Mosaic Overlay Target

Abstract

The mosaic overlay target can include two or more cell sets distributed across the sample, each cell set including one or more cells, and each cell set oriented to have at least one of reflection symmetry about a central axis of the mosaic overlay target or rotation symmetry about a center point of the mosaic overlay target. The cell sets can be configured according to a metrology recipe, whereby an image of the mosaic overlay target generated based on the metrology recipe includes metrology data appropriate for two or more overlay measurements. A particular one of the overlay measurements can be based on a portion of the image associated with at least one of the cell sets. At least two of the two or more overlay measurements can be surrogate measurements of a common property of the sample.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63 / 411,640, entitled "MOSAIC TARGETS AND THEIR MEASUREMENTS CONCEPTS," filed September 30, 2022, inventor Yoel Feler, which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates generally to overlay targets, and more particularly to metrology targets that provide multiple alternative overlay measurements. [Background technology]

[0003] Overlay metrology measurements (e.g., overlay measurements) characterize the relative alignment (or misregistration) of different layers of a sample. Image-based overlay techniques typically generate overlay measurements based on the relative positions of imaged overlay target features. As the size of fabricated features decreases and feature density increases, the demands on the overlay metrology systems needed to characterize these features increase. Different overlay metrology techniques can offer different trade-offs between accuracy, repeatability, or throughput. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2018 / 0364179 [Patent Document 2] U.S. Patent Application Publication No. 2022 / 0283514 [Patent Document 3] U.S. Patent Application Publication No. 2019 / 0041329 Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, there is a need to develop a system and method to address the above-mentioned shortcomings. [Means for solving the problem]

[0006] A mosaic overlay target is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the target includes two or more cell sets distributed across a sample, each cell set including one or more cells, and each cell set oriented to have at least one of reflection symmetry about a central axis of the mosaic overlay target or rotation symmetry about a center point of the mosaic overlay target. In another exemplary embodiment, the two or more cell sets are configured according to a metrology recipe, whereby one or more images of the mosaic overlay target generated according to the metrology recipe include metrology data appropriate for two or more overlay measurements, a particular one of the two or more overlay measurements being based on a portion of the one or more images associated with at least one of the two or more cell sets. In another exemplary embodiment, at least two of the two or more overlay measurements are surrogate measurements of a common property of the sample, and at least two of the two or more cell sets are configured according to the metrology recipe to provide surrogate portions of the metrology data associated with the surrogate measurements.

[0007] An overlay metrology system is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system includes an illumination source configured to generate one or more illumination beams. In another exemplary embodiment, the system includes one or more optical elements configured to illuminate a mosaic overlay target on a sample with the one or more illumination beams when implementing a metrology recipe. In another exemplary embodiment, the target includes two or more cell sets distributed across the sample, each cell set including one or more cells, and each cell set oriented to have at least one of reflection symmetry about a central axis of the mosaic overlay target or rotation symmetry about a center point of the mosaic overlay target. In another exemplary embodiment, the two or more cell sets are configured according to a metrology recipe, whereby one or more images of the mosaic overlay target generated according to the metrology recipe include metrology data appropriate for two or more overlay measurements, wherein a particular one of the two or more overlay measurements is based on a portion of the one or more images associated with at least one of the two or more cell sets. In another exemplary embodiment, at least two of the two or more overlay measurements are surrogate measurements of a common property of the sample, and at least two of the two or more cell sets are configured according to the metrology recipe to provide surrogate portions of the metrology data associated with the surrogate measurements. In another exemplary embodiment, the system includes one or more detectors that generate one or more images of the mosaic overlay target based on illumination from the one or more illumination beams when implementing the metrology recipe. In another exemplary embodiment, the system includes a controller. In another exemplary embodiment, the controller implements the metrology recipe by receiving one or more images of the mosaic overlay target and generating at least two overlay measurements of the sample based on the one or more images.In another exemplary embodiment, a particular one of the two or more overlay measurements is based on portions of one or more images associated with at least one of the two or more cell sets, at least two of the two or more overlay measurements are surrogate measurements of a common property of the sample, and at least two of the two or more cell sets are configured according to a metrology recipe to provide surrogate portions of metrology data associated with the surrogate measurements.

[0008] An overlay metrology method is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the method includes illuminating one or more mosaic overlay targets on a sample with one or more illumination beams according to a metrology recipe, each of the mosaic overlay targets including two or more cell sets distributed across the sample. In another exemplary embodiment, each cell set includes one or more cells, each cell set being oriented to have at least one of reflection symmetry about a central axis of the mosaic overlay target or rotational symmetry about a center point of the mosaic overlay target, the two or more cell sets being configured according to the metrology recipe, whereby one or more images of the mosaic overlay target generated according to the metrology recipe include metrology data appropriate for two or more overlay measurements, a particular one of the two or more overlay measurements being based on a portion of the one or more images associated with at least one of the two or more cell sets. In another exemplary embodiment, the method includes generating one or more images of the mosaic overlay target based on illumination from the one or more illumination beams. In another exemplary embodiment, a method includes generating at least two overlay measurements of a sample based on one or more images, wherein a particular one of the two or more overlay measurements is based on a portion of the one or more images associated with at least one of two or more cell sets, at least two of the two or more overlay measurements being surrogate measurements of a common property of the sample, and at least two of the two or more cell sets being configured according to a metrology recipe to provide surrogate portions of metrology data associated with the surrogate measurements.

[0009] A method for designing a mosaic overlay target is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the method includes selecting two or more overlay measurements for generation using the mosaic overlay target. In another exemplary embodiment, the method includes designing two or more cell sets for the mosaic overlay target. In another exemplary embodiment, the target includes two or more cell sets distributed across a sample, each cell set including one or more cells, each cell set oriented to have at least one of reflection symmetry about a central axis of the mosaic overlay target or rotational symmetry about a center point of the mosaic overlay target, the two or more cell sets configured according to a metrology recipe, whereby one or more images of the mosaic overlay target generated according to the metrology recipe include metrology data appropriate for the two or more overlay measurements, and a particular one of the two or more overlay measurements is based on a portion of the one or more images associated with at least one of the two or more cell sets. In another exemplary embodiment, at least two of the two or more overlay measurements are surrogate measurements of a common property of the sample, and at least two of the two or more cell sets are configured according to the metrology recipe to provide surrogate portions of the metrology data associated with the surrogate measurements.

[0010] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of 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.

[0011] The many advantages of the present disclosure may be better understood by those skilled in the art by reference to the accompanying drawings. [Brief explanation of the drawings]

[0012] [Figure 1A]FIG. 1 is a conceptual diagram illustrating an overlay metrology system in accordance with one or more embodiments of the present disclosure. [Figure 1B] FIG. 1 is a simplified schematic diagram of an overlay metrology subsystem in accordance with one or more embodiments of the present disclosure. [Figure 1C] FIG. 1 is a simplified schematic diagram of a first illumination pupil plane illustrating a single illumination beam providing a normal angle of incidence, in accordance with one or more embodiments of the present disclosure. [Figure 1D] FIG. 10 is a simplified schematic diagram of a second illumination pupil plane illustrating two illumination beams in a dipole configuration, in accordance with one or more embodiments of the present disclosure. [Figure 1E] FIG. 10 is a simplified schematic diagram of a third illumination pupil plane illustrating four illumination beams in a quadrupole configuration, in accordance with one or more embodiments of the present disclosure. [Figure 2A] FIG. 1 is a simplified top view of a first design of a mosaic overlay target in accordance with one or more embodiments of the present disclosure. [Figure 2B] FIG. 10 is a simplified top view of a second design of a mosaic overlay target in accordance with one or more embodiments of the present disclosure. [Figure 2C] FIG. 2B is a top view of a variation of the target of FIG. 2A that provides multiple alternative overlay measurements along different measurement directions, in accordance with one or more embodiments of the present disclosure. [Figure 3] FIG. 1 is a simplified top view of a cell of a mosaic overlay target having a box-in-box feature in accordance with one or more embodiments of the present disclosure. [Figure 4A] FIG. 1 is a simplified side view of a cell of a mosaic overlay target having overlapping features, in accordance with one or more embodiments of the present disclosure. [Figure 4B] FIG. 4B is a simplified top view of the cell of FIG. 4A according to one or more embodiments of the present disclosure. [Figure 5] FIG. 1 is a simplified side view of a cell including features associated with a single patterning process for a single layer of a sample, in accordance with one or more embodiments of the present disclosure. [Figure 6]1 is a flow chart illustrating steps performed in a method according to one or more embodiments of the present disclosure. [Figure 7] 1 is a flow chart illustrating steps performed in a method for designing a mosaic overlay target in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with reference to certain embodiments and certain features thereof. The embodiments described herein are to be construed as illustrative and not limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made therein without departing from the spirit and scope of the present disclosure.

[0014] Embodiments of the present disclosure relate to systems and methods for overlay metrology based on imaging of a mosaic overlay target, where the mosaic overlay target is designed to provide multiple overlay measurements based on different portions of one or more images of the mosaic overlay target.

[0015] For purposes of this disclosure, the term overlay is generally used to describe the relative position of features on a sample fabricated by two or more patterning steps (e.g., lithographic exposure and subsequent etching steps, direct etching steps, etc.), while the term overlay error describes the deviation of features from their nominal placement. For example, a multilayer device can contain features patterned on multiple sample layers using different patterning steps for each layer, and the alignment of features between layers must typically be tightly controlled to ensure proper performance of the resulting device. Thus, overlay measurements can characterize the relative positions of features on two or more sample layers. As another example, features can be fabricated on a single sample layer using multiple patterning steps. Such techniques, commonly referred to as double-patterning or multiple-patterning techniques, can facilitate the fabrication of very high densities of features near the resolution of the lithography system. Overlay measurements in this context can characterize the relative positions of features from different lithography steps on this single layer. It should be understood that the examples and descriptions throughout this disclosure of specific applications of overlay metrology are provided for illustrative purposes only and should not be construed as limiting the disclosure.

[0016] In some embodiments, the mosaic overlay target includes multiple cell sets distributed across the sample, each cell set can include one or more cells, and different cell sets can include different arrangements of features suitable for facilitating overlay measurements.

[0017] A mosaic overlay target may be designed to facilitate multiple simultaneous overlay measurements (e.g., two or more overlay measurements) based on one or more images of the mosaic overlay target, with different overlay measurements based on different portions of the image containing different sets of cells or different combinations of cell sets. As used herein, the term simultaneous overlay measurement is used broadly to indicate that multiple overlay measurements can be generated based on a single set of one or more images of the mosaic overlay target (e.g., taken with different lighting and / or imaging conditions) based on different portions of one or more images. It is recognized herein that some overlay measurement techniques can generate measurements based on a single image of the overlay target, while other techniques can generate measurements based on multiple images of the overlay target (e.g., taken with different lighting and / or imaging conditions). It is believed herein that a mosaic overlay target can enable substantial flexibility in overlay metrology, can efficiently utilize space on the sample (e.g., providing a relatively small target size), and / or can enable high-throughput measurements.

[0018] By way of example, an overlay metrology tool may illuminate a mosaic overlay target with illumination, collect light (e.g., sample light) emitted from the mosaic overlay target in response to the illumination, and generate one or more images of the mosaic overlay target based on at least a portion of the sample light. Such images may include any combination of field plane images, in which a detector is located in a field plane conjugate with the mosaic overlay target (or the sample from which the mosaic overlay target is fabricated), or pupil plane images, in which a detector is located in a pupil plane associated with the angular distribution of light emitted from the sample.

[0019] Each cell set on a mosaic overlay target may be designed to facilitate overlay measurements, either alone or in combination with one or more additional cell sets. In other words, each cell set may include features designed to allow overlay measurements to be generated based on an image of the cell set alone or images of two or more cell sets. Thus, an image of a mosaic overlay target may be considered a composite of images of various cell sets, such that the various cell sets may be imaged simultaneously.

[0020] A cell can include any distribution of features associated with one or more patterning processes suitable for at least one overlay measurement. Furthermore, such features can be aperiodic or periodic in one or more directions (e.g., exhibiting different spatial frequencies). For example, a cell can include overlapping features associated with two or more patterning processes, such that an image of the cell can include information associated with two or more processes. As another example, a cell can include features associated with a single patterning process. In this configuration, overlay measurements can be based on cells (or sets of cells), each containing features associated with a different patterning process.

[0021] In a general sense, a mosaic overlay target may include cells having any size or shape. However, in some applications, it may be desirable to design cell sets with rotational and / or mirror symmetry to mitigate undesirable effects such as, but not limited to, tool-induced shift (TIS) errors. For example, a cell set may include one or more pairs of cells (e.g., cell pairs) arranged with mirror symmetry about a central axis of the cell set and / or rotational symmetry about a midpoint of the cell set (e.g., 180-degree symmetry, 90-degree symmetry, etc.). As another example, a cell set may include a single cell with mirror and / or rotational symmetry. Furthermore, the various cell sets of a mosaic overlay target may all be arranged to share a common symmetry (e.g., share a common central axis and / or midpoint), although in some cases the cell sets may be intentionally offset in accordance with overlay metrology techniques. In this configuration, the mosaic overlay target may include at least one cell set with one or more cell pairs arranged with a selected symmetry, and optionally a central cell set with a single cell also arranged with a selected symmetry.

[0022] The mosaic overlay target may support multiple overlay measurements based on different sets of cells or combinations of sets of cells, e.g., different overlay measurements may be generated based on portions of one or more images of the mosaic overlay target associated with different sets of cells or different combinations of sets of cells.

[0023] It is recognized herein that the accuracy and / or sensitivity of an overlay measurement may depend on various factors, such as, but not limited to, the layout of features on the sample being characterized during the measurement (e.g., feature size and / or orientation, sample layer thickness, etc.), the nature of the illumination used to facilitate the measurement (e.g., spectrum, polarization, angle of incidence, beam shape, etc.), the nature of the light emitted from the sample used during the measurement (e.g., spectrum, polarization, emission angle, etc.), or the focal position of the sample (e.g., working distance between the sample and the overlay metrology tool). As a result, process variations (e.g., layer thickness variations, etc.) across a particular sample and / or between samples within a lot can affect both the actual overlay error (e.g., misalignment between sample layers) as well as the accuracy and / or sensitivity of the particular overlay metrology technique used to measure the overlay error.

[0024] Numerous overlay metrology techniques have been developed that require or can benefit from different layouts of features on the sample (e.g., different overlay target designs) and / or different configurations of the overlay metrology tool (e.g., different illumination and / or collection conditions). These techniques can offer different trade-offs between measurement accuracy, measurement sensitivity, measurement robustness to process variations, systematic error, measurement speed (e.g., measurement throughput), or required space on the sample (e.g., required target size, required number or distribution of targets on the sample, etc.). As a result, different overlay metrology techniques performed at a particular location on the sample can provide different results and / or can yield results of different quality.

[0025] For example, field plane imaging techniques can determine overlay measurements based on the relative imaged positions of non-overlapping features from different patterning processes. Such features can be non-periodic or periodic. Non-limiting examples of related overlay targets include box-in-box targets, advanced imaging metrology (AIM) targets, or triple AIM (t-AIM) targets. As another example, scatterometry overlay (SCOL) techniques can generate overlay measurements based on pupil and / or field plane images of overlapping features from different patterning processes. In some cases, non-overlapping features are formed as overlapping periodic features and can be characterized as grating-over-grating features. Furthermore, such overlapping periodic features can have the same or different pitches. Non-limiting examples of related overlay targets include grating-over-grating targets, moiré targets, or robust AIM targets.

[0026] It is contemplated herein that a mosaic overlay target can enable multiple overlay measurements based on different overlay techniques or variations thereof, for example, different cell sets can have different designs or different variations of a similar design.

[0027] In some embodiments, the mosaic overlay target is designed to enable overlay measurements along two or more measurement directions, some of which may be, but need not be, orthogonal. For example, the mosaic target may be designed to have features in a first group of one or more cell sets suitable for overlay measurements along a first measurement direction, and may further be designed to have features in a second group of one or more cell sets suitable for overlay measurements along a second measurement direction. As another example, the mosaic target may be designed to have features in one or more cell sets suitable for simultaneous overlay measurements along two or more measurement directions.

[0028] In some embodiments, the mosaic overlay target is designed to enable measurements between different combinations of layers. For example, the mosaic overlay target may include three or more cell sets, each having features in a different layer. In this way, overlay measurements between different combinations of layers can be generated based on different combinations of the associated cell sets.

[0029] In some embodiments, a mosaic overlay target is designed to enable alternative overlay measurements. As used herein, the term alternative overlay measurements refers to multiple measurements of a particular quantity, such as, but not limited to, overlay measurements between two specific sample layers along a particular measurement direction. For example, the alternative measurements may be based on different features or sets of features within a mosaic overlay target as disclosed herein. It is contemplated herein that such alternative overlay measurements may exhibit different performance characteristics, such as, but not limited to, sensitivity to overlay, measurement accuracy, or robustness to printing errors unrelated to overlay. Thus, a mosaic overlay target designed to provide alternative overlay measurements can facilitate flexibility and high performance (e.g., as measured by any suitable performance metric) in the overlay metrology process.

[0030] It is further contemplated herein that alternative overlay measurements from a mosaic overlay target can be utilized in a variety of ways.

[0031] For example, an overlay metrology tool can capture one or more images of various mosaic overlay targets distributed across a sample using a common set of illumination and collection conditions (e.g., associated with a metrology recipe). The overlay metrology tool can then select a particular one of the alternative overlay measurements for each of the mosaic overlay targets based on an associated performance metric. Because the performance metric may differ between samples, different selections from the alternative overlay measurements may be used for different mosaic overlay targets.

[0032] As another example, a mosaic overlay target can enable fine-tuning of a metrology recipe without having to switch between different target designs. A metrology recipe can generally include a set of parameters associated with the overlay target design, the illumination conditions for the overlay target, and / or the acquisition conditions for imaging the overlay target. In this manner, a metrology recipe can specify conditions suitable for obtaining one or more images of the overlay target suitable for overlay measurement. The metrology recipe can further include one or more analysis steps for generating overlay measurements based on the one or more images. It is contemplated herein that it may be desirable to adjust one or more aspects of a metrology recipe across and / or between samples within a lot in response to variations in the manufacturing process. It is contemplated herein that a mosaic overlay target disclosed herein can include different cell sets with variations in sample features to enable multiple simultaneous metrology recipe variations. Furthermore, capturing additional images of the mosaic overlay target with different illumination and / or acquisition conditions (e.g., metrology recipe parameters) can enable additional fine-tuning of the metrology recipe.

[0033] Additional embodiments of the present disclosure are directed to methods for designing a mosaic overlay target. For example, designing the mosaic overlay target may include selecting a layout of target features in two or more cell sets suitable for providing two or more different simultaneous overlay measurements based on one or more images of the mosaic overlay target.

[0034] Additional embodiments of the present disclosure are directed to an overlay metrology system suitable for imaging a mosaic overlay target and generating two or more overlay measurements based on the images.

[0035] In some embodiments, the overlay metrology system is configured to illuminate the mosaic overlay target with off-axis illumination (e.g., oblique illumination with a non-normal angle of incidence). Off-axis illumination may be well suited, without limitation, to reducing the pitch of periodic features that can be resolved and / or reducing cell size. The angle of diffraction from periodic features may be related to both the wavelength of the illumination and the pitch of the periodic features, with decreasing pitch increasing the angle of diffraction. Thus, off-axis illumination may enable capturing diffraction from smaller pitches than normal illumination. As a non-limiting example, off-axis illumination may enable capturing diffraction from pitches smaller than 600 nm using illumination with visible wavelengths.

[0036] In some embodiments, the overlay metrology system illuminates the mosaic overlay target with two or more off-axis illumination beams (e.g., dipole distribution, quadrupole distribution, etc.). Such illumination can be generated simultaneously or sequentially (e.g., generating multiple consecutive images that can be combined for overlay measurements). In some embodiments, the illumination beams are arranged in a Littrow condition such that the distance between poles corresponds to λ / pitch, where λ is the wavelength of the illumination. Littrow illumination can provide particularly robust measurements.

[0037] In some embodiments, the overlay metrology system illuminates the mosaic overlay target with a quadrupole distribution of illumination beams formed as two dipoles oriented along orthogonal directions, the two dipoles having different properties (e.g., different polarizations, different spectral properties, etc.). The overlay metrology system can further include various components in the collection paths (e.g., polarizers, spectral filters, etc.) to isolate the light associated with each dipole into different collection channels. In this manner, optically isolated overlay measurements along different measurement directions can be generated.

[0038] 1A-7, systems and methods for overlay metrology using mosaic overlay targets are described in more detail, in accordance with one or more embodiments of the present disclosure.

[0039] 1A is a conceptual diagram illustrating an overlay metrology system 100, in accordance with one or more embodiments of the present disclosure. In some embodiments, the overlay metrology system 100 may be characterized as an overlay metrology tool.

[0040] In some embodiments, the overlay metrology system 100 includes an overlay metrology subsystem 102 that acquires overlay signals from the overlay target based on any number of metrology recipes. For example, the overlay metrology subsystem 102 can direct illumination 104 to a mosaic overlay target 106 on a sample 108, collect light or other radiation (referred to herein as sample light 110) emanating from the mosaic overlay target 106, and generate one or more images of the mosaic overlay target 106 using one or more detectors 112. The images can include one or more field plane images from a detector 112 located in a field plane conjugate with the sample 108 (or at least one layer therein) and / or one or more pupil plane images from a detector 112 located in a pupil plane (e.g., a diffraction plane) associated with the angular distribution of light emanating from the mosaic overlay target 106.

[0041] The overlay metrology subsystem 102 can further generate two or more measurements based on one or more images of the mosaic overlay target 106. For example, the overlay metrology subsystem 102 can generate different overlay measurements based on portions of one or more images associated with different sets of cells of the mosaic overlay target 106.

[0042] In some embodiments, overlay metrology system 100 includes a controller 114. Controller 114 may include one or more processors 116 configured to execute program instructions maintained on a memory 118 or memory medium. In this regard, the one or more processors 116 of controller 114 may perform any of the various process steps described throughout this disclosure. Additionally, controller 114 may be communicatively coupled to overlay metrology subsystem 102 or any component therein.

[0043] The one or more processors 116 of the controller 114 may include any processor or processing element known in the art. For 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 116 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in memory 118). In some embodiments, the one or more processors 116 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 programs configured to operate in conjunction with the overlay metrology system 100, as described throughout this disclosure.

[0044] Furthermore, different subsystems of the overlay metrology system 100 may include processors or logic elements suitable for performing at least some of the steps described herein. Accordingly, the above description should not be construed as a limitation on the embodiments of the present disclosure, but merely as examples. Furthermore, the steps described throughout the present disclosure may be performed by a single controller 114 or, alternatively, by multiple controllers. Additionally, the controller 114 may include one or more controllers housed within a common housing or multiple housings. In this manner, any controller or combination of controllers may be separately packaged as a module suitable for integration into the overlay metrology system 100.

[0045] The memory 118 may include any storage medium known in the art suitable for storing program instructions executable by the associated processor(s) 116. For example, the memory 118 may include a non-transitory memory medium. As another example, the memory 118 may include, but is not limited to, read-only memory (ROM), random access memory (RAM), magnetic or optical memory devices (e.g., disks), magnetic tape, solid-state drives, etc. It is further noted that the memory 118 may be housed within a common controller housing with the one or more processors 116. In some embodiments, the memory 118 may be located remotely relative to the physical location of the one or more processors 116 and the controller 114. For example, the one or more processors 116 of the controller 114 may access a remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, etc.).

[0046] Additionally, the overlay tool may be configurable (e.g., using the controller 114) to generate overlay signals based on any number of metrology recipes that define conditions for generating one or more images of the mosaic overlay target 106 suitable for two or more overlay measurements. For example, a metrology recipe may include design parameters of the mosaic overlay target 106 or a set of cells thereof, such as, but not limited to, the distribution of target features, the pitch of the target features, the dimensions of the target features (e.g., width, sidewall angle, etc.), the orientation of the target features, or the sample height during measurement (e.g., working distance between the sample 108 and the overlay metrology subsystem 102). As another example, a metrology recipe may include illumination parameters (e.g., properties of the illumination 104), such as, but not limited to, spectrum, polarization, illumination angle (e.g., in elevation and / or azimuth), or illumination field size (e.g., spot size of the illumination 104). As another example, the metrology recipe may include collection parameters associated with the light (e.g., a portion of the sample light 110) used to image the mosaic overlay target 106, such as, but not limited to, spectrum, polarization, collection angle (e.g., in elevation and / or azimuth), or collection field size. As another example, the metrology recipe may include parameters associated with one or more detectors 112 used to generate one or more images of the mosaic overlay target 106, such as, but not limited to, gain settings or measurement timing settings. As another example, the metrology recipe may include one or more steps for generating at least two overlay measurements based on one or more images of the mosaic overlay target 106. Such steps may, but need not, be performed by the controller 114. By way of example, some overlay techniques may generate overlay measurements by determining centers of symmetry of non-overlapping features associated with different patterning processes in one or more field plane images and determining overlay measurements based on the relative positions of these centers of symmetry.As another example, some overlay techniques can generate overlay measurements based on interference patterns of overlapping features associated with different patterning processes captured using field plane and / or pupil plane images.

[0047] 2A-2B, the mosaic overlay target 106 is described in more detail, in accordance with one or more embodiments of the present disclosure.

[0048] In some embodiments, the mosaic overlay target 106 includes two or more cell sets 202 spatially distributed across the mosaic overlay target 106, with each cell set 202 including one or more cells 204. Furthermore, each cell 204 may include target features (referred to herein simply as features) associated with one or more patterning processes. Note that for clarity, the target features are not shown in Figures 2A-2B. Rather, the cells 204 are illustrated with a hatched pattern to indicate the relevant areas of the mosaic overlay target 106.

[0049] 2A and 2B are simplified top views of a first and second design of a mosaic overlay target 106, respectively, in accordance with one or more embodiments of the present disclosure.

[0050] 2A and 2B, the mosaic overlay target 106 is illustrated as a series of cells 204 shown as squares, with cells 204 that share a common hatch pattern being associated with a common cell set 202. In a general sense, the mosaic overlay target 106 can include two or more cell sets 202, each having one or more cells 204. Furthermore, the cells 204 can generally have any shape, and the illustrated squares are merely exemplary.

[0051] As an example, the mosaic overlay target 106 of Figure 2A includes 18 cell sets 202 (labeled 202-1 through 202-18), each formed of two cells 204, sometimes referred to as a cell pair. As another example, the mosaic overlay target 106 of Figure 2B includes 16 cell sets 202 (labeled 202-1 through 202-8 and 202-11 through 202-18), each having two cells 204, and a central cell set 202 (labeled 202-0) having a single cell 204. However, it should be understood that the cell sets 202 are not limited to one or two cells 204 as illustrated in Figures 2A and 2B, and may have three or more cells 204 in some embodiments.

[0052] 3-5, various non-limiting feature layouts are described in accordance with one or more embodiments of the present disclosure. In a general sense, the mosaic overlay target 106 may be designed to facilitate multiple overlay measurements (e.g., two or more overlay measurements), with each overlay measurement being based on one or more cell sets 202. Any cell 204 within any of the cell sets 202 can include features associated with a single patterning process or multiple patterning processes, and the different patterning processes may be on a common layer (e.g., for overlay measurements associated with multiple patterning techniques) or on different layers (e.g., for overlay measurements between different layers). Different cell sets 202 may include features on different layers or combinations of layers. Furthermore, different cell sets 202 may have different designs and / or layouts of corresponding features. In other words, there are no requirements imposed on the similarities or differences between target features (or more generally, cells 204) in different cell sets 202. As a result, each cell set 202 can have a fully customizable design, and different overlay techniques can be used to generate overlay measurements based on the features in the different cell sets 202 .

[0053] The features within any particular cell 204 can have any layout suitable for overlay measurements. For example, the features within any cell 204 can be non-periodic or periodic in one or more directions (e.g., exhibiting different spatial frequencies). It is recognized herein that periodic features, particularly when illuminated by an angularly restricted beam of illumination 104, can produce discrete diffraction orders, which can aid in determining overlay. For example, periodic structures can improve the signal-to-noise ratio associated with an image of a feature (e.g., of a resolved image in a field plane image, or of discrete diffraction orders in a pupil plane image), and therefore improve measurement accuracy for non-periodic features.

[0054] It should be noted that FIGS. 3-5 illustrate different, non-limiting target designs suitable for providing overlay measurements between a first feature 302 associated with a first patterning process and a second feature 304 associated with a second patterning process. In particular, FIGS. 3-5 illustrate non-limiting examples in which the first feature 302 is located on a first layer 306 of the sample 108 and the second feature 304 is located on a second layer 308 of the sample 108. Thus, the illustrated examples may be suitable for determining overlay between layers of the sample 108. However, it should be understood that these depictions are purely for illustrative purposes and are not intended to limit the present disclosure. For example, it should be noted that the sample 108 can include any number of layers on the substrate 310, and in some embodiments, can include additional layers above, below, and / or between the first layer 306 and the second layer 308.

[0055] 3 illustrates a non-limiting configuration of a cell 204 including a box-in-box feature associated with two patterning processes on two layers of a sample 108. Figure 3 is a simplified top view of a cell 204 of a mosaic overlay target 106 having a box-in-box feature, in accordance with one or more embodiments of the present disclosure. By way of example, such a cell 204 may be associated with the central cell set 202-0 of FIG. 2B. Furthermore, overlay measurements may be generated based on this single cell 204.

[0056] 3, the first feature 302 may correspond to the center box, and the second feature 304 may correspond to the outer frame, where the first feature 302 and the second feature 304 do not overlap. In this manner, an overlay measurement between the first and second exposures may be determined based on the relative positions of the first feature 302 and the second feature 304 (e.g., as observable in the field plane image of the mosaic overlay target 106). For example, the first feature 302 may be centered within the second feature 304 in the X and / or Y directions in the absence of overlay error, such that any deviation from this configuration can be attributed to overlay error in the X and / or Y directions.

[0057] 4A-4B illustrate non-limiting configurations of a cell 204 including overlapping features associated with two patterning processes on two layers of a sample 108. FIG. 4A is a simplified side view of a cell 204 of a mosaic overlay target 106 having overlapping features, according to one or more embodiments of the present disclosure. FIG. 4B is a simplified top view of the cell 204 of FIG. 4A, according to one or more embodiments of the present disclosure. Illustratively, such a cell 204 may be suitable for any of the cell sets 202 of FIGS. 2A-2B.

[0058] As illustrated in FIGS. 4A-4B, the first feature 302 may include a first set of periodic features, and the second feature 304 may correspond to a second set of periodic features. Such a configuration may be referred to as a grating-over-grating structure, and may generate diffraction orders associated with the first feature 302 and the second feature 304, either singly or in combination (e.g., double diffraction). In some embodiments, the first feature 302 and the second feature 304 have a common pitch (or, more generally, periodicity), as illustrated in FIGS. 4A-4B, such that the diffraction orders from the first feature 302 and the second feature 304 overlap and interfere. In some embodiments, not illustrated, the first feature 302 and the second feature 304 have different pitches (or, more generally, periodicities). Such a configuration may also be referred to as a Moiré structure. In this configuration, the diffraction orders from the first feature 302 and the second feature 304 may have different angles and may partially overlap, although this is not a requirement. Such a structure can further generate Moire diffraction (eg, double diffraction) at different angles based on the difference between the pitch of the first features 302 and the second features 304 .

[0059] The first feature 302 and / or the second feature 304 may generally have any periodic distribution along one or more directions and thus may be suitable for facilitating overlay measurements along one or more directions. For example, the first feature 302 and / or the second feature 304 may include a line / space pattern with any pitch or duty cycle along any direction. Furthermore, either the first feature 302 or the second feature 304 may be arranged at two or more characteristic pitches. Illustratively, either feature may be segmented with a coarse pitch and a fine pitch.

[0060] The first feature 302 and second feature 304 of any particular cell 204 may, but need not, be intentionally offset along one or more measurement directions. For example, Figures 4A-4B show a configuration with an intended offset of f. In some embodiments, the induced shift is at least an order of magnitude smaller than the size of the cell 204 (e.g., the length of the cell 204 in the direction of the intended offset).

[0061] It is contemplated herein that a mosaic overlay target 106 including at least some cell sets 202 that include a grating-over-grating structure can facilitate overlay measurements using a wide variety of techniques. Overlay measurements using grating-over-grating structures are generally described in U.S. Pat. No. 7,277,172, issued October 2, 2007; U.S. Pat. No. 7,616,313, issued November 11, 2009; U.S. Pat. No. 8,004,679, issued August 23, 2011; U.S. Pat. No. 7,884,936, issued February 8, 2011; U.S. Pat. No. 8,848,186, issued September 30, 2014; and U.S. Pat. No. 9,739,702, issued August 22, 2017, all of which are incorporated herein by reference in their entireties. For example, zero-order SCOL techniques allow for the measurement of overlays with a common periodicity but different intended offsets (e.g., ±f 0,1 and ±f 0,2) can be based on four cell sets 202 including grating-over-grating structures with a common periodicity but different intended offsets (e.g., ±f0). As another example, a first-order SCOL technique can be based on two cell sets 202 including grating-over-grating structures with a common periodicity but different intended offsets (e.g., ±f0). As another example, a Moiré technique may utilize a first cell set 202 including one or more cells 204 where a first feature 302 has a first pitch (P) and a second feature 304 has a second pitch (Q), and a second cell set 202 including one or more cells 204 where the first feature 302 has a second pitch (Q) and the second feature 304 has the first pitch (P). In this configuration, overlay errors can induce shifts in Moiré diffraction along opposite directions to facilitate self-calibration and self-referencing overlay measurements. It should be understood that these examples are merely illustrative and should not be construed as limiting the present disclosure. In any of these configurations, the mosaic overlay target 106 can substantially increase measurement efficiency (e.g., throughput). Unlike existing SCOL techniques in which separate cells 204 with different intended offsets (f) are measured separately, the mosaic overlay target 106 can enable simultaneous measurement of cells 204 or cell sets 202 with different intended offsets (f) to increase throughput. Furthermore, different cell sets 202 with different variations in intended offset (f), pitch, etc., may be provided on the same mosaic overlay target 106, such that alternative measurements with different parameters can be generated based on one or more measurements (e.g., field plane image, pupil plane image, etc.) of the mosaic overlay target 106.

[0062] 5 is a simplified side view of a cell 204 including features 502 associated with a single patterning process on a single layer (e.g., first layer 306 or second layer 308) of sample 108, in accordance with one or more embodiments of the present disclosure. Illustratively, such a cell 204 may be suitable for any of the cell sets 202 of FIGS. 2A-2B.

[0063] It is contemplated herein that overlay measurements may be generated based on two or more cell sets 202 similar to that illustrated in FIG. 5 , each having features associated with a different patterning process. For example, a first cell set 202 having features associated with a first patterning process and a second cell set 202 having features associated with a second patterning process may operate as an advanced imaging metrology (AIM) target, such that overlay measurements associated with the first and second patterning processes may be generated using any suitable overlay technique. However, it should be noted that such first and second cell sets 202 may be distributed anywhere across the mosaic overlay target 106. This approach may be extended to generate overlay measurements between three or more patterning processes on the same or different layers. For example, a first cell set 202 having features associated with a first patterning process, a second cell set 202 having features associated with a second patterning process, and a third cell set 202 having features associated with a third patterning process may operate as a triple AIM (t-AIM) target such that overlay measurements associated with the first and second patterning processes may be generated using any suitable overlay technique.

[0064] Referring again generally to FIGS. 2A-2B, additional considerations for designing the mosaic overlay target 106, according to one or more embodiments of the present disclosure, are described in more detail.

[0065] In some embodiments, at least some of the cell sets 202 are designed to have reflection symmetry about a central axis and / or rotational symmetry about a central point (e.g., rotational invariance). Such symmetry can be beneficial for mitigating certain sources of noise or error in measurements, such as, but not limited to, tool-induced shift (TIS). In the case of rotational symmetry, such cell sets 202 can be invariant to rotations through any angle, such as, but not limited to, 90 degrees (e.g., 90-degree rotational symmetry) or 180 degrees (e.g., 180-degree rotational symmetry). Note that such symmetry can refer to the distribution of target features in the cell sets 202 (or cells 204 therein) across the mosaic overlay target 106, as well as the shape and orientation of the associated cells 204. For example, cells 204 within cell sets 202 at symmetric locations can have a common size to provide the desired symmetry across the mosaic overlay target 106.

[0066] 2A and 2B, cell pairs in cell sets 202-1 through 202-18 and cell sets 202-1 through 202-8 and 202-11 through 202-18 are distributed with 180-degree rotational symmetry about midpoint 206. As another example, cell set 202-0, which has a single cell 204, may exhibit mirror symmetry along vertical central axis 208 or horizontal central axis 210. As another example, cell set 202-0, which has a single cell 204, may exhibit rotational symmetry (e.g., 90-degree or 180-degree rotational symmetry) about midpoint 206. Note that while FIGS. 2A and 2B illustrate only the location and shape of cells 204, target features within cells 204 of any particular cell set 202 may be positioned such that cell set 202 has any desired symmetry.

[0067] In some embodiments, one or more cell sets 202 are designed to share a common center of symmetry with the entire mosaic overlay target 106 (or with other cell sets 202) under certain conditions, such as, but not limited to, zero-overlay conditions (e.g., conditions under which features associated with different cell sets 202 are printed without unintentional overlay error). Continuing with the example of FIGS. 2A and 2B, all of cell sets 202-0 through 202-18 may be rotationally symmetrical by 180 degrees about center point 206. However, as previously described herein, features within a cell set 202 may be printed with an intentional (e.g., designed) overlay offset that may shift the associated center of symmetry of the cell set 202.

[0068] The ability of the mosaic overlay target 106 to facilitate multiple simultaneous metrology measurements, in accordance with one or more embodiments of the present disclosure, will now be described in more detail.

[0069] The mosaic overlay target 106 can be designed to facilitate two or more simultaneous metrology measurements, each based on one or more images (e.g., one or more field plane images and / or one or more pupil plane images) of the mosaic overlay target 106. For example, a first metrology measurement may be generated based on a first group of one or more cell sets 202, a second metrology measurement may be generated based on a second group of one or more cell sets 202, and so on. In this example, the first, second, and third sets of cell sets 202 include unique combinations of cell sets 202 from the mosaic overlay target 106. However, in some embodiments, some cell sets 202 may be included in multiple sets of cell sets 202 and thus may be utilized in different ways to generate multiple metrology measurements.

[0070] It is contemplated herein that the mosaic overlay target 106 can provide substantial flexibility and efficiency in metrology applications. For example, the mosaic overlay target 106 can enable simultaneous overlay measurements between many sample layers and / or simultaneous alternative metrology measurements of common aspects of the sample 108 (e.g., based on different measurement techniques and / or different feature geometries).

[0071] The mosaic overlay target 106 may be configured to provide simultaneous metrology measurements along multiple measurement directions, which may be, but need not be, orthogonal. As an example in the context of FIG. 2A , cell sets 202 in the upper left and lower right quadrants (e.g., cell sets 202-1 through 202-9) may be configured to provide metrology measurements along a first direction (e.g., the X direction), while cell sets 202 in the upper right and lower left quadrants (e.g., cell sets 202-10 through 202-18) may be configured to provide metrology measurements along a second direction (e.g., the Y direction).

[0072] In some embodiments, the mosaic overlay target 106 is configured to provide simultaneous metrology measurements between multiple different patterning processes. For example, the mosaic overlay target 106 can include multiple cell sets 202, each having features associated with a different patterning process. As an example based on FIG. 2A , cell sets 202-1 through 202-9 can each include features suitable for X-direction overlay measurements on a different layer of the sample 108. Similarly, cell sets 202-10 through 202-18 can each include features suitable for Y-direction overlay measurements on a different layer of the sample 108. For example, cell set 202-1 can include features on a first layer suitable for X-direction measurements, cell set 202-10 can include features on a first layer suitable for Y-direction measurements, cell set 202-2 can include features on a second layer suitable for X-direction measurements, cell set 202-11 can include features on a second layer suitable for Y-direction measurements, and so on. Furthermore, the features on each cell set 202 can include features, such as, but not limited to, those illustrated in FIG. 5 , oriented along the X or Y direction, as appropriate for X or Y direction measurements, respectively. In this configuration, simultaneous overlay measurements between any combination of nine sample layers along two measurement directions can be generated based on one or more images of the mosaic overlay target 106. For example, such targets can be fabricated with approximately the same dimensions as a conventional AIM target, suitable for overlay measurements of two layers, or a t-AIM target, suitable for overlay measurements of three layers. Therefore, the mosaic overlay target 106 can provide high measurement efficiency (e.g., high throughput). Furthermore, this technique can be extended to any number of sample layers.

[0073] In some embodiments, at least some cell sets 202 of the mosaic overlay target 106 are configured to provide surrogate measurements of a common parameter of the sample 108 (e.g., overlay measurements between two specific patterning processes along a specific measurement direction). In this manner, the mosaic overlay target 106 can enable robust and flexible measurements.

[0074] As previously described herein, any particular set of cells 202 or combination of sets of cells 202 may be designed to provide metrology measurements. In some embodiments, the mosaic overlay target 106 may include a first group of sets of cells 202 designed to provide a first overlay measurement between two specific patterning processes along a specific measurement direction and a second group of sets of cells 202 designed to provide at least a second overlay measurement between the same two specific patterning processes along the same specific measurement direction. However, the first and second groups of sets of cells 202 may include features having different layouts. As a result, the first and second overlay measurements may be generated using different overlay metrology techniques or variations of the same technique. In either case, the measurement accuracy, measurement sensitivity, and / or measurement robustness for handling variations on the sample 108 may differ for the first and second overlay measurements.

[0075] By way of example, FIG. 2C is a top view of a variation of the target of FIG. 2A that provides multiple alternative overlay measurements along different measurement directions, in accordance with one or more embodiments of the present disclosure.

[0076] In FIG. 2C, cell sets 202 in the upper left and lower right quadrants (e.g., cell sets 202-1 to 202-9) may be configured to provide metrology measurements along a first direction (e.g., the X direction), while cell sets 202 in the upper right and lower left quadrants (e.g., cell sets 202-10 to 202-18) may be configured to provide metrology measurements along a second direction (e.g., the Y direction).

[0077] Additionally, the mosaic overlay target 106 of FIG. 2C includes a first group of cell sets 202 (cell sets 202-1, 202-2, 202-4, and 202-5) having features on a first layer 306 (e.g., first feature 302) that are suitable for a first directional measurement but have different cell designs. For example, the cells 204 in this first group of cell sets 202 may all be periodic in the first direction, but may have different pitches, feature widths (e.g., duty cycles of line / space patterns), finer segmentation, or other differences. Similarly, the mosaic overlay target 106 of FIG. 2C includes a second group of cell sets 202 (cell sets 202-3, 202-6, 202-7, 202-8, and 202-9) having features on a second layer 308 (e.g., second feature 304) that are suitable for a first directional measurement but have different cell designs.

[0078] The mosaic overlay target 106 of FIG. 2C further includes a third group of cell sets 202 (cell sets 202-10, 202-11, 202-13, and 202-14) having features on a first layer 306 (e.g., first feature 302) that are suitable for second directional measurements but have a different cell design. For example, the cells 204 in this third group of cell sets 202 may all be periodic in the second direction but may have different pitches, feature widths (e.g., duty cycles of line / space patterns), finer segmentation, or other differences. The mosaic overlay target 106 of FIG. 2C also includes a fourth group of cell sets 202 (cell sets 202-12, 202-15, 202-16, 202-17, and 202-18) having features on a second layer 308 (e.g., second feature 304) that are suitable for second directional measurements but have a different cell design.

[0079] In this configuration, overlay measurements between the first layer 306 and the second layer 308 along a first direction may be generated based on any combination of cell sets 202 from the first and second groups, and overlay measurements between the first layer 306 and the second layer 308 along a second direction may be generated based on any combination of cell sets 202 from the third and fourth groups. In particular, the mosaic overlay target 106 of FIG. 2C may provide 20 combinations of cell sets 202 along each direction and thus 20 alternative overlay measurements between the first layer 306 and the second layer 308 along each direction.

[0080] However, it should be understood that FIG. 2C and the related description are provided for illustrative purposes only and should not be construed as limiting. For example, the mosaic overlay target 106 can generally include any number of groups of cell sets 202 in any arrangement suitable for any number of alternative overlay measurements. As another example, the mosaic overlay target 106 can provide alternative measurements using any overlay metrology technique and any associated cell design. In this manner, the mosaic overlay target 106 can provide alternative measurements using a SCOL technique that utilizes grating-over-grating features. In this case, different cell sets 202 can include cells 204 with different intended offsets (f0), as well as (or alternatively) different pitches, feature widths (e.g., duty cycles of line / space patterns), fine segmentation, or any other differences. As another example, the mosaic overlay target 106 may include one or more groups of cell sets 202 suitable for overlay measurement using a first overlay metrology technique (e.g., a field plane imaging technique, etc.) and one or more additional groups of cell sets 202 suitable for overlay measurement using a second overlay metrology technique (e.g., a SCOL technique, etc.).

[0081] Referring now to FIG. 6, a method for overlay metrology that provides alternative overlay measurements from a mosaic overlay target 106 is described in accordance with one or more embodiments of the present disclosure.

[0082] 6 is a flow diagram illustrating steps performed in a method 600, in accordance with one or more embodiments of the present disclosure. Applicant notes that the embodiments and enabling techniques described herein above in the context of overlay metrology system 100 should be construed to extend to method 600. However, it is further noted that method 600 is not limited to the architecture of overlay metrology system 100.

[0083] In some embodiments, the method 600 includes illuminating 602 one or more mosaic overlay targets 106 on the sample 108, each mosaic overlay target 106 including two or more cell sets 202, at least two of the two or more cell sets 202 configured according to a metrology recipe to provide alternative overlay measurements of a common parameter based on one or more images of respective portions of the mosaic overlay target 106 generated based on the metrology recipe. For example, the common parameter may be overlay between two particular process steps along a particular measurement direction.

[0084] In some embodiments, method 600 includes generating 604 one or more images of each mosaic overlay target 106 based on a metrology recipe. For example, the metrology recipe may define parameters associated with the illumination of the mosaic overlay target 106 (e.g., spectrum, polarization, angle of incidence, etc.), the collection of light from the mosaic overlay target 106 for image formation (e.g., spectrum, polarization, collection angle), detector parameters, or any other parameters of the overlay metrology tool that may affect the overlay measurement.

[0085] In some embodiments, the method 600 includes generating 606 at least one overlay measurement of a common parameter from each mosaic overlay target 106 .

[0086] It is contemplated herein that the alternative overlay measurements enabled by the mosaic overlay target 106 can be utilized in a variety of ways within the spirit and scope of the present disclosure. As previously described herein, the alternative overlay measurements can provide different accuracy, sensitivity, and / or robustness to process variations based on the particular physical properties of the sample 108 at a particular location of a particular mosaic overlay target 106. Because the alternative overlay measurements can be generated based on a single capture of one or more images of the mosaic overlay target 106 (e.g., based on different portions of the associated images), measurement throughput can be substantially higher than measuring separate targets, with the primary cost of generating the alternative overlay measurements related only to the computational resources required to process the images.

[0087] In some embodiments, step 606 may include generating, for at least some of the mosaic overlay targets 106, at least some of the alternative overlay measurements enabled by the mosaic overlay targets 106. These alternative overlay measurements may then be used individually and / or combined to generate a composite overlay measurement. For example, step 606 may include combining multiple alternative overlay measurements using any suitable technique (e.g., using averaging, weighted averaging, or any suitable technique) to generate a composite overlay measurement that may be more accurate, sensitive, and / or robust than any of the individual alternative measurements. Such a composite overlay measurement may be generated for multiple mosaic overlay targets 106 distributed across at least one sample 108, thereby providing an accurate and sensitive metrology that is relatively robust to process variations. Furthermore, the availability of multiple alternative overlay measurements may enable mitigation of pattern placement error (PPE) or other inaccuracy issues.

[0088] In some embodiments, step 606 may include generating a single alternative overlay measurement for at least some of the mosaic overlay targets 106. For example, a particular one of the alternative overlay measurements may be generated that has accuracy and / or sensitivity above a selected threshold (or, more generally, a quality threshold). By way of example, it may be more computationally efficient to generate a single measurement per mosaic overlay target 106 (or a single measurement per direction per mosaic overlay target 106) based on a selected cell set 202. As another example, process variations across the location of a particular mosaic overlay target 106 may cause one or more of the alternative overlay measurements to be inaccurate or invalid. In this case, such alternative measurements may be discarded. As long as at least one measurement based on at least one cell set 202 meets a desired threshold, valid measurements can be obtained from the particular mosaic overlay target 106. As a result, overall measurement throughput may remain high.

[0089] 7, which is a flow diagram illustrating steps performed in a method 700 for designing a mosaic overlay target 106, in accordance with one or more embodiments of the present disclosure. Applicant notes that the embodiments and enabling techniques described herein above in the context of overlay metrology system 100 should be construed to extend to method 700. However, it is further noted that method 700 is not limited to the architecture of overlay metrology system 100.

[0090] In this specification, generally, it may be desirable to provide overlay measurement values within certain tolerances. However, specific tolerance requirements may vary for different applications and / or may change over time. By way of example, overlay tolerances can be characterized as -N < OVL1 < N for one layer and -M < OVL2 < M for another layer. As another example, overlay tolerances can be characterized as -N < OVL1 < N and -M < 2*OVL1 + OVL2 < M. In a general sense, it may be desirable to determine an overlay within a tolerance sufficient to maintain the electrical robustness of the printed features. As the feature size of the fabricated features decreases, the overlay measurement tolerance can become complex. For example, it may be necessary to implement complex requirements between multiple layers and / or develop non-linear requirements associated with the relationships between different layers.

[0091] In this specification, the mosaic overlay target 106 disclosed herein is considered to be able to enable simultaneous or selective overlay measurements based on different cell sets 202 and possibly different measurement techniques or algorithms. In this way, a user can meet various overlay measurement tolerances or considerations.

[0092] Furthermore, process variations may be able to change the sensitivity of any particular cell set 202. For example, variations in the printed line width due to process variations can affect the diffraction efficiency from the target features and thus the measurement sensitivity. Therefore, it may be desirable to design the mosaic overlay target 106 to include different cell sets 202 having different feature characteristics (e.g., feature width, etc.). In this configuration, the various cell sets 202 can be evaluated on-the-fly based on specific printed characteristics to provide overlay measurement values within the selected tolerances.

[0093] In some embodiments, the method 700 includes selecting 702 two or more overlay measurements for simultaneous generation using the mosaic overlay target 106, where at least two of the two or more overlay measurements correspond to alternative measurements of a common parameter of the sample 108. For example, the two or more overlay measurements can correspond to measurements along two or more directions or measurements between different combinations of patterning processes (e.g., overlay measurements between different combinations of three or more patterning processes on one or more layers). Furthermore, the common parameter can refer to overlay measurements associated with two particular patterning processes in a particular direction, such that the alternative measurements can be generated using different techniques (e.g., associated with different metrology recipes or variations of a metrology recipe) to generate a value for this common parameter.

[0094] In some embodiments, method 700 includes step 704, in which two or more cell sets 202 having designed features according to a metrology recipe are designed, so that one or more images of the mosaic overlay target 106 generated according to the metrology recipe can include metrology data for generating the two or more metrology measurements selected in step 702.

[0095] 1B, various additional aspects of the overlay metrology subsystem 102 are described in more detail, in accordance with one or more embodiments of the present disclosure.

[0096] FIG. 1B is a simplified schematic diagram of an overlay metrology subsystem 102 in accordance with one or more embodiments of the present disclosure.

[0097] In some embodiments, the overlay metrology subsystem 102 includes an illumination subsystem 120 that generates illumination in the form of one or more illumination beams 122 to illuminate the sample 108, and a collection subsystem 124 that collects light (e.g., sample light 110) from the illuminated sample 108.

[0098] In some embodiments, the illumination subsystem 120 includes an illumination source 126 configured to generate at least one illumination beam 122. The illumination from the illumination source 126 may include one or more selected wavelengths of light, including, but not limited to, ultraviolet (UV), visible, or infrared (IR) radiation. The illumination source 126 may include any type of illumination source suitable for providing at least one illumination beam 122. In some embodiments, the illumination source 126 is a laser source. For example, the illumination source 126 may include, but is not limited to, one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, etc. In this regard, the illumination source 126 may provide the illumination beam 122 with high coherence (e.g., high spatial and / or temporal coherence). In some embodiments, the illumination source 126 includes a laser-sustained plasma (LSP) source. For example, the illumination source 126 may include, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for housing one or more elements capable of emitting broadband illumination when excited into a plasma state by a laser source.

[0099] In embodiments having two or more illumination beams 122, these beams can be generated using a variety of techniques. In some embodiments, the illumination subsystem 120 includes two or more apertures in the illumination field plane 132. In some embodiments, the illumination subsystem 120 includes one or more beam splitters that split illumination from the illumination source 126 into two or more illumination beams 122. In some embodiments, at least one illumination source 126 directly generates two or more illumination beams 122. In a general sense, each illumination beam 122 can be considered to be part of a different illumination channel, regardless of the technique by which the various illumination beams 122 are generated.

[0100] In some embodiments, the illumination subsystem 120 includes one or more optical components suitable for modifying and / or conditioning the one or more illumination beams 122 and directing the one or more illumination beams 122 to the sample 108. For example, the illumination subsystem 120 may include one or more illumination lenses 128 (e.g., to collimate the one or more illumination beams 122, relay the illumination pupil plane 130 and / or the illumination field plane 132, etc.). In some embodiments, the illumination subsystem 120 includes one or more illumination control optics 134 that shape or otherwise control the one or more illumination beams 122. For example, the illumination control optics 134 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, etc.).

[0101] In some embodiments, the overlay metrology subsystem 102 includes an objective lens 136 that focuses one or more illumination beams 122 onto the sample 108 (e.g., an overlay target having overlay target elements located on two or more layers of the sample 108).

[0102] In some embodiments, the one or more illumination beams 122 may be angularly confined on the sample 108 so that the periodic structure in one or more cells 204 of the mosaic overlay target 106 can generate discrete diffraction orders. Additionally, the one or more illumination beams 122 may be spatially confined so that they can illuminate selected portions of the sample 108. For example, each of the one or more illumination beams 122 may be spatially confined to the size of the mosaic overlay target 106. In this manner, the one or more illumination beams 122 can completely illuminate (e.g., overfill) the mosaic overlay target 106.

[0103] In some embodiments, the collection subsystem 124 includes one or more detectors 112, and any detector 112 can be located at a collection field plane 138 conjugate with the mosaic overlay target 106 or a collection pupil plane 140 (e.g., a diffraction plane) associated with the angular distribution of the sample light 110.

[0104] The collection subsystem 124 may include one or more optical elements suitable for modifying and / or conditioning the sample light 110 from the sample 108. In some embodiments, the collection subsystem 124 includes one or more collection lenses 142 (e.g., to collimate the sample light 110, relay a pupil plane and / or a field plane, etc.) and may, but need not, include an objective lens 136. In some embodiments, the collection subsystem 124 includes one or more collection control optics 144 that shape or otherwise control the sample light 110. For example, the collection control optics 144 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, etc.).

[0105] In some embodiments, the overlay metrology subsystem 102 includes a translation stage 146 that positions the sample 108 relative to the objective lens 136 during measurement.

[0106] In some embodiments, the collection subsystem 124 includes two or more collection channels 148, each having at least one detector 112. For example, as shown in FIG. 1B, the overlay metrology subsystem 102 may include one or more beam splitters 150 positioned to split the sample light 110 among the collection channels 148. Additionally, the beam splitters 150 may be polarizing beam splitters, non-polarizing beam splitters, or a combination thereof.

[0107] In some embodiments, as shown in FIG. 1B , the overlay metrology subsystem 102 includes a beam splitter 152 that combines the illumination subsystem 120 and the collection subsystem 124 so that the objective lens 136 can direct the illumination 104 to the sample 108 and collect the sample light 110 from the sample 108.

[0108] 1C-1E, illumination and collection profiles according to one or more embodiments of the present disclosure are described in more detail.

[0109] In a general sense, the overlay metrology subsystem 102 can illuminate the mosaic overlay target 106 with any combination of one or more illumination beams 122 of any distribution.

[0110] 1C is a simplified schematic diagram of a first illumination pupil plane 130 illustrating a single illumination beam 122 providing a normal incidence angle, in accordance with one or more embodiments of the present disclosure. For example, the single illumination beam 122 is centered within a boundary 154 of the illumination pupil plane 130.

[0111] 1D is a simplified schematic diagram of a second illumination pupil plane 130 illustrating two illumination beams 122 in a dipole configuration, in accordance with one or more embodiments of the present disclosure. Such a dipole configuration may be well suited for, but not limited to, overlay measurements along an axis separating the two illumination beams 122. Furthermore, the two illumination beams 122 may provide any combination of angles of incidence. For example, as illustrated in FIG. 1D , the two illumination beams 122 may provide symmetric and opposing angles of incidence within the illumination pupil plane 130, although this is not a requirement.

[0112] In some embodiments, the two illumination beams 122 are configured (e.g., according to a metrology recipe) to satisfy the Littrow condition for the periodic structures in one or more cells 204 of the mosaic overlay target 106. In the Littrow condition, the separation between the illumination beams 122 is equal to λ / pitch, where λ is the wavelength of the illumination beams 122 and pitch is the pitch of the target structures (e.g., along the axis connecting the two illumination beams 122). In this configuration, first-order diffraction (e.g., specular reflection) of the illumination beam 122 from associated features of the mosaic overlay target 106 counter-propagates along the direction of incidence of the illumination beam 122. It is believed herein that the Littrow condition can provide relatively robust measurements. However, precise adherence to the Littrow condition is not required. In some cases, the separation between the illumination beams 122 at the dipole is selected to be within a specific tolerance for features in one or more cells 204.

[0113] FIG. 1E is a simplified schematic diagram of a third illumination pupil plane 130 illustrating four illumination beams 122 in a quadrupole configuration, in accordance with one or more embodiments of the present disclosure. A quadrupole configuration can be thought of as two dipoles with orthogonal orientations. For example, FIG. 1E illustrates a first dipole with illumination beams 122a, b oriented along the X direction and a second dipole with illumination beams 122c, d oriented along the Y direction. In this manner, the description of FIG. 1D can also be applied to FIG. 1E. For example, it should be noted that the quadrupole configuration of illumination beams 122a-d can satisfy the Littrow condition for features oriented along both the X and Y directions, and the separation distances of the dipoles along the X and Y directions can be different. Furthermore, although the separation distances of both dipoles in FIG. 1E are equal, this is not a requirement.

[0114] The overlay metrology subsystem 102 can be configured in various ways to image the mosaic overlay target 106 with multiple illumination beams 122. In some embodiments, a single image can be generated based on simultaneous illumination of the mosaic overlay target 106 with multiple illumination beams 122. In this configuration, only one collection channel 148 may be required. In some embodiments, the overlay metrology subsystem 102 sequentially illuminates the mosaic overlay target 106 with one or more illumination beams 122 and sequentially generates corresponding images. Such images may be analyzed separately (e.g., by the controller 114) or may be combined (e.g., summed, averaged, etc.) when generating various overlay measurements.

[0115] In some embodiments, the overlay metrology subsystem 102, including two collection channels 148, can generate separate (e.g., isolated) images from different illumination beams 122. Such a configuration can be particularly useful for optically isolating overlay measurements along different directions, without limitation. For example, in the case of quadrupole illumination, one or more first images can be generated in the first collection channel 148 based on a first dipole (e.g., illumination beams 122a, b), and one or more second images can be generated in the second collection channel 148 based on a second dipole (e.g., illumination beams 122c, d). Again, the illumination beams 122 can be directed simultaneously or sequentially toward the mosaic overlay target 106. For example, illumination beams 122a, c can be directed toward the sample 108 first, followed by illumination beams 122b, d.

[0116] The isolated images can be generated using any technique known in the art. Continuing with the quadrupole example above, the illumination beams 122 at the first and second dipoles may have different properties (e.g., different spectra, different polarizations, etc.). Additionally, the collection subsystem 124 can include various components (e.g., a beam splitter 150 and / or collection control optics 144 in any of the collection channels 148) for separating or isolating the associated sample light 110 on the detector 112 in the respective channel. For example, the beam splitter 150 and / or collection control optics 144 can include or operate as a spectral filter, a polarizer, etc.

[0117] 1C-1E , each illumination beam 122 can have any desired shape corresponding to an incident angle profile, and different illumination beams 122 can have different shapes. Various illumination beam 122 profiles and associated measurement conditions that may be implemented as part of one or more metrology recipes are generally described in U.S. Patent Application Publication No. 2022 / 0357674, published November 10, 2022, which is incorporated herein by reference in its entirety.

[0118] The subject matter described herein may depict different components contained within or connected to other components. It should be understood that any such depicted architectures are merely exemplary, and that in fact many other architectures may be implemented that achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Thus, any two components herein that are combined to achieve a particular function can be considered to be “associated” with each other such that the desired functionality is achieved, 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 achieve the desired functionality, and any two components so associateable can also be considered to be “couplable” with each other to achieve the desired functionality. Specific examples of combinable components include, but are not limited to, components that are physically interactable and / or physically interacting, components that are wirelessly interactable and / or wirelessly interacting, and / or components that are logically interactable and / or logically interacting.

[0119] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes in form, construction, and arrangement of the elements can be made without departing from the disclosed subject matter or sacrificing all of its material advantages. The described forms are merely illustrative, and it is the intent of the following claims to embrace and cover all such modifications. It will further be understood that the invention is defined by the appended claims.

Claims

1. A mosaic overlay target, comprising: two or more cell sets distributed across the sample, each cell set including one or more cells, each cell set oriented to have at least one of reflection symmetry about a central axis of the mosaic overlay target or rotation symmetry about a central point of the mosaic overlay target; Equipped with the two or more cell sets are configured according to a metrology recipe, whereby one or more images of the mosaic overlay target produced according to the metrology recipe include metrology data appropriate for two or more overlay measurements, a particular one of the two or more overlay measurements being based on a portion of the one or more images associated with at least one of the two or more cell sets; at least two of the two or more overlay measurements are surrogate measurements of a common property of the sample, and at least two of the two or more cell sets are configured according to the metrology recipe to provide surrogate portions of the metrology data associated with the surrogate measurements. Mosaic overlay target.

2. The common property of the samples is Overlay measurements associated with two or more patterning processes along a particular measurement direction The mosaic overlay target of claim 1 , comprising:

3. The two or more measurements are Overlay measurements along two or more directions The mosaic overlay target of claim 1 , comprising:

4. The surrogate measure is: Overlay measurements generated using two or more different overlay metrology techniques The mosaic overlay target of claim 1 , comprising:

5. At least one of the two or more different overlay metrology techniques comprises: Scatterometry Overlay Metrology Technique The mosaic overlay target of claim 4 , comprising:

6. At least one of the two or more different overlay metrology techniques comprises: Imaging overlay measurement technique The mosaic overlay target of claim 4 , comprising:

7. At least one of the two or more cell sets one or more cell pairs, each cell pair including two cells, the two cells being oriented to have at least one of reflection symmetry about the central axis of the mosaic overlay target or rotation symmetry about the central point of the mosaic overlay target; The mosaic overlay target of claim 1 , comprising:

8. At least one of the two or more cell sets a single cell centered on the central point of the mosaic overlay target, the single cell having at least one of reflection symmetry about the central axis of the mosaic overlay target or rotation symmetry about the central point of the mosaic overlay target; The mosaic overlay target of claim 1 , comprising:

9. The mosaic overlay target of claim 1 , wherein each of the one or more cells in at least one of the two or more cell sets is rotationally symmetric by 180 degrees.

10. The mosaic overlay target of claim 1 , wherein the one or more cells in at least one of the two or more cell sets include a periodic feature.

11. The mosaic overlay target of claim 10 , wherein the periodic features are periodic along a single direction corresponding to a measurement direction.

12. The mosaic overlay target of claim 10 , wherein the periodic features are periodic along two directions corresponding to two measurement directions.

13. The mosaic overlay target of claim 1 , wherein the one or more cells in at least one of the two or more cell sets comprise overlapping features on two or more layers of the sample.

14. The overlapping feature is: Periodic features 14. The mosaic overlay target of claim 13, comprising:

15. The mosaic overlay target of claim 14 , wherein the periodic features on the two or more layers have a common periodicity.

16. The mosaic overlay target of claim 14 , wherein the periodic features on the two or more layers have different pitches along a particular direction.

17. The mosaic overlay target of claim 14 , wherein the periodic features on the two or more layers have different pitches along a particular measurement direction.

18. The mosaic overlay target of claim 14 , wherein the periodic features on the two or more layers have different pitches along different measurement directions.

19. 1. An overlay metrology system, comprising: an illumination source configured to generate one or more illumination beams; one or more optical elements configured to illuminate a mosaic overlay target on the sample with the one or more illumination beams when implementing a metrology recipe, the mosaic overlay target comprising: two or more cell sets distributed across the sample, each cell set including one or more cells, each cell set oriented to have at least one of reflection symmetry about a central axis of the mosaic overlay target or rotation symmetry about a central point of the mosaic overlay target; one or more optical elements comprising: one or more detectors that generate one or more images of the mosaic overlay target based on the illumination by the one or more illumination beams when implementing the metrology recipe; 1. A controller including one or more processors configured to execute program instructions, the one or more processors comprising: receiving the one or more images of the mosaic overlay target; and generating at least two overlay measurements of the sample based on the one or more images, a particular one of the two or more overlay measurements being based on portions of the one or more images associated with at least one of the two or more cell sets, at least two of the two or more overlay measurements being surrogate measurements of a common property of the sample, and at least two of the two or more cell sets being configured according to the metrology recipe to provide surrogate portions of metrology data associated with the surrogate measurements; a controller that implements the measurement recipe by An overlay measurement system comprising:

20. The overlay metrology system of claim 19 , wherein the system generates a composite overlay measurement based on at least some of the alternative measurements.

21. The overlay metrology system of claim 19 , wherein the one or more illumination beams comprise a single illumination beam.

22. 22. The overlay metrology system of claim 21, wherein the one or more optical elements are configured to illuminate the mosaic overlay target with the single illumination beam at a normal angle of incidence.

23. 20. The overlay metrology system of claim 19, wherein the one or more illumination beams comprise two illumination beams in a dipole configuration, and the one or more optical elements are configured to illuminate the mosaic overlay target with the two illumination beams at an oblique angle of incidence.

24. 20. The overlay metrology system of claim 19, wherein the one or more illumination beams comprise four illumination beams in a quadrupole configuration, and the one or more optical elements are configured to illuminate the mosaic overlay target with the four illumination beams at an oblique angle of incidence.

25. The common property of the samples is Overlay measurements associated with two or more patterning processes along a particular measurement direction 20. The overlay metrology system of claim 19, comprising:

26. The two or more measurements are Overlay measurements along two or more directions 20. The overlay metrology system of claim 19, comprising:

27. The surrogate measure is: Overlay measurements generated using two or more different overlay metrology techniques 20. The overlay metrology system of claim 19, comprising:

28. At least one of the two or more different overlay metrology techniques comprises: Scatterometry Overlay Metrology Technique 28. The overlay metrology system of claim 27, comprising:

29. At least one of the two or more different overlay metrology techniques comprises: Imaging overlay measurement technique 28. The overlay metrology system of claim 27, comprising:

30. At least one of the two or more cell sets one or more cell pairs, each cell pair including two cells, the two cells being oriented to have at least one of reflection symmetry about the central axis of the mosaic overlay target or rotation symmetry about the central point of the mosaic overlay target; 20. The overlay metrology system of claim 19, comprising:

31. At least one of the two or more cell sets a single cell centered on the central point of the mosaic overlay target, the single cell having at least one of reflection symmetry about the central axis of the mosaic overlay target or rotation symmetry about the central point of the mosaic overlay target; 20. The overlay metrology system of claim 19, comprising:

32. 20. The overlay metrology system of claim 19, wherein each of the one or more cells in at least one of the two or more cell sets is rotationally symmetric by 180 degrees.

33. 20. The overlay metrology system of claim 19, wherein the one or more cells in at least one of the two or more cell sets include a periodic feature.

34. 34. The overlay metrology system of claim 33, wherein the periodic features are periodic along a single direction corresponding to a measurement direction.

35. 34. The overlay metrology system of claim 33, wherein the periodic feature is periodic along two directions corresponding to two measurement directions.

36. 20. The overlay metrology system of claim 19, wherein the one or more cells in at least one of the two or more cell sets comprise overlapping features on two or more layers of the sample.

37. The overlapping feature is: Periodic features 37. The overlay metrology system of claim 36, comprising:

38. 38. The overlay metrology system of claim 37, wherein the periodic features on the two or more layers have a common periodicity.

39. 38. The overlay metrology system of claim 37, wherein the periodic features on the two or more layers have different pitches along a particular measurement direction.

40. 38. The overlay metrology system of claim 37, wherein the periodic features on the two or more layers have different pitches along different measurement directions.

41. 1. An overlay metrology method, comprising: illuminating one or more mosaic overlay targets on a sample with one or more illumination beams according to a metrology recipe, each of the mosaic overlay targets comprising: two or more cell sets distributed across the sample, each cell set including one or more cells, each cell set oriented to have at least one of reflection symmetry about a central axis of the mosaic overlay target or rotation symmetry about a central point of the mosaic overlay target; and generating one or more images of the mosaic overlay target based on the illumination by the one or more illumination beams; generating at least two overlay measurements of the sample based on the one or more images, a particular one of the two or more overlay measurements being based on a portion of the one or more images associated with at least one of the two or more cell sets, at least two of the two or more overlay measurements being surrogate measurements of a common property of the sample, and at least two of the two or more cell sets being configured according to the metrology recipe to provide surrogate portions of the metrology data associated with the surrogate measurements; An overlay measurement method, including:

42. 1. A method for designing a mosaic overlay target, comprising: selecting two or more overlay measurements to generate using the mosaic overlay target; designing two or more cell sets of the mosaic overlay target, the mosaic overlay target comprising: the two or more cell sets distributed across the sample, each cell set including one or more cells, and each cell set oriented to have at least one of reflection symmetry about a central axis of the mosaic overlay target or rotation symmetry about a central point of the mosaic overlay target. To have Including, the two or more cell sets are configured according to a metrology recipe, whereby one or more images of the mosaic overlay target produced according to the metrology recipe include metrology data suitable for the two or more overlay measurements, a particular one of the two or more overlay measurements being based on a portion of the one or more images associated with at least one of the two or more cell sets; at least two of the two or more overlay measurements are surrogate measurements of a common property of the sample, and at least two of the two or more cell sets are configured according to the metrology recipe to provide surrogate portions of the metrology data associated with the surrogate measurements. method.

43. Designing the two or more cell sets of the mosaic overlay target includes: designing a layout of features in said two or more cell sets; 43. The method of claim 42, comprising:

Images