Multi-directional overlay metrology using multiple illumination parameters and isolated imaging

Abstract

An optical metrology system can include an overlay metrology tool for characterizing an overlay target on a sample, where the overlay target includes first direction periodic features in a first set of layers of the sample and second direction periodic features in a second set of layers of the sample. The overlay metrology tool can simultaneously illuminate the overlay target using first and second illumination beams and can further generate an image of the overlay target based on diffraction of the first and second illumination beams through the overlay target, where diffraction orders of the first illumination beam contribute to resolved image formation of only the first direction periodic features, and where diffraction orders of the second illumination beam contribute to resolved image formation of only the second direction periodic features. The system can further generate overlay measurements along first and second measurement directions based on the image.

Description

Technical Field

[0001] This disclosure generally relates to imaging overlay metrology and, more specifically, to simultaneous isolated imaging overlay metrology measurements along multiple directions. Background Technology

[0002] Image-based overlay metrology typically generates overlay measurements by imaging multiple features on samples manufactured using different lithographic exposures and determining the relative positions of the imaged features. In this way, overlay measurements can provide an indication of registration errors between lithographic exposures. However, the need to manufacture smaller feature sizes leads to tighter overlay tolerances. Therefore, there is a need to develop systems and methods that provide overlay metrology with high accuracy and processing power. Summary of the Invention

[0003] According to one or more illustrative embodiments of this disclosure, an optical metrology system is disclosed. In one illustrative embodiment, the system includes a superposition metrology tool for implementing a metrological formulation for characterizing superposition targets on a sample. According to one or more illustrative embodiments of this disclosure, the superposition target includes a first-direction periodicity feature distributed along a first measurement direction and a second-direction periodicity feature in a second set of layers of the sample. In another illustrative embodiment, the superposition metrology tool includes illumination optics for illuminating the superposition 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 simultaneously incident on the superposition target. In another illustrative embodiment, the superposition metrology tool further includes light-collecting optics configurable to generate an image of the superposition target on one or more detectors based on the diffraction of the first illumination beam and the second illumination beam through the superposition target. In another illustrative embodiment, the diffraction order of the first illumination beam contributes to the formation of a resolved image of only the first-direction periodicity feature, and the diffraction order of the second illumination beam contributes to the formation of a resolved image of only the second-direction periodicity feature. In another illustrative embodiment, the system further includes a controller for generating first and second stacked measurements along the first and second measurement directions based on the image.

[0004] According to one or more illustrative embodiments of this disclosure, an optical metrology system is disclosed. In one illustrative embodiment, the system includes illumination optics for illuminating a stacked target on a sample using a first illumination beam and a second illumination beam during the implementation of a metrology formulation, wherein at least one of the first illumination beams and at least one of the second illumination beams are simultaneously incident on the stacked target. In another illustrative embodiment, the stacked target according to the metrology formulation includes a first-direction periodic feature distributed along a first measurement direction and a second-direction periodic feature distributed along a second measurement direction different from the first measurement direction. In another illustrative embodiment, the system further includes light-collecting optics for generating an image of the stacked target on one or more detectors based on the diffraction of the first illumination beam and the second illumination beam through the stacked target. In another illustrative embodiment, the diffraction order of the first illumination beam contributes to the formation of a resolved image of only the first-direction periodic feature, and the diffraction order of the second illumination beam contributes to the formation of a resolved image of only the second-direction periodic feature. In another illustrative embodiment, the system further includes a controller for generating first and second stacked measurements along the first and second measurement directions based on the image.

[0005] According to one or more illustrative embodiments of this disclosure, an optical metrology method is disclosed. In one illustrative embodiment, the method includes illuminating a stacked target on a sample using a first illumination beam and a second illumination beam, wherein at least one of the first illumination beam and at least one of the second illumination beam are simultaneously incident on the stacked target. In another illustrative embodiment, the stacked target includes a first-direction periodic feature distributed along a first measurement direction and a second-direction periodic feature distributed along a second measurement direction different from the first measurement direction. In another illustrative embodiment, the method includes generating an image of the stacked target on one or more detectors based on the diffraction of the first illumination beam and the second illumination beam through the stacked target. In another illustrative embodiment, the diffraction order of the first illumination beam contributes to the formation of a resolved image of only the first-direction periodic feature, and the diffraction order of the second illumination beam contributes to the formation of a resolved image of only the second-direction periodic feature. In another illustrative embodiment, the method includes generating a first stacked measurement along the first measurement direction based on the one or more images. In another illustrative embodiment, the method includes generating a second stacked measurement along the second measurement direction based on the one or more images.

[0006] It should be understood that the foregoing overview and the following detailed description are merely exemplary and illustrative and do not necessarily limit the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the overview, serve to explain the principles of the invention. Attached Figure Description

[0007] Those skilled in the art will better understand several advantages of the present invention by referring to the accompanying drawings.

[0008] Figure 1A This is a conceptual diagram illustrating a stacked metering system according to one or more embodiments of the present disclosure.

[0009] Figure 1B This is a conceptual diagram illustrating a stacking measurement tool according to one or more embodiments of the present disclosure.

[0010] Figure 1C This is a conceptual diagram of a stacked metering tool comprising two optical collection channels according to one or more embodiments of the present disclosure.

[0011] Figure 2A It is a top view of a stack of targets having non-overlapping features according to one or more embodiments of the present disclosure.

[0012] Figure 2B This is a top view of a stacked target unit having a Moiré structure according to one or more embodiments of the present disclosure.

[0013] Figure 2C On a substrate according to one or more embodiments of this disclosure Figure 2B Side view of the unit in the image.

[0014] Figure 3A This is a conceptual diagram of the collection of diffraction orders from a normally incident illumination beam according to one or more embodiments of the present disclosure.

[0015] Figure 3B This is a conceptual diagram of the collection of diffraction orders from an obliquely incident illumination beam according to one or more embodiments of the present disclosure.

[0016] Figure 4A This is a conceptual diagram of an illumination pupil plane, which is contained within the boundary of an illumination pupil and positioned to provide oblique illumination along an orthogonal azimuth direction, according to one or more embodiments of this disclosure.

[0017] Figure 4B This describes one or more embodiments based on the present disclosure. Figure 4A A conceptual diagram of the light-gathering pupil plane for directional isolation imaging of the illumination profile.

[0018] Figure 5AThis is a conceptual diagram illustrating an illumination pupil plane having a directional orientation corresponding to the illumination beam according to one or more embodiments of the present disclosure.

[0019] Figure 5B This is a conceptual diagram illustrating the illumination pupil plane of the illumination beam based on NA-distinguished direction according to one or more embodiments of the present disclosure.

[0020] Figure 5C This is a conceptual diagram illustrating the illumination pupil plane of the illumination beam based on tilt-distinguished direction according to one or more embodiments of the present disclosure.

[0021] Figure 5D This is a conceptual diagram illustrating the illumination pupil plane of a beam of light with spectral properties differentiated according to one or more embodiments of the present disclosure.

[0022] Figure 5E This is a conceptual diagram illustrating the illumination pupil plane of an illumination beam based on intensity differentiation according to one or more embodiments of the present disclosure.

[0023] Figure 5F This is a conceptual diagram illustrating the illumination pupil plane of the illumination beam based on the direction of polarization differentiation according to one or more embodiments of the present disclosure.

[0024] Figure 6 This describes one or more embodiments based on the present disclosure. Figure 4A The diagram shows a conceptual illustration of the focusing pupil plane in a tilted bright-field imaging mode with a tilted illumination distribution.

[0025] Figure 7A This is a conceptual diagram illustrating the light-gathering pupil plane of a stacking metrology tool, such as one collected by an objective lens, according to one or more embodiments of the present disclosure.

[0026] Figure 7B According to one or more embodiments of this disclosure Figure 7A A conceptual diagram of the focusing pupil plane, in which the 0th order diffraction lobe is blocked to provide dark-field imaging.

[0027] Figure 8A This is a conceptual diagram of generating various diffraction lobes according to one or more embodiments of this disclosure.

[0028] Figure 8B This describes one or more embodiments based on the present disclosure. Figure 8A A conceptual diagram of the focusing pupil plane in the optical Mohr's mode of diffraction lobe imaging, as described in the diagram.

[0029] Figure 8C According to one or more embodiments of this disclosure Figure 8BA conceptual diagram of a focusing pupil plane, which is contained within the focusing pupil plane to selectively block the 0th order diffraction lobe.

[0030] Figure 9 This is a conceptual diagram of an illumination pupil plane comprising four illumination beams positioned to provide symmetrical tilted illumination along orthogonal azimuth directions, according to one or more embodiments of the present disclosure.

[0031] Figure 10 This is a flowchart illustrating the steps performed in a method for directional isolation imaging according to one or more embodiments of the present disclosure. Detailed Implementation

[0032] The subject matter of the disclosure will now be described in detail with reference to the accompanying drawings. This disclosure has been particularly shown and described with respect to certain embodiments and their specific features. The embodiments set forth herein are to be regarded as illustrative rather than restrictive. It will be readily understood by those skilled in the art that various changes and modifications in form and detail can be made without departing from the spirit and scope of this disclosure.

[0033] Embodiments of this disclosure relate to a system and method for image-based overlay metrology that provides directional isolation imaging of sample features along different directions using simultaneous illumination with illumination beams employing different illumination conditions. For example, an image (or a portion thereof) of sample features along a first direction (e.g., a first measurement direction) may be formed by illumination associated with the first illumination condition, and an image (or a portion thereof) of sample features along a second direction (e.g., a second measurement direction) may be formed by illumination associated with the second illumination condition. For the purposes of this disclosure, the illumination conditions may include a set of parameters for the illumination beams used to generate the image, including (but not limited to) numerical aperture (NA), beam shape, beam tilt, azimuth angle of incidence, height angle of incidence, wavelength, spectral bandwidth, polarization, or intensity.

[0034] In some embodiments, superposition metrology is performed by illuminating a superposition target having at least two sets of periodic target features arranged to facilitate superposition measurements along at least two different (e.g., orthogonal) measurement directions. For example, a set of periodic target features may comprise a periodic distribution of features along a particular measurement direction. By way of non-limiting illustration, this periodic distribution of features may comprise a diffraction grating (e.g., a grating structure) characterized by a grating pitch along a grating direction. In this way, a superposition target designed for superposition measurements along two different directions may comprise a set of periodic features having a first grating direction and a second set of periodic features having a second grating direction.

[0035] In this paper, it has been carefully considered that various image quality metrics associated with images of periodic target features can be affected by the number and arrangement of diffraction orders from the periodic target features used to generate the image. Furthermore, for challenging applications (e.g., (but not limited to) imaging sample features at or near the optical resolution of an imaging system), the specific number and arrangement of diffraction orders used to generate the image can have a more significant impact. As an example involving dark-field imaging techniques, 0th-order diffraction (e.g., specular reflection) can introduce DC bias that reduces image contrast. As another example, particularly relevant to overlay metrology, diffraction from features of objects not specifically being measured can similarly reduce image contrast and / or introduce other artifacts that can affect the sensitivity of the resulting measurements. For example, diffraction from a Y-direction grating can negatively affect the image of an X-direction grating (e.g., reduce contrast) and thus image-based overlay measurements.

[0036] Embodiments of this disclosure relate to systems and methods for providing illumination-isolated imaging of features with different grating orientations. In this manner, image quality (e.g., contrast or any other suitable image quality metric) can be improved relative to conventional techniques. In some embodiments, the overlay metrology system simultaneously illuminates an overlay target using multiple illumination beams with different orientations according to illumination conditions, wherein the overlay target comprises features with different (e.g., orthogonal) grating orientations. In this manner, each illumination beam can diffract along each of the grating orientations. However, in embodiments of this disclosure, the overlay metrology tool (e.g., using a metrology formula) is configured such that diffraction lobes from any particular illumination beam form an image of periodic features along only one particular orientation. In this configuration, diffraction of particular illumination beams along other orientations is insufficient to form a resolved image of the periodic structure.

[0037] It should be understood throughout this document that forming an image of a periodic structure requires at least two diffraction lobes to be collected and delivered to a detector to facilitate image formation. For the purposes of this disclosure, directional isolation imaging refers to a configuration in which, for any given illumination beam, only two or more diffraction lobes exist for one direction in which they contribute to image formation. For other directions, at most one diffraction lobe is collected and delivered to the detector. Under these conditions, periodic features along other directions cannot be resolved. In some embodiments, diffraction orders associated with other directions are not collected to avoid or mitigate any residual effects of these other diffraction orders (e.g., DC bias associated with 0th-order reflected light along other directions) that could negatively impact image quality. In some embodiments, a single diffraction order along other directions is allowed to be delivered to the detector and contribute to image formation (e.g., 0th-order reflected light). In such cases, the residual effects of a single diffraction lobe may be within the tolerances of a particular application.

[0038] For example, a stacked target containing orthogonal grating features (e.g., an X-direction grating and a Y-direction grating) can be simultaneously illuminated by a first illumination beam having a first set of illumination conditions and a second illumination beam having a second set of illumination conditions. However, only the diffraction of the first illumination beam through the X-direction grating contributes to the formation of a portion of the image containing the X-direction grating. Similarly, only the diffraction of the second illumination beam through the Y-direction grating contributes to the formation of a portion of the image containing the Y-direction grating. Therefore, although the X and Y-direction gratings are imaged simultaneously, the corresponding images (or portions thereof) are formed based on the different illumination conditions provided by the first and second illumination beams.

[0039] For reference Figures 1A to 10 The present disclosure provides a more detailed description of a system and method for optical isolation imaging using directional phase according to the disclosed conditions, based on one or more embodiments.

[0040] Figure 1A This is a conceptual diagram illustrating a stacked metering system 100 according to one or more embodiments of the present disclosure.

[0041] In some embodiments, the overlay metrology system 100 includes an overlay metrology tool 102, which can be configured according to a metrology formula (e.g., an overlay formula) to generate overlay measurements associated with an overlay target 104 having a design based on the metrology formula. For example, the overlay metrology tool 102 can direct two or more illumination beams 106 (e.g., beams 106 with different illumination conditions and directions relative to the illumination beams 106) from at least one illumination source 108 onto the overlay target 104 on the sample 110, collect light or other radiation emitted from the overlay target 104 in response to the illumination beams 106 (referred to herein as measurement light 112), and generate a detection signal from at least one detector 114 based on the measurement light 112.

[0042] The overlay metrology tool 102 may comprise any type of tool known in the art for generating overlay signals suitable for determining overlays associated with overlay targets on sample 110. In some embodiments, the overlay metrology tool 102 is an imaging metrology tool that generates overlay measurements based on one or more images of the overlay targets 104. The overlay metrology 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 metrology tool 102 may (e.g., based on metrology formulations) be configured to provide optically isolated imaging with orientational correlation according to illumination conditions to provide features oriented along different directions.

[0043] Some embodiments of this disclosure relate to providing a formulation for configuring a pairing metrology tool 102 to facilitate pairing measurements based on a selected diffraction order. The metrology formulation may include a set of parameters for controlling various aspects of the pairing measurement, such as (but not limited to) the illumination of the sample, the collection of light from the sample, or the position of the sample during the measurement. In this way, the pairing metrology tool 102 can be configured to provide a selected type of measurement for a selected pairing target. For example, the metrology formulation may include parameters of the illumination beam 106, such as (but not limited to) the illumination wavelength, the illumination pupil distribution (e.g., the distribution of the illumination angle and the associated intensity of the illumination at said angle), the polarization of the incident illumination, or the spatial distribution of the illumination. By another example, the metrology formulation may include light-gathering parameters, such as (but not limited to) the light-gathering pupil distribution (e.g., the desired distribution of angular light from the pairing target 104 to be measured and the associated filtered intensity at said angle), a light-gathering field aperture setting for selecting a portion of the pairing sample 104 of interest, the polarization of the collected light, a wavelength filter, or parameters for controlling one or more detectors. By another example, the metrology formula may include various parameters associated with the design of the superimposed target 104, such as (but not limited to) the position and orientation of sample features (e.g., the pitch of grating features along a particular direction). By a further example, the metrology formula may include various parameters associated with the position of sample 110 during measurement, such as (but not limited to) sample height, sample orientation, whether the sample is static or in motion during measurement (along with associated parameters describing speed, scanning pattern, or the like).

[0044] In this way, the overlay metrology tool 102 can be configured according to a metrology formula to provide a selected distribution of light in the focusing pupil when analyzing a specific overlay target 104 with a known design. This distribution of light in the focusing pupil can then be further modified as needed using various optics to produce the desired overlay measurement.

[0045] In some embodiments, the overlay metrology system 100 further includes a controller 116 having one or more processors 118 configured to execute program instructions held on memory 120 (e.g., memory media). The controller 116 may be communicatively coupled to any component of the overlay metrology system 100 (e.g., but not limited to detector 114). In this way, the controller 116 may generate overlay measurements based on the detection signals according to the metrology recipe.

[0046] One or more processors 118 of controller 116 may comprise any processor or processing element known in the art. For the purposes of this disclosure, the terms “processor” or “processing element” may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application-specific integrated circuit (ASIC) devices, one or more field-programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, one or more processors 118 may comprise any device configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). In one embodiment, one or more processors 118 may embody a desktop computer, host computer system, workstation, graphics computer, parallel processor, network-linked computer, or any other computer system configured to execute programs (which are configured to operate or in conjunction with the operation of the stack-to-metering system 100), as described throughout this disclosure.

[0047] Furthermore, different subsystems of the stacked metering system 100 may include processors or logic elements suitable for performing at least a portion of the steps described in this disclosure. Therefore, the above description should not be construed as limiting the embodiments of this disclosure but is merely illustrative. Additionally, the steps described throughout this disclosure may be performed by a single controller 116 or alternatively by multiple controllers. Furthermore, controller 116 may include one or more controllers housed within a common housing or multiple housings. In this manner, any controller or combination of controllers may be individually packaged as a module suitable for integration into the stacked metering system 100.

[0048] Memory 120 may comprise any storage medium known in the art suitable for storing program instructions executable by one or more associated processors 118. For example, memory 120 may comprise a non-transitory memory medium. By another example, memory 120 may comprise (but is not limited to) read-only memory (ROM), random access memory (RAM), magnetic or optical storage devices (e.g., magnetic disks), magnetic tape, solid-state drives, and the like. It should be further noted that memory 120 may be housed together with one or more processors 118 within a common controller housing. In one embodiment, memory 120 may be remotely located relative to the physical location of one or more processors 118 and controller 116. For example, one or more processors 118 of controller 116 may access remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, and the like).

[0049] For reference Figures 2A to 2C Various non-limiting instances of the superimposed target 104 are described in more detail according to one or more embodiments of the present disclosure.

[0050] For the purposes of this disclosure, the term "overlap" is generally used to describe the relative positions of features on a sample 110 fabricated by two or more photolithographic patterning steps, wherein the term "overlap error" describes the deviation of a feature from its nominal arrangement. In this context, overlap measurement can be expressed as a measurement of relative positions or overlap errors associated with those relative positions. For example, a multilayer device may contain features patterned on multiple sample layers using different photolithographic steps for each layer, where the alignment of features between layers must typically be tightly controlled to ensure proper performance of the resulting device. Therefore, overlap measurement can characterize the relative positions of features on two or more sample layers. By another example, multiple photolithographic steps can be used to fabricate features on a single sample layer. Such techniques (often referred to as dual-patterning or multi-patterning techniques) facilitate the fabrication of highly dense features approaching the resolution of a photolithography system. In this context, overlap measurement can characterize the relative positions of features from different photolithographic steps on this single layer. It should be understood that the examples and descriptions throughout this disclosure relating to specific applications of overlap metrology are illustrative only and should not be construed as limiting the scope of this disclosure.

[0051] Furthermore, the term "pairing target 104" is used extensively herein to refer to any set of features on a sample that have known periodicity (e.g., corresponding to grating features) suitable for pairing measurements. In some embodiments, pairing target 104 comprises a dedicated target having features on one or more sample layers manufactured for the purpose of providing pairing measurements, which typically represent pairings of device features on the same layer. For example, a dedicated pairing target may comprise one or more cells having grating features designed to provide pairing measurements according to a particular pairing technique (e.g., grating pitch, feature size, grating orientation, or the like). Such dedicated pairing targets may be printed at various locations on the sample, including (but not limited to) within cut channels or within the die. In some embodiments, pairing targets comprise device features having known periodicity suitable for direct pairing measurements.

[0052] Figure 2A This is a top view of a stacked target 104 having non-overlapping features according to one or more embodiments of this disclosure. Specifically, Figure 2A This describes a non-limiting configuration of a stacking target 104 comprising four units 202a to 202d (represented here as quadrants of the stacking target 104). In this configuration, each unit 202a to 202d may include a first set of periodic features 204 associated with a first photolithographic exposure and a second set of periodic features 206 associated with a second photolithographic exposure. Furthermore, units 202b and 202d may be configured to provide stacking measurements along the X-direction, such as... Figure 2AAs explained below. For example, a superposition measurement along the X-direction can be performed by directly comparing the relative positions of the first set of periodic features 204 and the second set of periodic features 206 within each cell or between cell 202b and cell 202d. In another example, a superposition measurement along the X-direction can be performed by comparing the rotationally symmetric points (e.g., rotational symmetry, reflection symmetry, mirror symmetry, or similar) between the first set of periodic features 204 distributed across cell 202b and cell 202d and the symmetric points between the second set of periodic features 206 distributed across cell 202b and cell 202d. Similarly, cells 202a and 202c can be configured to provide superposition measurements along the Y-direction, as... Figure 2A As explained below. In this manner, the first set of periodic features 204 and the second set of periodic features 206 in units 202b and 202d that have periodicity along a first measurement direction (e.g., the X direction) may be referred to as first direction periodic features, while the first set of periodic features 204 and the second set of periodic features 206 in units 202a and 202c that have periodicity along a second measurement direction (e.g., the Y direction) may be referred to as second direction periodic features.

[0053] The first set of periodic features 204 and the second set of periodic features 206 in any particular unit 202 can be located on any layer of sample 110. For example, the first set of periodic features 204 and the second set of periodic features 206 can be located on a common layer of sample 110 to facilitate overlay measurement between the first and second lithographic exposures in a multi-exposure process. By another example, the first set of periodic features 204 can be located in the first layer of sample 110 and the second set of periodic features 206 can be located on the second layer of sample 110 to facilitate overlay measurement between the first and second layers. Furthermore, the first set of periodic features 204 and the second set of periodic features 206 associated with a first measurement direction (e.g., first direction periodic features) can be located in the first set of layers of sample 110, while the first set of periodic features 204 and the second set of periodic features 206 associated with a second measurement direction (e.g., second direction periodic features) can be located in the second set of layers of sample 110 (which may be the same as or different from the first direction periodic features). As an explanation, units 202b and 202d may be included in the first set of periodic features 204 in the first layer 210 of sample 110 and the second set of periodic features 206 in the second layer 212 of sample 110, as described above, while units 202a and 202c may be included in the first set of periodic features 204 in the first layer 210 of sample 110 and the second set of periodic features 206 in the third layer (not explicitly stated) of sample 110.

[0054] In some embodiments, the stacking target 104 comprises different configurations of printed elements oriented in different directions. For example, units 202b and 202d may include a first set of periodic features 204 in the first layer 210 and a second set of periodic features 206 in the second layer 212, while units 202a and 202c may include a first set of periodic features 204 in the first layer 210 and a second set of periodic features 206 in the third layer of the sample 110. In this way, the stacking target 104 can facilitate simultaneous stacking measurements between multiple different layer pairs.

[0055] Furthermore, the first set of periodic features 204 and the second set of periodic features 206 in any particular unit 202 may have the same or different pitches. For example, Figure 2A This describes the configuration of stacked targets 104 in each unit 202a to 202d, where the first group of periodic features 204 and the second group of periodic features 206 share a common pitch. However, the first group of periodic features 204 and the second group of periodic features 206 may have different pitches.

[0056] In some embodiments, a first set of periodic features 204 and a second set of periodic features 206 within any particular unit 202 are formed in different layers of the sample 110. For example, the first set of periodic features 204 and the second set of periodic features 206 within any particular unit 202 may be formed in at least a partially overlapping region of the sample to create a grating-on-grating structure or formed in a non-overlapping region. In this configuration, the first set of periodic features 204 and the second set of periodic features 206 may have the same or different pitches. As an illustration, a configuration in which the first set of periodic features 204 and the second set of periodic features 206 have different pitches can form a moiré structure. This moiré structure can produce moiré diffraction (e.g., double diffraction, combined diffraction, or the like) associated with diffraction from both the first set of periodic features 204 and the second set of periodic features 206. In this document, with careful consideration, different stacking techniques (e.g., associated with different dosing formulations) may be used alone or in combination with moiré diffraction lobes to utilize any combination of diffraction lobes from constitutive features (e.g., the first set of periodic features 204 and the second set of periodic features 206). For example, the first dosing formulation may utilize first-order diffraction lobes from each of the constitutive features, while the second dosing formulation may utilize moiré diffraction lobes alone or in combination with diffraction lobes from one or more constitutive features.

[0057] Figure 2B This is a top view of a unit 202 of a stacked target 104 having a molar structure 208 according to one or more embodiments of the present disclosure. Figure 2C According to one or more embodiments of this disclosure Figure 2B A side view of unit 202. Specifically, Figure 2B and2C The pitches of the first set of periodic features 204 (e.g., the first layer grating) in the first layer 210 of sample 110 and the second set of periodic features 206 (e.g., the second layer grating) in the second layer 212 of sample 110 are respectively described as P and Q. Figure 2C The substrate 214 on which various layers are deposited is further illustrated. In some embodiments, although not explicitly shown, the stacked target 104 includes two units 202 per measurement direction, thereby providing an inverted moiré structure pair. For example, the first unit 202 may include a first set of periodic features 204 with a pitch P and a second set of periodic features 206 with a pitch Q, while the second unit 202 may include a first set of periodic features 204 with a pitch Q and a second set of periodic features 206 with a pitch P.

[0058] General reference Figures 2A to 2C The stacked target 104 may typically comprise any stacked target design known to be suitable for image-based diffraction. For example, the stacked target 104 may comprise (but is not limited to) an advanced imaging metrology (AIM) target, a triple AIM target characterized on three layers, a robust AIM (rAIM) target comprising one or more moiré structures, or the like.

[0059] For reference Figure 1B Various aspects of the superimposed measuring tool 102 are described according to one or more embodiments of the present disclosure.

[0060] Figure 1B This is a conceptual diagram illustrating an overlay metrology tool 102 according to one or more embodiments of the present disclosure. In one embodiment, the overlay metrology tool 102 includes an illumination source 108 configured to generate at least one illumination beam 106. Illumination from the illumination source 108 may include light of one or more selected wavelengths, including (but not limited to) ultraviolet (UV) radiation, visible light radiation, or infrared (IR) radiation.

[0061] In another embodiment, the overlay metrology tool 102 directs illumination from illumination source 108 to overlay target 104 via illumination path 122. Illumination path 122 may include one or more optical components suitable for modifying and / or adjusting illumination beam 106 and directing illumination beam 106 to sample 110. In one embodiment, illumination path 122 includes one or more illumination path lenses 124 (e.g., for collimating illumination, for relay pupils and / or field planes or the like). In another embodiment, illumination path 122 includes one or more illumination path optics 126 for shaping or otherwise controlling illumination. For example, illumination path optics 126 may include (but are not limited to) one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translation mirrors, scanning mirrors, or the like). Furthermore, the illumination path optics 126 can be positioned in any suitable location (including, but not limited to, the illumination pupil plane 128 or the illumination field plane).

[0062] In another embodiment, the stacking metrology tool 102 includes an objective lens 130 for focusing illumination onto the stacking target 104. In another embodiment, the sample 110 is placed on a sample stage 132 adapted to fix the sample 110 and further configured to position the stacking target 104 relative to the illumination beam 106.

[0063] In some embodiments, the overlay metrology tool 102 includes at least one detector 114 configured to capture light or other illumination (e.g., measurement light 112) emitted from the overlay target 104 via a light-collecting path 134. The light-collecting path 134 may include one or more optical elements suitable for modifying and / or adjusting the measurement light 112 from the overlay target 104. In one embodiment, the light-collecting path 134 includes one or more light-collecting path lenses 136 (e.g., for collimating the illumination beam 106, for relaying pupils and / or field planes or the like), which may include (but do not necessarily include) an objective lens 130. In another embodiment, the light-collecting path 134 includes one or more light-collecting path optics 138 for shaping or otherwise controlling the measurement light 112. For example, the light-collecting path optics 138 may include (but is not limited to) one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translation mirrors, scanning mirrors, or the like). Furthermore, the light-collecting path optics 138 may be positioned in any suitable location, including (but not limited to) a light-collecting pupil plane 140 or a light-collecting field plane (not shown).

[0064] Detector 114 can be positioned at any selected location within light-collecting path 134. In some embodiments, the overlay metrology tool 102 includes detector 114 at the field plane (e.g., the plane conjugate to sample 110) to generate an image of overlay target 104.

[0065] The illumination path 122 and light-collecting path 134 of the stacked metrology tool 102 can be adapted to a wide range of configuration orientations for illuminating the sample 110 with the illumination beam 106 and collecting light emitted from the sample 110 in response to the incident illumination beam 106. For example, as Figure 1B As explained, the stacking metrology tool 102 may include a beam splitter 142 oriented such that the common objective lens 130 can simultaneously direct the illumination beam 106 to and collect light from the sample 110. By another example, the illumination path 122 and the light-collecting path 134 may contain non-overlapping optical paths.

[0066] Furthermore, the illumination path 122 and / or the light-collecting 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 a dedicated illumination channel. By another example, the light-collecting path 134 may include a single detector 114 in a single light-collecting channel or multiple detectors 114 distributed among multiple light-collecting channels.

[0067] As an explanation, Figure 1B This describes a stacking metering tool 102 with a single light-gathering channel 144. Figure 1C This is a conceptual diagram of a stacked metrology tool 102 comprising two beam-collecting channels 144 according to one or more embodiments of the present disclosure. For example, the stacked metrology tool 102 may include one or more beam splitters 146 for separating the measurement light 112 into at least two beam-collecting channels 144. Furthermore, each beam-collecting channel 144 may include a separate beam-collecting path optics 138 (e.g., polarizer, spectral filter, neutral density filter, blocker, aperture, or the like) for individually modifying the measurement light 112 within each beam-collecting channel 144 to provide directional isolation imaging. It has been carefully considered herein that using multiple beam-collecting channels 144 allows for greater flexibility in producing directional isolation images but may add additional complexity compared to using beam-collecting channels 144. In this way, specific embodiments of the systems and methods disclosed herein can be selected or adapted for the tolerances of a particular application.

[0068] For reference Figures 3A to 9 The present disclosure describes in more detail, according to one or more embodiments, directional isolation imaging based on features oriented along different directions, and superimposed measurements.

[0069] After careful consideration, this paper superimposes periodic structures on target 104 (e.g., Figures 2A to 2C The first set of periodic features 204 and the second set of periodic features 206 described herein can produce discrete diffraction steps when illuminated with an illumination beam 106 having a narrow spectral range and a limited angular range. Furthermore, the specific arrangement of the diffraction steps of the illumination beam 106 in the focusing pupil plane 140 can be influenced by various properties of the illumination beam 106 (e.g., spectral, polarized, incident angle in the azimuth and / or height directions, numerical aperture (NA) or the like), the focusing path 134 (e.g., the NA or the like of the objective lens 130), or the superimposed target 104 (e.g., the pitch of the printed features, the orientation of the printed features relative to the incident illumination beam 106, or the like).

[0070] As an explanation, Figure 3A and 3B The effect of the height of the incident angle on the distribution of diffraction order from the grating (e.g., on the stacked target 104) is depicted. Figure 3A This is a conceptual diagram of the collection of diffraction orders from a normally incident illumination beam 106 according to one or more embodiments of the present disclosure. Figure 3B This is a conceptual diagram of the collection of diffraction orders from an obliquely incident illumination beam 106 according to one or more embodiments of this disclosure. Specifically, Figure 3A and 3B This demonstrates the control of a specific diffraction order collected by objective lens 130 based on the incident angle.

[0071] Therefore, in some embodiments, the stacked metrology tool 102 and / or sample are configured via metrology formulation to provide collection of selected diffraction orders to facilitate directional isolation imaging.

[0072] In some embodiments, the stacking metrology tool 102 simultaneously illuminates the stacking target 104 using two or more illumination beams 106, wherein various parameters of each illumination beam 106 are arranged to facilitate the separation of the diffraction order of the illumination beam 106 along different directions (e.g., in the focusing pupil plane 140). Various parameters of the objective lens 130 and / or the focusing path 134 may then be configured to provide directional isolation imaging on one or more detectors 114, wherein a grating with a specific grating orientation is imaged using only light from a specific illumination beam 106.

[0073] In this paper, after careful consideration, directional isolation imaging can be implemented using various configurations of the overlay metrology tool 102.

[0074] In some embodiments, the overlay metrology tool 102 is configured such that the objective lens 130 collects only selected diffraction orders associated with each illumination beam 106 that provides directional isolation imaging as disclosed herein. In this configuration, the objective lens 130 may provide directional isolation imaging using a single detector 114, wherein portions of the generated image associated with grating structures having different grating orientations are imaged based on different illumination beams 106.

[0075] Figure 4A and 4B This describes a moiré structure based on illumination beams with different azimuth angles of incidence (e.g., as described in one or more embodiments of this disclosure) of 106 pairs of illumination beams. Figure 2B and 2C (As explained in the text) directional isolation imaging. Specifically, Figure 4A This describes the configuration in which objective lens 130 collects only selected diffraction orders associated with each illumination beam 106 that provides directional isolation imaging.

[0076] Figure 4A This is a conceptual diagram of an illumination pupil plane 128 containing two illumination beams 106a, 106b positioned within an illumination pupil boundary 402 to provide oblique illumination along an orthogonal azimuth direction, according to one or more embodiments of this disclosure. Figure 4B This describes one or more embodiments based on the present disclosure. Figure 4A A conceptual diagram of the light-gathering pupil plane 140 for directional isolation imaging of the illumination profile. For example, Figure 4B Explanation of response Figure 2A The diagram illustrates the diffraction lobes produced by superimposing illumination onto the target 104.

[0077] like Figure 4B The diagram explains that illuminating the target 104 with illumination beam 106a results in diffraction lobes 404 distributed along both the X and Y directions. However, a selected diffraction order is located only at the pupil boundary 406 along the X direction and is therefore used to facilitate the formation of an image of the corresponding structure. Similarly, illuminating the target 104 with illumination beam 106b results in diffraction lobes 408 distributed along both the X and Y directions, but a selected diffraction order is located only at the pupil boundary 406 along the Y direction and is therefore used to facilitate the formation of an image of the corresponding structure.

[0078] In this way, portions of the image of features distributed along the X direction are optically isolated from portions of the image of features distributed along the Y direction. In other words, grating formation is encoded according to illumination conditions provided, such as by selecting the diffraction order that facilitates image formation. Therefore, various image quality metrics associated with features oriented along the X direction can be entirely (or at least substantially) dependent on the selected diffraction order from illumination beam 106a, and image quality metrics associated with features oriented along the Y direction can be entirely (or at least substantially) dependent on the selected diffraction order from illumination beam 106b.

[0079] General reference Figures 3A to 4B It should be understood that Figures 3A to 4B Provided for illustrative purposes only and should not be construed as restrictive. For example, in Figure 4A and 4B In this context, the primary difference between the illumination conditions associated with illumination beams 106a and 106b is the azimuth angle of incidence. However, with careful consideration, azimuth-dependent illumination isolation imaging can be achieved using multiple illumination beams 106 with illumination conditions differentiated based on any combination of parameters, including (but not limited to) NA, beam shape, wavelength, spectral bandwidth, polarization, or intensity. Furthermore, such differentiation of illumination conditions can be achieved using any technique known in the art, including (but not limited to) illumination path optics 126 or the direct generation of illumination beams 106 with different illumination conditions.

[0080] Additionally, the overlay metrology tool 102 may include various configurations of the light-collecting path 134 to further isolate selected diffraction lobes to provide directional isolation imaging.

[0081] In some embodiments, the light-collecting path 134 includes one or more light-collecting path optics 138 to filter or block selected diffraction lobes in the light-collecting pupil plane 140 (e.g., collected by the objective lens 130) that are not desired by a particular imaging technique. For example, as will be described in more detail below, it may be desirable to block 0th-order diffraction light along one or more directions (e.g., specular reflection) to ensure optical isolation and / or to enable dark-field imaging.

[0082] In some embodiments (e.g., as in...) Figure 1C (As explained below), the superimposed measurement tool 102 includes multiple light-collecting channels 144. In this way, each light-collecting channel 144 may include different light-collecting path optics 138 to filter or block various diffraction orders. For example, each light-collecting channel 144 may provide an image of a grating along different selected directions based on diffracted light from different illumination beams 106.

[0083] For reference Figures 5A to 5F Various techniques for providing orientation-dependent illumination isolation imaging are described in more detail according to one or more embodiments of this disclosure. It should be noted that... Figures 5A to 5F The distinction between lighting conditions based on both azimuth angle of incidence and additional properties is described, but it should be understood that a distinction based on azimuth angle of incidence is not necessary.

[0084] Figures 5A to 5F Various non-limiting techniques are described for distinguishing illumination beam 106 based on its position, size, shape, or orientation in illumination pupil plane 128.

[0085] Figure 5A This is a conceptual diagram illustrating an illumination pupil plane 128 having a rotated configuration and oriented relative to the illumination beam 106, according to one or more embodiments of the present disclosure. Specifically, Figure 5A The description is similar to Figure 4A The illumination lobe distribution in the image is such that the illumination beams 106a and 106b are relative to the grating direction of the superimposed target 104 (e.g., Figure 2A The illumination beams 106a and 106b are rotated relative to the grating direction of the superimposed target 104, but the associated diffraction order will still be distributed along the grating direction. However, using a rotated lobe allows for further separation of the diffraction order in the focusing pupil plane 140 and is suitable for some applications.

[0086] Figure 5B This is a conceptual diagram illustrating the illumination pupil plane 128 of the illumination beam 106 based on NA-distinguished direction according to one or more embodiments of the present disclosure. Specifically, Figure 5B The diagram describes apertures 502a and 502b of different sizes (labeled NA1 and NA2) for providing illumination beams 106a and 106b. Furthermore, apertures 502a and 502b can be implemented as separate elements or as spatially selectable elements.

[0087] Additionally, although not shown, the illumination beams 106a and 106b can typically have any selected shape in the illumination pupil plane 128 that corresponds to an associated diffraction order. For example, the shape of the illumination beams 106a and 106b in the illumination pupil plane 128 can include (but is not limited to) circles, ellipses, or cat's-eye shapes (e.g., geometric lenses). Furthermore, the illumination beams 106a and 106b can have the same shape or different shapes. In some embodiments, the shape of the illumination beams 106a and 106b in the illumination pupil plane 128 is controlled by apertures 502a and 502b in the illumination pupil plane 128.

[0088] Figure 5C This is a conceptual diagram illustrating the illumination pupil plane 128 of the illumination beam 106 based on tilt angle differentiation according to one or more embodiments of the present disclosure. Specifically, Figure 5CApertures 504a and 504b are described at different radial positions (labeled θ1 and θ2) in the illumination pupil plane 128 to provide illumination beams 106a and 106b with different incident angles. Furthermore, apertures 502a and 502b can be implemented as separate elements or through spatially selectable elements.

[0089] Figure 5D This is a conceptual diagram illustrating the illumination pupil plane 128 of the illumination beam 106, differentiated by spectral properties according to one or more embodiments of the present disclosure. Specifically, Figure 5D This describes spectral filters 506a and 506b (labeled BW1 and BW2) used to impart different spectral properties to illumination beams 106a and 106b. Spectral filters 506a and 506b 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. In this way, spectral filters 506a and 506b can distinguish illumination beams 106a and 106b based on spectral properties (e.g., but not limited to center wavelength or bandwidth). Furthermore, spectral filters 506a and 506b can be implemented as individual elements or implemented through spatially selectable elements.

[0090] Figure 5E This is a conceptual diagram illustrating the illumination pupil plane 128 of the illumination beam 106 based on intensity differentiation according to one or more embodiments of the present disclosure. Specifically, Figure 5E The description includes neutral density filters 508a and 508b (labeled ND1 and ND2) used to impart different intensities to illumination beams 106a and 106b. Furthermore, neutral density filters 508a and 508b can be implemented as individual components or as spatially selectable components.

[0091] Figure 5F This is a conceptual diagram illustrating the illumination pupil plane 128 of the illumination beam 106 based on polarization differentiation according to one or more embodiments of the present disclosure. Specifically, Figure 5F The description includes polarizers 510a and 510b (denoted as S and P) for imparting different polarizations (e.g., crossed polarizations) to illumination beams 106a and 106b. Furthermore, polarizers 510a and 510b can be implemented as separate elements or as spatially selectable elements.

[0092] General reference Figures 4A to 5F In this document, after careful consideration, the superimposed metrology tool 102 can typically implement any combination of such techniques. For example, Figures 4A to 5CThis is generally applicable (but not limited to) manipulating the distribution of diffraction lobes collected by objective lens 130 and thus can be used to facilitate imaging. However, as will be described in more detail below, it may be desirable to provide additional filtering and / or blocking of the collected diffraction lobes to implement fully isolated per-direction imaging or to implement specific imaging techniques. Figures 5D to 5F The additional properties typically applicable (but not limited to) manipulating illumination beams 106a, 106b enable any additional elements in the light-collecting channel 144 to isolate and / or filter associated diffraction lobes.

[0093] For reference Figures 6 to 8C Various non-limiting imaging modes based on directional isolation imaging are described in more detail according to one or more embodiments of the present disclosure. Figures 6 to 8C Based on having Figure 4A The lighting is used to illuminate the outline shown in the image. Furthermore... Figures 6 to 7B This indicates a shared periodicity characteristic (e.g., such as...). Figure 2A The image of target 104 is superimposed (as described in the text), and Figures 8A to 8C This indicates different pitch periodicity characteristics (e.g., such as...) Figures 2B to 2C Imaging of target 104 by superimposing the molar structure described in the diagram.

[0094] exist Figures 6 to 8C In the imaged superimposed target 104, the imaged target includes objects along the orthogonal grating direction (e.g., as shown in the image). Figures 2A to 2C The periodic structure oriented in the X and Y directions as described in the text.

[0095] After careful consideration, the principles of directional isolation imaging disclosed herein are generally applicable to a wide range of imaging techniques. Therefore, it should be understood that... Figures 6 to 8C Provided for illustrative purposes only and should not be construed as restrictive.

[0096] Figure 6 This describes one or more embodiments based on the present disclosure. Figure 4A The diagram shows a conceptual illustration of the light-gathering pupil plane 140 in a tilted bright-field imaging mode with a tilted illumination distribution. Specifically, Figure 6 The description only provides the first illumination beam 106a through a periodic structure in the X direction (e.g., Figure 2A The 0th-order diffraction lobe 602 (e.g., specular reflection) and the 1st-order diffraction lobe 604 of units 202b and 202d, as well as the second illumination beam 106b, pass through a periodic structure in the Y direction (e.g., Figure 2A The configuration of the stacking metrology tool 102 (e.g., based on metrology formula) for the 0th order diffraction lobe 606 and the 1st order diffraction lobe 608 of units 202a and 202c in the unit(s).

[0097] In this way, a periodic structure in the X direction is formed by the first illumination beam 106a (e.g., Figure 2A The image (or a portion thereof) of units 202b, 202d in the image is formed by the second illumination beam 106b to create a periodic structure in the Y direction (e.g., Figure 2A Images (or portions thereof) of units 202a and 202c in the dataset.

[0098] However, it should be noted that, based on Figure 6 A single image from the focusing pupil plane 140 can reveal residual DC bias originating from the 0th-order diffraction lobes 602 and 606 from orthogonal directions. For example, an image of a periodic structure in the X direction can be affected by the residual DC bias associated with the 0th-order diffraction lobe 606. Similarly, an image of a periodic structure in the Y direction can be affected by the residual DC bias associated with the 0th-order diffraction lobe 602. In some applications, this residual DC bias is within operating tolerances and is acceptable.

[0099] However, in some applications, the overlay metering tool 102 may include one or more additional elements to remove or mitigate this residual DC bias. In some embodiments, the overlay metering tool 102 imparts orthogonally polarized light to the illumination beams 106a, 106b (e.g., as shown in the image). Figure 5F (as described in the description) to provide polarization isolation. Furthermore, the light-collecting path 134 may include (but does not necessarily include) one or more polarizers to isolate diffraction lobes from the illumination beams 106a, 106b. For example, the overlay metrology tool 102 may include two light-collecting channels and one or more polarizers (e.g., as beam splitters 146 or other light-collecting path optics 138 in any suitable location) such that the detectors 114 in the two light-collecting channels 144 image the overlay target 104 separately with orthogonally polarized light. By another example, the light-collecting path 134 may include structured image plane (e.g., field plane) polarizers providing different polarization directions in the image plane corresponding to locations with associated periodic features.

[0100] In some embodiments, the overlay metrology tool 102 imparts different spectral contents (e.g., center wavelength, bandwidth, or the like) to the illumination beams 106a, 106b (e.g., as shown in the figure). Figure 5D (See description below). In this way, the overlay metrology tool 102 may include spectral filters for isolation based on spectral content. For example, in a configuration with two light-collecting channels 144, dichroic beam splitters 146 and / or different spectral filters located in different light-collecting channels 144 can provide separate images of orthogonal target features.

[0101] Figure 7A and 7B This describes directional isolation imaging in a dark field imaging mode according to one or more embodiments of the present disclosure. Figure 7AThis is a conceptual diagram illustrating the light-gathering pupil plane 140 of a stacking measurement tool 102, such as that collected by objective lens 130, according to one or more embodiments of this disclosure. Specifically, Figure 7A The description explains that the light-gathering pupil plane 140 includes a first illumination beam 106a passing through a periodic structure in the X direction (e.g., Figure 2A The 0th-order diffraction lobe 702, the 1st-order diffraction lobe 704, and the 2nd-order diffraction lobe 706 of units 202b and 202d, along with the second illumination beam 106b, pass through a periodic structure in the Y direction (e.g., Figure 2A The configuration of the stacking metrology tool 102 (e.g., based on metrology formula) for the 0th order diffraction lobe 708, 1st order diffraction lobe 710 and 2nd order diffraction lobe 712 of units 202a and 202c.

[0102] Figure 7B According to one or more embodiments of this disclosure Figure 7A A conceptual diagram of the focusing pupil plane 140, where the 0th-order diffraction lobe is blocked to provide dark-field imaging. For example, Figure 7B This describes a blocker 714 that selectively blocks the 0th-order diffraction lobes 702 and 708 in the light-collecting pupil plane 140 (e.g., a portion of the light-collecting path optics 138). This blocker 714 can typically have any shape and can be formed from any number of elements. In this way, Figure 7B The specific configurations described herein are not limited to those described in this disclosure.

[0103] In this configuration, a periodic structure in the X direction is formed only by the first illumination beam 106a (e.g., Figure 2A The image (or a portion thereof) of units 202b, 202d in the image, while only through the second illumination beam 106b forming a periodic structure in the Y direction (e.g., Figure 2A The image (or a portion thereof) of units 202a and 202c in the image. Specifically, the blocking of the 0th order diffraction lobes 702 and 708 eliminates any residual effects of the orthogonal structure. Furthermore, the resulting dark-field image will have full contrast (e.g., 100% contrast).

[0104] Figure 8A This is a conceptual diagram of generating various diffraction lobes according to one or more embodiments of this disclosure. Figure 8B This describes one or more embodiments based on the present disclosure. Figure 8A The diagram illustrates a concept of the focusing pupil plane 140 in the optical Mohr's mode of diffraction lobes for directional isolation imaging. For example, the superimposed target 104 may include, for instance... Figures 2B to 2C The grating stack features with different pitches (e.g., moiré structures) described herein, but include different units 202 having moiré structures oriented along orthogonal directions (e.g., X and Y directions). Specifically, Figure 8BThe description describes the configuration of a superimposed metrology tool 102 (e.g., based on metrology formula) in which the light-gathering pupil plane 140 includes a 0th-order diffraction lobe 802 and a 1st-order diffraction lobe 804 from a first illumination beam 106a of a first set of periodic features 204 (labeled 1) distributed along the X direction, and a 1st-order diffraction lobe 806 from a second set of periodic features 206 (labeled 1') distributed along the X direction. Figure 8B It also describes the 0th-order diffraction lobe 808 and the 1st-order diffraction lobe 810 of the second illumination beam 106b from the first set of periodic features 204 (labeled 1) distributed along the Y direction, and the 1st-order diffraction lobe 812 of the second illumination beam 106b from the second set of periodic features 206 (labeled 1') distributed along the Y direction.

[0105] Figure 8C According to one or more embodiments of this disclosure Figure 8B A conceptual diagram of the focusing pupil plane 140, which includes a blocker 814 within the focusing pupil plane 140 to selectively block the 0th-order diffraction lobes 802, 808. This blocker 814 can generally have any shape and can be formed from any number of elements. In this way, the specific configuration illustrated in FIG8 is not limited to this disclosure. In this configuration, an image (or a portion thereof) of the periodic structure in the X direction is formed only by the first illumination beam 106a, and an image (or a portion thereof) of the periodic structure in the Y direction is formed only by the second illumination beam 106b. Specifically, the blocking of the 0th-order diffraction lobes 802, 808 eliminates any residual effects of the orthogonal structure. Furthermore, as previously described herein, various distinguishing parameters (e.g., but not limited to, spectral content or polarization) of the illumination beams 106a, 106b can be used to further isolate the images of the X-direction and Y-direction structures in one or both focusing channels 144.

[0106] For general reference Figures 4A to 8C It should be understood that the imaging configurations described are for illustrative purposes only and should not be construed as limiting. For example, directional isolation imaging can be extended to other imaging modes in which different combinations of diffraction orders in each direction are utilized. By another example, it is desirable to provide images with symmetrical tilted illumination conditions.

[0107] Figure 9 This is a conceptual diagram of an illumination pupil plane 128 comprising four illumination beams 106a, 106b, 106c, 106d positioned to provide symmetrical tilted illumination along orthogonal azimuth directions, according to one or more embodiments of this disclosure. For example, Figure 9 Can represent Figure 4A Symmetrical variation in the lighting distribution.

[0108] In some embodiments, the superimposed target 104 is simultaneously illuminated using all four illumination beams 106a, 106b, 106c, and 106d, wherein directionally isolated images are generated in one or more light-collecting channels 144, as disclosed herein. For example, Figure 6 The tilted bright-field imaging mode described herein is applicable (but not limited to) simultaneous illumination using illumination beams 106a, 106b, 106c, and 106d.

[0109] In some embodiments, symmetrically opposed illumination beams 106 are used to sequentially illuminate the superimposed target 104. For example, illumination beams 106a and 106b may first be used to illuminate the superimposed target 104 to form a first set of directional isolation images in one or more light-collecting channels 144, and then illumination beams 106c and 106d may be used to illuminate the superimposed target 104 to form a second set of directional isolation images in one or more light-collecting channels 144. The resulting images can then be analyzed together to provide superimposed measurements.

[0110] Now refer to again Figure 1A and 1B Various additional components of the stacked metering system 100 are described in more detail according to one or more embodiments of the present disclosure.

[0111] The illumination source 108 may comprise 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 comprise (but is not limited to) one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, or the like. In this respect, 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 comprises a laser sustained plasma (LSP) source. For example, the illumination source 108 may comprise (but is not limited to) an LSP lamp, LSP bulb, or LSP chamber suitable for housing one or more elements capable of emitting broadband illumination when excited into a plasma state by a laser source. In another embodiment, the illumination source 108 comprises a lamp source. For example, the illumination source 108 may comprise (but is not limited to) an arc lamp, discharge lamp, electrodeless lamp, or the like. In this regard, the illumination source 108 can provide an illumination beam 106 with low coherence (e.g., low spatial coherence and / or temporal coherence).

[0112] The superimposed metering 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 manner, including (but not limited to) dipole illumination, orthogonal illumination, or the like.

[0113] In some embodiments, the illumination source 108 directly generates two or more illumination beams 106. In some embodiments, the overlay metrology tool 102 includes two or more apertures in the illumination pupil plane 128 (e.g., illumination path optics 126) to divide the illumination from the illumination source 108 into two or more illumination beams 106 or illumination lobes. Furthermore, the spatial profile 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.

[0114] In some embodiments, illumination source 108 provides light in two or more optical fibers, wherein the illumination beam 106 of light output from each optical fiber has an illumination lobe. For example, the output surface of the optical fiber may be located at or imaged onto the illumination pupil plane 128. In some embodiments, the stacking metrology tool 102 diffracts the illumination from illumination source 108 into two or more diffraction orders, wherein the illumination beam 106 is formed by at least some diffraction orders of the light source. Multiple illumination lobes are substantially described by controlled diffraction in U.S. Patent No. 11,118,903, issued September 14, 2021, entitled “Efficient Illumination Shaping for Scatterometry Overlay,” the entire contents of which are incorporated herein by reference.

[0115] The overlay metrology tool 102 may typically include any number or type of detectors 114 suitable for capturing light indicating overlay from the sample 110. In one embodiment, detectors 114 include one or more detectors 114 suitable for characterizing a static sample. In this respect, the overlay metrology tool 102 may operate in a static mode in which the sample 110 is static during measurement. For example, detectors 114 may include a two-dimensional pixel array, such as (but not limited to) a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) device. In this respect, detectors 114 may generate a two-dimensional image in a single measurement. In one embodiment, detectors 114 include one or more detectors 114 suitable for characterizing a moving sample (e.g., a scanned sample), such as (but not limited to) a 2D pixel array, a time-delay integration (TDI) detector, or the like. In this respect, the overlay metrology tool 102 may operate in a scanning mode in which the sample 110 is scanned relative to the measurement field during measurement.

[0116] In another embodiment, the superimposed metrology tool 102 includes a scanning subsystem for scanning the sample 110 relative to the measurement field during metrology measurements. 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 one or more adjustable stages, such as (but not limited to) linear translation stages, rotation stages, or tilt / flip stages. In another embodiment, although not shown, the scanning subsystem includes one or more beam scanning optics (e.g., rotatable mirrors, galvanometers, or the like) for scanning the illumination beam 106 relative to the sample 110.

[0117] Figure 10 This is a flowchart illustrating the steps performed in a method 1000 for directional isolation imaging according to one or more embodiments of this disclosure. Applicants should note that the embodiments and implementation techniques previously described in the background content of the overlay metrology system 100 herein should 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 metrology system 100.

[0118] In some embodiments, method 1000 includes step 1002 of illuminating a stacked target on a sample using one or more first illumination beams and one or more second illumination beams, wherein the stacked target comprises a first-direction periodicity feature distributed along a first measurement direction in a first set of layers of the sample and a second-direction periodicity feature distributed along a second measurement direction different from the first measurement direction in a second set of layers of the sample. In this manner, the stacked target can generate diffraction lobes of the first and second illumination beams in both the X and Y directions. Step 1002 may further include simultaneously illuminating the stacked target using the first and second illumination beams.

[0119] Stacked targets can typically encompass any stacked target design known to be suitable for image-based diffraction. For example, stacked targets can include (but are not limited to) advanced imaging metrology (AIM) targets, triple AIM targets with features on three layers, robust AIM (rAIM) targets containing one or more moiré structures, or the like. Furthermore, stacked targets can contain periodic features in any number of layers, where a periodic feature in one measurement direction (e.g., the X direction) does not need to be in the same layer as a periodic feature in another measurement direction (e.g., the Y direction).

[0120] In some embodiments, method 1000 includes step 1004 of generating one or more images of a superimposed target on one or more detectors based on the diffraction of one or more first illumination beams and one or more second illumination beams through a superimposed target using one or more light-collecting optics, wherein the diffraction order of the one or more first illumination beams facilitates the formation of a resolved image of only a first set of periodic features, and wherein the diffraction order of the one or more second illumination beams facilitates the formation of a resolved image of only a second set of periodic features. In some embodiments, the light-collecting optics, the superimposed target, and the first and second illumination beams may (e.g., according to a metrological formulation) be configured such that the first illumination beam is collected through the diffraction order of the periodic features in a first direction, but the first illumination beam is not collected through the diffraction order of the periodic features in a second direction (e.g., located outside the NA of the light-collecting optics, outside the boundary of the light-collecting pupil, or the like). Similarly, the light-collecting optics, the stacked target, and the first and second illumination beams can (e.g., according to a metrological formulation) be configured such that the second illumination beam is not collected through the diffraction order of the first-direction periodicity feature, but is collected through the diffraction order of the second-direction periodicity feature. In this way, the first-direction periodicity structure can be resolved only based on the diffraction of the first illumination beam, and the second-direction periodicity structure can be resolved only based on the diffraction of the second illumination beam.

[0121] In some embodiments, method 1000 includes step 1006 of generating a first stacked measurement along a first measurement direction based on one or more images. For example, step 1006 may include generating the stacked measurement based on a first illumination beam based on resolved periodic features of the first direction. In some embodiments, method 1000 includes step 1008 of generating a second stacked measurement along a second measurement direction based on one or more images. For example, step 1008 may include generating the stacked measurement based on a second illumination beam based on resolved periodic features of the second direction.

[0122] The objects described herein sometimes indicate that other components contain or are connected to other components. It should be understood that such depicted architectures are merely exemplary, and many other architectures can in fact be implemented to achieve the same functionality. Conceptually, any arrangement of components used to achieve the same functionality is effectively “associated” to achieve the desired functionality. Therefore, any two components combined herein to achieve a particular functionality can be considered “associated” with each other to achieve the desired functionality, regardless of the architecture or intermediate components. Similarly, any two such associated components can also be considered “connected” or “coupled” to each other to achieve the desired functionality, and any two components that can be suchly associated can also be considered “coupleable” to each other to achieve the desired functionality. Specific examples of coupleability include (but are not limited to) physically interactive and / or physically interactive components and / or wirelessly interactive and / or logically interactive components.

[0123] It is believed that this disclosure and many of its accompanying advantages will be understood from the foregoing description, and it will be appreciated that various changes can be made to the form, construction, and arrangement of the components without departing from the subject matter disclosed or sacrificing all its material advantages. The forms described are merely illustrative, and the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. An optical metrology system, comprising: A pairwise metrology tool configured to implement a metrology formulation for a pairwise target on a characteristic sample, wherein the pairwise target according to the metrology formulation comprises a first-direction periodic feature on a first set of layers of the sample, the first-direction periodic feature being distributed along a first measurement direction, wherein the pairwise target according to the metrology formulation further comprises a second-direction periodic feature on a second set of layers of the sample, the second-direction periodic feature being distributed along a second measurement direction different from the first measurement direction, wherein the pairwise metrology tool according to the metrology formulation includes: One or more illumination optics configured to illuminate the stacked target using 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 stacked target; and One or more light-collecting optical devices configured to generate one or more images of the stacked target on one or more detectors based on the diffraction of the one or more first illumination beams and the one or more second illumination beams through the stacked target, wherein the diffraction order of the one or more first illumination beams contributes to the formation of a resolved image with periodicity characteristics only in the first direction, and wherein the diffraction order of the one or more second illumination beams contributes to the formation of a resolved image with periodicity characteristics only in the second direction; and A controller communicatively coupled to the one or more detectors, the controller comprising one or more processors configured to execute program instructions, thereby causing the one or more processors to: Based on the one or more images, a first stacked measurement is generated along the first measurement direction; and A second stacked measurement is generated along the second measurement direction based on the one or more images.

2. The optical metrology system according to claim 1, wherein the first illumination beam and the second illumination beam are distinguished by at least one of the following: azimuth angle of incidence on the stacked target and height angle of incidence on the stacked target, wavelength, bandwidth, polarization, intensity, numerical aperture in the illumination pupil of the one or more illumination optics, and lobe shape or tilt in the illumination pupil.

3. The optical metrology system of claim 1, wherein the first illumination beam comprises a single first illumination beam providing a first azimuth angle of incidence on the stacked target, and wherein the second illumination beam comprises a single second illumination beam providing a second azimuth angle of incidence on the stacked target.

4. The optical metrology system according to claim 3, wherein the first and second incident angles are orthogonal.

5. The optical metrology system according to claim 1, wherein the first illumination beam comprises a first set of two illumination beams providing a first set of symmetrically opposite azimuth angles of incidence on the stacked target, wherein the second illumination beam comprises a second set of two illumination beams providing a second set of symmetrically opposite azimuth angles of incidence on the stacked target.

6. The optical metrology system according to claim 5, wherein the first and second sets of azimuth incident angles are orthogonal.

7. The optical metrology system of claim 5, wherein the one or more illumination optics simultaneously guide the first set of two illumination beams and the second set of two illumination beams to the stacked target when implementing the metrology formulation.

8. The optical metrology system of claim 5, wherein the one or more illumination optics guide one of the two illumination beams in the first group and one of the two illumination beams in the second group to the stacked target for a first exposure, wherein the one or more illumination optics guide the other of the two illumination beams in the first group and the other of the two illumination beams in the second group to the stacked target for a second exposure.

9. The optical metrology system according to claim 1, wherein the one or more light-collecting optics comprises a single light-collecting channel, and wherein the one or more detectors comprises a single detector.

10. The optical metrology system of claim 1, wherein the one or more light-collecting optics comprises two light-collecting channels, wherein the one or more detectors comprises two detectors, wherein each of the two light-collecting channels comprises one of the two detectors, wherein the one or more light-collecting optics separates the diffraction order from the first illumination beam into the first of the two light-collecting channels and separates the diffraction order from the second illumination beam into the second of the two light-collecting channels, wherein the first of the two light-collecting channels provides one or more images of the superimposed target wherein only periodic features in the first direction are resolved, and wherein the second of the two light-collecting channels provides one or more images of the superimposed target wherein only periodic features in the second direction are resolved.

11. The optical metrology system of claim 1, wherein, according to the metrology formula, the stacking metrology tool collects only: Two or more diffraction lobes along the first measurement direction are generated from each of the one or more first illumination beams by means of the periodic characteristics of the first direction; and Two or more diffraction lobes along the second measurement direction are generated from each of the one or more second illumination beams by the periodic characteristics of the second direction.

12. The optical metrology system of claim 1, wherein, according to the metrology formula, the stacking metrology tool collects only: The 0th-order and 1st-order diffraction lobes along the first measurement direction generated from each of the one or more first illumination beams by the periodic characteristics of the first direction; and The 0th-order and 1st-order diffraction lobes along the second measurement direction are generated from each of the one or more second illumination beams by means of the periodic characteristics of the second direction. The one or more images of the superimposed target are tilted bright-field images.

13. The optical metrology system of claim 1, wherein, according to the metrology formula, the stacking metrology tool collects only: The 0th-order diffraction lobes, 1st-order diffraction lobes, and 2nd-order diffraction lobes generated along the first measurement direction from each of the one or more first illumination beams by means of the periodic characteristics of the first direction; and The 0th-order diffraction lobes, 1st-order diffraction lobes, and 2nd-order diffraction lobes generated along the second measurement direction from each of the one or more second illumination beams by means of the periodic characteristics of the second direction. The one or more light-collecting optical devices include one or more elements for blocking the 0th-order diffraction lobes along the first and second measurement directions. The one or more images of the superimposed target are dark field images.

14. The optical metrology system of claim 1, wherein the first directional periodicity feature comprises gratings having a first pitch and a second pitch distributed along the first measurement direction to form a first directional moiré structure, wherein the second directional periodicity feature comprises gratings having the first pitch and the second pitch distributed along the second measurement direction to form a second directional moiré structure, wherein, according to the metrology formula, the stacked metrology tool collects only: The 0th-order diffraction lobe, the 1st-order diffraction lobe, and the 1st-order diffraction lobe of the grating having the first pitch in the first-direction moiré structure, associated with each of the one or more first illumination beams; and The 0th-order diffraction lobe, the 1st-order diffraction lobe, and the 1st-order diffraction lobe of the grating with the second pitch in the second-direction moiré structure associated with each of the one or more second illumination beams.

15. The optical metrology system of claim 14, wherein the one or more light-collecting optics further comprises one or more elements for blocking the 0th-order diffraction lobes along the first and second measurement directions.

16. The optical metrology system of claim 1, wherein the stacked target comprises: At least one of Advanced Imaging Metrology (AIM) target, Triple AIM target, or Robust AIM (rAIM) target.

17. The optical metrology system according to claim 1, wherein the first group of layers and the second group of layers of the sample are a common sample layer.

18. The optical metrology system of claim 1, wherein the first set of layers is different from the second set of layers.

19. The optical metrology system of claim 18, wherein the first set of layers comprises a first layer of the sample and a second layer of the sample, wherein the second set of layers comprises the first layer of the sample and a third layer of the sample.

20. The optical metrology system of claim 1, wherein at least one of the first or second directional periodic features comprises features associated with different lithographic exposures on a single layer.

21. An optical metrology system, comprising: One or more illumination optics are configured to illuminate a stacked target on a sample using one or more first illumination beams and one or more second illumination beams during the implementation of a metrology formulation, wherein at least one of the first illumination beams and at least one of the second illumination beams are simultaneously incident on the stacked target, wherein the stacked target according to the metrology formulation includes a first directional periodicity feature in a first set of layers of the sample, the first directional periodicity feature being distributed along a first measurement direction, wherein the stacked target according to the metrology formulation further includes a second directional periodicity feature in a second set of layers of the sample, the second directional periodicity feature being distributed along a second measurement direction different from the first measurement direction; One or more light-collecting optics configured to generate one or more images of the stacked target on one or more detectors based on the diffraction of the one or more first illumination beams and the one or more second illumination beams through the stacked target during the implementation of the metrological formulation, wherein the diffraction order of the one or more first illumination beams contributes to the formation of a resolved image with periodicity characteristics only in the first direction, and wherein the diffraction order of the one or more second illumination beams contributes to the formation of a resolved image with periodicity characteristics only in the second direction; and A controller communicatively coupled to the one or more detectors, the controller comprising one or more processors configured to execute program instructions, thereby causing the one or more processors to: Based on the one or more images, a first stacked measurement is generated along the first measurement direction; and A second stacked measurement is generated along the second measurement direction based on the one or more images.

22. An optical metrology method, comprising: A stacked target on a sample is illuminated using 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 simultaneously incident on the stacked target, wherein the stacked target according to the metrological formulation contains a first directional periodicity feature in a first set of layers of the sample, the first directional periodicity feature being distributed along a first measurement direction, wherein the stacked target according to the metrological formulation further contains a second directional periodicity feature in a second set of layers of the sample, the second directional periodicity feature being distributed along a second measurement direction different from the first measurement direction; Based on the diffraction of the one or more first illumination beams and the one or more second illumination beams on the stacked target, one or more images of the stacked target are generated on one or more detectors, wherein the diffraction order of the one or more first illumination beams contributes to the formation of a resolved image with periodic features only in the first direction, and wherein the diffraction order of the one or more second illumination beams contributes to the formation of a resolved image with periodic features only in the second direction. A first stacked measurement along the first measurement direction is generated based on the one or more images; and A second stacked measurement is generated along the second measurement direction based on the one or more images.

23. The optical metrology method according to claim 22, wherein the first illumination beam and the second illumination beam are distinguished by at least one of the following: azimuth angle of incidence on the stacked target and height angle of incidence on the stacked target, wavelength, bandwidth, polarization, intensity, numerical aperture in the illumination pupil of one or more illumination optics, and lobe shape or tilt in the illumination pupil.

24. The optical metrology method of claim 22, wherein the first illumination beam comprises a single first illumination beam providing a first azimuth angle of incidence on the stacked target, and wherein the second illumination beam comprises a single second illumination beam providing a second azimuth angle of incidence on the stacked target.

25. The optical metrology method of claim 22, wherein the first illumination beam comprises a first set of two illumination beams providing a first set of symmetrically opposite azimuth angles of incidence on the stacked target, wherein the second illumination beam comprises a second set of two illumination beams providing a second set of symmetrically opposite azimuth angles of incidence on the stacked target.

26. The optical metrology method of claim 25, wherein illuminating the stacked target on the sample using the one or more first illumination beams and the one or more second illumination beams comprises: The first set of two illumination beams and the second set of two illumination beams are simultaneously guided to the stacked target.

27. The optical metrology method of claim 25, wherein illuminating the stacked target on the sample using one or more first illumination beams and one or more second illumination beams comprises: One of the two illumination beams in the first group and one of the two illumination beams in the second group are directed to the superimposed target as the first exposure; and The other of the two illumination beams in the first group and the other of the two illumination beams in the second group are directed to the stacked target as a second exposure.

28. The optical metrology method of claim 23, wherein generating one or more images of the superimposed target on one or more detectors based on the diffraction of the one or more first illumination beams and the one or more second illumination beams through the superimposed target using one or more light-collecting optics comprises: The following methods are used to generate the one or more images of the overlay target: Two or more diffraction lobes along the first measurement direction are generated from each of the one or more first illumination beams by the periodic characteristics of the first direction; and Two or more diffraction lobes along the second measurement direction are generated from each of the one or more second illumination beams by the periodic characteristics of the second direction.

29. The optical metrology method of claim 23, wherein generating one or more images of the superimposed target on one or more detectors based on the diffraction of the one or more first illumination beams and the one or more second illumination beams through the superimposed target using one or more light-collecting optics comprises: The following methods are used to generate the one or more images of the overlay target: The 0th-order and 1st-order diffraction lobes along the first measurement direction are generated from each of the one or more first illumination beams by the periodic characteristics of the first direction. and The 0th-order and 1st-order diffraction lobes along the second measurement direction are generated from each of the one or more second illumination beams by means of the periodic characteristics of the second direction. The one or more images of the superimposed target are tilted bright-field images.

30. The optical metrology method of claim 23, wherein generating one or more images of the superimposed target on one or more detectors based on the diffraction of the one or more first illumination beams and the one or more second illumination beams through the superimposed target using one or more light-collecting optics comprises: The following methods are used to generate the one or more images of the overlay target: The 0th-order diffraction lobes, 1st-order diffraction lobes, and 2nd-order diffraction lobes along the first measurement direction are generated from each of the one or more first illumination beams by means of the periodic characteristics of the first direction. and The 0th-order diffraction lobes, 1st-order diffraction lobes, and 2nd-order diffraction lobes generated along the second measurement direction from each of the one or more second illumination beams by means of the periodic characteristics of the second direction. The one or more light-collecting optical devices include one or more elements for blocking the 0th-order diffraction lobes along the first and second measurement directions. The one or more images of the superimposed target are dark field images.

31. The optical metrology method of claim 23, wherein the first directional periodicity feature comprises gratings having a first pitch and a second pitch distributed along the first measurement direction to form a first directional moiré structure, wherein the second directional periodicity feature comprises gratings having the first pitch and the second pitch distributed along the second measurement direction to form a second directional moiré structure, wherein generating one or more images of the superimposed target on one or more detectors based on the diffraction of the one or more first illumination beams and the one or more second illumination beams by one or more light-collecting optical devices comprises: The following methods are used to generate the one or more images of the overlay target: The 0th-order diffraction lobe, the 1st-order diffraction lobe of the grating having the first pitch in the first-direction moiré structure, and the 1st-order diffraction lobe of the grating having the second pitch in the first-direction moiré structure, associated with each of the one or more first illumination beams. and The 0th-order diffraction lobe, the 1st-order diffraction lobe, and the 1st-order diffraction lobe of the grating with the second pitch in the second-direction moiré structure associated with each of the one or more second illumination beams.

Images