Forming a reference irradiance pattern on the detector

Abstract

This document describes a method comprising: illuminating an optical element with reference illumination, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising a plurality of reference irradiance spots; and determining position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots. A computer program product is also described. Additionally, this document describes an apparatus including a processor configured to determine position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots.

Description

Cross-references to related applications

[0001] This application claims priority to European Application 24160465.1, filed on 29 February 2024; European Application 24169424.9, filed on 10 April 2024; and European Application 24177559.2, filed on 23 May 2024, all of which are incorporated herein by reference in their entirety. Technical Field

[0002] The present invention relates to a method and apparatus for forming a reference irradiance pattern on a detector (e.g., a detector of a measuring device) to achieve accurate determination of position-related parameters of the detector. Background Technology

[0003] A lithography apparatus is a machine configured to apply a desired pattern onto a substrate. Lithography apparatuses can be used, for example, to manufacture integrated circuits (ICs). For instance, a lithography apparatus can project a pattern (also commonly referred to as a “design layout” or “design”) at a patterning apparatus (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed 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, for example, radiation with a wavelength of 193 nm, photolithography apparatuses using extreme ultraviolet (EUV) radiation (EUV radiation with wavelengths in the range of 4 to 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 smaller than the classical resolution limit of lithography apparatuses. In such a process, the resolution formula can be expressed as: Here, 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 the empirical resolution factor. Generally, the smaller k1 is, the more difficult it becomes to reproduce on the substrate a pattern with a shape and size similar to those planned by the circuit designer to achieve specific electrical functions and performance. To overcome these difficulties, fine-tuning steps can be applied to the lithography projection apparatus and / or design layout. These steps include, but are not limited to: optimizing NA, customizing the illumination scheme, using phase-shifting patterning apparatus, various optimizations of the design layout such as optical proximity correction (OPC, sometimes also called "optical and process correction"), or other methods generally defined as "resolution enhancement techniques" (RET). Alternatively, a tight control loop used to control the stability of the lithography apparatus can be used to improve pattern reproduction at low k1.

[0006] In photolithography and other manufacturing processes, frequent measurements of the created structures are desirable, for example, for process control and verification. Various tools are known for performing such measurements, including scanning electron microscopes (often used to measure critical dimensions (CD)) and specialized tools for measuring overlay (the accuracy of alignment between 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 manufacturing processes.

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

[0009] In addition to reconstructing the shape of the measurement feature, this apparatus can also be used to measure diffraction-based overlay, as described in published patent application US2006066855A1. Diffraction-based overlay metrology using dark-field imaging with diffraction order enables overlay measurements of smaller targets. These targets can be smaller than the illumination spot and can be surrounded by the product structure on the wafer. Examples of dark-field imaging metrology can be found in numerous published patent applications, such as, for example, US2011102753A1 and US20120044470A. Using composite grating targets, multiple gratings can be measured in a single image. Known scatterometers tend to use light in the visible or near-infrared (IR) wavelength range, which requires the grating pitch to be much coarser than the actual product structure, the characteristics of which are of practical 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 often unavailable or unusable for the metrology.

[0010] On the other hand, the dimensions of modern product structures are so small that they cannot be imaged using optical metrology techniques. Small features include, for example, features formed by 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 error or critical dimensions of the product are the characteristics of interest. Measurement results are only indirectly correlated with the dimensions of the actual product structure and may be inaccurate because the measured target is not subjected to the same distortion under optical projection in the lithography apparatus and / or is treated differently in other steps of the manufacturing process. While scanning electron microscopy (SEM) can directly resolve these modern product structures, SEM is much more time-consuming than optical measurements. Furthermore, electrons cannot penetrate thick process layers, making it less suitable for metrology applications. Other techniques, such as measuring electrical properties using contact pads, are also known, but they only provide indirect evidence of the actual product structure.

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

[0012] Measurement devices may include detectors, also known as image sensors. In order to perform a measurement (e.g., using broadband soft X-ray radiation), it is necessary to determine the position of the detector relative to the object being measured (e.g., a substrate such as a wafer). Summary of the Invention

[0013] This disclosure provides improved methods and apparatus that can lead to the alignment and / or calibration of measurement devices. In particular, determining the position of a detector by fitting six degrees of freedom (DoF) (or even 12 DoF in the case of a dual-detector arrangement, or 18 DoF in the case of a triple-detector arrangement) can be very difficult due to the required level of accuracy.

[0014] Therefore, a calibration is needed, which is preferably implemented with an accuracy smaller than the detector pixel size.

[0015] According to a first aspect of this disclosure, a method is provided, comprising: illuminating an optical element with reference illumination, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern including a plurality of reference irradiance spots; and determining position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots.

[0016] According to a second aspect of this disclosure, a method is provided comprising: illuminating an optical element with reference illumination, the optical element including a computer-generated hologram, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern including a plurality of reference irradiance spots.

[0017] According to a third aspect of this disclosure, a method is provided, comprising: illuminating an optical element with reference illumination, the optical element including a photonic integrated circuit configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern including a plurality of reference irradiance spots; and determining position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots.

[0018] According to a fourth aspect of this disclosure, a method is provided, comprising: illuminating an optical element with a reference illumination, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern including a plurality of reference irradiance spots; aligning the reference illumination relative to the optical element based on reflection of the reference illumination by the optical element; and determining position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots.

[0019] According to a fifth aspect of this disclosure, a method is provided, comprising: illuminating an optical element with reference illumination, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, at least one of the reference irradiance beams having an astigmatic profile, the reference irradiance pattern comprising a plurality of reference irradiance spots; and determining position-related parameters of the detector relative to the optical element based on the shape of the irradiance spots formed by the reference irradiance beams having astigmatic profiles.

[0020] According to a sixth aspect of this disclosure, a method is provided comprising: illuminating an optical element with reference illumination, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, two or more of the reference irradiance beams having different focal points, the reference irradiance pattern comprising a plurality of reference irradiance spots; and determining position-related parameters of the detector relative to the optical element based on the size of the reference irradiance spots formed by the reference irradiance beams having different focal points.

[0021] According to a seventh aspect of this disclosure, an apparatus is provided, comprising: a reference illumination source configured to illuminate an optical element with reference illumination; a detector; and a processor; wherein the optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern including a plurality of reference irradiance spots; and wherein the processor is configured to determine position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots.

[0022] According to an eighth aspect of this disclosure, an apparatus is provided, comprising: a reference illumination source configured to illuminate an optical element with reference illumination, the optical element including a computer-generated hologram; a detector; and a processor; wherein the optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern including a plurality of reference irradiance spots; and wherein the processor is configured to determine position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots.

[0023] According to a ninth aspect of this disclosure, an apparatus is provided, comprising: a reference illumination source configured to illuminate an optical element with reference illumination, the optical element including a photonic integrated circuit; a detector; and a processor; wherein the optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern including a plurality of reference irradiance spots; and wherein the processor is configured to determine position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots.

[0024] According to a tenth aspect of this disclosure, an apparatus is provided, comprising: a reference illumination source configured to illuminate an optical element with reference illumination, wherein the reference illumination source is configured to align relative to the optical element based on reflection of the reference illumination by the optical element; a detector; and a processor; wherein the optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern including a plurality of reference irradiance spots; and determining position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots.

[0025] According to an eleventh aspect of this disclosure, an apparatus is provided, comprising: a reference illumination source configured to illuminate an optical element with reference illumination; a detector; and a processor; wherein the optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, at least one of the reference irradiance beams having an astigmatic profile, the reference irradiance pattern comprising a plurality of reference irradiance spots; and wherein the processor is configured to determine position-related parameters of the detector relative to the optical element based on the shape of the irradiance spots formed by the reference irradiance beams having astigmatic profiles.

[0026] According to a twelfth aspect of this disclosure, an apparatus is provided, comprising: a reference illumination source configured to illuminate an optical element with reference illumination; a detector; and a processor; wherein the optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, two or more of the reference irradiance beams having different focal points, the reference irradiance pattern including a plurality of reference irradiance spots; and wherein the processor is configured to determine position-related parameters of the detector relative to the optical element based on the size of the reference irradiance spots formed by the reference irradiance beams having different focal points.

[0027] The following examples may correspond to embodiments of one or more of the aspects described herein.

[0028] In some examples, the positional parameters of the detector relative to the optical elements are determined based on the position of a reference irradiance spot on the detector.

[0029] Position-related parameters can be fitted, such as the position, shape, and / or size of the reference irradiance spot on the detector.

[0030] In some examples, the reference irradiance pattern comprises at least three reference irradiance spots. For example, three reference irradiance spots arranged in a triangle (preferably a non-equilateral triangle). In some examples, the reference irradiance pattern comprises at least four reference irradiance spots. Preferably, the at least four reference irradiance spots are not arranged in a square. Such an irregular pattern of at least four reference irradiance spots may be particularly suitable for determining position-related parameters in cases of detector surface curvature (e.g., due to stress).

[0031] Preferably, the reference illumination comprises monochromatic radiation (e.g., a laser beam) having a known wavelength. For example, the reference illumination source may include a laser. In this example, the wavelength of the reference illumination is 633 nm (e.g., the reference illumination source may include a helium-neon laser). However, other wavelengths, such as those in the infrared (IR), near-infrared (NIR), visible, near-ultraviolet (NUV), or ultraviolet (UV) ranges, may also be suitable.

[0032] The optical elements can be considered to form multiple point sources from which the reference irradiance beam is emitted.

[0033] In some examples, the optical elements include phase masks.

[0034] In some examples, the optical elements include amplitude masks.

[0035] In some examples, the optical elements include gratings (e.g., diffraction gratings).

[0036] In some examples, the optical elements include spatial light modulators.

[0037] In some examples, the optical elements include holograms.

[0038] In some examples, the optical elements include computer-generated holograms (CGHs). Advantageously, CGHs allow the optical elements to be designed to impart any desired characteristics to the reference irradiance beams, including their focal points (e.g., on the plane of the detector), the shape and / or size of the reference irradiance spots, the shape of the reference irradiance pattern, and / or the number of reference irradiance beams / spots in the reference irradiance pattern.

[0039] In some examples, the optical element includes a pinhole mask.

[0040] In some examples, the optical elements include multiple curved mirrors, such as parabolic mirrors, ellipsoidal mirrors, and / or spherical mirrors. These curved mirrors may include concave and / or convex mirrors. In some examples, any aberrations introduced into the reference irradiance beam by the curved mirrors can be corrected through subsequent data processing.

[0041] In some examples, at least a portion of the optical element is reflective of the reference illumination. For example, the optical element may be configured to reflect the reference illumination (in the form of a reference irradiance pattern) toward the detector.

[0042] In some examples, at least a portion of the optical element is transmissive to reference illumination. For example, the optical element can be illuminated from below (i.e., from the side of the optical element opposite to the detector). This arrangement can advantageously result in a more compact measurement device. For example, when the detector is a detector for a device for measuring a substrate, the illumination source can be provided to the optical element via a substrate support or substrate stage, wherein the optical element can be located on the substrate support, thereby resulting in a modular design.

[0043] In some examples, the reference illumination (or reference illumination source) may be aligned (or configured to be aligned) relative to the optical element based on the reflection of the reference illumination by the optical element. For example, the reference illumination may be aligned based on backscattered radiation propagating back to the illumination source.

[0044] In some examples, the optical element may include an alignment guide. The alignment guide may include a portion of the optical element that reflects a reference illumination. For example, the optical element may include a transmissive portion and a reflective portion (e.g., surrounding the transmissive portion).

[0045] The reference illumination reflected by the optical elements and used for reference illumination alignment can be detected by one or more alignment detectors. For example, one or more alignment detectors can be integrated with the substrate support.

[0046] In some examples, optical elements include integrated optical devices, such as photonic integrated circuits (PICs).

[0047] In some examples, optical elements can be illuminated via a reference beam through an optical fiber.

[0048] Using PIC and / or optical fibers can advantageously reduce the sensitivity of the reference irradiance pattern to the beam pointing and / or beam profile quality of the reference irradiation.

[0049] Furthermore, compared to some other types of optical elements, optics including PICs can be more easily manufactured within the required tolerances to generate some reference irradiance patterns.

[0050] In some examples, the optical element includes a PIC, which comprises a die. For example, the die can be formed by dicing a wafer or substrate. The die can be arranged such that a reference irradiance beam is emitted from the edge of the die (i.e., in the plane of the die, or on the wafer forming the die). Coupling light (i.e., the reference irradiance beam) from the side or edge of the die can be advantageous for more efficient light coupling from the die compared to coupling light from, for example, the top surface of the die.

[0051] In some examples, as described herein, the first optical element may include a first PIC, which includes a die, and as described herein, the second optical element may include a second PIC, which also includes a die. The first and second PICs may be arranged such that a reference irradiance beam is emitted from a respective edge of each die. The first and second PICs may be arranged such that the respective edges of the dies are perpendicular to each other.

[0052] In some examples, the PIC described herein includes a waveguide comprising a grating output coupler, which in turn includes multiple grating lines. A reference irradiance beam can be coupled out from these multiple grating lines. The grating lines can be arranged in a direction perpendicular to the propagation direction of the waveguide. Since the reference irradiance propagates through the center of the waveguide, the lateral position of the reference irradiance beam (e.g., a point source at the output of the grating output coupler) (i.e., perpendicular to the propagation direction through the waveguide) is advantageously defined very precisely.

[0053] In some examples, the optical element itself comprises optical fibers, or even multiple optical fibers. The optical fiber may include a cladding surrounding a fiber core. One or more portions of the fiber cladding may be removed or altered to expose the fiber core and form one or more light output points, i.e., point sources. For example, the optical fiber may be altered by forming one or more holes in the cladding, which are light output points. Preferably, in the case where the removed area of ​​the cladding is a hole, the diameter of the hole is smaller than the wavelength of the reference illumination. In some examples, one or more removed areas of the cladding may include exposed portions of the fiber core, formed, for example, by scraping or otherwise removing one or more portions of the cladding. One or more light output points may include optical antennas or multiple optical antennas placed on the exposed portion of the fiber core. For example, the optical antenna(s) may include particles of suitable material, such as metals, such as gold, copper, silver, or other suitable metals. The size of the optical antenna(s) may be on the order of the reference illumination wavelength. Light emitted via the optical antenna(s) may advantageously exhibit improved directivity.

[0054] In some examples, the optical elements include fiber optic arrays. For instance, a fiber optic array may include multiple optical fibers, which can be connected to a single (e.g., input) fiber via a fiber optic splitter. The fibers in the optical array may be attached to a support or other surface to ensure that all fibers in the array are at the same temperature, for example, so that any temperature change affects all fibers equally.

[0055] In some examples, the optical element is configured such that the reference illumination propagates in a planar pattern within the optical element. For example, the optical element may include a planar waveguide, and / or the reference illumination may pass through a cylindrical lens (e.g., the optical element may include a cylindrical lens). The optical element may include one or more optical antennas (e.g., sheets or particles of a metal such as copper, gold, or silver), and the optical element may be configured to output a reference irradiance beam via one or more optical antennas. In this example, each optical antenna may act as a point source providing a predictable radiation pattern.

[0056] In some examples, the reference irradiance pattern includes a coarse pattern and a fine pattern. For example, the fine pattern may include reference irradiance spots that are closer together than the reference irradiance spots that constitute the coarse pattern. Both the coarse and fine patterns may be generated by the same optical element, or alternatively, the coarse pattern may be generated by a first optical element and the fine pattern by a second optical element. The second optical element may be illuminated with the same reference illumination as the first optical element, or it may be illuminated by a second reference illumination (i.e., the device may include a second reference illumination source configured to illuminate the second optical element with the second reference illumination).

[0057] Advantageously, coarse patterns can be used to obtain rough estimates of the detector's position-related parameters, while fine patterns can be used to obtain more accurate estimates.

[0058] In some examples, coarse and fine patterns can each be formed from corresponding reference irradiance beam pairs, which can be generated one pair at a time (e.g., by irradiating an optical element or a portion of an optical element at a time). In some examples, the pattern can be formed from four pairs of reference irradiance beams (i.e., one pair in each of the x and y dimensions), with each pair generating one reference irradiance beam at a time. Irradiating a pair of point sources at a time makes it easier to calibrate the phase difference between the point sources.

[0059] In some examples, the optical elements are configured such that the reference irradiance pattern includes 10, 100, or even 1000 reference irradiance spots.

[0060] Preferably, the optical element is configured such that the size of the reference irradiance spot formed by the focused reference irradiance beam is smaller than the pixel size of the detector (e.g., less than 10 µm, less than 15 µm, less than 20 µm, or less than 25 µm in some examples).

[0061] As described herein, the detector can be a detector of a measurement device (e.g., for measuring a substrate, such as a wafer).

[0062] The position-related parameters of the detector can be determined relative to the substrate to be measured by the measuring device based on the following: the position-related parameters of the detector relative to the optical element; and the position of the optical element relative to the substrate.

[0063] The apparatus according to this disclosure may include the optical elements described herein.

[0064] In some examples, optical elements may be placed or located on a substrate to be measured by a measuring device.

[0065] In some examples, the optical elements are configured such that at least one of the reference irradiance beams has an astigmatic profile. Position-related parameters of the detector relative to the optical elements can be determined based on the shape of the irradiance spot formed by the at least one reference irradiance beam with an astigmatic profile. For example, the reference irradiance pattern can be formed by a combination of reference irradiance beams having astigmatic and non-astigmatic profiles, respectively. The shape of the reference irradiance spot formed by the reference irradiance beam with an astigmatic profile will depend on the detector's position, i.e., the position where the reference irradiance beam intersects the detector plane. For example, a beam with an astigmatic profile can be configured such that the spot formed by the beam on the detector is circular when the detector is in the desired position, and non-circular when the detector is not in the desired position. Alternatively, or further, a beam with an astigmatic profile (e.g., another beam) can be configured such that the spot formed by the beam (e.g., another spot) when the detector is in the desired position is non-circular. In some examples, using one or more reference irradiance beams with astigmatic profiles can enable the determination of positive or negative offsets of the detector position from the expected, nominal, or designed position, because the shape of the (multiple) formed spots will vary between positive and negative offsets.

[0066] In some examples, the optical elements are configured such that two or more reference irradiance beams have different focal points. For example, the size of the reference irradiance spot formed by the reference irradiance beams can depend on the detector's position. Therefore, position-related parameters of the detector relative to the optical elements can be determined based on the size of the reference irradiance spot formed by the reference irradiance beams with different focal points.

[0067] In some examples, the optical elements can be configured such that the reference irradiance beam comprises a combination of at least some beams having astigmatic profiles and / or different focal points.

[0068] In some examples, the reference irradiance pattern includes a speckle pattern.

[0069] In some examples, the location of the reference irradiance spot can be mapped to the pupil coordinates of the reference irradiance beam.

[0070] In some examples, a portion of the reference irradiance pattern and / or a second reference irradiance pattern may be formed on the second detector by a plurality of reference irradiance beams or by a second plurality of reference irradiance beams (e.g., where the second plurality of reference irradiance beams may be formed by a second optical element). The (partial) reference irradiance pattern formed on the second detector may include a second plurality of reference irradiance spots. Position-related parameters of the second detector relative to the optical element may be determined based on the second plurality of reference irradiance spots, for example, based on the position, shape, and / or size of the second plurality of reference irradiance spots as described herein with respect to the first detector.

[0071] The position-related parameters of the detector according to this disclosure may include, for example, coordinates in three-dimensional (3D) space (e.g., x, y, z), and / or rotation parameters. That is, the position-related parameters may define six degrees of freedom (DoF) for a given detector (three translational DoFs and three rotational DoFs). The position-related parameters (multiple) may define the plane of the detector (e.g., the plane where a reference irradiance beam intersects the detector and is incident on a pixel of the detector). The position of the detector may be defined relative to other things, such as optical elements and / or the substrate or wafer to be measured by the means including the detector. An expected or nominal position (also called a design position) (or set of position-related parameters) of the detector may exist, and the methods and apparatus described herein can enable the determination of deviations between the positions of the (multiple) detectors and the expected positions.

[0072] As described herein, the methods and apparatus according to this disclosure can be used in measurements, such as for measuring the properties of a substrate as described herein (e.g., the apparatus can be a measurement apparatus or inspection apparatus as described herein). The radiation used for measuring the substrate can be referred to as measurement irradiation and can differ from reference irradiation (e.g., provided by a different source, such as a measurement irradiation source). For example, measurement irradiation can be broadband irradiation and can include radiation in the hard X-ray (HXR), soft X-ray (SXR), extreme ultraviolet (EUV), visible to near-infrared (IR), and / or IR wavelength ranges.

[0073] Measurement illumination and detectors (multiple) can be used to obtain calibration data (e.g., calibration data regarding wavelength and / or intensity). For example, measurement illumination can be directed onto the detector in the form of a diffraction pattern. The diffraction pattern can be generated by a reference target that is illuminated by the measurement illumination. The reference target can be different from and / or separate from the optical elements described herein. The reference target can be configured to diffract the measurement illumination such that the diffraction pattern is incident on the detector. Position-related parameters of the reference target relative to the detector can be determined. The position of the reference target relative to the optical elements can be determined. The measurement illumination may include multiple spectral peaks. The wavelengths of the spectral peaks can be determined from the diffraction pattern incident on the detector.

[0074] For the purpose of obtaining calibration data, the measurement illumination (source) and / or reference target can be arranged such that the diffraction pattern is substantially focused on the detector. In some examples, a reflector (e.g., a toroidal mirror) can be used when performing measurements on the substrate (i.e., during measurement). When calibration data is to be obtained, the reflector can be rotated to direct the measurement illumination toward the reference target.

[0075] An illumination monitoring sensor (e.g., an array sensor) can be used to monitor the measurement illumination during measurement. For example, during measurement, a reflector (e.g., a toroidal mirror) can be aligned such that the measurement illumination is guided through a transmission diffraction grating, thereby partially diffracting the measurement illumination and incident on the illumination monitoring sensor to monitor the spectral and / or intensity characteristics of the measurement illumination. As described above, for calibration, the reflector can be rotated such that the measurement illumination bypasses the transmission diffraction grating and / or the illumination monitoring sensor.

[0076] The methods and apparatus described herein may include obtaining calibration for illumination monitoring sensors.

[0077] For example, the wavelength of the determined spectral peak can be used to obtain wavelength calibration for illumination monitoring sensors.

[0078] In some examples, an intensity spectrum for the measurement illumination can also be obtained (e.g., based on the spectrum of the measurement illumination incident on the detector). The intensity spectrum can also be determined based on the diffraction efficiency spectrum of a reference target.

[0079] The determined intensity spectrum can be used to obtain intensity calibration for the illumination monitoring sensor.

[0080] In some examples, the reference target includes a diffraction grating with variable line spacing or variable line density (e.g., a grating or mask with curved lines of variable pitch). Advantageously, the variable line spacing allows the wavelength components of the diffracted measurement illumination (i.e., the line focal points) to be straight lines, which would otherwise be curved lines. This can produce improved accuracy for the calibration measurements described herein.

[0081] This document also describes a computer program product comprising instructions that, when executed by a computer (particularly a computer processor), cause the computer to perform any of the methods described herein. Attached Figure Description

[0082] The embodiments will now be described by way of example with reference to the accompanying drawings, wherein: - Figure 1 A schematic overview of a lithography system, including the lithography apparatus and the radiation source, is depicted. - Figure 2 A schematic overview of the photolithography unit is depicted; - Figure 3 A schematic representation of overall photolithography is depicted, illustrating the collaboration between three key technologies for optimizing semiconductor manufacturing; - Figure 4 The scattering measurement device is illustrated schematically. - Figure 5 The diagram illustrates a transmission scattering measurement device. - Figure 6 A schematic representation of a measurement apparatus using EUV and / or SXR radiation is depicted; - Figure 7 A simplified schematic diagram of the irradiation source is depicted; - Figure 8 At least a portion of an apparatus for determining position-related parameters of a detector, according to the present disclosure, is depicted; - Figure 9 At least a portion of the apparatus according to the present disclosure is depicted, wherein the optical elements include periodic gratings; - Figure 10 At least a portion of the apparatus according to the present disclosure is depicted, wherein the optical elements are at least partially transmissive to reference illumination; - Figure 11 Examples of at least a portion of the apparatus according to this disclosure are depicted, wherein the optical elements include alignment guides; - Figure 12 Examples of at least a portion of the apparatus according to the present disclosure are depicted, wherein the reference illumination can be aligned with the optical element based on the reference illumination reflected by the optical element; - Figure 13 Examples of at least a portion of the apparatus according to the present disclosure are depicted, wherein reference illumination is coupled to an optical element via an optical fiber; - Figure 14 An example of at least a portion of an apparatus comprising two detectors according to this disclosure is depicted; - Figure 15A A schematic representation of multiple point sources that can be generated by optical elements is depicted; - Figure 15B Depicting by Figure 15A An example of a reference irradiance pattern formed by a point source; - Figure 16 An example of at least a portion of the apparatus according to the present disclosure is schematically illustrated, wherein two overlapping reference irradiance patterns are formed on the detector; - Figure 17 Examples of reference irradiance spots formed by reference irradiance beams with various focal points and / or astigmatisms are depicted; - Figure 18 Examples of intersections between a reference irradiance beam with various focal points and / or astigmatism and the detector plane are schematically illustrated. - Figure 19 At least a portion of the measuring device is schematically illustrated; - Figure 20 The diagram schematically illustrates the arrangement for obtaining spectral calibration of the measurement irradiation using a measuring device. - Figure 21 The method according to this disclosure is illustrated schematically; - Figure 22 An example of an optical element including a photonic integrated circuit according to the present disclosure is schematically illustrated. The photonic integrated circuit includes a die, wherein the photonic integrated circuit is arranged such that a reference irradiance beam is emitted from the edge of the die. - Figure 23 An example of an optical element including a fiber optic array according to the present disclosure is schematically illustrated; - Figure 24 Various examples of arrangements of point source pairs and point source triplets according to this disclosure are illustrated schematically (i.e., reference irradiance beams): (A) three point sources, (B) two pairs of point sources, (C) five point sources, (D) four pairs of point sources, and (E) two point source triplets. - Figure 25 An example of an optical element including an optical fiber according to the present disclosure is schematically illustrated, the optical fiber including a plurality of holes in the fiber cladding; - Figure 26 An example of an optical element comprising (A) an optical fiber with a large portion of its cladding removed, according to the present disclosure, and (B) an example of its cross-section are illustrated schematically. - Figure 27 An example of an optical element including a waveguide according to the present disclosure is schematically illustrated, the waveguide including a plurality of grating lines; and - Figure 28 An example of an optical element including a planar waveguide according to the present disclosure is schematically illustrated. Detailed Implementation

[0083] Before describing the embodiments of the present invention in detail, it is illustrative to present example environments in which the embodiments of the present invention may be implemented.

[0084] Figure 1 A lithography system including a radiation source SO and a lithography apparatus LA is shown. The radiation source SO is configured to generate an EUV radiation beam B and provide 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 pattern forming apparatus MA (e.g., a mask), a projection system PS, and a substrate stage WT configured to support a substrate W. The irradiation system IL is configured to modulate the EUV radiation beam B before it is incident on the pattern forming apparatus MA. For this purpose, the irradiation system IL may include a faceted field mirror assembly 10 and a faceted pupil mirror assembly 11. The faceted field mirror assembly 10 and the faceted pupil mirror assembly 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. In addition to or in place of the faceted field mirror assembly 10 and the faceted pupil mirror assembly 11, the irradiation system IL may also include other mirrors or devices. After such adjustment, the EUV radiation beam B interacts with the patterning apparatus MA. Due to this interaction, a patterned EUV radiation beam B' is generated. A 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 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate stage WT. The projection system PS can apply a reduction factor to the patterned EUV radiation beam B' to form an image with features smaller than the corresponding features on the patterning apparatus MA. For example, a reduction factor of 4 or 8 can be applied. Although in Figure 1 The projection system PS is illustrated as having only two mirrors 13 and 14, but the projection system PS may include a different number of mirrors (e.g., six or eight mirrors). 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.

[0085] A relative vacuum (i.e., a small amount of gas (e.g., hydrogen) with a pressure much lower than atmospheric pressure) can be provided in the radiation source SO, the irradiation system IL, and / or the projection system PS.

[0086] 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 carbon dioxide laser) is arranged to deposit energy into a fuel, such as tin (Sn) supplied from a fuel emitter 3, via a laser beam 2. Although tin is mentioned in the following description, any suitable fuel can be used. For example, the fuel can be in liquid form, or it can be a metal or alloy. The fuel emitter 3 may include a nozzle configured to guide tin (e.g., in droplet form) along a trajectory toward a plasma-forming region 4. The laser beam 2 is incident on the tin in the plasma-forming region 4. Depositing laser energy into the tin produces a tin plasma 7 in the plasma-forming region 4. During the de-excitation and recombination of electrons with ions in the plasma, radiation, including EUV radiation, is emitted from the plasma 7.

[0087] EUV radiation from the plasma is collected and focused by collector 5. For example, collector 5 includes a near-normal incident radiation collector 5 (sometimes more generally referred to as a normal incident radiation collector). Collector 5 may have a multi-layer 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 ellipsoidal configuration with two foci. As discussed below, the first foci may be located at plasma formation region 4, and the second foci may be located at intermediate foci 6.

[0088] Laser system 1 can be spatially separated from radiation source SO. In this case, laser beam 2 can be transmitted from laser system 1 to radiation source SO by means of a beam delivery system (not shown), which includes, for example, suitable directional 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.

[0089] 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 an opening 8 in the surrounding structure 9 of the radiation source SO.

[0090] 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.

[0091] like Figure 2As shown, the lithography apparatus LA can constitute part of the lithography unit LC, sometimes referred to as a lithocell or (lithography) cluster. It typically also includes devices for performing pre- and post-exposure processes on the substrate W. Conventionally, these devices include a spin coater SC for depositing a resist layer, a developer DE for developing 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 and I / O2, moves them between different process units, and delivers the substrate W to the feed stage LB of the lithography apparatus LA. The devices in the lithography unit are often collectively referred to as the coating and developing system (track), which can be controlled by a coating and developing control unit TCU. The TCU itself can be controlled by a management control system SCS, which can also control the lithography apparatus LA, for example, via the lithography control unit LACU.

[0092] In photolithography, it is desirable to frequently measure the created structure, for example, for process control and verification. The tools used to perform these measurements are called metrology tools (MTs). Different types of metrology tools (MTs) for this purpose are known, including scanning electron microscopes (SEMs) or various forms of scatterometer metrology tools (MTs). A scatterometer is a versatile instrument that allows for the measurement of photolithography process parameters by placing a sensor at or near the pupil of the scatterometer's objective lens, or at or near the conjugate plane of the pupil; these measurements are typically referred to as pupil-based measurements. Alternatively, the measurement can be performed by placing a sensor at or near the image plane, or at or near a plane conjugate to the image plane; in this case, the measurement is typically referred to as image-based or field-based measurements. Such scattering instruments and associated measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, all of 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 can optionally be a small-angle X-ray scattering measurement tool.

[0093] To ensure correct and consistent exposure of the substrate W by the lithography apparatus LA, it is desirable to inspect the substrate to measure characteristics of the patterned structure, such as overlay errors between subsequent layers, line thickness, critical dimensions (CD), and structural shape. For this purpose, the lithography unit LC may include inspection tools and / or measurement tools (not shown). If errors are detected, adjustments can be made, for example, to the exposure of subsequent substrates or other processing steps to be performed on the substrate W, particularly when inspection is performed before other substrates W in the same batch or group have been exposed or processed.

[0094] An inspection apparatus (which may also be referred to as a measurement apparatus) is used to determine the characteristics of a substrate W, particularly how the characteristics of different substrates W vary, or how the characteristics associated with different layers of the same substrate W vary with each layer. The inspection apparatus may alternatively be configured to identify defects on the substrate W and may be, for example, part of a photolithography unit LC, or may be integrated into a photolithography apparatus LA, or may even be a stand-alone device. The inspection apparatus can measure characteristics on: latent images (images in a resist layer after exposure), or semi-latent images (images in a resist layer after a post-exposure baking step PEB), 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).

[0095] In the first embodiment, the scatterer MT is an angle-resolved scatterer. In such a scatterer, reconstruction methods can be applied to the measured signal to reconstruct or calculate the characteristics of the grating. For example, this reconstruction can be caused by simulating the interaction between the scattered radiation and a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the mathematical model are adjusted until the diffraction pattern produced by the simulated interaction is similar to the diffraction pattern observed from the real target.

[0096] In the second embodiment, the scatterer MT is a spectroscopic scatterer MT. In this spectroscopic scatterer MT, radiation emitted by a radiation source is directed onto the target, and radiation reflected, transmitted, or scattered from the target is directed to a spectroscopic detector that measures the spectrum of specularly reflected radiation (i.e., an intensity measurement as a function of wavelength). Based on this data, the structure or profile of the target that generated the detected spectrum can be reconstructed, for example, through rigorous coupled-wave analysis and nonlinear regression, or by comparison with a simulated spectral library.

[0097] In the third embodiment, the scatterer MT is an elliptically polarized scatterer. An elliptically polarized scatterer allows for the determination of parameters of a photolithography process by measuring the scattered or transmitted radiation for each polarization state. Such a measurement device emits polarized light (such as linearly polarized, circularly polarized, or elliptically polarized light) by using a suitable polarizing filter in the illumination portion of the measurement device, for example. A source suitable for this measurement device can also provide polarized radiation. Various embodiments of existing elliptically polarized scatterers are described in US 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, all of which are incorporated herein by reference in their entirety.

[0098] In one embodiment of the scattering instrument MT, the scattering instrument MT is adapted to measure the overlay of two misaligned gratings or periodic structures by measuring the reflectance spectrum and / or detecting asymmetry in the configuration, the asymmetry being related to the degree of overlay. These two (potentially overlapping) grating structures can be applied to two different layers (not necessarily consecutive layers) and can be formed substantially at the same location on the wafer. The scattering instrument can have a symmetrical detection configuration, such as that described in the co-owned patent application EP1,628,164A, such that any asymmetry can be clearly distinguished. This provides a direct method for measuring misalignment in gratings. Further examples for measuring the overlay error between two layers containing the periodic structure as a target by means of asymmetry in the periodic structure can be found in PCT patent application publication WO 2011 / 012624 or US patent application US 20160161863, both of which are incorporated herein by reference in their entirety.

[0099] Other parameters of interest may be focus and dose. Focus and dose can be determined simultaneously by scattering measurements (or alternatively by scanning electron microscopy), as described in U.S. Patent Application US2011-0249244, which is incorporated herein by reference in its entirety. A single structure can be used that has a unique combination of critical size and sidewall angle measurements for each point in the focal length energy matrix (FEM—also known as the focus position exposure matrix). If these unique combinations of critical size and sidewall angle are available, the focus and dose values ​​can be uniquely determined based on these measurements.

[0100] The measurement target can be an assembly of composite gratings, formed by photolithography, mostly within a resist, but also after other manufacturing processes, such as etching. The pitch and linewidth of the structures within the grating can be largely 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 "overlap"), 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 subsegments configured to simulate the dimensions of functional portions of the design layout within the target. Due to these subsegments, the target will behave more similarly to the functional portions of the design layout, thus making the overall process parameter measurements more similar to the functional portions of the design layout. The target can be measured in underfill or overfill modes. In underfill mode, the measurement beam generates a spot smaller than the overall target. In overfill mode, the measurement beam generates a spot larger than the overall target. In this overfill mode, it is also possible to measure different targets simultaneously, thereby determining different process parameters simultaneously.

[0101] The overall measurement quality of a lithography parameter using a specific target is determined at least in part by the measurement formulation used to measure that lithography parameter. The term "substrate measurement formulation" 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 formulation is a diffraction-based optical measurement, one or more parameters of that measurement 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 the measurement formulation could be, for example, the sensitivity of one of the measurement parameters to process variations. Further examples are described in U.S. Patent Application US2016-0161863 and published U.S. Patent Application US2016 / 0370717A1, both of which are incorporated herein by reference in their entirety.

[0102] Patterning in a photolithography (LA) apparatus is perhaps one of the most critical steps in the process, requiring extremely high accuracy in the size and placement of the structures on the substrate W. To ensure this high accuracy, 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 the lithography apparatus LA, which is (virtually) connected to the metrology tool MT (second system) and the computer system CL (third system). The key to this "holistic" environment is optimizing the collaboration between these three systems to expand the overall process window and provide a tight control loop to ensure that 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) within which a specific manufacturing process produces a defined result (e.g., a functional semiconductor device)—process parameters in the lithography or patterning process can be allowed to vary within this range.

[0103] The computer system CL can use the design layout (partially) to be patterned to predict which resolution enhancement techniques to use, and perform computational lithography simulations and calculations to determine which mask layouts and lithography apparatus settings achieve the maximum overall process window (within) the patterning process. Figure 3 (Depicted by a double arrow in the first scale SC1). Resolution enhancement techniques can be arranged to match the patterning possibilities of the lithography apparatus LA. The computer system CL can also be used to detect where the lithography apparatus LA is currently operating within the process window (e.g., using input from the metrology tool MET) to predict whether defects may exist due to, for example, suboptimal processes (in... Figure 3 The arrow pointing to "0" in the second scale SC2 is used to depict this.

[0104] The measurement tool MT can provide input to the computer system CL for accurate simulation and prediction, and can provide feedback to the lithography apparatus LA to identify possible drifts, such as drifts in the calibration state of the lithography apparatus LA (in...). Figure 3 (The middle section is depicted by multiple arrows in the third scale SC3).

[0105] Many different types of measurement tools (MTs) are available for measuring structures created using photolithographic patterning apparatuses. MTs can interrogate structures using electromagnetic radiation. The characteristics of the radiation (e.g., wavelength, bandwidth, power) can affect the various measurement features of the tool; shorter wavelengths generally allow for higher resolution. The radiation wavelength influences the resolution achievable by the measurement tool. Therefore, for measuring structures with small-sized features, MTs with short-wavelength radiation sources are preferred.

[0106] 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 penetration depth, radiation can be used for measurements in either transmission or reflection. The type of measurement can affect whether information about the surface of the structure / substrate and / or the interior of the body is obtained. Therefore, penetration depth and opacity are another factor to consider when selecting a radiation wavelength for a measurement tool.

[0107] To achieve higher resolution measurements of lithographically patterned structures, measurement tools (MTs) with short wavelengths are preferred. These can include wavelengths shorter than visible light, such as the UV, EUV, and X-ray portions of the electromagnetic spectrum. Hard X-ray methods, such as transmission small-angle X-ray scattering (TSAXS), utilize the high resolution and deep penetration of hard X-rays, thus allowing operation under transmission conditions. On the other hand, soft X-rays and EUV, while not penetrating very deeply into the target, can induce rich optical responses in the material being probed. This can be due to the optical properties of many semiconductor materials, and the size of the structure being comparable to the probe wavelength. Therefore, EUV and / or soft X-ray measurement tools (MTs) can operate under reflection conditions, for example, by imaging the lithographically patterned structure or by analyzing the diffraction patterns emanating from it.

[0108] For hard X-rays, soft X-rays, and EUV radiation, their application in high-volume manufacturing (HVM) applications is limited due to the lack of available high-brightness sources at the desired wavelengths. In the case of hard X-rays, commonly used sources in industrial applications include X-ray tubes. X-ray tubes, including advanced X-ray tubes based on liquid metal anodes or rotating anodes, can be relatively economical and compact, but may lack the brightness required for HVM applications. High-brightness X-ray sources such as synchrotron light sources (SLSs) and X-ray free-electron lasers exist, but their size (100m) and high cost (hundreds of millions of euros) make them too large and expensive for metrology applications. Similarly, there is a lack of sufficiently bright EUV and soft X-ray sources available.

[0109] An example of a measuring device (such as a scatterometer) is as follows: Figure 4 As depicted in the figure. 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 passed to a spectrometer detector 4, which measures the spectrum 6 of the specular reflected radiation (i.e., a measurement of intensity I as a function of wavelength λ). From this data, the structure or profile 8 of the detected spectrum can be reconstructed by a processing unit PU, for example by rigorous coupled-wave analysis and nonlinear regression, or by comparison with a simulated spectral library, such as... Figure 4As shown at the bottom. Typically, for reconstruction, the general form of the structure is known, and some parameters are assumed based on the knowledge of the manufacturing process of the structure, leaving only a few parameters of the structure to be determined based on scattering measurement data. This scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0110] Figure 5 Examples of measuring devices (such as...) are described in the text. Figure 4 The scatterer shown is a transmission version. Transmitted radiation 11 is passed to spectrometer detector 4, which measures spectrum 6, as shown for... Figure 4 The scatterer discussed here can be configured as a normal incidence scatterer or an oblique incidence scatterer. Optionally, this transmission version uses hard X-ray radiation with wavelengths less than 1 nm (optionally less than 0.1 nm, optionally less than 0.01 nm).

[0111] 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: less than 0.01 nm, less than 0.1 nm, less than 1 nm, between 0.01 nm and 100 nm, between 0.01 nm and 50 nm, between 1 nm and 50 nm, between 1 nm and 20 nm, between 5 nm and 20 nm, and between 10 nm and 20 nm. An example of a measurement instrument operating within one of the wavelength ranges presented above is transmission small-angle X-ray scattering (such as T-SAXS in US 2007224518A, which is incorporated herein by reference in its entirety). Lemaillet et al. discussed profile (CD) measurements using T-SAXS in “Intercomparison between optical and X-ray scatterometry measurements of FinFET structures” (Proc. of SPIE, 2013, 8681). It should be noted that the use of laser-generated plasma (LPP) X-ray sources is described in U.S. Patent Publication Nos. 2019 / 003988A1 and 2019 / 215940A1, the entire contents of which are incorporated herein by reference. Reflectance measurement techniques using X-ray (GI-XRS) and extreme ultraviolet (EUV) radiation at grazing incidence can be used to measure the properties of stacks of thin films and layers on a substrate. Within the general field of reflectance measurement, goniometric and / or spectroscopic techniques can be applied. In goniometric methods, the variation of the reflected beam with different incident angles can be measured. On the other hand, spectroscopic reflectance measurement measures the wavelength spectrum of the reflected light at a given angle (using broadband radiation). For example, EUV reflectance measurement has been used to inspect the mask substrate before manufacturing a mask (patterning apparatus) for use in EUV lithography.

[0112] The application scope may not be sufficient using wavelengths in, for example, hard X-rays, soft X-rays, or EUV domains. Published patent applications US 20130304424A1 and US 2014019097A1 (Bakeman et al. / KLA) describe hybrid metrology techniques in which measurements using X-rays are combined with optical measurements in the wavelength range of 120 nm and 2000 nm to obtain measurements of parameters such as CD. CD measurements are obtained by coupling X-ray mathematical models and optical mathematical models through one or more common terms. The contents of the cited U.S. patent applications are incorporated herein by reference in their entirety.

[0113] Figure 6A 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 adapted for hard X-ray, soft X-ray and / or EUV domains.

[0114] Figure 6 The illustration shows a schematic physical arrangement of a measurement apparatus 302 including a spectroscopic scatterometer using hard X-rays, soft X-rays, and / or EUV radiation (optionally at grazing incidence), for illustrative purposes only. An alternative form of the inspection apparatus could be an angle-resolved scatterometer, which could use radiation at normal or near-normal incidence, similar to conventional scatterometers operating at longer wavelengths, and could also use radiation with a direction greater than 1° or 2° parallel to the substrate. An alternative form of the inspection apparatus could also be a transmission scatterometer. Figure 5 The configuration in [the document] applies here.

[0115] The inspection apparatus 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.

[0116] 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) technique shown can also be other types of irradiation sources, such as liquid metal jet sources, inverse Compton scattering (ICS) sources, plasma channel sources, magnetic undulator sources, free electron laser (FEL) sources, compact storage ring sources, discharge-generated plasma sources, soft X-ray laser sources, rotating anode sources, solid anode sources, particle accelerator sources, microfocus sources, or laser-generated plasma sources.

[0117] HHG sources and other types of sources can have a gas target and can be a gas jet / nozzle source, capillary / fiber source, or gas chamber source. HHG sources and other types of sources can have a solid or liquid target. Although HHG sources with gas targets are described below, it should be understood that the invention is not limited to HHG sources with gas targets and can be used with HHG sources with solid or liquid targets, as well as other types of sources with any target. Gas targets, solid targets, and liquid targets can be referred to as generation / target media.

[0118] Examples for HHG sources, such as Figure 6As shown, the main components of the radiation source are a pump radiation source 330 operable to emit pump radiation and a gas delivery system 332. The pump radiation source 330 may optionally be a laser, specifically a pulsed high-power infrared or optical laser. The pump radiation source 330 can be, for example, a fiber-based laser with an optical amplifier, thereby generating infrared radiation pulses, for example, each pulse duration can be less than 1 ns (1 nanosecond), with a pulse repetition rate up to several megahertz, as required. The wavelength of the infrared radiation can be in the range of 200 nm to 10 µm, for example, around 1 µm (1 micrometer). Optionally, the laser pulse is delivered as a first pump radiation 340 to the gas delivery system 332, wherein in the gas, a portion of the radiation is converted into emitted radiation 342 at a higher frequency than the first radiation. A gas supply source 334 supplies suitable gas to the gas delivery system 332, in which the gas is optionally ionized by a power source 336. The gas delivery system 332 may be a cut tube.

[0119] The gas provided by the gas delivery system 332 defines a gas target, which can be a gas flow rate 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 selectable options within the same apparatus. The emitted radiation can contain multiple wavelengths. The emission divergence angle of the emitted radiation can be wavelength-dependent. For example, different wavelengths will provide different levels of contrast when imaging structures of different materials. For example, for the inspection of metallic or silicon structures, a wavelength different from that used for characterizing (carbon-based) resists or for detecting contamination in such different materials can be selected. One or more filtering devices 344 can be provided. For example, filters such as thin films of aluminum (Al) or zirconium (Zr) can be used to block further entry of the underlying infrared radiation into the inspection apparatus. A grating (not shown) can be provided to select one or more specific wavelengths from the generated wavelengths. Optionally, the irradiation source includes a space configured to be evacuated, and the gas delivery system is configured to provide the gas target in that space. Optionally, part or all of the beam path can be contained within a vacuum environment; it should be noted that SXR and / or EUV radiation is absorbed as it propagates in air. Various components of the radiation source 310 and the irradiation optics 312 can be adjustable to achieve different measurement “recipes” within the same apparatus. For example, different wavelengths and / or polarizations can be selected.

[0120] Depending on the material of the structure being inspected, different wavelengths can provide the desired level of penetration to deeper layers. Shorter wavelengths may be preferred for distinguishing minimal device features and defects within them. For example, one or more wavelengths in the range of 0.01 to 20 nm (or optionally in the range of 1 to 10 nm, or optionally in the range of 10 to 20 nm) can be selected. Wavelengths shorter than 5 nm may suffer from extremely small critical angles when reflected from the material of interest in semiconductor manufacturing. Therefore, selecting wavelengths greater than 5 nm can provide stronger signals at higher incident angles. On the other hand, if the inspection task is to detect the presence of a certain material, such as detecting contamination, then wavelengths up to 50 nm can be useful.

[0121] A filtered beam 342 from radiation source 310 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 at a near-vacuum state by vacuum pump 352, allowing SXR and / or EUV radiation to pass through the atmosphere without excessive attenuation. Irradiation system 312 has the function of focusing radiation into a focused beam 356 and may include, for example, two-dimensional curved mirrors or a series of one-dimensional curved mirrors, as described in the published U.S. patent application US2017 / 0184981A1 mentioned above (the contents of which are incorporated herein by reference in their entirety). Focusing is performed to achieve a circular or elliptical spot S with a diameter of less than 10 µm when projected onto the structure of interest. Substrate support 316 includes, for example, an XY translation stage and a rotation stage, by which any portion of the substrate W can be brought to the focal point of the beam in a desired orientation. Thus, the radiation spot S is formed on the structure of interest. Alternatively, or additionally, the substrate support 316 may include, for example, a tilting stage that can tilt the substrate W at an angle to control the incident angle of the focused beam on the structure of interest T.

[0122] Optionally, the illumination system 312 provides a radiation reference beam to a reference detector 314, which can be configured to measure the spectrum and / or intensity of different wavelengths in the filtered beam 342. The reference detector 314 can be configured to generate a signal 315 provided to the processor 320, and the filter can include information about the spectrum of the filtered beam 342 and / or the intensity of different wavelengths in the filtered beam.

[0123] The reflected radiation 360 is captured by detector 318, and the spectrum is provided to processor 320 for calculating the properties of the target structure T. Therefore, the irradiation system 312 and the detection system 318 form an inspection apparatus. This inspection apparatus may include hard X-ray, soft X-ray, and / or EUV spectroreflectometers as described in US2016282282A1, the entire contents of which are incorporated herein by reference.

[0124] If the target Ta has a certain periodicity, the radiation from the focused beam 356 can also be partially diffracted. The diffracted radiation 397 follows a different path than the reflected radiation 360, which forms a well-defined angle with respect to the angle of incidence. 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 another detection system 398 that detects at least a portion of the diffraction radiation 397 and / or images it. Figure 6 The diagram depicts a single additional detection system 398, 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 diffracted radiation 397 in multiple diffraction directions. In other words, the (higher) diffraction order of the focused radiation beam impinging on the target Ta is detected and / or imaged by one or more additional detection systems 398. One or more detection systems 398 generate signals 399 that are provided to the measurement processor 320. Signals 399 may include information about the diffracted light 397 and / or may include an image obtained from the diffracted light 397.

[0125] To assist in the alignment and focusing of the light spot S with the desired product structure, the inspection apparatus 302 may also provide auxiliary optics that utilize auxiliary radiation under the control of the measurement processor 320. The measurement processor 320 may also communicate with a position controller 372 that operates a translation stage, a rotation stage, and / or a tilt stage. The processor 320 receives highly accurate feedback regarding the substrate position and orientation via sensors. Sensors 374 may include, for example, interferometers, which can provide picometer-level accuracy. During operation of the inspection apparatus 302, spectral data 382 captured by the detection system 318 is delivered to the measurement processing unit 320.

[0126] As described above, alternative forms of the inspection apparatus may use hard X-rays, soft X-rays, and / or EUV radiation under normal or near-normal incidence, for example, to perform diffraction-based asymmetry measurements. Another alternative form of the inspection apparatus uses hard X-rays, soft X-rays, and / or EUV radiation with a direction greater than 1° or 2° to the direction parallel to the substrate. Both types of inspection apparatus can be incorporated into a hybrid metrology system. The performance parameters to be measured may include overlay accuracy (OVL), critical dimension (CD), focal point of the lithography apparatus when the target structure is printed, coherent diffraction imaging (CDI), and overlay at resolution (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 range of 5 to 30 nm, or optionally radiation in the range of 10 to 20 nm. This radiation may be narrow-band or broadband in nature. The radiation may have discrete peaks in a specific wavelength band, or it may have more continuous characteristics.

[0127] 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 lithography unit (post-development inspection or ADI), and / or to measure structures after they have been formed in harder materials (post-etching inspection or AEI). For example, a substrate can be inspected using inspection device 302 after it has been treated by a developing apparatus, an etching apparatus, an annealing apparatus, and / or other apparatus.

[0128] 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. This 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 photolithographic patterns on a semiconductor substrate. The type and quality of the measurement can depend on several characteristics of the radiation used by the measurement instrument MT. For example, the resolution of an electromagnetic measurement can depend on the wavelength of the radiation; shorter wavelengths can measure smaller features, for example, 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 the measurement. To perform measurements at a specific wavelength or wavelength range, the measurement instrument MT needs access to a source that provides that / those wavelengths(s). Different types of sources exist to provide radiation at different wavelengths. Depending on the wavelength(s) provided by the source(s), different types of radiation generation methods can be used. For extreme ultraviolet (EUV) radiation (e.g., 1 nm to 100 nm) and / or soft X-ray (SXR) radiation (e.g., 0.1 nm to 10 nm), the source can use HHG or any other source of the above types to obtain radiation at (multiple) desired wavelengths.

[0129] Figure 7 A simplified schematic diagram of embodiment 600 of the irradiation source 310 is shown, which can be an irradiation source for HHG. Regarding Figure 6 One or more features of the irradiation source in the described measuring instrument may also be present in the irradiation source 600, where appropriate. The irradiation source 600 includes a chamber 601 and is configured to receive pump radiation 611, the direction of propagation of which is indicated by an arrow. The pump radiation 611 shown here is an example of pump radiation 340 from pump radiation source 330, as... Figure 6 As shown. Pump radiation 611 can be directed into chamber 601 via radiation input 605, which can be an observation port and optionally made of fused silica or a similar material. Pump radiation 611 can have a Gaussian or hollow (e.g., annular) transverse cross-sectional profile and can be incident (optionally focused) onto gas flow 615 within chamber 601, the flow direction of which is indicated by a second arrow. Gas flow 615 comprises a small volume (referred to as a gas volume or gas target, e.g., a few cubic millimeters) 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. Gas flow 615 can be a steady flow. Other media, such as metallic plasma (e.g., aluminum plasma), can also be used.

[0130] 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. At least a majority of the region generating the emitted radiation 613 is referred to as the interaction region. The interaction region can vary from tens of micrometers (for tightly focused pump radiation) to several millimeters or centimeters (for moderately focused pump radiation), or even several meters (for extremely loosely focused pump radiation). The gas delivery system is configured to provide a gas target for generating the emitted radiation at the interaction region of the gas target, and optionally, the irradiation source is configured to receive the pump radiation and provide the pump radiation at the interaction region. Optionally, the gas flow 615 is provided by the gas delivery system to a vacuumed or near-vacuumed space. The gas delivery system may include a gas nozzle 609, such as... Figure 6 As shown, the gas nozzle 609 includes an opening 617 in 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 volume by extracting residual gas flow and maintaining a vacuum or near-vacuum atmosphere inside the chamber 601. Optionally, the gas nozzle 609 may be made of a thick-walled tube and / or a material with high thermal conductivity to avoid thermal deformation caused by high-power pump radiation 611.

[0131] It is conceivable that the size of the gas nozzle 609 could also be used in scaled-down or scaled-down versions, ranging from micrometer-sized nozzles to meter-sized nozzles. This wide size range stems from the fact that settings can be scaled so that the intensity of the pump radiation at the gas flow ultimately falls within a specific range beneficial to the emitted radiation. This necessitates different size designs for different pump radiation energies, which could be pulsed lasers, and the pulse energy could vary from tens of microjoules to joules. Optionally, the gas nozzle 609 may have thicker walls to reduce nozzle deformation caused by thermal expansion effects, which can be detected, for example, by a camera. A gas nozzle with thicker walls can produce a stable gas volume with reduced variation. Optionally, the irradiation source includes a gas trap near the gas nozzle to maintain the pressure in chamber 601.

[0132] Due to the interaction between the pump radiation 611 and the gas atoms in the gas flow 615, the gas flow 615 converts a portion of the pump radiation 611 into emitted radiation 613. This emitted radiation can be... Figure 6An example of emitted radiation 342 is shown. The central axis of emitted radiation 613 may be collinear with the central axis of incident pump radiation 611. Emitted radiation 613 may have a wavelength in the X-ray or EUV range, wherein the wavelength is in the range of 0.01 nm to 100 nm, optionally 0.1 nm to 100 nm, optionally 1 nm to 100 nm, optionally 1 nm to 50 nm, or optionally 10 nm to 20 nm.

[0133] In operation, the emitted radiation beam 613 can pass through the radiation output 607 and can subsequently be irradiated by the irradiation system 603 (which may be...). Figure 6 (Example of illumination system 312) is manipulated and directed onto the substrate to be inspected for measurement purposes. Emitted radiation 613 can be directed (optionally focused) onto a structure on the substrate.

[0134] Because air (and virtually any gas) absorbs a large amount of SXR or EUV radiation, the volume between the gas flow 615 and the wafer under inspection can be evacuated or nearly evacuated. Since the central axis of the emitted radiation 613 can be collinear with the central axis of the incident pump radiation 611, it may be necessary to block the pump radiation 611 to prevent it from passing through the radiation output 607 and entering the irradiation system 603. This can be achieved by... Figure 6 The filter 344 shown is incorporated into the radiation output 607. This filter 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 multiple materials in a multilayer configuration. When the pump radiation 611 has a hollow (optionally annular) transverse cross-sectional profile, the filter can be a hollow (optionally annular) block. Optionally, the filter is neither perpendicular nor parallel to the propagation direction of the emitted radiation beam to achieve effective pump radiation filtering. Optionally, the filter 344 comprises a hollow block and a thin-film filter, such as an aluminum (Al) or zirconium (Zr) thin-film filter. Optionally, the filter 344 may also include a mirror that effectively reflects emitted radiation but poorly reflects pump radiation, or a metal mesh that effectively transmits emitted radiation but poorly transmits pump radiation.

[0135] This document describes methods, apparatus, and components for obtaining emitted radiation (optionally at a high harmonic frequency of the pump radiation). The radiation generated by this process (optionally HHG, which uses nonlinear effects to generate radiation optionally at a harmonic frequency of the provided pump radiation) can be provided as radiation in a metrology tool (MT) for inspecting and / or measuring a substrate. If the pump radiation comprises short pulses (i.e., few periods), the generated radiation may not necessarily be exactly at a harmonic of the pump radiation frequency. The substrate may be a photolithographically patterned substrate. The radiation obtained by this process can also be provided in a photolithography apparatus (LA) and / or a photolithography cell (LC). The pump radiation may be pulsed radiation, which can provide peak intensity within a short burst.

[0136] Pump radiation 611 may include radiation having one or more wavelengths higher than the emitted radiation. Pump radiation may include infrared radiation. Pump radiation may include (multiple) radiation with wavelengths in the range of 500 nm to 1500 nm. Pump radiation may include (multiple) radiation with wavelengths in the range of 800 nm to 1300 nm. Pump radiation may include (multiple) radiation with wavelengths in the range of 900 nm to 1300 nm. Pump radiation may be pulsed radiation. Pulsed pump radiation may include pulses with durations in the femtosecond range.

[0137] 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.

[0138] 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 the source radiation to perform measurements on a substrate exposed by a photolithography apparatus. This measurement can be used to determine one or more parameters of the structure on the substrate. Using shorter wavelength radiation, such as EUV, SXR, and / or HXR wavelengths included in the aforementioned wavelength range, allows smaller features of the structure to be resolved by the metrology tool 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.

[0139] In a measurement tool (MT), source radiation can be emitted from a radiation source and directed onto a target structure (or other structure) on a substrate. 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 MT can include one or more sensors for detecting diffracted radiation. For example, the MT can include detectors for detecting positive (+1st order) and negative (-1st order) first-order diffraction orders. The MT can also measure specularly reflected or transmitted radiation (0th-order diffraction). Additional sensors may be present in the MT for measurement, such as those for measuring other diffraction orders (e.g., higher diffraction orders).

[0140] In an example photolithography measurement application, the radiation generated by HHG can be focused onto a target on a substrate using an array of optics (which may be called an irradiator), which transmits the radiation from the HHG source to the target. The HHG radiation can then be reflected from the target, detected, and processed, for example, to measure and / or infer the characteristics of the target.

[0141] Gas target HHG configurations can be broadly categorized into three separate types: gas jets, gas chambers, and gas capillaries. Figure 7 An example gas jet configuration is depicted, in which a gas volume is introduced into the driving radiation laser beam. In the gas jet configuration, the interaction between the driving radiation and the solid portion 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 enclosed within a gas chamber. In a gas capillary arrangement, the capillary structure containing the gas has a small lateral dimension, thus significantly affecting the propagation of the driving radiation laser beam. The capillary structure may, for example, be a hollow fiber, wherein the hollow core is configured to contain the gas.

[0142] The gas jet HHG configuration offers relative freedom in shaping the spatial profile of the driving radiation beam in the far field because it is not constrained by the limitations imposed by the gas capillary structure. The gas jet configuration can also have less stringent alignment tolerances. On the other hand, the gas capillary can provide an increased interaction region between the driving radiation and the gaseous medium, which can optimize the HHG process.

[0143] To utilize HHG radiation, such as in measurement applications, it is separated from the driving radiation downstream of the gas target. The separation of HHG and driving radiation can differ depending on the gas jet and capillary configuration. In both cases, driving radiation suppression schemes can include a metallic transmission filter to filter out any remaining driving radiation from the short-wavelength radiation. However, before such a filter can be used, the intensity of the driving radiation should be significantly reduced according to its intensity at the gas target to avoid damaging the filter. The methods that can be used for this intensity reduction differ for the gas jet and capillary configurations. For a gas jet HHG, due to the relative degrees of freedom in the shape and spatial profile (also referred to as spatial distribution and / or spatial frequency) of the driving radiation beam focused onto the gas target, it can be designed to have low intensity in the far field along the direction of propagation of the short-wavelength radiation. This spatial separation in the far field means that an aperture can be used to block the driving radiation and reduce its intensity.

[0144] In contrast, in gas capillary structures, the spatial profile of the beam as it passes through the gaseous medium can be 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, in the case where hollow-core fiber is used as the capillary structure, the shape and material of the fiber structure determine which driving radiation modes are supported for propagation through the fiber. For most standard fibers, the supported propagation modes result in a spatial profile in which 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 a Gaussian or near-Gaussian profile in the far field.

[0145] Although HHG is specifically referenced, it should be understood that the invention can be practiced using any radiation source where the context permits. In one embodiment, the radiation source is a laser-generated plasma (LPP) source as described above for generating hard X-rays, soft X-rays, EUV, DUV, and visible light irradiation. In one embodiment, the radiation source is one of the following: a liquid metal jet source, an inverse Compton scattering (ICS) source, a plasma channel source, a magnetic undulator source, a free electron laser (FEL) source, a compact storage ring source, a discharge-generated plasma source, a rotating anode source, a solid anode source, a particle accelerator source, and a microfocus source.

[0146] Figure 8 At least a portion of the apparatus 800 according to this disclosure is illustrated. Apparatus 800 may correspond to a portion of the measuring apparatus 302 described herein.

[0147] Apparatus 800 includes a detector 804. Detector 804 may be referred to as an image sensor. In some examples, detector 804 is configured to measure one or more non-zero diffraction orders of illumination diffracted from a structure. Typically, detector 804 may include multiple pixels. In some examples, apparatus 800 may include two detectors 804 (which may be referred to as a first detector and a second detector, respectively). In some examples, apparatus 800 may include more than two detectors. Apparatus 800 may also include a substrate support 802 that may support a substrate W (e.g., a wafer). Reference illumination 805 (e.g., a laser beam, optionally a collimated laser beam) is provided by a reference illumination source (not shown) and is directed onto or into optical element 806. In some examples, as described in more detail below, reference illumination 805 may be coupled into optical element 806 via an optical fiber. Figure 8 As shown, optical element 806 can be placed on substrate support 802 (e.g., attached to substrate support 802). In some examples, optical element 802 can be attached (e.g., glued) to the substrate W itself, or optical element 802 can even be integrated with wafer W as part of substrate W (e.g., as a structure on substrate W).

[0148] Optical element 806 is configured to generate a plurality of reference irradiance beams 808 incident on detector 804 from reference illumination 805 incident on optical element 806. At the intersection of the reference irradiance beams 808 and detector 804, a plurality of reference irradiance spots 810 are formed on detector 804. The reference irradiance spots 810 collectively form a reference irradiance pattern. It should be understood that... Figure 8 This is a side view of device 800, and the reference irradiance pattern can be a two-dimensional (2D) pattern on detector 804.

[0149] Preferably, the optical element 806 is configured (e.g., designed) such that the reference irradiance spot 810 is smaller than the pixel size of the detector 804. Preferably, the optical element 806 is configured such that the focal point of the reference irradiance beam 808 is located at or near the plane of the detector 804. For example, where the numerical aperture NA = 0.1 and the wavelength is 633 nm, the reference irradiance spot size should be approximately 4 µm in diameter, which is smaller than the typical image sensor pixel diameter (e.g., approximately 10 µm, approximately 15 µm, approximately 20 µm, or approximately 25 µm in some examples). Preferably, the optical element 806 is configured such that at least three reference irradiance spots 810 are generated at the detector 804. The optical element 806 can be configured to generate 10, 100, or even 1000 reference irradiance spots 810. In an example, a grid of 100 reference irradiance spots 810 can be distributed across the detector. In one embodiment, the grid of reference irradiance spots 810 is uniformly spaced. In one embodiment, the grid of the reference irradiance spot 810 does not need to be uniformly spaced.

[0150] The position-related parameters of detector 804 can be determined by obtaining the pixel coordinates of the reference irradiance spot 810 on detector 804 (e.g., capturing an image using detector 804 when the reference irradiance beam 808 is incident on detector 804).

[0151] In the example, the wavelength of the reference irradiation 805 is 633 nm (e.g., generated by a helium-neon laser as the reference irradiation source). However, other wavelengths can also be used, such as infrared (IR), near-infrared (NIR), visible light, near-ultraviolet (NUV), ultraviolet (UV), extreme ultraviolet (EUV), or X-ray wavelengths.

[0152] Because the reference irradiance spot 810 (at the plane of detector 804) is small and the wavelength of the reference irradiance 805 is known, a large amount of data will be available for accurately measuring the position of detector 804 relative to the optical element (in six degrees of freedom (DoF)). For example, position-related parameters according to this disclosure may include the distance of detector 804 from optical element 806. Position-related parameters may include the distance of detector 804 from optical element 806 in a specific dimension (i.e., x, y, or z) in 3D space. In some examples, position-related parameters may include rotational parameters of detector 804.

[0153] Optical element 806 can be designed such that, in conjunction with the known incident and azimuth angles of reference illumination 805 relative to optical element 806, the principal ray vector 812 of each reference irradiance beam 808 is also known. Computer-generated holograms (CGHs) can be particularly suitable as optical elements 806 that can be designed in this manner. For example, optical element 806 may include a glass plate on which a CGH is formed. Typically, suitable optical elements 806 may include one or more of the following: phase mask, amplitude mask, (2D) grating, spatial light modulator, hologram, CGH, pinhole mask, and / or multiple curved (e.g., parabolic) mirrors. The diameter of optical element 806 can be several millimeters (e.g., 1 to 20 mm), which can be convenient for illumination by a laser beam. In some examples described herein, optical element 806 may include integrated optics, such as photonic integrated circuits (PICs). The hologram or CGH can be implemented as a phase hologram, an amplitude hologram, or a combination thereof. The hologram can be a thin hologram or a volume hologram.

[0154] The position-related parameters (e.g., the six DoFs of detector 804) of detector 804 can be fitted such that the observed coordinates (i.e., pixel coordinates) of the reference irradiance spot 810 are matched with the point where the principal ray vector 812 of the reference irradiance beam 808 intersects the plane of detector 804.

[0155] Alternatively, or otherwise, pixels can be mapped to the polar angle of the main ray.

[0156] For measurement purposes, a reference point 814 can be defined on the optical element 806 (e.g., at or near the center of the optical element 806). After calibration of the device 800 (i.e., once the positional correlation parameters of the detector 804 relative to the optical element 806 have been determined), the substrate stage 802 can be moved such that the measurement target (e.g., located on the substrate W) is exactly where the reference point 814 was during calibration. In another example, the position of the substrate W or the measurement target (which may be on the substrate W) can be determined using the positional correlation parameters of the detector 804 relative to the optical element 806, and additionally based on a known distance between the substrate W or the measurement target and the optical element 806.

[0157] Figure 9 The diagram illustrates the relationship with Figure 8 The illustrated device 800 is similar to device 900. In Figure 9 In the middle, reference irradiation 905 (e.g.) Figure 9 As shown, it may not be collimated, but in other examples it may be collimated) incident on optical element 906. Optical element 906 may include a periodic pattern (e.g., a grating pattern), which may be more than about Figure 8Some examples of the optical elements are cheaper and easier to manufacture (e.g., periodic optical element 906 can be cheaper and easier to manufacture than CGH or PIC). The reference irradiance beams 908 generated by the reference illumination 905 incident on the periodic optical element 906 may not all be focused on the plane of detector 804, resulting in different sizes of reference irradiance spots 910 on detector 804.

[0158] In some examples, at least a portion of the optical element is transmissive to a reference illumination.

[0159] Figure 10 Another example of a device 1000 according to the present disclosure is illustrated, which includes an optical element 1006 that at least partially transmits light to a reference illumination 1005. Figure 10 In this example, optical element 1006 is illuminated from below (e.g., from the side of optical element 1006 opposite to detector 804). Reference illumination 1005 may be provided via optical fiber 1024 (e.g., single-mode fiber), for example, through an adapted substrate support 1002. Optional collimating lens 1022 may be used to collimate the reference illumination 1005 incident on optical element 1006. In some examples (not shown), the reference illumination source may be directly integrated with optical element 1006, and a combination of the reference illumination source and optical element 1006 may be integrated with substrate support 1002. Reference irradiance beam 1008 and thus reference irradiance spot 1010 incident on detector 804 are formed by the interaction of reference illumination 1005 with transmissive optical element 1006. Optical element 1006 (which is at least partially transmissive to reference illumination 1005) may include CGH, gratings, and / or any other suitable type of optical element described herein or otherwise. Optical element 1006, lens 1022, and / or reference illumination source can be collectively referred to as calibration device 1020, which can be integrated with substrate support 1002. Therefore, in some examples, transmission optical element 1006 can achieve a more compact or modular device. Calibration device 1020 can advantageously be aligned and tested before integration with measurement devices.

[0160] In some examples, the reference illumination can be aligned relative to the optical element based on the reflection of the reference illumination by the optical element. That is, at least a portion of the optical element can be reflective of the reference illumination. In some examples, the optical element may include a first portion (which may be referred to as an alignment portion or alignment guide) that is reflective of the reference illumination, and a second portion that is transmissive of the reference illumination.

[0161] Figure 11 The diagram illustrates the relationship with Figure 10The illustrated device 1000 is an example of a similar device 1100, wherein the optical element 1106 includes a transmission portion 1134 and an alignment guide 1132 that is reflective to the reference illumination 1005 (see [reference]). Figure 11 (Planar view of optical element 1106 in the illustration). Device 1100 may also include one or more alignment marks or detectors 1140 (e.g., photodiodes) arranged to facilitate alignment of reference illumination 1005 (e.g., alignment of reference illumination source and / or fiber optic 1024) relative to optical element 1106 by detecting and / or enabling visualization of reference illumination reflected by alignment guide 1132. In some examples, such as... Figure 11 As shown, the alignment mark or detector 1140 may form part of the calibration device 1120 and / or may be integrated into the adaptable substrate support 1102. The alignment guide 1132 may include, for example, a reflective coating, such as Cr. Figure 11 As shown, the alignment guide 1132 can be placed around the periphery of the optical element 1106. Advantageously, online alignment of the device 1100 can be performed without additional measurement time.

[0162] Alternatively, the optical element can be illuminated from above (i.e., from the same side as the detector), such as Figure 8 and Figure 9 As shown. In this arrangement, the reference illumination can also be based on the reflection of the reference illumination by the optical element, which is aligned relative to the optical element.

[0163] Figure 12 An example of an arrangement based on reference illumination reflected by optical element 1206, wherein the reference illumination may be aligned relative to optical element 1206 is schematically illustrated. Figure 12 The arrangement shown may correspond to the apparatus described herein, such as Figure 8 The device 800 and / or shown Figure 9The apparatus 900 is shown. Reference illumination provided by a reference illumination source 1250 (e.g., a laser) can be directed toward an optical element 1206 (e.g., via a lens 1252, an optical fiber 1224, and / or a combination of one or more steering mirrors 1254). A portion of the reference illumination is reflected by the optical element 1206 and propagates back toward the reference illumination source 1250, and is partially redirected by a beam splitter 1257 toward an alignment detector 1256 (e.g., a photodiode) to facilitate alignment. The optical element 1206 can be designed such that if the optical element 1206 is illuminated at a specific angle, the beam is propagated back toward the reference illumination source 1250. A beam collector 1258 can also be employed, for example, to collect the reference illumination emitted by the reference illumination source 1250 and reflected by the beam splitter 1257 toward the optical element 1206. In the example, for an optical element 1206 comprising a CGH designed for illumination at an incident angle of 30 degrees, a linear grating having a pitch equal to the reference illumination wavelength would be suitable. Figure 12 The arrangement is as follows: If the reference illumination illuminates the CGH at the correct angle, the reflected illumination will propagate back to the fiber 1224 and reach the alignment detector 1256. Multiple steering mirrors 1254 can be used to maximize the signal at the alignment detector 1256.

[0164] In some examples, such as Figure 13 In the illustrated device 1300, reference illumination 1305 is directly coupled to optical element 1306 via optical fiber 1324. For example, optical element 1306 (which may be located on substrate support 1302) may include integrated optical devices, such as photonic integrated circuits (PICs). The integrated optical devices are designed (configured) such that the focal point and / or principal ray vector of the reference irradiance beam 1308 are known and can be used to determine the position of detector 804 relative to optical element 1306 based on a reference irradiance pattern including reference irradiance spot 1310. As described herein, a reference point 1314 may be defined on optical element 1306.

[0165] Advantageously, the optical element 1306, which includes an integrated optical device (such as a PIC), can result in reduced stray light (e.g., due to interference / speckle effects) and / or improved tolerance for the directionality / profile quality of the reference illumination beam.

[0166] Integrated optics such as PICs can generate reference irradiance beams from multiple point sources from a reference illumination. As long as the locations of the point sources are accurately known, they do not need to be precisely in the same plane as any substrate being measured.

[0167] In some examples, such as Figure 14As shown, a reference irradiance pattern can be formed on the first detector 804a and the second detector 804b. It should be understood that any device in the apparatus described herein may include a first detector and a second detector, and more generally may include any number of detectors 804. Figures 8 to 13 The single detector 804 shown is only illustrated for clarity.

[0168] Figure 14 An example is illustrated in which calibration of position-related parameters of detectors(s) ...

[0169] In some examples, the position-related parameters of the second detector(s) 804b(s) can be determined relative to the position-related parameters of the first detector(s) 804a(s), thereby fixing 6 of the 12 DoFs (in the case of a dual-detector arrangement). In this example, the position-related parameters of the first detector(s) 804a(s) can be determined by any of the methods and / or means described herein.

[0170] In some examples, the optical elements may include spatial light modulators (SLMs). SLMs can be particularly advantageous when the detector is displaced over a wide range of distances.

[0171] In some examples, the optical elements may include a test pattern on the substrate W itself. The test pattern may include, for example, a grating (e.g., a 2D grating) as described herein, or a CGH, or any other suitable optical element. Depending on the desired arrangement, the test pattern may be made to reflect and / or transmit light to a reference illumination.

[0172] In some examples, the reference point described herein may comprise a small (e.g., 20–40 µm in diameter) unpatterned region of an optical element. This region may be aligned with the focal point of the measurement illumination. If all the measurement illumination energy is incident on this region, there will be strong specular reflection and little or no diffraction. Alternatively, the reference point may be marked by a fine pattern on this region (e.g., with a pitch smaller than the reference illumination wavelength), which will generate a strong and identifiable measurement illumination (e.g., SXR) diffraction pattern.

[0173] Detector 804 may include a filter for blocking residual infrared light generated by the measurement irradiation. The wavelength and / or source power of the reference irradiation may be selected such that the filter will not interfere with the calibration described herein.

[0174] In some examples, instead of or in addition to fitting the sensor using 6 DoF, a mesh mapping from pixel coordinates to pupil coordinates can be generated. Pupil coordinates are the x and y components of a unit vector from a reference point of the optics, in a coordinate system where the z-axis is perpendicular to the substrate's W-plane. For example, if the CGH generates a 10x10 mesh of known ray vectors (10x10 known pupil vectors), the pixel coordinates where these vectors intersect the detector are obtained; an interpolation function can then be constructed to map from the pixel coordinates to the pupil vector. However, if the detector is not flat due to mechanical stress, a 6 DoF fit may be inaccurate; instead, a direct mapping can be created instead of a parameterized mapping with too few parameters.

[0175] Figure 22 Another example of an optical element according to the present disclosure is schematically illustrated. As shown in FIG15, the PIC may include a die, for example, formed from a wafer or substrate. In the example shown in FIG15, two PICs, namely PIC-x and PIC-y, are placed on surface 2202. Each PIC, namely PIC-x and PIC-y, is illuminated by corresponding optical fibers Fx and Fy, and includes waveguide 2204 and splitter 2206, such that light (in the form of a reference irradiance beam) is coupled out from each PIC at points (i.e., forming point sources) Px1, Px2 and Py1, Py2, respectively. Surface 2202 is arranged in relation to the measurement target (or substrate) W ( Figure 22 (Not shown in the image) In the same plane. PIC, namely PIC-x and PIC-y, are arranged on surface 2202 such that the reference irradiance beam is emitted from the edge of the die (i.e., the narrow edge corresponding to the wafer plane forming the die, which is perpendicular to the plane of surface 2202). Coupling light from the side of the die can advantageously have higher efficiency compared to light coupled from the "top" of the die.

[0176] exist Figure 22 In the example shown, the first PIC PIC-x is oriented along a first direction (e.g., the x-direction), while the second PIC PIC-y is oriented perpendicular to the first PIC PIC-x (e.g., the y-direction), thereby producing two pairs of reference illumination beams (point sources) with corresponding vertical spacing.

[0177] Figure 23 An example of an optical element including a fiber array FA according to the present disclosure is schematically illustrated. Reference illumination can be provided to the fiber array FA by fiber 2310 and split into multiple fibers by fiber splitter 2306, for example... Figure 23 The two optical fibers F1 and F2 are shown. The fiber array FA can be configured to define output points P1 and P2 (where a reference irradiance beam is generated), comprising multiple fiber tips spaced apart with controlled spacing down to the micrometer or submicrometer level. Figure 23In the example shown, the fiber array FA is attached to bracket 2302, which also holds the fiber splitter 2306 and the two fibers F1 and F2 from the splitter to the fiber array FA. Because bending and temperature changes can affect the phase difference between points P1 and P2, a short distance from the fiber splitter 2306 to points P1 and P2 is preferred; fibers F1 and F2 can be attached to bracket 2302 to prevent bending and to ensure that they are both at the same temperature (so that any temperature change affects both fibers equally, for example, with respect to any temperature-induced phase change).

[0178] Two or more fiber arrays (FAs) can be similar to, for example Figure 22 The diagram shows a lateral output coupling configuration from the PIC. However, in the case of a fiber array FA, ​​the optical fibers are attached (e.g., glued) to the wafer or substrate to form the fiber array FA, ​​while... Figure 22 In the example shown, the PIC is created from a wafer, or as a die, via, for example, a photolithography step.

[0179] Figure 25 An example of an optical element including optical fiber 2510 is schematically illustrated. Optical fiber 2510 is illuminated by reference irradiation entering at input 2511 of optical fiber 2510, and point sources P1 and P2 (referred to as optical output points) are formed by removing portions of the fiber cladding at specific locations on optical fiber 2510. The reference irradiance beam is output from optical fiber 2510 at the optical output points. Any residual reference irradiation continues through optical fiber 2510 and exits at output 2512 of optical fiber. It should be understood that multiple optical fibers 1510 and / or more than two optical output points are included. Figure 25 Variations of the optical element shown are also possible. Figure 25 In the example shown, the optical fiber is modified by forming holes in the cladding. Preferably, when the light output point is formed by the holes in the cladding, the diameter of these holes is smaller than the wavelength of the reference illumination. Although Figure 25 The fiber optic cable 2510 shown includes a U-shaped bend, but it should be understood that other configurations are also possible, including a straight fiber optic cable 2510. For example... Figure 25 As shown, the optical fiber 2510 can be placed on a suitable surface 2502, which can be configured to have a temperature that is stable over time (e.g., temperature controlled) to ensure that the phase difference and / or position of the optical output point remain stable over time.

[0180] Figure 26 (A) and (B) schematically illustrate another example of an optical element including optical fiber 2610 according to this disclosure. Figure 26As shown in (A), a large portion of the cladding 2613 can be removed (e.g., scraped off) to expose a portion of the fiber core 2614 of the optical fiber 2610, thereby forming a region 2618 including multiple optical output points (e.g., Figure 26 (As shown in more detail in the cross-section of (B)). Figure 26 In the examples shown in (A) and (B), the light output point may include an optical antenna 2616 (also referred to as a plasmon particle) comprising particles of a suitable material (e.g., a metal such as gold, copper, or silver) placed on an exposed portion of the fiber core 2614, resulting in an emitted reference irradiance beam comprising dipole radiation, which is at least partially directional. For example, the optical antenna 2616 as described herein may comprise metal particles sized to have a plasmon resonance that matches the wavelength of light in the underlying fiber core 2614. The scattering cross-section of the optical antenna 2616 is much larger than the physical size of the optical antenna 2616, so each optical antenna 2616 will form a point source with a predictable radiation pattern (e.g., a dipole for a rod). Figure 26 As shown in (A), the modified optical fiber 2610 can be placed on a suitable surface 2602, which can be temperature-controlled, similar to... Figure 25 Surface 2502 shown and described herein.

[0181] In some examples, tapered optical fibers can be prepared (e.g., by heating and stretching the fiber) to create (multiple) exposed portions of the fiber core.

[0182] In some examples, the effective refractive index of the removed cladding sections (multiple sections) can be calibrated by immersing optical fibers 2510 and 2610 in a liquid and measuring the optical path length of light emitted and reflected from the light output point, and comparing these back-reflection optical path lengths with those of optical fibers 2510 and 2610 without immersion in the liquid. For measurement purposes, the liquid can be used to replace the removed cladding sections.

[0183] Figure 27 An example of an optical element (e.g., a PIC) including a waveguide 2720 comprising multiple grating lines 2725 is schematically illustrated. In some examples, Figure 27 The optical element shown can be called a "grating coupler". Waveguide 2720 is formed by the input terminal 2721 entering waveguide 2720 and passing through waveguide 2720 toward output terminal 2722. Figure 27 The middle is shown as x The light is illuminated using a reference illumination (direction). Light is coupled out from grating line 2725. Figure 27 In the diagram, four raster lines are drawn, but different numbers can be used. The spacing of the raster lines (2725) can be selected to adjust the overall light distribution. xEmitted in a direction (e.g., pupil) The range of values, for example, mostly within the range (Inside). However, in the direction perpendicular to x The direction of the direction (i.e.) y In terms of direction, the position of the output light (i.e., the reference irradiance beam) is very clearly defined because the light travels through the center of waveguide 2720. Therefore, a well-defined... y The point source of the location. Similarly, it can be derived from parallel to... y The creation of axially arranged waveguides has specific limitations. x The point source of the location. Although Figure 27 The grating line 2725 shown is in y The grating line 2725 is shown as shorter than the width of waveguide 2720 in the direction, but it should be understood that in some examples, the grating line 2725 may be longer than the width of waveguide 2720 (e.g., in the case where waveguide 2720 is formed in a PIC).

[0184] Figure 28 An example of an optical element is illustrated, configured such that a reference illumination propagates in a planar pattern within a plane 2802 of the optical element (e.g., a PIC). In the example shown in Figure 2821, the reference illumination is provided at input 2821 to a waveguide 2820 formed in the PIC. Waveguide 2820 includes at least a portion configured as a planar waveguide 2822. The planar waveguide may have one or more optical antennas 2816 (also referred to as plasma particles) placed thereon, comprising metals such as copper, gold, or silver, with the size of the optical antennas 2816 on the order of the reference illumination wavelength. For example, the optical antennas 2816 as described herein may comprise metal particles whose size is designed to have a plasma resonance matching the wavelength of light in the underlying waveguide 2820. In some examples, the optical antennas 2816 may comprise rods. The scattering cross-section of the optical antennas 2816 is much larger than the physical size of the optical antennas 2816, so each optical antenna 2816 will form a point source with a predictable radiation pattern (e.g., a dipole for the rod). In some examples (not shown), the optical element may include a cylindrical lens, and the reference illumination may pass through the cylindrical lens to produce a flat plate pattern.

[0185] Some examples of appropriate reference irradiance patterns will now be described.

[0186] In some examples, the reference irradiance pattern can include a diffraction pattern (e.g., generated by any suitable optical element or mask). For example, the pattern can be generated via the Talbot effect. In some examples, the reference irradiance pattern can be generated by interference. For example, the optical element can include a pinhole mask comprising several (e.g., three) pinholes (illuminated from below) with diameters on the order of the reference irradiance wavelength. Light can diffract from these pinholes, and interference between the light from the pinholes can generate a pattern on the image sensor. This can generate ten thousand or more spots. For optical elements illuminated from above, a similar effect can be achieved using an optical element comprising multiple curved (e.g., parabolic) mirrors.

[0187] Figure 15A The illustration shows an example of a series of point sources that can be formed by, for example, integrated optical devices (such as PICs as described herein). Point sources can also be formed by any other suitable type of optical device (such as CGHs or multiple curved mirrors as described herein). Figure 15B The diagram illustrates the process of... Figure 15A An example of a reference irradiance pattern produced by a point source. It should be understood that... Figure 15A and 15B The size of the spots in the image represents their brightness (i.e., larger spots are brighter than smaller spots), and Figure 15A and 15B In practice, the spots in the image can be the same or similar in size. Figure 15A The point sources are arranged in a triangle around the origin, which is the reference point for the optical element described herein. In some examples, the triangle need not be equilateral. In some examples, the reference point (origin) can be defined outside the triangle. Although Figure 15A The distance between points at the corners of the triangle is shown as approximately 15 µm, but it should be understood that larger distances can be used in practice to achieve a tighter reference irradiance pattern (e.g., with a spot pitch of 3 to 4 pixels or less). Darker points located between the corners of the triangle can be arranged on an equally spaced grid, i.e., such that the two nearest neighbors of a darker point are always at the same distance. This ensures that the diffraction pattern from the darker points is aligned with the pattern from the brighter points.

[0188] Three point sources arranged in a triangle can produce dense patterns (or constellations) on the detector, such as... Figure 15BAs shown. Multiple darker point sources result in a "grid" of brighter points in the pattern on the detector. If the relative phase of the light emitted by the point sources and the positions of the point sources are known, the position of the detector can be inferred from the positions of the spots on the detector. In other examples, other numbers of point sources can be used, such as four point sources. In some examples, pairs of point sources can be illuminated one at a time (i.e., by reference illumination reaching or incident on an optical element (e.g., a PIC). For example, three or four point sources can be illuminated two at a time (i.e., as two pairs of point sources, illuminating one pair at a time). A pair of point sources can produce a reference irradiance pattern that includes stripes rather than a dot pattern. According to this disclosure, the reference irradiance spot can include stripes.

[0189] If the distance between point sources is Then the spots (from the center of the dot source pattern); Figure 15A The angular spacing of the origin in the equation will be approximately... (In radians). Ideally, choose This allows the speckle pitch on the detector to be between 3 and 4 pixels, meaning the specks are as close to each other as possible while still being visible as individual specks. The Nyquist limit is at a speckle pitch of 2 pixels; this can be selected... This results in a spot pitch just slightly above this limit, for example, a spot pitch between 2.1 and 3 pixels. In the example, the pixel size is between 5 µm and 15 µm (e.g., 13.5 µm), and the distance from the optics is between 20 mm and 50 mm (e.g., 40 mm), thus yielding the optimal point source distance. Between approximately 470 µm and approximately 900 µm, for example, between approximately 470 µm and approximately 630 µm (e.g., in some examples, d It can be approximately 500 µm, 525 µm, 550 µm, 575 µm, or 600 µm. Figure 15B The pattern in the image is for d = 15 µm, which causes a coarser blot pattern, making it easier to visualize. In this case, d It refers to the maximum distance between two point sources in a point source pattern that simultaneously contribute to the diffraction pattern on the sensor.

[0190] It can be difficult to distinguish detector positions offset by a single point-to-point distance (e.g., 3 pixels). For this distinction, a second point source pattern can be used, i.e. Figure 15A The smaller markers are spaced more closely together than the three main markers. This second point source pattern is generated. Figure 15B Brighter spots in the middle. Coarse position estimation (±1 pixel) can be performed based on the second pattern, while fine sub-pixel position estimation can be performed based on the fine pattern.

[0191] The primary and secondary point source patterns can be activated simultaneously. Alternatively, they can be in two separate optical elements, for example, both attached to a substrate support. The substrate support can be moved sequentially such that the first and then the second optical element are in the target position (where the measurement illumination will be focused). Two separate patterns will be recorded; one pattern is used for a coarse estimate of the detector position, and the other for a fine (subpixel) estimate. In some examples, the optical element can include two patterns on the same optical element; for example, a PIC with two patterns can be illuminated by two different optical fibers relative to each pattern, and each corresponding pattern can be selectable via a switch.

[0192] Figure 16 An example of an optical element 1606 generating a coarse pattern 1602 and a fine pattern 1604 by reference illumination 1605 is schematically illustrated.

[0193] Data processing is highly robust to background stray light. For example, a coarse estimate of the detector position can be used to transform a recorded image into the pupil space. The pupil space is derived from the center of the optical element (as described above). Figure 15A The representation of the ray vector (from the origin in the image), where the z-axis is perpendicular to the plane of the optical element and / or the plane of the point source. If the detector's pixel is located at position... If , then the corresponding pupil coordinates are In the pupil space, the reference irradiance pattern is nearly periodic with a known unit cell. The signal can be filtered using standard Fourier methods. When the reference irradiance pattern is generated from point sources (e.g., in some examples by PIC, CGH, or multiple curved mirrors), as described herein, the position of the reference irradiance spot may be influenced by the phase difference of the point sources rather than their amplitude. This makes the pattern less sensitive to the quality of the beam profile.

[0194] Figure 15A A dot pattern formed by numerous point sources is shown to create a coarse pattern for coarse position measurements. In some examples, coarse and fine position measurements may be performed using only a small number of point sources (i.e., reference irradiance beams), such as two or four pairs of point sources (reference irradiance beams), i.e., only three or five point sources in total. This can help produce higher resolutions than... Figure 15A The large number of spots shown require fewer and / or simpler optical devices.

[0195] For example, Figure 24 (A) The diagram illustrates three point sources Px1, Px2, and P0. The distance between P0 and Px2 is shown. It doesn't need to be the distance between Px1 and Px2. Integer multiples of . The P0-Px1 pair will generate a fine line pattern on the detector, having the same as . Proportional line pitch. P0-Px2 pairs will generate different line patterns, with the same... Proportional line pitch. These line patterns will be in accordance with... Proportional periodicity: in-phase and out-of-phase: the "beat frequency" between two different "frequency" frequencies.

[0196] In some examples, It is possible Between 0.5% and 10%. For example, you can select between 0.5% and 10% for line patterns with a period of 3 pixels. ≈630 µm, and for a shooting frequency cycle of 378 pixels. µm. In some examples, µm, or µm. All three point sources (P0, Px1, Px2) can be activated (i.e., irradiated) simultaneously, and Fourier analysis is used to analyze the beat frequency pattern. Therefore, it is possible to determine the relationship with... x Position parameters of the axis-dependent image sensor.

[0197] Alternative sites can use two pairs of point sources, such as Figure 24 As shown in (B). First, point sources Px0A / Px2 are illuminated, and the resulting line pattern is recorded in a first record; then, sources Px0B / Px1 are illuminated, and the corresponding resulting line pattern is recorded in a second record. Optionally, in xy The optical elements (containing all four point sources) are moved in the plane so that the active point sources are in approximately the same position in the first and second records.

[0198] Similar processes can be used y Axis. Specifically, Figure 24 (C) shows the configuration of simultaneously illuminating 5 point sources (thus creating a dot pattern). Figure 24 (D) shows four pairs of point sources (PaX1, PaX2, PaY1, PaY2), irradiating one pair at a time. Figure 24 (E) shows two triples (TrX and TrY), with one triple being irradiated at a time.

[0199] In some examples, it is easier to calibrate the phase difference between point sources when only two point sources (i.e., a pair) are illuminated at a given time.

[0200] Examples of optical elements suitable for generating point source pairs (i.e., reference illumination beam pairs) include Figure 22 The lateral PICs shown are PIC-x and PIC-y. Figure 23 The fiber array FA shown is Figure 25 and 26 The modified fiber optic cables 2510 and 2610 shown, and Figure 27 and28 Waveguides 2720 and 2820 are shown. Two or more optical elements can be arranged such that the spacing between corresponding point source pairs is perpendicular to each other.

[0201] In some examples, more specifically, if the detector's location is approximately known, the image data generated by the detector and processor can be mapped (e.g., approximately) to the pupil space. As described herein, the pupil coordinates are the x and y projections of a unit vector from a point defined in the xy (i.e., wafer or substrate) plane. Preferably, the defined point is near the point source of the optical element, and more preferably near the geometric center of the point source. The pupil space can then be transformed to reciprocal space: ,in It is the wavelength (e.g., 633 nm). Therefore, an intensity image in reciprocal space can be obtained as... If the image is Fourier transformed, then... For all The combination, which will It has a sharp peak, among which It is the first The coordinates of each point source. Even if the exact location of the detector is not known, these peaks will be easily identified. In the measurement of light emitted simultaneously from multiple point sources, Fourier ( There will usually be in the space Each peak. Utilizing, for example... Figure 24 The configuration shown, each peak (except for) This can be attributed to a specific point source pair. By... The remainder is reduced to zero (i.e., points other than the peak are removed, or the rest is reduced to zero). The rest of the data is "zeroed out", and then an inverse Fourier transform is performed to obtain a low-noise pattern corresponding to a specific point source pair.

[0202] In some examples, the optics can be configured to generate an astigmatic reference irradiance beam. In other examples, the optics can be configured to generate a reference irradiance beam that is off-focus on the designed detector plane. The spot shape at the detector will provide information about the distance from the detector plane to the optics (e.g., a reference point). This is in Figure 17 The diagram is shown in the image. A standard beam can have a single focal point and a roughly circular spot shape. An astigmatic beam can have two line focal points. If the sensor plane deviates from the focal point (offset)... If the standard beam has a larger spot diameter on the detector, then the standard beam can have a larger spot diameter. Figure 17 (Column S1 in the text).

[0203] Like the beam splitter A1, it can be designed to be in It has a line focus at a certain point, and in some... There is another focal point. Based on the shape of the spot, it can be estimated... Values, for example, for Another astigmatic beam, A2, was designed to enable estimation. Bundle A3 shows that the orientation of the line focus can be arbitrarily designed. Bundle D1 is designed to be astigmatic, but has intentional defocus at the nominal (designed) detector plane. Combining information from bundles S1 and D1 will also allow one to estimate... Value. Typically, one or both of astigmatism and / or defocusing can be used to determine this. .

[0204] For example, optical elements can be configured to generate many (e.g., 10 or 100) reference irradiance beams, each with a different (and known) focal point, such that for each spot on the detector, the in-plane ( ) and out-of-plane ( Both location information and location information are available. Optical elements are designed to generate various... The bundle with the focal point at the value will have (a) enough bundles with focal points on the sensor plane (for accurate) and (a) position), and (b) enough beams with focal points at locations far from the sensor plane (which may be for accurate (Better location). This is in Figure 18 The diagram is shown; beam B has a focal point on the detector plane. The beam diameter is small, but the z-coordinate cannot be accurately inferred from the spot diameter because the spot diameter as a function of z has zero derivative at that point. For beams A, C, and D, the spot diameter is relative to the detector plane at that point. A better measure of location. If the detectors as a whole are negative... If the direction is shifted, beam C will be focused (ensuring accuracy). Position), while beam B will be off-focus (to ensure accuracy) (Position), and bundles A and D will be too far off-focus, so that The accuracy will be very low.

[0205] In some examples, it is not necessary to use Information (e.g., because) It is also encoded along the lines between spots on the detector. or (within the distance). Overall accuracy is still improved because there are always enough points with good X and / or y accuracy, since the corresponding beams have a focal point on the detector plane.

[0206] The detector's (multiple) position-related parameters can be used to obtain spectral calibration, for example, for measurement devices.

[0207] Figure 19 An example of a portion of a measuring device according to this disclosure is illustrated. Figure 19 The portion of the measuring device shown in the diagram can correspond to Figure 6 The scatterer shown is a portion of the image. Measurement irradiation 1901 is directed onto a measurement target on a substrate W (e.g., a wafer). For example, measurement irradiation 1901 can be broadband irradiation and can include radiation in the hard X-ray (HXR), soft X-ray (SXR), extreme ultraviolet (EUV), visible to near-infrared (IR), and / or IR wavelength ranges. Measurement irradiation 1901 can be generated by, for example... Figure 1 and Figure 6 The radiation sources SO and 310 shown and described in this article are generated.

[0208] The diffraction from the measurement target to the detector 804 is captured. The diffraction efficiency of the target pattern for various wavelength components can be measured and converted into estimates for parameters of interest, such as the overlay and critical dimensions of the substrate W.

[0209] like Figure 19 As shown, the measurement illumination 1901 can be guided toward the substrate W via a reflector 1902 (e.g., a toroidal mirror). The measurement illumination 1901 can be monitored using an illumination monitoring sensor 1903 (e.g., an array sensor). For example, a portion of the measurement illumination 1901 can be diffracted onto the illumination monitoring sensor 1903 by a transmission diffraction grating 1904. In some examples, the transmission diffraction grating 1904 can be integrated with the reflector 1902.

[0210] According to this disclosure, such as Figure 20 As shown, measurement illumination 1901 can be directed onto reference target 1907. Measurement illumination 1901 may include multiple unique spectral peaks (e.g., approximately 25 spikes), for example, if measurement illumination 1901 is generated by HHG.

[0211] The reference target 1907 may include a periodic grating (which may resemble the target pattern but may be optimized for the purpose of this calibration). In some examples, the reference target 1907 may include a grating with variable line spacing (VLS) and / or with curved lines. These features can straighten and focus all line focal points (which may otherwise be curved lines and not all focused on the plane of detector 804) of the wavelength components incident on detector 804, thereby improving accuracy.

[0212] In some examples, the mirror 1902 can be rotated or tilted such that the measurement illumination 1901 is directed toward the reference target 1907 (e.g., to avoid illuminating the monitoring sensor 1903 and / or diffraction grating 1904 for calibration purposes). Rotating the mirror 1902 can also ensure that the wavelength component 1910 of the diffracted measurement illumination is focused on the detector 804. For example, using grazing-incidence optics, such mirror tilting can introduce astigmatism in the beam and can cause defocusing, which would cause the measurement illumination beam to be focused onto the detector 804 instead of the substrate W (the astigmatic beam would form a line focal point with the line orientation perpendicular to the substrate W). Figure 20 (Page plane in the middle).

[0213] Therefore, each wavelength component is focused. When focused, the spot size on the detector can be similar to the pixel size (e.g., approximately 10 µm, approximately 15 µm, approximately 20 µm, or approximately 25 µm FWHM). When the detector position is known (e.g., by determining the position-related parameters of detector 804 using any of the methods or apparatus described herein), the diffraction pattern on detector 804 can be converted into a wavelength spectrum with a calibrated wavelength axis. This spectrum can be used to assign wavelength values. Figure 19 The pixels on the illumination monitoring sensor 1903 are shown. In particular, the peaks of the spectrum can be used to match the calibration spectrum on the detector 804 with the spectrum on the illumination monitoring sensor 1903.

[0214] In some examples, if the diffraction efficiency spectrum of the reference target 1907 is known, the intensity axis of the spectrum can also be calibrated.

[0215] In some examples, the area under each peak can be matched with the calibrated area under the peak on the spectrum from detector 804.

[0216] After obtaining (multiple) calibrations, the reflector 1902 can be rotated back to the position required for measurement.

[0217] If the raw spectrum measured on the irradiation monitoring sensor 1903 is some kind of signal ,in It's the position on the sensor. It is the signal level (e.g., in ADU µm). -1 s -1 (where ADU refers to the modulus unit), and then matching peaks will result in a mapping function. Map wavelength to position and the second mapping function Mapping digital signal levels to units of radiation measurement, such as spectral flux according to the following expression. (by (in units) .

[0218] In some examples, multiple diffraction patterns can be obtained for different rotation angles of mirror 1902. Effectively resampling the spectrum in this way can improve sub-pixel accuracy.

[0219] The reference target 1907 is preferably large enough to be irradiated by the entire off-focus measurement beam.

[0220] The pitch of the reference target 1907 is preferably small enough to cover the full SXR wavelength range (e.g., about 100 nm).

[0221] Preferably, the reference target 1907 exhibits a smooth spectral response. Preferably, the reference target 1907 suppresses the second diffraction order to prevent blurring between overlapping first and second diffraction orders, for example by having a pitch with a duty cycle close to 50%.

[0222] Preferably, the reference target has a known diffraction efficiency spectrum (e.g., the diffraction efficiency spectrum can be calibrated individually).

[0223] Figure 21 An example of method 2100 according to this disclosure is illustrated. Method 2100 can be performed using any of the apparatus or arrangement described or illustrated herein.

[0224] At S2102, method 2100 includes illuminating an optical element with a reference irradiation, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference irradiation to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising a plurality of reference irradiance spots.

[0225] For example, the detector may correspond to detector 804 as described and illustrated herein. Optical elements may correspond to one or more of the following: phase mask, amplitude mask, (2D) grating, spatial light modulator, hologram, CGH, pinhole mask, and / or multiple curved (e.g., parabolic) mirrors, as described herein. The reference irradiance pattern may include, for example, spots formed by reference irradiance beams focused on and / or not focused on the detector, and reference irradiance beams having astigmatic and / or non-astigmatic beam profiles (e.g., as shown below). Figure 17 (as shown in the figure), as described in this article.

[0226] At S2104, method 2100 includes determining position-related parameters of the detector relative to the optical elements based on a plurality of reference irradiance spots. For example, the position-related parameters can be determined by any of the fitting and / or mapping techniques described herein.

[0227] Method 2100 can be executed at least in part by a processor as described herein.

[0228] Embodiments may include a computer program comprising one or more sequences of machine-readable instructions describing optical metrology methods and / or analytical measurement methods to obtain information about a photolithography process. Embodiments may include computer code comprising one or more sequences of machine-readable instructions or data describing the method. The computer program or code may, for example, be in... Figure 6 The unit MPU and / or Figure 3 The execution is performed within the control unit CL. For example, the "processor" described and referred to herein may correspond to the unit MPU. A data storage medium (e.g., semiconductor memory, disk, or optical disk, etc.) in which such computer program or code is stored may also be provided. If existing measuring devices (e.g.) Figure 6 If the type shown is already in production and / or use, embodiments of the invention can be implemented by providing an updated computer program product for causing a processor to perform one or more of the methods described herein. The computer program or code may optionally be arranged to control optical systems, substrate supports, etc., to perform methods for measuring lithography process parameters on suitable plurality of targets. The computer program or code may update lithography and / or metrology formulations for measuring other substrates. The computer program or code may be arranged to (directly or indirectly) control lithography apparatus for patterning and processing other substrates.

[0229] The irradiation source can be provided, for example, in a measurement device (MT), an inspection device, a lithography device (LA), and / or a lithography unit (LC).

[0230] The characteristics of the emitted radiation used to perform measurements can affect the quality of the obtained measurements. For example, the shape and size of the transverse beam profile (cross-section), the intensity of the radiation, and the power spectral density of the radiation can all affect the measurements performed by the radiation. Therefore, it is beneficial to have a source of radiation that provides characteristics that produce high-quality measurements.

[0231] Further embodiments are disclosed in the following numbered clauses: 1. A method comprising: An optical element is illuminated with a reference illumination, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising a plurality of reference irradiance spots; and Based on the plurality of reference irradiance spots, position-related parameters of the detector relative to the optical element are determined. 2. The method according to Clause 1, wherein the reference irradiance pattern comprises at least three reference irradiance spots. 3. The method according to Clause 1 or 2, wherein the optical element includes a phase mask. 4. The method according to any one of the preceding clauses, wherein the optical element includes an amplitude mask. 5. The method according to any one of the preceding clauses, wherein the optical element comprises a grating. 6. The method according to any one of the preceding clauses, wherein the optical element comprises a spatial light modulator. 7. The method according to any one of the preceding clauses, wherein the optical element comprises a hologram. 8. The method according to any one of the preceding clauses, wherein the optical element comprises a computer-generated hologram. 9. The method according to any one of the preceding clauses, wherein the optical element comprises a pinhole mask. 10. The method according to any one of the preceding clauses, wherein the optical element comprises a plurality of curved mirrors. 11. The method according to any one of the preceding clauses, wherein at least a portion of the optical element is reflective of the reference illumination. 12. The method according to any one of the preceding clauses, wherein at least a portion of the optical element is transmissive to the reference illumination. 13. The method according to any one of the preceding clauses, wherein the optical element comprises a photonic integrated circuit. 14. The method according to Clause 13, wherein the photonic integrated circuit comprises a die, and wherein the photonic integrated circuit is arranged such that the reference irradiance beam is emitted from the edge of the die. 15. The method according to Clause 13, wherein the photonic integrated circuit includes a waveguide, the waveguide including a grating output coupler, the grating output coupler including a plurality of grating lines. 16. The method according to Clause 15 includes arranging the grating lines perpendicular to the propagation direction of the waveguide. 17. The method according to any one of the preceding clauses includes aligning the reference illumination relative to the optical element based on the reflection of the reference illumination by the optical element. 18. The method according to any one of the preceding clauses, wherein illuminating the optical element with the reference illumination comprises providing the reference illumination via an optical fiber. 19. The method according to any one of Clauses 1 to 17, wherein the optical element comprises an optical fiber, the optical fiber comprising a cladding, wherein one or more portions of the cladding are removed to form one or more light output points, the one or more light output points being configured to output the reference irradiance beam in a direction perpendicular to the axis of the optical fiber. 20. The method according to Clause 19, wherein the light output point comprises a plurality of holes in the cladding, the diameter of the holes being smaller than the wavelength of the reference illumination. 21. The method according to Clause 19 or 20, wherein the one or more optical output points include an optical antenna disposed on an exposed portion of the core of the optical fiber. 22. The method according to any one of the preceding clauses, wherein the optical element comprises an optical fiber array. 23. The method according to any one of the preceding clauses, wherein the optical element is configured such that the reference irradiation propagates in the optical element in a planar pattern. 24. The method according to Clause 23, wherein the optical element comprises one or more optical antennas, and wherein the optical element is configured to output the reference irradiance beam via the one or more optical antennas. 25. The method according to any one of the preceding clauses, wherein the detector is a detector of a measuring device, wherein the method includes determining the position-related parameters of the detector relative to a substrate to be measured by the measuring device based on: The position-related parameters of the detector relative to the optical element; and The position of the optical element relative to the substrate. 26. The method according to any one of clauses 1 to 24, wherein the detector is a detector of a measuring device, and wherein the optical element is placed on a substrate to be measured by the measuring device. 27. The method according to any one of the preceding clauses, wherein the optical element is configured such that at least one of the reference irradiance beams has an astigmatic profile; and The method includes determining the position-related parameters of the detector relative to the optical element based on the shape of the irradiance spot formed by the at least one reference irradiance beam having the astigmatic profile. 28. The method according to any one of the preceding clauses, wherein the optical element is configured such that two or more of the reference irradiance beams have different focal points. 29. The method according to Clause 28, comprising determining the position-related parameters of the detector relative to the optical element based on the size of the reference irradiance spot formed by the reference irradiance beams having different focal points. 30. The method according to any one of the preceding clauses, wherein the reference irradiance pattern comprises a speckle pattern. 31. The method according to any one of the preceding clauses, comprising determining the position-related parameters of the detector relative to the optical element based on the position of the reference irradiance spot on the detector. 32. The method according to any one of the preceding clauses, wherein the optical element includes an alignment guide, and wherein the method includes aligning the reference illumination relative to the optical element based on radiation reflected by the alignment guide. 33. The method according to any one of the preceding clauses, wherein determining the position-related parameter of the detector relative to the optical element based on the reference irradiance spot includes fitting the position-related parameter to the position of the reference irradiance spot on the detector. 34. The method according to any one of the preceding clauses, wherein determining the position-related parameters of the detector relative to the optical element based on the reference irradiance spot comprises mapping the position of the reference irradiance spot on the detector to the pupil coordinates of the reference irradiance beam. 35. The method according to any one of the preceding clauses, wherein the reference irradiance pattern includes a coarse pattern and a fine pattern. 36. The method according to Clause 35, wherein each of the coarse pattern and the fine pattern is formed according to a corresponding reference irradiance beam pair, optionally, the method comprising irradiating the optical element such that the reference irradiance beam pair is generated one pair at a time. 37. The method according to any one of the preceding clauses, wherein the optical element is further configured such that the plurality of reference irradiance beams are incident on a second detector to form a second reference irradiance pattern on the second detector, the second reference irradiance pattern comprising a second plurality of reference irradiance spots; and The method further includes determining position-related parameters of the second detector relative to the optical element based on the second plurality of reference irradiance spots. 38. The method according to any one of the preceding clauses further includes: A reference target is illuminated with a measurement illumination, wherein the spectrum of the measurement illumination includes multiple spectral peaks, and wherein the reference target is configured to diffract the measurement illumination such that the diffraction pattern is incident on the detector. Based on the position-related parameters of the detector relative to the optical element and the position of the reference target relative to the optical element, the position-related parameters of the reference target relative to the detector are determined; and The wavelength of the spectral peak is determined based on the diffraction pattern incident on the detector. 39. The method according to Clause 38, wherein illuminating the reference target includes rotating a reflector to direct the measurement illumination toward the reference target. 40. The method according to clause 38 or 39 further includes using the wavelength of the determined spectral peak to obtain wavelength calibration for the illumination monitoring sensor. 41. The method according to any one of clauses 38 to 40, further comprising: Based on the diffraction efficiency spectrum of the reference target, the intensity spectrum for the measured irradiation is determined. 42. The method according to Clause 41 further includes using the determined intensity spectrum to obtain an intensity calibration for the illumination monitoring sensor. 43. The method according to any one of clauses 38 to 42, wherein the reference target comprises a diffraction grating having a variable line spacing. 44. An apparatus comprising: A reference illumination source, the reference illumination source being configured to illuminate an optical element with reference illumination; Detector; and processor; The optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising a plurality of reference irradiance spots; and The processor is configured to determine position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots. 45. The apparatus according to Clause 44, wherein the reference irradiance pattern comprises at least three reference irradiance spots. 46. ​​The apparatus according to clause 44 or 45, wherein the optical element includes a phase mask. 47. The apparatus according to any one of clauses 44 to 46, wherein the optical element comprises an amplitude mask. 48. The apparatus according to any one of clauses 44 to 47, wherein the optical element comprises a grating. 49. The apparatus according to any one of clauses 44 to 48, wherein the optical element comprises a spatial light modulator. 50. The apparatus according to any one of clauses 44 to 49, wherein the optical element comprises a hologram. 51. The apparatus according to any one of clauses 44 to 50, wherein the optical element comprises a computer-generated hologram. 52. The apparatus according to any one of clauses 44 to 51, wherein the optical element comprises a pinhole mask. 53. The apparatus according to any one of clauses 44 to 52, wherein the optical element comprises a plurality of parabolic mirrors. 54. The apparatus according to any one of clauses 44 to 53, wherein at least a portion of said optical element is reflective of said reference illumination. 55. The apparatus according to any one of clauses 44 to 54, wherein at least a portion of said optical element is transmissive to said reference illumination. 56. The apparatus according to any one of clauses 44 to 55, wherein the optical element comprises a photonic integrated circuit. 57. The apparatus of claim 56, wherein the photonic integrated circuit comprises a die, and wherein the photonic integrated circuit is arranged such that the reference irradiance beam is emitted from the edge of the die. 58. The apparatus according to Clause 56, wherein the photonic integrated circuit includes a waveguide, the waveguide including a grating output coupler, the grating output coupler including a plurality of grating lines. 59. The apparatus according to Clause 58, wherein the grating lines are arranged perpendicular to the propagation direction of the waveguide. 60. The apparatus according to any one of clauses 44 to 59, wherein the reference illumination source is configured to be aligned relative to the optical element based on the reflection of the reference illumination by the optical element. 61. The apparatus according to any one of clauses 44 to 60, comprising an optical fiber configured to provide the reference illumination to the optical element. 62. The apparatus according to any one of claims 44 to 60, wherein the optical element comprises an optical fiber, the optical fiber comprising a cladding, wherein one or more portions of the cladding are removed to form one or more light output points, the one or more light output points being configured to output the reference irradiance beam in a direction perpendicular to the axis of the optical fiber. 63. The apparatus according to Clause 62, wherein the light output point comprises a plurality of holes in the cladding, the diameter of the holes being smaller than the wavelength of the reference illumination. 64. The apparatus according to clause 62 or 63, wherein the one or more optical output points include an optical antenna disposed on an exposed portion of the core of the optical fiber. 65. The apparatus according to any one of the preceding clauses, wherein the optical element comprises an optical fiber array. 66. The apparatus according to any one of the preceding clauses, wherein the optical element comprises a planar waveguide. 67. The apparatus according to Clause 66, wherein the optical element comprises one or more optical antennas, and wherein the optical element is configured to output the reference irradiance beam via the one or more optical antennas. 68. The apparatus according to any one of clauses 44 to 67, wherein the apparatus is a measurement apparatus, and wherein the processor is further configured to determine position-related parameters of the detector relative to a substrate to be measured by the measurement apparatus based on: The position-related parameters of the detector relative to the optical element; and The position of the optical element relative to the substrate. 69. The apparatus according to any one of clauses 44 to 67, wherein the apparatus is a measuring device, and wherein the optical element is placed on a substrate to be measured by the measuring device. 70. The apparatus according to any one of clauses 44 to 69, wherein the optical element is configured such that at least one of the reference irradiance beams has an astigmatic profile; and The processor is configured to determine the position-related parameters of the detector relative to the optical element based on the shape of the irradiance spot formed by the reference irradiance beam having the astigmatic profile. 71. The apparatus according to any one of clauses 44 to 70, wherein the optical element is configured such that two or more of the reference irradiance beams have different focal points. 72. The apparatus according to Clause 71, wherein the processor is configured to determine the position-related parameters of the detector relative to the optical element based on the size of the reference irradiance spot formed by the reference irradiance beams having different focal points. 73. The apparatus according to any one of clauses 44 to 72, wherein the optical element is configured such that the reference irradiance pattern includes a speckle pattern. 74. The apparatus according to any one of clauses 44 to 73, wherein the processor is configured to determine the position-related parameters of the detector relative to the optical element based on the position of the reference irradiance spot on the detector. 75. The apparatus according to any one of clauses 44 to 74, wherein the optical element includes an alignment guide, and wherein the reference illumination source is configured to be aligned relative to the optical element based on radiation reflected by the alignment guide. 76. The apparatus according to any one of clauses 44 to 75, wherein the processor is configured to determine the position correlation parameter of the detector relative to the optical element by fitting the position correlation parameter to the position of the reference irradiance spot on the detector. 77. The apparatus according to any one of clauses 44 to 76, wherein the processor is configured to determine the position-related parameters of the detector relative to the optical element by mapping the position of the reference irradiance spot on the detector to the pupil coordinates of the reference irradiance beam. 78. The apparatus according to any one of clauses 44 to 77, wherein the optical element is configured such that the reference irradiance pattern includes a coarse pattern and a fine pattern. 79. The apparatus according to Clause 78, wherein the optical element is configured such that each of the coarse pattern and the fine pattern is formed according to a corresponding reference irradiance beam pair. 80. The apparatus according to Clause 79, wherein the reference irradiation source is configured to irradiate the optical element such that the reference irradiance beam pair is generated one pair at a time. 81. The apparatus according to any one of claims 44 to 80, further comprising a second detector, wherein the optical element is further configured such that the plurality of reference irradiance beams are incident on the second detector to form a second reference irradiance pattern, the second reference irradiance pattern comprising a second plurality of reference irradiance spots; and The processor is further configured to determine the position-related parameters of the second detector relative to the optical element based on the second plurality of reference irradiance spots. 82. The apparatus according to any one of claims 44 to 81 further includes a measuring illumination source configured to illuminate a reference target with measuring illumination, the spectrum of the measuring illumination comprising a plurality of spectral peaks, wherein the reference target is configured to diffract the measuring illumination such that a diffraction pattern is incident on the detector; The processor is further configured to: Based on the position-related parameters of the detector relative to the optical element and the position of the reference target relative to the optical element, the position-related parameters of the reference target relative to the detector are determined; and The wavelength of the spectral peak is determined based on the diffraction pattern incident on the detector. 83. The apparatus according to Clause 82 further includes a reflector rotatable to direct the measurement illumination toward the reference target. 84. The apparatus according to clause 82 or 83 further includes an illumination monitoring sensor, wherein the processor is further configured to use the wavelength of the determined spectral peak to obtain wavelength calibration for the illumination monitoring sensor. 85. The apparatus according to any one of clauses 82 to 84, wherein the processor is further configured to determine an intensity spectrum for the measured irradiation based on the diffraction efficiency spectrum of the reference target. 86. The apparatus according to Clause 85, wherein the processor is further configured to use the determined intensity spectrum to determine intensity calibration for the illumination monitoring sensor. 87. The apparatus according to any one of clauses 82 to 86, wherein the reference target comprises a diffraction grating having a variable line spacing. 88. A method comprising: An optical element is illuminated with a reference illumination, the optical element comprising a computer-generated hologram, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising a plurality of reference irradiance spots; and Based on the plurality of reference irradiance spots, position-related parameters of the detector relative to the optical element are determined. 89. An apparatus comprising: A reference illumination source configured to illuminate an optical element with reference illumination, the optical element comprising a computer-generated hologram; Detector; and processor; The optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising a plurality of reference irradiance spots; and The processor is configured to determine position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots. 90. A method comprising: An optical element is illuminated with a reference illumination, the optical element including a photonic integrated circuit configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern including a plurality of reference irradiance spots; and Based on the plurality of reference irradiance spots, position-related parameters of the detector relative to the optical element are determined. 91. An apparatus comprising: A reference illumination source configured to illuminate an optical element with reference illumination, the optical element comprising a photonic integrated circuit; Detector; and processor; The optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising a plurality of reference irradiance spots; and The processor is configured to determine position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots. 92. A method comprising: An optical element is illuminated with a reference irradiation, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference irradiation to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising a plurality of reference irradiance spots. Based on the reflection of the reference illumination by the optical element, the reference illumination is aligned relative to the optical element; and Based on the plurality of reference irradiance spots, position-related parameters of the detector relative to the optical element are determined. 93. An apparatus comprising: A reference illumination source is configured to illuminate an optical element with reference illumination, wherein the reference illumination source is configured to be aligned relative to the optical element based on the reflection of the reference illumination by the optical element. Detector; and processor; The optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising a plurality of reference irradiance spots; and The processor is configured to determine position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots. 94. A method comprising: An optical element is illuminated with a reference illumination, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, at least one of the reference irradiance beams having an astigmatic profile, and the reference irradiance pattern comprising a plurality of reference irradiance spots; and Based on the shape of the irradiance spot formed by the reference irradiance beam having the astigmatic profile, position-related parameters of the detector relative to the optical element are determined. 95. An apparatus comprising: A reference illumination source, the reference illumination source being configured to illuminate an optical element with reference illumination; Detector; and processor; The optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference illumination to form a reference irradiance pattern on the detector, at least one of the reference irradiance beams having an astigmatic profile, and the reference irradiance pattern comprising a plurality of reference irradiance spots; and The processor is configured to determine position-related parameters of the detector relative to the optical element based on the shape of the irradiance spot formed by the reference irradiance beam having the astigmatic profile. 96. A method comprising: An optical element is illuminated by a reference illumination, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference illumination to form a reference irradiance pattern on the detector, wherein two or more of the reference irradiance beams have different focal points, and the reference irradiance pattern comprises a plurality of reference irradiance spots; and The position-related parameters of the detector relative to the optical element are determined based on the size of the reference irradiance spot formed by the reference irradiance beams with different focal points. 97. An apparatus comprising: A reference illumination source, the reference illumination source being configured to illuminate an optical element with reference illumination; Detector; and processor; The optical element is configured to generate a plurality of reference irradiance beams incident on the detector from the reference irradiation to form a reference irradiance pattern on the detector, wherein two or more of the reference irradiance beams have different focal points, and the reference irradiance pattern comprises a plurality of reference irradiance spots; and The processor is configured to determine position-related parameters of the detector relative to the optical element based on the size of the reference irradiance spot formed by the reference irradiance beams with different focal points. 98. A computer program product comprising instructions that, when executed by a computer, cause the computer to perform the method according to any one of clauses 1 to 43, 88, 90, 92, 94, or 96.

[0232] While specific embodiments of the invention have been described above, it should be understood that the invention can be practiced in ways other than those described. The description above is intended to illustrate and not limit. Therefore, it will be apparent to those skilled in the art that modifications can be made to the described invention without departing from the scope of the claims set forth below.

[0233] 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 the fabrication of integrated optical systems, patterning for guiding and detecting magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0234] While this document may specifically refer to embodiments of the invention within the context of a photolithography apparatus, these embodiments can be used with other apparatuses. Embodiments of the invention can form part of a mask inspection apparatus, a measurement apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning apparatuses). These apparatuses are generally referred to as photolithography tools. Such photolithography tools can use vacuum conditions or ambient (non-vacuum) conditions.

[0235] 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 mechanism 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 propagation signals (e.g., carrier waves, infrared signals, digital signals, etc.), and so on. Furthermore, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and such actions are actually produced by a computing device, processor, controller, or other device executing firmware, software, routines, instructions, etc., and in doing so, may enable actuators or other devices to interact with the physical world.

[0236] While the foregoing may specifically refer to embodiments of the invention within the context of optical lithography, it should be understood that the invention can be used in other applications, such as imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, the morphology in the patterning apparatus defines a pattern created on a substrate. The morphology of the patterning apparatus can be pressed into a resist layer supplied to the substrate, and then the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist has been cured, the patterning apparatus is removed from the resist, leaving the pattern therein.

[0237] It should be understood that the term color is used synonymously with wavelength or spectral component throughout this document, and color can include colors outside the visible light band (e.g., infrared or ultraviolet wavelengths).

[0238] In this document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic and particle radiation, including ultraviolet radiation (e.g., wavelengths of 365, 248, 193, 157, or 126 nm), EUV (extreme ultraviolet radiation, e.g., wavelengths in the range of about 1 to 100 nm), X-ray radiation, electron beam radiation, and other particle radiation.

[0239] As used herein, the terms “mask,” “mask,” or “patterning apparatus” can be broadly interpreted to refer to a general patterning apparatus that can be used to impart a patterned cross-section to an incident radiation beam, corresponding to a pattern to be created in a target portion of a substrate. The term “optical valve” can also be used in this context. Examples of other such patterning apparatuses besides classic masks (transmission or reflection, binary, phase-shifting, hybrid, etc.) include programmable mirror arrays and programmable LCD arrays.

[0240] The term "lens," when the context permits, can refer to any type of optical component or combination thereof, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components. Reflective components may be used in devices operating in the UV and / or EUV range.

[0241] Additional objects, advantages, and features of the invention are set forth in this specification and will in part become apparent to those skilled in the art upon examination of the following, or may be learned by practicing the invention. The invention disclosed in this application is not limited to any particular set or combination of the objects, advantages, and features. It will be understood that various combinations of the stated objects, advantages, and features constitute the invention disclosed in this application.

Claims

1. An apparatus comprising: A reference illumination source, the reference illumination source being configured to illuminate an optical element with reference illumination; Detector; as well as processor; The optical element is configured to generate multiple reference irradiance beams incident on the detector from the reference irradiation to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising multiple reference irradiance spots; and The processor is configured to determine position-related parameters of the detector relative to the optical element based on the plurality of reference irradiance spots.

2. The apparatus of claim 1, wherein the reference irradiance pattern comprises at least three reference irradiance spots.

3. The apparatus according to claim 1 or 2, wherein the optical element comprises one or more of the following: a phase mask, an amplitude mask, a grating, a spatial light modulator, a hologram, a computer-generated hologram, a pinhole mask, and a plurality of parabolic mirrors.

4. The apparatus according to any one of claims 1 to 3, wherein at least a portion of the optical element is reflective of the reference illumination.

5. The apparatus according to any one of claims 1 to 4, wherein at least a portion of the optical element is transmissive to the reference illumination.

6. The apparatus according to any one of claims 1 to 5, wherein the optical element comprises a photonic integrated circuit.

7. The apparatus according to any one of claims 1 to 6, wherein the reference illumination source is configured to be aligned relative to the optical element based on the reflection of the reference illumination by the optical element.

8. The apparatus according to any one of claims 1 to 7, comprising an optical fiber configured to provide the reference illumination to the optical element.

9. The apparatus according to any one of claims 1 to 8, wherein the apparatus is a measurement device, and wherein the processor is further configured to determine position-related parameters of the detector relative to a substrate to be measured by the measurement device based on: The position-related parameters of the detector relative to the optical element; and The position of the optical element relative to the substrate.

10. The apparatus according to any one of claims 1 to 8, wherein the apparatus is a measuring device, and wherein the optical element is placed on a substrate to be measured by the measuring device.

11. The apparatus of any one of claims 1 to 10, wherein the processor is configured to determine the position-related parameters of the detector relative to the optical element based on the position of the reference irradiance spot on the detector.

12. The apparatus according to any one of claims 1 to 11, further comprising a second detector, wherein the optical element is further configured such that the plurality of reference irradiance beams are incident on the second detector to form a second reference irradiance pattern, the second reference irradiance pattern comprising a second plurality of reference irradiance spots; and The processor is further configured to determine the position-related parameters of the second detector relative to the optical element based on the second plurality of reference irradiance spots.

13. The apparatus according to any one of claims 1 to 12, further comprising a measurement illumination source configured to illuminate a reference target with measurement illumination, the spectrum of the measurement illumination comprising a plurality of spectral peaks, wherein the reference target is configured to diffract the measurement illumination such that a diffraction pattern is incident on the detector; The processor is further configured to: Based on the position-related parameters of the detector relative to the optical element and the position of the reference target relative to the optical element, the position-related parameters of the reference target relative to the detector are determined; as well as The wavelength of the spectral peak is determined based on the diffraction pattern incident on the detector.

14. A method comprising: An optical element is illuminated with a reference irradiation, wherein the optical element is configured to generate a plurality of reference irradiance beams incident on a detector from the reference irradiation to form a reference irradiance pattern on the detector, the reference irradiance pattern comprising a plurality of reference irradiance spots. as well as Based on the plurality of reference irradiance spots, position-related parameters of the detector relative to the optical element are determined.

15. A computer program product comprising instructions that, when executed by a computer, cause the computer to perform the method according to claim 14.

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