Multi-overlay laminated grating measurement target

Abstract

The overlay metrology target includes a multi-layer grating structure formed as overlapping grating structures having different pitches on three or more layers of the sample. The three or more layers of the sample may include at least a first layer, a second layer, and a third layer, and the overlapping grating structures are periodic along at least one of the scanning direction and a direction orthogonal to the scanning direction. The multi-layer grating structure may include a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS Applicant claims the benefit under 35 U.S.C. § 119 of U.S. Provisional Application No. 63 / 450,975, filed March 9, 2023, which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates generally to overlay metrology, and more particularly to scanning scatterometry overlay metrology. [Background technology]

[0003] Overlay metrology generally refers to the measurement of the relative alignment of layers on a sample, such as, but not limited to, a semiconductor device. Overlay metrology, or the measurement of overlay error, typically refers to the measurement of misalignment of features fabricated on two or more sample layers. In a general sense, proper alignment of features fabricated on multiple sample layers is necessary for proper functioning of the device.

[0004] The demand for decreasing feature size and increasing feature density has resulted in a corresponding increase in demand for accurate and efficient overlay metrology systems. Metrology systems typically generate metrology data associated with a sample by measuring or otherwise inspecting overlay metrology targets distributed across the sample.

[0005] Overlay metrology targets are typically designed to provide diagnostic information regarding the alignment of multiple layers of a sample by characterizing an overlay target having target features located on the sample layer of interest. Furthermore, the overlay alignment of multiple layers is typically determined by aggregating overlay measurements of multiple overlay targets at various locations across the sample.

[0006] Some overlay metrology targets include multiple single overlay targets (e.g., scatterometry overlay (SCOL) metrology targets or Moiré fringe metrology targets) that are measured sequentially. Such metrology targets (e.g., SCOL metrology targets or Moiré fringe metrology targets) include periodic structures configured to generate diffraction patterns that can be analyzed to determine metrology measurements. Such metrology targets (e.g., SCOL metrology targets or Moiré fringe metrology targets) that include multiple cells occupy a larger surface area of ​​the sample, reducing measurement throughput because measurement time scales with each additional overlay metrology target to be measured.

[0007] Additional metrology targets (e.g., imaging AIM metrology targets) contain features in multiple layers that are spatially separated within the plane of the sample and arranged to have a common center of symmetry, and overlay is a measurement of the difference in the center of symmetry between the pair of layers of interest. Such metrology targets (e.g., imaging AIM metrology targets) require more space on the sample. Furthermore, due to the different optical properties of each layer, it can be difficult to obtain optimal imaging conditions for multiple layers simultaneously in a single image data collection. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent Application Publication No. 2022 / 0034652 [Patent Document 2] U.S. Patent Application Publication No. 2018 / 0188663 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, it would be desirable to provide a system and method to overcome the above-mentioned deficiencies. [Means for solving the problem]

[0010] An overlay metrology system is disclosed according to one or more embodiments of the present disclosure. In an embodiment, the overlay metrology system includes an illumination subsystem. In an embodiment, the illumination subsystem includes an illumination source configured to generate an illumination beam. In an embodiment, the illumination subsystem includes one or more illumination optics configured to direct the illumination beam to an overlay target on the sample as the sample is scanned relative to the illumination beam along a scan direction when executing a metrology recipe. In an embodiment, the overlay target includes one or more cells having a multi-layer grating structure formed as overlapping grating structures having different pitches on three or more layers of the sample according to the metrology recipe, the three or more layers of the sample including at least a first layer, a second layer, and a third layer, and the overlapping grating structure is periodic along at least one of the scan direction or a direction orthogonal to the scan direction. In an embodiment, the overlay metrology system includes a collection subsystem including a first photodetector positioned at a first position in a pupil plane to capture overlapping diffraction orders from the multi-layer grating structure in the one or more cells when a metrology recipe is executed, and a second photodetector positioned at a second position in the pupil plane to capture overlapping diffraction orders from the multi-layer grating structure in the one or more cells when a metrology recipe is executed. In an embodiment, the overlay metrology system includes a controller communicatively coupled to the first photodetector and the second photodetector. In an embodiment, the controller includes one or more processors configured to execute program instructions that cause the one or more processors to receive time-varying interference signals from the first photodetector and the second photodetector associated with the multi-layer grating structure in the one or more cells when the overlay target is scanned according to the metrology recipe. In an embodiment, the controller includes one or more processors configured to execute program instructions that cause the one or more processors to determine an overlay error between one of a first layer, a second layer, or a third layer of a sample based on the time-varying interference signals.

[0011] According to one or more embodiments of the present disclosure, an overlay metrology target is disclosed. In an embodiment, the overlay metrology target includes a multi-layer grating structure formed as overlapping grating structures having different pitches on three or more layers of a sample, the three or more layers of the sample including at least a first layer, a second layer, and a third layer, and the overlapping grating structures are periodic along at least one of the scanning direction or a direction orthogonal to the scanning direction. In an embodiment, the multi-layer grating structure includes a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch.

[0012] A method is disclosed according to one or more embodiments of the present disclosure. In an embodiment, the method includes receiving time-varying interference signals from first and second photodetectors associated with multi-layer grating structures in one or more cells when an overlay target is scanned according to a metrology recipe, where the overlay target according to the metrology recipe includes one or more cells having multi-layer grating structures formed as overlapping grating structures with different pitches on three or more layers of the sample, the three or more layers of the sample including at least a first layer, a second layer, and a third layer, and the overlapping grating structures are periodic along at least one of the scan direction or a direction orthogonal to the scan direction. In an embodiment, the method includes determining an overlay error between one of the first layer, the second layer, or the third layer of the sample based on the time-varying interference signals.

[0013] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention, as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention.

[0014] The many advantages of the present disclosure may be better understood by those skilled in the art by reference to the following drawings. [Brief explanation of the drawings]

[0015] [Figure 1A] FIG. 1 is a conceptual diagram of a system for performing scatterometry overlay metrology on an overlay target having at least one multi-layer grating structure, 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. [Figure 2] FIG. 1 illustrates a side view of a single cell of an overlay target on a sample in accordance with one or more embodiments of the present disclosure. [Figure 3A] FIG. 1 is a top view of an illumination pupil at an illumination pupil plane of an overlay metrology tool in accordance with one or more embodiments of the present disclosure. [Figure 3B] FIG. 3B is a top view of a collection pupil at a collection pupil plane of an overlay metrology tool including grating diffraction lobes associated with the illumination profile of FIG. 3A by a multi-layer grating structure in accordance with one or more embodiments of the present disclosure. [Figure 4A] 1 is a Fast Fourier Transform plot according to one or more embodiments of the present disclosure. [Figure 4B] 1 is a Fast Fourier Transform plot according to one or more embodiments of the present disclosure. [Figure 5] FIG. 1 is a flow diagram illustrating steps performed in a method for scanning overlay metrology of an overlay target having a multi-layer grating structure in accordance with one or more embodiments of the present disclosure. [Figure 6A] FIG. 1 illustrates a top view of a cell of an overlay target having a multi-layer grating structure in accordance with one or more embodiments of the present disclosure. [Figure 6B] FIG. 1 illustrates a top view of a cell of an overlay target having a multi-layer grating structure in accordance with one or more embodiments of the present disclosure. [Figure 6C] FIG. 1 illustrates a top view of a cell of an overlay target having a multi-layer grating structure in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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 specific features thereof. The embodiments described herein are to be considered illustrative and not restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made therein without departing from the spirit and scope of the present disclosure.

[0017] Embodiments of the present disclosure relate to scanning scatterometry overlays that use overlay targets that include multi-layer grating structures. For example, the multi-layer grating structure may include a grating-over-grating structure in which the constituent gratings have different pitches.

[0018] For the purposes of this disclosure, the term "scatterometry metrology" is used 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 different diffraction orders are collected for measurement. Additionally, the term "scanning metrology" is used to describe metrology measurements made when the sample is in motion relative to the illumination used for the measurement. In a general sense, scanning metrology can be implemented by moving the sample, the illumination, or both.

[0019]

[0003] Embodiments of the present disclosure relate to systems and methods for scanning overlay metrology based on time-varying interference signals from a multilayer grating structure in a collection pupil plane. It is contemplated herein that measurement conditions that result in overlapping diffraction orders from constituent gratings of the multilayer grating structure can cause interference. Such interference signals can include information associated with asymmetries in the target structure, such as, but not limited to, overlay between the top and bottom gratings, overlay between the top and middle gratings, and overlay between the middle and bottom gratings. It is further contemplated herein that scanning the multilayer grating structure relative to an illumination beam (or vice versa) can provide a characterization of the position-dependent overlay of the multilayer grating structure, thereby enabling the determination of asymmetries, such as, but not limited to, overlay.

[0020] Some embodiments of the present disclosure relate to scanning scatterometry overlay measurements based on overlapping diffraction lobes from gratings (e.g., top, middle, or bottom gratings) of a multi-layer grating structure, or time-varying interference signals associated with diffraction from a multi-layer grating structure. For example, scanning-based scatterometry techniques may include a high-speed detector for capturing the time-varying interference signals generated as the sample is scanned. The detector may be positioned in the pupil plane at the location of overlap between selected diffraction orders to capture the time-varying interference signals as the sample is scanned. Various non-limiting scanning scatterometry overlay metrology techniques are described in U.S. Patent No. 11,300,405, issued April 12, 2022, U.S. Patent No. 11,378,394, issued July 5, 2022, U.S. Patent Application No. 17 / 708,958, filed March 30, 2022, U.S. Patent Application No. 17 / 709,200, filed March 30, 2022, U.S. Patent Application No. 17 / 709,104, filed March 30, 2022, and U.S. Patent Application No. 18 / 110,746, filed February 16, 2023, all of which are incorporated by reference in their entireties. It is contemplated herein that the systems and methods of the above-incorporated references may be extended or otherwise adapted to provide overlay measurements of multilayer grating structures.

[0021] In some embodiments, the overlay metrology system includes a photodetector positioned in the pupil plane at a position corresponding to a diffraction lobe from the multilayer grating structure. For example, the photodetector may be positioned at a position of overlap between the diffraction lobe and the zeroth diffraction order (e.g., specular reflection). It is contemplated herein that these combined diffraction orders may exhibit a time-varying interference signal (e.g., an AC signal) during the scanning measurement and may be captured using the photodetector. For example, the characteristics of the multilayer grating structure (e.g., pitch of the constituent gratings) and / or measurement conditions (e.g., illumination wavelength, illumination angle of incidence, collection angle, etc.) may be selected to provide that the positive and negative diffraction orders associated with combined diffraction by the gratings of the multilayer grating structure are collected by the system and captured by the photodetector.

[0022] Some embodiments of the present disclosure relate to providing recipes for configuring overlay metrology tools. Overlay metrology tools are typically configurable according to recipes that include sets of parameters for controlling various aspects of overlay measurements, such as, but not limited to, illumination of the sample, collection of light from the sample, or position of the sample during measurement. In this manner, the 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, the number of illumination beams, 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 sample used for measurement and associated filtered intensities at those angles), collection field aperture settings for selecting portions of the sample of interest, polarization of collected light, wavelength filters, position of one or more detectors (e.g., photodetectors), or parameters for controlling one or more detectors. As a further example, the metrology recipe may include various parameters associated with the sample position during the measurement, such as, but not limited to, sample height, sample orientation, whether the sample is stationary during the measurement or whether the sample is moving during the measurement (along with related parameters describing the speed, scan pattern, etc.).

[0023] In some embodiments, the properties of the multilayer grating structure (e.g., pitch of the constituent gratings, etc.) and measurement conditions (e.g., illumination wavelength, illumination incidence angle, or collection angle, etc.) are arranged or otherwise selected (e.g., using a metrology recipe) to provide a selected distribution of diffracted and / or combined diffraction orders, and further provide that the photodetector is positioned in an appropriate position to capture these orders to generate a time-varying interference signal of interest.

[0024] It is further contemplated herein that the systems and methods disclosed herein can provide high-throughput, high-sensitivity overlay metrology. For example, the non-imaging configuration allows for the use of high-speed photodetectors suitable for fast scanning speeds. As a non-limiting example, a photodetector with a 1 GHz bandwidth may enable a scanning speed of approximately 10 centimeters per second on a target with a 1 micrometer pitch.

[0025] The multilayer grating structure may generally be formed as part of an overlay target and may generally be located anywhere on the sample. Furthermore, the overlay target may include one or more measurement cells, each containing printed elements in the overlapping region of one or more layers on the sample to form the multilayer grating structure. The overlay measurement may then be based on any combination of measurements of various cells of the overlay target. For example, the multiple cells of the overlay target may be designed with different intended offsets (e.g., grating structures in various layers of the sample intentionally shifted by a known offset value), which may improve the accuracy and / or sensitivity of the measurement.

[0026] It is contemplated herein that scatterometry overlay metrology of the multilayer grating structures disclosed herein may offer numerous benefits. For example, the systems and methods disclosed herein may utilize multilayer overlay targets including stacked gratings, which may consume less space on the same target compared to target designs with side-by-side layer designs. As another example, the systems and methods disclosed herein may save scribe line space both when multiple overlay measurements are needed on a given layer or when they are needed on standard layers where target stacking is useful. As another example, the metrology overlay targets of the disclosed systems may have higher performance due to their smaller pitch compared to conventional optical imaging systems based on multilayer targets. As another example, the systems and methods disclosed herein may overcome the difficulty of measuring each layer in its ideal condition because the performance of laser scanning methods is not strongly dependent on the wavelength of light used.

[0027] 1A-6C, systems and methods for scatterometry overlay metrology using multi-overlay stacked grating metrology targets are described in more detail in accordance with one or more embodiments of the present disclosure.

[0028] FIG. 1A is a conceptual diagram of an overlay metrology system 100 for performing scatterometry overlay metrology on a multi-overlay stacked grating metrology target, in accordance with one or more embodiments of the present disclosure.

[0029] In an embodiment, the overlay metrology system 100 includes an overlay metrology tool 102 for performing scatterometry overlay measurements on a sample 104. For example, the overlay metrology tool 102 may perform scatterometry overlay measurements on a portion of the sample 104 that has a multilayer grating structure.

[0030] FIG. 1B is a schematic diagram of an overlay metrology tool 102 in accordance with one or more embodiments of the present disclosure.

[0031] In embodiments, the overlay metrology tool 102 includes an illumination subsystem 106 that generates illumination in the form of one or more illumination beams 108 to illuminate the sample 104, and a collection subsystem 110 that collects light from the illuminated sample 104. For example, the one or more illumination beams 108 may be angularly limited on the sample 104 to enable a multilayer grating structure (e.g., within one or more cells of the overlay target) to generate discrete diffraction orders. Additionally, the one or more illumination beams 108 may be spatially limited to illuminate selected portions of the sample 104. For example, each of the one or more illumination beams 108 may be spatially limited to illuminate a specific cell of the overlay target. In some embodiments, the one or more illumination beams 108 underfill a specific cell of the overlay target.

[0032] The collection subsystem 110 may then collect at least some diffraction orders associated with the diffraction of the illumination beam 108 from the multi-layer grating structure. Additionally, the collection subsystem 110 may include at least two photodetectors 112 positioned in the collection pupil plane 114 at locations associated with the time-varying interference signal indicative of the overlay. For example, as described in more detail below, suitable locations for the photodetectors 112 may include, but are not limited to, locations associated with positive and negative diffraction orders or locations associated with overlap between the diffraction orders of the constituent gratings of the multi-layer grating structure (e.g., overlap regions between the +1 diffraction order of the top, middle, and bottom gratings and overlap regions between the −1 diffraction order of the top, middle, and bottom gratings).

[0033] In an embodiment, the overlay metrology tool 102 includes a translation stage 116 that scans the sample 104 through a measurement field of view of the overlay metrology tool 102 during measurement to implement scanning metrology.

[0034] In an embodiment, the overlay metrology tool 102 includes a beam scanning subsystem 118 configured to modify or otherwise control the position of at least one illumination beam 108 on the sample 104. For example, the beam scanning subsystem 118 may scan the illumination beam 108 in a direction orthogonal to a scan direction (e.g., a direction in which the translation stage 116 scans the sample 104) during measurement.

[0035] 2-3B, the arrangement of the photodetector 112 for collection of diffraction orders from the grating structure and scanning scatterometry overlay measurement is described in more detail in accordance with one or more embodiments of the present disclosure.

[0036] FIG. 2 is a side view of a cell 202 according to one or more embodiments of the present disclosure.

[0037] In an embodiment, the overlay target 204 includes one or more cells 202, and any particular cell 202 of the one or more cells 202 may include a multi-layer grating structure 206 having periodicity along any direction. For example, the overlay target 204 may include a single cell 202 with a multi-layer grating structure 206 having periodicity along a common direction. As another example, the overlay target 204 may include multiple cells 202, with different cells 202 having different configurations of associated grating periodicity. For example, the overlay target 204 may include multiple cells 202, each cell including a multi-layer grating structure 206 having periodicity along a common direction, with different cells 202 having different configurations of associated grating periodicity.

[0038] In an embodiment, the multi-layer grating structure 206 includes three or more layers. For example, the multi-layer grating structure 206 may include a first layer grating 208 (e.g., top grating) disposed on a first layer 210 of the sample 104, a second layer grating 212 (e.g., middle grating) disposed on a second layer 214 of the sample 104, and a third layer grating 216 (e.g., bottom grating) disposed on a third layer 218, where the layers are oriented such that regions including the first layer grating 208, the second layer grating 212, and the third layer grating 216 overlap to form a grating-over-grating structure.

[0039] In an embodiment, the multilayer grating structure 206 is formed with gratings having different pitches. For example, the first layer grating 208, the second layer grating 212, and the third layer grating 216 of the multilayer grating structure 206 may have different pitches. For example, FIG. 2 illustrates the pitches of the first layer grating 208, the second layer grating 212, and the third layer grating 216 as P, Q, and R, respectively. In another example, the pitches of the first layer grating 208, the second layer grating 212, and the third layer grating 216 may be Q, P, and R, respectively. In another example, the pitches of the first layer grating 208, the second layer grating 212, and the third layer grating 216 may be R, Q, and P, respectively. Note that the configuration illustrated in FIG. 2 is provided for illustrative purposes only and should not be construed as limiting the scope of the present disclosure. Thus, the multilayer grating structure 206 may be formed with any number of layers having any variety of pitches. For example, the multi-layer grating structure 206 may be formed from three or more layers.

[0040] However, it should be understood that the overlay target 204 of FIG. 2 and the associated description are provided for illustrative purposes only and should not be construed as limiting. Rather, the overlay target 204 may include any suitable multi-layer grating overlay target design. For example, the overlay target 204 may include any number of cells 202 suitable for measurement. Furthermore, the cells 202 may be distributed in any pattern or arrangement. In an embodiment, the overlay target 204 includes one or more cell groups distributed along a scan direction (e.g., the direction of movement of the sample 104), with the cells 202 within each particular cell group oriented to have a multi-layer grating structure 206 that is periodic along a common direction. For example, a first cell group may include one or more cells 202 with periodicity along the X direction, a second cell group may include one or more cells 202 with periodicity along the X direction, and a third cell group may include one or more cells 202 with periodicity along the X direction. In this manner, all cells 202 within a particular cell group can be imaged simultaneously while the sample 104 is scanned through the measurement field of view of the collection subsystem 110 .

[0041] 3A-3B, various non-limiting configurations for generating and measuring time-varying interference signals from a multi-layer grating structure 206 in a cell 202 of an overlay target 204 are described in accordance with one or more embodiments of the present disclosure.

[0042] 3A is a top view of an illumination pupil 302 at an illumination pupil plane 120 of an overlay metrology tool 102 in accordance with one or more embodiments of the present disclosure. For example, the illumination pupil plane 120 may correspond to a pupil plane within the illumination subsystem 106 as shown in FIG. 1B. In an embodiment, the illumination subsystem 106 illuminates the overlay target 204 with one or more illumination beams 108 at normal incidence (or near-normal incidence), as shown in FIG. 3A. Furthermore, the one or more illumination beams 108 may illuminate the overlay target 204 over a limited range of incidence angles, as indicated by their limited size at the collection pupil plane 114. In this regard, the overlay target 204 may diffract the one or more illumination beams 108 into discrete diffraction orders.

[0043] 3B illustrates a non-limiting configuration for capturing time-varying interference signals from an overlay target 204 having a multilayer grating structure 206 in a scanning configuration. Specifically, FIG. 3B illustrates a non-limiting configuration of the diffraction orders of the illumination beam 108 shown in FIG. 3A at the collection pupil plane 114 and the associated positions of photodetectors 112 suitable for capturing time-varying interference signals from which overlay measurements can be extracted. It is contemplated herein that photodetectors 112 positioned at positions within the collection pupil plane 114 associated with overlapping diffraction lobes (e.g., regions where first-order diffraction lobes from the first layer grating 208, second layer grating 212, and third layer grating 216 of the multilayer grating structure 206 may overlap) can capture time-varying interference signals indicative of overlay. It is further contemplated herein that time-varying interference signals associated with combined diffraction lobes can be captured by the photodetector 112 when each of the associated diffraction lobes is incident on the photodetector 112 (e.g., when within a measurement region of the photodetector 112). In this way, the associated diffraction lobes do not necessarily overlap at the collection pupil plane 114 , but rather may overlap on the photodetector 112 .

[0044] It is recognized herein that the distribution of diffraction orders of the illumination beam 108 by a periodic structure, such as the multilayer grating structure 206, can be affected by various parameters, such as, but not limited to, the wavelength of the illumination beam 108, the angle of incidence of the illumination beam 108 in both the elevation and azimuth directions, the pitch of the gratings of the multilayer grating structure 206, or the numerical aperture (NA) of the collection lens. Accordingly, in embodiments of the present disclosure, the illumination subsystem 106, the collection subsystem 110, and the overlay target 204 may be configured (e.g., according to a metrology recipe defining a selected set of relevant parameters) to provide a desired distribution of diffraction orders in the collection pupil plane 114 suitable for generating a time-varying interference pattern indicative of overlay. For example, the illumination subsystem 106 and / or the collection subsystem 110 may be configured to generate measurements for grating structures having a selected range of periodicity to provide the desired distribution in the collection pupil plane 114. Furthermore, various components of the illumination subsystem 106 and / or the collection subsystem 110 (e.g., iris, pupil, etc.) may be adjustable to provide the desired distribution in the collection pupil plane 114.

[0045] Furthermore, the size and shape of the diffraction orders at the collection pupil plane 114 may generally be related to the size and shape of the illumination beam 108 on the sample 104. For example, if the illumination beam 108 is elongated, the associated diffraction orders may be similarly elongated (e.g., in the orthogonal direction).

[0046] 3B is a top view of a collection pupil 304 at the collection pupil plane 114 of the overlay metrology tool 102, including grating diffraction lobes associated with the illumination profile of FIG. 3A by the multilayer grating structure 206, in accordance with one or more embodiments of the present disclosure. For example, the collection pupil plane 114 may correspond to the pupil plane in the collection subsystem 110 as shown in FIG. 1B. In particular, FIG. 3B shows the 0th diffraction order 306, the −1st grating diffraction order 308, and the +1st grating diffraction order 310 distributed along the direction of the periodicity of the multilayer grating structure 206 (e.g., the X direction here) at the collection pupil plane 114. For example, the −1st grating diffraction order 308 and the +1st grating diffraction order 310 may be associated with grating diffractions from the first layer grating 208, the second layer grating 212, and the third layer grating 216, with the diffraction angles based on the pitch of each of the three gratings and the illumination wavelength. In this regard, the respective diffraction lobes of the +1 order grating diffraction 310 from each layer 208, 212, 216 may overlap, and the −1 order grating diffraction 308 from each layer 208, 212, 216 may overlap.

[0047] It is contemplated herein that the phase of each of the grating diffraction orders (e.g., −1st grating diffraction order 308 and +1st grating diffraction order 310) may be oscillated during scanning to form a time-varying interference signal, and overlay may be determined based on the asymmetry of these oscillations. As a result, by capturing and comparing these time-varying interference patterns, overlay measurements may be performed. For example, the phase difference between the −1st and +1st grating diffraction orders 308, 310 from each individual grating may be used to measure the position of the grating relative to the optical system.

[0048] In an embodiment, the overlay metrology tool 102 includes photodetectors 112 positioned in positions suitable for capturing overlapping zeroth and grating diffraction orders. For example, FIG. 3B illustrates a configuration (e.g., provided by a metrology recipe) in which a grating diffraction lobe overlaps with the zeroth diffraction order at the collection pupil plane 114. For example, as shown in FIG. 3B, the grating diffraction lobes from the +1st and −1st diffraction orders 310 and 308 may overlap with the diffraction lobe of the zeroth diffraction order 306. FIG. 3B also illustrates a first photodetector 112a positioned in the overlap region with the −1st diffraction order 308, and a second photodetector 112b positioned in the overlap region with the +1st diffraction order 310. Each of the photodetectors 112 may then capture a time-varying interference signal as the sample 104 is scanned, and a difference between the time-varying interference signals captured by the photodetectors 112 indicates overlay.

[0049] However, it should be understood that the particular configuration shown in Figure 3B and the associated description are not limiting. For example, as previously described herein, the zeroth diffraction order 306 does not necessarily overlap with the -1st grating diffraction order 308 and the +1st grating diffraction order 310 at the collection pupil 304, as shown in Figure 3B. Rather, in some embodiments, these diffraction lobes are sufficiently close to one another that the zeroth diffraction order 306 overlaps with the -1st grating diffraction order 308 on the first photodetector 112a, and the zeroth diffraction order 306 overlaps with the +1st grating diffraction order 310 on the second photodetector 112b. Furthermore, in some embodiments, the overlay measurement is determined based on a time-varying signal associated with only the first grating diffraction order lobe (e.g., without reference to the zeroth diffraction order 306). For example, the overlay measurement may be determined based on a time-varying signal associated with the overlap between the auxiliary illumination and the + / -1st order diffraction lobes, as generally described in U.S. patent application Ser. No. 18 / 110,746, filed February 16, 2023 (the entire contents of which are incorporated herein by reference).

[0050] 3A-3B in general, it should be understood that FIGS. 3A-3B are provided for illustrative purposes only and should not be construed as limiting. For example, FIGS. 3A-3B illustrate the non-limiting case of diffraction of illumination beam 108 incident on a sample at normal incidence. However, it is contemplated herein that illumination beam 108 may generally have any profile suitable for enabling collection of combined or overlapping diffraction orders as disclosed herein (e.g., grating diffraction orders associated with combined diffraction from overlapping gratings of grating structure 206, overlapping grating diffraction and zeroth diffraction orders, or overlapping first diffraction orders from constituent gratings of grating structure 206, etc.). In some embodiments, illumination beam 108 has an annular profile. It is contemplated herein that the annular profile of illumination beam 108 can facilitate separation of overlapping diffraction orders at collection pupil plane 114. The use of an annular aperture to separate overlapping diffraction orders is generally described in U.S. Patent No. 10,197,389, issued February 9, 2019, which is incorporated herein by reference in its entirety. While U.S. Patent No. 10,197,389 includes a description of static measurements, it should be noted that the annular illumination beam 108 may similarly be utilized in scanning measurements as disclosed herein. In particular, in some embodiments, the photodetector 112 is positioned at the location of overlapping diffraction orders (e.g., overlapping grating diffraction and zeroth diffraction orders, or overlapping first diffraction orders from constituent gratings of the multilayer grating structure 206) generated based on the annular illumination beam 108.

[0051] 4A-4B show fast Fourier transform plots 400-450 according to one or more embodiments.

[0052] In embodiments, an overlay measurement between layers 210-218 of overlay target 204 may be determined based on a comparison of interference signals detected by the photodetectors. For example, controller 122 may be configured to determine the overlay measurement based on the magnitude (plots 410, 440) and / or phase (plots 420, 450) of the interference signals, as shown in Figures 4A-4B.

[0053] In an embodiment, the phase difference for each grating may be measured using a Fast Fourier Transform (FFT) algorithm used to convert the signal from the raw data (shown in plots 400, 430) into the frequency domain (as shown in plots 410, 420, 440, 450). In this regard, as shown in plot 420, the phase difference in the frequency domain may correspond to the grating pitch. Note that as each grating modulates, the time signal may be proportional to its spatial frequency (e.g., the inverse pitch 1 / P, 1 / Q, or 1 / R).

[0054] Note that the parameters of the metrology recipe may be selected based on the particular parameter to be resolved. The parameters need to be sufficient to resolve the particular pitch. For example, the pitch, cell length, or number of features may be selected such that the particular pitch in the plot is resolvable.

[0055] In a non-limiting example, the cell length may be selected so that a particular pitch in the plot is resolvable. For example, as shown in FIG. 4A, the phase difference of the −1st and +1st order grating diffractions 308, 310 from each individual grating in plot 420 is distinguishable for a cell having a length of about 15 μm. In comparison, as shown in FIG. 4B, the phase difference of the −1st and +1st order grating diffractions 308, 310 from each individual grating in plot 450 is not clearly distinguishable for a cell having a length of about 7.5 μm.

[0056] Referring again to FIG. 1A, additional components of the overlay metrology tool 102 are described in more detail in accordance with one or more embodiments of the present disclosure.

[0057] The photodetector 112 may generally include any type of photodetector known in the art suitable for capturing interference signals generated when the sample 104 is translated by the translation stage 116 and / or when the one or more illumination beams 108 are scanned by the beam scanning subsystem 118. For example, the photodetector 112 may include, but is not limited to, a high-speed photodiode, a photomultiplier tube, or an avalanche photodiode.

[0058] In general terms, the bandwidth or response time of the photodetector 112 should be sufficient to resolve the temporal frequency of the interference fringes, which is related to the pitch of the top, middle, and bottom gratings of the multilayer grating structure 206 and the scanning speed along the measurement direction (the direction of the periodicity of the multilayer grating structure 206). For example, if the scanning speed along the measurement direction is 10 centimeters per second and the target pitch is 1 micrometer, the interference signal will oscillate at a rate of approximately 100 kHz. In some embodiments, the photodetector 112 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 112, the translation speed along the measurement direction, and the pitch of the multilayer grating structure may be selected together to provide a desired sampling rate of the interference signal.

[0059] In an embodiment, overlay metrology system 100 includes a controller 122 communicatively coupled to overlay metrology tool 102. Controller 122 may include one or more processors 124 and a memory device 126, or memory. For example, one or more processors 124 may be configured to execute a set of program instructions retained in memory device 126.

[0060] 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 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 (e.g., program instructions stored in memory). In some embodiments, the one or more processors 124 may be embodied as a desktop computer, mainframe computer system, workstation, image computer, parallel processor, networked computer, or any other computer system configured to execute programs configured to operate or in conjunction with the overlay metrology system 100, as described throughout this disclosure. Furthermore, different subsystems of overlay metrology system 100 may include processors or logic elements suitable for performing at least some of the steps described in this disclosure. Accordingly, the above description should not be construed as a limitation on embodiments of the present disclosure, but merely as examples. Furthermore, the steps described throughout this disclosure may be performed by a single controller, or alternatively, by multiple controllers. Additionally, controller 122 may include one or more controllers housed within a common housing or within multiple housings. In this manner, any controller or combination of controllers may be separately packaged as a module suitable for integration into overlay metrology system 100.Additionally, the controller 122 may analyze or otherwise process the data received from the photodetector 112 and provide the data to additional components within the overlay metrology system 100 or external to the overlay metrology system 100 .

[0061] Additionally, memory device 126 may include any storage medium known in the art suitable for storing program instructions executable by associated one or more processors 124. For example, memory device 126 may include a non-transitory memory medium. As additional examples, memory device 126 may include, but is not limited to, 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 within a common controller housing along with one or more processors 124.

[0062] 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 otherwise control the overlay metrology tool 102 or any components thereof. For example, the controller 122 may be configured to direct the translation stage 116 to translate the sample 104 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 102, and / or direct the beam scanning subsystem 118 to position or scan one or more illumination beams 108 over the sample 104. As another example, the controller 122 may be configured to receive a signal corresponding to a time-varying interference signal from the photodetector 112. As another example, the controller 122 may generate corrections for one or more additional fabrication tools as feedback and / or feedforward control of the one or more additional fabrication tools based on the overlay measurements from the overlay metrology tool 102.

[0063] In an embodiment, controller 122 captures the interference signal detected by photodetector 112. 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, frequency domain analysis (e.g., FFT) and one or more phase-locked loops. Additionally, 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.

[0064] In an embodiment, the controller 122 determines an overlay measurement between the layers (e.g., the first layer 210, the second layer 214, and the third layer 218) of the overlay target 204 along the measurement direction based on a comparison of the interference signals. For example, the controller 122 may determine the overlay measurement based on the magnitude and / or phase of the interference signals, as shown in FIG. 4 . For example, U.S. Pat. No. 10,824,079, issued November 3, 2020, which is incorporated herein by reference in its entirety, generally describes the electric field of a diffraction order at the collection pupil and further provides a specific relationship between overlay and measured intensity at the pupil plane. 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 positioned in the overlap region between the 0th and + / −1st diffraction orders. In particular, it is contemplated herein that the overlay on the sample may be proportional to an asymmetry, such as, but not limited to, the relative phase shift between two time-varying interference signals.

[0065] Additionally, the controller 122 may calibrate or otherwise correct the overlay measurements based on known, expected, or measured features of the sample that may also affect the time-varying interference signal, such as, but not limited to, sidewall angle or other sample asymmetries.

[0066] Referring again to FIG. 1B, various components of the overlay metrology tool 102 are described in more detail in accordance with one or more embodiments of the present disclosure.

[0067] In an embodiment, the illumination subsystem 106 includes an illumination source 128 configured to generate at least one illumination beam 108. The illumination from the illumination source 128 may include one or more selected wavelengths of light, including, but not limited to, ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0068] Illumination source 128 may include any type of illumination source suitable for providing at least one illumination beam 108. In some embodiments, illumination source 128 is a laser source. For example, illumination source 128 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, illumination source 128 may provide illumination beam 108 with high coherence (e.g., high spatial coherence and / or temporal coherence). In some embodiments, illumination source 128 includes a laser-sustained plasma (LSP) source. For example, illumination source 128 may include, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for housing one or more elements capable of emitting broadband illumination when excited into a plasma state by a laser source.

[0069] In embodiments, the illumination subsystem 106 includes one or more optical components suitable for modifying and / or conditioning the illumination beam 108 and directing the illumination beam 108 to the sample 104. For example, the illumination subsystem 106 may include one or more illumination lenses 130 (e.g., to collimate the illumination beam 108 or to relay the illumination pupil plane 120 and / or the illumination field plane 132, etc.). In some embodiments, the illumination subsystem 106 includes one or more illumination control optics 134 for shaping or otherwise controlling the illumination beam 108. For example, the illumination control optics 134 may include, but are not limited to, one or more field diaphragms, one or more pupil diaphragms, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, etc.).

[0070] In an embodiment, the overlay metrology tool 102 includes an objective lens 136 for focusing the illumination beam 108 onto the sample 104 (e.g., an overlay target having overlay target elements located on two or more layers of the sample 104).

[0071] In embodiments, the illumination subsystem 106 illuminates the sample 104 with two or more illumination beams 108. Furthermore, the two or more illumination beams 108 may be incident on different portions of the sample 104 (e.g., different cells of an overlay target) within the measurement field of view (e.g., the field of view of the objective lens 136), although this is not required. It is contemplated herein that the two or more illumination beams 108 may be generated using a variety of techniques. In some embodiments, the illumination subsystem 106 includes two or more apertures in the illumination field plane 132. In some embodiments, the illumination subsystem 106 includes one or more beam splitters for splitting illumination from the illumination source 128 into the two or more illumination beams 108. In some embodiments, at least one illumination source 128 directly generates the two or more illumination beams 108. In a general sense, each illumination beam 108 may be considered to be part of a different illumination channel, regardless of the technique by which the various illumination beams 108 are generated.

[0072] In embodiments, the collection subsystem 110 includes at least two photodetectors 112 (e.g., photodetectors 112a, b) located at a collection pupil plane 114 configured to capture light from the sample 104 (e.g., collected light 138), where the collected light 138 includes at least a zeroth diffraction order 306, a −1st diffraction order 308, and a +1st diffraction order 310, as shown in FIG. 3B . The collection subsystem 110 may include one or more optical elements suitable for modifying and / or conditioning the collected light 138 from the sample 104. In some embodiments, the collection subsystem 110 includes one or more collection lenses 140 (e.g., for collimating the illumination beam 108 or relaying a pupil plane and / or field plane, etc.), which may, but need not, include the objective lens 136. In some embodiments, the collection subsystem 110 includes one or more collection control optics 142 for shaping or otherwise controlling the collected light 138. For example, the collection control optics 142 may include, but are not limited to, one or more field diaphragms, one or more pupil diaphragms, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, etc.).

[0073] In an embodiment, the collection subsystem 110 includes two or more collection channels 144, each having a separate pair of photodetectors 112. For example, as shown in FIG. 1B, the overlay metrology tool 102 may include one or more beam splitters 146 positioned to split the collected light 138 into the collection channels 144. Further, the beam splitters 146 may be polarizing beam splitters, non-polarizing beam splitters, or a combination thereof. However, it should be understood that the illustration of two collection channels 144 in FIG. 1B is provided for illustrative purposes only and should not be construed as limiting. For example, the collection subsystem 110 may include a single collection channel 144 or multiple collection channels 144.

[0074] In embodiments, the multiple collection channels 144 are configured to collect light from multiple illumination beams 108 on the sample 104. For example, if the overlay target 204 has one or more cells 202 distributed in a direction different from the scanning direction, the overlay metrology tool 102 may simultaneously illuminate different cells 202 with different illumination beams 108 and simultaneously capture interference signals associated with each illumination beam 108. Furthermore, in some embodiments, the multiple illumination beams 108 directed at the sample 104 may have different polarizations. In this manner, the diffraction orders associated with each illumination beam 108 can be separated. For example, the polarizing beam splitter 146 may efficiently separate the diffraction orders associated with the different illumination beams 108. As another example, a polarizer may be used in one or more collection channels 144 to separate desired diffraction orders for measurement.

[0075] In an embodiment, the overlay metrology tool 102 includes a beam scanning subsystem 118 for positioning, scanning, or modulating the position of one or more illumination beams 108 on the sample 104 during measurement.

[0076] The beam scanning subsystem 118 may include any type or combination of elements suitable for scanning the position of one or more illumination beams 108. In some embodiments, the beam scanning subsystem 118 includes one or more deflectors suitable for changing the direction of the illumination beams 108. 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 118 may include an electro-optic modulator, an acousto-optic modulator, or the like.

[0077] Deflectors may further be located at any suitable location within the overlay metrology tool 102. In some embodiments, one or more deflectors are located at one or more pupil planes common to both the illumination subsystem 106 and the collection subsystem 110. In this regard, the beam scanning subsystem 118 may be a pupil plane beam scanner, and an associated deflector may change the position of the one or more illumination beams 108 on the sample 104 without affecting the position of the diffraction orders at the collection pupil plane 114. Furthermore, the distribution of the one or more illumination beams 108 at the illumination field plane 132 may be more stable as the beam scanning subsystem 118 changes the position of the one or more illumination beams 108 on the sample 104. Pupil plane beam scanning is generally described in U.S. patent application Ser. No. 17 / 142,783, filed Jan. 6, 2021, the entire contents of which are incorporated herein by reference.

[0078] 5 is a flow diagram illustrating steps performed in a method 500 of scanning overlay metrology of an overlay target having at least one multi-layer grating structure, in accordance with one or more embodiments of the present disclosure. Applicant notes that the embodiments and implementation techniques previously described herein in the context of overlay metrology system 100 should be construed to extend to method 500. However, it is further noted that method 500 is not limited to the architecture of overlay metrology system 100.

[0079] In step 502, one or more cells of an overlay target are illuminated. For example, one or more cells 202 of an overlay target 204 on a sample 104 are illuminated as the sample 104 is scanned relative to the illumination, and the one or more cells include a multi-layer grating structure 206 formed from overlapping gratings having different pitches.

[0080] In step 504, time-varying interference signals may be collected from one or more photodetectors 112 a, b, such as two photodetectors 112 a, b positioned in a region of the collection pupil associated with overlapping diffractions from gratings in the multi-layer grating structure 206. For example, non-limiting configurations may include, but are not limited to, photodetectors positioned at positions that include only grating diffraction orders, both grating diffraction orders and the zeroth diffraction order, or first diffraction orders from the top, middle, and bottom gratings of the multi-layer grating structure 206.

[0081] In step 506, an overlay error between one or more sample layers associated with a multi-layer grating structure may be determined. For example, the overlay error between sample layers associated with a multi-layer grating structure in one or more cells 202 of the overlay target 204 may be determined based on signals from two photodetectors 112a, b. For example, the overlay error along the direction of periodicity of the multi-layer grating structure 206 may be proportional to the phase difference between the time-varying interference signals from the two photodetectors. The phase difference may be determined using any technique known in the art, including, but not limited to, frequency-domain analysis techniques (e.g., fast Fourier transform, etc.) applied to the two time-varying interference signals. Furthermore, in some embodiments, an overlay measurement of a sample along a specific measurement direction may be generated based on data from multiple cells of an overlay target comprising a multi-layer grating structure having periodicity along the specific measurement direction.

[0082] In an embodiment, the overlay error between one or more sample layers associated with the multi-layer grating structure 206 may be determined based on Equations 1.1-1.3 shown and described below.

number

[0083] Here, the position X of the grating having pitches P, Q, and R is expressed by the following equations 2.1 to 2.3, which are expressed by the + / - first-order phase φ i is derived from

number

[0084] It is contemplated herein that the method 500 may be applied to a wide range of overlay target designs suitable for 1D or 2D metrology measurements.

[0085] In some embodiments, an overlay measurement is generated based on a signal from an overlay target having a single cell using method 500.

[0086] In some embodiments, the overlay measurements are generated based on signals from an overlay target having multiple cells with different deformations of the multilayer grating structure. For example, in optional step 508, tool-induced shift (TIS) errors may be reduced or eliminated by averaging the measurements. For example, the TIS error of the overlay target 204 may be determined based on the difference between the overlay errors of one or more of the multiple cells 202.

[0087] 6A-6C are top views of multiple cells 202 of an overlay target 204 having a multi-layer grating structure 206 in accordance with one or more embodiments of the present disclosure.

[0088] In an embodiment, the overlay target 204 includes a plurality of cells 202. For example, the overlay target 204 may include a first cell 202a, a second cell 202b, and a third cell 202c.

[0089] The first cell 202a may include a first layer grating (e.g., top grating) located in a first layer of the sample 104, a second layer grating (e.g., middle grating) located in a second layer of the sample 104, and a third layer grating (e.g., bottom grating) located in a third layer, where the gratings have different pitches. For example, the pitches of the first layer grating, the second layer grating, and the third layer grating of the first cell 202a may be P, Q, and R, respectively.

[0090] The second cell 202b may include a first layer grating (e.g., a top grating) located in a first layer of the sample 104, a second layer grating (e.g., a middle grating) located in a second layer of the sample 104, and a third layer grating (e.g., a bottom grating) located in a third layer, where the gratings have different pitches. For example, the pitches of the first layer grating, the second layer grating, and the third layer grating of the second cell 202b may be Q, P, and R, respectively.

[0091] The third cell 202c may include a first layer grating (e.g., top grating) located in a first layer of the sample 104, a second layer grating (e.g., middle grating) located in a second layer of the sample 104, and a third layer grating (e.g., bottom grating) located in a third layer, where the gratings have different pitches. For example, the pitches of the first layer grating 208, the second layer grating 212, and the third layer grating 216 of the third cell 202c may be R, Q, and P, respectively.

[0092] In an embodiment, the TIS error may be determined based on the overlay error between one of the first cell 202a, the second cell 202b, or the third cell 202c. For example, TIS correction with two layers is typically performed by averaging measurements from two cells (e.g., PQ / QP, PR / RP, QR / RP) with inverted pitch distributions for those layers. Determination of TIS error is generally described in U.S. patent application Ser. No. 18 / 099,798, filed Dec. 20, 2023, which is incorporated herein by reference in its entirety. Note that not all are necessary for every application, and in some cases, having just two cells (rather than three as shown in FIGS. 6A-6B) may be sufficient.

[0093] In an embodiment, the method 500 includes simultaneously scanning multiple illumination beams and collecting associated overlapping diffraction orders for parallel measurements.

[0094] In an embodiment, 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 sample. In this regard, cells having multilayer grating structures with different periodicity directions may be efficiently measured by a common illumination beam within the measurement swath.

[0095] 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 many other architectures that achieve the same functionality may actually be implemented. In a conceptual sense, any arrangement of components to achieve the same functionality is substantially “associated” such that the desired functionality is achieved. Thus, any two components combined herein to achieve a particular functionality can be considered to be “associated” with each other such that the desired functionality is achieved, regardless of the architecture or intervening components. Similarly, any two components so associated can also be considered to be “connected” or “coupled” to each other to achieve the desired functionality, and any two components capable of being so associated can also be considered to be “couplable” to each other to achieve the desired functionality. Examples of what is combinable include, but are not limited to, components that can and / or do physically interact, components that can and / or do wirelessly interact, and / or components that can and / or do logically interact.

[0096] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes in form, construction, and arrangement of elements can be made without departing from the disclosed subject matter or sacrificing all of its important advantages. The described forms are merely illustrative, and it is the intent of the following claims to encompass and cover all such modifications. It is to be further understood that the invention is defined by the appended claims.

Claims

1. 1. An overlay metrology system, comprising:

1. A lighting subsystem comprising: an illumination source configured to generate an illumination beam; one or more illumination optics configured to direct the illumination beam to an overlay target on the sample as the sample is scanned relative to the illumination beam along a scan direction when executing a metrology recipe, wherein the overlay target according to the metrology recipe includes one or more cells having a multi-layer grating structure formed as overlapping grating structures having different pitches on three or more layers of the sample, the three or more layers of the sample including at least a first layer, a second layer, and a third layer, and the overlapping grating structure is periodic along at least one of the scan direction or a direction orthogonal to the scan direction; a lighting subsystem comprising: a collection subsystem, a first photodetector positioned at a first position in a pupil plane to capture overlapping diffraction orders from the multi-layer grating structure in the one or more cells when executing the metrology recipe; a second photodetector positioned at a second position in the pupil plane to capture overlapping diffraction orders from the multi-layer grating structure in the one or more cells when executing the metrology recipe; a collection subsystem comprising: a controller communicatively coupled to the first photodetector and the second photodetector, the controller transmitting to one or more processors: receiving time-varying interference signals from the first photodetector and the second photodetector associated with the multi-layer grating structure in the one or more cells as the overlay target is scanned according to the metrology recipe; determining an overlay error between one of the first layer, the second layer, or the third layer of the sample based on the time-varying interference signal; a controller including the one or more processors configured to execute program instructions; An overlay measurement system comprising:

2. the one or more cells of the overlay target a single cell including a multilayer grating structure having periodicity along the scanning direction; The overlay metrology system of claim 1 , comprising:

3. The multilayer lattice structure of the single cell is a first layer grating on the first layer having a first pitch; a second layer grating on the second layer having a second pitch; a third layer grating on the third layer having a third pitch; The overlay metrology system of claim 2 , comprising:

4. the one or more cells of the overlay target three cells, each including a multilayer grating structure with periodicity along the scanning direction; The overlay metrology system of claim 1 , comprising:

5. The three cells are a first cell having a first multilayer grating structure formed as a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch; a second cell having a second multilayer grating structure formed as a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch; a third cell having a third multi-layer grating structure formed as a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch; The overlay metrology system of claim 4 , comprising:

6. The controller instructs the one or more processors to: determining a tool-induced shift (TIS) error of the overlay target based on a difference between one of the overlay measurement of the first cell, the overlay measurement of the second cell, or the overlay measurement of the third cell; 6. The overlay metrology system of claim 5, configured to execute the program instructions that cause the metrology recipe to be executed by:

7. 2. The overlay metrology system of claim 1, wherein the first location including the first photodetector includes locations of +1 grating order diffraction and 0th order diffraction associated with grating diffraction from the overlapping grating structure of the multi-layer grating structure, and the second location including the second photodetector includes locations of −1 grating order diffraction and 0th order diffraction associated with grating diffraction from the overlapping grating structure of the multi-layer grating structure.

8. The one or more processors may instruct the one or more processors: extracting at least one of intensity or phase information associated with the time-varying interference signal using frequency domain analysis techniques; determining the overlay error between the first layer and the second layer of the sample based on at least one of the intensity or phase information; The overlay metrology system of claim 1 , further configured to execute program instructions.

9. The overlay metrology system of claim 1 , wherein the one or more illumination optics direct the illumination beams to the overlay target at a normal angle of incidence.

10. The illumination beam spatially coherent illumination beam The overlay metrology system of claim 1 , comprising:

11. a translation stage that translates the sample along the scan direction, the one or more illumination optics directing the illumination beam to the overlay target on the sample as the sample is scanned by the translation stage; The overlay metrology system of claim 1 , further comprising:

12. one or more beam scanning optics for scanning the illumination beam along the scan direction; The overlay metrology system of claim 1 , further comprising:

13. 1. An overlay metrology target, comprising: a multi-layer grating structure formed as overlapping grating structures having different pitches on three or more layers of a sample, the three or more layers of the sample including at least a first layer, a second layer, and a third layer, the overlapping grating structures being periodic along at least one of a scanning direction or a direction orthogonal to the scanning direction; Equipped with The multilayer grating structure is a first layer grating on the first layer having a first pitch; a second layer grating on the second layer having a second pitch; a third layer grating on the third layer having a third pitch; Equipped with Overlay measurement targets.

14. the overlay metrology target is A single cell including the multilayer grating structure having periodicity along the scanning direction The overlay metrology target of claim 13 , comprising:

15. the overlay metrology target is a plurality of cells, each cell including the multilayer grating structure having a periodicity along the scanning direction; The overlay metrology target of claim 13 , comprising:

16. The overlay metrology target of claim 15 , wherein the plurality of cells comprises three cells.

17. The three cells are a first cell having a first multilayer grating structure formed as a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch; a second cell having a second multilayer grating structure formed as a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch; a third cell having a third multi-layer grating structure formed as a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch; 17. The overlay metrology target of claim 16, comprising:

18. 1. A method comprising: receiving time-varying interference signals from first and second photodetectors associated with a multi-layer grating structure in one or more cells as an overlay target is scanned according to a metrology recipe, the overlay target according to the metrology recipe including the one or more cells having the multi-layer grating structure formed as an overlapping grating structure having different pitches on three or more layers of a sample, the three or more layers of the sample including at least a first layer, a second layer, and a third layer, and the overlapping grating structure is periodic along at least one of a scan direction or a direction orthogonal to the scan direction; determining an overlay error between one of the first layer, the second layer, or the third layer of the sample based on the time-varying interference signal; A method comprising:

19. the one or more cells of the overlay target A single cell including a multilayer grating structure having a periodicity along the scanning direction, wherein the multilayer grating structure of the single cell comprises: a first layer grating on the first layer having a first pitch; a second layer grating on the second layer having a second pitch; a third layer grating on the third layer having a third pitch; A single cell comprising:

20. The method of claim 18, comprising:

20. the one or more cells of the overlay target Three cells, each cell including a multilayer grating structure having a periodicity along the scanning direction, the three cells comprising: a first cell having a first multilayer grating structure formed as a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch; a second cell having a second multilayer grating structure formed as a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch; a third cell having a third multi-layer grating structure formed as a first layer grating on the first layer having a first pitch, a second layer grating on the second layer having a second pitch, and a third layer grating on the third layer having a third pitch; Three cells comprising 20. The method of claim 18, comprising:

Images