Single capture overlay measurement of high targets

Abstract

A overlay metrology system may include an objective lens, illumination optics to illuminate an overlay target, the overlay target including a first grating having a first pitch on a first sample layer and a second grating having a second pitch on a second sample layer, wherein the first sample layer is separated from the second sample layer by a layer separation distance greater than a depth of field of the objective lens. The system may further include light collecting optics having a radially varying defocus profile to compensate for the layer separation distance such that the first grating and the second grating are simultaneously focused on a detector.

Description

Technical Field

[0001] The present disclosure relates generally to overlay metrology, and more particularly to overlay metrology on overlay targets having features with relatively large axial separations. Background Art

[0002] Advanced packaging schemes for semiconductor devices increasingly utilize three-dimensional (3D) manufacturing techniques, such as die-to-wafer (D2W) or wafer-to-wafer (W2W) processing, in order to support aggressive roadmaps for connection density and data transfer speeds. Such techniques may provide for reduced bond sizes, which may reduce the allowable space on the sample dedicated to overlay measurements, while simultaneously requiring tighter overlay tolerances and high measurement throughput. In addition, 3D manufacturing techniques may require registration measurements between features with relatively large axial separations (e.g., on the order of 100 microns or more). Therefore, there is a need to develop systems and methods that address these challenges. Summary of the invention

[0003] According to one or more illustrative embodiments of the present disclosure, a superposition metrology system is disclosed. In one illustrative embodiment, the system includes an objective lens. In another illustrative embodiment, the system includes one or more illumination optical devices configured to direct illumination from an illumination source to a superposition target on a sample through the objective lens when implementing a metrology recipe, wherein the superposition target according to the metrology recipe includes a first grating with a first pitch on a first sample layer and a second grating with a second pitch on a second sample layer, and wherein the second pitch is smaller than the first pitch, wherein the first sample layer is separated from the second sample layer by a layer separation distance greater than the depth of field of the objective lens. In another illustrative embodiment, the system includes a detector. In another illustrative embodiment, the system includes one or more light collection optical devices configured to direct at least a portion of the light collected by the objective lens to the detector, wherein the metrology recipe stipulates that the diffraction orders of the illumination by the first grating collected by the objective lens are positioned below a threshold radius in a pupil plane and the diffraction orders of the illumination by the second grating collected by the objective lens are positioned above the threshold radius in the pupil plane. In another illustrative embodiment, the one or more collecting optics provide a radially varying defocus profile to compensate for the layer separation distance, wherein the first grating and the second grating are simultaneously focused on the detector. In another illustrative embodiment, the system includes a controller. In another illustrative embodiment, the controller receives one or more images of the superposition target from the detector, wherein the first grating and the second grating are simultaneously focused on the detector. In another illustrative embodiment, the controller determines a superposition measurement between the first layer and the second layer of the sample based on the one or more images.

[0004] According to one or more illustrative embodiments of the present disclosure, a superposition metrology system is disclosed. In one illustrative embodiment, the system includes a controller communicatively coupled to a superposition metrology subsystem. In another illustrative embodiment, the controller receives one or more images of a superposition target from a detector of the superposition metrology subsystem, wherein a first grating and a second grating are simultaneously focused on the detector. In another illustrative embodiment, the superposition metrology subsystem includes an objective lens. In another illustrative embodiment, the superposition metrology subsystem includes one or more illumination optical devices configured to direct illumination from an illumination source to the superposition target on a sample through the objective lens when implementing the metrology recipe, wherein the superposition target according to the metrology recipe includes a first grating with a first pitch on a first sample layer and a second grating with a second pitch on a second sample layer, and wherein the second pitch is less than the first pitch, wherein the first sample layer and the second sample layer are separated by a layer separation distance greater than the depth of field of the objective lens. In another illustrative embodiment, the superposition metrology subsystem includes a detector. In another illustrative embodiment, the superposition metrology subsystem includes one or more collection optics configured to direct at least a portion of the light collected by the objective to the detector, wherein the metrology recipe provides that diffraction orders of the illumination by the first grating collected by the objective are positioned below a threshold radius in a pupil plane and diffraction orders of the illumination by the second grating collected by the objective are positioned above the threshold radius in the pupil plane. In another illustrative embodiment, the one or more collection optics provide a radially varying defocus profile to compensate for the layer separation distance, wherein the first grating and the second grating are simultaneously focused on the detector. In another illustrative embodiment, the controller determines a superposition measurement between the first layer and the second layer of the sample based on the one or more images.

[0005] According to one or more illustrative embodiments of the present disclosure, a superposition metrology method is disclosed. In one illustrative embodiment, the method includes receiving one or more images of a superposition target on a sample from a detector of a superposition metrology subsystem, wherein the superposition target according to a metrology recipe includes a first grating with a first pitch on a first sample layer and a second grating with a second pitch on a second sample layer, and wherein the second pitch is less than the first pitch. In another illustrative embodiment, the first grating and the second grating are simultaneously focused on the detector. In another illustrative embodiment, the superposition metrology subsystem includes an objective lens. In another illustrative embodiment, the superposition metrology subsystem includes one or more illumination optical devices configured to direct illumination from an illumination source to the superposition target on the sample through the objective lens when implementing the metrology recipe, wherein the first sample layer and the second sample layer are separated by a layer separation distance greater than the depth of field of the objective lens. In another illustrative embodiment, the superposition metrology subsystem includes a detector. In another illustrative embodiment, the superposition metrology subsystem includes one or more collection optics configured to direct at least a portion of the light collected by the objective to the detector, wherein the metrology recipe provides that the diffraction orders of the illumination by the first grating collected by the objective are positioned below a threshold radius in a pupil plane and the diffraction orders of the illumination by the second grating collected by the objective are positioned above the threshold radius in the pupil plane. In another illustrative embodiment, the one or more collection optics provide a radially varying defocus profile to compensate for the layer separation distance, wherein the first grating and the second grating are simultaneously focused on the detector. In another illustrative embodiment, the method includes determining a superposition measurement between the first layer and the second layer of the sample based on the one or more images.

[0006] 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 as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Those skilled in the art may better appreciate the numerous advantages of the present disclosure by referring to the accompanying drawings.

[0008] Figure 1A is a block diagram of a superimposed metering system according to one or more embodiments of the present disclosure.

[0009] Figure 1B is a conceptual diagram of a superposition metrology subsystem according to one or more embodiments of the present disclosure.

[0010] Figure 1C is a conceptual diagram of a portion of a superposition metrology subsystem illustrating a collection field stop for blocking zero-order reflections from a top surface of a sample in accordance with one or more embodiments of the present disclosure.

[0011] Figure 1D is a conceptual diagram of a superposition metrology subsystem including a Linnik interferometer according to one or more embodiments of the present disclosure.

[0012] Figure 2A is a side view of a cell of a superimposed target according to one or more embodiments of the present disclosure.

[0013] Figure 2B According to one or more embodiments of the present disclosure Figure 2A A top view of the unit.

[0014] Figure 2C is a top view of a stacked target including four units according to one or more embodiments of the present disclosure.

[0015] Figure 2D is a top view of a portion of a sample depicting two superimposed targets having cells with features separated between die and scribe lanes in accordance with one or more embodiments of the present disclosure.

[0016] Figure 3A is a top view of a collection pupil plane including a phase plate having a radius smaller than a boundary of the collection pupil plane according to one or more embodiments of the present disclosure.

[0017] Figure 3B is a top view of a collection pupil plane including an annular phase plate according to one or more embodiments of the present disclosure.

[0018] Figure 4A is a top view of an illumination pupil plane providing a single illumination beam at normal incidence in accordance with one or more embodiments of the present disclosure.

[0019] Figure 4B is a device configured for mixed brightfield and darkfield imaging according to one or more embodiments of the present disclosure having the following features: Figure 3A 1 is a top view of the collection pupil plane of a phase plate configured as described in FIG.

[0020] Figure 4C is a device configured for mixed brightfield and darkfield imaging according to one or more embodiments of the present disclosure having the following features: Figure 3B 1 is a top view of the collection pupil plane of a phase plate configured as described in FIG.

[0021] Figure 4D is a device configured for dark field imaging according to one or more embodiments of the present disclosure having the following features: Figure 3A 1 is a top view of the collection pupil plane of a phase plate configured as described in FIG.

[0022] Figure 4E is a device configured for dark field imaging according to one or more embodiments of the present disclosure having the following features: Figure 3B 1 is a top view of the collection pupil plane of a phase plate configured as described in FIG.

[0023] Figure 5A is a top view of an illumination pupil plane providing an illumination beam at an oblique incident angle according to one or more embodiments of the present disclosure.

[0024] Figure 5B is configured for imaging based on oblique illumination according to one or more embodiments of the present disclosure and has Figure 3A 1 is a top view of the collection pupil plane of a phase plate configured as described in FIG.

[0025] Figure 5C is configured for imaging based on oblique illumination according to one or more embodiments of the present disclosure and has Figure 3B 0013] A top view of the collection pupil plane of a phase plate configured as described in 0013 for imaging based on oblique illumination.

[0026] Fig. 6A is a top view of an illumination pupil plane providing two illumination beams at symmetrically opposite azimuthal angles of incidence according to one or more embodiments of the present disclosure.

[0027] Figure 6B is configured for use in a Littrow configuration according to one or more embodiments of the present disclosure. Fig. 6A The two illumination beams described in the figure are imaged based on oblique illumination and have the following characteristics: Figure 3A 1 is a top view of the collection pupil plane of a phase plate configured as described in FIG.

[0028] Figure 6C is configured according to one or more embodiments of the present disclosure for use in a generalized configuration such as Fig. 6A The two illumination beams described in the figure are imaged based on oblique illumination and have the following characteristics: Figure 3A 1 is a top view of the collection pupil plane of a phase plate configured as described in FIG. DETAILED DESCRIPTION

[0029] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with respect to specific embodiments and specific features thereof. The embodiments described herein should be regarded as illustrative and not restrictive. It should be readily apparent to one of ordinary skill in the art that various changes and modifications in form and details may be made without departing from the spirit and scope of the present disclosure.

[0030] Embodiments of the present disclosure relate to systems and methods for image-based overlay metrology of overlay targets having features separated axially by a distance greater than the depth of focus of a light collecting objective, wherein the features are simultaneously focused in a single image grab. In this way, features separated by a large axial distance (e.g., relative to the depth of focus of the objective) can be simultaneously focused in a single image of the overlay target. For purposes of this disclosure, an overlay target having features on layers separated axially is referred to as a high overlay target.

[0031] It is contemplated herein that a superposition metrology system (or subsystem) may be configured according to various metrology recipes suitable for producing superposition measurements on superposition targets having various designs. For example, a metrology recipe may include various design parameters associated with the design of a particular superposition target and various parameters of a superposition metrology subsystem suitable for measuring the superposition target. In this manner, various aspects of a superposition target and a superposition metrology subsystem suitable for characterizing the superposition target may be designed together to provide measurements according to a metrology recipe.

[0032] In some embodiments, a metrology recipe provides that a superposition target comprises first grating features having a first pitch in a first layer of a sample and a second grating having a second pitch different from the first pitch in a second layer of the sample, wherein an axial distance between the first layer and the second layer of the sample (e.g., a layer separation distance) is greater than a depth of focus (DOF) of a superposition metrology subsystem used to characterize the target. In this manner, without further consideration, the gratings in the first and second layers will not be in focus at the same time. For purposes of this disclosure, a grating of a superposition target having a relatively large pitch is referred to as a large pitch grating and a grating of the superposition target having a relatively small pitch is referred to as a small pitch grating.

[0033] In some embodiments, metrology further provides that the diffraction orders of interest for a particular measurement scheme are completely separated in different radial regions of the collection pupil of the superposition metrology subsystem. For example, a grating with a relatively large pitch (e.g., a large pitch grating) may provide diffraction orders 0 within a first radial range of the collection pupil. <r<r t , while a grating with a relatively small pitch (e.g., a fine pitch grating) can provide diffraction orders r within the second radial range of the collection pupil. t <r<r max Here, r max corresponds to the boundary of the collection pupil (eg, the maximum collection numerical aperture (NA)) and r t Corresponds to a threshold radius separating the diffraction orders of the first and second gratings.

[0034] In some embodiments, a superposition metrology subsystem configured according to a metrology recipe to measure superposition of a sample based on a superposition target includes light collection optics that provide a radially varying defocus profile to compensate for a layer separation distance. Diffraction orders illuminated by a first and second illumination grating pair may experience different portions of the radially varying defocus profile. Thus, the first and second gratings may be focused on a detector simultaneously.

[0035] The superposition metrology subsystem may generally include any type or combination of elements that provide radially varying defocus.

[0036] In some embodiments, the superposition metrology subsystem includes a lens in a pupil plane (e.g., a relay pupil plane), wherein the lens has a radius equal to a threshold radius. In this way, the lens can operate on diffraction orders from a large pitch grating, but not on diffraction orders from a small pitch grating. In addition, the lens optionally can be a positive or negative lens to adjust the focal plane associated with the large pitch grating to match the focal plane of the small pitch grating. For example, the lens can be a positive lens when the large pitch grating is closer to the objective lens than the small pitch grating, and can be a negative lens when the large pitch grating is farther from the objective lens than the small pitch grating.

[0037] In some embodiments, the superposition metrology subsystem includes an objective lens having a correction ring that can be adjusted to provide a selected amount of spherical aberration. It is contemplated herein that spherical aberration corresponds to radially dependent defocus. In this manner, increasing spherical aberration in the lens increases the amount of defocus difference between light incident on the center of the objective lens relative to light incident near the edge of the lens. It is further contemplated herein that such a correction ring can be used to compensate for layer separation distance and provide that large pitch and small pitch gratings are simultaneously in focus.

[0038] Additional embodiments of the present disclosure relate to high-overlap target designs suitable for measurement using the systems and methods disclosed herein.

[0039] Reference Figures 1A to 6C , according to one or more embodiments of the present disclosure, a system and method for image-based overlay metrology on high overlay targets are described in more detail.

[0040] Figure 1A 1 is a block diagram of an overlay metrology system 100 according to one or more embodiments of the present disclosure. In some embodiments, the overlay metrology system 100 includes an overlay metrology subsystem 102 to generate overlay measurements associated with the sample 104 based on characterization of an overlay target 106 on the sample 104. For example, the overlay target 106 may include features on multiple layers of the sample 104. In this way, overlay measurements of the sample 104 may be generated based on one or more images of the overlay target 106.

[0041] In some embodiments, overlay metrology subsystem 102 generates at least one image of overlay target 106. As an illustration, overlay metrology subsystem 102 may illuminate overlay target 106 with illumination including one or more illumination beams 108, collect light from overlay target 106 (which is referred to herein as sample light 110), and generate an image of overlay target 106 based on at least a portion of sample light 110.

[0042] Furthermore, the overlay metrology subsystem 102 may be configurable to generate measurements based on any number of metrology recipes that define various aspects of the overlay target 106 (e.g., a target design) or measurement parameters of the overlay metrology subsystem 102 that are suitable for generating overlay measurements of a particular overlay target 106 having a particular target design.

[0043] In other words, the overlay metrology subsystem 102 may be configured to provide selected measurement types for a selected overlay target design. For example, the metrology recipe may include various parameters associated with the design of the overlay target 106, such as, but not limited to, the location and orientation of sample features (e.g., the pitch of grating features along a particular direction). By another example, the metrology recipe may include various parameters associated with the location of the sample 104 during the measurement, such as, but not limited to, the height, the orientation, whether the sample 104 is static during the measurement, or whether the sample 104 is in motion during the measurement (and associated parameters describing the speed, scanning mode, or the like). By another example, the metrology recipe may include parameters of the illumination beam 108, such as, but not limited to, the illumination wavelength, the illumination pupil distribution (e.g., the distribution of illumination angles and the associated illumination intensities at those angles), the polarization of the incident illumination, or the spatial distribution of the illumination. By way of another example, a metrology recipe may include collection parameters associated with collection or filtering of the sample light 110, such as, but not limited to, a collection pupil distribution, a collection field stop setting for selecting a portion of the overlay target 106 of interest for imaging, polarization of the sample light 110, wavelength filters, or parameters for controlling one or more detectors.

[0044] In some embodiments, the overlay metrology subsystem 102 and / or overlay target 106 are configured (e.g., according to a metrology recipe) to be able to capture images in which features of the overlay target 106 located on layers of the sample 104 that are axially separated by a distance greater than the DOF (e.g., a layer separation distance) are simultaneously focused in a single image. Thus, such an overlay metrology subsystem 102 may be applicable to, but not limited to, overlay metrology of samples manufactured by advanced packaging techniques (e.g., but not limited to, die-to-wafer (D2W) techniques, wafer-to-wafer (W2W) techniques, or other three-dimensional (3D) processing techniques). For example, a D2W or W2W technique may require overlay measurements (e.g., more generally, misregistration measurements) between features on constituent substrates or these constituent substrates. As an illustration, a D2W or W2W technique may require overlay measurements of features having a layer separation distance on the order of hundreds of microns or more. It should be further contemplated herein that simultaneously imaging such disparate features in a single image grab may substantially increase measurement throughput relative to alternative tools or techniques that produce separate images for features on axially separated layers. In some embodiments, features of superposition target 106 positioned on layers of sample 104 that are axially separated by a distance greater than the DOF (e.g., a layer separation distance) are simultaneously focused in a single image plane, but multiple detectors positioned at different instances of this image plane (e.g., in multiple light collection channels) are used to capture different portions of superposition target 106. In this way, sample light 110 associated with features on different layers of superposition target 106 can be isolated to improve image contrast, signal-to-noise ratio, or another quality metric.

[0045] In some embodiments, the overlay metrology system 100 includes a sample positioning subsystem 112 configured to adjust the sample 104 and / or the illumination beam 108 before, during, and / or after measurement. For example, the overlay metrology subsystem 102 may operate in a move-and-measure (MAM) mode of operation in which the sample 104 is stationary during measurement or in a scanning mode of operation in which the sample 104 is in motion during measurement.

[0046] Reference Figures 2A to 2D , in accordance with one or more embodiments of the present disclosure, a stacking target 106 having features separated by a relatively large axial distance is described.

[0047] Figure 2A is a side view of a unit 202 of a superimposed target 106 in accordance with one or more embodiments of the present disclosure. Figure 2B According to one or more embodiments of the present disclosure Figure 2A A top view of unit 202 is shown.

[0048] In some embodiments, the cell 202 includes a large pitch grating 204 (e.g., a first layer grating) positioned on a first layer 206 of the sample 104 and a small pitch grating 208 (e.g., a second layer grating) positioned on a second layer 210 of the sample 104. The first layer 206 and the second layer 210 may be further separated by Figure 2A 2 is represented as an axial separation distance along the Z direction. For example, the first layer 206 and the second layer 210 can be separated by any number of intermediate layers 214.

[0049] The stacking target 106 (or more generally, the sample 104) may further include one or more substrates. As an illustration, Figure 2A A first substrate 216 is depicted proximate to the large pitch grating 204 and a second substrate 218 is depicted proximate to the small pitch grating 208. In this manner, the overlay target 106 can be formed on a wide range of sample types. For example, the sample 104 can be a D2W bonded sample, where the first substrate 216 is a die and the second substrate 218 is a wafer. In this configuration, prior to bonding, at least some of the large pitch grating 204 and optionally the intermediate layer 214 are fabricated as part of the die, while the small pitch grating 208 and optionally at least some of the intermediate layer 214 are fabricated as part of the wafer. As another example, the sample 104 can be a W2W bonded sample, where the first substrate 216 is a first wafer and the second substrate 218 is a second wafer. In this configuration, prior to bonding, at least some of the large pitch grating 204 and optionally the intermediate layer 214 are fabricated as part of the first wafer, while the small pitch grating 208 and optionally at least some of the intermediate layer 214 are fabricated as part of the second wafer.

[0050] Reference Figure 2B and 2C , various non-limiting designs of overlay target 106 are described in more detail according to one or more embodiments of the present disclosure.

[0051] The stacking target 106 may generally be formed of one or more cells 202, wherein any particular cell 202 may include cells having any period and along any direction (e.g., Figure 2A 2 (X direction illustrated in FIG. 2 ) has a periodic grating structure (e.g., large pitch grating 204 and small pitch grating 208). In addition, the constituent gratings within any particular cell 202 may be positioned in an overlapping region, a partially overlapping region, or a non-overlapping region. In this manner, the overlay target 106 may have any suitable design, including but not limited to an advanced imaging metrology (AIM) target, a robust AIM (rAIM) target, a triple AIM target, or a Moire target (e.g., a grating-on-grating target).

[0052] As a graphic illustration, Figure 2B2 is a top view of a stacked target 106 including a single unit 202 suitable for measurement along one direction (eg, here, the X direction). As another illustration, Figure 2C 2 is a top view of a stacked target 106 including four cells 202 according to one or more embodiments of the present disclosure. For example, Figure 2B The superposition target 106 in can be characterized as having an AIM target design. Specifically, Figure 2B The superimposed target 106 in FIG. 1 includes cells 202a, 202c constituting a grating oriented along an X direction (eg, a first measuring direction) and cells 202b, 202d oriented along a Y direction (eg, a second measuring direction).

[0053] The overlay target 106 and / or any particular cell 202 may generally be positioned at any suitable location on the sample 104, such as, but not limited to, within a scribe street between dies or within a die.

[0054] In some embodiments, different portions of the overlay target 106 and / or any particular cell 202 are separated between scribe lanes and dies. Figure 2D 2 is a top view of a portion of a sample 104 depicting two superimposed targets 106 having cells 202 with features separated between a die 220 and a scribe line 222, according to one or more embodiments of the present disclosure. For example, the sample 104 may be a D2W sample, where the die 220 may correspond to a first substrate 216 and the scribe line 222 is on a second substrate 218. Specifically, Figure 2D A first superimposed target 106a and a second superimposed target 106b are depicted, wherein each of the superimposed targets 106a, 106b is configured with a plurality of superimposed targets 106a, 106b arranged for 1D measurement. Figure 2B . For example, the first superposition target 106a has features distributed along the X direction for measurement along the X direction, and the second superposition target 106b has features distributed along the Y direction for measurement along the Y direction. In addition, each of the superposition targets 106a, 106b has a large pitch grating 204 positioned in the die 220 and a small pitch grating 208 positioned in the scribe line 222. As shown in FIG. Figure 2A As described, the intra-die features (e.g., here, large pitch gratings 204) may be located on the surface of the die 220 or may be buried within the sample 104. In this way, this design may be applicable to, but not limited to, applications including two or more stacked dies 220. Furthermore, it should be understood that the specific configuration of the large pitch gratings 204 in the die 220 and the small pitch gratings 208 in the scribe lanes 222 is merely illustrative and does not limit the present disclosure. Rather, any suitable arrangement of the large pitch gratings 204 and the small pitch gratings 208 is within the spirit and scope of the present disclosure.

[0055] It is contemplated herein that the design of the overlay targets 106a, 106b may provide several benefits. For example, a single unit 1D design may enable such overlay targets 106 to be relatively small and thus limit the space on the sample 104 dedicated to overlay measurements. As another example, using separate overlay targets 106a, 106b to perform separate measurements along different directions (e.g., X and Y directions) positioned at different locations on the sample 104 may facilitate compensation for rotation of the sample 104 relative to the overlay metrology subsystem 102. As another example, placement of such overlay targets 106 near intersections between scribe lanes 222 (e.g., intersections between adjacent die 220) may enable efficient measurement sampling. For example, both overlay targets 106a, 106b may be within a single field of view 224 of the overlay metrology subsystem 102 at the same time and thus be characterized at the same time. Furthermore, such overlay targets 106a, 106b may provide accurate measurements for all four adjacent die 220 (or at least portions thereof).

[0056] Reference Figure 1B , Figure 1B is a conceptual diagram of a superposition metrology subsystem 102 according to one or more embodiments of the present disclosure.

[0057] In some embodiments, the overlay metrology subsystem 102 includes an illumination source 114 configured to generate illumination to be directed to the sample 104 in the form of one or more illumination beams 108. In some embodiments, the overlay metrology system 100 includes an illumination path 116 (e.g., an illumination subsystem) containing one or more components that direct the one or more illumination beams 108 to the sample 104. For example, the illumination path 116 may include one or more illumination lenses 118 to direct the one or more illumination beams 108 from the illumination source 114 to the sample 104. In addition, the illumination lenses 118 may be arranged to provide one or more conjugate or relayed illumination pupil planes 120 and / or illumination field planes 122. The illumination path 116 may further include one or more illumination adjustment components 124 adapted to modify and / or adjust the one or more illumination beams 108. The illumination adjustment components 124 may, but are not required to, be positioned in the illumination pupil plane 120 and / or illumination field plane in the illumination path 116. For example, the one or more illumination adjustment components 124 may include, but are not limited to, an illumination aperture stop, an illumination field stop, one or more polarizers, one or more compensators, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, one or more mirrors, or one or more lenses.

[0058] In some embodiments, the superposition metrology subsystem 102 includes a collection light path 126 (e.g., an imaging subsystem) that includes one or more components to collect sample light 110 (e.g., light emitted from the sample 104 in response to one or more illumination beams 108) and direct at least a portion of this sample light 110 to a detector 128. The sample light 110 may include any type of light emitted from the sample 104, including but not limited to diffracted, scattered, or reflected light. In some embodiments, the collection light path 126 includes one or more collection lenses 130 to direct the sample light 110 from the sample 104 to the detector 128. Furthermore, the collection lenses 130 may be arranged to provide one or more conjugate or relayed collection pupil planes 132 and / or collection light field planes 134. In some embodiments, the collection light path 126 includes one or more collection light conditioning components 136 adapted to modify and / or condition the sample light 110. For example, the one or more light collection adjustment components 136 may include, but are not limited to, a light collection aperture stop, a light collection field stop, one or more polarizers, one or more compensators, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, one or more mirrors, or one or more lenses.

[0059] The detector 128 may include any optical detector known in the art suitable for capturing sample light 110 received from the sample 104. Furthermore, the detector 128 may be suitable for capturing images of a stationary or moving sample 104. For example, the detector 128 may include, but is not limited to, a photodiode array (PDA), a charge coupled device (CCD), a complementary metal oxide semiconductor (CMOS) device, a time delay integration (TDI) detector, a line scan detector, a photomultiplier tube (PMT), an avalanche photodiode (APD), or the like. In some embodiments, the detector 128 may include a spectral detector suitable for identifying the wavelength of radiation emitted from the sample 104 and dispersed onto a sensor using a dispersive element.

[0060] In some embodiments, although not explicitly shown, the overlay metrology subsystem 102 includes two or more detectors 128. For example, the collection path 126 may include one or more additional beam splitters to separate the sample light 110 into two or more collection channels. Furthermore, the collection path 126 may separate the sample light 110 into the various collection channels using any technique known in the art. For example, the collection path 126 may include one or more optical elements to separate the sample light 110 based on polarization, wavelength, or any other suitable optical property (e.g., using additional beam splitters, polarizers, dichroic mirrors, or other elements). This configuration may be applicable to, but is not limited to, situations where the sample light 110 associated with features on different layers of the overlay target 106 are optically distinguishable. As another example, the collection path 126 may include one or more spatial filters or beam blocks to spatially isolate features on different layers of the overlay target 106 in the various collection channels.

[0061] In some embodiments, the superposition metrology subsystem 102 includes an objective lens 138 for simultaneously directing one or more illumination beams 108 to the sample 104 and capturing sample light 110 from the sample 104. For example, Figure 1B As illustrated in , the superposition metrology subsystem 102 can include a beam splitter 140 common to both the illumination path 116 and the collection path 126. In addition, a pupil plane 142 can also be common to both the illumination path 116 and the collection path 126 and is thus conjugate to the illumination pupil plane 120 and the collection pupil plane 132.

[0062] Reference Figures 3A to 3B , in accordance with one or more embodiments of the present disclosure, overlay metrology on a high overlay target 106 is described in more detail. For example, the high overlay target 106 may have a large pitch grating 204 and a small pitch grating 208 having a layer separation distance greater than the DOF of the objective lens 138 or more generally the collection light path 126.

[0063] In some embodiments, the superposition metrology subsystem 102 (e.g., the collection path 126 of the superposition metrology subsystem 102) can be configured with a radially varying defocus profile according to a metrology recipe to compensate for the layer separation distance 212. In this way, the diffraction orders of the one or more illumination light beams 108 by the large pitch grating 204 and the small pitch grating 208 can be subjected to different portions of the radially varying defocus profile. Therefore, the large pitch grating 204 and the small pitch grating 208 can be focused on the detector 128 at the same time.

[0064] The overlay metrology subsystem 102 may provide any radially varying defocus profiles suitable for compensating for the layer separation distances 212 between features of the overlay target 106 such that features within respective layers are simultaneously focused on the detector 128. Furthermore, the radially varying defocus profiles may be implemented using any combination of components in the overlay metrology subsystem 102, including but not limited to components of the collection path 126 (e.g., the collection lens 130, the collection adjustment component 136, or the like).

[0065] In some embodiments, the overlay metrology subsystem 102 includes a phase plate in the collection pupil plane 132 to provide a radially varying defocus distribution. The phase plate can have any size or spatially varying phase distribution suitable for providing a selected radially varying defocus distribution.

[0066] Figure 3A is a boundary 304 (r 204 ) smaller than the collection pupil plane 132 according to one or more embodiments of the present disclosure. b ) is a top view of the collecting pupil plane 132 of the phase plate 302 with a radius of . Specifically, Figure 3A The phase plate 302 described in the embodiment has r t In this way, the phase plate 302 can introduce defocus into the collection pupil plane 132 at a radius r of up to the phase plate 302. t The portion of light at the position (e.g., 0≤r <r t The radius value), while the light collecting pupil plane 132 exceeds the radius r t The portion of light at the position where the phase plate 302 is not affected (eg, t ≤r≤r b Thus, the phase plate 302 may compensate for the layer separation distance 212 between the layers of the stacking target 106 so that features on the layers (e.g., the large pitch grating 204 and the small pitch grating 208 in FIG. 2 ) may be focused on the detector 128 at the same time.

[0067] Figure 3B is a top view of a collection pupil plane 132 including an annular phase plate 302 according to one or more embodiments of the present disclosure. Specifically, Figure 3B The phase plate 302 illustrated in FIG. 1 spans r within the collection pupil plane 132. t ≤r≤r b In this way, phase plate 302 can introduce defocus into collection pupil plane 132 at angles exceeding radius r. t The portion of light at the position (e.g., r t ≤r≤r b The radius value), while the light collecting pupil plane 132 is below the radius r tThe portion of light at the position of may not be affected by the phase plate 302 (eg, 0≤r <r t radius value).

[0068] Generally speaking Figure 3A and 3B The phase plate 302 may be positioned at any suitable location. For example, the phase plate 302 may be positioned at a relayed collection pupil plane 132 corresponding to a relayed version (eg, a conjugate version) of the back focal plane of the objective lens 138 .

[0069] Furthermore, the phase plate 302 may provide a phase delay having any spatial distribution. In some embodiments, the phase plate 302 provides a uniform phase delay. This phase plate 302 may be suitable for configurations where the phase plate 302 is smaller than the boundary 304 of the collection pupil plane 132 (e.g., such as Figure 3A and 3B 132). In this way, because the phase plate 302 interacts with only a portion of the light within the collection pupil plane 132, a radially varying defocus profile can be produced across the collection pupil plane 132. In addition, the superposition metrology subsystem 102 can include multiple radially symmetric phase plates 302 to provide different phase delays in multiple radial regions of the illumination pupil plane 120. These phase plates 302 can be positioned in a single relay pupil plane 132 or in different relay planes (e.g., conjugate planes). This configuration can be applicable to, but is not limited to, providing that features on three or more layers of a superposition target 106 (e.g., a triple AIM target or the like) are simultaneously focused on the detector 128.

[0070] In some embodiments, phase plate 302 provides a non-uniform phase retardation across collection pupil plane 132. For example, phase plate 302 may provide different uniform phase retardation in two or more radial regions within collection pupil plane 132. As an illustration, a single phase plate 302 may be provided for a region below a threshold radius 0≤r≤r t The light provides a first phase delay and is above the threshold radius r t <r≤r b In this way, a single phase plate 302 spanning the collection pupil plane 132 can be similar to Figure 3A Operate in the manner described in the configuration.

[0071] As another example, phase plate 302 may provide a radially symmetric, smoothly varying phase retardation profile across collection pupil plane 132. For example, phase plate 302 may be formed as a lens positioned in collection pupil plane 132. As an illustration, a lens positioned in collection pupil plane 132 having a radius smaller than boundary 304 of collection pupil plane 132 may be similar to Figure 3AAs another illustration, a lens positioned in collection pupil plane 132 having a radius equal to or greater than boundary 304 of collection pupil plane 132 may have a sufficiently large phase retardation distribution across collection pupil plane 132 to directly compensate for layer separation distance 212.

[0072] It is further contemplated herein that spherical aberration in one or more components (e.g., one or more lenses) may provide a radially varying defocus profile. Accordingly, the overlay metrology subsystem 102 may include one or more lenses having spherical aberration sufficient to compensate for the layer separation distance of the overlay target 106 so that features on multiple layers of the overlay target 106 may be simultaneously focused on the detector 128.

[0073] In some embodiments, the overlay metrology subsystem 102 includes an objective lens 138 having spherical aberration to provide a radially varying defocus profile sufficient for overlay measurements on the tall cells 202. For example, the objective lens 138 may include one or more components to provide an adjustable amount of spherical aberration. Such an objective lens 138 may include, but is not required to include, one or more optical elements (e.g., lenses) having positions adjustable with an adjustment device (e.g., correction ring, adjustment ring, or the like).

[0074] The objective lens 138 with adjustable spherical aberration is generally useful for compensating for spherical aberration induced by a microscope cover glass or other components in the optical path before the sample of interest. However, it is contemplated herein that the superposition metrology subsystem 102 may utilize the objective lens 138 with adjustable spherical aberration to intentionally introduce radially varying defocus during measurement. Furthermore, the amount of spherical aberration, and thus the amount of radially varying defocus, may be selected (e.g., based on a metrology recipe) to compensate for the layer separation distance 212 between layers of the superposition target 106 so that features on the layers can be simultaneously focused on the detector 128. Furthermore, it is contemplated herein that the objective lens 138 with adjustable spherical aberration may directly compensate for the layer separation distance 212 without requiring additional components in the relayed collection pupil plane 132, which may advantageously provide a relatively simple and robust design of the superposition metrology subsystem 102.

[0075] Reference Figures 4A to 6C , in accordance with one or more embodiments of the present disclosure, overlay metrology on a high overlay target 106 using different imaging modes is described in more detail. The overlay metrology subsystem 102 may be configured to operate in various imaging modes, including but not limited to brightfield imaging mode or darkfield imaging mode.

[0076] Figure 4A 1 is a top view of an illumination pupil plane 120 providing a single illumination beam 108 at normal incidence according to one or more embodiments of the present disclosure. In particular, Figure 4AA single illumination beam 108 is illustrated centered within the boundaries 402 of the illumination pupil plane 120 .

[0077] Figures 4B to 4E Description Based on Figure 4A Various non-limiting imaging configurations for illumination of the contours shown in FIG. Figure 4B is a device configured for imaging according to one or more embodiments of the present disclosure having the following features: Figure 3A 1 is a top view of the collection pupil plane 132 of the phase plate 302 configured as described in FIG. Figure 4C is a device configured for imaging according to one or more embodiments of the present disclosure having the following features: Figure 3B 1 is a top view of the collection pupil plane 132 of the phase plate 302 configured as described in FIG.

[0078] Figure 4B and 4C A 0-order diffraction lobe 404 (e.g., a specular reflection of the illumination beam 108), two large-pitch diffraction lobes 406 associated with diffraction of the illumination beam 108 by the large-pitch grating 204, and two small-pitch diffraction lobes 408 associated with diffraction of the illumination beam 108 by the small-pitch grating 208 are illustrated. For example, the large-pitch diffraction lobes 406 and the small-pitch diffraction lobes 408 may have any diffraction orders. For example, the large-pitch diffraction lobes 406 and / or the small-pitch diffraction lobes 408 may include, but are not limited to, + / -1-order (first order) diffraction lobes.

[0079] Since the large pitch grating 204 and the small pitch grating 208 have different pitches, the large pitch diffraction lobe 406 and the small pitch diffraction lobe 408 may be positioned at different radial positions in the collection pupil plane 132. Therefore, the superposition metrology subsystem 102 may provide a radially varying defocus profile to introduce different amounts of defocus to the large pitch diffraction lobe 406 and the small pitch diffraction lobe 408 to compensate for the layer separation distance 212, so that the large pitch grating 204 and the small pitch grating 208 may be focused on the detector 128 at the same time.

[0080] As a graphic illustration, Figure 4B Phase plate 302 is depicted having a radius (r t) to introduce defocus into the large pitch diffraction lobes 406 but not into the small pitch diffraction lobes 408. In this configuration, the detector 128 can be positioned at a field plane conjugate to the small pitch grating 208 so that the small pitch grating 208 is in focus and the phase plate 302 can introduce enough defocus into the large pitch diffraction lobes 406 to provide that the large pitch grating 204 is also in focus on the detector (despite the layer separation distance 212). Since the phase plate 302 also introduces at least some defocus into the 0th order diffraction lobes 404, the portion of the image containing the large pitch grating 204 can be a bright field image. However, the 0th order diffraction lobe 404 may contribute less to the image of the small pitch grating 208.

[0081] As another illustration, Figure 4C An annular phase plate 302 is depicted having an inner radius (r ) equal to or greater than a boundary 304 in the collection pupil plane 132. t ) and outer radius to introduce defocus into the small pitch diffraction lobes 408 but not into the large pitch diffraction lobes 406. In this configuration, the detector 128 can be positioned at a field plane conjugate to the large pitch grating 204 so that the large pitch grating 204 is in focus and the phase plate 302 can introduce enough defocus into the small pitch diffraction lobes 408 to provide that, despite the layer separation distance 212, the small pitch grating 208 is also in focus on the detector.

[0082] It should be understood that although Figure 4B and 4C The use of a phase plate 302 that may be positioned in any collection pupil plane 132 is depicted, but this is for illustrative purposes only and does not limit the present disclosure. Rather, the superposition metrology subsystem 102 may include any suitable phase plate 302 at any position suitable for providing a radially varying defocus selected to compensate for the layer separation distance 212 such that the large pitch grating 204 and the small pitch grating 208 are simultaneously focused on the detector 128. In some embodiments, the superposition metrology subsystem 102 includes an objective lens 138 that provides spherical aberration that introduces different amounts of defocus to the large pitch diffraction lobes 406 and the small pitch diffraction lobes 408 to provide that the large pitch grating 204 and the small pitch grating 208 are simultaneously focused on the detector 128.

[0083] Figure 4D and 4E Depicts dark field imaging of a high-overlay target 106 in accordance with one or more embodiments of the present disclosure. Specifically, Figure 4D is a device configured for dark field imaging according to one or more embodiments of the present disclosure having the following features: Figure 3A 1 is a top view of the collection pupil plane 132 of the phase plate 302 illustrated in FIG. Figure 4E is a device configured for dark field imaging according to one or more embodiments of the present disclosure having the following features: Figure 3B1 is a top view of the collection pupil plane 132 of the phase plate 302 illustrated in FIG. Figure 4D and 4E Respectively similar to Figure 4B and 4C ,Apart from Figure 4D and 4E Depicted is a blocker 410 positioned to block the 0-order diffraction lobe 404 and thus provide dark field imaging for both the large pitch grating 204 and the small pitch grating 208. The blocker 410 may be positioned in any collection pupil plane 132 (e.g., a relayed collection pupil plane 132). In some embodiments, the blocker 410 is positioned in a plane common to the phase plate 302. In some embodiments, the blocker 410 is positioned in a collection pupil plane 132 different from the phase plate 302 (e.g., relayed).

[0084] Reference Figures 5A to 5C , various non-limiting imaging configurations associated with oblique illumination are described in more detail according to one or more embodiments of the present disclosure.

[0085] Figure 5A is a top view of an illumination pupil plane 120 providing an illumination beam 108 at an oblique angle of incidence in accordance with one or more embodiments of the present disclosure.

[0086] Figure 5B is configured for imaging based on oblique illumination according to one or more embodiments of the present disclosure and has Figure 3A 1 is a top view of the collection pupil plane 132 of the phase plate 302 configured as described in FIG. Figure 5C is configured for imaging based on oblique illumination according to one or more embodiments of the present disclosure and has Figure 3B 1 is a top view of the collection pupil plane 132 of the phase plate 302 configured as described in FIG. 1 for imaging based on oblique illumination.

[0087] Figure 5B and 5C A 0th order diffraction lobe 404 (e.g., a specular reflection of the illumination beam 108), a single small pitch diffraction lobe 408 associated with diffraction of the illumination beam 108 by the small pitch grating 208, and two large pitch diffraction lobes 406 associated with diffraction of the illumination beam 108 by the large pitch grating 204 are illustrated. In addition, Figure 5B and 5C Depicts a Littrow configuration (e.g., according to a metrology recipe) of superimposed metrology subsystem 102 and fine pitch grating 208, wherein a single fine pitch diffraction lobe 408 is disposed along Figure 5AIn addition, the overlay metrology subsystem 102 and the overlay target 106 are further configured (e.g., according to a metrology recipe) to provide that both large-pitch diffraction lobes 406 (e.g., a first-order diffraction lobe and a second-order diffraction lobe) are positioned at smaller radial locations in the collection pupil plane 132, so that the light from the large-pitch grating 204 and the small-pitch grating 208 can experience different amounts of defocus based on the radially varying defocus profiles as disclosed herein.

[0088] For example, Figure 5B A configuration is illustrated in which the phase plate 302 introduces defocus into the large pitch diffraction lobe 406 but not into the 0th order diffraction lobe 404 or the small pitch diffraction lobe 408. In this configuration, the detector 128 can be positioned at a field plane conjugate to the small pitch grating 208 so that a bright field image is formed based on the 0th order diffraction lobe 404 and the small pitch diffraction lobe 408. In addition, the defocus introduced by the phase plate 302 simultaneously provides a focused image of the large pitch grating 204 on the detector 128. Similarly, Figure 5C The reverse configuration is illustrated, wherein the detector 128 is positioned at a field plane conjugate to the large pitch grating 204, and the phase plate 302 introduces defocus to the 0th order diffraction lobe 404 and the small pitch diffraction lobe 408 to provide focused images of the large pitch grating 204 and the small pitch grating 208 simultaneously.

[0089] In some embodiments, the superposition metrology subsystem 102 includes two detectors 128 (e.g., in two collection channels) that respectively image the large pitch grating 204 and the small pitch grating 208. For example, the first collection channel may include one or more blockers (e.g., in the collection pupil plane 132) to block the 0-order diffraction lobe 404 and the small pitch diffraction lobe 408. In this way, the detector 128 in this channel can produce a dark field image of the large pitch grating 204 based only on the large pitch diffraction lobe 406. Similarly, the second collection channel may include one or more blockers (e.g., in the collection pupil plane 132) to block the large pitch diffraction lobe 406 to produce an image of the small pitch grating 208 based only on the 0-order diffraction lobe 404 and the small pitch diffraction lobe 408.

[0090] Reference Figures 6A to 6C In some embodiments, the superposition metrology subsystem 102 generates superposition measurements based on illuminating the superposition target 106 with two or more illumination beams 108. The two or more illumination beams 108 may be provided simultaneously or sequentially. In addition, multiple illumination beams 108 may be used for measurements along a particular direction (e.g., along Figure 2B The method may be used to measure in the X direction or in multiple directions.

[0091] Fig. 6A1 is a top view of an illumination pupil plane 120 providing two illumination beams 108a, 108b at symmetrically opposed azimuthal angles of incidence in accordance with one or more embodiments of the present disclosure. Illumination with symmetrically opposed azimuthal angles of incidence can mitigate the effects of asymmetry of features of the overlay target 106 and / or the profiles of the illumination beams 108. In addition, the two illumination beams 108 can be directed to the overlay target 106 simultaneously or sequentially to facilitate simultaneous or sequential imaging. However, it should be understood that the overlay metrology subsystem 102 can illuminate the overlay target 106 with any number of illumination beams 108 having any azimuthal angles of incidence.

[0092] Figure 6B is a method according to one or more embodiments of the present disclosure configured for use under Littrow conditions as follows Fig. 6A The two illumination beams 108 described in the figure are imaged based on oblique illumination and have the following characteristics: Figure 3A FIG. 1 is a top view of the collection pupil plane 132 of the phase plate 302 configured as described in FIG. Figure 6B Describes all the corresponding Figure 5B The following diffraction lobes of the diffraction lobes depicted in FIG: a 0th order diffraction lobe 404a, first and second order large pitch diffraction lobes 406a, and a first order small pitch diffraction lobe 408a. Figure 6B The following diffraction lobes associated with the diffraction of the illumination beam 108b are further depicted: 0th order diffraction lobe 404b, first and second order large pitch diffraction lobes 406b, and first order small pitch diffraction lobe 408b. These diffraction lobes follow a similar pattern to Figure 5B , but oriented in reverse order along the X direction based on the incident angle of the illumination beam 108 b. Furthermore, because the illumination beams 108 a, 108 b and the fine pitch grating 208 are arranged in a Littrow configuration (e.g., according to a metrology recipe), the patterns of diffraction lobes of the illumination beams 108 a, 108 b overlap in the collection pupil plane 132.

[0093] Similar to Figures 5A to 5CIn the manner described above, in some embodiments, the superposition metrology subsystem 102 includes two detectors 128 (e.g., in two collection channels) that respectively image the large pitch grating 204 and the small pitch grating 208. For example, the first collection channel may include one or more blockers (e.g., in the collection pupil plane 132) to block the 0-order diffraction lobes 404a-404b and the small pitch diffraction lobes 408a-408b. In this way, the detector 128 in this channel can generate a dark field image of the large pitch grating 204 based only on the large pitch diffraction lobes 406a-406b. Similarly, the second collection channel may include one or more blockers (e.g., in the collection pupil plane 132) to block the large pitch diffraction lobes 406a-406b to produce an image of the small pitch grating 208 based only on the 0th order diffraction lobes 404a-404b and the small pitch diffraction lobes 408a-408b.

[0094] Generally speaking Figures 3A to 6B , it should be understood that Figures 3A to 6B and the associated description are provided for illustrative purposes only and should not be construed as limiting the present disclosure.For example, the overlay metrology subsystem 102 may illuminate the overlay target 106 with any number of illumination beams 108 at any combination of amplitude or azimuthal incidence angles.

[0095] As a graphic illustration, Figure 6C is configured according to one or more embodiments of the present disclosure for use in a generalized configuration such as Fig. 6A The two illumination beams 108 described in the figure are imaged based on oblique illumination and have the following characteristics: Figure 3A FIG. 1 is a top view of the collection pupil plane 132 of the phase plate 302 configured as described in FIG. Figure 6C Corresponds to Figure 6B a variation in which the illumination beams 108a, 108b and the fine pitch grating 208 are not in a Littrow configuration, but it is still provided that the diffraction orders from the large pitch grating 204 and the fine pitch grating 208 are located in different radial bands in the collection pupil plane 132 to facilitate simultaneous imaging based on a radially varying defocus profile as disclosed herein.

[0096] As another illustration, although not shown, illumination using illumination beams 108a, 108b may also be used with additional configurations of the superimposed metrology subsystem 102, including but not limited to, as previously disclosed herein, such as Figure 3B The annular phase plate 302 depicted in FIG. 1 or the objective lens 138 with adjustable spherical aberration.

[0097] As another illustration, although not shown, the overlay metrology subsystem 102 may illuminate the overlay target 106 with illumination beams 108 directed along different azimuthal directions (e.g., X and Y directions) to facilitate simultaneous imaging of target features having periodicity along different directions (e.g., as Figure 2B ).

[0098] Reference Figure 1C and 1D It is contemplated herein that reflections from the top surface of sample 104 may reduce the contrast of the image of overlay target 106 , particularly under oblique illumination.

[0099] In some embodiments, the overlay metrology subsystem 102 includes an illumination collection field stop sized to match the field of view of the overlay target 106 (e.g., the unit 202 thereon) or the detector 128. For example, this field stop may be configured as a confocal field stop sized to match the field of view of the overlay target 106 and / or the detector 128. Figure 1C is a conceptual diagram of a portion of a superposition metrology subsystem 102 illustrating a field stop for blocking zero-order reflections from the top surface of a sample 104 in accordance with one or more embodiments of the present disclosure. Figure 1C , the image of the field stop 144 is at the plane of the detector 128 .

[0100] Specifically, Figure 1C The objective lens 138 and a pupil plane 142 (eg, a back focal plane of the objective lens 138) common to both the illumination path 116 (not shown) and the collection path 126 are illustrated. Figure 1C Further depicted is illumination using a single oblique illumination beam 108 emanating from pupil plane 142, but it should be understood that illumination beam 108 may be directed via a plurality of channels such as the Figure 1B The illumination path 116 depicted in FIG. 1 is provided to a pupil plane 142 .

[0101] At an inclination angle (θ inc ) An illumination beam 108 incident on sample 104 may result in various zero-order reflected beams, including, but not limited to, a top surface reflected beam 146 associated with reflection of illumination beam 108 by a top surface 148 of sample 104, and a buried feature reflected beam 150 associated with reflection of illumination beam 108 by buried features of overlay target 106. Each of these beams may have a width (w) that may be controlled by an illumination field stop or by any other suitable technique. Figure 1C As described in the above, these beams can be inc), the width (w) of the illumination beam 108, and the depth (h) of the buried features within the sample 104. Specifically, the reflected beams overlap (e.g., begin to glare) under the following conditions:

[0102]

[0103] This condition can also be written based on Snell's law in sample 104 as:

[0104]

[0105] where n s is the refractive index of the sample 104 and NA min，obsc is the minimum numerical aperture (NA) that illumination beam 108 can have to avoid glare.

[0106] If the reflected beams do not overlap (e.g., no glare occurs), then the top surface reflected beam 146 may be filtered using a collection field stop. Figure 1C In FIG. 1 , this is illustrated as the top surface reflected beam 146 falling outside the field of the detector 128. However, it should be understood that the superposition metrology subsystem 102 may also include a collection field stop in the relayed field plane in the collection path 126 to filter the top surface reflected beam 146 prior to the detector 128.

[0107] As a consideration, a target feature (e.g., n s =3.5) and a 50 micron wide illumination beam 108 (eg, w=50 μn), the minimum NA (NA mi，obsc ) is 0.323, which can be achieved with oblique illumination as disclosed in this article.

[0108] The overlay metrology subsystem 102 may be further configured (e.g., according to a metrology recipe) to provide customized illumination and / or feature sets on each layer of the overlay target 106. For example, the overlay metrology subsystem 102 may illuminate the overlay target 106 with a plurality of illumination beams 108, wherein different illumination beams 108 and / or associated components of the light collection paths 126 are customized for each layer.

[0109] In some embodiments, overlay metrology subsystem 102 provides two illumination beams 108 having a common angle of incidence (e.g., having overlapping positions in illumination pupil plane 120), but where the two illumination beams 108 have different beam widths (w) selected to prevent glare between the corresponding top surface reflected beam 146 and the buried feature reflected beam 150 for features at different depths. For example, first illumination beam 108 may have a first width (w) selected to prevent glare between top surface reflected beam 146 and buried feature reflected beam 150 at a first depth (h) associated with first layer 206 of overlay target 106, while second illumination beam 108 may have a second width (w) selected to prevent glare between top surface reflected beam 146 and buried feature reflected beam 150 at a second depth (not illustrated). Furthermore, light collection path 126 may include one or more field stops customized to block top surface reflected beam 146 associated with each of illumination beams 108.

[0110] Any technique known in the art may be used to generate multiple illumination beams 108 having overlapping incident angles but different beam widths (w). For example, the illumination path 116 may provide two illumination beams 108 in two arms including an illumination field stop having different widths (w), and may further include a beam combiner to overlap the two illumination beams 108 at a common illumination pupil plane 120.

[0111] It is contemplated herein that the overlay target 106 may have features (e.g., large pitch grating 204 or small pitch grating 208) at any layer or at any depth (h). In configurations where the overlay target 106 includes features (e.g., large pitch grating 204 or small pitch grating 208) on the top surface 148 of the sample 104 (e.g., h=0), an interferometer (e.g., but not limited to, a Linnik interferometer with a reference beam tuned to an opposite phase to the undesired top surface reflected beam 146) may be used to mitigate (e.g., ashing) the undesired zeroth order reflection.

[0112] Figure 1D is a conceptual diagram of a superposition metrology subsystem 102 including a Linnik interferometer according to one or more embodiments of the present disclosure.

[0113] In one embodiment, the superposition metrology subsystem 102 includes a reference objective 152 configured to receive a portion of the illumination beam 108 through the beam splitter 140, direct the portion of the illumination beam 108 to a reference sample 154, and collect light reflected from the reference sample 154. In this regard, the objective 138 and the sample 104 can form a measurement arm 156 of a Linnik interferometer, while the reference objective 152 and the reference sample 154 can form a reference arm 158 of the Linnik interferometer.

[0114] Reference sample 154 may include any sample suitable for providing reference light in a Linnik interferometer. For example, reference sample 154 may be designed to at least partially replicate sample 104. In this regard, the Linnik interferometer may be balanced and the optical properties of light propagating through reference sample 154 may be the same or substantially similar to the optical properties of light propagating through sample 104.

[0115] In some embodiments, the Linnik interferometer further includes a phase adjuster 160 configured to provide that the phase of the top surface reflected light beam 146 from the sample 104 may have an opposite phase to the corresponding top surface reflected light beam 162 from the reference sample 154. In this way, the top surface reflected light beam 146 from the sample 104 and the top surface reflected light beam 162 from the reference sample 154 may negatively interfere on the detector 128. In addition, the phase adjuster 160 may include any combination of one or more optical components suitable for adjusting the optical phase of light, such as, but not limited to, a wedge or a wave plate.

[0116] It should be understood that Figure 1D The associated description of the LINQ interferometer is provided for illustrative purposes only and should not be construed as limiting. Specifically, the superposition metrology subsystem 102 may include any type of interferometer known in the art to mitigate undesirable top surface reflected beams 146 from target features on the top surface 148 of the sample 104.

[0117] Again, generally refer to Figures 1A to 1D , various additional aspects of the superposition metrology subsystem 102 are described in more detail according to one or more embodiments of the present disclosure.

[0118] The illumination source 114 may include any type of light source known in the art. In one embodiment, the illumination source 114 includes one or more coherent sources, such as but not limited to one or more laser sources. In this regard, the illumination source 114 may generate an illumination beam 108 having high coherence (e.g., high spatial coherence and / or temporal coherence). For example, the illumination source 114 may include one or more broadband lasers, such as but not limited to one or more supercontinuum lasers or white light lasers. By another example, the illumination source 114 may include one or more narrowband lasers. By another example, the illumination source 114 may include one or more tunable lasers that provide an illumination beam 108 having a tunable spectral intensity. In addition, the coherent illumination source 114 may be based on any type of technology or product design. For example, the illumination source 114 may include but not limited to any combination of one or more fiber lasers, one or more diode lasers, or one or more gas lasers.

[0119] In another embodiment, the illumination source 114 includes one or more sources that provide an illumination beam 108 having low or partial coherence (e.g., spatial and / or temporal coherence). For example, the illumination source 114 may include one or more light emitting diodes (LEDs) or superluminescent LEDs. By another example, the illumination source 114 may include a laser sustained plasma (LSP) source, such as, but not limited to, an LSP lamp, an LSP bulb, or an LSP chamber adapted to house one or more elements that can emit broadband illumination when excited into a plasma state by a laser source. By another example, the illumination source 114 may include a lamp source, such as, but not limited to, an arc lamp, a discharge lamp, an electrodeless lamp, or the like.

[0120] The illumination source 114 may provide an illumination beam 108 having any selected wavelength or range of wavelengths (e.g., spectrum). It is contemplated herein that the spectrum of the illumination beam 108 may be selected to transmit through at least a portion of the sample 104 to reach features on the superimposed target 106 in the subsurface layer with minimal or at least acceptable absorption. For example, in the case of a sample 104 formed as two joined semiconductor substrates, the spectrum of the illumination beam 108 may be selected to include wavelengths in the infrared spectral range. However, it should be understood that the systems and methods disclosed herein may be broadly applicable to a wide range of samples such that the illumination beam 108 may have any selected spectrum based on the composition of the sample 104.

[0121] The illumination source 114 may further provide light having any selected temporal characteristics. In one embodiment, the illumination source 114 includes one or more continuous wave sources that provide a continuous wave illumination beam 108. In another embodiment, the illumination source 114 includes one or more pulse sources that provide a pulse modulated or otherwise modulated illumination beam 108. For example, the illumination source 114 may include one or more mode-locked lasers, one or more Q-switched lasers, or the like. It is contemplated herein that illumination using a pulsed laser source may provide high throughput measurements in static or scanning modes of operation.

[0122] It is contemplated herein that an illumination source 114 providing a pulsed laser illumination beam 108 may provide various benefits to the measurement of a high-overlay target 106 as disclosed herein.

[0123] For example, the pulsed laser illumination beam 108 may provide a relatively high peak power suitable for superposition measurements coupled with a relatively low NA. It is contemplated herein that reducing the NA of the illumination beam 108 may generally ease the requirement for a radially varying defocus profile as disclosed herein. In particular, the size of the diffraction lobes in the collection pupil plane 132 is based on the NA of the illumination beam 108. Thus, reducing the NA of the illumination beam 108 relaxes the requirement to separate the associated diffraction lobes into different radial bands of the collection pupil plane 132 (e.g., the required pitch difference between the large pitch grating 204 and the small pitch grating 208, or the like). In the case of a step-wise radially varying defocus profile, reducing the NA of the illumination beam 108 may relax the width and / or radius requirements of the phase plate 302 that provides the radially varying defocus profile. In the case of a continuously varying defocus profile (eg, as provided by an objective 138 having adjustable spherical aberration, or the like), reducing the NA of the illumination beam 108 can reduce the effect of the spatially varying defocus across the beam profile of the collected diffraction orders.

[0124] As another example, a pulsed laser illumination beam 108 may facilitate high throughput measurements in a scanning mode of operation. As a non-limiting illustration, an illumination beam 108 having pulses on the order of 1 nanosecond may be suitable for sampling at approximately 250 measurements per second. However, in a general sense, the illumination beam 108 may have any suitable pulse duration and / or repetition rate. In this manner, the illumination beam 108 may have, but is not limited to, a pulse duration on the order of microseconds, nanoseconds, picoseconds, or femtoseconds. Furthermore, the illumination beam 108 may have, but is not limited to, a repetition rate on the order of kHz, MHz, or GHz.

[0125] The sample positioning subsystem 112 may include any components suitable for translating the sample 104 relative to the illumination beam 108 and / or translating the illumination beam 108 relative to the sample 104. For example, the sample positioning subsystem 112 may include at least one translation stage 164 that adjusts the position of the sample 104 along any dimension, such as, but not limited to, lateral position within the XY plane, axially along a Z axis (e.g., the optical axis of the objective lens 138), flipping, tilting, or the like. As another example, although not shown, the sample positioning subsystem 112 may include one or more beam scanning optical elements (not shown), such as, but not limited to, a galvanometer or a rotatable mirror, that are suitable for scanning the illumination beam 108 across the sample 104.

[0126] In some embodiments, the superposition metrology system 100 includes a controller 166. The controller 166 may include one or more processors 168 configured to execute program instructions maintained on a memory 170 or storage medium. In this regard, the one or more processors 168 of the controller 166 may perform any of the various program steps described throughout this disclosure. In addition, the controller 166 may be communicatively coupled to the superposition metrology subsystem 102 or any component therein.

[0127] The one or more processors 168 of the controller 166 may include any processor or processing element known in the art. For the purposes of this disclosure, the term "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, the one or more processors 168 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in a memory). In one embodiment, the one or more processors 168 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute a program configured to operate or operate in conjunction with the overlay metrology system 100, as described throughout this disclosure.

[0128] In addition, the different subsystems of the stacking metering system 100 may include processors or logic elements suitable for implementing at least a portion of the steps described in the present disclosure. Therefore, the above description should not be interpreted as limiting the embodiments of the present disclosure, but is merely illustrative. In addition, the steps described throughout the present disclosure may be implemented by a single controller 166 or alternatively multiple controllers. In addition, the controller 166 may include one or more controllers housed in a common housing or in multiple housings. In this way, any controller or combination of controllers can be individually packaged as a module suitable for integration into the stacking metering system 100.

[0129] The memory 170 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 168. For example, the memory 170 may include a non-transitory storage medium. By way of another example, the memory 170 may include, but is not limited to, a read-only memory (ROM), a random access memory (RAM), a magnetic or optical storage device (e.g., a disk), a tape, a solid state drive, and the like. It should be further noted that the memory 170 may be housed in a common controller housing with the one or more processors 168. In one embodiment, the memory 170 may be remotely located relative to the physical location of the one or more processors 168 and the controller 166. For example, the one or more processors 168 of the controller 166 may access a remote memory (e.g., a server) that is accessible via a network (e.g., the Internet, an intranet, and the like).

[0130] All methods described herein may include storing the results of one or more steps of a method embodiment in a memory. The results may include any of the results described herein and may be stored in any manner known in the art. The memory may include any memory described herein or any other suitable storage medium known in the art. After the results have been stored, the results may be accessed in the memory and used by any of the method or system embodiments described herein; formatted for display to a user; used by another software module, method or system, and the like. In addition, the results may be stored "permanently", "semi-permanently", "temporarily" or for a period of time. For example, the memory may be a random access memory (RAM), and the results may not necessarily remain in the memory indefinitely.

[0131] It should be further considered that each of the embodiments of the method described above may include any other steps of any other method described herein.In addition, each of the embodiments of the method described above may be performed by any of the systems described herein.

[0132] Those skilled in the art will recognize that, for conceptual clarity, the components, operations, devices, objects, and accompanying discussions described herein are used as examples, and various configuration modifications are contemplated. Thus, as used herein, the specific examples set forth and the accompanying discussions are intended to represent their more general class. In general, the use of any specific example is intended to represent its class, and the non-inclusion of specific components, operations, devices, and objects should not be considered limiting.

[0133] As used herein, directional terms such as "top", "bottom", "above", "below", "up", "upward", "down", "downward", and "downwards" are intended to provide relative positions for descriptive purposes and are not intended to specify an absolute reference system. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments.

[0134] With respect to the use of substantially any plural and / or singular terms herein, those skilled in the art may translate from the plural to the singular and / or from the singular to the plural as appropriate to the context and / or application. For clarity, the various singular / plural arrangements are not explicitly set forth herein.

[0135] The objects described herein sometimes illustrate different components contained in or connected to other components. It should be understood that such depicted architectures are exemplary only, and in fact many other architectures that realize the same functionality can be implemented. In a conceptual sense, any arrangement of components that realize the same functionality is effectively "associated" so that the desired functionality is realized. Therefore, any two components combined to realize a specific functionality herein can be considered to be "associated" with each other so that the desired functionality is realized, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" to each other to realize the desired functionality, and any two components that can be so associated can also be considered to be "coupleable" to each other to realize the desired functionality. Specific examples that can be coupled include but are not limited to physically mateable and / or physically interacting components and / or wirelessly interacting and / or wirelessly interacting components and / or logically interacting and / or logically interacting components.

[0136] In addition, it should be understood that the present invention is defined by the appended claims. Those skilled in the art will understand that, in general, the terms used herein and in particular in the appended claims (e.g., the body of the appended claims) are generally intended to be "open" 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" and the like). Those skilled in the art will further understand that if a specific number of introduced claim recitations is intended, such intent will be explicitly recited in the claims, and in the absence of such a recitation, such intent does not exist. For example, to aid understanding, the appended claims below may contain the use of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed as implying that the introduction of a claim recitation by the indefinite article "a" or "an" limits any particular claim containing such introduced claim recitation to an invention containing only one such recitation, even when the same claim contains the introductory phrases "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should generally be construed to mean "at least one" or "one or more"); the same is true of the use of definite articles to introduce claim recitations. In addition, even if a specific number of introduced claim recitations is explicitly recited, those skilled in the art will recognize that such recitation should generally be construed to mean at least the recited number (e.g., the mere recitation of "two recitations" without other modifiers generally means at least two recitations, or two or more recitations). Furthermore, in examples where a convention similar to “at least one of A, B, and C, and the like” is used, such construction is generally contemplated in the sense that one skilled in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, and the like). In examples where a convention similar to “at least one of A, B, or C, and the like” is used, such construction is generally contemplated in the sense that one skilled in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, and the like). Those skilled in the art will further understand that, in fact, any transition word and / or phrase presenting two or more alternative terms, whether in the description, claims or drawings, should be understood to contemplate the possibility of including one of the terms, either of the terms, or both of the terms.For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0137] It is believed that, through the foregoing description, the present disclosure and its many attendant advantages will be appreciated, and it will be apparent that various changes may be made to the form, construction and arrangement of components without departing from the disclosed object or sacrificing all of its material advantages. The described form is illustrative only, and the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. A superposition metering system, comprising: Objective lens; one or more illumination optics configured to direct illumination from an illumination source through the objective to a superposition target on a sample when implementing a metrology recipe, wherein the superposition target according to the metrology recipe comprises a first grating having a first pitch on a first sample layer and a second grating having a second pitch on a second sample layer, and wherein the second pitch is smaller than the first pitch, wherein the first sample layer is separated from the second sample layer by a layer separation distance greater than a depth of field of the objective; Detector; and one or more collecting optics configured to direct at least a portion of the light collected by the objective to the detector, wherein the metrology recipe provides that diffraction orders of the illumination by the first grating collected by the objective are positioned below a threshold radius in a pupil plane and diffraction orders of the illumination by the second grating collected by the objective are positioned above the threshold radius in the pupil plane, wherein the one or more collecting optics provide a radially varying defocus profile to compensate for the layer separation distance, wherein the first grating and the second grating are simultaneously focused on the detector; and A controller comprising one or more processors configured to execute program instructions that cause the one or more processors to execute the metering recipe by: receiving one or more images of the superimposed object from the detector, wherein the first grating and the second grating are simultaneously focused on the detector; and An overlay measurement between the first layer and the second layer of the sample is determined based on the one or more images.

2. The superposition metrology system of claim 1 , wherein the one or more collecting optical devices include a phase plate in the pupil plane, the phase plate having a radius equal to the threshold radius to provide the radially varying defocus profile, wherein the phase plate introduces phase delays into the diffraction orders of the illumination by the first grating to compensate for the layer separation distance.

3. The superposition metrology system of claim 1 , wherein the one or more collecting optics comprise a lens in the pupil plane, the lens having a radius equal to the threshold radius to provide the radially varying defocus profile, wherein a focal power of the lens compensates for the layer separation distance by adjusting a focal position of the diffraction orders of the illumination by the first grating to match a focal position of the diffraction orders of the illumination by the second grating outside the lens.

4. The superposition metrology system of claim 1, wherein the one or more light collecting optics comprise an objective lens having one or more adjustable optics to provide adjustable spherical aberration as the radially varying defocus profile.

5. The superposition metrology system of claim 4, wherein the one or more adjustable optical devices of the objective lens that provide the adjustable spherical aberration as the radially varying defocus profile include: Correction ring.

6. The superimposed metrology system of claim 1, wherein the illumination from the illumination source is pulsed.

7. The stacking metering system according to claim 1, further comprising: At least one of a translation stage or one or more beam scanning optics to translate the relative position of the sample and the illumination during measurement.

8. The superposition metrology system of claim 1, wherein according to the metrology recipe, the first grating and the second grating are positioned in an overlapping region of the sample.

9. The superposition metrology system of claim 1, wherein according to the metrology recipe, the first grating and the second grating are positioned in non-overlapping areas of the sample.

10. The overlay metrology system of claim 1, wherein the layer separation distance is greater than 10 microns.

11. The overlay metrology system of claim 1 , wherein the layer separation distance is greater than 100 microns.

12. The superposition metrology system of claim 1, wherein according to the metrology recipe, the first sample layer is closer to the objective lens than the second sample layer.

13. The superposition metrology system of claim 1, wherein according to the metrology recipe, the second sample layer is closer to the objective lens than the first sample layer.

14. The superimposed metrology system of claim 1, wherein the sample comprises a first substrate bonded to a second substrate according to the metrology recipe, wherein the first grating is positioned on the first substrate, wherein the second grating is positioned on the second substrate.

15. The overlay metrology system of claim 1, wherein the sample comprises a die bonded to a substrate according to the metrology recipe, wherein the first grating is positioned on the die, wherein the second grating is positioned on the substrate.

16. The overlay metrology system of claim 1, wherein the sample comprises a die bonded to a substrate according to the metrology recipe, wherein the first grating is positioned on the die, wherein the second grating is positioned on a scribe street.

17. The superposition metrology system of claim 1, wherein the metrology recipe provides that the one or more illumination optics direct the illumination from the illumination source at a normal angle of incidence, wherein + / - 1st order diffraction lobes from the first grating are positioned below the threshold radius in the pupil plane, and wherein + / - 1st order diffraction lobes from the second grating are positioned above the threshold radius in the pupil plane.

18. The superposition metrology system of claim 17, wherein the one or more collection optics further comprise one or more elements to block a zeroth order diffraction of the illumination from reaching the detector.

19. The superposition metrology system of claim 1 , wherein the metrology recipe provides that the one or more illumination optics direct a first illumination beam of the illumination from the illumination source at a first azimuthal angle of incidence, wherein first and second order diffraction lobes of the first illumination beam from the first grating are located below the threshold radius in the pupil plane, and wherein a first order diffraction lobe and a zeroth order diffraction lobe of the first illumination beam from the second grating are positioned above the threshold radius in the pupil plane.

20. The stacking metering system of claim 19, further comprising: An additional detector, wherein the detector receives the first and second order diffraction lobes of the first illumination beam from the first grating, wherein the additional detector receives the first and zeroth order diffraction lobes of the first illumination beam from the second grating.

21. The superposition metrology system of claim 19, wherein the metrology recipe provides that the one or more illumination optics direct a second illumination beam of the illumination from the illumination source at a first azimuthal angle of incidence, wherein first and second order diffraction lobes of the second illumination beam from the first grating are located below the threshold radius in the pupil plane, and wherein a first order diffraction lobe and a zeroth order diffraction lobe of the second illumination beam from the second grating are positioned above the threshold radius in the pupil plane.

22. The stacking metering system of claim 21, further comprising: an additional detector, wherein the detector receives: the first and second order diffraction lobes of the first illumination beam from the first grating; and the first and second order diffraction lobes of the second illumination beam from the first grating; wherein the additional detector receives: the first-order diffraction lobe and the zero-order diffraction lobe of the first illumination light beam from the second grating; and The first-order diffraction lobe and the zero-order diffraction lobe of the first illumination light beam from the second grating.

23. The superposition metrology system of claim 21, wherein the first azimuthal incident angle and the second azimuthal incident angle satisfy a Littrow condition.

24. The superposition metrology system of claim 21, wherein the first azimuthal angle of incidence and the second azimuthal angle of incidence are symmetric along a measurement direction.

25. The superimposed metrology system of claim 21, wherein the first azimuthal angle of incidence and the second azimuthal angle of incidence are orthogonal.

26. The superposition metrology system of claim 19, wherein the one or more illumination optics further comprises a field stop to prevent reflections of the first illumination beam from a surface of the sample from reaching the detector.

27. The superposition metrology system of claim 19, wherein one of the first grating or the second grating is on a surface of the sample, wherein the one or more light collection optical devices include an interferometer that provides a reference beam having an opposite phase to the zeroth order diffraction lobe to mitigate the zeroth order diffraction lobe.

28. A superimposed metering system comprising: A controller communicatively coupled to the overlay metering subsystem, the controller comprising one or more processors configured to execute program instructions that cause the one or more processors to execute a metering recipe by: receiving one or more images of a superposition target from a detector of the superposition metrology subsystem, wherein the first grating and the second grating are simultaneously focused on the detector, wherein the superposition metrology subsystem comprises: Objective lens; one or more illumination optics configured to direct illumination from an illumination source through the objective to the superposition target on a sample when implementing the metrology recipe, wherein the superposition target according to the metrology recipe comprises a first grating having a first pitch on a first sample layer and a second grating having a second pitch on a second sample layer, wherein the second pitch is smaller than the first pitch, wherein the first sample layer is separated from the second sample layer by a layer separation distance greater than a depth of field of the objective; detector; and one or more collecting optics configured to direct at least a portion of the light collected by the objective to the detector, wherein the metrology recipe provides that diffraction orders of the illumination by the first grating collected by the objective are positioned below a threshold radius in a pupil plane and diffraction orders of the illumination by the second grating collected by the objective are positioned above the threshold radius in the pupil plane, wherein the one or more collecting optics provide a radially varying defocus profile to compensate for the layer separation distance, wherein the first grating and the second grating are simultaneously focused on the detector; and An overlay measurement between the first layer and the second layer of the sample is determined based on the one or more images.

29. The superposition metrology system of claim 28, wherein the metrology recipe provides that the one or more illumination optics direct the illumination from the illumination source at a normal angle of incidence, wherein + / - 1st order diffraction lobes from the first grating are positioned below the threshold radius in the pupil plane, and wherein + / - 1st order diffraction lobes from the second grating are positioned above the threshold radius in the pupil plane.

30. The superposition metrology system of claim 29, wherein the one or more collection optics further comprise one or more elements to block a zeroth order diffraction of the illumination from reaching the detector.

31. The superposition metrology system of claim 28, wherein the metrology recipe provides that the one or more illumination optics direct a first illumination beam of the illumination from the illumination source at a first azimuthal angle of incidence, wherein first and second order diffraction lobes of the first illumination beam from the first grating are located below the threshold radius in the pupil plane, and wherein a first order diffraction lobe and a zeroth order diffraction lobe of the first illumination beam from the second grating are positioned above the threshold radius in the pupil plane.

32. The stacking metering system of claim 31 , further comprising: An additional detector, wherein the detector receives the first and second order diffraction lobes of the first illumination beam from the first grating, wherein the additional detector receives the first and zeroth order diffraction lobes of the first illumination beam from the second grating.

33. The superposition metrology system of claim 31 , wherein a metrology recipe provides that the one or more illumination optics direct a second illumination beam of the illumination from the illumination source at a second azimuthal angle of incidence, wherein first and second order diffraction lobes of the second illumination beam from the first grating are located below the threshold radius in the pupil plane, and wherein a first order diffraction lobe and a zeroth order diffraction lobe of the second illumination beam from the second grating are positioned above the threshold radius in the pupil plane.

34. The stacking metering system of claim 33, further comprising: an additional detector, wherein the detector receives: the first and second order diffraction lobes of the first illumination beam from the first grating; and the first and second order diffraction lobes of the second illumination beam from the first grating; wherein the additional detector receives: the first-order diffraction lobe and the zero-order diffraction lobe of the first illumination light beam from the second grating; and The first-order diffraction lobe and the zero-order diffraction lobe of the first illumination light beam from the second grating.

35. The superposition metrology system of claim 33, wherein the first azimuthal angle of incidence and the second azimuthal angle of incidence satisfy the Littrow condition.

36. The superimposed metrology system of claim 28, wherein the illumination from the illumination source is pulsed.

37. The superimposed metrology system of claim 28, wherein the superimposed metrology subsystem further comprises: At least one of a translation stage or one or more beam scanning optics to translate the relative position of the sample and the illumination during measurement.

38. A superposition measurement method, comprising: receiving one or more images of a superposition target on a sample from a detector of a superposition metrology subsystem, wherein the superposition target according to a metrology recipe comprises a first grating having a first pitch on a first sample layer and a second grating having a second pitch on a second sample layer, wherein the second pitch is smaller than the first pitch, wherein the first grating and the second grating are simultaneously focused on the detector, wherein the superposition metrology subsystem comprises: Objective lens; one or more illumination optics configured to direct illumination from an illumination source through the objective to the superimposed target on the sample when implementing the metrology recipe, wherein the first sample layer is separated from the second sample layer by a layer separation distance greater than a depth of field of the objective; detector; and one or more collecting optics configured to direct at least a portion of the light collected by the objective to the detector, wherein the metrology recipe provides that diffraction orders of the illumination by the first grating collected by the objective are positioned below a threshold radius in a pupil plane and diffraction orders of the illumination by the second grating collected by the objective are positioned above the threshold radius in the pupil plane, wherein the one or more collecting optics provide a radially varying defocus profile to compensate for the layer separation distance, wherein the first grating and the second grating are simultaneously focused on the detector; and An overlay measurement between the first layer and the second layer of the sample is determined based on the one or more images.

39. A superimposed metrology target, comprising: a first substrate; a second substrate bonded to the first substrate; The first overlay target includes: a first grating having a first pitch on one of the first sample layer or the second sample layer; a second grating having a second pitch on a sample layer of the first sample layer or the second sample layer that is different from the first grating target, wherein features of the first grating and the second grating are distributed in a first direction, wherein one of the first or second sample layers corresponds to a scribe street on the second substrate and the other of the first or second sample layers corresponds to a layer in a die of the first substrate; The second overlay target includes: a third grating having the first pitch on one of the first sample layer or the second sample layer; A fourth grating having the second pitch on a sample layer different from the third grating target of the first sample layer or the second sample layer, wherein features of the third and fourth gratings are distributed in a first direction.

40. The stacking target of claim 39, wherein the first sample layer and the second sample layer are designed according to a metrology recipe to be separated by a layer separation distance that is greater than the depth of field of an objective of a metrology system, wherein the first and second pitches are designed according to the metrology recipe to specify that diffraction orders illuminated by the first and third grating pairs collected by the objective are positioned below a threshold radius in a pupil plane and diffraction orders illuminated by the second and fourth grating pairs collected by the objective are positioned above the threshold radius in the pupil plane, wherein a stacking measurement associated with the first sample layer and the second sample layer can be determined based on images of the first and second stacking targets, wherein the metrology system provides a defocus profile having a radial variation to compensate for the layer separation distance such that the first, second, third, and fourth gratings are simultaneously focused on one or more collection optics in the image.

Images