Method for measuring for robust advanced imaging techniques

Abstract

An overlay metrology system can receive an image of an overlay target on a sample according to a metrology recipe, wherein the image is generated by illuminating an overlay target comprising a plurality of overlay structures via oblique illumination with one or more pairs of illumination beams, wherein portions of the image associated with one or more overlay structures of the plurality of overlay structures having periodicity along a measurement direction are formed via an overlay diffraction order from a pair of the one or more pairs of illumination beams having a dipole separation axis orthogonal to the measurement direction, wherein the plurality of overlay structures includes overlay structures comprising two or more gratings having overlapping regions. The overlay metrology system can determine an overlay measurement associated with a relative position of sample layers based on the image of the overlay target.

Description

[0001] Cross-referencing related applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 631,457, filed April 9, 2024, pursuant to 35 USC § 119(e), which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure relates to the measurement of targets in imaging systems, and more particularly to the measurement of robust advanced imaging technology (rAIM) targets in semiconductor metrology systems. Background Technology

[0004] Alignment metrology systems typically characterize the alignment of multiple layers of a sample by measuring the relative positions of target features located on the layer of interest. As the size of fabricated features decreases and feature density increases, the demand for alignment metrology systems required to characterize these features increases. Furthermore, metrology systems developed for measuring smaller feature sizes are less efficient at measuring larger feature sizes. Therefore, there is a need to develop systems and methods to address these requirements. Summary of the Invention

[0005] According to one or more embodiments of this disclosure, a superposition metrology system is disclosed. In one illustrative embodiment, the superposition metrology system includes one or more controllers, the controllers including one or more processors configured to execute program instructions. In another illustrative embodiment, the program instructions include an image of a superposition target on a sample according to a metrological prescription, wherein the superposition target includes one or more moiré structures having a periodic orientation along one or more measurement directions, wherein the image is generated by illuminating the superposition target with oblique illumination using one or more oblique illumination beams, wherein a particular moiré structure among the one or more moiré structures includes an overlapping grating with a different pitch along the particular measurement direction, wherein a portion of the image associated with the particular moiré structure is formed via a moiré diffraction order from at least one oblique illumination beam having an azimuthal incident direction orthogonal to the particular measurement direction. In another illustrative embodiment, the program instructions include determining a superposition measurement associated with the relative position of a sample layer along the one or more measurement directions based on the image of the superposition target.

[0006] According to one or more embodiments of this disclosure, a superimposed metrology system is disclosed. In one illustrative embodiment, the superimposed metrology system includes: an illumination subsystem comprising one or more lenses configured to illuminate a superimposed target on a sample via oblique illumination according to a metrological prescription, wherein the superimposed target comprises one or more ridge structures having a periodic orientation along one or more measurement directions, wherein an image is generated by illuminating the superimposed target with one or more oblique illumination beams, wherein a particular ridge structure among the one or more ridge structures includes overlapping gratings having different pitches along the particular measurement direction, wherein a portion of the image associated with the particular ridge structure is formed via a ridge diffraction order from at least one oblique illumination beam having an azimuth incident direction orthogonal to the particular measurement direction. In another illustrative embodiment, the metrology subsystem includes: a collection subsystem comprising at least one objective lens configured to collect at least one ridge diffraction order associated with the diffraction of the one or more ridge structures by the one or more oblique illumination beams. In another illustrative embodiment, the overlay metrology subsystem further includes: a detector configured to generate an image of the overlay target using illumination collected by the collection subsystem. In another illustrative embodiment, the overlay metrology subsystem further includes: a controller communicatively coupled to the collection subsystem, the controller including one or more processors configured to execute program instructions such that the one or more processors: receive the image of the overlay target; and determine, based on the image of the overlay target, an overlay measurement associated with the relative position of the sample layer along the one or more measurement directions.

[0007] According to one or more embodiments of this disclosure, a metrology method is disclosed. In one illustrative embodiment, the metrology method includes: receiving an image of a stacked target on a sample according to a metrology prescription, wherein the stacked target comprises one or more ridge structures having a periodic orientation along one or more measurement directions, wherein the image is generated by illuminating the stacked target with oblique illumination using one or more oblique illumination beams, wherein a particular ridge structure among the one or more ridge structures comprises an overlapping grating with a different pitch along the particular measurement direction, wherein a portion of the image associated with the particular ridge structure is formed via a ridge diffraction order from at least one oblique illumination beam having an azimuthal incident direction orthogonal to the particular measurement direction. In another illustrative embodiment, the metrology method includes: determining a stacking measurement associated with the relative position of a sample layer along the one or more measurement directions based on the image of the stacked target.

[0008] It should be understood that both the foregoing general description and the following detailed description are exemplary and illustrative only and do not necessarily limit the invention claimed. The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention. Attached Figure Description

[0009] Figure 1A This is a conceptual diagram of a stacked metering system according to one or more embodiments of the present disclosure.

[0010] Figure 1B This is a schematic diagram illustrating a stacked metering subsystem according to one or more embodiments of the present disclosure.

[0011] Figure 2A The illustration shows a top view of an overlapping target according to one or more embodiments of the present disclosure.

[0012] Figure 2B The illustration shows a side view of a unit according to one or more embodiments of the present disclosure, the unit comprising elements formed as shown in the figure. Figure 2A The rAIM superimposed texture structure of the quadrant portion of the target is depicted in the figure.

[0013] Figure 2C The illustration shows a side view of a unit according to one or more embodiments of the present disclosure, the unit comprising elements formed as shown in the figure. Figure 2A The rAIM superimposed texture structure of the quadrant portion of the target is depicted in the figure.

[0014] Figure 3A This is a top view illustrating a pair of illumination pupils of an illumination beam according to one or more embodiments of the present disclosure.

[0015] Figure 3B This is a top view illustrating the illumination pupils of two pairs of illumination beams according to one or more embodiments of the present disclosure.

[0016] Figure 4 The illustration illustrates a configuration for imaging a textured structure having periodicity along the X direction using oblique illumination with an azimuth angle of incidence along the Y direction, according to one or more embodiments of the present disclosure.

[0017] Figure 5 This is a conceptual schematic diagram illustrating the collection of stacked diffraction lobes from a stacked target according to one or more embodiments of the present disclosure.

[0018] Figure 6 The illustrations depict typical configurations for illumination and imaging of normal samples according to one or more embodiments of this disclosure.

[0019] Figure 7AThe illustration depicts an illumination pupil providing quadrupole illumination according to one or more embodiments of the present disclosure.

[0020] Figure 7B Illustrated illustration of one or more embodiments of the present disclosure using... Figure 7A The quadrupole illumination profile shown in the figure is used to illuminate the distribution of diffraction orders in the collection pupil produced by a periodic lattice structure along the X direction.

[0021] Figure 7C The illustration shows the process after filtering out unwanted diffraction lobes according to one or more embodiments of this disclosure. Figure 7B The distribution of diffraction lobes in the image.

[0022] Figure 8 This is a flowchart depicting a method for overlay metrology according to one or more embodiments of the present disclosure. The method can be performed via an overlay metrology system as described herein. Detailed Implementation

[0023] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings. This disclosure has been particularly shown and described with respect to specific embodiments and features. The embodiments set forth herein are to be considered illustrative rather than restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of this disclosure.

[0024] Embodiments of this disclosure relate to a system and method for imaging a textured structure on a stacked target using oblique illumination having an azimuth angle orthogonal to the periodic direction of the textured structure. The textured structure can be formed as an overlapping periodic structure with different pitches but having a common periodic direction corresponding to the measurement direction. In embodiments, the textured structure having periodicity along a specific measurement direction (e.g., the X direction) is imaged based on at least one illumination beam having an azimuth angle orthogonal to this specific measurement direction (e.g., the Y direction).

[0025] This paper considers that, compared to conventional imaging techniques based on normal illumination with an azimuth angle aligned with the periodic direction of the textured structure, or rotated illumination with an azimuth angle rotated less than 90 degrees relative to the periodic direction of the textured structure, imaging based on an azimuth angle or azimuth direction or orthogonal to the periodic direction offers substantially greater flexibility in selecting measurement parameters (e.g., measurement wavelength, target pitch, etc.). Specifically, orthogonal tilted illumination, as disclosed herein, achieves greater flexibility in selecting the polar incident angle compared to existing techniques.

[0026] As an illustration, the systems and methods disclosed herein offer greater flexibility for measuring stacked targets containing textured structures with specific pitches compared to existing technologies. Specifically, conventional imaging techniques may limit the bandwidth of permissible wavelengths suitable for imaging textured structures with relatively large pitches (e.g., approximately 600 nm or higher). Furthermore, the permissible bandwidth may not necessarily provide the desired sensitivity. However, the systems and methods disclosed herein enable imaging of such textured structures using a wider range of wavelengths and / or more desired wavelengths.

[0027] As another illustration, the systems and methods disclosed herein enable greater flexibility in designing stacked targets to include textured structures with specific pitch values ​​(e.g., to meet fabrication requirements, etc.). Specifically, the imaging wavelength flexibility provided by the systems and methods disclosed herein allows textured structures that would otherwise be difficult to measure to be used in stacked targets.

[0028] Now for reference Figures 1A to 8 Systems and methods for imaging for superimposed metrology are described in more detail according to one or more embodiments of the present disclosure.

[0029] Figure 1A This is a conceptual diagram of a superimposed metrology system 100 according to one or more embodiments of the present disclosure. In an embodiment, the superimposed metrology system 100 includes a superimposed metrology subsystem 102 configured to image a superimposed target 104 having one or more textured structures based on oblique illumination using one or more illumination beams 108 having azimuth angles of incidence orthogonal to the periodic direction of the textured structure (e.g., associated with the measurement direction). For example, Figure 1A The image is depicted using a pair of illumination beams 108a and 108b.

[0030] The overlay metrology system 100 may include a controller 110 communicatively coupled to the overlay metrology subsystem 102. The controller includes one or more processors 112 configured to execute a set of program instructions maintained in memory 114. The controller 110 can thus be configured to perform various processing steps described herein, such as, but not limited to, receiving one or more images of an overlay target 104 from the overlay metrology subsystem 102 or generating overlay measurements based on said one or more images. In some embodiments, the controller 110 may instruct or otherwise control other components of the overlay metrology system 100 and / or external components. For example, the controller 110 may instruct the overlay metrology subsystem 102 to generate images based on one or more selected metrological prescriptions. As another example, the controller 110 may generate a calibrable amount based on the overlay measurements to control one or more processing tools (e.g., lithography tools, etching tools, polishing tools, etc.).

[0031] For the purposes of this disclosure, the term "overlap" is generally used to describe the relative positions of features on a sample fabricated by two or more photolithographic patterning steps, while the term "overlap error" describes the deviation of said features from their nominal arrangement. In this context, overlap measurement can be expressed as a measurement of relative positions or a measurement of overlap errors associated with those relative positions. For example, a multilayer device may include features patterned on multiple sample layers using different photolithographic steps for each layer, where feature alignment between layers must typically be tightly controlled to ensure proper performance of the resulting device. Thus, overlap measurement characterizes the relative positions of features on two or more sample layers. In another instance, multiple photolithographic steps can be used to fabricate features on a single sample layer. Such techniques, often referred to as dual patterning or multiple patterning techniques, facilitate the fabrication of high-density features close to the resolution of a photolithography system. In this context, overlap measurement characterizes the relative positions of features from different photolithographic steps on this single layer. It should be understood that the examples and descriptions relating to specific applications of overlap measurement throughout this disclosure are provided for illustrative purposes only and should not be construed as limiting the disclosure.

[0032] Figure 1B This is a schematic diagram illustrating a superimposed metrology subsystem 102 according to one or more embodiments of the present disclosure. In an embodiment, the superimposed metrology subsystem 102 includes an illumination source 118 configured to generate one or more suitable illumination beams 108. The illumination beams 108 may contain light having any wavelength or spectrum, including, but not limited to, ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0033] Irradiation source 118 may comprise any type of irradiation source suitable for providing at least one irradiation beam 108. In an embodiment, irradiation source 118 is a laser source. For example, irradiation source 118 may comprise, but is not limited to, one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, or white light laser sources. In an embodiment, irradiation source 118 comprises a laser-supplied plasma (LSP) source. For example, irradiation source 118 may comprise, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for housing one or more elements that can emit broadband irradiation when excited into a plasma state by a laser source.

[0034] In one embodiment, the overlay metrology subsystem 102 directs the illumination beam 108 to the overlay target 104 via the illumination subsystem 120. The illumination subsystem 120 may include one or more optical components adapted to modify and / or adjust the illumination beam 108 and direct the illumination beam 108 to the overlay target 104.

[0035] In an embodiment, the illumination subsystem 120 includes one or more illumination subsystem lenses 122 (e.g., for collimating the illumination beam 108, relay pupils, and / or field planes, etc.). In an embodiment, the illumination subsystem 120 includes one or more illumination subsystem optics 124 for shaping or otherwise controlling the illumination beam 108. For example, the illumination subsystem optics 124 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more equalizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translation mirrors, scanning mirrors, etc.). In an embodiment, the stacking metrology subsystem 102 may include a stage 126.

[0036] The illumination subsystem 120 may use any technique known in the art to provide the illumination beam 108. In an embodiment, the illumination subsystem 120 includes one or more apertures located at the illumination pupil plane to split illumination from the illumination source 118 into two or more illumination beams 108. In an embodiment, the illumination subsystem 120 generates the illumination beam 108 by providing light in two or more optical fibers, wherein the light output from each optical fiber is provided at or directed to the illumination pupil to provide the illumination beam 108. In an embodiment, the illumination source 118 generates the illumination beam 108 by diffracting illumination from the illumination source 118 into two or more diffraction orders, wherein at least one of the diffraction orders forms at least one illumination beam 108. Generally, U.S. Patent Publication No. 2020 / 0124408, entitled "Efficient Illumination Shaping for Scatterometry Overlay," describes the efficient generation of multiple illumination beams through controlled diffraction, which is incorporated herein by reference in its entirety.

[0037] In one embodiment, the stacking metrology subsystem 102 includes an objective lens 142 for directing one or more illumination beams 108 onto the stacking target 104. The objective lens 142 may further capture light emitted from the stacking target 104 (e.g., collected light 143).

[0038] In one embodiment, the stacking metrology subsystem 102 includes a collection subsystem 130 for guiding at least a portion of the collected light 143 from the objective lens 142 to one or more detectors 144. The collection subsystem 130 may include one or more optical elements adapted to modify and / or adjust the collected light 143 from the sample 106. In one embodiment, the collection subsystem 130 includes one or more collection subsystem lenses 145 (e.g., for collimating the illumination beam 108, relay pupils, and / or field planes, etc.), which may include, but are not required to include, the objective lens 142. In one embodiment, the collection subsystem 130 includes one or more collection subsystem optics 146 for shaping or otherwise controlling the collected light 143. For example, the collecting subsystem optics 146 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more equalizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translation mirrors, scanning mirrors, etc.).

[0039] In one embodiment, the overlay metrology subsystem 102 includes at least one detector 144 located at a detection plane 148 to capture collected light 143 associated with the diffraction of light from the overlay target 104, wherein the detection plane 148 corresponds to the collection field plane. In this way, an image of the overlay structure within the overlay target 104 can correspond to an interference pattern (e.g., a fringe pattern) associated with the interference of the diffraction lobes transmitted to the detector 144.

[0040] The stacking measurement subsystem 102 may typically include any number or type of detectors 144 suitable for capturing light from the sample 106 that indicates the stacking. In embodiments, detectors 144 may include a two-dimensional pixel array (e.g., a focal plane array), such as, but not limited to, charge-coupled devices (CCDs) or complementary metal-oxide-semiconductor (CMOS) devices.

[0041] In some embodiments, the overlay metrology subsystem 102 includes multiple detectors 144 in multiple collection channels adapted to individually image an overlay structure with different periodic orientations. For example, although not shown, the overlay metrology subsystem 102 may include one or more channel-splitting optics for splitting the collected light 143 into different collection channels. The channel-splitting optics may include, but are not limited to, one or more wavelength filters, one or more polarizers, or one or more pupil-splitting components (e.g., prisms, etc.).

[0042] The irradiation subsystem 120 and collection subsystem 130 of the superimposed metrology subsystem 102 can be oriented in a wide range of configurations suitable for irradiating the sample 106 with the irradiation beam 108 and collecting the light emitted by the sample 106 in response to the incident irradiation beam 108. For example, such as Figure 1B As illustrated in the diagram, the superimposed metrology subsystem 102 may include a beam splitter 150, which is oriented such that the common objective lens 142 can simultaneously direct the illumination beam 108 to the sample 106 and collect light from the sample 106. Alternatively, the illumination subsystem 120 and the collection subsystem 130 may contain non-overlapping optical paths, such that the illumination beam 108 is directed to the sample 106 outside the objective lens 142.

[0043] Furthermore, the superposition metrology subsystem 102 can be configured to generate measurements based on any number of prescriptions that define measurement parameters. For example, the prescriptions of the superposition metrology subsystem 102 may include, but are not limited to, parameters associated with the incident illumination beam 108 (e.g., wavelength, angle of incidence, polarization, spot size, depth of focus, etc.), parameters associated with the portion of the collected light 143 reaching the detector 144 (e.g., wavelength, collection angle, polarization, imaging depth, etc.), or parameters associated with the detector 144 (e.g., integration time, gain, etc.).

[0044] Now, for general reference Figures 1A to 1B In this document, please consider that the distribution of diffraction orders from the rippled structure depends on various characteristics of both the illumination and the grating structure, including the pitch of the constituent gratings in the rippled structure, the difference between pitches in the rippled structure (e.g., associated with ripple gain), the wavelength of the illumination beam 108, the azimuth angle of incidence of the illumination beam 108, and the polar angle of incidence of the illumination beam 108. Therefore, embodiments of this disclosure are intended to select or otherwise control the properties of the illumination used in the stacking measurement based on the properties of the stacking target or a predetermined stacking target design, in order to achieve a desired distribution of diffraction orders from the stacking target. For example, various parameters of the illumination directed to the sample (e.g., wavelength and / or distance between illumination lobes) can be controlled to provide selected diffraction orders, which are collected by collecting optics and thus can be used to facilitate an image or associated measurement of the sample.

[0045] Some embodiments of this disclosure are directed to providing a prescription for configuring a pairwise metrology subsystem 102 to generate images based on selected imaging conditions. The pairwise metrology subsystem 102 can typically be configured according to a prescription that includes a set of parameters for controlling various aspects of the pairwise measurement, such as, but not limited to, the illumination of the sample, the collection of light from the sample, or the position of the sample during measurement. In this way, the pairwise metrology subsystem 102 can be configured to provide selected types of measurements for one or more pairs of interest. For example, the metrology prescription may include illumination parameters, such as, but not limited to, illumination wavelength, illumination band, illumination pupil distribution, incident illumination polarization, or illumination spatial distribution (e.g., the distance between illumination beams). By another example, the metrology prescription may include collection parameters, such as, but not limited to, collection pupil distribution (e.g., the desired distribution of angular light from the sample to be used for measurement and the associated filtered intensity at those angles), wavelength filters, or parameters for controlling one or more detectors. In another example, the metrological prescription may include various aspects of the design of the target 104, including, but not limited to, the number of overlapping structures, the arrangement of the overlapping structures, the pitch values ​​of the constituent gratings in the overlapping structures, etc. In another example, the metrological prescription may include various parameters associated with the sample position during measurement, such as, but not limited to, sample height, sample orientation, whether the sample is stationary or in motion during measurement (and associated parameters describing speed or scanning pattern).

[0046] Now for reference Figures 2A to 7C According to one or more embodiments of the present disclosure, imaging of a stacked target 104 containing a textured structure using oblique illumination having an azimuth angle of incidence orthogonal to the periodic direction of the textured structure is described in more detail.

[0047] Figure 2A The illustration shows a top view of an overlay target 104 (e.g., an rAIM overlay target) according to one or more embodiments of the present disclosure. Figure 2B and Figure 2C The illustration shows a side view of two units 202a, 202b including a textured structure 204a, 204b according to one or more embodiments of the present disclosure. The textured structure can be formed as follows: Figure 2A The portion of rAIM superimposed on target 104 as depicted in the image.

[0048] The ribbed structures 204a and 204b may include two gratings in the overlapping region of the sample 106, wherein the gratings located on different sample layers have different pitches. The stacked target 104 may typically contain any number of ribbed structures 204 arranged in any manner. For example, Figure 2AA non-limiting configuration is depicted, wherein the stacked target 104 includes a first overlay structure 204a and a second overlay structure 204b oriented to facilitate measurement along orthogonal measurement directions (e.g., the X and Y directions in the figure), wherein the first overlay structure 204a may have a different pitch and / or pitch configuration than the second overlay structure 204b.

[0049] As an explanation, Figure 2B A first frescoed structure 204a is depicted having an upper grating 206a (e.g., a first grating) with a first pitch (P) on a first layer 208 of the sample 106 and a lower grating 210a (e.g., a second grating) with a second pitch (Q) on a second layer 212 of the sample 106. The first frescoed structure may be referred to as a PQ frescoed structure. Figure 2C The diagram illustrates a second fresco structure 204b, which has an upper grating 206b (e.g., a third grating) with a second pitch (Q) on a first layer 208 of sample 106 and a lower grating 210b (e.g., a fourth grating) with a first pitch (P) on a second layer 212 of sample 106. This second fresco structure may be referred to as a QP fresco structure. This complementary PQ and QP fresco structure layout can result in a relative shift of the imaging interference fringes in the presence of physical (e.g., non-predetermined) alignment errors.

[0050] As another example, although not explicitly shown, the second pleated structure 204b has an upper grating 206b with a pitch of (S) on the first layer 208 of the sample 106 and a lower grating 210b with a pitch of (T) on the second layer 212 of the sample 106.

[0051] In the context of this disclosure, references to “first layer,” “second layer,” “third layer,” etc., are intended only to distinguish between different sample layers and do not indicate the physical order of the layers on a sample. Therefore, a “first layer” on a sample may be above or below a “second layer.”

[0052] Figures 3A to 7C Describe the illumination and collection of a double diffraction stage (e.g., a scrambled diffraction stage) that provides scrambled gain.

[0053] In an embodiment, the overlay metrology subsystem 102 images the ridge structure by guiding at least one illumination beam to the ridge structure having periodicity along a specific measurement direction, the at least one illumination beam having an angled polar incidence angle and an azimuth incidence angle orthogonal to the specific measurement direction. The overlay metrology subsystem 102 can then collect ridge diffraction lobes (e.g., double diffraction lobes) from this orthogonal illumination for image generation. In some embodiments, the pitch of the ridge structure, the wavelength associated with one or more illumination beams, and / or the combination of incidence angles are selected according to a metrological prescription to limit the collection of light to the ridge diffraction lobes of interest (and, in some cases, zero-order diffraction).

[0054] Figure 3A This is a top view illustrating an illumination pupil 302 of a pair of illumination beams 108a, 108b according to one or more embodiments of the present disclosure. The pair of illumination beams 108a, 108b may correspond to dipole illumination having a dipole separation axis along the X direction in the figure and are therefore suitable for illumination of a textured structure 204 having periodicity along the Y direction (e.g., Figure 2A Imaging is performed on the overlapping structures 204a and 204b in the upper right and lower left quadrants. For example, the pair of illumination beams 108a and 108b provide illumination with opposite azimuth angles of incidence and a common polar angle of incidence. Illumination beams 108a to 108b are shown as circular illumination lobes on the illumination pupil 302. However, the illumination lobes can take any shape or form, including but not limited to circular, elliptical, or other circular shapes.

[0055] This document considers that imaging based on dipole illumination (e.g., a pair of illumination beams 108) can mitigate illumination asymmetry and associated errors in overlay measurements. However, dipole illumination is not required, and in some embodiments a single illumination beam 108 may be used.

[0056] Figure 3B This is a top view illustrating the illumination pupils 302 of two pairs of illumination beams 108a to 108d according to one or more embodiments of the present disclosure. Specifically, Figure 3B A first pair of illumination beams 108a, 108b oriented along the X direction and a second pair of illumination beams 108c, 108d oriented along the Y direction are depicted (e.g., quadrupole illumination). It is considered herein that the quadrupole illumination distribution is suitable for imaging a 2D stacked target 104 having a grating structure oriented along two different (e.g., orthogonal) directions, wherein the illumination beams 108a, 108b are suitable for imaging a stacked structure having periodicity along the Y direction (e.g., Figure 2A Imaging of the textured structures 204a and 204b in the upper right and lower left quadrants, and the illumination beams 108c and 108d are suitable for imaging textured structures with periodicity along the X direction (e.g., Figure 2A Imaging of the superimposed texture structures 204a and 204b in the lower right and upper left quadrants.

[0057] Figure 4 The illustration illustrates a configuration for imaging a textured structure 204 having periodicity along the X direction using oblique illumination with an azimuth angle of incidence along the Y direction, according to one or more embodiments of the present disclosure. The illumination pupil 302 is shown having two illumination lobes 402a, 402b in a dipole configuration having a dipole separation direction along the Y direction (e.g., an azimuth angle of incidence along the Y direction). The collection pupil 303 is shown containing first textured diffraction orders 404a to 404d (+ / - 1M), while excluding higher-order diffractions (+ / - n) 406a to 406d, wherein the higher-order diffractions 406a to 406d may include higher-order textured diffractions and / or diffractions from individual gratings in the textured structure (e.g., diffractions associated only with the P-pitch or Q-pitch). In this manner, the objective lens 142 can operate as a filter to exclude the higher-order diffractions 406a to 406d. In some embodiments, the superposition metrology subsystem 102 may include one or more blockers in the collection pupil 203, the one or more blockers being configured to block unwanted diffraction levels collected by the objective lens 142.

[0058] Figure 5 This is a conceptual schematic diagram illustrating the collection of rippled diffraction lobes 502 (e.g., double diffraction lobes) from a stacked target 104 (e.g., rAIM stacked target) according to one or more embodiments of the present disclosure. Figure 5 The illumination beam 108 is depicted being guided to the stacked target 104 at an azimuth angle along the Y direction and orthogonal to the periodic direction of the ribbed structure 204, wherein the ribbed diffraction lobes are associated with first-order diffraction from two gratings 206, 210 along the X direction. For example, the ribbed diffraction lobe 502 may be formed by a first-order diffraction lobe 504 from the upper grating 206, which serves as the basis for a first-order diffraction lobe 506 from the lower grating 310b. Furthermore, the ribbed diffraction lobe 502 is shown entering the collection NA 500.

[0059] Refer again Figure 4 Note that although the irradiation beams 602a and 602b have azimuth angles of incidence along the Y direction, the overlay structure produces diffraction orders distributed according to a periodic direction (here, the X direction). However, the polar angle of incidence (e.g., associated with the deviation of the irradiation beams 402a and 402b from the center of the irradiation pupil 302) controls the placement of the associated diffraction (including the zeroth-order diffraction) along the Y direction.

[0060] In this paper, please consider that an image of the fringe structure 204 may contain fringe patterns with a fringe pitch (e.g., a pitch associated with the fringe diffraction lobe 502) that overlaps with the spatial variation between gratings on different sample layers. The fringe pitch is typically a pitch longer than any other pitch in the grating structure and relates to the difference between the pitches of the grating structures. For example, the fringe pitch (M) can be characterized as:

[0061]

[0062] Where P is the period of the first grating structure on the first layer, and Q is the period of the second grating structure on the second layer.

[0063] In an embodiment, a physical displacement of one grating relative to another in the overlay structure along a periodic direction (e.g., an overlay error associated with the relative displacement of two sample layers on a sample) will result in a corresponding lateral displacement of the overlay fringes along the measurement direction. Furthermore, the magnitude of the overlay fringes displacement is typically greater than the magnitude of the physical displacement. Specifically, the magnitude of the overlay fringes displacement is proportional to the physical displacement (e.g., the overlay error) according to a conditional overlay factor, which depends on the reference frame. In this regard, overlay measurements can be performed by measuring the displacement of the overlay fringes along the periodic direction of the associated grating structure on the metrology target and adjusting this value by an overlay gain, which will depend on the specific design of the metrology target and the specific measurement being performed. The use of overlay structures in overlay measurement is generally described in U.S. Patent No. 7,540,105, published October 21, 2008; U.S. Patent No. 7,249,105, published March 25, 2008; and U.S. Patent Application Publication No. 2018 / 0188663, published July 5, 2018. All of these patents are incorporated herein by reference.

[0064] Further considerations are needed in this article, such as... Figure 4 The orthogonal tilted illumination shown in the figure provides substantial flexibility in terms of the pitch of the overlay structure 204 and / or the wavelength used for imaging.

[0065] As an explanation, Figure 6 The illustrations depict typical configurations for illumination and imaging of normal samples according to one or more embodiments of this disclosure. Figure 6 In this configuration, the illumination lobe 602 is directed normally to the rippled structure (e.g., located at the center of the illumination pupil 302). The diffracted light (e.g., the rippled diffraction lobe) can be distributed along the periodic direction of the imaging rippled structure (here, the X direction), but not displaced along the Y direction.

[0066] Figure 6The typical normal illumination conditions described herein can impose substantial limitations on the wavelength and pitch combinations that allow imaging based on ripple-based diffraction lobes, especially when considering relatively large pitches. For Figure 6 The configuration shown in the image illustrates the pitch (P and Q) of the two layers, the illumination wavelength (λ), and the illumination NA (NA). ill ) and collect NA (NA coll The relationship between ) is shown below:

[0067]

[0068] .

[0069] As an illustration, this refers to a structure with a first layer pitch P = 600 nm, a second layer pitch Q = 500 nm, and NA... ill = 0.4 and NA coll The first stack of target 104 with a value of 0.7 yielded the following results:

[0070] .

[0071] In this scenario, the available spectrum for the first set of stacked targets is between 660 nm and 900 nm, which may be undesirably limited.

[0072] As another illustration, this refers to a structure with a first layer pitch P = 750 nm, a second layer pitch Q = 600 nm, and NA... ill =0.4 and NA coll The second stack of target 104 with a value of 0.7 yielded the following results:

[0073]

[0074] In this case with a larger pitch, the available spectrum for the first set of stacked targets is between 825 nm and 900 nm, which is more limiting.

[0075] However, imaging based on tilted orthogonal illumination, as disclosed herein, can provide a wider range of imaging conditions. For example, for tilted dipole illumination, assuming d is the dipole separation distance 408 between illumination lobes 602a and 602b (center to center) and the radii of illumination lobes 602a and 602b are r (e.g., in the pupil plane space), the pitch (P), the dipole separation distance 408 (d), and the collection NA (NA) coll The relationship between them can be described as follows:

[0076]

[0077] Similarly, pitch Q, d and NAcoll The relationship between them can be described as follows:

[0078]

[0079] When both pitch P and pitch Q are considered and constrained, such that the first stacked diffraction orders 604a and 604b are within the collection NA range, the relationship can be described as follows:

[0080]

[0081] Consider the same instance as above, where P = 600 nm and Q = 500 nm, d = 0.8, r = 0.14 and NA coll With a stacking ratio of 0.7 for target 104, the following results were obtained:

[0082]

[0083] In this case, the available bandwidth is in the range of 443 nm to 1175 nm, which is substantially larger than the range of 660 nm to 900 nm for normal irradiation.

[0084] Similarly, for P = 750 nm and Q = 600 nm, d = 0.8, r = 0.14 and NA coll When the value is 0.7, the following results are obtained:

[0085]

[0086] .

[0087] In this case, the available bandwidth is in the range of 554 nm to 1175 nm, which is also significantly larger than the range of 825 nm to 900 nm for normal irradiation.

[0088] Further consideration in this paper is that changing the polar incident angle of the irradiated beam 108 (or, in the case of a dipole, changing the dipole separation distance d) can further affect the spectral range suitable for the measurement wavelength. As an illustration, increasing the dipole separation distance to d = 1 in the above example provides the following results:

[0089] .

[0090] In this case, increasing the polar incident angle shifts the permissible wavelength to the lower end of the range of 506 nm to 756 nm.

[0091] While the above examples are illustrative and not limiting, they demonstrate that tilted orthogonal illumination provides substantially enhanced flexibility in wavelength selection based on a specific selected pitch of the fringe structure 204. Furthermore, tilted orthogonal illumination, as disclosed herein, allows target designs to have pitches unavailable using conventional imaging techniques. In a general sense, tilted orthogonal illumination enables flexible control over combinations of wavelengths, pitches, and dipole separation distances for a particular image, which can be defined using a metrological prescription. This flexibility allows for preferred wavelengths suitable for robust measurements of a wide range of target designs. For example, the metrological prescription can select the dipole separation distance of one or more pairs of illumination beams, which allows the collection pupil to exclude diffraction orders other than the first fringe diffraction order and the zero diffraction order. In another example, the metrological prescription can select one or more pairs of illumination beams, which produces an additional available bandwidth associated with one or more pairs of illumination beams, which allows the collection pupil to exclude diffraction orders other than the first fringe diffraction order and the zero diffraction order. In another example, the metrological prescription may select a stacked target having a rippled structure 204 (e.g., one or two or more gratings of the rippled structure 204 having a specific pitch), which produces an additional available bandwidth associated with one of one or more pairs of illumination beams, which enables the collection pupil to exclude diffraction orders other than the first rippled diffraction order and the zero diffraction order.

[0092] Furthermore, the tilted orthogonal illumination disclosed herein allows for the selection of different wavelengths for different pitches in the stacked target 104. As an example in the case where the stacked target 104 includes both PQ and ST textured structures, one or more illumination beams 108 may include a first wavelength (or a set of wavelengths) suitable for imaging the PQ textured structure and a second wavelength (or a second set of wavelengths) suitable for imaging the ST textured structure. In this way, the wide bandwidth achieved by the system and method disclosed herein allows for flexible selection of both the first and second wavelengths.

[0093] Now for reference Figures 7A to 7C According to one or more embodiments of the present disclosure, an imaging stacked target 104 having a number of overlapping textures 204 periodically along one measurement direction and a number of overlapping textures 204 periodically along another measurement direction is described.

[0094] Figure 7A The illustration depicts an illumination pupil 302 providing quadrupole illumination according to one or more embodiments of the present disclosure. Figure 7AIn the illumination pupil 302, there are a first pair of illumination lobes 602a to 602b (e.g., first and second illumination lobes) oriented along the Y-axis and suitable for imaging the textured structure 204 having a periodic direction along the X-axis, and a second pair of illumination lobes 700a, 700b (e.g., third and fourth illumination lobes) oriented along the X-axis (e.g., orthogonal to the Y-axis) and suitable for imaging the textured structure 204 having a periodic direction along the Y-axis.

[0095] When measurements are taken in two directions (e.g., orthogonal directions), it is desirable to distinguish the signal in each measurement direction. In some embodiments, the overlay metrology subsystem 102 includes two collection channels for individually imaging an overlay structure having orthogonal periodic orientations. For example, a first collection channel may capture an image of one or more overlay structures 204 having periodicity along the X direction based on the diffraction of one or more illumination beams 108 having azimuth angles along the Y direction, while a second collection channel may capture an image of one or more overlay structures 204 having periodicity along the Y direction based on the diffraction of one or more illumination beams 108 having azimuth angles along the X direction.

[0096] Therefore, it is expected that the diffraction of the illumination beam 108 with a specific azimuth angle can be filtered out (e.g., blocked) by the textured structure 204, which has a periodicity parallel to the specific azimuth angle from the collection channel.

[0097] Figure 7B Illustrated illustration of one or more embodiments of the present disclosure using... Figure 7A The quadrupole illumination profile shown in the figure is used to illuminate the distribution of diffraction orders in the collection pupil 303 produced by the periodic textured structure 204 along the X direction. Figure 7B The distribution of collecting pupil 303 in the middle is similar to Figure 4 The distribution of collecting pupils in the image is only... Figure 7B It also includes overlapping diffraction lobes 704a, 704c and zero-order diffraction lobes 704b, 704d associated with the illumination beams 700a, 700b (oriented along the X direction), which are undesirable and should not participate in image formation. Figure 7C The illustration shows the process after filtering out unwanted diffraction lobes according to one or more embodiments of this disclosure. Figure 7B The distribution of diffraction lobes in the image.

[0098] Various techniques can be used to block these unwanted diffraction lobes, including but not limited to wavelength filtering, polarization filtering, or pupil segmentation techniques (e.g., directing different portions of the collecting pupil 303 to different collecting channels).

[0099] In some embodiments, wavelength-based techniques can be used to filter out unwanted diffraction lobes. For example, illumination beams 602a and 602b may have different spectral contents than illumination beams 700a and 700b. In this configuration, the superposition metrology subsystem 102 may include wavelength filters located in the two collection channels to filter out unwanted diffraction lobes and / or isolate desired diffraction lobes.

[0100] In some embodiments, polarization-based techniques can be used to filter out unwanted diffraction lobes. For example, illumination beams 602a and 602b may have different polarization than illumination beams 700a and 700b (e.g., orthogonally polarized). In this configuration, the superposition metrology subsystem 102 may include one or more polarizers (e.g., analyzers) to separate diffraction lobes into individual collection channels.

[0101] In some embodiments, pupil splitting techniques can be used to filter out unwanted diffraction lobes. For example, the superposition metrology subsystem 102 may include one or more prisms or other pupil splitting devices to distribute light into different collection channels based on their positions in the collection pupil 303.

[0102] It should be understood that, for the sake of clarity, Figure 7B and 7C Only the diffraction lobes associated with the periodic truncation structure 204 along the X-direction are depicted. However, the collecting pupil 303 may also include the diffraction order distribution from the periodic truncation structure 204 along the Y-direction, which may correspond to... Figure 7B and 7C A 90-degree rotation.

[0103] Figure 8 This is a process flow diagram depicting a method 800 for overlay metrology according to one or more embodiments of the present disclosure. Method 800 may be performed via an overlay metrology system 100 as described herein.

[0104] In an embodiment, method 800 includes step 802 of receiving an image of a stacked target on a sample according to a dosage prescription, wherein the stacked target comprises one or more ridge structures having a periodic orientation along one or more measurement directions, wherein the image is generated by illuminating the stacked target with oblique illumination using one or more oblique illumination beams, wherein a particular ridge structure among the one or more ridge structures comprises overlapping gratings having different pitches along the particular measurement direction, wherein the portion of the image associated with the particular ridge structure is formed via a ridge diffraction order from at least one oblique illumination beam having an azimuthal incident direction orthogonal to the particular measurement direction. The plurality of ridge structures may also comprise a ridge structure including two or more gratings having overlapping regions.

[0105] In an embodiment, method 800 includes step 804 of determining a pair of measurements associated with the relative position of a sample layer along one or more measurement directions based on an image of the pair of targets.

[0106] As previously described herein, the overlay metrology subsystem 102 can be configured according to one or more metrology prescriptions that control various parameters of the overlay metrology subsystem 102, including but not limited to components in the illumination subsystem 117, components in the collection subsystem 130, or detector 144. In this way, the overlay metrology subsystem 102 can be configured to provide only two selected diffraction lobes in response to illumination channels 118a, 118b passing through a known overlay target 104 (or target design) in the collection pupil plane. For example, the metrology prescription may specify that only the two selected diffraction lobes are collected by the collection pupil 303. In another example, the metrology prescription may specify that only three directional lobes (e.g., the first fringe diffraction orders 404a to 404d (+ / - 1M) and the zeroth order diffraction) are collected by the collection pupil. In yet another example, an image formed by one or more illumination beams 108 may be generated using only the first fringe diffraction order and the zeroth order.

[0107] As described herein, the system and method's ability to include first-order stacked diffraction lobes and exclude second and larger diffraction orders can also increase the available illumination bandwidth and the measurable grating pitch range, thereby enabling the system to measure not only fine pitch structures in robust advanced imaging (rAIM) techniques, but also larger features, such as those utilized in continuous diffraction-based stacked pair (CDBO) patterns.

[0108] One or more processors 112 of controller 110 may comprise any processor or processing element known in the art. For the purposes of this disclosure, the terms “processor” or “processing element” may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application-specific integrated circuit (ASIC) devices, one or more field-programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, one or more processors 112 may comprise any device configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). In one embodiment, one or more processors 112 may embody a desktop computer, host computer system, workstation, graphics computer, parallel processor, networked computer, or any other computer system configured to execute a program configured to operate the stacked metering system 100 or to operate in conjunction with the stacked metering system, as described throughout this disclosure.

[0109] Furthermore, different subsystems of the stacking metering system 100 may include processors or logic elements suitable for performing at least a portion of the steps described in this disclosure. Therefore, the above description should not be construed as a limitation on the embodiments of this disclosure but is merely illustrative. Additionally, the steps described throughout this disclosure may be performed by a single controller 110 or alternatively by multiple controllers. Furthermore, controller 110 may include one or more controllers housed in a common housing or multiple housings. In this manner, any controller or combination of controllers may be individually packaged as a module suitable for integration into the stacking metering system 100.

[0110] Although embodiments of method 800 have been discussed herein, it should be further considered that various steps of method 800 may be included, excluded, rearranged, and / or implemented in many ways without departing from the spirit of this disclosure. Therefore, the foregoing embodiments and implementations of method 800 are included by way of example only and are not intended to limit this disclosure in any way.

[0111] In embodiments, one or more processors 112 of controller 110 may include any processing element known in the art. In this sense, one or more processors 112 may include any microprocessor-type device configured to execute algorithms and / or instructions. Furthermore, memory 114 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 112. For example, memory 114 may include non-transitory memory media. As additional examples, memory 114 may include, but is not limited to, read-only memory, random access memory, magnetic or optical memory devices (e.g., disks), magnetic tape, solid-state drives, etc. Further note that memory 114 may be housed in a common processor housing one or more processors 112.

[0112] All methods described herein may include storing the results of one or more steps of the method embodiments in a memory medium. The results may include any of the results described herein and may be stored in any manner known in the art. The memory medium may include any memory medium described herein or any other suitable memory medium known in the art. After the results have been stored, they may be accessed in the memory medium and used by any of the method or system embodiments described herein, formatted for display to a user, or used by another software module, method, or system. Furthermore, the results may be stored “permanently,” “semi-permanently,” “temporarily,” or for a period of time. For example, the memory medium may be random access memory (RAM), and the results may not necessarily be retained in the memory medium indefinitely.

[0113] Furthermore, each of the embodiments of the methods described above may include any other step of any other method described herein. Additionally, each of the embodiments of the methods described above may be performed by any of the systems described herein.

[0114] The objects described herein sometimes illustrate different components contained within or connected to other components. It should be understood that these depicted architectures are merely exemplary, and many other architectures can in fact be implemented to achieve the same functionality. Conceptually, any arrangement of components achieving the same functionality is effectively “associated” to achieve the desired functionality. Therefore, any two components combined herein to achieve a particular functionality can be considered “associated” to achieve the desired functionality, regardless of the architecture or intermediate components. Similarly, any two such associated components can also be considered “connected” or “coupled” to achieve the desired functionality, and any two components that can be suchly associated can also be considered “coupled” to achieve the desired functionality. Specific instances of coupling include, but are not limited to, components that can physically interact and / or physically interact with each other, and / or components that can wirelessly interact and / or wirelessly interact with each other, and / or components that can logically interact and / or logically interact with each other.

[0115] Those skilled in the art will recognize that it is common practice within the art to describe devices and / or processes in the manner set forth herein and to subsequently integrate such described devices and / or processes into data processing systems through engineering practice. That is, at least a portion of the devices and / or processes described herein can be integrated into a data processing system through a reasonable amount of experimentation. Those skilled in the art will recognize that a typical data processing system generally includes one or more of the following: a system unit housing; a video display device; memory, such as volatile and non-volatile memory; a processor, such as a microprocessor and a digital signal processor; computing entities, such as an operating system, drivers, a graphical user interface, and applications; one or more interactive devices, such as a touchpad or a touchscreen; and / or a control system including a feedback loop and control motors (e.g., feedback for sensing position and / or speed; control motors for moving and / or adjusting components and / or quantities). Typical data processing systems can be implemented using any suitable commercially available components (e.g., components commonly found in data computing / communication and / or network computing / communication systems).

[0116] Those skilled in the art will understand that, generally, the terms used herein, and especially in the appended claims (e.g., the body of the appended claims), are intended to be “open-ended” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “including but not limited to,” etc.). Those skilled in the art will further understand that if there is an intention to describe a particular number of technical solutions, this intention will be explicitly stated in the technical solutions, and if such a statement is absent, this intention does not exist. For example, as an aid to understanding, the appended claims may contain the introductory phrases “at least one” and “one or more” to describe the technical solutions. However, the use of such phrases should not be construed as implying that the description of a technical solution introduced by the indefinite article "(a or an)" limits any particular technical solution containing this described technical solution to an invention containing only one such description, even when the same technical solution contains the introductory phrase "one or more" or "at least one" and an indefinite article such as "one (a or an)" (e.g., "one (a and / or an)" should generally be interpreted as meaning "at least one" or "one or more"); the same applies to the use of definite articles used for describing technical solutions. Furthermore, even if a specific number of described technical solutions is explicitly stated, a person skilled in the art will recognize that this statement should generally be interpreted as meaning at least the number described (e.g., an explicit statement of "two descriptions" without other modifiers generally means at least two descriptions, or two or more descriptions). Furthermore, in instances where a convention similar to "at least one of A, B, and C" is used, this construction is generally intended to mean that a person skilled in the art will understand the meaning of the convention (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C). In instances where a convention similar to "at least one of A, B, or C" is used, this construction is generally intended to mean that a person skilled in the art will understand the meaning of the convention (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C).Those skilled in the art will further understand that any transition word and / or phrase (whether in the description, claims, or drawings) that substantially represents two or more alternative terms should be understood to encompass the possibility of including one, any, or both of the terms. For example, the phrase "A or B" would be understood to include the possibility of including "A" or "B" or "A and B".

[0117] It is believed that many advantages of this disclosure and its accompanying advantages will be understood from the foregoing description, and it will become apparent that various changes in the form, construction, and arrangement of the components can be made without departing from the subject matter of the disclosure or without sacrificing all its material advantages. The forms described are merely illustrative, and the appended claims are intended to encompass and include such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. A stacked metering system, comprising: One or more controllers, including one or more processors configured to execute program instructions, said one or more processors being configured to: An image of a stacked target on a received sample according to a metrological prescription, wherein the stacked target comprises one or more ridge structures having a periodic orientation along one or more measurement directions, wherein the image is generated by irradiating the stacked target with oblique illumination using one or more oblique illumination beams, wherein a particular ridge structure among the one or more ridge structures comprises an overlapping grating with a different pitch along the particular measurement direction, wherein a portion of the image associated with the particular ridge structure is formed via a ridge diffraction order from at least one oblique illumination beam having an azimuthal incident direction orthogonal to the particular measurement direction; and Based on the image of the stacked target, a stacking measurement is determined that is associated with the relative position of the sample layer along one or more measurement directions.

2. The stacking metering system according to claim 1, wherein the one or more overlapping structures include a first overlapping structure, the first overlapping structure comprising: A first grating having a first pitch on a first layer of the sample; and A second grating having a second pitch on a second layer of the sample, wherein the first grating and the second grating are formed in a first overlapping region of the sample, wherein the first grating and the second grating have different pitches and have a common periodic orientation.

3. The stacked metering system according to claim 1, wherein the one or more stacked structures comprise: The first overlapping structure includes: A first grating having a first pitch on a first layer of the sample; and A second grating having a second pitch on a second layer of the sample, wherein the first grating and the second grating are formed in a first overlapping region of the sample, wherein the first grating and the second grating have different pitches and a common periodic orientation; and The second overlapping structure includes: A third grating having the second pitch on the first layer of the sample; and A fourth grating having the first pitch of the second layer of the sample, wherein the third grating and the fourth grating are formed in the second overlapping region of the sample and have a common periodic orientation.

4. The stacked metering system according to claim 1, wherein the one or more stacked structures comprise: The first overlapping structure includes: A first grating having a first pitch on a first layer of the sample; and A second grating having a second pitch on a second layer of the sample, wherein the first grating and the second grating are formed in a first overlapping region of the sample, wherein the first grating and the second grating have different pitches and a common periodic orientation; and The second overlapping structure includes: A third grating having a third pitch on the first layer of the sample; and A fourth grating having a fourth pitch of the second layer of the sample, wherein the third grating, the fourth grating, and at least one of the first grating or the second grating all have different pitches, wherein the third grating and the fourth grating are formed in the second overlapping region of the sample and have a common periodic orientation.

5. The stacked metering system according to claim 1, wherein the one or more oblique illumination beams comprise a dipole distribution.

6. The stacked metering system according to claim 1, wherein the one or more oblique illumination beams comprise a quadrupole distribution.

7. The stacked metering system according to claim 1, wherein the one or more stacked structures comprise: One or more first folded structures having a periodic orientation along a first measurement direction among the one or more measurement directions, wherein a portion of the image associated with the one or more first folded structures is formed via a folded diffraction order from at least one oblique illumination beam having an azimuth angle orthogonal to the first measurement direction among the one or more oblique illumination beams; and One or more second folded structures having a periodic orientation along a second measurement direction among the one or more measurement directions, wherein a portion of the image associated with the one or more second folded structures is formed via a folded diffraction order from at least one oblique illumination beam having an azimuthal incident direction orthogonal to the second measurement direction among the one or more oblique illumination beams.

8. The stacked measurement system of claim 7, wherein the one or more tilted illumination beams comprise a quadrupole distribution, wherein two illumination beams have an azimuth angle of incidence orthogonal to the first measurement direction and two illumination beams have an azimuth angle of incidence orthogonal to the second measurement direction.

9. The stacking metrology system of claim 7, further comprising an analyzer configured to polarize the illumination from one of the one or more oblique illumination beams.

10. The stacking metering system of claim 1, further comprising an optical element configured to split the illumination into different channels based on the position of the illumination in the collecting pupil.

11. The superimposed measurement system of claim 1, wherein the image formed by one or more illumination beams is generated using only the first superimposed diffraction order and the zero diffraction order.

12. The stacking metering system according to claim 1, wherein the polar incident angle of the one or more tilted illumination beams is adjustable.

13. The stacking metering system according to claim 1, wherein the first stacking target comprises: Robust advanced imaging metrology (rAIM) target.

14. The stacking metering system according to claim 1, wherein at least two of the one or more oblique illumination beams have different wavelengths.

15. The stacking metering system of claim 14, further comprising a collection subsystem configured to individually collect illumination of different wavelengths from each of two of the one or more oblique illumination beams.

16. A stacked metering system, comprising: An illumination subsystem comprising one or more lenses configured to illuminate a stacked target on a sample via oblique illumination according to a metrological prescription, wherein the stacked target comprises one or more ridge structures having a periodic orientation along one or more measurement directions, wherein an image is generated by illuminating the stacked target with one or more oblique illumination beams, wherein a particular ridge structure among the one or more ridge structures comprises an overlapping grating having a different pitch along a particular measurement direction, wherein a portion of the image associated with the particular ridge structure is formed via a ridge diffraction order from at least one oblique illumination beam having an azimuthal incident direction orthogonal to the particular measurement direction. A collection subsystem comprising at least one objective lens configured to collect at least one sgrain diffraction order associated with the diffraction of the one or more sgrain structures by the one or more obliquely illuminating beams; A detector configured to generate an image of the superimposed target using illumination collected by the collection subsystem; as well as A controller communicatively coupled to the collection subsystem, the controller comprising one or more processors configured to execute program instructions, thereby causing the one or more processors to: Receive the image of the superimposed target; and Based on the image of the stacked target, a stacking measurement is determined that is associated with the relative position of the sample layer along one or more measurement directions.

17. The stacking metering system according to claim 16, wherein the one or more overlapping structures include a first overlapping structure, the first overlapping structure comprising: A first grating having a first pitch on a first layer of the sample; and A second grating having a second pitch on a second layer of the sample, wherein the first grating and the second grating are formed in a first overlapping region of the sample, wherein the first grating and the second grating have different pitches and have a common periodic orientation.

18. The stacked metering system according to claim 16, wherein the one or more stacked structures comprise: The first overlapping structure includes: A first grating having a first pitch on a first layer of the sample; and A second grating having a second pitch on a second layer of the sample, wherein the first grating and the second grating are formed in a first overlapping region of the sample, wherein the first grating and the second grating have different pitches and a common periodic orientation; and The second overlapping structure includes: A third grating having the second pitch on the first layer of the sample; and A fourth grating having the first pitch of the second layer of the sample, wherein the third grating and the fourth grating are formed in the second overlapping region of the sample and have a common periodic orientation.

19. The stacked metering system according to claim 16, wherein the one or more stacked structures comprise: The first overlapping structure includes: A first grating having a first pitch on a first layer of the sample; and A second grating having a second pitch on a second layer of the sample, wherein the first grating and the second grating are formed in a first overlapping region of the sample, wherein the first grating and the second grating have different pitches and a common periodic orientation; and The second overlapping structure includes: A third grating having a third pitch on the first layer of the sample; and A fourth grating having a fourth pitch of the second layer of the sample, wherein the third grating, the fourth grating, and at least one of the first grating or the second grating all have different pitches, wherein the third grating and the fourth grating are formed in the second overlapping region of the sample and have a common periodic orientation.

20. The stacked metering system of claim 16, wherein the one or more oblique illumination beams comprise a dipole distribution.

21. The stacked metering system of claim 16, wherein the one or more oblique illumination beams comprise a quadrupole distribution.

22. The stacked metering system according to claim 16, wherein the one or more stacked structures comprise: One or more first folded structures having a periodic orientation along a first measurement direction among the one or more measurement directions, wherein a portion of the image associated with the one or more first folded structures is formed via a folded diffraction order from at least one oblique illumination beam having an azimuth angle orthogonal to the first measurement direction among the one or more oblique illumination beams; and One or more second folded structures having a periodic orientation along a second measurement direction among the one or more measurement directions, wherein a portion of the image associated with the one or more second folded structures is formed via a folded diffraction order from at least one oblique illumination beam having an azimuthal incident direction orthogonal to the second measurement direction among the one or more oblique illumination beams.

23. The stacked measurement system of claim 22, wherein the one or more oblique illumination beams comprise a quadrupole distribution, wherein two illumination beams have an azimuth angle of incidence orthogonal to the first measurement direction and two illumination beams have an azimuth angle of incidence orthogonal to the second measurement direction.

24. The stacking metering system of claim 16, further comprising an optical element configured to split the illumination into different channels based on the position of the illumination in the collecting pupil.

25. The stacking metrology system of claim 22, further comprising an analyzer configured to polarize the illumination from one of the one or more oblique illumination beams.

26. The superimposed metering system of claim 16, wherein the image formed by one or more illumination beams is generated using only the first superimposed diffraction order and the zero diffraction order.

27. The stacking metering system of claim 16, wherein the polar incident angle of the one or more tilted illumination beams is adjustable.

28. The stacking metering system of claim 16, wherein the first stacking target comprises: Robust advanced imaging metrology (rAIM) target.

29. The stacking metering system of claim 16, wherein at least two of the one or more oblique illumination beams have different wavelengths.

30. The stacking metering system of claim 29, further comprising a collection subsystem configured to individually collect illumination of different wavelengths from each of two of the one or more oblique illumination beams.

31. A measurement method, comprising: An image of a stacked target on a received sample according to a metrological prescription, wherein the stacked target comprises one or more ridge structures having a periodic orientation along one or more measurement directions, wherein the image is generated by irradiating the stacked target with oblique illumination using one or more oblique illumination beams, wherein a particular ridge structure among the one or more ridge structures comprises an overlapping grating with a different pitch along the particular measurement direction, wherein a portion of the image associated with the particular ridge structure is formed via a ridge diffraction order from at least one oblique illumination beam having an azimuthal incident direction orthogonal to the particular measurement direction; and Based on the image of the stacked target, a stacking measurement is determined that is associated with the relative position of the sample layer along one or more measurement directions.

Images