Scanning overlay metrology using overlay targets with multiple spatial frequencies

Abstract

The overlay metrology system may include an illumination source and illumination optics to illuminate an overlay target on a specimen with illumination from the illumination source while the specimen is moving relative to the illumination from the illumination source according to a metrology recipe. The overlay target may include one or more cells, where a single cell is suitable for measurement along a particular direction. Such a cell may include two or more gratings having different pitches. Additionally, the system may include two or more photodetectors, where each photodetector is configured to capture three diffraction lobes from the two or more grating structures. The system may further include a controller to determine an overlay metrology associated with each cell of the overlay target.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 63 / 295,959, filed on January 3, 2022, entitled “NEW OVL METROLOGY TARGET DESIGN FOR SCANNING SCATTEROMETRY OPTICAL TARGET,” to Itay Gdor, Yuval Lubashevsky, Daria Negri, and Eitan Hajaj, which is incorporated by reference in its entirety.

[0002] FIELD OF THE DISCLOSURE This disclosure relates to overlay metrology, and more particularly, to scanning overlay metrology. [Background technology]

[0003] The increasing demand for smaller semiconductor devices has led to a corresponding increase in the demand for accurate and efficient metrology. One approach to increase the efficiency and throughput of metrology tools is to generate metrology data on a specimen while it is moving, rather than when it is in a stationary position within the measurement field of view. In this way, the time delay associated with positioning a translation stage prior to measurement can be eliminated or reduced. However, increasing the sensitivity and throughput of such measurements remains a central challenge for such scanning metrology methods. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0364279 [Patent Document 2] U.S. Patent No. 10,824,079 [Patent Document 3] U.S. Patent No. 10,197,389 Summary of the Invention [Problem to be solved by the invention]

[0005] It would therefore be desirable to provide a system and method for overcoming the above-mentioned shortcomings. [Means for solving the problem]

[0006] An overlay metrology system is disclosed in accordance with one or more exemplary embodiments. In one exemplary embodiment, the system includes an illumination source. In another exemplary embodiment, the system includes an illumination subsystem with one or more illumination optics, and illuminates an overlay target on a specimen with illumination from the illumination source according to a metrology recipe while the specimen is moving relative to the illumination from the illumination source. In another exemplary embodiment, the overlay target includes one or more cells according to a metrology recipe, at least a portion of the cells including a double grating having a first series of features distributed along a measurement direction with a first pitch and a second pitch in an overlap region, and further includes a single grating having a second series of features distributed along the measurement direction with the first pitch. In another exemplary embodiment, the system includes a collection subsystem with one or more collection optics, and directs positive and negative first order diffractions of the illumination by both the double grating and the single grating associated with the first and second pitches to one or more detectors disposed at a pupil plane according to the metrology recipe, where the one or more detectors generate time-varying interference signals associated with the positive and negative first order diffractions of the illumination by both the double grating and the single grating. In another exemplary embodiment, a system includes a controller to determine an overlay metrology between the dual grating and the single grating based on a time-varying interference signal.

[0007] An overlay target is disclosed in accordance with one or more exemplary embodiments. In one exemplary embodiment, the target includes one or more cells on the specimen, at least some of the cells including a double grating having a first series of features distributed along the measurement direction at a first pitch and a second pitch in the overlap region, and further includes a single grating on a second layer of the specimen having a second series of features distributed along the measurement direction at the first pitch. In another exemplary embodiment, the first and second pitches are selected such that, for at least one operating wavelength, positive first order diffractions from the first and second pitches overlap in a first overlap angle region, and negative first order diffractions from the first and second pitches overlap in a second overlap angle region. In another exemplary embodiment, a time-varying interference signal in the first and second overlap regions generated when the overlay target is scanned relative to the illumination beam indicates overlay between the double grating and the single grating.

[0008] An overlay metrology system is disclosed in accordance with one or more exemplary embodiments. In one exemplary embodiment, the system includes an illumination source. In another exemplary embodiment, the system includes an illumination subsystem with one or more illumination optics, and illuminates an overlay target on a specimen with illumination from the illumination source according to a metrology recipe while the specimen is moving relative to the illumination from the illumination source. In another exemplary embodiment, the overlay target includes one or more cells according to a metrology recipe, at least a portion of the cells including a first grating having a first series of features distributed along a measurement direction with a first pitch on a first layer of the specimen and a second grating having a second series of features distributed along the measurement direction with a second pitch different from the first pitch on a second layer of the specimen. In another exemplary embodiment, the system includes a collection subsystem with one or more collection optics, and directs measured diffraction orders to one or more detectors at a pupil plane according to a metrology recipe, where the measured diffraction orders include positive and negative first diffraction orders of illumination by the first grating and positive and negative first and second diffraction orders of illumination by the second grating. In another exemplary embodiment, a system includes a controller to determine an overlay metrology between a first layer and a second layer of the specimen based on the measured diffraction orders.

[0009] An overlay target is disclosed according to one or more exemplary embodiments. In one exemplary embodiment, the target includes one or more cells on the specimen, at least some of the cells include a first grating including a first series of features distributed along the measurement direction at a first pitch on a first layer of the specimen, and a second grating including a second series of features distributed along the measurement direction at a second pitch different from the first pitch on a second layer of the specimen. In another exemplary embodiment, the first and second pitches are selected such that positive first diffraction order from the first grating overlaps with positive first and second diffraction orders from the second grating in a first set of overlapping regions, where negative first diffraction order from the first grating overlaps with negative first and second diffraction orders from the second grating in a second set of overlapping regions. In another exemplary embodiment, a time-varying interference signal in the first and second sets of overlapping regions indicates overlay between the first and second layers of the specimen.

[0010] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention. [Brief description of the drawings]

[0011] The many advantages of the present disclosure may be better understood by those skilled in the art by reference to the following drawings. [Figure 1A] FIG. 1 is a conceptual diagram of a system for performing scatterometry overlay metrology on an overlay target suitable for single cell measurements along any particular measurement direction, in accordance with one or more embodiments of the present disclosure. [Figure 1B] FIG. 1 is a schematic diagram of an overlay metrology tool in accordance with one or more embodiments of the present disclosure. [Diagram 2] FIG. 2 is a top view of an illumination pupil plane of an overlay metrology tool in accordance with one or more embodiments of the present disclosure. [Figure 3A] FIG. 2 is a top view of a single pitch grating in accordance with one or more embodiments of the present disclosure. [Figure 3B] FIG. 2 is a top view of a dual pitch grating in accordance with one or more embodiments of the present disclosure. [Figure 3C] 3C depicts a series of panels illustrating the conceptual configuration of the dual pitch grating of FIG. 3B in accordance with one or more embodiments of the present disclosure. [Figure 3D] FIG. 1C illustrates a top view of a cell of an overlay target in which a single pitch grating and a dual pitch grating are printed in non-overlapping areas within the cell in accordance with one or more embodiments of the present disclosure. [Figure 3E] FIG. 13 is a top view of a cell of an overlay target in which a single pitch grating and a dual pitch grating are printed on different layers of a specimen in an overlapping area within a cell, in accordance with one or more embodiments of the present disclosure. [Figure 3F] FIG. 3C is a conceptual diagram of a collection pupil plane of an overlay metrology tool including diffraction from a single pitch grating and a dual pitch grating as shown in FIG. 3D or FIG. 3E in accordance with one or more embodiments of the present disclosure. [Figure 4A] FIG. 1 is a top view of a cell of an overlay target comprising a first grating having a first pitch (P1) printed in a non-overlapping area within the cell, and a second grating having a second pitch (P2) different from the first pitch, in accordance with one or more embodiments of the present disclosure. [Figure 4B] FIG. 4B is a conceptual diagram of a collection pupil plane of an overlay metrology tool including diffraction from a single pitch grating and a dual pitch grating as shown in FIG. 4A in accordance with one or more embodiments of the present disclosure. [Diagram 5] FIG. 1 is a flow diagram illustrating steps performed in a method for single cell scanning overlay metrology in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with respect to certain embodiments and certain features thereof. The embodiments described herein are to be considered as illustrative and not restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail may be made therein without departing from the spirit and scope of the present disclosure.

[0013] Embodiments of the present disclosure relate to systems and methods for single-cell scanning overlay metrology, and in particular, some embodiments of the present disclosure relate to overlay targets suitable for single-cell scanning overlay metrology, and some embodiments relate to overlay metrology tools suitable for characterizing such targets and thereby generating overlay metrology.

[0014] In some embodiments, an overlay target suitable for single-cell scanning overlay metrology includes a cell having grating structures associated with two lithography exposures oriented at a pitch along a particular measurement direction, where the grating structures may be in the same or different layers of the specimen. Additionally, an overlay metrology tool suitable for generating overlay metrology associated with two lithography exposures may include two photodetectors, where each is positioned (e.g., in a pupil plane) to capture at least a portion of three diffraction lobes from the grating structure. For example, a first photodetector may capture at least a portion of three positive order diffraction lobes, and a second photodetector may capture at least a portion of three negative order diffraction lobes. It is contemplated herein that an overlay metrology along a measurement direction between two lithography exposures may be generated based on a difference between time-varying interference signals captured by the photodetectors as the specimen is scanned.

[0015] In addition, the overlay target may include multiple cells having grating structures oriented along different measurement directions to provide overlay metrology along the different measurement directions.

[0016] It is recognized herein that many scatterometry overlay metrology techniques generally determine overlay by illuminating an overlay target having grating structures in two layers (e.g., grating-over-grating structures), where the overlay metrology is based on the asymmetry between positive and negative diffraction orders. For example, various scatterometry techniques are described in U.S. Patent Publication No. 2021 / 0364279, published March 11, 2021, U.S. Patent No. 10,824,079, issued November 3, 2020, U.S. Patent No. 10,197,389, issued February 9, 2019, and Adel et al., "Diffraction order control in overlay metrology: a review of the roadmap options," Proc. SPIE. 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 692202. (2008), all of which are incorporated by reference in their entireties herein.

[0017] However, existing scatterometry overlay techniques typically require or benefit from the measurement of two or more cells having different grating structure configurations. For example, different cells may include grating structures having different intentional overlay offsets. As another example, an overlay target including grating structures having different pitches may include different cells whose configuration pitches are provided in different layers.

[0018] Embodiments of the present disclosure relate to scanning overlay metrology using overlay targets suitable for providing overlay metrology and single cell per overlay metrology. It is contemplated herein that single cell metrology may provide higher measurement throughput than multi-cell metrology.

[0019] In some embodiments, a cell of an overlay target suitable for single-cell scanning overlay metrology includes a single pitch grating on one layer and a dual pitch grating (e.g., a dual grating) on ​​another layer. For example, a dual pitch grating may be functionally characterized by two grating structures with different pitches that overlap on a common area of ​​a specimen layer. However, it should be understood that the constituent features of the dual pitch grating are fabricated using a common lithographic exposure. Thus, the characterization of a dual grating as being formed from two grating structures with different pitches is purely conceptual, with the overlapping portions of the two grating structures with different pitches being formed as a common element.

[0020] It is contemplated herein that illuminating a dual pitch grating can generate two sets of diffraction orders associated with the two constituent pitches, and further, illuminating an overlay target (or a cell therein) with both a single pitch grating and a dual pitch grating can generate three sets of diffraction orders.

[0021] In some embodiments, the pitches of the single pitch grating and the dual pitch grating are selected such that the first order diffraction lobes associated with the three selected pitches at least partially overlap (e.g., in the pupil plane). For example, the +1 order diffraction lobes associated with the three pitches may at least partially overlap at a first position in the pupil plane, and the -1 order diffraction lobes associated with the three pitches may at least partially overlap at a second position in the pupil plane. It is contemplated herein that photodetectors disposed at first and second positions in the pupil plane may capture time-varying interference signals as the specimen is scanned, where an overlay metrology between the single pitch grating and the dual pitch grating may be generated based on the difference between these time-varying interference signals. It is further contemplated herein that such overlay metrology may be similar to the overlay metrology associated with triple grating targets generally described in U.S. Patent Application Serial No. 17 / 119,536, filed December 11, 2020, the entirety of which is incorporated herein by reference. However, it is noted that overlay targets including single pitch gratings and dual pitch gratings as disclosed herein may have several advantages over triple grating overlay targets described in U.S. Patent Application No. 17 / 119,536, filed December 11, 2020, which is incorporated by reference and referenced above. In particular, overlay targets including single pitch gratings and dual pitch gratings as disclosed herein may avoid undesirable edge diffraction and scattering effects associated with triple grating structures.

[0022] In some embodiments, a cell of an overlay target suitable for single-cell scanning overlay metrology includes two single-pitch gratings having different pitches (e.g., a first pitch and a second pitch), where the first diffraction order lobe associated with the first pitch overlaps with portions of both the first and second diffraction orders associated with the second pitch. For example, the +1 diffraction order lobe (D P1,+1 ) are both the +1 and +2 order diffraction lobes (D P2,+1 and D. P2,+2) may overlap with the −1 order diffraction lobe (D P1,-1 ) is the diffraction lobe of both the -1st and -2nd orders associated with the second pitch (D P2,-1 and D. P2,-2 In some embodiments, the overlay metrology tool may overlap D P2,+1 and D. P2,+2 Both and D P1,+1 a first photodetector positioned at a first position in the pupil plane and sized to capture the overlap of D P2,-1 and D. P2,-2 Both and D P1,-1 and a second photodetector disposed at a first position in the pupil plane and sized appropriately to capture an overlap of the first and second photodetectors. It is contemplated herein that such first and second photodetectors may capture time-varying interference signals as the specimen is scanned, and an overlay measurement between the two single pitch gratings may be generated based on these time-varying interference signals.

[0023] Some embodiments of the present disclosure relate to providing recipes for configuring an overlay metrology tool to facilitate overlay metrology based on selected diffraction orders. An overlay metrology tool is typically configurable according to a recipe that includes a set of parameters for controlling various aspects of the overlay metrology, such as, but not limited to, illumination of the specimen, collection of light from the specimen, or position of the specimen during measurement. In this manner, an overlay metrology tool may be configured to provide a selected type of measurement for one or more overlay target designs of interest. For example, a metrology recipe may include illumination parameters, such as, but not limited to, illumination wavelength, illumination pupil distribution (e.g., distribution of illumination angles and associated intensities of illumination at those angles), polarization of incident illumination, or spatial distribution of illumination. As another example, a metrology recipe may include collection parameters, such as, but not limited to, collection pupil distribution (e.g., desired distribution of angular light from the specimen used for measurement and associated filtered intensities at those angles), collection field stop settings for selecting portions of the specimen of interest, polarization of collected light, wavelength filters, or parameters for controlling one or more detectors. As a further example, a metrology recipe may include various parameters associated with the specimen position during measurement, such as, but not limited to, the specimen height, the specimen orientation, whether the specimen is stationary during the measurement or whether the specimen is moving during the measurement (along with associated parameters describing the speed, scan pattern, etc.).

[0024] 1A-4B, systems and methods for single-cell scanning scattering overlay metrology in accordance with one or more embodiments of the present disclosure are described in more detail.

[0025] Figure 1A is a conceptual diagram of an overlay metrology system 100 for performing scatterometry overlay metrology on an overlay target 102 suitable for single cell measurements along any particular measurement direction, in accordance with one or more embodiments of the present disclosure. In some embodiments, the overlay metrology system 100 includes an overlay metrology tool 104 for performing scatterometry overlay metrology on overlay targets 102 distributed throughout a specimen 106. Figure 1B is a schematic diagram of the overlay metrology tool 104, in accordance with one or more embodiments of the present disclosure.

[0026] For the purposes of this disclosure, the term overlay is generally used to describe the relative positions of features on a specimen created by two or more lithographic patterning steps, and the term overlay error describes the deviation of features from a nominal arrangement. In this context, overlay metrology may be expressed as a measurement of the relative positions, or a measurement of the overlay error associated with these relative positions. For example, a multi-layer device may include features patterned on multiple specimen layers using different lithographic steps for each layer, and the alignment of features between layers typically needs to be tightly controlled to ensure proper performance of the resulting device. Thus, overlay metrology may characterize the relative positions of features on two or more specimen layers. As another example, features may be created on a single specimen layer using multiple lithographic steps. Such techniques, commonly referred to as double or multiple patterning techniques, may facilitate the creation of high density features close to the resolution of the lithography system. In this regard, overlay metrology may characterize the relative positions of features from different lithographic steps on this single layer. It should be understood that examples and illustrations throughout this disclosure relating to particular applications of overlay metrology are provided for illustrative purposes only and should not be construed as limiting the disclosure.

[0027] Further, the term scatterometry metrology is used herein to broadly encompass the terms scatterometry-based metrology and diffraction-based metrology, in which a specimen having periodic features on one or more specimen layers is illuminated with an illumination beam having a limited angular range, and one or more different diffraction orders are collected for measurement. Additionally, the term scanning metrology is used to describe metrology measurements that are generated when the specimen is moving relative to the illumination used for the measurement. In a general sense, scanning metrology may be performed by moving the specimen, the illumination, or both. Thus, specific descriptions herein of particular techniques for performing scanning metrology are merely exemplary and should not be construed as limiting.

[0028] In some embodiments, the overlay metrology tool 104 includes an illumination subsystem 108 for generating illumination in the form of one or more illumination beams 110 to illuminate the specimen 106, and a collection subsystem 112 for collecting light from the illuminated specimen 106. For example, the one or more illumination beams 110 may be angularly confined on the specimen 106 such that a grating structure within one or more cells of the overlay target 102 may generate distinct diffraction orders. Additionally, the one or more illumination beams 110 may be spatially confined such that they illuminate selected portions of the overlay target 102. For example, each of the one or more illumination beams 110 may be spatially confined to illuminate a particular cell of the overlay target. In some embodiments, the one or more illumination beams 110 underfill a particular cell of the overlay target.

[0029] The collection subsystem 112 may then collect at least some diffraction orders associated with the diffraction of the illumination beam 110 from the overlay target 102. Additionally, the collection subsystem 112 may include at least two photodetectors 114a,b positioned in the collection pupil plane 116 at positions associated with a time-varying interference signal indicative of overlay. For example, as described in more detail below, suitable positions for the photodetectors 114 may include, but are not limited to, positions indicative of capture of three diffraction orders from a grating structure in the overlay target 102.

[0030] In some embodiments, the overlay metrology tool 104 includes a translation stage 118 to scan the specimen 106 through a measurement field of view of the overlay metrology tool 104 during measurement to perform scanning metrology. In some embodiments, the overlay metrology tool 104 includes a beam scanning subsystem 120 configured to modify or control a position of the at least one illumination beam 110 on the specimen 106. For example, the beam scanning subsystem 120 may scan the illumination beam 110 in a direction orthogonal to a scanning direction (e.g., a direction in which the translation stage 118 scans the specimen 106) during measurement. In this manner, scanning metrology may be performed with any relative motion of the specimen 106 and the illumination beam 110.

[0031] In some embodiments, the overlay metrology system 100 includes a controller 122 communicatively coupled to the overlay metrology tool 104. The controller 122 may include one or more processors 124 and a memory device 126, or memory. For example, the one or more processors 124 may be configured to execute a set of program instructions retained in the memory device 126. In this manner, the controller 122 may perform any of the various process steps described throughout this disclosure, such as, but not limited to, receiving a time-varying interference signal from the optical detector 114, processing or filtering the time-varying interference signal, or generating an overlay metrology associated with the specimen 106 based on the time-varying interference signal.

[0032] 2-4B, the collection of diffraction orders from the overlay target 102 and the arrangement of the photodetector 114 for single-cell scanning scatterometry overlay metrology will be described in more detail in accordance with one or more embodiments of the present disclosure. In particular, FIG. 2 illustrates a non-limiting illumination pupil distribution, FIGS. 3A-3F illustrate a first non-limiting design of the overlay target 102, and FIGS. 4A-4B illustrate a second non-limiting design of the overlay target 102.

[0033] 2 is a top view of an illumination pupil plane 128 of an overlay metrology tool 104 (e.g., as shown in FIG. 1B ) in accordance with one or more embodiments of the present disclosure. In some embodiments, the illumination subsystem 108 illuminates the overlay target 102 at normal incidence (or near normal incidence) with one or more illumination beams 110, as shown in FIG. 2A . For example, FIG. 2A illustrates the illumination beams 110 at the center of the pupil boundary 202 of the illumination pupil plane 128. Furthermore, the one or more illumination beams 110 may illuminate the overlay target 102 at a limited range of incidence angles, as indicated by their limited size within the collection pupil plane 116. In this regard, the overlay target 102 may diffract the one or more illumination beams 110 into separate diffraction orders.

[0034] It is recognized herein that the distribution of diffraction orders of the illumination beam 110 due to periodic structures in the overlay target 102 can be affected by various parameters, such as, but not limited to, the wavelength of the illumination beam 110, the angle of incidence of the illumination beam 110 in both elevation and azimuth directions, the pitch of the grating of the overlay target 102, or the numerical aperture (NA) of the collection lens. Thus, in embodiments of the present disclosure, the illumination subsystem 108, the collection subsystem 112, and the overlay target 102 can be configured to provide a desired distribution of diffraction orders in a collection pupil suitable for generating a time-varying interference pattern indicative of overlay. For example, the illumination subsystem 108 and / or the collection subsystem 112 can be configured to generate metrology (e.g., using a metrology recipe) on an overlay target 102 having grating features with a selected range of pitches to provide a desired collection pupil distribution. Additionally, various components (e.g., aperture, pupil, etc.) of the illumination subsystem 108 and / or collection subsystem 112 may be adjustable (e.g., using a metrology recipe) to provide a desired collection pupil distribution.

[0035] Furthermore, the size and shape of the diffraction orders at the collection pupil plane 116 may generally be related to the size and shape of the illumination beam 110 on the specimen 106. For example, although not shown, if the illumination beam 110 is elongated, the associated diffraction orders may be elongated as well.

[0036] 3A-3D show a first non-limiting embodiment of an overlay target 102 suitable for scanning scatterometry overlay metrology of a single cell, where the cell 302 includes a single pitch grating 304 associated with a first lithography exposure and a dual pitch grating 306 associated with a second lithography exposure. In some embodiments, the single pitch grating 304 is fabricated on a first layer and the dual pitch grating 306 is fabricated on a second layer. In this manner, the associated overlay metrology may correspond to a measurement of the relative placement error between the first layer and the second layer. Furthermore, the single pitch grating 304 and / or the dual pitch grating 306 may be formed on a fully processed layer or as a patterned photoresist layer. For example, one grating may be formed on a fully processed layer and another grating may be formed on a photoresist layer that is subsequently exposed. In some embodiments, both the single pitch grating 304 and the dual pitch grating 306 are formed on a single layer. In this manner, the associated overlay metrology may correspond to the measurement of the relative placement error between different exposures of a multiple exposure fabrication process (eg, double patterning, etc.).

[0037] 3A is a top view of a single pitch grating 304 in accordance with one or more embodiments of the present disclosure. In some embodiments, the single pitch grating 304 has a selected pitch (P S ) along a measurement direction 310.

[0038] 3B is a top view of a dual pitch grating 306 in accordance with one or more embodiments of the present disclosure. In some embodiments, the dual pitch grating 306 has two characteristic pitches (P D1 ) and (P D2 ) in a set of grating features 312 having a pitch P D1 and P D2 may be provided.

[0039] FIG. 3C provides a series of panels illustrating a conceptual configuration of the dual pitch grating 306 of FIG. 3B in accordance with one or more embodiments of the present disclosure. Panel A shows a first pitch (P D1 ) and a second pitch (P D2 3C shows a second conceptual grating 316 having a first pitch grating 314 and a second conceptual grating 316 having a second pitch grating 316. Panels B and C show a conceptual overlap of the first conceptual grating 314 and the second conceptual grating 316 in a common area. In this manner, the grating feature 312 may be formed as a combination of the first conceptual grating 314 and the second conceptual grating 316. However, it should be understood that the depiction of FIG. 3C is merely for illustrative purposes to clarify the layout of the dual pitch grating 306. In particular, the first conceptual grating 314 and the second conceptual grating 316 are not fabricated in themselves, but are merely associated with the design of the dual pitch grating 306. As an example, the grating feature 312a is a single feature based on a combination of features from each of the first conceptual grating 314 and the second conceptual grating 316 shown in FIG. 3C.

[0040] 3D and 3E show non-limiting layouts of a single pitch grating 304 and a dual pitch grating 306 within a cell 302 of the overlay target 102.

[0041] 3D is a top view of a cell 302 of the overlay target 102 in which a single pitch grating 304 and a dual pitch grating 306 are printed (e.g., side-by-side) in non-overlapping areas within the cell 302, in accordance with one or more embodiments of the present disclosure. In this configuration, the single pitch grating 304 and the dual pitch grating 306 may be fabricated on different layers of the specimen 106 or on a common layer of the specimen 106.

[0042] 3E is a top view of a cell 302 of the overlay target 102 in which a single pitch grating 304 and a dual pitch grating 306 are printed on different layers of the specimen 106 within an overlapping area within the cell 302, in accordance with one or more embodiments of the present disclosure. As such, the cell 302 can include a variation of a grating-over-grating structure formed with the single pitch grating 304 and the dual pitch grating 306.

[0043] 3D and 3E, the illumination beam 110 may be incident on both the single pitch grating 304 and the dual pitch grating 306 simultaneously. In this manner, the single pitch grating 304 and the dual pitch grating 306 may be incident on the single pitch grating 304 at the pitch P S and the pitch P of the dual pitch grating 306 D1 and P D2 Additionally, although not shown, the illumination beam 110 may be extended in a direction perpendicular to the measurement direction 310 to mitigate target induced noise caused by imperfections in the cell 302, such as, but not limited to, roughness of the single pitch grating 304 or dual pitch grating 306.

[0044] FIG. 3F is a conceptual diagram of the collection pupil plane 116 of the overlay metrology tool 104, including diffraction from a single pitch grating 304 and a dual pitch grating 306, as shown in FIG. 3D or 3E, in accordance with one or more embodiments of the present disclosure.

[0045] In some embodiments, the pitch associated with the cells 302 (e.g., the pitch P of the single-pitch grating 304) S , the pitch P of the dual pitch grating 306 D1 and P D2 ) and / or various parameters in the metrology recipe (e.g., the wavelength of the illumination beam 110) are S , P D1 and P D2 are chosen so that the first order diffraction lobes from each of the pitches P S , P D1 and P D2The +1st order diffraction lobe D associated with the diffraction of the illumination beam 110 by S,+1 , D D1,+1 , and D D2,+1 , which overlap at a first overlap region 318. FIG. 3F further illustrates the pitch P S , P D1 and P D2 The −1 order diffraction lobe D associated with the diffraction of the illumination beam 110 by S,-1 , D D1,-1 , and D D2,-1 , which overlap at a second overlap region 320. Figure 3F also shows the zeroth diffraction order (D0) (e.g., specular reflection).

[0046] It is contemplated herein that scanning the overlay target 102 along the measurement direction 310 relative to the illumination beam 110 (or vice versa) will result in time-varying interference signals at the first overlap region 318 and the second overlap region 320 that are indicative of overlay error between the first and second lithographic exposures associated with the single pitch grating 304 and the dual pitch grating 306. Accordingly, in some embodiments, the overlay metrology tool 104 includes photodetectors 114 at the overlap region of the collection pupil plane 116. For example, FIG. 3F illustrates a first photodetector 114a at the first overlap region 318 and a second photodetector 114b at the second overlap region 320.

[0047] It is further noted herein that the active area of ​​the photodetector 114 (e.g., as shown by the dashed circle in FIG. 3F) may generally be any suitable size sufficient to capture the associated time-varying signal. For example, the active area of ​​the photodetector 114 may be larger than the associated overlap area. In this configuration, the photodetector 114 may capture additional signals beyond the associated time-varying signal, such as, but not limited to, a constant signal. However, such signals may be filtered out or ignored using any technique known in the art.

[0048] In particular, the intensity measured by the photodetector 114 is S , PD1 and P D2 is the product of all the fields associated with

number

[0049] Focusing only on the time-varying signal of the +1st order diffraction lobe, we can write

number

[0050] Because these terms have different frequencies, these signals may be separated (e.g., by controller 122) so that the phase difference of each component may be measured. In the phase difference, the constant phase contribution from the specimen 106 may be eliminated so that the phase contribution is obtained from the initial pitch position (e.g., the initial GP and associated initial phase of the illumination beam 110 from the start of the scan). Overlay may then be determined as follows:

number

number

[0051] It is recognized herein that the determination of overlay represented by equations (1)-(4) is similar to the approach of determining overlay using a triple grating target as described in U.S. Patent Application No. 17 / 119,536, filed December 11, 2020, which is incorporated by reference in its entirety. However, as previously described herein, because measurements of overlay targets 102 having single pitch gratings 304 and dual pitch gratings 306 disclosed herein avoid undesirable edge effects and scattering associated with triple grating designs, the systems and methods disclosed herein may provide overlay metrology with greater sensitivity than the triple grating approach.

[0052] 4A-4B, which show a second non-limiting embodiment of an overlay target 102 suitable for single cell scanning scatterometry overlay metrology, where the cell 302 includes two single pitch gratings having different pitches.

[0053] 4A is a top view of a cell 302 of an overlay target 102 in which a first grating 402 having a first pitch (P1) and a second grating 404 having a second pitch (P2) different from the first pitch are printed (e.g., side-by-side) in a non-overlapping region in the cell 302. In a manner similar to the design shown in FIG. 3D, the first grating 402 and the second grating 404 can be fabricated on a common layer or different layers of the specimen 106. Furthermore, although not shown, the first grating 402 and the second grating 404 can be fabricated on different layers of the specimen 106 in the overlapping region to form a grating-over-grating structure (e.g., similar to the design shown in FIG. 3F). Furthermore, in both configurations, the illumination beam 110 can be incident on both the single pitch grating 304 and the dual pitch grating 306 simultaneously.

[0054] FIG. 4B is a conceptual diagram of the collection pupil plane 116 of the overlay metrology tool 104, including diffraction from the single pitch grating 304 and the dual pitch grating 306 as shown in FIG. 4A, in accordance with one or more embodiments of the present disclosure.

[0055] In some embodiments, the pitches associated with the cells 302 (e.g., pitch P1 of the first grating 402 and pitch P2 of the second grating 404) and / or various parameters of the metrology recipe (e.g., the wavelength of the illumination beam 110, etc.) are selected such that a first order diffraction lobe from the first grating 402 overlaps with portions of both the first and second order diffraction lobes from the second grating 404.

[0056] For example, FIG. 4B shows the +1 order diffraction lobe (D P1,+1 ) is the +1st order diffraction lobe (D P2,+1 ) in the first overlap region 406, and further overlaps with a +2nd order diffraction lobe (D P2,+2 4B shows that the −1 order diffraction lobe (D P1,-1 ) is the −1st order diffraction lobe (D P2,-1 ) at a third overlap region 410, and further overlaps with a −2nd order diffraction lobe (D P2,-2 ) at a fourth overlap region 412. FIG. 4B also shows the zeroth diffraction order (D0) (e.g., specular reflection).

[0057] It is contemplated herein that scanning the overlay target 102 along the measurement direction 310 relative to the illumination beam 110 (or vice versa) will result in a time-varying interference signal at the overlap regions 406-412 that is indicative of an overlay error between the first and second lithographic exposures associated with the first grating 402 and the second grating 404. Accordingly, in some embodiments, the overlay metrology tool 104 includes photodetectors 114 at the overlap regions in the collection pupil plane 116. For example, FIG. 4B shows a first photodetector 114a capturing the first and second overlap regions 406, 408 and a second photodetector 114b capturing the third and fourth overlap regions 410, 412. It is contemplated herein that the overlay between the lithographic exposures forming the first grating 402 and the second grating 404 may be derived in a manner similar to that shown in equations (1)-(4) for the design of the overlay target 102 shown in Figures 3A-3F.

[0058] Further, in a manner similar to that described in FIG. 3F, it is noted herein that the active area of ​​the photodetector 114 (e.g., shown by a dashed circle in FIG. 4B) may generally be any suitable size sufficient to capture the associated time-varying signal. For example, the active area of ​​the photodetector 114 may be larger than the associated overlap area. In this configuration, the photodetector 114 may capture additional signals beyond the associated time-varying signal, such as, but not limited to, a constant signal. However, such signals may be filtered out or ignored using any technique known in the art.

[0059] 3A-4B generally, it is noted that FIGS. 3A-4B illustrate various non-limiting designs of a particular cell 302 associated with a particular measurement direction 310. However, it should be understood that overlay target 102 may include any number of cells 302 along any number of different measurement directions, which may have any orientation relative to the direction of movement of specimen 106 (e.g., a stage scan direction provided by translation stage 118) or relative to the direction of movement of illumination beam 110 (e.g., a beam scan direction provided by beam scanning subsystem 120). For example, this specification contemplates any of the cell 302 arrangements and associated measurement configurations (e.g., stage scan direction or beam scan direction) provided in U.S. patent application Ser. No. 17 / 178,089, filed February 17, 2021, or U.S. patent application Ser. No. 17,708,958, filed March 30, 2022, both of which are incorporated by reference in their entireties into this specification and may be extended to the cell designs disclosed herein.

[0060] Referring again to FIG. 1A, additional components of the overlay metrology tool 104 are described in greater detail, in accordance with one or more embodiments of the present disclosure.

[0061] The photodetector 114 may generally include any type of photodetector known in the art suitable for capturing interference signals generated as the specimen 106 is translated by the translation stage 118 and / or the one or more illumination beams 110 are scanned by the beam scanning subsystem 120. For example, the photodetector 114 may include, but is not limited to, a high-speed photodiode, a photomultiplier tube, or an avalanche photodiode.

[0062] In a general sense, the bandwidth or response time of the photodetector 114 should be sufficient to resolve the temporal frequency of the interference fringes, which is related to the pitch of the constituent grating structures and the scanning speed along the measurement direction 310. For example, if the scanning speed along the measurement direction 310 is 10 centimeters per second and the target pitch is 1 micrometer, the interference signal will oscillate at a rate on the order of 100 kHz. In some embodiments, the photodetector 114 includes a photodetector having a bandwidth of at least 1 GHz. However, it should be understood that this value is not required. Rather, the bandwidth of the photodetector 114, the translation speed along the measurement direction, and the pitch of the moiré structures may be selected together to provide a desired sampling rate of the interference signal.

[0063] In some embodiments, the overlay metrology system 100 includes a controller 122 communicatively coupled to the overlay metrology tool 104. The controller 122 may include one or more processors 124 and a memory device 126 or memory. For example, the one or more processors 124 may be configured to execute a set of program instructions retained in the memory device 126.

[0064] The one or more processors 124 of the controller 122 may generally include any processor or processing element known in the art. For purposes of this disclosure, the term "processor" or "processing element" may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application specific integrated circuits (ASIC) devices, one or more field programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, the one or more processors 124 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in a memory). In some embodiments, the one or more processors 124 may be realized as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute programs configured to operate or operate in conjunction with the overlay metrology system 100 as described throughout this disclosure. Additionally, different subsystems of the overlay metrology 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 the present disclosure, but merely as illustrative. Furthermore, the steps described throughout the present disclosure may be performed by a single controller or may be performed by multiple controllers. In addition, the controller 122 may include one or more controllers housed in a common housing or in multiple housings. In this manner, any controller or combination of controllers may be packaged separately as a module suitable for integration into the overlay metrology system 100. Furthermore, the controller 122 may analyze or process data received from the optical detector 114 and provide the data to additional components within the overlay metrology system 100 or external to the overlay metrology system 100.

[0065] Additionally, memory device 126 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 124. For example, memory device 126 may include a non-transitory memory medium. By way of further example, memory device 126 may include, without limitation, read-only memory, random access memory, magnetic or optical memory devices (e.g., disks), magnetic tape, solid-state drives, and the like. It is further noted that memory device 126 may be housed in a common controller housing with one or more processors 124.

[0066] In this regard, the controller 122 may perform any of a variety of processing steps associated with overlay metrology. For example, the controller 122 may be configured to generate control signals to direct or control the overlay metrology tool 104 or any components thereof. For example, the controller 122 may be configured to direct the translation stage 118 to translate the specimen 106 along one or more measurement paths or swaths to scan one or more overlay targets through a measurement field of view of the overlay metrology tool 104, and / or direct the beam scanning subsystem 120 to position or scan one or more illumination beams 110 over the specimen 106. As another example, the controller 122 may be configured to receive a signal corresponding to a time-varying interference signal from the photodetector 114. As another example, the controller 122 may generate corrections to one or more additional fabrication tools based on the overlay metrology from the overlay metrology tool 104 as feedback and / or feedforward control of the one or more additional fabrication tools.

[0067] In another embodiment, the controller 122 captures the interference signal detected by the photodetector 114. The controller 122 may generally capture data, such as, but not limited to, the magnitude or phase of the time-varying interference signal, using any technique known in the art, such as, but not limited to, one or more phase-locked loops. Additionally, the controller 122 may capture the interference signal, or any data associated with the interference signal, using any combination of hardware (e.g., circuitry) or software techniques.

[0068] In some embodiments, the controller 122 determines an overlay metrology between layers of the overlay target 102 along the measurement direction based on a comparison of the interference signals. For example, the controller 122 may compare the magnitude and / or phase of the interference signals to generate an overlay metrology. For example, U.S. Pat. No. 10,824,079, issued Nov. 3, 2020, and incorporated herein by reference in its entirety, outlines the electric field of diffraction orders in a collection pupil and further provides a specific relationship between overlay in a pupil plane and measured intensity. It is contemplated herein that the systems and methods disclosed herein may extend the teachings of U.S. Pat. No. 10,824,079 to time-varying interference signals captured by photodetectors disposed in overlap regions as disclosed herein. In particular, it is contemplated herein that the overlay on the specimen may be proportional to an asymmetry, such as, but not limited to, the relative phase shift between two time-varying interference signals. In another example, the relative intensities of the diffraction orders in the pupil plane may be extracted from the time-varying interference signal. In this manner, any overlay algorithm based on the relative intensity difference of the diffraction orders known in the art may be applied to generate an overlay metrology.

[0069] Additionally, the controller 122 may calibrate or correct the overlay metrology based on known, assumed, or measured features of the specimen that may also affect the time-varying interference signal, such as, but not limited to, sidewall angles or other specimen asymmetries.

[0070] Referring again to FIG. 1B, various components of the overlay metrology tool 104 are described in greater detail, in accordance with one or more embodiments of the present disclosure.

[0071] In some embodiments, the illumination subsystem 108 includes an illumination source 136 configured to generate at least one illumination beam 110. The illumination from the illumination source 136 may include one or more selected wavelengths of light, including, but not limited to, ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0072] The illumination source 136 may include any type of illumination source suitable for providing at least one illumination beam 110. In some embodiments, the illumination source 136 is a laser source. For example, the illumination source 136 may include, but is not limited to, one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, etc. In this regard, the illumination source 136 may provide an illumination beam 110 having high coherence (e.g., high spatial coherence and / or temporal coherence). In some embodiments, the illumination source 136 includes a laser sustained plasma (LSP) source. For example, the illumination source 136 may include, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for housing one or more elements that may emit broadband illumination when excited into a plasma state by a laser source.

[0073] In some embodiments, the illumination subsystem 108 includes one or more optical components suitable for modifying and / or conditioning the illumination beam 110 and directing the illumination beam 110 to the specimen 106. For example, the illumination subsystem 108 may include one or more illumination lenses 138 (e.g., for collimating the illumination beam 110 and relaying the illumination pupil plane 128 and / or the illumination field plane 140). In some embodiments, the illumination subsystem 108 includes one or more illumination control optics 142 to shape or control the illumination beam 110. For example, the illumination control optics 142 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., stationary mirrors, translating mirrors, scanning mirrors, etc.).

[0074] In some embodiments, the overlay metrology tool 104 includes an objective lens 144 to focus the illumination beam 110 onto the specimen 106 (e.g., an overlay target having overlay target elements located on two or more layers of the specimen 106).

[0075] In some embodiments, the illumination subsystem 108 illuminates the specimen 106 with two or more illumination beams 110. Additionally, the two or more illumination beams 110 may, but are not required to, be incident on different portions of the specimen 106 (e.g., different cells of an overlay target) within a measurement field of view (e.g., the field of view of the objective lens 144). It is contemplated herein that the two or more illumination beams 110 may be generated using a variety of techniques. In some embodiments, the illumination subsystem 108 includes two or more apertures in the illumination field plane 140. In some embodiments, the illumination subsystem 108 includes one or more beam splitters to split illumination from the illumination source 136 into two or more illumination beams 110. In some embodiments, at least one illumination source 136 directly generates the two or more illumination beams 110. In a general sense, each illumination beam 110 may be considered to be part of a different illumination channel, regardless of the technique by which the various illumination beams 110 are generated.

[0076] In some embodiments, the collection subsystem 112 includes at least two photodetectors 114 (e.g., photodetectors 114a, b) disposed at a collection pupil plane 116 configured to capture light (e.g., collected light 146) from the specimen 106, where the collected light 146 includes overlap regions that provide a time-varying interference signal during scanning (e.g., overlap regions 318, 320 shown in FIG. 3F, overlap regions 406-412 shown in FIG. 4B, etc.). The collection subsystem 112 may include one or more optical elements suitable for modifying and / or conditioning the collected light 146 from the specimen 106. In some embodiments, the collection subsystem 112 includes one or more collection lenses 148 (e.g., to collimate the illumination beam 110 or relay a pupil and / or field plane), which may, but need not, include an objective lens 144. In some embodiments, the collection subsystem 112 includes one or more collection control optics 150 to shape or control the collected light 146. For example, the collection control optics 150 may include, without limitation, 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., stationary mirrors, translating mirrors, scanning mirrors, etc.).

[0077] In some embodiments, the illumination subsystem 108 and the collection subsystem 112 may utilize an objective lens 144. For example, FIG. 1B shows a beam splitter 152 that is used to couple the illumination beam 110 into the objective lens 144 to illuminate the specimen 106 and to couple collected light 146 from the objective lens 144 to the photodetector 114.

[0078] The overlay metrology tool 104 may include one or more collection channels 154. For example, as shown in FIG. 1B, the overlay metrology tool 104 may include one or more beam splitters 156 arranged to split the collected light 146 into the collection channels 154. Furthermore, FIG. 1B illustrates a configuration with two collection channels 154. It is contemplated herein that the photodetectors 114 may be arranged in any desired distribution among the one or more collection channels 154. In some embodiments, each collection channel 154 includes a single photodetector 114 (e.g., photodetector 114a or photodetector 114b). In this manner, each photodetector 114 may be positioned anywhere within the collection pupil plane 116, regardless of its physical size or associated components. In some embodiments, multiple photodetectors 114 are arranged in at least one collection channel 154. In this configuration, the multiple collection channels 154 may facilitate simultaneous measurement of different cells 302 (e.g., associated with different measurement directions).

[0079] In some embodiments, the collection subsystem 112 includes two or more photodetectors 114. In this manner, the photodetectors 114 may be distributed as desired. For example, as shown in FIG. 1B, the overlay metrology tool 104 may include one or more beam splitters 158 positioned to split the collected light 146 into collection channels 154. Further, the beam splitters 158 may be polarizing beam splitters, non-polarizing beam splitters, or combinations thereof. However, it should be understood that the illustration of two collection channels 154 in FIG. 1B is provided for illustrative purposes only and should not be construed as limiting. For example, the collection subsystem 112 may include a single collection channel 154 or multiple collection channels 154.

[0080] In some embodiments, the multiple collection channels 154 are configured to collect light from multiple illumination beams 110 on the specimen 106. For example, if the overlay target 102 has two or more cells 302 distributed in a direction different from the scanning direction, the overlay metrology tool 104 may simultaneously illuminate different cells 302 with different illumination beams 110 and simultaneously capture interference signals associated with each illumination beam 110. Additionally, in some embodiments, the multiple illumination beams 110 directed at the specimen 106 may have different polarizations. In this manner, the diffraction orders associated with each of the illumination beams 110 may be separated. For example, the polarizing beam splitter 158 may efficiently separate the diffraction orders associated with the different illumination beams 110. As another example, a polarizer may be used in one or more collection channels 154 to separate the desired diffraction orders for measurement.

[0081] In some embodiments, the overlay metrology tool 104 includes a beam scanning subsystem 120 to position, scan, or modulate the position of one or more illumination beams 110 on the specimen 106 during measurement.

[0082] The beam scanning subsystem 120 may include any type of element or combination of elements suitable for scanning the position of one or more illumination beams 110. In some embodiments, the beam scanning subsystem 120 includes one or more deflectors suitable for modifying the direction of the illumination beam 110. For example, the deflectors may include, but are not limited to, rotatable mirrors (e.g., mirrors with adjustable tip and / or tilt). Furthermore, the rotatable mirrors may be actuated using any technique known in the art. For example, the deflectors may include, but are not limited to, galvanometers, piezoelectric mirrors, or microelectromechanical systems (MEMS) devices. As another example, the beam scanning subsystem 120 may include an electro-optic modulator, an acousto-optic modulator, or the like.

[0083] The deflector may further be located at any suitable location within the overlay metrology tool 104. In some embodiments, the one or more deflectors are located at one or more pupil planes common to both the illumination subsystem 108 and the collection subsystem 112. In this regard, the beam scanning subsystem 120 may be a pupil plane beam scanner, and the associated deflector may modify the position of the one or more illumination beams 110 on the specimen 106 without affecting the position of the diffraction orders in the collection pupil plane 116. Furthermore, the distribution of the one or more illumination beams 110 in the illumination field plane 140 may be more stable as the beam scanning subsystem 120 changes the position of the one or more illumination beams 110 on the specimen 106. Pupil plane beam scanning is generally described in U.S. Patent Application No. 17 / 142,783, filed January 6, 2021, which is incorporated by reference in its entirety.

[0084] Reference is now made to Figure 5, which is a flow diagram illustrating steps performed in a method 500 for single-cell scanning overlay metrology, in accordance with one or more embodiments of the present disclosure. Applicants note that the embodiments and enabling techniques described herein above in connection with overlay metrology system 100 should be construed as extending to method 500. However, it is further noted that method 500 is not limited to the architecture of overlay metrology system 100.

[0085] In some embodiments, the method 500 includes illuminating 502 the overlay target with a single cell per measurement direction, the single cell including features having two or more pitches.

[0086] In some embodiments, the method 500 includes collecting 504 a time-varying interference signal from two photodetectors, each photodetector capturing signals associated with three diffraction orders from two or more pitches. For example, the overlay target may include a dual-pitch grating characterized by two pitches on a first layer and a single-pitch grating on a second layer. In this configuration, the first photodetector may capture +1 order diffraction from each of the three constituent pitches, and the second photodetector may capture -1 order diffraction from each of the three constituent pitches. As another example, the overlay target may include single-pitch gratings with different pitches. In this configuration, the first photodetector may capture +1 and +2 order diffraction from one single-pitch grating and +1 order diffraction from another single-pitch grating, and the second photodetector may capture -1 and -2 order diffraction from one single-pitch grating and -1 order diffraction from another single-pitch grating.

[0087] In some embodiments, the method 500 includes determining 506 an overlay error associated with the overlay target based on the time-varying interference signals captured by the two optical detectors. For example, the overlay error along the periodic direction of the constituent grating structures may be determined based on any combination of intensity or phase information of the time-varying interference signals generated during the scan.

[0088] It is contemplated herein that the method 500 may be applied to a wide variety of overlay target designs suitable for 1D or 2D metrology measurements. In some embodiments, the method 500 includes simultaneously scanning multiple illumination beams and collecting associated overlapping diffraction orders for parallel measurements. In some embodiments, the method 500 includes scanning one or more illumination beams along a beam scan direction different from the stage scan direction to provide a diagonal or triangular wave path across the specimen. In this regard, overlay targets having multiple cells suitable for determining overlay along different measurements (e.g., orthogonal measurements) may be efficiently interrogated by a common illumination beam within the measurement range.

[0089] The subject matter described herein may depict different components contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and that in fact many other architectures that achieve the same functionality may be implemented. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" to achieve the desired functionality. Thus, any two components herein that are combined to achieve a particular functionality may be considered to be "associated" with one another, such that the desired functionality is achieved without regard to the architecture or intermediate components. Similarly, any two components so associated may also be considered to be "connected" or "coupled" with one another to achieve the desired functionality, and any two components that may be so associated may also be considered to be "couplable" with one another to achieve the desired functionality. Specific examples of components that may be coupled include, but are not limited to, components that are physically interactable and / or physically interacting, and / or components that are wirelessly interactable and / or wirelessly interacting, and / or components that are logically interactable and / or logically interacting.

[0090] It will be apparent that the present disclosure and many of its attendant advantages will be understood from the foregoing description, and that various changes in the form, construction and arrangement of the elements may be made without departing from the disclosed subject matter or sacrificing all of its important advantages. The forms described are merely illustrative, and it is the intent of the following claims to encompass and include all such modifications. It is to be understood, further, that the invention is defined by the appended claims.

Claims

1. An illumination source; an illumination subsystem including one or more illumination optics for illuminating an overlay target on a specimen with illumination from the illumination source according to a metrology recipe as the specimen moves relative to the illumination from the illumination source, the overlay target including one or more cells according to the metrology recipe, at least a portion of the one or more cells including: a dual grating including a first series of features distributed along a measurement direction at a first pitch and a second pitch within an overlap region; an illumination subsystem including a single grating including a second series of features distributed along the measurement direction at the first pitch; a collection subsystem including one or more collection optics that directs positive and negative first order diffraction of the illumination by both the double grating and the single grating associated with the first and second pitches in accordance with the metrology recipe to one or more detectors disposed in a pupil plane, where the one or more detectors generate time-varying interference signals associated with the positive and negative first order diffraction of the illumination by both the double grating and the single grating; a controller communicatively coupled to the one or more detectors, the controller including one or more processors, the controller executing program instructions to cause the one or more processors to determine an overlay metrology between the double grating and the single grating based on the time-varying interference signal; An overlay metrology system comprising:

2. The overlay metrology system of claim 1 , wherein the double grating and the single grating overlap on the specimen.

3. The overlay metrology system of claim 1 , wherein the dual grating and the single grating are disposed in adjacent non-overlapping regions of the specimen.

4. The overlay metrology system of claim 1 , wherein the dual grating and the single grating are disposed on different layers of the specimen.

5. The overlay metrology system of claim 1 , wherein the double grating and the single grating are disposed in a common layer of the specimen.

6. the positive first order diffraction associated with the first and second pitches overlap in a first overlap region of the pupil plane and the negative first order diffraction associated with the first and second pitches overlap in a second overlap region of the pupil plane, and determining the overlay metrology between the first and second layers of the specimen based on the positive and negative first order diffraction of the illumination by the double grating and the single grating associated with the first and second pitches; determining the overlay metrology between the first and second layers of the specimen based on a time-varying interference signal generated by the one or more detectors at the first and second overlap regions; The overlay metrology system of claim 1 .

7. The overlay metrology system of claim 1 , wherein the dual grating is fabricated in a single exposure step.

8. One or more cells on the specimen, at least a portion of the one or more cells comprising: a dual grating including a first series of features distributed along a measurement direction at a first pitch and a second pitch within an overlap region; and one or more cells including a single grating on a second layer of the specimen including a second series of features distributed along the measurement direction at the first pitch, where the first and second pitches are selected such that, for at least one operating wavelength, positive first order diffractions from the first and second pitches overlap at a first overlap angular region and negative first order diffractions from the first and second pitches overlap at a second overlap angular region, where a time-varying interference signal in the first and second overlap regions generated when the overlay target is scanned relative to an illumination beam indicates overlay between the double grating and the single grating; 1. An overlay target comprising:

9. The overlay target of claim 8 , wherein the double grating is fabricated in a single exposure step.

10. The overlay target of claim 8 , wherein the first layer is fabricated prior to the second layer.

11. The overlay target of claim 8 , wherein the first layer is fabricated subsequent to the second layer.

12. The overlay target of claim 8 , wherein the double grating and the single grating are disposed on different layers of the specimen.

13. The overlay target of claim 8 , wherein the double grating and the single grating are disposed in a common layer of the specimen.

14. An illumination source; an illumination subsystem including one or more illumination optics for illuminating an overlay target on a specimen with illumination from the illumination source according to a metrology recipe as the specimen moves relative to the illumination from the illumination source, the overlay target including one or more cells according to the metrology recipe, at least a portion of the one or more cells being: a first grating on a first layer of the specimen, the first grating including a first series of features distributed along a measurement direction at a first pitch; and an illumination subsystem including a second grating on a second layer of the specimen including a second series of features distributed along the measurement direction at a second pitch different from the first pitch; a collection subsystem including one or more collection optics for directing measured diffraction orders to one or more detectors at a pupil plane according to the metrology recipe, where the measured diffraction orders are: positive and negative first order diffraction of the illumination by the first grating; positive and negative first and second order diffraction of the illumination by the second grating; and a light collection subsystem including a controller communicatively coupled to the one or more detectors, the controller including one or more processors and executing program instructions to cause the one or more processors to determine an overlay metrology between the first layer and the second layer of the specimen based on the measured diffraction orders; An overlay metrology system comprising:

15. the positive first order diffraction from the first grating overlaps with the positive first and second order diffraction from the second grating at a first set of overlapping regions, and the negative first order diffraction from the first grating overlaps with the negative first and second order diffraction from the second grating at a second set of overlapping regions, and determining the overlay metrology between the first and second layers of the specimen based on the measured diffraction orders; determining the overlay metrology between the first and second layers of the specimen based on time-varying interference signals generated by the one or more detectors at overlap regions of the first and second sets as the specimen is moving according to the metrology recipe. The overlay metrology system of claim 14.

16. The overlay metrology system of claim 14 , wherein the double grating and the single grating overlap on the specimen.

17. The overlay metrology system of claim 14 , wherein the dual grating and the single grating are disposed in adjacent non-overlapping regions of the specimen.

18. The overlay metrology system of claim 14 , wherein the first layer is fabricated prior to the second layer.

19. The overlay metrology system of claim 14 , wherein the first layer is fabricated subsequent to the second layer.

20. One or more cells on the specimen, at least a portion of the one or more cells comprising: a first grating on a first layer of the specimen, the first grating including a first series of features distributed along a measurement direction with a first pitch; and one or more cells including a second grating on a second layer of the specimen including a second series of features distributed along the measurement direction at a second pitch different from the first pitch, wherein the first and second pitches are selected such that positive first order diffraction from the first grating overlaps with positive first and second order diffraction from the second grating in a first set of overlapping regions and the negative first order diffraction from the first grating overlaps with negative first and second order diffraction from the second grating in a second set of overlapping regions, wherein a time-varying interference signal in the first and second sets of overlapping regions indicates overlay between the first and second layers of the specimen; An overlay target comprising:

21. 21. The overlay target of claim 20, wherein the first layer is fabricated prior to the second layer.

22. 21. The overlay target of claim 20, wherein the first layer is fabricated subsequent to the second layer.

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