Scanning overlay metrology using overlay targets with multiple spatial frequencies

Abstract

An overlay metrology system may include an illumination source and illumination optics to illuminate an overlay target on a sample with illumination from the illumination source as the sample moves relative to the illumination from the illumination source according to a measurement recipe. The overlay target may include one or more cells, wherein a single cell is adapted to measure along a particular direction. This cell may include two or more gratings having different pitches. In addition, the system may include two or more photodetectors, each configured to capture three diffraction lobes from the two or more grating structures. The system may further include a controller to determine an overlay measurement associated with each cell of the overlay target.

Description

[0001] CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 295,959, filed on January 3, 2022, entitled “NEW OVL METROLOGY TARGET DESIGN FOR SCANNING SCATTEROMETRY OPTICALTARGET,” by Itay Gdor, Yuval Lubashevsky, Daria Negri, and Eitan Hajaj, under 35 U.S.C. §119(e), the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to overlay metrology, and more particularly, to scanning overlay metrology. Background Art

[0004] The growing demand for smaller semiconductor devices has led to a correspondingly increasing demand for accurate and efficient metrology. One approach to increasing the efficiency and throughput of metrology tools is to generate metrology data on a sample while it is in motion rather than in a static position in the measurement field of view. In this way, the time delay associated with settling of a translation stage prior to measurement can be eliminated or reduced. However, increasing the sensitivity and throughput of such measurements remains a major challenge for such scanning metrology methods. Therefore, it is desirable to provide systems and methods for addressing the above-mentioned shortcomings. Summary of the invention

[0005] According to one or more illustrative embodiments, an overlay metrology system is disclosed. In one illustrative embodiment, the system includes an illumination source. In another illustrative embodiment, the system includes an illumination subsystem having one or more illumination optics to illuminate an overlay target on a sample with illumination from the illumination source as the sample moves relative to the illumination from the illumination source according to a measurement recipe. In another illustrative embodiment, according to the measurement recipe, the overlay target includes one or more cells, wherein at least some of the cells include a dual grating having a first series of features distributed at a first pitch and a second pitch in an overlap region along a measurement direction, and further includes a single grating having a second series of features distributed at the first pitch along the measurement direction. In another illustrative embodiment, the system includes a collection subsystem having one or more collection optics to direct positive and negative first order diffraction of illumination by both the dual grating and the single grating associated with the first and second pitches to one or more detectors positioned in a pupil plane according to the measurement recipe, wherein the one or more detectors generate a time-varying interference signal associated with the positive and negative first order diffraction of the illumination by both the dual grating and the single grating. In another illustrative embodiment, the system includes a controller to determine an overlay measurement between the dual grating and the single grating based on the time-varying interference signal.

[0006] An overlay target is disclosed according to one or more illustrative embodiments. In one illustrative embodiment, the target includes one or more cells on a sample, wherein at least some of the cells include a double grating having a first series of features distributed at a first pitch and a second pitch in an overlap region along a measurement direction, and further includes a single grating located on a second layer of the sample, the single grating having a second series of features distributed at the first pitch along the measurement direction. In another illustrative embodiment, the first and second pitches are selected so that for at least one operating wavelength, positive first-order diffractions from the first and second pitches overlap in a first overlap angular region, and negative first-order diffractions from the first and second pitches overlap in a second overlap angular region. In another illustrative embodiment, 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 an overlay between the double grating and the single grating.

[0007] According to one or more illustrative embodiments, an overlay metrology system is disclosed. In one illustrative embodiment, the system includes an illumination source. In another illustrative embodiment, the system includes an illumination subsystem having one or more illumination optics to illuminate an overlay target on a sample with illumination from the illumination source as the sample moves relative to illumination from the illumination source according to a measurement recipe. In another illustrative embodiment, according to the measurement recipe, the overlay target includes one or more cells, wherein at least some of the cells include a first grating on a first layer of the sample, the first grating having a first series of features distributed at a first pitch along a measurement direction, and a second grating on a second layer of the sample, the second grating having a second series of features distributed at a second pitch along the measurement direction different from the first pitch. In another illustrative embodiment, the system includes a collection subsystem having one or more collection optics to direct measured diffraction orders according to the measurement recipe to one or more detectors at a pupil plane, wherein the measured diffraction orders include positive and negative first order diffraction of illumination by the first grating, and positive and negative first and second order diffraction of illumination by the second grating. In another illustrative embodiment, the system includes a controller to determine an overlay measurement between the first and second layers of the sample based on the measured diffraction orders.

[0008] An overlay target is disclosed according to one or more illustrative embodiments. In one illustrative embodiment, the target includes one or more cells on a sample, wherein at least some of the cells include a first grating on a first layer of the sample, the first grating including a first series of features distributed at a first pitch along a measurement direction, and a second grating on a second layer of the sample, the second grating including a second series of features distributed at a second pitch along the measurement direction different from the first pitch. In another illustrative embodiment, the first and second pitches are selected so that in a first set of overlap regions, positive first-order diffraction from the first grating overlaps positive first and second-order diffraction from the second grating, wherein in a second set of overlap regions, negative first-order diffraction from the first grating overlaps negative first and second-order diffraction from the second grating. In another illustrative embodiment, the time-varying interference signals in the first and second sets of overlap regions indicate an overlay between the first and second layers of the sample.

[0009] It should be understood that both the foregoing summary and the following detailed description are exemplary and explanatory only and do not necessarily limit the invention.The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the summary, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Those skilled in the art may better appreciate the numerous advantages of the present disclosure by referring to the accompanying drawings.

[0011] Figure 1A is a conceptual diagram of a system for performing scatterometry overlay metrology on an overlay target suitable for single-cell measurement along any particular measurement direction, according to one or more embodiments of the present disclosure.

[0012] Figure 1B is a schematic diagram of an overlay metrology tool according to one or more embodiments of the present disclosure.

[0013] Figure 2 is a top view of an illumination pupil plane of an overlay metrology tool according to one or more embodiments of the present disclosure.

[0014] Figure 3A is a top view of a single-pitch grating according to one or more embodiments of the present disclosure.

[0015] Figure 3B is a top view of a dual-pitch grating according to one or more embodiments of the present disclosure.

[0016] Figure 3C Provides a description of one or more embodiments of the present disclosure Figure 3B The concept of double pitch grating forms a series of panels.

[0017] Figure 3D is a top view of a cell of an overlay target according to one or more embodiments of the present disclosure, wherein a single-pitch grating and a double-pitch grating are printed in non-overlapping areas within the cell.

[0018] Figure 3E is a top view of a cell of an overlay target according to one or more embodiments of the present disclosure, wherein a single-pitch grating and a double-pitch grating are printed on different layers of a sample in an overlapping region within the cell.

[0019] Figure 3F According to one or more embodiments of the present disclosure, Figure 3D Conceptual diagram of the collection pupil plane of the diffraction overlay metrology tool of the single-pitch grating and the double-pitch grating illustrated in 3F.

[0020] Figure 4A is a top view of a cell of an overlay target according to one or more embodiments of the present disclosure, wherein the cell has a first grating having a first pitch (P1) and a second grating having a second pitch (P2) different from the first pitch, wherein the gratings are printed in non-overlapping areas within the cell.

[0021] Figure 4B According to one or more embodiments of the present disclosure, Figure 4AConceptual diagram of the collection pupil plane of the diffraction overlay metrology tool for single-pitch and double-pitch gratings illustrated in FIG.

[0022] Figure 5 is a flow chart illustrating steps performed in a method for single-cell scanning overlay metrology according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0023] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with respect to specific embodiments and specific features thereof. The embodiments set forth herein are to be regarded as illustrative and not restrictive. It will be readily apparent to one of ordinary skill in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of the present disclosure.

[0024] Embodiments of the present disclosure relate to systems and methods for single-cell scanning overlay metrology. 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 generating overlay measurements by characterizing such targets.

[0025] In some embodiments, an overlay target suitable for single-cell scanning overlay metrology includes a cell having a grating structure associated with two lithographic exposures and oriented with a pitch along a particular measurement direction, wherein the grating structure may be in the same or different layers of a sample. Furthermore, an overlay metrology tool suitable for generating overlay measurements associated with the two lithographic exposures may include two photodetectors, wherein each photodetector is arranged (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, while scanning the sample, an overlay measurement along the measurement direction between the two lithographic exposures may be generated based on a difference between time-varying interference signals captured by the photodetectors.

[0026] Additionally, the overlay target may include a plurality of cells having grating structures oriented along different measurement directions to provide overlay measurements along different measurement directions.

[0027] It is recognized herein that many scatterometry overlay metrology techniques typically determine overlay by illuminating an overlay target having a grating structure in two layers (e.g., a grating-on-grating structure), where the overlay measurement 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 on March 11, 2021; U.S. Patent No. 10,824,079, issued on November 3, 2020; U.S. Patent No. 10,197,389, issued on 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); the entire contents of all of the aforementioned U.S. patents are incorporated herein by reference.

[0028] However, existing scatterometry overlay techniques often 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, where the constituent pitches are provided in different layers.

[0029] Embodiments of the present disclosure relate to scanning overlay metrology using an overlay target adapted to provide overlay measurements and single cells per overlay measurements. It is contemplated herein that single cell measurements may provide higher measurement throughput than multi-cell measurements.

[0030] In some embodiments, a cell of an overlay target suitable for single cell scanning overlay metrology comprises a single pitch grating on one layer and a double pitch grating (e.g., a dual grating) on ​​another layer. For example, the dual pitch grating may be functionally characterized by two grating structures with different pitches overlapping on a common area of ​​a sample layer. However, it should be understood that the constituent features of the dual pitch grating are fabricated with common lithographic exposures. In this manner, the characterization of the dual grating formed by two grating structures with different pitches is purely conceptual, and the overlapping portion of the two grating structures with different pitches is formed as a common element.

[0031] It is contemplated herein that illuminating a double pitch grating may produce two sets of diffraction orders associated with the two constituent pitches. Furthermore, illuminating an overlay target (or a cell therein) with both a single pitch grating and a double pitch grating may produce three sets of diffraction orders.

[0032] In some embodiments, the pitches of the single-pitch and double-pitch gratings are selected so 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 in a first position in the pupil plane, and the -1-order diffraction lobes associated with the three pitches may at least partially overlap in a second position in the pupil plane. It is contemplated herein that when scanning a sample, photodetectors placed at first and second positions in the pupil plane may capture time-varying interference signals, wherein an overlay measurement between the single-pitch and double-pitch gratings may be generated based on the difference between these time-varying interference signals. It is further contemplated herein that this overlay measurement may be similar to the overlay measurement associated with a triple-grating target generally described in U.S. Patent Application No. 17 / 119,536, filed on December 11, 2020, the entire contents of which are incorporated herein by reference. However, it should be noted that the overlay target disclosed herein including a single-pitch grating and a double-pitch grating may have several advantages over the three-grating overlay target described in U.S. Patent Application No. 17 / 119,536, filed on December 11, 2020, incorporated and referenced above. In particular, the overlay target including a single-pitch grating and a double-pitch grating as disclosed herein may avoid undesirable edge diffraction and scattering effects associated with a three-grating structure.

[0033] In some embodiments, a cell of an overlay target suitable for single-cell scanning overlay metrology includes two single-pitch gratings with different pitches (e.g., a first pitch and a second pitch), wherein a first-order diffraction lobe associated with the first pitch overlaps with portions of both first-order and second-order diffraction lobes associated with the second pitch. For example, a +1-order diffraction lobe associated with the first pitch ( ) can be associated with the +1 and +2 diffraction lobes associated with the second pitch ( and ) partially overlap. Similarly, the -1st order diffraction lobe associated with the first pitch ( ) can be associated with the -1st and -2nd order diffraction lobes associated with the second pitch ( and ) partially overlap. In some embodiments, the overlay metrology tool includes a lens having a first position in the pupil plane adapted to capture and and The first photodetector has an overlap size and is placed in a first position in the pupil plane and has a size suitable for capturing and and It is contemplated herein that such first and second photodetectors may capture time-varying interference signals while scanning a sample, wherein an overlay measurement between two single-pitch gratings may be generated based on these time-varying interference signals.

[0034] Some embodiments of the present disclosure are directed to providing recipes for configuring an overlay metrology tool to facilitate overlay measurements based on selected diffraction orders. An overlay metrology tool may generally be configured according to a recipe that includes a set of parameters for controlling various aspects of an overlay measurement, such as, but not limited to, illumination of a sample, collection of light from a sample, or position of a sample during a measurement. In this manner, an overlay metrology tool may be configured to provide selected types of measurements 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 illumination intensities 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 a sample to be used for measurement and associated filtered intensities at those angles), collection field aperture settings to select portions of a sample of interest, polarization of the collection 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 sample position during measurement, such as, but not limited to, sample height, sample orientation, whether the sample is static during measurement, or whether the sample is in motion during measurement (as well as associated parameters describing speed, scan pattern, or the like).

[0035] Reference Figures 1A to 4B According to one or more embodiments of the present disclosure, a system and method for single-cell scanning scattering overlay metrology are described in more detail.

[0036] Figure 1A 1 is a conceptual diagram of an overlay metrology system 100 for performing scatterometry overlay metrology on an overlay target 102 suitable for single cell measurement 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 to perform scatterometry overlay measurement on the overlay target 102 distributed across a sample 106. Figure 1B is a schematic diagram of an overlay metrology tool 104 according to one or more embodiments of the present disclosure.

[0037] For the purposes of this disclosure, the term overlay is generally used to describe the relative positions of features on a sample fabricated by two or more lithographic patterning steps, wherein the term overlay error describes the deviation of the features from the nominal arrangement. In this context, overlay measurements may be expressed as either a measurement of relative positions or a measurement of overlay errors associated with these relative positions. For example, a multilayer device may include features patterned on multiple sample layers using different lithographic steps for each layer, wherein the alignment of features between layers must generally be tightly controlled to ensure proper performance of the resulting device. Thus, overlay measurements may characterize the relative positions of features on two or more sample layers. By way of another example, features may be fabricated on a single sample layer using multiple lithographic steps. Such techniques, often referred to as double patterning or multi-patterning techniques, may facilitate the fabrication of highly dense features approaching the resolution of a lithographic system. In this context, overlay measurements may characterize the relative positions of features from different lithographic steps on this single layer. It should be understood that the examples and illustrations throughout this disclosure relating to specific applications of overlay metrology are provided for illustrative purposes only and should not be construed as limiting this disclosure.

[0038] Furthermore, the term scatterometry metrology is used herein to broadly encompass the terms scatterometry-based metrology and diffraction-based metrology, in which a sample having periodic features on one or more sample layers is illuminated with an illumination beam having a limited angular range, and one or more distinct diffraction orders are collected for measurement. Furthermore, the term scanning metrology is used to describe metrology measurements produced when the sample is in motion relative to the illumination used for measurement. In a general sense, scanning metrology can be implemented by moving the sample, the illumination, or both. In this manner, the specific descriptions herein of specific techniques for implementing scanning metrology are merely illustrative and should not be construed as limiting.

[0039] In some embodiments, the overlay metrology tool 104 includes an illumination subsystem 108 to generate illumination in the form of one or more illumination beams 110 to illuminate the sample 106, and a collection subsystem 112 to collect light from the illuminated sample 106. For example, the one or more illumination beams 110 may be angularly confined on the sample 106 so that a grating structure in one or more cells of the overlay target 102 may produce discrete diffraction orders. In addition, the one or more illumination beams 110 may be spatially confined so that they may 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 specific cell of the overlay target. In some embodiments, the one or more illumination beams 110 do not fill a specific cell of the overlay target.

[0040] 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. Furthermore, the collection subsystem 112 may include at least two photodetectors 114a, 114b positioned at locations associated with the time-varying interference signal indicative of overlay in a collection pupil plane 116. For example, as will be described in more detail below, suitable locations for the photodetectors 114 may include, but are not limited to, locations that demonstrate capture of three diffraction orders from a grating structure within the overlay target 102.

[0041] In some embodiments, the overlay metrology tool 104 includes a translation stage 118 to scan the sample 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 otherwise control the position of at least one illumination beam 110 on the sample 106. For example, the beam scanning subsystem 120 may scan the illumination beam 110 along a direction orthogonal to a scanning direction (e.g., a direction in which the translation stage 118 scans the sample 106) during measurement. In this way, scanning measurements may be performed with any relative motion of the sample 106 and the illumination beam 110.

[0042] 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 maintained in the memory device 126. In this manner, the controller 122 may implement any of the various processing steps described throughout the present disclosure, such as, but not limited to, receiving a time-varying interferometer signal from the photodetector 114, processing or filtering the time-varying interferometer signal, or generating an overlay measurement associated with the sample 106 based on the time-varying interferometer signal.

[0043] Reference Figures 2 to 4B , in accordance with one or more embodiments of the present disclosure, the collection of diffraction orders from the overlay target 102 and the placement of the photodetector 114 for single-cell scanning scatterometry overlay metrology are described in more detail. Specifically, Figure 2 Describes the non-restrictive illumination pupil distribution, Figures 3A to 3F A first non-limiting design of an overlay target 102 is described, and Figures 4A to 4B A second non-limiting design of the overlay target 102 is illustrated.

[0044] Figure 2 is an overlay metrology tool 104 (e.g., as in Figure 1B 128. Figure 2 As shown in FIG. 1 , the illumination subsystem 108 illuminates the overlay target 102 with one or more illumination beams 110 at normal incidence (or near normal incidence). For example, Figure 2 The illumination beam 110 is illustrated in 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 incident angles, as illustrated by the finite size in the collection pupil plane 116. In this regard, the overlay target 102 may diffract the one or more illumination beams 110 into discrete diffraction orders.

[0045] It is recognized herein that the distribution of diffraction orders of the illumination beam 110 by the periodic structure in the overlay target 102 may 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 the 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 may be configured to provide a desired distribution of diffraction orders in a collection pupil suitable for producing a time-varying interference pattern indicative of an overlay. For example, the illumination subsystem 108 and / or the collection subsystem 112 may be configured (e.g., using a measurement recipe) to produce measurements on an overlay target 102 having grating features with a pitch in a selected range to provide a desired collection pupil distribution. Furthermore, various components of the illumination subsystem 108 and / or the collection subsystem 112 (eg, a stop, pupil, or the like) may be adjustable (eg, using a measurement recipe) to provide a desired collection pupil distribution.

[0046] Furthermore, the size and shape of the diffraction orders in collection pupil plane 116 may be generally related to the size and shape of illumination beam 110 on sample 106. For example, although not shown, where illumination beam 110 is elongated, the associated diffraction orders may be similarly elongated.

[0047] Figures 3A to 3DA first non-limiting embodiment of an overlay target 102 suitable for single-cell scanning scatterometry overlay measurement is described, wherein the cell 302 includes a single pitch grating 304 associated with a first lithographic exposure and a double pitch grating 306 associated with a second lithographic exposure. In some embodiments, the single pitch grating 304 is fabricated on a first layer and the double pitch grating 306 is fabricated on a second layer. In this way, the associated overlay measurement may correspond to a measurement of a relative placement error between the first and second layers. In addition, the single pitch grating 304 and / or the double pitch grating 306 may be formed on a fully processed layer or as a patterned photoresist layer. For example, one of the gratings may be formed on a fully processed layer and the other grating may be formed on a subsequently exposed photoresist layer. In some embodiments, both the single pitch grating 304 and the double pitch grating 306 are formed on a single layer. In this way, the associated overlay measurement may correspond to a measure of relative placement error between different exposures of a multiple exposure manufacturing process (eg, double patterning or the like).

[0048] Figure 3A 304 according to one or more embodiments of the present disclosure. In some embodiments, the single pitch grating 304 includes a plurality of gratings having a selected pitch (P) along the measurement direction 310. S ) is a set of identical grating features 308 distributed over the entire surface.

[0049] Figure 3B FIG. 3 is a top view of a dual pitch grating 306 according to one or more embodiments of the present disclosure. In some embodiments, the dual pitch grating 306 is formed to have two characteristic pitches (P D1 ) and (P D2 ) of a set of grating features 312. In this way, the grating features 312 can have different sizes and relative positions to provide a pitch P D1 and P D2 .

[0050] Figure 3C Provides a description of one or more embodiments of the present disclosure Figure 3B The concept of a double pitch grating 306 is formed into a series of panels. Panel A illustrates a first pitch (P D1 ) and a first concept grating 314 having a second pitch (P D2 ). Panels B and C illustrate the conceptual overlap of the first conceptual grating 314 and the second conceptual grating 316 in a common area. In this way, the grating feature 312 can be formed as a combination of the first conceptual grating 314 and the second conceptual grating 316. However, it should be understood that Figure 3CThe depiction in FIG. 3 is for illustration only to clarify the layout of the dual pitch grating 306. In particular, the first concept grating 314 and the second concept grating 316 are not themselves manufactured but are merely associated with the design of the dual pitch grating 306. As an illustration, the grating feature 312a is a single feature based on a combination of features from each of the first concept grating 314 and the second concept grating 316, such as Figure 3C Depicted in.

[0051] Figure 3D and 3E A non-limiting layout of a single pitch grating 304 and a double pitch grating 306 within a cell 302 of an overlay target 102 is illustrated.

[0052] Figure 3D 3 is a top view of a cell 302 of an overlay target 102 according to one or more embodiments of the present disclosure, wherein a single pitch grating 304 and a double pitch grating 306 are printed (e.g., side by side) in non-overlapping regions within the cell 302. In this configuration, the single pitch grating 304 and the double pitch grating 306 may be fabricated on different layers of the sample 106 or on a common layer of the sample 106.

[0053] Figure 3E 3 is a top view of a cell 302 of an overlay target 102 according to one or more embodiments of the present disclosure, wherein a single pitch grating 304 and a double pitch grating 306 are printed on different layers of a sample 106 within an overlapping region within the cell 302. In this manner, the cell 302 may include a variation of a grating-on-grating structure formed with a single pitch grating 304 and a double pitch grating 306.

[0054] In addition, Figure 3D and 3E In the two designs described in FIG. 1 , the illumination beam 110 can be incident on both the single-pitch grating 304 and the double-pitch grating 306 at the same time. In this way, the single-pitch grating 304 and the double-pitch grating 306 can simultaneously generate the same pitch P as the single-pitch grating 304. S and the pitch P of the double pitch grating 306 D1 and P D2 Furthermore, although not shown, the illumination beam 110 may be elongated 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 the double pitch grating 306).

[0055] Figure 3F According to one or more embodiments of the present disclosure, Figure 3D 3F or a conceptual diagram of the collection pupil plane 116 of the diffractive overlay metrology tool 104 of the single pitch grating 304 and the double pitch grating 306 illustrated in FIG.

[0056] In some embodiments, the pitch associated with the cell 302 (eg, the pitch P of the single-pitch grating 304) is selected to be S , the pitch P of the double pitch grating 306 D1 and P D2 or the like) and / or various parameters in the metering recipe (e.g., the wavelength of the illumination beam 110 or the like), so that the pitch P S , P D1 and P D2 The first-order diffraction lobes of each of overlap. For example, Figure 3F Depict through pitch P S , P D1 and P D2 The +1st order diffraction lobe D associated with the diffraction of the illumination beam 110 S，+1 , D D1，+1 and D D2，+1 , the diffraction lobes overlap in a first overlapping region 318 . Figure 3B Further depiction through the pitch P S , P D1 and P D2 The −1st order diffraction lobe D associated with the diffraction of the illumination beam 110 S，-1 , D D1，-1 and D D2，-1 , the diffraction lobes overlap in the second overlapping region 320. Figure 3F It also shows that the 0th order diffraction (D 0 ) (e.g., specular reflection).

[0057] It is contemplated herein that scanning the overlay target 102 relative to the illumination beam 110 along the measurement direction 310 (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 errors between the first and second lithographic exposures associated with the single-pitch grating 304 and the double-pitch grating 306. Thus, in some embodiments, the overlay metrology tool 104 includes a photodetector 114 in the collection pupil plane 116 at the overlap region. For example, Figure 3F The first photodetector 114a at the first overlap region 318 and the second photodetector 114 at the second overlap region 320 are illustrated.

[0058] Furthermore, it should be noted herein that the active area of ​​the photodetector 114 (e.g., as indicated by Figure 3F) can generally be any suitable size sufficient to capture the associated time-varying signal. For example, the active area of ​​the photodetector 114 can be larger than the associated overlap region. In this configuration, the photodetector 114 can capture additional signals beyond the associated time-varying signal, such as, but not limited to, a constant signal. However, such signals can be filtered out or otherwise ignored using any technique known in the art.

[0059] Specifically, the intensity measured at the photodetector 114 is a function of the three pitches P S , P D1 and P D2 The product of all associated fields:

[0060]

[0061] in and Corresponding to the pitch P S , P D1 and P D2 The intensity of the associated diffraction order. In addition, GP represents the grating position (eg, along the scan).

[0062] Focusing only on the time-varying signal of the +1 diffraction lobe, we can write:

[0063]

[0064] Since the terms have different frequencies, these signals can be separated so that the phase difference of each of the components can be measured (e.g., by controller 122). In the phase difference, the constant phase contribution from sample 106 can be eliminated so that the phase contribution is from the initial pitch position (e.g., the initial GP and associated initial phase of illumination beam 110 from a starting position of the scan). The overlay can then be determined as:

[0065]

[0066]

[0067] It should be recognized herein that the determination of the overlay depicted by equations (1) to (4) is similar to the method of determining overlay using a three-grating target described in U.S. Patent Application No. 17 / 119,536, filed on December 11, 2020, the entire contents of which are incorporated herein by reference. However, as previously described herein, measuring the overlay target 102 with the single-pitch grating 304 and the double-pitch grating 306 as disclosed herein avoids the undesirable edge effects and scattering associated with the three-grating design, such that the systems and methods disclosed herein can provide overlay measurements with higher sensitivity than the three-grating method.

[0068] Reference Figures 4A to 4B , Figures 4A to 4B A second non-limiting embodiment of an overlay target 102 suitable for single-cell scanning scatterometry overlay measurements is illustrated in which the cell 302 includes two single-pitch gratings having different pitches.

[0069] Figure 4A is a top view of a cell 302 of an overlay target 102 according to one or more embodiments of the present disclosure, the cell having a first grating 402 having a first pitch (P1) and a second grating 404 having a second pitch (P2) different from the first pitch, the gratings being printed (e.g., side by side) in non-overlapping areas within the cell 302. Figure 3D In the manner of the design described in FIG. 1 , the first grating 402 and the second grating 404 can be fabricated on a common layer or different layers of the sample 106. In addition, although not shown, the first grating 402 and the second grating 404 can be fabricated on different layers of the sample 106 in the overlapping region to form a grating-on-grating structure (e.g., similar to Figure 3F ). Furthermore, in both configurations, the illumination beam 110 may be incident on both the single-pitch grating 304 and the double-pitch grating 306 simultaneously.

[0070] Figure 4B According to one or more embodiments of the present disclosure, Figure 4A 1. Conceptual diagram of the collection pupil plane 116 of the diffractive overlay metrology tool 104 of the single pitch grating 304 and the double pitch grating 306 illustrated in FIG.

[0071] In some embodiments, the pitch associated with the cell 302 (eg, the pitch P of the first grating 402) is selected to be 1 and the pitch P of the second grating 404 2 ) and / or selecting various parameters in the metering recipe (e.g., the wavelength of the illumination beam 110 or the like) so that the first-order diffraction lobe from the first grating 402 partially overlaps with both the first-order and second-order diffraction lobes from the second grating 404.

[0072] For example, Figure 4B The +1 order diffraction lobe from the first grating 402 is depicted ( ) in the first overlapping region 406 with the +1 order diffraction lobe ( ) and also overlaps with the +2nd order diffraction lobe ( ). Similarly, Figure 4B The -1st order diffraction lobe from the first grating 402 is depicted ( ) in the third overlapping region 410 with the -1 order diffraction lobe ( ) and also overlaps with the -2 order diffraction lobe ( ) partially overlap. Figure 4B It also shows that the 0th order diffraction (D 0 ) (e.g., specular reflection).

[0073] It is contemplated herein that scanning the overlay target 102 relative to the illumination beam 110 along the measurement direction 310 (or vice versa) will result in a time-varying interference signal at the overlap region 406-412 indicating an overlay error between the first and second lithographic exposures associated with the first grating 402 and the second grating 404. Thus, in some embodiments, the overlay metrology tool 104 includes a photodetector 114 in the collection pupil plane 116 at the overlap region. For example, Figure 4B The first photodetector 114a capturing the first and second overlap regions 406, 408 and the second photodetector 114b capturing the third and fourth overlap regions 410, 412 are illustrated. It is contemplated herein that the overlay between the photolithographic exposures forming the first grating 402 and the second grating 404 may be similar to Figures 3A to 3F The design of the overlay target 102 depicted in FIG. 1 is derived in a similar manner to that depicted in Equations (1) through (4).

[0074] In addition, similar to Figure 3F In the manner described in the foregoing, it should be noted herein that the active area of ​​the photodetector 114 (e.g., Figure 4B ) can generally be any suitable size sufficient to capture the associated time-varying signal. For example, the active area of ​​the photodetector 114 can be larger than the associated overlap region. In this configuration, the photodetector 114 can capture additional signals in addition to the associated time-varying signal, such as, but not limited to, a constant signal. However, such signals can be filtered out or otherwise ignored using any technique known in the art.

[0075] Now generally refer to Figures 3A to 4B , it should be noted that Figures 3A to 4BVarious non-limiting designs of particular cells 302 associated with particular measurement directions 310 are described. However, it should be understood that the 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 motion of the sample 106 (e.g., the stage scanning direction provided by the translation stage 118) or the direction of motion of the illumination beam 110 (e.g., the beam scanning direction provided by the beam scanning subsystem 120). For example, it is contemplated herein that any arrangement of cells 302 and associated measurement configurations (e.g., stage scanning direction or beam scanning direction) provided in U.S. Patent Application No. 17 / 178,089 filed on February 17, 2021 or U.S. Patent Application No. 17,708,958 filed on March 30, 2022, the entire contents of which are incorporated herein by reference, may be extended to the cell designs disclosed herein.

[0076] Reference again Figure 1A , additional components of the overlay metrology tool 104 are described in more detail, according to one or more embodiments of the present disclosure.

[0077] The photodetector 114 may generally include any type of optical detector known in the art that is suitable for capturing interference signals generated when the sample 106 is translated by the translation stage 118 and / or when 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 fast photodiode, a photomultiplier, or an avalanche photodiode.

[0078] 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, with a scanning speed of 10 centimeters per second along the measurement direction 310 and a target pitch of 1 micron, the interference signal will oscillate at a rate of approximately 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. In fact, the bandwidth of the photodetector 114, the translation speed along the measurement direction, and the pitch of the Moore structure can be selected together to provide a desired sampling rate of the interference signal.

[0079] 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 maintained in the memory device 126.

[0080] The one or more processors 124 of the controller 122 may generally include any processor or processing element known in the art. For the purposes of this disclosure, the term "processor" or "processing element" may be broadly defined to encompass any device having one or more processing or logic elements, such as one or more microprocessor devices, one or more application specific integrated circuit (ASIC) devices, one or more field programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs). In this sense, the one or more processors 124 may include any device configured to execute algorithms and / or instructions, such as program instructions stored in a memory. In some embodiments, the one or more processors 124 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a network-linked computer, or any other computer system configured to execute a program configured to operate or operate in conjunction with the overlay metrology system 100, as described throughout this disclosure. Furthermore, 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 is merely illustrative. Furthermore, the steps described throughout the present disclosure may be performed by a single controller or alternatively multiple controllers. Additionally, the controller 122 may include one or more controllers housed in a common housing or multiple housings. In this manner, any controller or combination of controllers may be separately packaged as a module suitable for integration into the metrology overlay metrology system 100. Furthermore, the controller 122 may analyze or otherwise process data received from the photodetector 114 and feed the data to additional components within the overlay metrology system 100 or external to the overlay metrology system 100.

[0081] Furthermore, the memory device 126 may include any storage media known in the art suitable for storing program instructions executable by the associated one or more processors 124. For example, the memory device 126 may include a non-transitory memory medium. As additional examples, the memory device 126 may include, but is not limited to, a read-only memory, a random access memory, a magnetic or optical storage device (e.g., a disk), a tape, a solid-state disk, and the like. It should be further noted that the memory device 126 may be housed in a common controller housing with the one or more processors 124.

[0082] In this regard, the controller 122 may perform any of the various processing steps associated with overlay metrology. For example, the controller 122 may be configured to generate control signals to direct or otherwise control the overlay metrology tool 104 or any component thereof. For example, the controller 122 may be configured to direct the translation stage 118 to translate the sample 106 along one or more measurement paths or scan lines to scan one or more overlay targets through the 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 on the sample 106. By way of another example, the controller 122 may be configured to receive a signal corresponding to a time-varying interferometric signal from the photodetector 114. As another example, the controller 122 may generate correctable terms for one or more additional manufacturing tools based on the overlay measurements from the overlay metrology tool 104 as feedback and / or feed-forward control of the one or more additional manufacturing tools.

[0083] In another embodiment, the controller 122 captures the interference signal detected by the photodetector 114. The controller 122 may generally use any technique known in the art (such as, but not limited to, one or more phase-locked loops) to capture data, such as, but not limited to, the magnitude or phase of the time-varying interference signal. In addition, the controller 122 may use any combination of hardware (e.g., circuitry) or software techniques to capture the interference signal or any data associated with the interference signal.

[0084] In some embodiments, the controller 122 determines an overlay measurement between layers of the overlay target 102 along a 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 measurement. For example, U.S. Pat. No. 10,824,079, issued on November 3, 2020, generally describes collecting electric fields of diffraction orders in a pupil, and further provides a specific relationship between overlay and measured intensity in a pupil plane, and the entire contents of the U.S. Pat. No. 10,824,079 are incorporated herein by reference. 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 a photodetector placed in an overlap region as disclosed herein. In particular, it is contemplated herein that the overlay on a sample may be proportional to an asymmetry, such as, but not limited to, a 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 signals. In this way, any overlay algorithm known in the art based on relative intensity differences of diffraction orders may be applied to generate an overlay measurement.

[0085] Furthermore, the controller 122 may calibrate or otherwise modify the overlay measurement based on known, assumed, or measured characteristics of the sample that may also affect the time-varying interferometer signal, such as, but not limited to, sidewall angle or other sample asymmetries.

[0086] Reference again Figure 1B , various components of the overlay metrology tool 104 are described in more detail, according to one or more embodiments of the present disclosure.

[0087] In some embodiments, illumination subsystem 108 includes an illumination source 136 configured to generate at least one illumination beam 110. Illumination from illumination source 136 may include light of one or more selected wavelengths including, but not limited to, ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0088] 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, or the like. 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 can emit broadband illumination when excited into a plasma state by a laser source.

[0089] In some embodiments, the illumination subsystem 108 includes one or more optical components suitable for modifying and / or adjusting the illumination beam 110 and directing the illumination beam 110 to the sample 106. For example, the illumination subsystem 108 may include one or more illumination lenses 138 (e.g., to collimate the illumination beam 110, relay an illumination pupil plane 128 and / or an illumination field plane 140, or the like). In some embodiments, the illumination subsystem 108 includes one or more illumination control optics 142 to shape or otherwise 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., static mirrors, translatable mirrors, scanning mirrors, or the like).

[0090] In some embodiments, the overlay metrology tool 104 includes an objective lens 144 to focus the illumination beam 110 onto the sample 106 (eg, an overlay target having overlay target elements positioned on two or more layers of the sample 106 ).

[0091] In some embodiments, the illumination subsystem 108 illuminates the sample 106 with two or more illumination beams 110. Furthermore, the two or more illumination beams 110 may, but are not required to, be incident on different portions of the sample 106 (e.g., different cells of an overlay target) within a measurement field of view (e.g., a field of view of an 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 located at an illumination field plane 140. In some embodiments, the illumination subsystem 108 includes one or more beam splitters to split illumination from an 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 part of a different illumination channel, regardless of the techniques for generating the various illumination beams 110.

[0092] In some embodiments, the collection subsystem 112 includes at least two photodetectors 114 (e.g., photodetectors 114a, 114b) positioned at a collection pupil plane 116 configured to capture light (e.g., collected light 146) from the sample 106, wherein the collected light 146 includes an overlap region (e.g., Figure 3F The overlapping areas 318, 320 described in Figure 4B 406 to 412 illustrated in FIG. 4 , or the like). The collection subsystem 112 may include one or more optical elements suitable for modifying and / or conditioning the collected light 146 from the sample 106. In some embodiments, the collection subsystem 112 includes one or more collection lenses 148 (e.g., to collimate the illumination beam 110, relay a pupil and / or field plane, or the like), which may include, but is not required to include, the objective lens 144. In some embodiments, the collection subsystem 112 includes one or more collection control optics 150 to shape or otherwise control the collected light 146. For example, the collection control optics 150 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, or the like).

[0093] In some embodiments, the illumination subsystem 108 and the collection subsystem 112 may utilize an objective lens 144. For example, Figure 1B A beam splitter 152 is illustrated for coupling the illumination beam 110 to the objective 144 for illuminating the sample 106 , and also coupling the collected light 146 from the objective 144 to the photodetector 114 .

[0094] The overlay metrology tool 104 may include one or more collection channels 154. For example, Figure 1B , the overlay metrology tool 104 may include one or more beam splitters 156 arranged to split the collected light 146 into collection channels 154. In addition, Figure 1B A configuration with two collection channels 154 is illustrated. It is contemplated herein that the photodetectors 114 may be distributed in any desired distribution between 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 placed at any location in the collection pupil plane 116, regardless of its physical size or any associated components. In some embodiments, multiple photodetectors 114 are positioned in at least one collection channel 154. In this configuration, multiple collection channels 154 may facilitate simultaneous measurement of different cells 302 (e.g., associated with different measurement directions).

[0095] In some embodiments, the collection subsystem 112 includes two or more photodetectors 114. In this way, the photodetectors 114 can be distributed as needed. Figure 1B , the overlay metrology tool 104 may include one or more beam splitters 158 arranged to split the collected light 146 into the collection channels 154. In addition, the beam splitters 158 may be polarizing beam splitters, non-polarizing beam splitters, or a combination thereof. However, it should be understood that Figure 1B The illustration of two collection channels 154 in is provided for illustrative purposes only and should not be considered limiting. For example, the collection subsystem 112 may include a single collection channel 154 or multiple collection channels 154.

[0096] In some embodiments, the plurality of collection channels 154 are configured to collect light from the plurality of illumination beams 110 on the sample 106. For example, where the overlay target 102 has two or more cells 302 distributed in a direction different from the scan 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 plurality of illumination beams 110 directed toward the sample 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 effectively 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 isolate desired diffraction orders for measurement.

[0097] 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 sample 106 during measurement.

[0098] The beam scanning subsystem 120 may include any type 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 deflector may include, but is not limited to, a rotatable mirror (e.g., a mirror with an adjustable tip and / or tilt). Furthermore, the rotatable mirror may be actuated using any technology known in the art. For example, the deflector may include, but is not limited to, a galvanometer, a piezoelectric mirror, or a micro-electromechanical system (MEMS) device. As another example, the beam scanning subsystem 120 may include an electro-optic modulator, an acousto-optic modulator, or the like.

[0099] The deflectors may further be positioned at any suitable location in the overlay metrology tool 104. In some embodiments, one or more deflectors are placed at one or more pupil planes common to 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 deflectors may modify the position of the one or more illumination beams 110 on the sample 106 without affecting the position of the diffraction orders in the collection pupil plane 116. Moreover, when the beam scanning subsystem 120 modifies the position of the one or more illumination beams 110 on the sample 106, the distribution of the one or more illumination beams 110 in the illumination field plane 140 may be further stabilized. Pupil plane beam scanning is generally described in U.S. Patent Application No. 17 / 142,783, filed on January 6, 2021, the entire contents of which are incorporated herein by reference.

[0100] Reference Figure 5 , Figure 5 is a flow chart illustrating steps performed in a method 500 for single cell scanning overlay metrology according to one or more embodiments of the present disclosure. Applicants should note that, in the context of the overlay metrology system 100, the embodiments and implementation techniques previously described herein should be interpreted as extending to the method 500. However, it should be further noted that the method 500 is not limited to the architecture of the overlay metrology system 100.

[0101] In some embodiments, method 500 includes step 502 of illuminating an overlay target having a unit cell in a measurement direction, wherein the unit cell includes a feature having two or more pitches.

[0102] In some embodiments, method 500 includes a step 504 of collecting a time-varying interference signal from two photodetectors, wherein each of the photodetectors captures signals associated with three diffraction orders from two or more pitches. For example, an 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, a first photodetector may capture +1 order diffraction from each of the three constituent pitches, while a second photodetector may capture -1 diffraction from each of the three constituent pitches. As another example, an overlay target may include a single-pitch grating having different pitches. In this configuration, a first photodetector may capture +1 and +2 order diffraction from one of the single-pitch gratings, and +1 diffraction from the other single-pitch grating, while a second photodetector may capture -1 and -2 order diffraction from one of the single-pitch gratings, and -1 diffraction from the other single-pitch grating.

[0103] In some embodiments, method 500 includes determining an overlay error associated with an overlay target based on the time-varying interference signal captured by the two photodetectors 506. For example, the overlay error along the periodic direction of the constituent grating structure may be determined based on any combination of intensity or phase information in the time-varying interference signal generated during scanning.

[0104] It is contemplated herein that the method 500 may be applied to a variety of overlay target designs suitable for 1D or 2D metrology measurements. In some embodiments, the method 500 includes scanning multiple illumination beams simultaneously and collecting associated overlapping diffraction orders for parallel measurement. In some embodiments, the method 500 includes scanning one or more illumination beams along a beam scan direction different from a stage scan direction to provide a diagonal or triangular wave path across the sample. In this regard, an overlay target having multiple cells suitable for determining measurements along different (e.g., orthogonal) directions may be effectively interrogated by a common illumination beam in a measurement scan line.

[0105] The objects described herein sometimes illustrate different components that are contained in or connected to other components. It should be understood that such depicted architectures are exemplary only, and in fact many other architectures that realize the same functionality can be implemented. In a conceptual sense, any arrangement of components that realize the same functionality is effectively "associated" so that the desired functionality is realized. Therefore, without considering the architecture or intermediate components, any two components in this article that are combined to realize a specific functionality can be considered to be "associated" with each other so that the desired functionality is realized. Similarly, any two components so associated can also be considered to be "connected" or "coupled" to each other to realize the desired functionality, and any two components that can be so associated can also be considered to be "coupleable" to each other to realize the desired functionality. Specific examples that can be coupled include but are not limited to components that can physically interact and / or physically interact, and / or components that can wirelessly interact and / or wirelessly interact, and / or components that can logically interact and / or logically interact.

[0106] It is believed that the present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be appreciated that various changes may be made to the form, construction and arrangement of components without departing from the disclosed object or sacrificing all of its significant advantages. The described form is illustrative only, and the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. An overlay metrology system, comprising: Illumination source; an illumination subsystem comprising one or more illumination optics to illuminate an overlay target on the sample with illumination from the illumination source as the sample moves relative to illumination from the illumination source in accordance with a measurement recipe, wherein the overlay target comprises one or more cells in accordance with the measurement recipe, wherein at least some of the one or more cells include: a double grating comprising a first series of features distributed at a first pitch and a second pitch in an overlap region along a measurement direction; and a single grating comprising a second series of features distributed at said first pitch along said measurement direction; a collection subsystem comprising one or more collection optics to direct positive and negative first order diffraction of illumination by both the dual grating and the single grating associated with the first and second pitches to one or more detectors positioned in a pupil plane according to the measurement recipe, wherein 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 dual grating and the single grating; and A controller is communicatively coupled to the one or more detectors, the controller including one or more processors to execute program instructions to cause the one or more processors to determine an overlay measurement between the dual grating and the single grating based on the time-varying interference signal. 2 . The overlay metrology system of claim 1 , wherein the double grating and the single grating are overlapped on the sample. 3 . The overlay metrology system of claim 1 , wherein the dual grating and the single grating are positioned in adjacent non-overlapping regions of the sample. 4 . The overlay metrology system of claim 1 , wherein the dual grating and the single grating are positioned in different layers of the sample. 5 . The overlay metrology system of claim 1 , wherein the dual grating and the single grating are positioned in a common layer of the sample.

6. The overlay metrology system of claim 1 , wherein the positive first order diffractions associated with the first and second pitches overlap in a first overlap region at the pupil plane, wherein the negative first order diffractions associated with the first and second pitches overlap in a second overlap region at the pupil plane, wherein determining the overlay measurement between the first and second layers of the sample based on the positive and negative first order diffractions of the illumination by the dual grating and the single grating associated with the first and second pitches comprises: An overlay measurement between the first and second layers of the sample is determined based on time-varying interference signals generated by the one or more detectors at the first and second overlap regions.

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

8. An overlay target, comprising: One or more cells located on the sample, wherein at least some of the one or more cells include: a double grating comprising a first series of features distributed at a first pitch and a second pitch in an overlap region along a measurement direction; and A single grating on a second layer of the sample, the single grating comprising a second series of features distributed at the first pitch along the measurement direction, wherein the first and second pitches are selected so that for at least one operating wavelength, positive first-order diffractions from the first and second pitches overlap in a first overlap region and negative first-order diffractions from the first and second pitches overlap in a second overlap region, wherein time-varying interference signals in the first and second overlap regions generated when the overlay target is scanned relative to an illumination beam indicate overlay between the dual grating and the single grating.

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

10. The overlay target of claim 8, wherein a first layer of the sample is fabricated before the second layer, and the dual grating is located on the first layer.

11. The overlay target of claim 8, wherein a first layer of the sample is manufactured after the second layer, and the double grating is located on the first layer.

12. The overlay target of claim 8, wherein the dual grating and the single grating are positioned in different layers of the sample.

13. The overlay target of claim 8, wherein the dual grating and the single grating are positioned in a common layer of the sample.

14. An overlay metrology system comprising: Illumination source; an illumination subsystem comprising one or more illumination optics to illuminate an overlay target on the sample with illumination from the illumination source as the sample moves relative to illumination from the illumination source in accordance with a measurement recipe, wherein the overlay target comprises one or more cells in accordance with the measurement recipe, wherein at least some of the one or more cells include: a first grating on a first layer of the sample, the first grating comprising a first series of features distributed at a first pitch along a measurement direction; and a second grating on a second layer of the sample, the second grating comprising a second series of features distributed along the measurement direction at a second pitch different from the first pitch; and a collection subsystem comprising one or more collection optics to direct measurement diffraction orders to one or more detectors at a pupil plane according to the measurement recipe, wherein the measurement diffraction orders include: positive and negative first order diffraction of illumination by said first grating; positive and negative first and second order diffraction of illumination by said second grating; and A controller is communicatively coupled to the one or more detectors, the controller including one or more processors to execute program instructions to cause the one or more processors to determine an overlay measurement between the first and second layers of the sample based on the measured diffraction orders.

15. The overlay metrology system of claim 14, wherein in a first set of overlap regions, the positive first-order diffraction from the first grating overlaps with the positive first-order and second-order diffraction from the second grating, wherein in a second set of overlap regions, the negative first-order diffraction from the first grating overlaps with the negative first-order and second-order diffraction from the second grating, wherein determining the overlay measurement between the first and second layers of the sample based on the measured diffraction orders comprises: According to the measurement recipe, the overlay measurement between the first and second layers of the sample is determined based on time-varying interference signals generated by the one or more detectors at the first and second sets of overlap regions while the sample is in motion.

16. The overlay metrology system of claim 14, wherein the first grating and the second grating overlap on the sample.

17. The overlay metrology system of claim 14, wherein the first grating and the second grating are positioned in adjacent non-overlapping regions of the sample.

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

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

20. An overlay target, comprising: One or more cells located on the sample, wherein at least some of the one or more cells include: a first grating on a first layer of the sample, the first grating comprising a first series of features distributed at a first pitch along a measurement direction; and A second grating on a second layer of the sample, the second grating comprising 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 so that positive first-order diffraction from the first grating overlaps with positive first-order and second-order diffraction from the second grating in a first set of overlap regions, wherein negative first-order diffraction from the first grating overlaps with negative first-order and second-order diffraction from the second grating in a second set of overlap regions, wherein time-varying interference signals in the first and second sets of overlap regions indicate an overlay between the first and second layers of the sample.

21. The overlay target of claim 20, wherein the first layer is manufactured before the second layer.

22. The overlay target of claim 20, wherein the first layer is manufactured after the second layer.

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