution of the single first-order diffraction beam 3800. This is significant for the shear directions of the periodic target 2100 and the reference mark 2200 (i.e., Figure 11C At any given location (in the y-direction), the dark fringe 3802 separates into two parts, which are in the direction corresponding to the separation direction of the periodic target 2100 and the reference mark 2200 (i.e., Figure 11C The dark fringe is separated in the x-direction. Furthermore, the position of this dark fringe in the separation direction (x-direction) may typically be at a different location corresponding to the shear direction of the periodic target 2100 and the reference mark 2200 (i.e., in...). Figure 11C (In the y-direction) changes.

[0251] In some embodiments, Figure 8 The method shown may include: measuring multiple interference patterns, each of which is formed by the contributions of both a first portion and a second portion of the radiation to different diffraction orders; and determining one or more parameters from the multiple interference patterns.

[0252] For a 1D pattern, the shearing direction of the periodic target 2100 and the reference mark 2200 can be defined as a direction substantially perpendicular to the lines of the pattern.

[0253] In some embodiments, the shear direction of each of the periodic target 2100 and the reference mark 2200 is perpendicular to the separation direction between the periodic target 2100 and the reference mark 2200. Such an arrangement is advantageous if the radiation projected onto the object comprises multiple wavelength components. For diffraction orders higher than 0th order, different wavelength components can be present in the far field along the shear direction (e.g., Figure 11BSeparation occurs in the y-direction of the radiation, but the two peaks formed by the out-of-phase first and second parts of the radiation can occur in the separation direction (e.g., in the y-direction). Figure 11B The separation occurs along the x-direction. Therefore, if the shear direction and the separation direction are perpendicular to each other, the relative phase of the first and second parts of the radiation can be more easily determined.

[0254] Alternatively, in some other embodiments, the shearing direction of the periodic target 2100 and the shearing direction of the reference mark 2200 may be parallel to the separation direction of the periodic target and the reference mark.

[0255] In some embodiments, the separation direction of the periodic target 2100 and the reference mark 2200 lies in the incident plane of the radiation 2500 (e.g., in...). Figure 10 (As shown in the diagram). The shear directions of the periodic target 2100 and the reference mark 2200 can be parallel to this separation direction. Using such an embodiment, for a typical diffraction order, an optical path difference may exist between the first and second portions of the radiation, and the radiation can have a coherence length greater than this optical path difference. Specifically, for the incident angle... and diffraction radiation angle coherence length It can satisfy: in It is the diffraction order. It is the pitch of a periodic target and It's the wavelength. Coherence length. It can refer to the coherence length of a single peak in a comb spectrum, i.e., ,in It is the bandwidth of the single peak.

[0256] Alternatively, in some embodiments, the separation direction of the periodic target 2100 and the reference mark 2200 may be perpendicular to the incident plane of the radiation. Such embodiments may allow for a shorter coherence length of the radiation.

[0257] Determining one or more parameters based on at least one interference pattern can be achieved in several ways. First, raw data can be determined, which includes one or more images of the interference pattern from the detector. Second, one or more parameters can be determined or inferred from the raw data in one of several different ways. As mentioned above, one or more parameters may include information related to the phase of the contribution of the first portion 2510 of radiation (which is incident on the periodic target 2100) to the (multiple) diffraction beams.

[0258] In some embodiments, step 1300 of determining one or more parameters may include using a trained machine learning model. In some embodiments, method 1000 may also include training the machine learning model using training data. For example, multiple different known calibration targets (such as one or more parameters, such as phase information, which are known to the calibration targets) may be used to generate raw data. The machine learning model can be trained using this raw data along with the known parameters.

[0259] In some embodiments, step 1300 of determining one or more parameters may include, for each at least one interference pattern: determining the phase response of the contribution from the reference mark 2200 to the interference pattern using a model-based reconstruction of the reference mark 2200; and combining the determined phase response with the interference pattern to determine the phase response of the contribution from the periodic target 2100 to the interference pattern. A simple resist grating (which can be used as a reference mark) has very few unknown parameters. In principle, complex-valued diffraction efficiencies can be constructed for such marks. This improves the diffraction efficiency. Depend on Given. For such an embodiment of model-based reconstruction using reference marker 2200, method 1000 may further include: projecting radiation onto the object such that it is incident only on the periodic target 2100, as further described below.

[0260] In some embodiments, method 1000 may further include generating radiation 2500 (e.g., using the above description and...). Figure 7 Irradiation source 600 of the type shown. Generating radiation 2500 may include generating a laser beam having a first wavelength and converting at least a portion of the laser beam into multiple different radiation components. The conversion of at least a portion of the laser beam into multiple different radiation components can be achieved using higher harmonic generation.

[0261] In some embodiments, method 1000 may further include: projecting radiation onto an object such that it is incident on a periodic target 2100; measuring at least one diffraction beam; and determining one or more parameters based on the at least one diffraction beam. This allows the diffraction efficiency of the periodic target 2100 to be determined in any known manner. Furthermore, this can help determine phase information related to the periodic target 2100 based on at least one interference pattern.

[0262] In some embodiments, method 1000 may further include: projecting radiation onto an object such that it is incident on a reference marker 2200; measuring at least one reference diffraction beam; and determining one or more parameters based on the at least one reference diffraction beam. This allows the diffraction efficiency of the reference marker to be determined in any known manner. Furthermore, this can help determine phase information related to a periodic target based on at least one interference pattern.

[0263] like Figure 14 As shown, in some embodiments, the periodic target 2100 is adjacent to the second reference mark 2600, the second reference mark 2600 has a pitch equal to that of the periodic target 2100, and the second reference mark 2600 has a fixed, non-zero spatial phase shift relative to the reference mark 2200.

[0264] In such an embodiment, method 1000 may further include: projecting radiation onto an object such that a first portion of the radiation is incident on a periodic target 2100 and a second portion of the radiation is incident on a second reference mark 2600; measuring at least one second interference pattern formed by the contributions of both the first and second portions of the radiation to a single diffraction order; and determining one or more parameters based on the at least one second interference pattern.

[0265] This is particularly advantageous because interference patterns typically consist of only a single dark fringe, and therefore, the information derived from measurements using only the periodic target 2100 and the reference marker 2200 may be insufficiently constrained and may not uniquely determine the phase of the contribution from the periodic target 2100 to the reference marker 2200. However, by repeating measurements using a second reference marker 2600 with a different spatial phase to the reference marker 2200, both the phase and amplitude of the fringes can be measured, even if only some fringes are visible.

[0266] The spatial phase shift 2700 of the second reference mark 2600 relative to the reference mark 2200 can be approximately 90°. Using this phase shift, the fringe pattern observed when using the second reference mark 2600 (which may be referred to as the second fringe pattern) is shifted relative to the fringe pattern observed when using the reference mark 2200 (which may be referred to as the first fringe pattern). Therefore, if a portion of the first pattern is dark (bright), the corresponding portion of the second pattern can be bright (dark). It is understood that the spatial phase shift of the second reference mark relative to the reference mark does not need to be precisely 90°.

[0267] In such an embodiment, method 1000 may further include: projecting radiation onto an object such that it is incident on a second reference mark 2600; measuring at least one second reference diffraction beam; and determining one or more parameters based on at least one second reference diffraction beam.

[0268] In the embodiments described above, the periodic target 2100 includes periodic patterns 2312, 2322 formed in process layers 2310, 2320, wherein the portions of these process layers 2310, 2320 below the reference mark 2200 are unpatterned (referred to herein as unpatterned regions). Thus, the reference mark 2200 is entirely defined by a grating structure formed in a photoresist layer 2400 on the substrate 2300. In practice, such unpatterned regions on the wafer W may adversely affect chemical processing in the patterned regions adjacent to such unpatterned regions. Therefore, as Figure 15 As shown, in some embodiments, patterns are not absent; the portions of process layers 2310 and 2320 surrounding or adjacent to the periodic target may also include patterns (e.g., grating structures) 2314 and 2324.

[0269] Despite the presence of the underlying additional patterns 2314 and 2324, such embodiments may still function as long as these additional underlying patterns 2314 and 2324 have a pitch different from that of the periodic target 2100 (and reference mark 2200). For example, if the periodic target 2100 has x-pitch and y-pitch of 50 nm and 70 nm, respectively, then the underlying enclosing patterns 2314 and 2324 can have x-pitch and y-pitch of 65 nm and 81 nm, respectively. The pitch of the underlying enclosing patterns 2314 and 2324 can be selected such that most diffraction orders from these patterns 2314 and 2324 do not overlap with the diffraction orders of the periodic target 2100. Furthermore, the orientation of the unit cells of the underlying enclosing patterns 2314 and 2324 can differ from the orientation of the periodic target 2100. For example, if the unit cells of the periodic target 2100 are rectangles aligned with the x and y axes of the wafer, then the unit cells of the underlying surrounding patterns 2314, 2324 can be rotated rectangles, with the axis of rotation set at an angle (e.g., 5 to 10 degrees) relative to the x and y axes of the wafer. This, too, can help ensure that fewer diffraction orders from these patterns 2314, 2324 overlap with the diffraction orders of the periodic target 2100.

[0270] Some embodiments of this disclosure relate to novel measuring devices for determining one or more parameters of a periodic target on an object. An example embodiment of such a novel measuring device 4000 is described in... Figure 16 It is shown schematically in the middle.

[0271] exist Figure 16 The new measuring device 4000 schematically shown in the diagram can typically be Figure 6 The measuring device 302 is depicted in the form described above. Figure 16 The new measuring device 4000, schematically shown in the diagram, may include [the following components]: Figure 6Any combination of the features of the measuring device 302 as described above.

[0272] The measuring device 4000 includes: an illumination optics 4100; a detector array 4200; and a controller 4300.

[0273] Illumination optics 4100 are arranged to project a radiation beam 410 onto an object W. A detector array 4200 is arranged to receive a portion of the radiation beam 4210, which is scattered from the object W and comprises multiple diffracted beams. A controller 4300 is operable to determine one or more parameters based on an interference pattern formed in at least one of the multiple diffracted beams. It is understood that the controller 4300 is operable to exchange signals 4310 with the detector array 4200.

[0274] Figure 16 The measuring device 4000 shown can be used to perform... Figure 8 Method 1000 is shown.

[0275] At least one reference mark 2200 may be disposed on the object adjacent to the periodic target 2100. Each of the plurality of diffraction beams may include a first portion of radiation scattered from the periodic target 2100 and a second portion of radiation scattered from the reference mark 2200.

[0276] Detector array 4200 includes a plurality of detector elements 4220. For example, detector array 4200 may include a two-dimensional array of detector elements 4220. Each of the plurality of detector elements 4220 is operable to determine a dose of a portion of the received scattered radiation 4210. Detector array 4200 may be referred to as a camera. Each of the plurality of detector elements 4200, or the measurement performed therefrom, may alternatively be referred to as a pixel.

[0277] Optionally, the measuring device 4000 may also include a detection optics 4400, which is arranged to receive at least a portion of the radiation 4210 scattered by the object W and guide it to the detector array 4200.

[0278] Irradiation optics 4100 can be arranged to focus radiation beam 4110 onto object W. That is, object W can be positioned at or near the waist of radiation beam 4110. In such an embodiment, detector array 4200 can be positioned in the far field. Specifically, detector array 4200 can be positioned outside the Rayleigh length of radiation from object W.

[0279] The detector array 4200 can be arranged such that it can resolve the interference pattern formed by the periodic target 2100 and the adjacent reference pattern 2200. As described above, such an interference pattern may include a single dark fringe. To resolve the fringe, the detector array 4200 can be positioned such that at least three sensing elements (pixels) 4220 of the detector array 4200 span the full width at half maximum (FWHM) of the spot region corresponding to the diffraction order in which the interference pattern is formed.

[0280] The controller 4300 can be operated to perform any step of any of the measurement methods described above.

[0281] Optionally, the measurement device 4000 may further include a radiation source 4500 operable to generate a radiation beam. The radiation source 4500 may include a seed source (e.g., a laser) operable to generate seed radiation having a first wavelength. The radiation source 4500 may include a conversion module arranged to convert at least a portion of the seed radiation into multiple different radiation components. The conversion of at least a portion of the seed radiation into multiple different radiation components may be achieved using higher harmonic generation.

[0282] Radiation source 4500 can typically be Figure 6 The irradiation source 310 shown (as described above) and / or Figure 7 The form of the irradiation source 600 shown (as described above). The radiation source 4500 may include... Figure 6 The irradiation source 310 shown and / or Figure 7 Any combination of the features of the irradiation source 600 shown.

[0283] In some embodiments, radiation 4110 may include soft X-rays. It will be understood that radiation 4110 includes sufficiently coherent radiation to produce at least one interference pattern.

[0284] In some embodiments, the radiation beam 4110 may include radiation in the spectral range of 10 nm to 20 nm. In some embodiments, the radiation 4110 may include multiple discrete wavelength components.

[0285] Optionally, the measurement apparatus 4000 may further include a support 4600 for supporting an object W, such that the object W can be positioned such that the illumination optics 4100 can project a radiation beam 4110 onto the object W. The support 4600 for supporting the substrate W may include a substrate holder operable to hold the substrate in place. For example, the support 4600 may include a clamp for holding the substrate to the support. The support 4600 may include a stage such as a wafer stage.

[0286] Optionally, in some embodiments, the measuring device 4000 may further include a moving mechanism 4700, operable to cause relative movement between the support 4600 and the illumination optics 4100. Such movement in Figure 16 The arrows 4710 and 4720 are schematically indicated in the diagram. This allows an object or substrate W to be stepped or scanned through the beam spot region 4120 of the optics 4100. As used herein, scanning of the object W refers to continuous movement of the object W. As used herein, stepping of the object W refers to movement of the object W in multiple successive (temporally separated) steps.

[0287] As previously mentioned, in scattering measurement tools, light can be used to create an image of a structure on a substrate (e.g., at one or both of the image plane and the pupil plane). Such tools can measure, for example, the intensity or amplitude of light detected after it has been scattered by the structure (or related measurement parameters, such as diffraction efficiency), and use the detected intensity or amplitude of the light to determine one or more parameters of interest for the structure. In many cases, as now discussed, knowing the complex field (i.e., amplitude and phase) of the light scattered by the structure can be beneficial.

[0288] Direct target reconstruction is impossible without the phase information of the measured diffraction pattern and the input beam. Current model-based reconstruction requires prior knowledge of the use case and well-calibrated tools. This method is computationally expensive and requires good estimation of the probe. Phase information of both the input beam and the diffraction field would allow direct reconstruction with limited prior knowledge. Furthermore, this paves the way for 3D SXR tomography. Embodiments of this disclosure relating to determining the phase of the diffraction pattern generated by the sample will now be discussed.

[0289] A non-iterative method for determining the complex field of the scattered radiation can now be described. The method involves imposing a hard constraint in a plane conjugate to the target. This hard constraint results in a symmetric relation of the electric field in the Fourier plane (i.e., the plane in which the electric field is the Fourier transform of the electric field in the target plane). This symmetric relation is called the Kramers-Kleinich relation (and its inverse, the second Kramers-Kleinich relation).

[0290] The mathematical foundation of the new method is outlined here.

[0291] Assume there exists an input radiation beam incident on the target structure; this input radiation beam can be called the probe beam. For simplicity, we can consider the target as a one-dimensional object, defined by a function... This can be described as follows: The probe beam can be a large, uniform beam, significantly larger than the target structure of interest. As a result, we can neglect the finite size of the input probe beam, such that within the Born approximation model, the scattered field is determined solely by the objective function. (This could essentially be represented by its dielectric constant distribution function.) Furthermore, the objective function can be expressed as: in It is the Heaviside function, given by the following equation: Make:

[0292] We will consider two functions (i.e., the positive constraint field) and negative constraint field ) is limited to:

[0293] In practice, positive constraints and negative constraints The physical implementation can be achieved, for example, by using any type of hard mask that blocks half of the input probe beam before it hits the target structure. If such a hard constraint is applied (e.g., through a hard mask), such that the electric field is controlled by a positive constraint field... Or negative constraint field Given that the camera is positioned in the far field, the camera can measure the intensity of the field separately: Or the intensity of the field: in It is spatial frequency, and This represents the Fourier transform operator.

[0294] Due to the positive constraint field and negative constraint field Each element is confined to a half-space, therefore the Fourier transform... and It is a complex number and its real and imaginary parts are not independent of each other. Conversely, the Fourier transform... and Complex numbers, along with their real and imaginary parts, are related via Cramers-Kleinich relations. These relations can be written as convolutions with Hilbert kernels: or: in: and:

[0295] These integral relations (equations (14) and (15)) each contain singularities, and special care must be taken to compute them numerically. This can be done, for example, by subtracting the singularities. In this case, the exact result can be obtained.

[0296] Of course, the real and imaginary parts of the Fourier transform cannot be directly measured. Instead, a camera in the far field can measure the field. and The intensity is the square of the amplitude. Therefore, the amplitude of these fields can be determined based on camera measurements. It is expected that the phase of the field can be determined based on these amplitudes. It has been found that similar Kramers-Klenich relations (to those in equations (14) and (15)) can be applied to the scattering field. and The amplitude and phase are defined. Specifically, it has been found that: as well as: in and They are fields and The phase and the sign function are limited to: and It is the inverse Fourier transform operator. However, those relations can also be converted into convolution, which gives: as well as: Therefore, once in the two experiments using semi-probes to illuminate the target structure (i.e., using a confined field) and The amplitude of the far field has been determined (based on the intensity measured by the camera), then the field... and phase and It can then be determined. Once the field and The amplitude and phase of each of these elements are known, and these can be converted into the real and imaginary parts of these fields (defined by equations (16) and (17)). Furthermore, the phase of the complete scattered field is thus determined. It can be obtained through the following relationship:

[0297] Now for reference Figure 17 and Figure 18 A new method 5000 is used to describe one or more parameters for determining periodic targets on an object (e.g., substrate W).

[0298] Figure 17 This is a schematic diagram of a new method 5000 for determining one or more parameters of a periodic target on an object. Figure 18 This is a plan view of part of the substrate W.

[0299] like Figure 18 As shown, the substrate W includes periodic targets 5500. Figure 18 The image also shows a first adjacent region 5510 and a second adjacent region 5520 of substrate W. The first adjacent region 5510 and the second adjacent region 5520 of substrate W are located on opposite sides of the periodic target 5500 (in...). Figure 18 (Separation in the x-direction) at the boundary. Figure 18 The diagram also shows a first beam spot region 5530 and a second beam spot region 5540 on the substrate W. The first beam spot region 5530 and the second beam spot region 5540 are... Figure 17 The diagram illustrates the areas of projected radiation at two different steps of method 5000.

[0300] The novel method 5000 includes step 5010: projecting radiation onto an object W such that a first portion of the radiation (corresponding to the first half 5532 of the first spot region 5530) is incident on a periodic target 5500 and a second portion of the radiation (corresponding to the second half 5534 of the first spot region 5530) is incident on a first adjacent region 5510 of the object W. At step 5010, radiation is projected onto the object W to generate multiple diffraction orders of the periodic target from the first portion of the radiation (corresponding to the first half 5532 of the first spot region 5530). The first adjacent region 5510 of the object W is such that at least one diffraction order of the periodic target 5500 exists in the measurement plane (e.g., in the far field), and at least one diffraction order of the periodic target 5500 does not intersect or overlap with the radiation from the second portion of the radiation (corresponding to the second half 5534 of the first spot region 5530).

[0301] It is understood that at step 5010, for at least one diffraction order of a periodic target 5500 in the measurement plane (e.g., in the far field) that does not intersect or overlap with the radiation boundary of the second portion (corresponding to the second half 5534 of the first beam spot region 5530), the electric field in the far field can be given by one of the fields defined by equations (12) and (13) (and equations (10) and (11)). For example, at step 5010, for at least one diffraction order of a periodic target 5500 in the measurement plane (e.g., in the far field), the electric field can be given by one of the fields defined by equations (12) and (13) (and equations (10) and (11)). Provided.

[0302] The new method 5000 also includes step 5020: measuring the first intensity distribution of at least one diffraction order of the periodic target in the measurement plane (e.g., using a camera). That is, at step 5020, the field... The intensity was measured.

[0303] The novel method 5000 further includes step 5030: projecting radiation onto the object W such that a third portion of the radiation (corresponding to the first half 5542 of the second beam spot region 5540) is incident on the periodic target 5500 and a fourth portion of the radiation (corresponding to the second half 5544 of the second beam spot region 5540) is incident on a second adjacent region 5520 of the object W. At step 5030, radiation is projected onto the object W to generate multiple diffraction orders of the periodic target 5500 from the third portion of the radiation (corresponding to the first half 5542 of the second beam spot region 5540). The second adjacent region 5520 of the object W results in at least one diffraction order of the periodic target 5500 in the measurement plane that does not intersect or overlap with the radiation from the fourth portion of the radiation (corresponding to the second half 5544 of the second beam spot region 5540).

[0304] It is understood that at step 5030, for at least one diffraction order of the periodic target 5500 in the measurement plane (e.g., in the far field) that does not intersect or overlap with the radiation from the fourth portion of the radiation (corresponding to the second half 5544 of the second beam spot region 5540), the electric field in the far field can be given by one of the fields defined by equations (12) and (13) (and equations (10) and (11)). For example, at step 5010, for at least one diffraction order of the periodic target 5500 in the measurement plane (e.g., in the far field), the electric field can be given by one of the fields defined by equations (12) and (13) (and equations (10) and (11)). Provided.

[0305] The new method 5000 also includes step 5040: measuring the second intensity distribution of at least one diffraction order of the periodic target in the measurement plane (e.g., using a camera). That is, at step 5040, the field... The intensity was measured.

[0306] The new method 5000 also includes step 5050: determining one or more parameters based on (a) a first intensity distribution determined from a first portion of the radiation (at step 5020); and (b) a second intensity distribution determined from a third portion of the radiation (at step 5040).

[0307] As is being discussed now, such as Figure 17 The method shown is advantageous.

[0308] If the first adjacent region 5510 and the second adjacent region 5520 of the object W are patterned using a pattern having substantially the same pitch and orientation as the periodic target 5500, they will produce a diffraction pattern similar to that of the periodic target 5500 (i.e., the two structures can produce diffraction patterns comprising diffracted beams scattered at substantially the same angle). Therefore, in the near field, each diffraction order of the periodic target 5500 may intersect and be adjacent to the corresponding diffraction order formed by one of the first adjacent region 5510 and the second adjacent region 5520. If radiation is focused onto the object W (i.e., the object W is positioned at or near the waist of the radiation beam), then in the far field, each diffraction order of the periodic target 5500 may at least partially overlap spatially with the corresponding diffraction order formed by one of the first adjacent region 5510 and the second adjacent region 5520.

[0309] In contrast, the first adjacent region 5510 of object W results in at least one diffraction order in the measurement plane that does not intersect or overlap with the radiation from the second portion 5534 of the radiation. In the measurement plane, at least one diffraction beam acts as if a hard mask has been provided to block the second portion 5534 of the radiation from reaching the measurement plane. Similarly, the second adjacent region 5520 of object W results in at least one diffraction order in the measurement plane that does not intersect or overlap with the radiation from the fourth portion 5544 of the radiation. In the measurement plane, at least one diffraction beam acts as if a hard mask has been provided to block the fourth portion 5544 of the radiation from reaching the measurement plane. That is, for at least these diffraction beams, the first adjacent region 5510 and the second adjacent region 5520 of the object produce an effect equivalent to providing a hard mask to block the incident radiation.

[0310] Furthermore, this constraint implies that the phase distribution of the diffracted beam in the measurement plane is related to the amplitude distribution of the diffracted beam in the measurement plane via the Kramers-Kleinich relation (see equations (21) and (22)). Advantageously, this implies that both the amplitude and phase of at least one diffraction order can be determined.

[0311] The intensity distribution of radiation in a plane of measurement (e.g., using a camera) is related to the square of the radiation amplitude. Therefore, the amplitude can be determined based on this intensity distribution. That is, the first amplitude distribution... It can be determined from the first intensity distribution, and the second amplitude distribution. The first phase distribution can be determined from the second intensity distribution. Using the Kramers-Krehnich relation (see equations (21) and (22)), the first phase distribution... From the first amplitude distribution Determined, and the second phase distribution It can be derived from the second amplitude distribution Confirmed. Finally, the phase distribution of the entire diffraction beam. It can be determined from the first phase distribution and the second phase distribution (see equation (23)).

[0312] Note that step 5010 may be performed slightly before step 5020 (in practice, it may be performed simultaneously with step 5020). Similarly, step 5030 may be performed slightly before step 5040 (in practice, it may be performed simultaneously with step 5040). However, steps 5010 and 5020 may be performed before or after (or even simultaneously with) steps 5030 and 5040.

[0313] In some embodiments, the first adjacent portion 5510 and / or the second adjacent portion 5520 are not patterned. Such portions or areas of the object W may be referred to as patternless areas.

[0314] In practice, such unpatterned areas on wafer W may adversely affect chemical processing in the patterned areas adjacent to such unpatterned areas. Therefore, in some embodiments, the first adjacent portion 5510 and / or the second adjacent portion 5520 are not unpatterned, but may also include patterns (e.g., grating structures).

[0315] In some embodiments, the first adjacent portion 5510 and / or the second adjacent portion 5520 may include patterns having a pitch and / or orientation different from that of the periodic target 5500. The pitch and / or orientation of the patterns in the first portion 5510 and the second portion 5520 may be selected such that most of the diffraction orders from these patterns do not intersect or overlap with the diffraction orders of the periodic target 5500.

[0316] like Figure 18As shown, in some embodiments, at step 5010, when radiation is projected onto object W such that a first portion 5532 of the radiation is incident on the periodic target 5500 and a second portion 5534 of the radiation is incident on a first adjacent region 5510 of the object, the first portion 5532 may include half of the radiation, and the second portion 5534 may also include half of the radiation.

[0317] like Figure 18 As shown, in some embodiments, at step 5030, when radiation is projected onto object W such that a third portion 5542 of the radiation is incident on a periodic target 5500 and a fourth portion 5544 of the radiation is incident on a second adjacent region 5520 of the object, the third portion 5542 may include half of the radiation, and the fourth portion 5544 may include half of the radiation.

[0318] Step 5050, which determines one or more parameters based on the following two, may include, as now combined Figure 19 The sub-steps discussed are: (a) a first intensity distribution determined from a first portion of the radiation (at step 5020); and (b) a second intensity distribution determined from a third portion of the radiation (at step 5040).

[0319] Step 5050 may include sub-step 5052: determining the first amplitude distribution from the first intensity distribution. (As determined in step 5020).

[0320] Step 5050 may further include sub-step 5054: determining the second amplitude distribution from the second intensity distribution. (As determined at step 5040).

[0321] Step 5050 may also include sub-step 5056: using the Kramers-Kleinich relation (e.g., equation (21)) from the first amplitude distribution Determine the first phase distribution .

[0322] Step 5050 may also include sub-step 5058: using the Kramers-Kleinich relation (e.g., equation (22)) from the second amplitude distribution Determine the second phase distribution .

[0323] Step 5050 may also include sub-step 5060: for example, using equation (23), from the first phase distribution Second phase distribution Determine the phase distribution of the entire diffraction beam .

[0324] As in other embodiments of this disclosure, radiation may include radiation in the spectral range of 10 nm to 20 nm.

[0325] As in other embodiments of this disclosure, radiation may include multiple discrete wavelength components.

[0326] As in other embodiments of this disclosure, measurement method 5000 may include: determining one or more parameters for each of a plurality of discrete wavelength components using at least one diffraction beam.

[0327] As in other embodiments of this disclosure, the measurement method 5000 may also include generating radiation.

[0328] Some embodiments of this disclosure relate to computer-readable media having the function of performing... Figure 17 The instructions of method 5000 shown and described above.

[0329] Despite the above references Figure 17 and Figure 18 The described method 5000 uses two adjacent portions 5510, 5520 of the substrate W to achieve hard confinement of the field in the plane of the periodic target 5500; however, in an alternative embodiment, this can be achieved by providing a hard mask in the optical path of the radiation beam. The hard mask can be in or near the plane of the periodic target 5500 or any plane conjugate to the plane of the periodic target 5500.

[0330] Embodiments may include a computer program comprising one or more sequences of machine-readable instructions describing optical metrology methods and / or analytical measurements to obtain information related to photolithography processes. Embodiments may include computer code comprising one or more sequences of machine-readable instructions or data describing methods. The computer program or code may, for example, be in... Figure 6 MPU unit and / or Figure 3 The control unit CL executes the operation. A data storage medium (e.g., semiconductor memory, disk, or optical disk) storing such a computer program or code may also be provided. When existing measuring devices (e.g., Figure 6When an apparatus of the type shown is already in production and / or use, embodiments of the invention can be implemented by providing an updated computer program product that causes a processor to execute one or more of the methods described herein. The computer program or code may optionally be arranged to control optical systems, substrate supports, etc., to perform methods for measuring parameters of a lithography process on suitable plurality of targets. The computer program or code may update lithography and / or measurement schemes for measuring other substrates. The computer program or code may be arranged to (directly or indirectly) control lithography apparatus to pattern and process other substrates.

[0331] The irradiation source can be provided in, for example, a measurement device (MT), an inspection device, a lithography device (LA), and / or a lithography unit (LC).

[0332] The properties of the emitted radiation used to perform a measurement can affect the quality of the resulting measurement. For example, the shape and size of the transverse beam profile (cross-section) of the radiation beam, the intensity of the radiation, and the power spectral density of the radiation can all influence the measurement performed by the radiation. Therefore, it is beneficial to have a source that provides radiation with properties that produce high-quality measurements.

[0333] Further embodiments are disclosed in the following numbered clauses: 1. A measurement method for determining one or more parameters of a periodic target on an object, the periodic target being adjacent to a reference marker having a pitch equal to that of the periodic target, the method comprising: Radiation is projected onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on the reference mark; Measuring at least one interference pattern formed by the contributions of both the first and second portions of the radiation to a single diffraction order; and The one or more parameters are determined based on the at least one interference pattern. 2. The measurement method according to Clause 1, wherein determining the one or more parameters based on the at least one interference pattern comprises: For each at least one interference pattern, the phase difference between the contributions of the first and second portions of the radiation to the diffraction beam is determined. 3. The measurement method according to Clause 1 or Clause 2, wherein determining the one or more parameters based on the at least one interference pattern includes: For each at least one interference pattern, determine the position of the interference pattern. 4. The measurement method according to any one of the preceding clauses, wherein determining the one or more parameters from the at least one interference pattern comprises: In the direction corresponding to the separation direction between the periodic target and the reference mark, the desired distribution is fitted to the intensity distribution in the spot region corresponding to the diffraction beam; and The one or more parameters of the periodic target are determined from one or more parameters of the desired distribution. 5. The measurement method according to any one of the preceding clauses, wherein the radiation includes radiation in the spectral range of 10 nm to 20 nm. 6. The measurement method according to any one of the preceding clauses, wherein the radiation comprises a plurality of discrete wavelength components. 7. The measurement method according to Clause 6, wherein the method comprises: For each of the plurality of discrete wavelength components, at least one interference pattern is measured, each interference pattern being formed by the contribution of both the first and second portions of the radiation to a single diffraction order of the single discrete wavelength component; and The one or more parameters are determined from the at least one interference pattern for each of the plurality of discrete wavelength components. 8. The measurement method according to any one of the preceding clauses, wherein the method comprises: Multiple interference patterns are measured, each interference pattern being formed by the contributions of both the first and second portions of the radiation to a single diffraction order; and The one or more parameters are determined from the plurality of interference patterns. 9. The measurement method according to any one of the preceding clauses, wherein the shear direction of each of the periodic target and the reference mark is perpendicular to the separation direction of the periodic target and the reference mark. 10. The measurement method according to any one of the preceding clauses, wherein determining the one or more parameters comprises: using a trained machine learning model. 11. The measurement method according to Clause 10, wherein the method further comprises: training the machine learning model using training data. 12. The measurement method according to any one of the preceding clauses, wherein determining the one or more parameters comprises for each at least one interference pattern: The model-based reconstruction of the reference markers is used to determine the phase response of the contribution from the reference markers to the interference pattern; and The determined phase response is combined with the interference pattern to determine the phase response of the contribution of the periodic target to the interference pattern. 13. The measurement method according to any one of the preceding clauses further includes: generating the radiation. 14. The measurement method according to any one of the preceding clauses, wherein the method further comprises: The radiation is projected onto the object such that it is incident on the periodic target; Measure at least one diffraction beam; and The one or more parameters are determined based on the at least one diffraction beam. 15. The measurement method according to any one of the preceding clauses, wherein the method further comprises: The radiation is projected onto the object such that it is incident on the reference mark; Measure at least one reference diffraction beam; and The one or more parameters are determined based on the at least one reference diffraction beam. 16. The measurement method according to any one of the preceding clauses, wherein the periodic target is adjacent to a second reference mark, the second reference mark having a pitch equal to that of the periodic target, the second reference mark having a fixed, non-zero spatial phase shift relative to the reference mark, and wherein the method further comprises: Radiation is projected onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on the second reference mark; Measuring at least one second interference pattern formed by the contributions of both the first and second portions of the radiation to a single diffraction order; and The one or more parameters are determined based on the at least one second interference pattern. 17. The measurement method according to Clause 16, wherein the method further comprises: The radiation is projected onto the object such that it is incident on the second reference mark; Measure at least one second reference diffraction beam; and The one or more parameters are determined based on the at least one second reference diffraction beam. 18. A measuring device for determining one or more parameters of a periodic target on an object, the measuring device comprising: Irradiation optics, which are arranged to project a radiation beam onto the object; A detector array, the detector array being arranged to receive a portion of the radiation beam scattered from the object, the radiation beam comprising at least one diffraction beam; and A controller operable to determine one or more parameters based on an interference pattern formed in at least one of the plurality of diffraction beams. 19. The measuring apparatus according to Clause 18, wherein the illumination optics are arranged to focus the radiation beam onto the object. 20. The measuring device according to Clause 18 or Clause 19, wherein the controller is operable to perform any step of the method according to any one of Clauses 1 to 17. 21. The measuring apparatus according to any one of clauses 18 to 20 further includes a radiation source operable to generate the radiation beam. 22. The measuring apparatus according to any one of clauses 18 to 21, wherein the radiation beam comprises radiation in the spectral range of 10 nm to 20 nm. 23. The measuring apparatus according to any one of clauses 18 to 22, wherein the radiation comprises a plurality of discrete wavelength components. 24. The measuring apparatus according to any one of clauses 18 to 23 further includes a support for supporting an object such that the object can be positioned such that the illumination optics can project the radiation beam onto the object. 25. The measuring device according to Clause 24 further includes a moving mechanism operable to cause relative movement between the support and the illumination optics. 26. A computer-readable medium having instructions for performing the method according to any one of clauses 1 to 17. 27. A measurement target for determining one or more parameters of a manufacturing process, said measurement target comprising: Periodic goals; A first reference marker, adjacent to the periodic target and having a pitch equal to that of the periodic target; and A second reference marker, which is adjacent to the periodic target and has a pitch equal to that of the periodic target, has a fixed, non-zero spatial phase shift relative to the reference marker. 28. The measurement target according to Clause 27, wherein one or more patterns are formed on the object in a process layer that spatially overlaps with the reference mark and / or the second reference mark, wherein the one or more patterns have a pitch different from the pitch of the reference mark and the pitch of the second reference mark. 29. A measurement method for determining one or more parameters of a periodic target on an object, the method comprising: Radiation is projected onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on a first adjacent region of the object, to generate a plurality of diffraction orders of the periodic target from the first portion of the radiation, wherein the first adjacent region of the object is such that at least one diffraction order of the periodic target exists in the measurement plane, and the at least one diffraction order of the periodic target does not intersect or overlap with the radiation from the second portion of the radiation; Measure the first intensity distribution of the at least one diffraction order of the periodic target in the measurement plane; Radiation is projected onto the object such that a third portion of the radiation is incident on the periodic target and a fourth portion of the radiation is incident on a second adjacent region of the object, to generate multiple diffraction orders of the periodic target from the third portion of the radiation, wherein the second adjacent region of the object provides for at least one diffraction order of the periodic target in the measurement plane that does not intersect or overlap with the radiation from the fourth portion of the radiation. The second intensity distribution of at least one diffraction order of the periodic target is measured in the measurement plane; The one or more parameters are determined based on: (a) the first intensity distribution determined from the first portion of the radiation; and (b) the second intensity distribution determined from the third portion of the radiation. 30. The measurement method according to Clause 29, wherein the first adjacent portion and / or the second adjacent portion does not have a pattern. 31. The measurement method according to Clause 29 or Clause 30, wherein the first adjacent portion and / or the second adjacent portion comprises a pattern having a pitch and / or orientation different from that of the periodic target. 32. The measurement method according to any one of clauses 29 to 31, wherein projecting radiation onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on a first adjacent region of the object is accomplished such that the first portion includes half of the radiation and the second portion includes half of the radiation. 33. The measurement method according to any one of clauses 29 to 32, wherein projecting radiation onto the object such that a third portion of the radiation is incident on the periodic target and a fourth portion of the radiation is incident on a second adjacent region of the object is accomplished such that the third portion includes half of the radiation and the fourth portion includes half of the radiation. 34. The measurement method according to any one of clauses 29 to 33, wherein determining the one or more parameters comprises: Determine the first amplitude distribution from the first intensity distribution; The second amplitude distribution is determined from the second intensity distribution; The first phase distribution is determined from the first amplitude distribution using the Kramers-Kleinich relation; The second phase distribution is determined from the second amplitude distribution using the Kramers-Klenich relation; and The phase distribution of the entire diffraction beam is determined from the first phase distribution and the second phase distribution. 35. The measurement method according to any one of clauses 29 to 34, wherein the radiation includes radiation in the spectral range of 10 nm to 20 nm. 36. The measurement method according to any one of clauses 29 to 35, wherein the radiation comprises a plurality of discrete wavelength components. 37. The measurement method according to Clause 36, wherein the method comprises: determining the one or more parameters using at least one diffraction beam for each of the plurality of discrete wavelength components. 38. The measurement method according to any one of clauses 29 to 37 further includes: generating the radiation. 39. A computer-readable medium having instructions for performing the method according to any one of clauses 29 to 38.

[0334] While specific embodiments have been described above, it should be understood that the invention can be practiced in ways different from those described. The foregoing description is intended to be illustrative and not restrictive. Therefore, it will likely be apparent to those skilled in the art that modifications can be made to the described invention without departing from the scope of the set forth claims.

[0335] While this article may specifically refer to the use of photolithography apparatus in IC manufacturing, it should be understood that the photolithography apparatus described herein can have other applications. Other possible applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0336] Although specific reference to embodiments of the invention may be made herein in the context of a lithography apparatus, embodiments of the invention may also be used in other apparatuses. Embodiments of the invention can form mask inspection apparatuses, measurement apparatuses, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses can generally be collectively referred to as lithography tools. Such lithography tools can use vacuum conditions or ambient (non-vacuum) conditions.

[0337] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any means for storing or transmitting information in a machine-readable (e.g., computing device) form. For example, a machine-readable medium may include read-only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Furthermore, firmware, software, programs, and instructions may be described herein as performing specific actions. However, it should be understood that such descriptions are for convenience only, and such actions are actually generated by a computing device, processor, controller, or other device executing the firmware, software, programs, instructions, etc., and in doing so may cause an actuator or other device to interact with the physical world.

[0338] While the foregoing may have specifically referred to embodiments of the invention in the context of optical lithography, it should be understood that the invention can also be used in other applications (e.g., imprint lithography) and is not limited to optical lithography where the context permits. In imprint lithography, a topology in a patterning apparatus defines a pattern created on a substrate. The topology of the patterning apparatus can be pressed into a resist layer provided to the substrate, which is then cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist has cured, the patterning apparatus removes the resist, thereby leaving a pattern therein.

[0339] In this document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic and particle radiation, including ultraviolet radiation (e.g., with wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), EUV (extreme ultraviolet radiation, e.g., with wavelengths in the range of about 1 nm to 100 nm), X-ray radiation, electron beam radiation, and other particle radiation.

[0340] As used herein, the terms “mask,” “mask,” or “patterning apparatus” can be broadly interpreted to refer to a general patterning apparatus that can be used to impart a patterned cross-section to an incoming radiation beam, the patterned cross-section corresponding to a pattern to be created in a target portion of the substrate. The term “optical valve” may also be used in this context. Examples of other such patterning apparatuses, besides classic masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), include programmable mirror arrays and programmable LCD arrays.

[0341] Where the context permits, the term "lens" can refer to any or a combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components. Reflective components may be used in devices operating in the UV and / or EUV range.

[0342] Additional objectives, advantages, and features of the invention are set forth in this specification and will, in part, become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The invention disclosed in this application is not limited to any particular set or combination of objectives, advantages, and features. It is contemplated that various combinations of said objectives, advantages, and features constitute the invention disclosed in this application.

Claims

1. A measurement method for determining one or more parameters of a periodic target on an object, the periodic target being adjacent to a reference marker having a pitch equal to that of the periodic target, the method comprising: Radiation is projected onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on the reference mark; The measurement is made by measuring at least one interference pattern formed by the contributions of both the first and second portions of the radiation to a single diffraction order; as well as The one or more parameters are determined based on the at least one interference pattern.

2. The measurement method according to claim 1, wherein determining the one or more parameters based on the at least one interference pattern comprises: For each at least one interference pattern, the phase difference between the contributions of the first and second portions of the radiation to the diffraction beam is determined.

3. The measurement method according to claim 1 or claim 2, wherein determining the one or more parameters based on the at least one interference pattern comprises: For each at least one interference pattern, determine the position of the interference pattern.

4. The measurement method according to any one of the preceding claims, wherein the method comprises: Multiple interference patterns are measured, each of which is formed by the contribution of both the first and second portions of the radiation to a single diffraction order; as well as The one or more parameters are determined based on the plurality of interference patterns.

5. The measurement method according to any one of the preceding claims, wherein the shear direction of each of the periodic target and the reference mark is perpendicular to the separation direction of the periodic target and the reference mark.

6. The metrology method of any of the preceding claims, wherein determining the one or more parameters comprises: Use a trained machine learning model.

7. The measurement method according to any one of the preceding claims, wherein determining the one or more parameters comprises for each at least one interference pattern: The model-based reconstruction of the reference markers is used to determine the phase response of the contribution from the reference markers to the interference pattern; and The determined phase response is combined with the interference pattern to determine the phase response of the contribution from the periodic target to the interference pattern.

8. The measurement method according to any one of the preceding claims, wherein the periodic target is adjacent to a second reference mark, the second reference mark having a pitch equal to that of the periodic target, the second reference mark having a fixed, non-zero spatial phase shift relative to the reference mark, and wherein the method further comprises: Radiation is projected onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on the second reference mark; The measurement is made by measuring at least one second interference pattern formed by the contributions of both the first and second portions of the radiation to a single diffraction order; as well as The one or more parameters are determined based on the at least one second interference pattern.

9. A measurement method for determining one or more parameters of a periodic target on an object, the method comprising: Radiation is projected onto the object such that a first portion of the radiation is incident on the periodic target and a second portion of the radiation is incident on a first adjacent region of the object, to generate a plurality of diffraction orders of the periodic target from the first portion of the radiation, wherein the first adjacent region of the object is such that at least one diffraction order of the periodic target exists in the measurement plane, and the at least one diffraction order does not intersect or overlap with the radiation from the second portion of the radiation. Measure the first intensity distribution of the at least one diffraction order of the periodic target in the measurement plane; Radiation is projected onto the object such that a third portion of the radiation is incident on the periodic target and a fourth portion of the radiation is incident on a second adjacent region of the object, to generate multiple diffraction orders of the periodic target from the third portion of the radiation, wherein the second adjacent region of the object provides for at least one diffraction order of the periodic target in the measurement plane that does not intersect or overlap with the radiation from the fourth portion of the radiation. The second intensity distribution of at least one diffraction order of the periodic target is measured in the measurement plane; The one or more parameters are determined based on: (a) the first intensity distribution determined from the first portion of the radiation; and (b) the second intensity distribution determined from the third portion of the radiation.

10. The measurement method according to claim 9, wherein the first adjacent portion and / or the second adjacent portion does not have a pattern.

11. The measurement method according to claim 9 or claim 10, wherein the first adjacent portion and / or the second adjacent portion comprises a pattern having a pitch and / or orientation different from that of the periodic target.

12. The measurement method according to any one of claims 9 to 11, wherein determining the one or more parameters comprises: Determine the first amplitude distribution from the first intensity distribution; The second amplitude distribution is determined from the second intensity distribution; The first phase distribution is determined from the first amplitude distribution using the Kramers-Kleinich relation; The second phase distribution is determined from the second amplitude distribution using the Kramers-Klenich relation; and The phase distribution of the entire diffraction beam is determined from the first phase distribution and the second phase distribution.

13. A computer-readable medium having instructions for performing the method according to any one of claims 1 to 12.

14. A measurement target for determining one or more parameters of a manufacturing process, said measurement target comprising: Periodic goals; A first reference mark, which is adjacent to the periodic target and has a pitch equal to that of the periodic target; as well as A second reference marker, which is adjacent to the periodic target and has a pitch equal to that of the periodic target, has a fixed, non-zero spatial phase shift relative to the reference marker.

15. The measurement target of claim 14, wherein one or more patterns are formed on the object in a process layer, the process layer spatially overlapping the reference mark and / or the second reference mark, wherein the one or more patterns have a pitch different from the pitch of the reference mark and the pitch of the second reference mark.

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