Multidirectional overlay measurement and separation imaging using multiple lighting parameters

Abstract

The optical metrology system can include an overlay metrology tool 102 for evaluating properties of an overlay target 104 on a sample 110, the overlay target 104 including periodic features in a first direction in a first set of layers of the sample 110 and periodic features in a second direction in a second set of layers of the sample 110. The overlay metrology tool 102 can simultaneously illuminate the overlay target 104 with a first illumination beam 106a and a second illumination beam 106b and can further generate an image of the overlay target 104 based on diffraction of the first illumination beam 106a and the second illumination beam 106b by the overlay target 104, where the diffraction orders of the first illumination beam 106a contribute to resolving images of only the periodic features in the first direction and the diffraction orders of the second illumination beam 106b contribute to resolving images of only the periodic features in the second direction. The system may further generate overlay measurements along the first and second measurement directions based on the images.

Description

Technical Field

[0001] The present disclosure generally relates to imaging overlay measurement, and more particularly to simultaneous separation imaging overlay measurement along multiple directions.

Background Art

[0002] Image-based overlay measurement typically generates overlay measurement values by imaging multiple features on a sample fabricated using various lithographic exposures and determining the relative positions of the imaged features. In this way, overlay measurement can provide an indicator of registration error between lithographic exposures. However, as manufacturing of smaller feature sizes is required, overlay tolerances become more stringent.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, there is a need to develop a system and method for providing overlay measurement with high accuracy and throughput.

Means for Solving the Problems

[0005] Optical measurement systems according to one or more exemplary embodiments of the present disclosure are disclosed. In one exemplary embodiment, the system includes an overlay measurement tool for carrying out a measurement recipe for evaluating the properties of an overlay target on a sample. According to one or more exemplary embodiments of the present disclosure, the overlay target includes a first directional periodic feature distributed along a first measurement direction and a second directional periodic feature in a second set of layers of the sample. In another exemplary embodiment, the overlay measurement tool includes an illumination optical element for illuminating the overlay target with one or more first illumination beams and one or more second illumination beams, wherein at least one of the first illumination beams and at least one of the second illumination beams are incident on the overlay target simultaneously. In another exemplary embodiment, the overlay measurement tool further includes a focusing optical element that can be configured to generate an image of the overlay target on one or more detectors based on the diffraction of the first and second illumination beams by the overlay target. In another exemplary embodiment, the diffraction order of the first illumination beam contributes to the formation of a resolution image of only periodic features in a first direction, and the diffraction order of the second illumination beam contributes to the formation of a resolution image of only periodic features in a second direction. In another exemplary embodiment, the system further includes a control device for generating first and second overlay measurements along the first and second measurement directions based on the image.

[0006] Optical measurement systems according to one or more exemplary embodiments of the present disclosure are disclosed. In one exemplary embodiment, the system includes an illumination optical element for illuminating an overlay target on a sample with a first illumination beam and a second illumination beam when performing a measurement recipe, wherein at least one of the first illumination beams and at least one of the second illumination beams are incident on the overlay target simultaneously. In another exemplary embodiment, the overlay target according to the measurement recipe includes a first directional periodic feature distributed along a first measurement direction and a second directional periodic feature distributed along a second measurement direction different from the first measurement direction. In another exemplary embodiment, the system further includes a focusing optical element for generating an image of the overlay target on one or more detectors based on the diffraction of the first and second illumination beams by the overlay target. In another exemplary embodiment, the diffraction order of the first illumination beam contributes to the formation of a resolution image of only the first directional periodic features, and the diffraction order of the second illumination beam contributes to the formation of a resolution image of only the second directional periodic features. In another exemplary embodiment, the system further includes a control device for generating first and second overlay measurements along first and second measurement directions based on an image.

[0007] Optical measurement methods according to one or more exemplary embodiments of the present disclosure are disclosed. In one exemplary embodiment, the method includes illuminating an overlay target on a sample with a first illumination beam and a second illumination beam, wherein at least one of the first illumination beams and at least one of the second illumination beams are incident on the overlay target simultaneously. In another exemplary embodiment, the overlay target includes a first directional periodic feature distributed along a first measurement direction and a second directional periodic feature distributed along a second measurement direction different from the first measurement direction. In another exemplary embodiment, the method includes generating an image of the overlay target on one or more detectors based on the diffraction of the first and second illumination beams by the overlay target. In another exemplary embodiment, the diffraction order of the first illumination beam contributes to the formation of a resolution image of only the first directional periodic features, and the diffraction order of the second illumination beam contributes to the formation of a resolution image of only the second directional periodic features. In another exemplary embodiment, the method includes generating a first overlay measurement along a first measurement direction based on one or more images. In another exemplary embodiment, the method includes generating a second overlay measurement along a second measurement direction based on one or more images.

[0008] It should be understood that both the general description above and the detailed description below are illustrative and descriptive, and do not necessarily limit the claimed invention. The accompanying drawings incorporated herein and forming part thereof illustrate embodiments of the invention and, together with this general description, serve to illustrate the principles of the invention.

[0009] Many of the advantages of this disclosure can be better understood by those skilled in the art by referring to the accompanying drawings. [Brief explanation of the drawing]

[0010] [Figure 1A] This is a conceptual diagram showing an overlay measurement system according to one or more embodiments of the present disclosure. [Figure 1B]This is a conceptual diagram showing an overlay measurement tool according to one or more embodiments of the present disclosure. [Figure 1C] This is a conceptual diagram of an overlay measurement tool including two focusing channels, according to one or more embodiments of the present disclosure. [Figure 2A] This is a top view of an overlay target having non-overlapping features according to one or more embodiments of the present disclosure. [Figure 2B] This is a top view of a cell of an overlay target having a moiré structure according to one or more embodiments of the present disclosure. [Figure 2C] This is a side view of the cell shown in Figure 2B on a substrate according to one or more embodiments of the present disclosure. [Figure 3A] This is a conceptual diagram of diffraction order focusing from a perpendicularly incident illumination beam according to one or more embodiments of the present disclosure. [Figure 3B] This is a conceptual diagram of diffraction order focusing from an obliquely incident illumination beam according to one or more embodiments of the present disclosure. [Figure 4A] This is a conceptual diagram of an illumination pupil plane, according to one or more embodiments of the present disclosure, which includes two illumination beams positioned within the illumination pupil boundary to provide oblique illumination along orthogonal azimuthal directions. [Figure 4B] This is a conceptual diagram of a focusing pupil showing direction-separated imaging based on the illumination profile of Figure 4A, according to one or more embodiments of the present disclosure. [Figure 5A] This is a conceptual diagram of an illumination pupil showing a direction-dependent illumination beam having a rotated configuration according to one or more embodiments of the present disclosure. [Figure 5B] This is a conceptual diagram of illumination pupils showing direction-dependent illumination beams distinguished based on NA, according to one or more embodiments of the present disclosure. [Figure 5C] This is a conceptual diagram of illumination pupils showing direction-dependent illumination beams distinguished based on inclination, according to one or more embodiments of the present disclosure. [Figure 5D] This is a conceptual diagram of an illumination pupil showing a direction-dependent illumination beam distinguished based on spectral characteristics, according to one or more embodiments of the present disclosure. [Figure 5E] A conceptual diagram of an illumination pupil plane showing illumination beams with direction dependence distinguished based on intensity, according to one or more embodiments of the present disclosure. [Figure 5F] A conceptual diagram of an illumination pupil plane showing illumination beams with direction dependence distinguished based on polarization, according to one or more embodiments of the present disclosure. [Figure 6] A conceptual diagram of a condenser pupil plane showing direction-separated imaging in an oblique bright-field imaging mode based on the illumination distribution shown in FIG. 4A, according to one or more embodiments of the present disclosure. [Figure 7A] A conceptual diagram of a condenser pupil plane showing the configuration of an overlay measurement tool focused by an objective lens, according to one or more embodiments of the present disclosure. [Figure 7B] A conceptual diagram of the condenser pupil plane of FIG. 7A in which the zero-order diffraction lobe is blocked to provide dark-field imaging, according to one or more embodiments of the present disclosure. [Figure 8A] A conceptual diagram of the generation of various diffraction lobes, according to one or more embodiments of the present disclosure. [Figure 8B] A conceptual diagram of a condenser pupil plane showing direction-separated imaging in an optical moiré mode based on the diffraction lobes shown in FIG. 8A, according to one or more embodiments of the present disclosure. [Figure 8C] A conceptual diagram of the condenser pupil plane of FIG. 8B including a blocking portion for selectively blocking the zero-order diffraction lobe in the condenser pupil plane, according to one or more embodiments of the present disclosure. [Figure 9] A conceptual diagram of an illumination pupil plane including four illumination beams positioned to provide symmetric oblique illumination along orthogonal azimuthal directions, according to one or more embodiments of the present disclosure. [Figure 10] A flowchart showing steps performed in a method for direction-separated imaging, according to one or more embodiments of the present disclosure.

Embodiments for Carrying Out the Invention

[0011] The following references to the subject matter disclosed in the accompanying drawings. This disclosure has been described and illustrated in detail with respect to specific embodiments and their detailed features. 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 modifications and variations in form and detail can be made without departing from the spirit and scope of this disclosure.

[0012] Embodiments of this disclosure relate to systems and methods for image-based overlay measurements that provide direction-separated imaging of sample features along different directions using simultaneous illumination by illumination beams having different illumination conditions. For example, an image (or part thereof) of sample features along a first direction (e.g., a first measurement direction) may be formed from illumination associated with a first illumination condition, and an image (or part thereof) of sample features along a second direction (e.g., a second measurement direction) may be formed from illumination associated with a second illumination condition. For the purposes of this disclosure, the illumination conditions may include, but are not limited to, a set of parameters of the illumination beam used to generate the image, which include numerical aperture (NA), beam shape, beam inclination, incident azimuth angle, incident elevation angle, wavelength, spectral bandwidth, polarization, or intensity.

[0013] In some embodiments, overlay measurement is performed by illuminating an overlay target having at least two sets of periodic target features arranged to facilitate overlay measurement along at least two different (e.g., orthogonal) measurement directions. For example, the set of periodic target features may include a periodic distribution of features along a particular measurement direction. As a non-limiting example, such a periodic distribution of features could be a diffraction grating (e.g., a lattice structure) characterized by a lattice pitch along a lattice direction. Thus, an overlay target designed for overlay measurement along two different directions may include a set of periodic features having a first lattice direction and a second set of periodic features having a second lattice direction.

[0014] This specification intends to show that various image quality metrics associated with images of periodic target features may be influenced by the number and composition of diffraction orders from the periodic target features used to generate the image. Furthermore, the influence of a particular number and composition of diffraction orders used to generate the image may be more pronounced in challenging applications, such as imaging sample features at or near the optical resolution of the imaging system, though this influence may not be limited. As an example involving dark-field imaging techniques, zero-order diffraction (e.g., specular reflection) may introduce a DC bias that can reduce image contrast. As another example particularly relevant to overlay measurements, diffraction from features not the target of the specific measurement may introduce other artifacts that similarly reduce image contrast and / or affect the sensitivity of the resulting measurement. For example, diffraction from a Y-direction grating may negatively affect the image of an X-direction grating (e.g., reduce contrast), which may negatively affect image-based overlay measurements.

[0015] Embodiments of this disclosure relate to systems and methods for providing illumination-separated imaging of features having different grid directions. In this way, image quality (e.g., contrast, or any other suitable image quality metric) can be improved compared to the prior art. In some embodiments, an overlay measurement system simultaneously illuminates an overlay target with multiple illumination beams having different direction-dependent illumination conditions, and the overlay target includes features having different (e.g., orthogonal) grid directions. In this way, each illumination beam can be diffracted along each of the grid directions. However, in embodiments of this disclosure, the overlay measurement tool is configured (e.g., using a measurement recipe) such that diffracted lobes from any particular illumination beam form an image of periodic features along one particular direction only. In this configuration, diffraction of a particular illumination beam along other directions is insufficient to form a resolution image of the periodic structure.

[0016] This specification recognizes that, in order to form an image of a periodic structure, at least two diffraction lobes must be focused and passed to the detector to contribute to image formation. For the purposes of this disclosure, direction-separated imaging refers to a configuration in which, for any given illumination beam, there is only one direction in which two or more diffraction lobes contribute to image formation. In other directions, at most one diffraction lobe is focused and passed to the detector. Under such conditions, periodic features along other directions are not resolved. In some embodiments, diffraction orders associated with other directions are not focused in order to avoid or mitigate the residual effects of these other diffraction orders (e.g., DC bias associated with zero-order reflected light along other directions) that may adversely affect image quality. In some embodiments, it is permissible for a single diffraction order along other directions to be passed to the detector and contribute to image formation (e.g., zero-order reflected light). In such cases, the residual effects of the single diffraction lobe may be within acceptable limits for a particular application.

[0017] For example, an overlay target containing orthogonal grid features (e.g., X-direction grids and Y-direction grids) can be simultaneously illuminated by a first illumination beam with a first set of illumination conditions and a second illumination beam with a second set of illumination conditions. However, only the diffraction of the first illumination beam by the X-direction grid contributes to the formation of the portion of the image containing the X-direction grid. Similarly, only the diffraction of the second illumination beam by the Y-direction grid contributes to the formation of the portion of the image containing the Y-direction grid. As a result, the X-direction and Y-direction grids are imaged simultaneously, but each image (or part thereof) is formed based on the different illumination conditions provided by the first and second illumination beams.

[0018] Referring here to Figures 1A to 10, a system and method for optically separated imaging using direction-dependent illumination conditions, according to one or more embodiments of the present disclosure, are described in more detail.

[0019] Figure 1A is a conceptual diagram showing an overlay measurement system 100 according to one or more embodiments of the present disclosure.

[0020] In some embodiments, the overlay measurement system 100 includes an overlay measurement tool 102, which can be configured to produce overlay measurements associated with an overlay target 104 having a design based on a measurement recipe (e.g., an overlay recipe). For example, the overlay measurement tool 102 can direct two or more illumination beams 106 (e.g., direction-dependent illumination beams 106 having different illumination conditions) from at least one illumination source 108 onto the overlay target 104 on the sample 110, collect light or other radiation (referred to herein as measurement light 112) emitted from the overlay target 104 in response to the illumination beams 106, and generate a detection signal from at least one detector 114 based on the measurement light 112.

[0021] The overlay measurement tool 102 may include any type of tool known in the art that is suitable for generating an overlay signal suitable for determining an overlay associated with an overlay target on the sample 110. In some embodiments, the overlay measurement tool 102 is an imaging measurement tool that generates overlay measurements based on one or more images of the overlay target 104. The overlay measurement tool 102 may generate images using any imaging technique or combination of imaging techniques known in the art, including but not limited to bright-field or dark-field imaging techniques. Furthermore, as disclosed herein, the overlay measurement tool 102 may be configured to provide direction-dependent illumination conditions for providing optically separated imaging of features oriented along different directions (e.g., based on a measurement recipe).

[0022] Some embodiments of this disclosure aim to provide recipes for configuring an overlay measurement tool 102 to facilitate overlay measurements based on a selected diffraction order. The measurement recipe may include, but is not limited to, a set of parameters for controlling various aspects of the overlay measurement, such as illumination of the sample, focusing of light from the sample, or the position of the sample during measurement. In this way, the overlay measurement tool 102 may be configured to achieve a selected type of measurement for a selected overlay target design. For example, the measurement recipe may include, but is not limited to, parameters of the illumination beam 106, such as illumination wavelength, illumination pupil distribution (e.g., distribution of illumination angles and the associated intensity of illumination at those angles), polarization of incident illumination, or spatial distribution of illumination. As another example, the measurement recipe may include, but is not limited to, focusing parameters, such as focusing pupil distribution (e.g., a desired distribution of angled light from the overlay target 104 used for measurement, and the associated filtered intensity at those angles), focusing aperture settings for selecting the target portion of the overlay target 104, polarization of the focused light, wavelength filters, or parameters for controlling one or more detectors. As another example, the measurement recipe may include, but is not limited to, various parameters associated with the design of the overlay target 104, such as the position and orientation of the sample features (e.g., the pitch of grid features along a particular direction). As yet another example, the measurement recipe may include, but is not limited to, various parameters associated with the position of the sample 110 during measurement, such as the height of the sample, the orientation of the sample, whether the sample is stationary or moving during measurement (in addition to related parameters describing velocity, scanning pattern, etc.).

[0023] In this way, the overlay measurement tool 102 may be configured to provide a selected distribution of light in the focusing pupil when analyzing a specific overlay target 104 having a known design according to a measurement recipe. This distribution of light in the focusing pupil can then be further modified by various optical elements as desired to perform the desired overlay measurement.

[0024] In some embodiments, the overlay measurement system 100 further includes a control unit 116 having one or more processors 118 configured to execute program instructions held in memory 120 (e.g., a memory medium). The control unit 116 may be communicatively coupled to any of the components of the overlay measurement system 100, such as a detector 114, but is not limited to these. In this way, the control unit 116 can generate overlay measurements based on detection signals according to a measurement recipe.

[0025] One or more processors 118 of the control unit 116 may include any processor or processing element known in the art. For the purposes of this disclosure, the terms “processor” or “processing element” may be broadly defined to include any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application-specific integrated circuit (ASIC) devices, one or more field-programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, one or more processors 118 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). In one embodiment, one or more processors 118 may be embodied as a desktop computer, mainframe computer system, workstation, image computer, parallel processor, networked computer, or any other computer system configured to operate an overlay measurement system 100 as described throughout this disclosure or to operate in conjunction with such an overlay measurement system 100.

[0026] Furthermore, various subsystems of the overlay measurement system 100 may include processors or logic elements suitable for performing at least some of the steps described herein. Therefore, the above description should be interpreted as merely an example and not as a limitation to embodiments of the disclosure. Furthermore, the steps described throughout this disclosure may be performed by a single control unit 116, or alternatively, by multiple control units. Furthermore, the control unit 116 may include one or more control units housed in one common housing or multiple housings. In this way, any control unit or combination of control units can be individually packaged as modules suitable for integration into the overlay measurement system 100.

[0027] The memory 120 may include any storage medium known in the art that is suitable for storing program instructions executable by one or more associated processors 118. For example, the memory 120 may include a non-temporary memory medium. Another example, the memory 120 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 devices, etc. It should be further noted that the memory 120 may be housed together with one or more processors 118 in a common control unit housing. In one embodiment, the memory 120 may be located remotely from the physical locations of one or more processors 118 and the control unit 116. For example, one or more processors 118 of the control unit 116 may have access to remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, etc.).

[0028] Referring here to Figures 2A to 2C, various non-limiting examples of the overlay target 104 according to one or more embodiments of the present disclosure are described in more detail.

[0029] For the purposes of this disclosure, the term overlay is generally used to describe the relative position of features on a sample 110 fabricated by two or more lithography patterning steps, in which case the term overlay error describes the deviation of the features from their nominal position. In this context, overlay measurement can be expressed as a measurement of relative position, or a measurement of overlay error associated with these relative positions. For example, a multilayer device may contain features patterned on multiple sample layers using different lithography steps for each layer, in which case the alignment of features between layers must usually be strictly controlled to ensure proper performance of the resulting device. As a result, overlay measurement can characterize the relative position of features on two or more of the sample layers. As another example, multiple lithography steps may be used to fabricate features on a single sample layer. Such a technique, generally called double patterning or multi-patterning, can facilitate the fabrication of high-density features close to the resolution of the lithography system. In this context, overlay measurement can characterize the relative position of features from different lithography steps on this single layer. Throughout this disclosure, examples and illustrations relating to specific applications of overlay measurement are provided for illustrative purposes only and should not be construed as limiting this disclosure.

[0030] Furthermore, the term overlay target 104 is used herein in a broader sense to refer to any set of features on a sample having a known periodicity suitable for overlay measurements (e.g., corresponding to grid features). In some embodiments, the overlay target 104 includes a dedicated target having features fabricated on one or more sample layers for the purpose of providing overlay measurements that typically represent overlays of device features on the same layer. For example, a dedicated overlay target may include one or more cells having grid features having features (e.g., grid pitch, feature size, grid orientation, etc.) designed to enable overlay measurements according to a particular overlay technique. Such a dedicated overlay target can be printed at various locations on the sample, including but not limited to within the scribe line or within the die. In some embodiments, the overlay target includes device features having a known periodicity suitable for direct overlay measurements.

[0031] Figure 2A is a top view of an overlay target 104 having non-overlapping features according to one or more embodiments of the present disclosure. In particular, Figure 2A shows a non-limiting configuration of the overlay target 104 including four cells 202a-d, which are represented here as a four-part division of the overlay target 104. In this configuration, each cell 202a-d may include a first set 204 of periodic features associated with a first lithography exposure and a second set 206 of periodic features associated with a second lithography exposure. Furthermore, cells 202b and 202d may be configured to enable overlay measurements along the X direction as shown in Figure 2A. For example, overlay measurements along the X direction can be performed by directly comparing the relative positions of the first set 204 of periodic features and the second set 206 of periodic features within each cell or between cells 202b and 202d. In another example, an overlay measurement along the X direction can be performed by comparing points that are rotationally symmetric (e.g., rotational, reflection, or mirror symmetry) between a first set 204 of periodic features distributed across cells 202b and 202d with points that are symmetric between a second set 206 of periodic features distributed across cells 202b and 202d. Similarly, cells 202a and 202c may be configured to achieve an overlay measurement along the Y direction, as shown in Figure 2A. In this case, the first set 204 and second set 206 of periodic features in cells 202b and 202d, which have periodicity along a first measurement direction (e.g., the X direction), may be referred to as periodic features in the first direction, while the first set 204 and second set 206 of periodic features in cells 202a and 202c, which have periodicity along a second measurement direction (e.g., the Y direction), may be referred to as periodic features in the second direction.

[0032] The first set 204 and the second set 206 of periodic features within any particular cell 202 can be placed on any layer of the sample 110. For example, the first set 204 and the second set 206 of periodic features may be located on a common layer of the sample 110 to facilitate overlay measurements between the first and second lithography exposures in a multiple exposure processing flow. As another example, the first set 204 of periodic features may be placed on the first layer of the sample 110, and the second set 206 of periodic features may be placed on the second layer of the sample 110, in order to facilitate overlay measurements between the first and second layers. Furthermore, a first set 204 and a second set 206 of periodic features associated with a first measurement direction (e.g., periodic features in the first direction) may be placed in the first set of layers of sample 110, while a first set 204 and a second set 206 of periodic features associated with a second measurement direction (e.g., periodic features in the second direction) may be placed in the second set of layers of sample 110, which may be the same as or different from the periodic features in the first direction. As an example, cells 202b and 202d may include a first set of periodic features 204 in the first layer 210 of sample 110 and a second set of periodic features 206 in the second layer 212 of sample 110, while cells 202a and 202c may include a first set of periodic features 204 in the first layer 210 of sample 110 and a second set of periodic features 206 in the third layer (not specified) of sample 110.

[0033] In some embodiments, the overlay target 104 includes various configurations of printed elements oriented along different directions. For example, cells 202b and 202d may include a first set 204 of periodic features in the first layer 210 and a second set 206 of periodic features in the second layer 212, while cells 202a and 202c may include a first set 204 of periodic features in the first layer 210 and a second set 206 of periodic features in the third layer of sample 110. In this way, the overlay target 104 can facilitate simultaneous overlay measurements between multiple pairs of different layers.

[0034] Furthermore, the pitches of the first set 204 and the second set 206 of periodic features within any given cell 202 may be the same or different. For example, Figure 2A shows the configuration of the overlay target 104 in which the first set 204 and the second set 206 of periodic features within each of cells 202a to d have a common pitch. However, the first set 204 and the second set 206 of periodic features may have different pitches.

[0035] In some embodiments, a first set 204 and a second set 206 of periodic features within any particular cell 202 are formed in different layers of the sample 110. For example, the first set 204 and the second set 206 of periodic features within any particular cell 202 may be formed in at least partially overlapping regions of the sample to generate a grating-over-grating structure, or they may be formed in non-overlapping regions. In this configuration, the pitches of the first set 204 and the second set 206 of periodic features may be the same or different. As an example, a configuration in which the first set 204 and the second set 206 of periodic features have different pitches may form a moiré structure. Such a moiré structure may produce moiré diffraction (e.g., double diffraction, composite diffraction, etc.) associated with diffraction from both the first set 204 and the second set 206 of periodic features. This specification envisions that various overlay techniques (e.g., associated with various measurement recipes) can utilize any combination of diffraction lobes from constituent features (e.g., a first set of periodic features 204 and a second set of periodic features 206) either alone or in combination with moiré diffraction lobes. For example, a first measurement recipe may utilize primary diffraction lobes from each of the constituent features, while a second measurement recipe may utilize moiré diffraction lobes either alone or in combination with diffraction lobes from one or more of the constituent features.

[0036] Figure 2B is a top view of a cell 202 of an overlay target 104 having a moiré structure 208 according to one or more embodiments of the present disclosure. Figure 2C is a side view of the cell 202 of Figure 2B according to one or more embodiments of the present disclosure. In particular, Figures 2B and 2C show the pitch of a first set 204 of periodic features (e.g., the grid of the first layer) in a first layer 210 of sample 110, and the pitch of a second set 206 of periodic features (e.g., the grid of the second layer) on a second layer 212 of sample 110, as P and Q, respectively. Figure 2B further shows a substrate 214 with various layers deposited. In some embodiments, though not explicitly shown, the overlay target 104 includes two cells 202 that provide inverted pairs of moiré structures for each measurement direction. For example, the first cell 202 may include a first set 204 of periodic features having pitch P and a second set 206 of periodic features having pitch Q, while the second cell 202 may include a first set 204 of periodic features having pitch Q and a second set 206 of periodic features having pitch P.

[0037] Referring to Figures 2A to 2C as a whole, the overlay target 104 may generally include known overlay target designs suitable for image-based diffraction. For example, the overlay target 104 may include, but is not limited to, advanced imaging measurement (AIM) targets, triple AIM targets with features on three layers, and robust AIM (rAIM) targets with one or more moiré structures.

[0038] Referring here to Figure 1B, various embodiments of the overlay measurement tool 102 according to one or more embodiments of the present disclosure are described.

[0039] Figure 1B is a conceptual diagram showing an overlay measurement tool 102 according to one or more embodiments of the present disclosure. In one embodiment, the overlay measurement tool 102 includes an illumination source 108 configured to produce at least one illumination beam 106. The illumination from the illumination source 108 may include one or more selected wavelengths of light, including but not limited to ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0040] In another embodiment, the overlay measurement tool 102 directs illumination from the illumination source 108 to the overlay target 104 via the illumination path 122. The illumination path 122 may include one or more optical components suitable for deforming and / or adjusting the illumination beam 106 and further directing the illumination beam 106 to the sample 110. In one embodiment, the illumination path 122 includes one or more illumination path lenses 124 (for example, for collimating the illumination, for relaying the pupil plane and / or field plane). In another embodiment, the illumination path 122 includes one or more illumination path optical elements 126 for shaping or otherwise controlling the illumination. For example, the illumination path optical elements 126 may include, but are not limited to, one or more field diaphragms, one or more pupil diaphragms, 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., stationary mirrors, translational mirrors, scanning mirrors, etc.). Furthermore, the illumination path optical element 126 may be placed in any suitable location, including but not limited to the illumination pupil surface 128 or the illumination field of view.

[0041] In another embodiment, the overlay measurement tool 102 includes an objective lens 130 that focuses illumination onto the overlay target 104. In yet another embodiment, the sample 110 is placed on a sample stage 132 which is suitable for fixing the sample 110 and is further configured to position the overlay target 104 relative to the illumination beam 106.

[0042] In some embodiments, the overlay measurement tool 102 includes at least one detector 114 for capturing light or other illumination (e.g., measurement light 112) emitted from the overlay target 104 via a focusing path 134. The focusing path 134 may include one or more optical elements suitable for deforming and / or adjusting the measurement light 112 from the overlay target 104. In one embodiment, the focusing path 134 includes one or more focusing path lenses 136 (e.g., for collimating the illumination beam 106, for relaying the pupil plane and / or field plane), which may include, but are not required to include, an objective lens 130. In another embodiment, the focusing path 134 includes one or more focusing path optical elements 138 for shaping or otherwise controlling the measurement light 112. For example, the focusing path optical element 138 may include, but is not limited to, one or more field diaphragms, one or more pupil diaphragms, 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., stationary mirrors, translational mirrors, scanning mirrors, etc.). Furthermore, the focusing path optical element 138 may be placed in any suitable location, including, but not limited to, a focusing pupil surface 140 or a focusing field surface (not shown).

[0043] The detector 114 can be placed at any selected location within the light-gathering path 134. In some embodiments, the overlay measurement tool 102 includes the detector 114 in the field of view (e.g., the plane conjugate to the sample 110) to generate an image of the overlay target 104.

[0044] The illumination path 122 and focusing path 134 of the overlay measurement tool 102 can be oriented in a wide range of configurations suitable for illuminating the sample 110 with the illumination beam 106 and focusing the light emitted from the sample 110 in response to the incident illumination beam 106. For example, as shown in Figure 1B, the overlay measurement tool 102 may include a beam splitter 142 in which a common objective lens 130 is oriented to simultaneously direct the illumination beam 106 towards the sample 110 and focus the light from the sample 110. As another example, the illumination path 122 and focusing path 134 may include non-overlapping optical paths.

[0045] Furthermore, the illumination path 122 and / or the focusing path 134 may include one or more channels. For example, the illumination path 122 may provide two or more illumination beams 106 from a single illumination channel or through multiple dedicated illumination channels. As another example, the focusing path 134 may include a single detector 114 in a single focusing channel or multiple detectors 114 distributed across multiple focusing channels.

[0046] As an example, Figure 1B shows an overlay measurement tool 102 having a single focusing channel 144. Figure 1C is a conceptual diagram of an overlay measurement tool 102 including two focusing channels 144 according to one or more embodiments of the present disclosure. For example, the overlay measurement tool 102 may include one or more beam splitters 146 for splitting the measurement light 112 into at least two focusing channels 144. Furthermore, each focusing channel 144 may include individual focusing path optical elements 138 (e.g., polarizers, spectral filters, attenuation filters, cutoff sections, apertures, etc.) to individually deform the measurement light 112 within each focusing channel 144 to provide direction-separated imaging. The use of multiple focusing channels 144 is intended to provide greater flexibility for generating direction-separated images than with a single focusing channel 144, but this may add further complexity. Thus, specific implementations of the systems and methods disclosed herein can be selected or adapted to the tolerances of a particular application.

[0047] Referring here to Figures 3A to 9, overlay measurements based on orientation-separated imaging of features oriented along different directions, according to one or more embodiments of this disclosure, are described in more detail.

[0048] In this specification, it is intended that periodic structures on the overlay target 104 (e.g., a first set of periodic features 204 and a second set of periodic features 206, shown in Figures 2A-2C) can generate discrete diffraction orders when illuminated by an illumination beam 106 having a narrow spectral range and a limited angular range. Furthermore, the specific arrangement of diffraction orders of the illumination beam 106 at the focusing pupil plane 140 may be influenced by various properties of the illumination beam 106 (e.g., spectrum, polarization, incident angle in the azimuthal and / or altitude directions, numerical aperture (NA), etc.), various properties of the focusing path 134 (e.g., NA of the objective lens 130, etc.), or various properties of the overlay target 104 (e.g., pitch of printed features, orientation of printed features relative to the incident illumination beam 106, etc.).

[0049] As an example, Figures 3A and 3B illustrate the effect of the altitude incidence angle on the distribution of diffraction orders from a grating (e.g., on an overlay target 104). Figure 3A is a conceptual diagram of focusing diffraction orders from a perpendicularly incident illumination beam 106 according to one or more embodiments of the present disclosure. Figure 3B is a conceptual diagram of focusing diffraction orders from an obliquely incident illumination beam 106 according to one or more embodiments of the present disclosure. In particular, Figures 3A and 3B illustrate the incident angle-based control of a specific diffraction order focused by the objective lens 130.

[0050] Thus, in some embodiments, the overlay measurement tool 102 and / or sample are configured, according to the measurement recipe, to achieve focusing of a selected diffraction order to facilitate directional separation imaging.

[0051] In some embodiments, the overlay measurement tool 102 simultaneously illuminates the overlay target 104 with two or more illumination beams 106, in which case the various parameters of each illumination beam 106 are configured to facilitate the separation of diffraction orders of the illumination beams 106 along different directions (e.g., at the focusing pupil plane 140). The various parameters of the objective lens 130 and / or focusing path 134 can then be configured to provide direction-separated imaging on one or more detectors 114, in which case a grating having a particular grating direction is imaged exclusively with light from a particular illumination beam 106.

[0052] This specification intends to show that directional separation imaging can be performed using various configurations of the overlay measurement tool 102.

[0053] In some embodiments, the overlay measurement tool 102 is configured such that the objective lens 130 focuses only on selected diffraction orders, associated with each illumination beam 106 that provides direction-separated imaging as disclosed herein. In such a configuration, the objective lens 130 can provide direction-separated imaging using a single detector 114, in which case portions of the generated image associated with grating structures having different grating directions are imaged based on different illumination beams 106.

[0054] Figures 4A and 4B illustrate directional separation imaging of a moiré pattern (for example, as shown in Figures 2B and 2C) based on illumination beams 106 having different azimuthal incidence angles, according to one or more embodiments of the present disclosure. In particular, Figure 4A shows a configuration in which the objective lens 130 focuses only on selected diffraction orders associated with each illumination beam 106 that provides directional separation imaging.

[0055] Figure 4A is a conceptual diagram of an illumination pupil plane 128, including two illumination beams 106a, b positioned within the illumination pupil boundary 402 to provide oblique illumination along orthogonal azimuthal directions, according to one or more embodiments of the present disclosure. Figure 4B is a conceptual diagram of a focusing pupil plane 140, showing directional separation imaging based on the illumination profile of Figure 4A, according to one or more embodiments of the present disclosure. For example, Figure 4B shows diffraction lobes generated in response to the illumination of the overlay target 104 shown in Figure 2A.

[0056] As shown in Figure 4B, illumination of the overlay target 104 by illumination beam 106a results in diffraction lobes 404 distributed along both the X and Y directions. However, only the selected diffraction order along the X direction is available, along with the focusing pupil boundary 406, and therefore contributes to the formation of an image of the corresponding structure. Similarly, illumination of the overlay target 104 by illumination beam 106b results in diffraction lobes 408 distributed along both the X and Y directions, but only the selected diffraction order along the Y direction is available, along with the focusing pupil boundary 406, and therefore contributes to the formation of an image of the corresponding structure.

[0057] In this way, the portion of the feature image distributed along the X direction is optically separated from the portion of the feature image distributed along the Y direction. In other words, the lattice information is coded for each illumination condition provided by the selection of diffraction order contributing to image formation. As a result, various image quality metrics associated with features oriented along the X direction may depend entirely (or at least substantially) on the selected diffraction order from the illumination beam 106a, and image quality metrics associated with features oriented along the Y direction may depend entirely (or at least substantially) on the selected diffraction order from the illumination beam 106b.

[0058] A general reference to Figures 3A to 4B will make it clear that these figures are provided for illustrative purposes only and should not be interpreted as limiting. For example, in Figures 4A and 4B, the main difference between the illumination conditions associated with illumination beams 106a and 106b is the azimuthal incidence angle. However, it is intended herein that direction-dependent illumination separation imaging can be achieved using multiple illumination beams 106 having illumination conditions distinguished based on any combination of parameters including, but not limited to, NA, beam shape, wavelength, spectral bandwidth, polarization, or intensity. Furthermore, such distinctions of illumination conditions can be achieved using any technique known in the art, including, but not limited to, illumination path optical elements 126 or the direct generation of illumination beams 106 having different illumination conditions.

[0059] Furthermore, the overlay measurement tool 102 may include a focusing path 134 of various configurations to further separate the diffraction lobes selected to provide direction-separated imaging.

[0060] In some embodiments, the focusing path 134 includes one or more focusing path optical elements 138 for filtering or blocking selected diffraction lobes at the focusing pupil plane 140 (e.g., those focused by the objective lens 130 but nevertheless undesirable for certain imaging techniques). For example, as described in more detail below, it may be desirable to block zero-order diffracted light (e.g., specular reflection) along one or more directions to ensure optical separation and / or to perform dark-field imaging.

[0061] In some embodiments (for example, as shown in Figure 1C), the overlay measurement tool 102 includes multiple focusing channels 144. Thus, each focusing channel 144 may include various focusing path optical elements 138 for filtering or blocking various diffraction lobes. For example, each focusing channel 144 may provide a grating image along different selected directions based on diffracted light from different illumination beams 106.

[0062] Referring here to Figures 5A to 5F, various techniques for providing direction-dependent illumination separation imaging according to one or more embodiments of this disclosure are described in more detail. It should be noted that Figures 5A to 5F depict distinctions of illumination conditions based on both azimuthal incidence angle and additional characteristics, but it should be understood that distinctions based on azimuthal incidence angle are not essential.

[0063] Figures 5A to 5F illustrate a variety of non-limiting techniques for distinguishing illumination beams 106 based on their location, size, shape, or orientation within the illumination pupil plane 128.

[0064] Figure 5A is a conceptual diagram of an illumination pupil 128 showing a direction-dependent illumination beam 106 having a rotated configuration according to one or more embodiments of the present disclosure. In particular, Figure 5A shows an illumination lobe distribution similar to that of Figure 4A, but in this case, the illumination beams 106a and 106b are rotated with respect to the grid direction of the overlay target 104 (e.g., the X and Y directions shown in Figure 2A). It should be noted that although the illumination beams 106a and 106b are rotated with respect to the grid direction of the overlay target 104, the associated diffraction lobes are still distributed along the grid direction. However, using rotated lobes may allow for further separation of diffraction orders at the focusing pupil 140, and such use may be suitable depending on the application.

[0065] Figure 5B is a conceptual diagram of an illumination pupil plane 128 showing a directionally dependent illumination beam 106 distinguished based on NA, according to one or more embodiments of the present disclosure. In particular, Figure 5B shows apertures 502a, b having different sizes (labeled NA1, NA2) for providing illumination beams 106a, b. Furthermore, apertures 502a, b may be implemented as separate elements or by spatially selective elements.

[0066] Furthermore, although not shown, the illumination beams 106a and 106b can generally have any selected shape at the illumination pupil 128 that can correspond to the shape of the associated diffraction order. For example, the shape of the illumination beams 106a and 106b at the illumination pupil 128 may include, but is not limited to, a circle, an ellipse, or a cat's eye (e.g., a geometric lens). Furthermore, the illumination beams 106a and 106b may have the same shape or different shapes. In some embodiments, the shape of the illumination beams 106a and 106b at the illumination pupil 128 is controlled by apertures 502a and 102b at the illumination pupil 128.

[0067] Figure 5C is a conceptual diagram of an illumination pupil 128 showing direction-dependent illumination beams 106 distinguished based on inclination, according to one or more embodiments of the present disclosure. In particular, Figure 5C shows apertures 504a, b at different radial positions (indicated as θ1, θ2) within the illumination pupil 128 for providing illumination beams 106a, b with different elevation incidence angles. Furthermore, apertures 502a, b may be implemented as separate elements or by spatially selective elements.

[0068] Figure 5D is a conceptual diagram of an illumination pupil plane 128 showing directionally dependent illumination beams 106 distinguished based on spectral characteristics, according to one or more embodiments of the present disclosure. In particular, Figure 5D shows spectral filters 506a, b (labeled BW1, BW2) for imparting different spectral characteristics to illumination beams 106a, b. Spectral filters 506a, b can be any type of spectral filter, including but not limited to high-pass filters, low-pass filters, band-pass filters, or band-reject filters. Thus, spectral filters 506a, b can distinguish illumination beams 106a, b based on spectral characteristics such as center wavelength or bandwidth, but are not limited to these. Furthermore, spectral filters 506a, b can be implemented as separate elements or by spatially selective elements.

[0069] Figure 5E is a conceptual diagram of an illumination pupil plane 128 showing intensity-based, direction-dependent illumination beams 106 according to one or more embodiments of the present disclosure. In particular, Figure 5E shows attenuation filters 508a, b (labeled ND1, ND2) for assigning different intensities to illumination beams 106a, b. Furthermore, the attenuation filters 508a, b may be implemented as separate elements or by spatially selective elements.

[0070] Figure 5F is a conceptual diagram of an illumination pupil plane 128 showing polarization-based, direction-dependent illumination beams 106 according to one or more embodiments of the present disclosure. In particular, Figure 5F shows polarizers 510a, b (labeled S, P) for imparting different polarizations (e.g., orthogonal polarizations) to illumination beams 106a, b. Furthermore, polarizers 510a, b may be implemented as separate elements or by spatially selective elements.

[0071] Referring to Figures 4A to 5F in general, it is intended herein that the overlay measurement tool 102 can generally implement any combination of such techniques. For example, Figures 4A to 5C may generally be suitable for manipulating the distribution of diffraction lobes focused by the objective lens 130, and thus available to contribute to imaging. However, as will be described in more detail below, it may be desirable to perform additional filtering and / or blocking of the focused diffraction lobes, either to implement completely isolated direction-by-direction imaging or to implement specific imaging techniques. Figures 5D to 5F may generally be suitable for manipulating additional properties of illumination beams 106a,b so that associated diffraction lobes can be separated and / or filtered by additional elements in any focusing channel 144.

[0072] Referring here to Figures 6 to 8C, various non-limiting imaging modes based on directional separation imaging according to one or more embodiments of the present disclosure are described in more detail. Figures 6 to 8C are based on illumination having the profile shown in Figure 4A. Furthermore, Figures 6 to 7B show imaging of an overlay target 104 having periodic features of a common pitch (e.g., as shown in Figure 2A), while Figures 8A to 8C show imaging of an overlay target 104 having periodic features of different pitches (e.g., a moiré structure as shown in Figures 2B to 2C).

[0073] In Figures 6 to 8C, the overlay target 104 being imaged includes a periodic structure oriented along orthogonal grid directions (for example, the X and Y directions as shown in Figures 2A to 2C).

[0074] This specification intends to extend the principles disclosed herein relating to direction-separated imaging to a wide range of imaging techniques in general. Therefore, it should be understood that Figures 6–8C are provided for illustrative purposes only and should not be construed as limiting.

[0075] Figure 6 is a conceptual diagram of a focusing pupil plane 140 showing direction-separated imaging in oblique brightfield imaging mode based on the illumination distribution shown in Figure 4A, according to one or more embodiments of the present disclosure. In particular, Figure 6 shows the configuration of an overlay measurement tool 102 (e.g., based on a measurement recipe), in which a zero-order diffraction lobe 602 (e.g., specular reflection) and a first-order diffraction lobe 604 of a first illumination beam 106a with a periodic structure in the X direction (e.g., cells 202b, d in Figure 2A) and a zero-order diffraction lobe 606 and a first-order diffraction lobe 608 of a second illumination beam 106b with a periodic structure in the Y direction (e.g., cells 202a, c in Figure 2A) are exclusively provided.

[0076] Thus, the first illumination beam 106a forms an image (or part thereof) of a periodic structure in the X direction (e.g., cells 202b and d in Figure 2A), while the second illumination beam 106b forms an image (or part thereof) of a periodic structure in the Y direction (e.g., cells 202a and c in Figure 2A).

[0077] However, it should be noted that a single image based on the focusing pupil plane 140 in Figure 6 may exhibit residual DC bias originating from the zero-order diffraction lobes 602 and 606 from orthogonal directions. For example, images of periodic structures in the X direction may be affected by residual DC bias associated with the zero-order diffraction lobe 606. Similarly, images of periodic structures in the Y direction may be affected by residual DC bias associated with the zero-order diffraction lobe 602. Depending on the application, such residual DC bias may be within operating tolerances and may be acceptable.

[0078] However, depending on the application, the overlay measurement tool 102 may include one or more additional elements to remove or mitigate this residual DC bias. In some embodiments, the overlay measurement tool 102 imparts orthogonal polarization to the illumination beams 106a,b (for example, as shown in Figure 5F) to provide polarization separation. Furthermore, the focusing path 134 may include, but is not required, one or more polarizers to separate diffraction lobes from the illumination beams 106a,b. For example, the overlay measurement tool 102 may include two focusing channels and one or more polarizers (for example, a beam splitter 146 or other focusing path optical element 138 located at any suitable location) so that detectors 114 in two focusing channels 144 image the overlay target 104 individually with orthogonal polarization. As another example, the focusing path 134 may include a structured image plane (e.g., field of view) polarizer that provides different polarization directions corresponding to the locations of associated periodic features in the image plane.

[0079] In some embodiments, the overlay measurement tool 102 (for example, as shown in Figure 5D) imparts different spectral content (e.g., center wavelength, bandwidth, etc.) to the illumination beams 106a and b. In this case, the overlay measurement tool 102 may include spectral filters for separation based on spectral content. For example, in a configuration having two focusing channels 144, different spectral filters placed in the dichroic beam splitter 146 and / or different focusing channels 144 may provide separate images of orthogonal target features.

[0080] Figures 7A and 7B illustrate directional separation imaging in dark-field imaging mode according to one or more embodiments of the present disclosure. Figure 7A is a conceptual diagram of a focusing pupil 140 showing the configuration of an overlay measurement tool 102 focused by an objective lens 130 according to one or more embodiments of the present disclosure. In particular, Figure 7A shows the configuration of the overlay measurement tool 102 (e.g., based on a measurement recipe), in which the focusing pupil 140 includes zero-order diffraction lobes 702, first-order diffraction lobes 704, and second-order diffraction lobes 706 of a first illumination beam 106a with a periodic structure in the X direction (e.g., cells 202b, d in Figure 2A), and zero-order diffraction lobes 708, first-order diffraction lobes 710, and second-order diffraction lobes 712 of a second illumination beam 106b with a periodic structure in the Y direction (e.g., cells 202a, c in Figure 2A).

[0081] Figure 7B is a conceptual diagram of the focusing pupil plane 140 of Figure 7A, in which zero-order diffraction lobes are blocked to provide dark-field imaging, according to one or more embodiments of the present disclosure. For example, Figure 7B shows a blocking portion 714 in the focusing pupil plane 140 (e.g., part of the focusing path optical element 138) for selectively blocking zero-order diffraction lobes 702, 708. This blocking portion 714 can generally have any shape and can be formed from any number of elements. Thus, the specific configuration shown in Figure 7B is not limiting to the present disclosure.

[0082] In this configuration, the image (or a portion thereof) of the periodic structure in the X direction (e.g., cells 202b and d in Figure 2A) is formed by the first illumination beam 106a alone, while the image (or a portion thereof) of the periodic structure in the Y direction (e.g., cells 202a and c in Figure 2A) is formed by the second illumination beam 106b alone. In particular, by blocking the zero-order diffraction lobes 702 and 708, any residual effects of orthogonal structures are eliminated. Furthermore, the resulting dark-field image will have perfect contrast (e.g., 100% contrast).

[0083] Figure 8A is a conceptual diagram of the generation of various diffraction lobes according to one or more embodiments of the present disclosure. Figure 8B is a conceptual diagram of a focusing pupil plane 140 showing direction-separated imaging in optical moiré mode based on the diffraction lobes shown in Figure 8A, according to one or more embodiments of the present disclosure. For example, the overlay target 104 may include lattice superposition features (e.g., moiré structures) with different pitches as shown in Figures 2B-2C, but may include different cells 202 having moiré structures oriented along orthogonal directions (e.g., X and Y directions). In particular, Figure 8B shows the configuration of the overlay measurement tool 102 (based on, for example, a measurement recipe), in which the focusing pupil plane 140 includes a zero-order diffraction lobe 802, a first-order diffraction lobe 804 (marked 1) of the first illumination beam 106a from a first set 204 of periodic features distributed along the X direction, and a first-order diffraction lobe 806 (marked 1') of the first illumination beam 106a from a second set 206 of periodic features distributed along the X direction. Figure 8B further shows a zero-order diffraction lobe 808, a first-order diffraction lobe 810 (marked 1) of the second illumination beam 106b from a first set 204 of periodic features distributed along the Y direction, and a first-order diffraction lobe 812 (marked 1') of the second illumination beam 106b from a second set 206 of periodic features distributed along the Y direction.

[0084] Figure 8C is a conceptual diagram of the focusing pupil 140 of Figure 8B, according to one or more embodiments of the present disclosure, including a shielding section 814 for selectively blocking zero-order diffraction lobes 802, 808 in the focusing pupil 140. This shielding section 814 can generally have any shape and can be formed from any number of elements. Thus, the specific configuration shown in Figure 8 is not limiting to the present disclosure. In this configuration, the image (or part thereof) of periodic structures in the X direction is formed by the first illumination beam 106a alone, while the image (or part thereof) of periodic structures in the Y direction is formed by the second illumination beam 106b alone. In particular, blocking the zero-order diffraction lobes 802, 808 eliminates any residual effects of orthogonal structures. Furthermore, as already described herein, the images of structures in the X and Y directions within one or two focusing channels 144 can be further separated using various identification parameters of the illumination beams 106a, b, such as spectral content or polarization, but not limited to these.

[0085] A general reference to Figures 4A through 8C should reveal that the imaging configurations shown are provided for illustrative purposes only and should not be interpreted as limiting. For example, direction-separated imaging can be extended to other imaging modes that utilize different combinations of diffraction orders for each direction. Another example is when it may be desirable to provide images under symmetrical oblique illumination conditions.

[0086] Figure 9 is a conceptual diagram of an illumination pupil plane 128, including four illumination beams 106a, b, c, and d positioned to provide symmetrical oblique illumination along orthogonal azimuthal directions, according to one or more embodiments of the present disclosure. For example, Figure 9 may represent a symmetrical variation of the illumination distribution in Figure 4A.

[0087] In some embodiments, the overlay target 104 is illuminated simultaneously by all four illumination beams 106a, b, c, and d, in which case a directionally separated image is generated within one or more focusing channels 144, as disclosed herein. For example, the oblique bright-field imaging mode shown in Figure 6 may be suitable for simultaneous illumination by illumination beams 106a, b, c, and d, but is not limited thereto.

[0088] In some embodiments, the overlay target 104 is sequentially illuminated by symmetrically opposing illumination beams 106. For example, the overlay target 104 may first be illuminated with illumination beams 106a and 106b to form a first set of directionally separated images within one or more focusing channels 144, and then illuminated with illumination beams 106c and 106d to form a second set of directionally separated images within one or more focusing channels 144. The resulting images can then be analyzed together to provide an overlay measurement.

[0089] Referring again to Figures 1A and 1B, various additional components of the overlay measurement system 100 according to one or more embodiments of the present disclosure are described in more detail.

[0090] The illumination source 108 may include any type of illumination source suitable for providing at least one illumination beam 106. In one embodiment, the illumination source 108 is a laser source. For example, the illumination source 108 may include, but is not limited to, one or more narrowband laser sources, broadband laser sources, ultra-broadband laser sources, white light laser sources, etc. In this context, the illumination source 108 may provide an illumination beam 106 having high coherence (e.g., high spatial coherence and / or temporal coherence). In another embodiment, the illumination source 108 includes a laser-sustained plasma (LSP) source. For example, the illumination source 108 may include, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for housing one or more elements that can emit broadband illumination when excited to a plasma state by a laser source. In another embodiment, the illumination source 108 includes a lamp source. For example, the illumination source 108 may include, but is not limited to, an arc lamp, a discharge lamp, an electrodeless lamp, etc. In this context, the illumination source 108 may provide an illumination beam 106 having low coherence (e.g., low spatial coherence and / or temporal coherence).

[0091] The overlay measurement tool 102 can generate two or more illumination beams 106 using any technique known in the art. Furthermore, the illumination beams 106 can be arranged in any configuration, including but not limited to dipole illumination and orthogonal illumination.

[0092] In some embodiments, the illumination source 108 directly generates two or more illumination beams 106. In some embodiments, the overlay measurement tool 102 includes two or more apertures on the illumination pupil plane 128 (e.g., illumination path optical element 126) for splitting the illumination from the illumination source 108 into two or more illumination beams 106 or illumination lobes. Furthermore, the spatial profiles of one or more illumination beams 106 on the sample 110 can be controlled by a field plane aperture to have any selected spatial profile.

[0093] In some embodiments, the illumination source 108 provides light to two or more optical fibers, in which case the light output from each optical fiber is an illumination lobe of the illumination beam 106. For example, the output surface of an optical fiber may be within or imaged onto the illumination pupil plane 128. In some embodiments, the overlay measurement tool 102 diffracts the illumination from the illumination source 108 into two or more diffraction orders, in which case the illumination beam 106 is formed from at least some of the diffraction orders of the light source. The efficient generation of multiple illumination lobes by controlled diffraction is described in general terms in U.S. Patent No. 11,118,903, “EFFICIENT ILLUMINATION SHAPING FOR SCATTEROMETRY OVERLAY,” issued on 14 September 2021, which is incorporated herein by reference.

[0094] The overlay measurement tool 102 may generally include any number or type of detectors 114 suitable for capturing light from the sample 110 exhibiting the overlay. In one embodiment, the detectors 114 include one or more detectors 114 suitable for characterizing a stationary sample. In this context, the overlay measurement tool 102 may operate in stationary mode, with the sample 110 stationary during measurement. For example, the detectors 114 may include, but are not limited to, a two-dimensional pixel array, such as a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) device. In this context, the detectors 114 may generate a two-dimensional image in a single measurement. In one embodiment, the detectors 114 may include, but are not limited to, one or more detectors 114 suitable for characterizing a moving sample (e.g., a scanned sample), such as a 2D pixel array or a time-delay integral (TDI) detector. In this context, the overlay measurement tool 102 may operate in scanning mode, with respect to the measurement field of view during measurement.

[0095] In another embodiment, the overlay measurement tool 102 includes a scanning subsystem for scanning the sample 110 with respect to the measurement field during measurement. For example, the sample stage 132 can position and orient the sample 110 within the focusing volume of the objective lens 130. In another embodiment, the sample stage 132 includes, but is not limited to, one or more adjustable stages such as a linear translation stage, a rotation stage, or a tip / tilt stage. In another embodiment, although not shown, the scanning subsystem includes one or more beam scanning optical elements (e.g., a rotatable mirror, a galvanometer, etc.) for scanning the illumination beam 106 with respect to the sample 110.

[0096] Figure 10 is a flowchart illustrating the steps performed in Method 1000 for Directional Separation Imaging according to one or more embodiments of the present disclosure. The applicant notes that embodiments and enabling techniques already described herein in the context of the overlay measurement system 100 are to be interpreted as extending to Method 1000. However, it should be further noted that Method 1000 is not limited to the architecture of the overlay measurement system 100.

[0097] In some embodiments, method 1000 includes step 1002 of illuminating an overlay target on a sample with one or more first illumination beams and one or more second illumination beams, wherein the overlay target includes a first-direction periodic feature in a first set of layers of sample distributed along a first measurement direction, and a second-direction periodic feature in a second set of layers of sample distributed along a second measurement direction different from the first measurement direction. In this way, the overlay target can generate diffraction lobes of the first and second illumination beams in both the X and Y directions. Step 1002 may further include illuminating the overlay target simultaneously with the first and second illumination beams.

[0098] Overlay targets can generally include known overlay target designs suitable for image-based diffraction. For example, overlay targets can include, but are not limited to, advanced imaging measurement (AIM) targets, triple AIM targets with features on three layers, and robust AIM (rAIM) targets with one or more moiré structures. Furthermore, overlay targets can include periodic features on any number of layers, in which case periodic features in one measurement direction (e.g., the X direction) do not need to be on the same layer as periodic features in another measurement direction (e.g., the Y direction).

[0099] In some embodiments, Method 1000 includes step 1004 of generating one or more images of an overlay target on one or more detectors based on the diffraction of one or more first illumination beams and one or more second illumination beams by an overlay target using one or more focusing optical elements, wherein the diffraction order of one or more first illumination beams contributes to the formation of a resolution image of only a first set of periodic features, and the diffraction order of one or more second illumination beams contributes to the formation of a resolution image of only a second set of periodic features. In some embodiments, the focusing optical elements, the overlay target, and the first and second illumination beams may be configured (e.g., according to a measurement recipe) such that the diffraction order of the first illumination beams by periodic features in a first direction is focused, but the diffraction order of the first illumination beams by periodic features in a second direction is not focused (e.g., outside the NA of the focusing optical element, outside the boundary of the focusing pupil, etc.). Similarly, the focusing optical element, overlay target, and first and second illumination beams may be configured (for example, according to a measurement recipe) such that the diffraction order of the second illumination beam by the periodic features in the first direction is not focused, but the diffraction order of the second illumination beam by the periodic features in the second direction is focused. In this way, the periodic structure in the first direction is resolvable only on the diffraction of the first illumination beam, while the periodic structure in the second direction is resolvable only on the diffraction of the second illumination beam.

[0100] In some embodiments, method 1000 includes step 1006 of generating a first overlay measurement along a first measurement direction based on one or more images. For example, step 1006 may include generating an overlay measurement based on a resolved periodic feature in the first direction based on a first illumination beam. In some embodiments, method 1000 includes step 1008 of generating a second overlay measurement along a second measurement direction based on one or more images. For example, step 1008 may include generating an overlay measurement based on a resolved periodic feature in the second direction based on a second illumination beam.

[0101] The subject matter described herein illustrates various components that, in some cases, are contained within or connected to other components. It should be understood that such configurations depicted are merely illustrative, and that in practice many other configurations can be implemented to achieve the same functionality. Conceptually, configurations of components that achieve the same functionality are effectively “associated” in such a way that the desired functionality is achieved. Thus, any two components combined herein to achieve a particular functionality, regardless of the configuration or intervening components, can be considered “associated” with each other in such a way that the desired functionality is achieved. Similarly, any two such associated components can be considered “connected” or “combined” with each other in such a way that the desired functionality is achieved, and any two such associable components can also be considered “combinable” with each other in such a way that the desired functionality is achieved. Specific examples of combinability include, but are not limited to, physically interactable and / or physically interacting components, as well as / or wirelessly interactable and / or wirelessly interacting components, as well as / or logically interactable and / or logically interacting components.

[0102] Many of the present disclosure and its associated advantages are understood from the above description, and it will be clear that various modifications can be made to the form, structure, and configuration of the components without departing from the disclosed subject matter or sacrificing all of its important advantages. The forms described are for illustrative purposes only, and such modifications are intended to be included in the following claims. Furthermore, it should be understood that the present invention is defined by the appended claims.

Claims

1. An overlay measurement tool configurable to perform a measurement recipe for evaluating the properties of an overlay target on a sample, wherein the overlay target according to the measurement recipe includes periodic features in a first direction in a first set of layers of the sample, the periodic features in the first direction being distributed along a first measurement direction, the overlay target according to the measurement recipe further includes periodic features in a second direction in a second set of layers of the sample, the periodic features in the second direction being distributed along a second measurement direction different from the first measurement direction, and the overlay measurement tool according to the measurement recipe, One or more illumination optical elements capable of illuminating the overlay target with one or more first illumination beams and one or more second illumination beams, wherein at least one of the first illumination beams and at least one of the second illumination beams simultaneously incident on the overlay target, and One or more focusing optical elements configured to generate one or more images of the overlay target on one or more detectors based on the diffraction of one or more first illumination beams and one or more second illumination beams by the overlay target, wherein one or more focusing optical elements generate an image of only periodic features in the first direction based on the diffraction order of the one or more first illumination beams, and generate an image of only periodic features in the second direction based on the diffraction order of the one or more second illumination beams. It includes an overlay measurement tool, A control device that is communicatively coupled to one or more detectors, and includes one or more processors configured to execute program instructions, wherein the program instructions are executed by the one or more processors, To generate a first overlay measurement along the first measurement direction based on one or more of the aforementioned images, and To generate a second overlay measurement along the second measurement direction based on one or more of the aforementioned images. A control device that makes it perform An optical measurement system characterized by comprising the following features.

2. An optical measurement system according to claim 1, characterized in that the first illumination beam and the second illumination beam are distinguished by the azimuthal incidence angle to the overlay target and at least one of the altitude incidence angle to the overlay target, wavelength, bandwidth, polarization, intensity, numerical aperture in the illumination pupil of one or more illumination optical elements, lobe shape in the illumination pupil, or inclination.

3. An optical measurement system according to claim 1, characterized in that the first illumination beam includes a single first illumination beam that provides a first azimuthal incidence angle to the overlay target, and the second illumination beam includes a single second illumination beam that provides a second azimuthal incidence angle to the overlay target.

4. An optical measurement system according to claim 3, characterized in that the first and second azimuthal incidence angles are orthogonal.

5. An optical measurement system according to claim 1, wherein the first illumination beam includes a first set of two illumination beams that provide a first set of azimuthal incidence angles symmetrically opposite to the overlay target, and the second illumination beam includes a second set of two illumination beams that provide a second set of azimuthal incidence angles symmetrically opposite to the overlay target.

6. An optical measurement system according to claim 5, characterized in that the first and second sets of azimuthal incidence angles are orthogonal.

7. An optical measurement system according to claim 5, wherein one or more illumination optical elements direct the first set of two illumination beams and the second set of two illumination beams simultaneously toward the overlay target when performing the measurement recipe.

8. An optical measurement system according to claim 5, characterized in that one or more illumination optical elements direct one of the first set of two illumination beams and one of the second set of two illumination beams to the overlay target as a first exposure, and the one or more illumination optical elements direct the other of the first set of two illumination beams and the other of the second set of two illumination beams to the overlay target as a second exposure.

9. An optical measurement system according to claim 1, characterized in that the one or more light-gathering optical elements include a single light-gathering channel, and the one or more detectors include a single detector.

10. An optical measurement system according to claim 1, wherein the one or more focusing optical elements include two focusing channels, the one or more detectors include two detectors, each of the two focusing channels includes one of the two detectors, the one or more focusing optical elements separate the diffraction order from the first illumination beam to the first of the two focusing channels and the diffraction order from the second illumination beam to the second of the two focusing channels, the first of the two focusing channels provides one or more images of the overlay target in which only periodic features in the first direction are resolved, and the second of the two focusing channels provides one or more images of the overlay target in which only periodic features in the second direction are resolved.

11. An optical measurement system according to claim 1, wherein, according to the measurement recipe, the overlay measurement tool is Two or more diffraction lobes along the first measurement direction, generated by periodic features in the first direction from each of the one or more first illumination beams, Two or more diffraction lobes along the second measurement direction, generated by periodic features in the second direction from each of the one or more second illumination beams, An optical measurement system characterized by exclusively focusing light.

12. An optical measurement system according to claim 1, wherein, according to the measurement recipe, the overlay measurement tool is A zero-order diffraction lobe and a first-order diffraction lobe along the first measurement direction, generated by periodic features in the first direction from each of the one or more first illumination beams, From each of the one or more second illumination beams, a zero-order diffraction lobe and a first-order diffraction lobe are generated by the periodic features in the second direction, along the second measurement direction. It exclusively focuses light, An optical measurement system characterized in that one or more images of the overlay target are oblique bright-field images.

13. An optical measurement system according to claim 1, wherein, according to the measurement recipe, the overlay measurement tool is A zero-order diffraction lobe, a first-order diffraction lobe, and a second-order diffraction lobe along the first measurement direction, generated by periodic features in the first direction from each of the one or more first illumination beams, From each of the one or more second illumination beams, a zero-order diffraction lobe, a first-order diffraction lobe, and a second-order diffraction lobe are generated by the second-direction periodic features and along the second measurement direction. It exclusively focuses light, The one or more focusing optical elements include one or more elements for blocking the zero-order diffraction lobes along the first and second measurement directions. An optical measurement system characterized in that one or more images of the overlay target are dark-field images.

14. An optical measurement system according to claim 1, wherein the periodic feature in the first direction includes a grid having a first pitch and a second pitch distributed along the first measurement direction such that a moiré structure in the first direction is formed, and the periodic feature in the second direction includes a grid having a first pitch and a second pitch distributed along the second measurement direction such that a moiré structure in the second direction is formed, and according to the measurement recipe, the overlay measurement tool is Associated with each of the one or more first illumination beams are a zero-order diffraction lobe, a first-order diffraction lobe from the grating having a first pitch in the moiré structure in the first direction, and a first-order diffraction lobe from the grating having a second pitch in the moiré structure in the first direction, Associated with each of the one or more second illumination beams are a zero-order diffraction lobe, a first-order diffraction lobe from the grating having the first pitch in the moiré structure in the second direction, and a first-order diffraction lobe from the grating having the second pitch in the moiré structure in the second direction. An optical measurement system characterized by exclusively focusing light.

15. An optical measurement system according to claim 14, wherein the one or more light-gathering optical elements further include one or more elements for blocking the zero-order diffraction lobes along the first and second measurement directions.

16. The optical measurement system according to claim 1, wherein the overlay target is An optical measurement system characterized by including at least one of an advanced imaging measurement (AIM) target, a triple AIM target, or a robust AIM (rAIM) target.

17. An optical measurement system according to claim 1, characterized in that the first and second sets of sample layers are a common set of sample layers.

18. An optical measurement system according to claim 1, characterized in that the first set of sample layers is different from the second set of sample layers.

19. An optical measurement system according to claim 18, characterized in that the first set of sample layers includes a first layer of the sample and a second layer of the sample, and the second set of sample layers includes the first layer of the sample and a third layer of the sample.

20. An optical measurement system according to claim 1, characterized in that at least one of the periodic features in the first or second direction includes features associated with different lithography exposures on a single layer.

21. One or more illumination optical elements configured to illuminate an overlay target on a sample with one or more first illumination beams and one or more second illumination beams when performing a measurement recipe, wherein at least one of the first illumination beams and at least one of the second illumination beams simultaneously incident on the overlay target, the overlay target according to the measurement recipe includes a first directional periodic feature in a first set of layers of the sample, the first directional periodic feature is distributed along a first measurement direction, and the overlay target according to the measurement recipe further includes a second directional periodic feature in a second set of layers of the sample, the second directional periodic feature is distributed along a second measurement direction different from the first measurement direction, When performing the measurement recipe, one or more focusing optical elements are configured to generate one or more images of the overlay target on one or more detectors based on the diffraction of one or more first illumination beams and one or more second illumination beams by the overlay target, and one or more focusing optical elements generate an image of only periodic features in the first direction based on the diffraction order of the one or more first illumination beams, and generate an image of only periodic features in the second direction based on the diffraction order of the one or more second illumination beams, A control device that is communicatively coupled to one or more detectors, and includes one or more processors configured to execute program instructions, wherein the program instructions are executed by the one or more processors, To generate a first overlay measurement along the first measurement direction based on one or more of the aforementioned images, and To generate a second overlay measurement along the second measurement direction based on one or more of the aforementioned images. A control device that makes it perform An optical measurement system characterized by comprising the following features.

22. Illuminating an overlay target on a sample with one or more first illumination beams and one or more second illumination beams, wherein at least one of the first illumination beams and at least one of the second illumination beams simultaneously incident on the overlay target, and the overlay target according to the measurement recipe includes periodic features in a first direction in a first set of layers of the sample, the periodic features in the first direction being distributed along a first measurement direction, and the overlay target according to the measurement recipe further includes periodic features in a second direction in a second set of layers of the sample, the periodic features in the second direction being distributed along a second measurement direction different from the first measurement direction, The method involves generating one or more images of the overlay target on one or more detectors based on the diffraction of one or more first illumination beams and one or more second illumination beams by the overlay target, wherein the method involves generating an image of only periodic features in a first direction based on the diffraction order of the one or more first illumination beams, and generating an image of only periodic features in a second direction based on the diffraction order of the one or more second illumination beams. To generate a first overlay measurement along the first measurement direction based on one or more of the aforementioned images, To generate a second overlay measurement along the second measurement direction based on one or more of the aforementioned images. An optical measurement method characterized by including

23. An optical measurement method according to claim 22, characterized in that the first illumination beam and the second illumination beam are distinguished by the azimuthal incidence angle to the overlay target and at least one of the altitude incidence angle to the overlay target, wavelength, bandwidth, polarization, intensity, numerical aperture in the illumination pupil of one or more illumination optical elements, lobe shape in the illumination pupil, or inclination.

24. An optical measurement method according to claim 22, characterized in that the first illumination beam includes a single first illumination beam that provides a first azimuthal incidence angle to the overlay target, and the second illumination beam includes a single second illumination beam that provides a second azimuthal incidence angle to the overlay target.

25. An optical measurement method according to claim 22, characterized in that the first illumination beam includes a first set of two illumination beams that provide a first set of azimuthal incidence angles symmetrically opposite to the overlay target, and the second illumination beam includes a second set of two illumination beams that provide a second set of azimuthal incidence angles symmetrically opposite to the overlay target.

26. The optical measurement method according to claim 25, wherein the overlay target on the sample is illuminated with one or more first illumination beams and one or more second illumination beams, An optical measurement method characterized by simultaneously directing the first set of two illumination beams and the second set of two illumination beams toward the overlay target.

27. The optical measurement method according to claim 25, wherein the overlay target on the sample is illuminated with one or more first illumination beams and one or more second illumination beams, Directing one of the first set of two illumination beams and one of the second set of two illumination beams towards the overlay target as the first exposure, The other of the first set of two illumination beams and the other of the second set of two illumination beams are directed towards the overlay target as a second exposure. An optical measurement method characterized by including

28. An optical measurement method according to claim 23, wherein one or more images of the overlay target are generated on one or more detectors based on the diffraction of one or more first illumination beams and one or more second illumination beams by the overlay target using one or more focusing optical elements, The one or more images of the overlay target Two or more diffraction lobes along the first measurement direction, generated by periodic features in the first direction from each of the one or more first illumination beams, Two or more diffraction lobes along the second measurement direction, generated by periodic features in the second direction from each of the one or more second illumination beams, An optical measurement method characterized by including the exclusive use of a certain element for generation.

29. An optical measurement method according to claim 23, wherein one or more images of the overlay target are generated on one or more detectors based on the diffraction of one or more first illumination beams and one or more second illumination beams by the overlay target using one or more focusing optical elements, The one or more images of the overlay target A zero-order diffraction lobe and a first-order diffraction lobe along the first measurement direction, generated by periodic features in the first direction from each of the one or more first illumination beams, From each of the one or more second illumination beams, a zero-order diffraction lobe and a first-order diffraction lobe are generated by the periodic features in the second direction, along the second measurement direction. This includes generating using exclusively, An optical measurement method characterized in that one or more images of the overlay target are oblique bright-field images.

30. An optical measurement method according to claim 23, wherein one or more images of the overlay target are generated on one or more detectors based on the diffraction of one or more first illumination beams and one or more second illumination beams by the overlay target using one or more focusing optical elements, The one or more images of the overlay target A zero-order diffraction lobe, a first-order diffraction lobe, and a second-order diffraction lobe along the first measurement direction, generated by periodic features in the first direction from each of the one or more first illumination beams, From each of the one or more second illumination beams, a zero-order diffraction lobe, a first-order diffraction lobe, and a second-order diffraction lobe are generated by the second-direction periodic features and along the second measurement direction. This includes generating using exclusively, The one or more focusing optical elements include one or more elements for blocking the zero-order diffraction lobes along the first and second measurement directions. An optical measurement method characterized in that one or more images of the overlay target are dark-field images.

31. An optical measurement method according to claim 23, wherein the periodic feature in the first direction includes a grid having a first pitch and a second pitch distributed along the first measurement direction such that a moiré structure in the first direction is formed, and the periodic feature in the second direction includes a grid having a first pitch and a second pitch distributed along the second measurement direction such that a moiré structure in the second direction is formed, and one or more images of the overlay target are generated on one or more detectors based on the diffraction of one or more first illumination beams and one or more second illumination beams by the overlay target using one or more focusing optical elements, The one or more images of the overlay target Associated with each of the one or more first illumination beams are a zero-order diffraction lobe, a first-order diffraction lobe from the grating having a first pitch in the moiré structure in the first direction, and a first-order diffraction lobe from the grating having a second pitch in the moiré structure in the first direction, Associated with each of the one or more second illumination beams are a zero-order diffraction lobe, a first-order diffraction lobe from the grating having the first pitch in the moiré structure in the second direction, and a first-order diffraction lobe from the grating having the second pitch in the moiré structure in the second direction. An optical measurement method characterized by including the exclusive use of a certain element for generation.

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