System and method for tracking real-time location for scanning overlay metrology

Abstract

A method may include receiving time-varying interference signals associated with a grating structure and a reference grating structure from two or more photodetectors. The grating structure may include one or more diffraction gratings, where the reference grating structure includes a reference grating disposed proximate to the one or more diffraction gratings of the grating structure, and where the reference grating is disposed proximate to the one or more diffraction gratings of the grating structure when scanning the sample relative to one or more illumination beams. The illumination beam interacts with the grating structure and the reference grating structure at the same time. The method may include determining at least one of a real-time position or a scan speed of the grating structure during the scan based on a reference grating signal. The method may include determining one or more superposition errors based on a grating signal from the grating structure and determining the real-time position of the grating structure during the scan based on the reference grating signal.

Description

[0001] Cross - Reference to Related Applications

[0002] The present applicant claims the benefit of U.S. Provisional Application No. 63 / 457,137, filed Apr. 4, 2023, under 35 U.S.C. § 119(e), which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present disclosure generally relates to overlay metrology and, more particularly, to scatterometry overlay metrology. BACKGROUND ART

[0004] Overlay metrology generally refers to the measurement of the relative alignment of layers on a sample (such as, but not limited to, semiconductor devices). The measurement of overlay or overlay error generally refers to the measurement of the misalignment of fabricated features on two or more sample layers. In a general sense, the proper alignment of fabricated features on multiple sample layers is necessary for the correct operation of the device.

[0005] The demand for reducing feature size and increasing feature density has led to a corresponding increase in the demand for accurate and effective overlay metrology systems. Metrology systems typically generate metrology data associated with a sample by measuring or otherwise inspecting overlay metrology targets across the sample distribution.

[0006] Overlay metrology targets are typically designed to provide diagnostic information about the alignment of multiple layers of a sample by characterizing an overlay target having target features located on the sample layers of interest. In addition, the overlay alignment of multiple layers is typically determined by aggregating overlay measurements of multiple overlay targets at various locations across the sample. For example, an overlay metrology target can be scanned to provide overlay measurement values at various locations across the sample.

[0007] During scanning, errors can arise from the stability of the scanning speed. Position can be used to improve the accuracy and stability of scanning measurements. Currently, the position is monitored using an encoder of a moving device (such as, a translator stage or a mirror). The main disadvantage of using an encoder of a moving device is that it does not give the real-time position of the target. Rather, it only provides the expected position because the sample and the moving device are spatially separated by a chuck (which holds the wafer) and a mount. Thus, for example, an error caused by chuck vibration will not be recorded by the stage encoder.

[0008] Accordingly, it would be desirable to provide systems and methods for addressing the above deficiencies. SUMMARY OF THE INVENTION

[0009] According to one or more embodiments of the present disclosure, a superposition metrology system is disclosed. In an embodiment, the superposition metrology system includes an illumination subsystem. In an embodiment, the illumination subsystem includes an illumination source configured to generate one or more illumination beams. In an embodiment, the illumination subsystem includes one or more illumination optics configured to direct the one or more illumination beams onto a superposition target on the sample along a scan direction when scanning the sample relative to the one or more illumination beams while implementing a metrology recipe. In an embodiment, the superposition target according to the metrology recipe includes one or more cells having a grating structure and a reference grating structure. In an embodiment, the grating structure includes one or more diffraction gratings, wherein the reference grating structure includes a reference grating arranged proximate to the one or more diffraction gratings of the grating structure, wherein when scanning the sample relative to the one or more illumination beams, the one or more illumination beams interact with the grating structure and the reference grating structure simultaneously, wherein the one or more diffraction gratings and the reference grating are periodic along the scan direction, and wherein the reference grating has one or more known parameters. In an embodiment, the superposition metrology system includes a collection photon subsystem. In an embodiment, the collection photon subsystem includes: two or more photodetectors positioned in a pupil plane to capture time-varying interference signals associated with diffraction orders of the grating structure in the one or more cells and time-varying interference signals associated with diffraction orders of the reference grating structure when implementing the metrology recipe. In an embodiment, the superposition metrology system includes a controller communicatively coupled to the two or more photodetectors. In an embodiment, the controller includes one or more processors configured to execute program instructions. In an embodiment, the program instructions are configured to cause the one or more processors to receive the time-varying interference signals from the two or more photodetectors, the time-varying interference signals including a grating signal associated with the grating structure in the one or more cells when scanning the superposition target according to the metrology recipe and a reference grating signal associated with the reference grating structure in the one or more cells when scanning the superposition target according to the metrology recipe. In an embodiment, the program instructions are configured to cause the one or more processors to determine at least one of a real-time position or a scan speed of the grating structure during the scan based on the reference grating signal from the reference grating. In an embodiment, the program instructions are configured to cause the one or more processors to determine one or more superposition errors based on the grating signal from the grating structure and to determine at least one of the real-time position or the scan speed of the grating structure during the scan based on the reference grating signal from the reference grating structure.

[0010] According to one or more embodiments of the present disclosure, a method is disclosed. In an embodiment, the method includes receiving time-varying interference signals from two or more photodetectors associated with a grating structure and a reference grating structure in one or more cells when scanning a superposition target according to a metrology recipe. In an embodiment, the superposition target according to the metrology recipe includes the one or more cells having the grating structure and the reference grating structure, wherein the grating structure includes one or more diffraction gratings, wherein the reference grating structure includes a reference grating arranged close to the one or more diffraction gratings of the grating structure, wherein when scanning a sample relative to one or more illumination beams, the illumination beams interact with the grating structure and the reference grating structure simultaneously, wherein the one or more diffraction gratings and the reference grating are periodic along a scanning direction, and wherein the reference grating has one or more known parameters. In an embodiment, the time-varying interference signals include a grating signal associated with the grating structure in the one or more cells when scanning the superposition target according to the metrology recipe and a reference grating signal associated with the reference grating structure in the one or more cells when scanning the superposition target according to the metrology recipe. In an embodiment, the method includes determining at least one of a real-time position or a scanning speed of the grating structure during the scanning based on the reference grating signal from the reference grating. In an embodiment, the method includes determining one or more superposition errors based on the grating signal from the grating structure and determining the real-time position of the grating structure during the scanning based on the reference grating signal from the reference grating structure.

[0011] According to one or more embodiments of the present disclosure, a superposition metrology target is disclosed. In an embodiment, the superposition metrology target includes one or more cells having a grating structure and a reference grating structure. In an embodiment, the grating structure includes one or more diffraction gratings. In an embodiment, the reference grating structure includes a reference grating arranged adjacent to the one or more diffraction gratings of the grating structure. In an embodiment, one or more illumination beams are configured to interact with the grating structure and the reference grating structure simultaneously when scanning a sample relative to the one or more illumination beams. In an embodiment, the one or more diffraction gratings and the reference grating are periodic along the scanning direction. In an embodiment, the reference grating has one or more known parameters.

[0012] It should be understood that both the foregoing summary and the following detailed description are merely exemplary and explanatory 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 summary, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Those skilled in the art can better understand many advantages of the present disclosure by referring to the accompanying drawings, where:

[0014] Figure 1A is a conceptual diagram of a system for performing scatterometry overlay metrology on an overlay target using pupil manipulation according to one or more embodiments of the present disclosure.

[0015] Figure 1B is a schematic diagram of an overlay metrology tool according to one or more embodiments of the present disclosure.

[0016] Figure 2A is a schematic diagram of a unit of an overlay target on a sample including a grating structure and a reference grating structure according to one or more embodiments of the present disclosure.

[0017] Figure 2B is a schematic diagram of a unit of an overlay target on a sample including a grating structure and a reference grating structure according to one or more embodiments of the present disclosure.

[0018] Figure 3A is a top view of an illumination pupil in an illumination pupil plane of an overlay metrology tool according to one or more embodiments of the present disclosure.

[0019] Figure 3B is according to one or more embodiments of the present disclosure and includes Figure 3A a top view of a collection pupil in a collection pupil plane of an overlay metrology tool including grating diffraction lobes associated with an illumination profile in

[0020] Figure 4A is a schematic diagram of an illumination beam spot on an overlay target according to one or more embodiments of the present disclosure.

[0021] Figure 4B is a plot depicting an illumination beam spot on an overlay target according to one or more embodiments of the present disclosure in Figure 4A

[0022] Figure 4C is a plot depicting an illumination beam spot on an overlay target according to one or more embodiments of the present disclosure.

[0023] Figure 5A is a schematic diagram of multiple illumination beam spots on an overlay target according to one or more embodiments of the present disclosure.

[0024] Figure 5B is a plot depicting multiple illumination beam spots on an overlay target according to one or more embodiments of the present disclosure in Figure 5A

[0025] Figure 5Cis a plot depicting a plurality of illumination beam spots on a superposition target according to one or more embodiments of the present disclosure.

[0026] Figure 6 is a flowchart illustrating steps performed in a method of scanning superposition metrology for a superposition target according to one or more embodiments of the present disclosure.

[0027] Figure 7A is a plot depicting a constant scan speed according to one or more embodiments of the present disclosure.

[0028] Figure 7B is a plot depicting a non-constant scan speed according to one or more embodiments of the present disclosure. Detailed Description

[0029] 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 certain embodiments and specific features thereof. The embodiments set forth herein are to be considered illustrative rather than restrictive. Those of ordinary skill in the art will readily appreciate that various changes and modifications in form and detail can be made without departing from the spirit and scope of the present disclosure.

[0030] Embodiments of the present disclosure relate to scanning scatterometry superposition using a superposition target that includes a grating structure and a reference grating structure. For example, the grating structure can include one or more diffraction gratings, where constituent gratings have different pitches and are not stacked on top of each other. For example, at least one of the diffraction gratings can be printed in a side-by-side target (e.g., an AIM target). As another example, the reference target can include a high-frequency grating target arranged to be close to the superposition target. In this regard, the reference target can be used for direct real-time position tracking, where the superposition target and the reference target can be scanned simultaneously.

[0031] For the purposes of the present disclosure, the term "scatterometry metrology" is used to broadly encompass the terms "scatterometry-based metrology" and "diffraction-based metrology", where 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. Additionally, the term "scanning metrology" is used to describe metrology measurements that are generated while 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.

[0032] Embodiments of the present disclosure relate to systems and methods for scanning overlay metrology based on time-varying interference signals in a collecting pupil plane from a grating structure and a reference grating structure (e.g., a clock grating structure). It is contemplated herein that the measurement conditions leading to the diffraction orders of the grating structure and the reference grating structure can lead to interference. Such interference signals can contain information associated with asymmetries in the target structure (e.g., but not limited to, superposition between top and bottom gratings and the like). It is further contemplated herein that scanning the grating structure relative to the illumination beam (or vice versa) can provide a characterization of the position-dependent superposition of the grating structure and thus enable determination of asymmetries (e.g., but not limited to, superposition). Additionally, it is contemplated herein that by simultaneously scanning the grating structure and the reference grating structure (e.g., a clock grating structure), the reference grating structure can be used as a reference for measuring and / or calibrating instabilities in the scan speed and the like. For example, the time-varying interference signal from the reference grating can be used to generate real-time position and / or scan speed measurements of the sample during the scan, such that any instabilities in the sample position and / or scan speed can be compensated for when providing the superposition measurement. It is contemplated herein that the time-varying interference signal from the reference grating can enable accurate superposition measurements under a wide range of measurement conditions, which can increase throughput. For example, requiring a constant scan speed during the measurement would require a relatively longer scan to allow the translation stage to achieve a constant scan speed before reaching the superposition target of interest. In contrast, using simultaneous capture of the time-varying interference signal from the reference grating on the sample and the time-varying interference signal from the grating structure obviates this requirement and enables measurements when the translation stage is accelerating, decelerating, or otherwise non-constant at the position of the superposition target of interest, which can substantially improve the measurement throughput.

[0033] Some embodiments of the present disclosure relate to scatterometry overlay metrology based on overlapping diffraction lobes from gratings (e.g., top or bottom gratings) of a grating structure or time-varying interference signals associated with diffraction from the grating structure. For example, a scanning-based scatterometry measurement technique may include a fast detector configured to capture time-varying interference signals generated when scanning a sample. The detector may be placed at an overlapping position between selected diffraction orders in the pupil plane to capture time-varying interference signals when scanning the sample. Various non-limiting scatterometry overlay metrology techniques are described in the following cases: 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 Publication No. 2023 / 0213875, published July 6, 2023; U.S. Patent Application No. 18 / 099,798, filed January 20, 2023; U.S. Patent Application No. 18 / 110,746, filed February 16, 2023; and U.S. Patent Application No. 18 / 372,444, filed September 25, 2023, all of which are incorporated herein by reference in their entirety. 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 grating structures.

[0034] In some embodiments, an overlay metrology system includes two or more photodetectors positioned at locations in the pupil plane corresponding to diffraction lobes from a grating structure. For example, the photodetectors may be positioned at an overlapping location between a first-order diffraction lobe and either a zero-order diffraction lobe (e.g., specular reflection) or a portion of the illumination separated from the generated illumination beam prior to incidence (e.g., split into primary illumination and auxiliary illumination). It is contemplated herein that these combined diffraction orders will exhibit time-varying interference signals (e.g., AC signals) during a scan measurement, which can be captured using two or more photodetectors. For example, the properties of the grating structure (e.g., the pitch constituting the grating) and / or the measurement conditions (e.g., illumination wavelength, illumination angle of incidence, collection angle, or the like) may be selected such that the positive and negative diffraction orders associated with the combined diffraction of the grating of the grating structure are collected by the system and captured by two or more photodetectors.

[0035] Some embodiments of the present disclosure relate to providing recipes for configuring overlay metrology tools. Overlay metrology tools can generally be configured according to a recipe that includes a set of parameters (such as, but not limited to, illumination of a sample during measurement, collection of light from the sample, or position of the sample) for controlling various aspects of overlay measurement. In this way, the overlay metrology tool can be configured to provide a selected type of measurement designed for one or more overlay targets of interest. For example, a metrology recipe can 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 intensity of illumination at those angles), polarization of incident illumination, or spatial distribution of illumination. As another example, a metrology recipe can include collection parameters such as, but not limited to, collection pupil distribution (e.g., desired distribution of angular light from the sample to be used for measurement and associated filtered intensity at those angles), collection field stop settings for selecting a portion of the sample of interest, polarization of the collected light, wavelength filters, position of one or more detectors (e.g., photodetectors), or parameters for controlling one or more detectors. As additional examples, a metrology recipe can include various parameters associated with the position of the sample 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 (along with associated parameters describing speed, scan pattern, or the like).

[0036] In some embodiments, the properties of the grating structure (such as, for example, the pitch or the like that makes up the grating) and the measurement conditions (such as, for example, illumination wavelength, illumination angle of incidence, collection angle, or the like) are arranged or otherwise selected (such as, for example, using a metrology recipe) to provide a selected distribution of diffracted and / or combined diffracted orders and further to place two or more photodetectors in suitable positions to capture these diffracted orders to generate a time-varying interference signal of interest.

[0037] It is further contemplated herein that the systems and methods disclosed herein can provide sensitive overlay metrology with high throughput. For example, a non-imaging configuration enables the use of fast photodetectors suitable for fast scan speeds. As a non-limiting example, a photodetector with a bandwidth of 1 GHz can achieve a scan speed of approximately 10 centimeters per second on a target with a pitch of 1 micron.

[0038] The grating structure can generally be formed as part of an overlay target and can generally be located anywhere on the sample. Additionally, the overlay target can include one or more measurement units, where each unit includes printed elements in non-overlapping regions of one or more layers on the sample to form a grating structure. The overlay measurement can then be based on any combination of measurements of the various units of the overlay target.

[0039] Upon careful consideration in this article, scatterometry overlay metrology using a reference grating as disclosed herein can provide many benefits. For example, the systems and methods disclosed herein can utilize an overlay target that includes non-stacked gratings. As another example, an overlay measurement between two or more layers can be determined in a single metrology measurement, where one or more layers of the metrology target are not stacked. In one example, pupil manipulation can enable the measurement of multi-layer overlay in a single scan. In another example, pupil manipulation can enable an overlay target (e.g., moiré, AIM, etc.), where different pitches that are not allowed to be printed stacked on top of each other due to design rules. As another example, the systems and methods disclosed herein can overcome the difficulty of measuring each layer under its ideal conditions because the performance of the laser scanning method does not strongly depend on the wavelength of the light used.

[0040] Reference is now made Figures 1A through 7B to a system and method for tracking a real-time position for scanning overlay metrology in more detail according to one or more embodiments of the present disclosure.

[0041] Figure 1A FIG. 9 is a conceptual diagram of an overlay metrology system 100 for performing scatterometry overlay metrology on a multi-overlay stacked grating metrology target according to one or more embodiments of the present disclosure.

[0042] 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 can perform scatterometry overlay measurements on a portion of the sample 104 having a grating structure.

[0043] Figure 1B FIG. 16 is a schematic diagram of the overlay metrology tool 102 according to one or more embodiments of the present disclosure.

[0044] In an embodiment, the overlay metrology tool 102 includes an illumination subsystem 106 for generating illumination in the form of one or more illumination beams 108 to illuminate the sample 104 and a photon collection subsystem 110 for collecting light from the illuminated sample 104. For example, the one or more illumination beams 108 can be angularly limited on the sample 104 such that the grating structure (e.g., in one or more cells of the overlay target) can generate discrete diffraction orders. In addition, the one or more illumination beams 108 can be spatially limited such that they can illuminate a selected portion of the sample 104. For example, each of the one or more illumination beams 108 can be spatially limited to illuminate a specific cell of the overlay target. In some embodiments, the one or more illumination beams 108 do not fill a specific cell of the overlay target.

[0045] The photon collection system 110 may then collect at least some of the diffraction orders associated with the diffraction of the illumination beam 108 from the grating structure. Additionally, the photon collection system 110 may include at least two photodetectors 112 positioned at locations in the collection pupil plane 114 associated with the location of the indicated time-varying interference signal of the superposition. For example, as will be described in more detail below, suitable locations for two or more photodetectors 112 may include, but are not limited to, locations associated with positive and negative diffraction orders, or locations associated with the overlap between the diffraction orders of the constituent gratings of the grating structure (e.g., the overlap region between the +1 diffraction order and the zero diffraction order of the grating or the overlap region between the -1 diffraction order and the zero diffraction order of the grating).

[0046] In an embodiment, the overlay metrology tool 102 includes a translation stage 116 to perform scanning metrology by scanning the sample 104 through the measurement field of view of the overlay metrology tool 102 during measurement.

[0047] 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 along the scan direction (e.g., the direction in which the translation stage 116 scans the sample 104) during measurement.

[0048] Now referring Figures 2A through 3B , the collection of diffraction orders from the grating structure and the placement of two or more photodetectors 112 for scanning scatterometry overlay metrology are described in more detail according to one or more embodiments of the present disclosure.

[0049] Figures 2A through 2B is a schematic diagram of one or more units 202 according to one or more embodiments of the present disclosure.

[0050] In an embodiment, the overlay target 204 includes one or more units 202, where any particular unit 202 of the one or more units 202 may include a grating structure 206 having periodicity along any direction and a reference grating structure 208 having periodicity along a similar direction. For example, as Figure 2A shown in Figure 2B , the overlay target 204 may include a single unit 202 having a grating structure 206 and a reference grating structure 208 that are periodic along a common direction. As another example, as Figure 2BAs shown, the superposed target 204 may include a plurality of units 202a, b, and each unit 202a, b includes a grating structure 206 having periodicity along a common direction and a reference grating 208 having periodicity along the common direction, wherein different units 202a, b have different configurations of the periodicity of the associated grating.

[0051] In an embodiment, as Figure 2A shown, the grating structure 206 includes two or more diffraction gratings. For example, the grating structure 206 may include a first exposure structure 210 located on the first layer 212 of the sample 104 and a second exposure structure 214 located on the second layer 216 of the sample 104. For example, the grating structure 206 may include a grating-on-grating structure, where the first exposure structure 210 and the second exposure structure 214 overlap.

[0052] In an embodiment, as Figure 2B shown, the grating structure 206 includes one or more diffraction gratings. For example, the grating structure 206 may include a first exposure structure 210 located on the first layer 212 of the sample 104 and a second exposure structure 214 located on the second layer 216 of the sample 104, where the first exposure structure 210 and the second exposure structure 214 are arranged along the scanning direction. For example, the second exposure structure 214 may be arranged adjacent to the first exposure structure 210 such that the first exposure structure 210 does not overlap with the second exposure structure 214. After careful consideration, the first exposure structure 210 may be associated with a first photolithographic exposure and the second exposure structure 214 may be associated with a second photolithographic exposure, where the first and second photolithographic exposures may be on the same layer or different layers (as Figures 2A through 2B shown).

[0053] In an embodiment, the first exposure structure 210 and the second exposure structure 214 may have different pitches. For example, Figure 2A the pitches of the first exposure structure 210 and the second exposure structure 214 are respectively described as P and Q. It should be noted that Figure 2A the configurations depicted are provided for illustrative purposes only and should not be construed as limiting the scope of the present disclosure. Thus, the grating structure 206 may be formed by any number of layers having any kind of pitch. For example, the grating structure 206 may be formed by two or more layers.

[0054] In an embodiment, the first exposure structure 210 and the second exposure structure 214 may have the same pitch. For example, as Figure 2B shown, the first exposure structure 210 and the second exposure structure 214 may have the same pitch. After careful consideration, in the case where the grating structure 206 has the same pitch, tool-induced shift (TIS) errors may be reduced (e.g., as Figure 2B shown).

[0055] In an embodiment, the reference grating structure 208 includes a reference grating 218. For example, the reference grating 218 may be positioned on the third layer 220 of the sample. Although Figures 2A through 2B the reference grating 218 is depicted on the third layer 220, upon due consideration, the reference grating 218 may be disposed on either the first or second layer, but Figures 2A through 2B is provided for illustrative purposes only.

[0056] Upon due consideration herein, the reference grating structure 208 may be in the same unit as or in a different unit from the grating structure 206.

[0057] The frequency (or pitch) of the reference grating 218 may be different from the frequencies (or pitches) of the gratings 210, 214 of the grating structure 206. For example, the frequency of the reference grating 218 may be greater than the frequencies of the gratings 210, 214 of the grating structure 206. In other words, the pitch of the reference grating 218 may be smaller than the pitches of the gratings 210, 214 of the grating structure 206. For example, as mentioned above in Figure 2A the pitch of the first exposure structure 210 and the second exposure structure 214 may be P and Q respectively, and the pitch of the reference grating 218 may be R.

[0058] The reference grating 218 may have one or more known parameters. For example, the frequency of the reference grating 218 may be known. In this regard, the frequency of the reference grating 218 may be monitored to determine one of the real-time position or the scanning speed, such that variations in the scanning speed can be corrected.

[0059] In an embodiment, the reference grating structure 208 is arranged close to the grating structure 206 (e.g., in a non-overlapping configuration). For example, the reference grating 218 may be arranged close to the first exposure structure 210 of the grating structure 206 and the second exposure structure 214 of the grating structure 206. In one example, as Figure 2A shown, the reference grating 218 may be disposed between the overlapping first exposure structure 210 and the second exposure structure 214 of the grating structure 206. In another example, as Figure 2B shown, the reference grating 218 may be disposed below the first exposure structure 210 of the grating structure 208 and the second exposure structure 214 of the grating structure 206. In this regard, as will be further discussed herein, when scanning the overlay target 204 with an illumination beam, the illumination beam may interact with both the grating structure 206 and the reference structure 206 simultaneously.

[0060] However, it should be understood that Figures 2A through 2BThe superposition target 204 and the associated description therein are provided for illustrative purposes only and should not be construed as limiting. Rather, the superposition target 204 may comprise any suitable grating superposition target design. For example, the superposition target 204 may comprise any number of cells 202 suitable for making measurements. Additionally, the cells 202 may be distributed in any pattern or arrangement. In an embodiment, the superposition target 204 comprises one or more cell groupings distributed along a scan direction (e.g., the direction of motion of the sample 104), wherein the cells 202 within each particular cell grouping are oriented to have a grating structure 206 that is periodic along a common direction.

[0061] Reference is now made Figures 3A through 3B , and various non-limiting configurations for generating and measuring time-varying interference signals from the grating structure 206 and the reference grating structure 208 in the cells 202 of the superposition target 204 are described in accordance with one or more embodiments of the present disclosure.

[0062] Figure 3A is a top view of the illumination pupil 302 in the illumination pupil plane 120 of the superposition metrology tool 102 in accordance with one or more embodiments of the present disclosure. For example, the illumination pupil plane 120 may correspond to the pupil plane in the illumination subsystem 106 as illustrated in Figure 1B . In an embodiment, the illumination subsystem 106 illuminates the superposition target 204 with one or more illumination beams 108 at normal incidence (or near-normal incidence), as illustrated in Figure 3A . In this regard, the superposition target 204 may diffract one or more illumination beams 108 into discrete diffraction orders.

[0063] Figure 3B Illustrates a non-limiting configuration of the diffraction orders of the illumination beam 108 associated with the superposition metrology target 204 shown in Figure 2A in the collection pupil plane 114 and the associated positions of two or more photodetectors 112 suitable for capturing time-varying interference signals from which superposition measurements can be extracted. It is contemplated herein that two or more photodetectors 112 placed at positions associated with diffraction lobes in the collection pupil plane 114 may capture time-varying interference signals indicative of superposition. It is further contemplated herein that when each relevant diffraction lobe impinges on the photodetector 112 (e.g., within the measurement area of the photodetector 112), the time-varying interference signal associated with the combined diffraction lobes may be captured by the photodetector 112. In this manner, the relevant diffraction lobes do not necessarily need to overlap in the collection pupil plane 114 but may overlap on the photodetector 112.

[0064] It should be appreciated herein that the distribution of diffraction orders of the illumination beam 108 through a periodic structure (e.g., grating structure 206 or reference grating structure 208) can be affected by various parameters, such as but not limited to the wavelength of the illumination beam 108, the incident angles of the illumination beam 108 in both the elevation angle direction and the azimuth angle direction, the pitch of the grating of the grating structure 206, or the numerical aperture (NA) of the condenser lens. Thus, in embodiments of the present disclosure, the illumination subsystem 106, the condenser subsystem 110, and the overlay target 204 can be configured (e.g., according to a metrology recipe that defines a set of selected associated parameters) to provide a desired distribution of diffraction orders in the condenser pupil plane 114 suitable for generating a time-varying interference pattern indicative of overlay. For example, the illumination subsystem 106 and / or the condenser subsystem 110 can be configured to perform measurements on grating structures having a selected range of periodicities to provide the desired distribution in the condenser pupil plane 114. Additionally, various components (e.g., apertures, pupils, or the like) of the illumination subsystem 106 and / or the condenser subsystem 110 can be adjustable to provide the desired distribution in the condenser pupil plane 114.

[0065] In an embodiment, the condenser pupil plane 114 can correspond to the pupil plane in the condenser subsystem 110 as described in Figure 1B . For example, Figure 3B for each grating of the overlay target 204 shown in Figure 2A , zero-order diffraction 306, -1st-order grating diffraction 308, and +1st-order grating diffraction 310 distributed along the periodicity direction (e.g., the X direction herein) of the grating structure 206 in the condenser pupil plane 114 are depicted. For example, -1st-order grating diffraction 308a and +1st-order grating diffraction 310a can be associated with the grating diffraction from the first exposure structure 208, -1st-order grating diffraction 308b and +1st-order grating diffraction 310b can be associated with the grating diffraction from the second exposure structure 214, and -1st-order grating diffraction 308c and +1st-order grating diffraction 310c can be associated with the grating diffraction from the reference grating 218, where the diffraction angles are based on the pitch of the grating and the illumination wavelength. In this regard, the corresponding diffraction lobes of the +1st-order grating diffractions 308a to c from the respective layers 210, 214, 218 can overlap and the -1st-order grating diffractions 310a to c from the respective layers 210, 214, 218 can overlap.

[0066] It is contemplated herein that the phase of each of the grating diffraction orders (e.g., -1st-order grating diffraction 308 and +1st-order grating diffraction 310) can oscillate during scanning to form a time-varying interference signal and the overlay can be determined based on these oscillating phases. Thus, the overlay measurement can be performed by capturing and comparing these time-varying interference patterns. For example, the phase difference between the -1st-order and +1st-order grating diffractions 308, 310 from each individual grating can be used to measure the position of the grating relative to the optical system.

[0067] However, it should be understood that Figure 3B the specific configurations and associated descriptions set forth herein are non-limiting. Specifically, various metrology overlay techniques may be used to capture time-varying interference signals as contemplated herein, such as generally discussed in the following cases: 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 Publication No. 2023 / 0213875, published July 6, 2023; U.S. Patent Application No. 18 / 099,798, filed January 20, 2023; and U.S. Patent Application No. 18 / 110,746, filed February 16, 2023, each of which is incorporated herein by reference in its entirety.

[0068] For example, a Moiré diffraction lobe may overlap with a 0th order diffraction in the light collection pupil plane (e.g., as provided by a metrology recipe). In this example, a first photodetector may be positioned at an overlap region between the -1st order Moiré diffraction and the 0th order diffraction, and a second photodetector may be positioned at an overlap region between the +1st order Moiré diffraction and the 0th order diffraction, where each of the photodetectors 112 may then capture a time-varying interference signal when scanning the sample 104. Additionally, an overlay measurement may be determined based on a time-varying signal associated only with a first order Moiré diffraction lobe (e.g., without reference to the 0th order diffraction). As another example, first order diffractions from the first exposure structure 210 and the second exposure structure 214 overlap in the light collection pupil 304. For example, a first photodetector may be positioned in a first overlap region between the -1st order diffraction (-1 TOP ) from the first exposure structure 210 and the -1st order diffraction (-1 BOTTOM ) from the second exposure structure 214, and a second photodetector may be positioned in a second overlap region between the +1st order diffraction (+1 TOP ) from the first exposure structure 210 and the +1st order diffraction (+1 BOTTOM) in a second overlapping region therebetween. As another example, the overlay measurement may be determined based on time-varying signals associated with the first-order grating diffraction lobes (e.g., without reference to the 0th-order diffraction 306) and the second-order diffraction lobes. Additionally, the first-order diffraction lobes do not necessarily need to overlap in the light collection pupil plane, and in some embodiments may overlap on the respective photodetectors 112a, b. Further, in some embodiments, the overlay measurement is determined based on time-varying signals associated with only the first-order grating diffraction lobes (e.g., without reference to the 0th-order diffraction 306). For example, the overlay measurement may be determined based on time-varying signals associated with the overlap between the auxiliary illumination (e.g., illumination separated from the generated illumination beam) and the first-order diffraction lobes, as generally discussed in U.S. Patent Application No. 18 / 110,746, filed Feb. 16, 2023, which is incorporated herein by reference in its entirety.

[0069] Upon further consideration, the 0th-order diffraction 306 does not necessarily need to overlap with the -1st-order grating diffraction 308 and the +1st-order grating diffraction 310 in the light collection pupil 304, as Figure 3B illustrated. Rather, in some embodiments, these diffraction lobes are close enough together such that the 0th-order diffraction 306 overlaps with the -1st-order grating diffraction 308 on the first photodetector 112a and the 0th-order diffraction 306 overlaps with the +1st-order grating diffraction 310 on the second photodetector 112b.

[0070] Generally referring to Figures 4A through 5C , in an embodiment, one or more illumination beams 108 of the illumination subsystem 106 interact with both the grating structure 206 and the reference grating structure 208 simultaneously. For example, when the overlay metrology target 204 is scanned by one or more illumination beams 108, the one or more illumination beams 108 interact with the gratings of the grating structure 206 (e.g., the first exposure structure 210 and the second exposure structure 214) and the reference grating 218 of the reference grating structure 208. In this regard, the reference grating structure 208 can be used as a reference to directly calibrate the time-varying interference signal from the grating structure 206 based on observations (e.g., the position or velocity of the reference beam) derived from the time-varying interference signal from the reference grating structure 208.

[0071] The simultaneous interaction of the illumination beams is generally discussed in U.S. Patent Application No. 18 / 372,444, filed Sep. 25, 2023, which is incorporated herein by reference in its entirety.

[0072] Figure 4A is a schematic diagram of a unit 202 of an overlay metrology target 204 scanned by an illumination beam 108 according to one or more embodiments of the present disclosure. Figure 4B is a depiction of a method for generating according to one or more embodiments of the present disclosure Figure 4ADiagram 400 of the apodizer function 402 of the illumination beam 108 in Figure 4C is a use according to one or more embodiments of the present disclosure Figure 4B Diagram 404 of the simulated illumination spots 401 generated by the apodizer function 402 in

[0073] Generally referring to Figures 4A through 4C , in an embodiment, one or more illumination beams 108 extend orthogonally in the scanning direction. For example, one or more illumination beams 108 may extend orthogonally in the scanning direction such that the grating structure 206 and the reference grating structure 208 are scanned simultaneously.

[0074] Referring to Figures 4B through 4C , in an embodiment, one or more optical elements 134 of the illumination subsystem 106 may be used to modify one or more illumination beams 108. For example, the apodizer function 402 in the illumination pupil field may be used to generate an elongated illumination beam 401. For example, Figure 4B the apodization function 402 in the pupil field shown in Figure 4A may be used to generate an elongated illumination beam 401. In this regard, as shown in

[0075] Figure 5A is a schematic diagram of the unit 202 of the superimposed metrology target 204 scanned by using two illumination beams 108 according to one or more embodiments of the present disclosure. Figure 5B is a depiction according to one or more embodiments of the present disclosure for generating Figure 5A Diagram 500 of the apodizer function 502 for separating the illumination beam 108 in Figure 5C is a depiction according to one or more embodiments of the present disclosure of the use of Figure 5B Diagram 504 of the separated simulated illumination spots 501a, b generated by the apodizer function 502 in

[0076] Generally referring to Figures 5A through 5C , in an embodiment, one or more illumination beams 108 are separated to generate two separate illumination beams 501a, 501b in the pupil field. For example, one or more illumination beams 108 may be separated to generate two separate illumination beams 501a, 501b. For example, the first illumination beam 501a may interact with the grating structure 206 and the second illumination beam 501b may interact with the reference grating structure 208.

[0077] In an embodiment, one or more optical elements 134 of the illumination subsystem 134 (e.g., an apodizer) may be used to generate separated illumination beams 501a, 501b by splitting one or more illumination beams 108. For example, an apodizer function 502 in the pupil field may be used to generate separated illumination beams 501a, 501b. For example, Figure 5B the apodized spots 502 in the pupil field shown in may be used to generate separated illumination beams 501a, 501b such that the separated illumination beams 501a, b are coherent with each other (e.g., the phases of the associated time-varying interference signals are synchronized). In this regard, as Figure 5A shown in, when scanning the overlay target 204, the separated illumination beams 501a, 501b may simultaneously interact with a first exposure structure 210 and a second exposure structure 214 of the grating structure 208 and a reference grating 216 of the reference grating structure 208.

[0078] Although Figures 5A through 5C two spots are depicted, it should be noted that Figures 5A through 5C this is provided for illustrative purposes only and should not be construed as limiting the scope of the present disclosure. For example, the systems and methods of the present disclosure may be used to measure three or more side-by-side gratings.

[0079] In addition, any optical element and / or illumination source may be used to generate either an elongated beam or a separated illumination beam, as contemplated herein, and thus, Figures 4A through 5C this is provided for illustrative purposes only and should not be construed as limiting the scope of the present disclosure.

[0080] Referring again to Figure 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.

[0081] In an embodiment, the overlay metrology system 100 includes a controller 122 communicatively coupled to the overlay metrology tool 102. 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.

[0082] In an embodiment, the controller 122 may perform any one 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 of its components. 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 scan bands to scan one or more overlay targets through the 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 modified illumination beams over the sample 104. As another example, the controller 122 may be configured to receive signals corresponding to time-varying interference signals from the photodetector 112. As another example, the controller 122 may generate correction terms for one or more additional fabrication tools as feedback and / or feedforward control for the one or more additional fabrication tools based on overlay measurements from the overlay metrology tool 102.

[0083] In an embodiment, the controller 122 captures the interference signal detected by the photodetector 112. For example, the controller 122 may generally capture data (such as but not limited to the amplitude 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), one or more phase-locked loops, and the like). Additionally, the controller 122 may capture the interference signal or any data associated with the interference signal using any combination of hardware (e.g., circuitry) or software techniques.

[0084] In an embodiment, the controller 122 separates the interference signal detected by the photodetector 112. For example, the interference signal associated with the reference grating structure 208 may be separated from the interference signal associated with the grating structure 206. In one example, the controller 122 may be configured to separate the respective interference signals using a Fourier transform. In another example, the controller 122 may be configured to separate the respective interference signals using model fitting.

[0085] In some embodiments, the interference signal associated with the reference grating structure 208 may be spatially separated from the interference signal associated with the grating structure 206. For example, dedicated diodes in the field may be used to read the spatially separated signals. In this regard, the controller 122 may receive the spatially separated signals such that the controller 122 may determine the real-time position or scan speed.

[0086] In an embodiment, the controller 122 determines either the real-time position or the scan speed of either the sample or the grating structure during scanning based on a reference grating signal from the reference grating. For example, in a non-limiting example, the controller 122 may be configured to determine a reference time-varying interference signal based on the separated time-varying interference signals. As another example, in a non-limiting example, the controller 122 may be configured to receive a reference time-varying interference signal from a dedicated diode.

[0087] In an embodiment, a reference time-varying interference signal can be used as a real-time position or a scan speed. For example, a reference grating time-varying interference signal can be used to analyze a grating time-varying interference signal from a grating structure 206. In this regard, the reference grating time-varying interference signal can be used as a feedback or feed-forward loop to adjust one or more parameters of the grating structure 206 or one or more components of the system (e.g., the scan speed of the system or the like).

[0088] In a non-limiting example, the frequency of the reference grating time-varying interference signal can be measured during a scan. If the frequency of the reference grating time-varying interference signal has shifted (e.g., does not correspond to the known frequency of the reference grating before the scan), then the grating time-varying interference signal can be adjusted based on the shift in the frequency of the reference grating time-varying interference signal.

[0089] In an embodiment, the controller 122 determines an overlay measurement between layers of an overlay target along a measurement direction based on a comparison of interference signals. For example, an overlay error between sample layers associated with a grating structure in one or more cells 202 of the overlay target 204 is determined based on a multi-layer time-varying interference signal and a real-time position is determined based on a reference grating time-varying interference signal. For example, the controller 122 can determine an overlay measurement based on the amplitude and / or phase of the interference signal. U.S. Patent No. 10,824,079, which is hereby incorporated by reference in its entirety, generally describes the electric field of diffraction orders in a collection pupil and further provides a specific relationship between an overlay in the pupil plane and a measured intensity. It is contemplated herein that the systems and methods disclosed herein can extend the teachings of U.S. Patent No. 10,824,079 to time-varying interference signals captured by a photodetector placed in an overlap region between 0 and + / -1 diffraction orders. Specifically, it is contemplated herein that an overlay on a sample can be proportional to a relative phase shift between two time-varying interference signals.

[0090] In addition, the controller 122 can calibrate or otherwise modify the overlay measurement based on known, assumed, or measured characteristics of the sample that can also affect the time-varying interference signal (e.g., but not limited to sidewall angle or other sample asymmetries).

[0091] The photodetector 112 can generally include any type of optical detector known in the art suitable for capturing interference signals generated when the sample 104 is translated by the translation stage 116 and / or when one or more illumination beams 108 are scanned by the beam scanning subsystem 118. For example, the photodetector 112 can include, but is not limited to, a fast photodiode, a photomultiplier tube, or an avalanche photodiode.

[0092] In a general sense, 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 gratings of the grating structure 206 and the reference grating structure 208 and the scanning speed along the measurement direction (the periodic direction of the grating structure 206 and the reference grating structure 208). For example, in the case of a scanning speed of 10 centimeters per second along the measurement direction and a target pitch of 1 micron, the interference signal will oscillate at a rate of approximately 100 kHz. In some embodiments, the photodetector 112 comprises a photodetector having a bandwidth of at least 200 kHz (Nyquist frequency limit). However, it should be understood that this value is not necessary. Rather, the bandwidth of the photodetector 112, the translation speed along the measurement direction, and the pitch of the grating structure and the reference grating structure can be selected together to provide the desired sampling rate of the interference signal.

[0093] One or more processors 124 of the controller 122 can generally comprise any processor or processing element known in the art. For the purposes of this disclosure, the term "processor" or "processing element" can 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 array (FPGA) or one or more digital signal processor (DSP)). In this sense, one or more processors 124 can comprise any device configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). In some embodiments, one or more processors 124 can be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute a program that is configured to operate the overlay metrology system 100 or operate in conjunction with the overlay metrology system 100, as described throughout this disclosure. Moreover, different subsystems of the overlay metrology system 100 can comprise processors or logic elements suitable for implementing at least a portion of the steps described in this disclosure. Thus, the foregoing description should not be construed as a limitation on the embodiments of this disclosure but merely as illustrative. Additionally, the steps described throughout this disclosure can be implemented by a single controller or alternatively multiple controllers. Further, the controller 122 can comprise one or more controllers housed within one common housing or multiple housings. In this manner, any controller or combination of controllers can be separately encapsulated as a module suitable for integration into the metrology overlay metrology system 100. Additionally, the controller 122 can analyze or otherwise process the data received from the photodetector 112 and feed the data to additional components within or external to the overlay metrology system 100.

[0094] In addition, the memory device 126 can include any storage medium known in the art suitable for storing program instructions executable by one or more associated processors 124. For example, the memory device 126 can include a non-transitory memory medium. As an additional example, the memory device 126 can include, but is not limited to, read-only memory, random access memory, magnetic or optical memory devices (e.g., magnetic disks), magnetic tapes, solid state drives, and the like. It should be further noted that the memory device 126 can be housed in a common controller housing together with one or more processors 124.

[0095] Referring again to Figure 1B , various components of the overlay metrology tool 102 are described in more detail according to one or more embodiments of the present disclosure.

[0096] 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 can include light of one or more selected wavelengths, including but not limited to ultraviolet (UV) radiation, visible light radiation, or infrared (IR) radiation.

[0097] The illumination source 128 can include any type of illumination source suitable for providing at least one illumination beam 108. In some embodiments, the illumination source 128 is a coherent light source. For example, the coherent light source can be a laser source. For example, the illumination source 128 can 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 128 can provide an illumination beam 108 having high coherence (e.g., high spatial coherence and / or temporal coherence). In some embodiments, the illumination source 128 includes a laser sustained plasma (LSP) source. For example, the illumination source 128 can include, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for containing one or more elements that can emit broadband illumination when excited into a plasma state by a laser source.

[0098] In an embodiment, the illumination subsystem 106 includes one or more optical components adapted to modify and / or condition the illumination beam 108 and direct the illumination beam 108 onto the sample 104. For example, the illumination subsystem 106 may include one or more illumination lenses 130 (e.g., for collimating the illumination beam 108, for relaying the illumination pupil plane 120 and / or the illumination field plane 132 or the like). 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 apodizers, 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 beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, or the like).

[0099] 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).

[0100] In an embodiment, the illumination subsystem 106 illuminates the sample 104 using two or more illumination beams 108. Additionally, the two or more illumination beams 108 may (but need not) impinge on different portions (e.g., different cells of the overlay target) of the sample 104 within the measurement field of view (e.g., the field of view of the objective lens 136). A variety of techniques may be used to generate the two or more illumination beams 108, as contemplated herein. In some embodiments, the illumination subsystem 106 includes two or more apertures at the illumination field plane 132. In some embodiments, the illumination subsystem 106 includes one or more beam splitters for separating the illumination from the illumination source 128 into two or more illumination beams 108. In some embodiments, at least one illumination source 128 directly generates two or more illumination beams 108. In a general sense, each illumination beam 108 may be considered part of a different illumination channel, independent of the technique used to generate the various illumination beams 108.

[0101] In an embodiment, the collection subsystem 110 includes at least two photodetectors 112 (e.g., photodetectors 112a, b) located at the collection pupil plane 114 configured to capture light from the sample 104 (e.g., the collected light 138), where the collected light 138 includes at least as Figure 3BThe zero-order diffraction 306, the -1st order diffraction 308, and the +1st order diffraction 310 described in. The photon collection system 110 may include one or more optical elements adapted to modify and / or condition the collected light 138 from the sample 104. In some embodiments, the photon collection system 110 includes one or more collection lenses 140 (e.g., for collimating the illumination beam 108, for relaying the pupil and / or field plane, or the like), and the one or more collection lenses 140 may include (but need not include) the objective lens 136. In some embodiments, the photon collection system 110 includes one or more collection control optical devices 142 for shaping or otherwise controlling the collected light 138. For example, the collection control optical devices 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).

[0102] In an embodiment, the photon collection system 110 includes two or more collection channels 144 each having a pair of separate photodetectors 112. For example, as Figure 1B described in, the overlay metrology tool 102 may include one or more beam splitters 146 configured to separate the collected light 138 into the collection channels 144. Additionally, the beam splitter 146 may be a polarizing beam splitter, a non-polarizing beam splitter, or a combination thereof. However, it should be understood that Figure 1B the illustration of the two collection channels 144 in is provided for illustrative purposes only and should not be construed as limiting. For example, the photon collection system 110 may include a single collection channel 144 or multiple collection channels 144.

[0103] In an embodiment, the multiple collection channels 144 are configured to collect light from multiple illumination beams 108 on the sample 104. For example, in the case where the overlay target 204 has one or more cells 202 distributed in a direction different from the scan direction, the overlay metrology tool 102 may simultaneously illuminate different cells 202 with different illumination beams 108 and simultaneously capture the interference signals associated with each illumination beam 108. Additionally, in some embodiments, the multiple illumination beams 108 directed to the sample 104 may have different polarizations. In this way, the diffraction orders associated with each illumination beam 108 can be separated. For example, a polarizing beam splitter 146 may effectively separate the diffraction orders associated with different illumination beams 108. As another example, polarizers may be used in one or more collection channels 144 to isolate the desired diffraction order for measurement.

[0104] 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.

[0105] The beam scanning subsystem 118 can 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 modifying the direction of the illumination beam 108. For example, the deflector can include, but is not limited to, a rotatable mirror (e.g., a mirror with adjustable flipping and / or tilting). Additionally, any technique known in the art can be used to actuate the rotatable mirror. For example, the deflector can include, but is not limited to, a galvanometer, a piezoelectric mirror, or a microelectromechanical system (MEMS) device. As another example, the beam scanning subsystem 118 can include an electro-optic modulator, an acousto-optic modulator, or the like.

[0106] The deflector can be further positioned at any suitable location in the overlay metrology tool 102. In some embodiments, one or more deflectors are placed at one or more pupil planes shared by both the illumination subsystem 106 and the collector subsystem 110. In this regard, the beam scanning subsystem 118 can be a pupil plane beam scanner and the associated deflector can modify the position of one or more illumination beams 108 on the sample 104 without affecting the position of the diffraction orders in the collection pupil plane 114. Additionally, as the beam scanning subsystem 118 modifies the position of one or more illumination beams 108 on the sample 104, the distribution of one or more illumination beams 108 in the illumination field plane 132 can be further stabilized. Pupil plane beam scanning is generally described in U.S. Patent No. 11,300,524, issued April 12, 2022, which is incorporated herein by reference in its entirety.

[0107] Figure 6 is a flow chart illustrating the steps performed in a method 600 for overlay metrology for scanning an overlay target in accordance with one or more embodiments of the present disclosure. Applicants note that the embodiments and implementation techniques previously described herein in the context of the overlay metrology system 100 should be interpreted as extending to the method 600. However, it should be further noted that the method 600 is not limited to the architecture of the overlay metrology system 100.

[0108] In step 602, one or more units of the overlay target are illuminated. For example, when scanning the sample 104 relative to illumination, one or more units 202 of the overlay target 204 on the sample 104 are illuminated, where the one or more units include a grating structure 206 formed by non-overlapping gratings having different pitches.

[0109] In step 604, a time-varying interference signal can be collected from one or more photodetectors 112a, b. For example, a time-varying interference signal from two photodetectors 112a, b placed in a region of a light collection pupil associated with an overlapping diffraction from a grating in the grating structure 206. For example, non-limiting configurations can include, but are not limited to, placing the photodetectors at positions that exclusively include grating diffraction orders from the grating of the grating structure 206, both grating diffraction orders and 0th order diffraction, or only one diffraction order.

[0110] In optional step 606, the time-varying interference signal from one or more photodetectors 112a, b can be separated. For example, the time-varying interference signal associated with the reference grating structure 208 can be separated from the time-varying interference signal associated with the grating structure 206. In one example, the controller 122 can be configured to separate the respective interference signals using Fourier transform techniques. In another example, the controller 122 can be configured to separate the respective interference signals using model fitting.

[0111] In some embodiments, the interference signal associated with the reference grating structure 208 can be spatially separated from the interference signal associated with the grating structure 206. For example, dedicated diodes in the field can be used to read the spatially separated signals. In this regard, the controller 122 can receive the spatially separated signals, as further discussed herein.

[0112] In step 608, either the real-time position or the scanning speed is determined based on the reference grating time-varying interference signal from the reference grating. For example, in a non-limiting example, the controller 122 can be configured to determine the reference time-varying interference signal based on the separated time-varying interference signal. As another example, in a non-limiting example, the controller 122 can be configured to receive the reference time-varying interference signal from a dedicated diode.

[0113] As previously discussed herein, errors can originate from the stability of the scanning speed, where the position can be used to improve the accuracy and stability of the scanning measurement. After careful consideration, the reference signal can be used to improve the accuracy and stability of the system. For example, in a non-limiting example, the frequency of the reference grating time-varying interference signal can be monitored during the scan. In this non-limiting example, if the frequency of the reference grating time-varying interference signal has changed during the scan, then the scanning speed has likely changed during the scan. Thus, any shift in the frequency of the reference grating time-varying interference signal can be used to adjust the grating time-varying interference signal such that the accuracy and stability of the scanning measurement are improved.

[0114] As another non-limiting example, the position of a time-varying interference signal of a reference grating during a scan can be monitored. In this non-limiting example, if the position of the time-varying interference signal of the reference grating has changed during the scan, then the position can have changed during the scan. Thus, any shift in the position of the time-varying interference signal of the reference grating can be used to adjust the time-varying interference signal of the grating such that the accuracy and stability of the scan measurement are improved.

[0115] Figure 7A is a plot 700 depicting a measurement signal at a constant scan speed in accordance with one or more embodiments of the present disclosure. Figure 7B is a plot 710 depicting a measurement signal at a non-constant scan speed in accordance with one or more embodiments of the present disclosure.

[0116] When the scan speed is constant (e.g., the speed is stable), as depicted in the plot 700 shown in Figure 7A the corresponding time-varying interference signal of the reference grating 208 can have a constant periodicity. However, when the scan speed is non-constant (e.g., the speed is unstable), as depicted in the plot 710 shown in Figure 7B the frequency and / or phase of the corresponding time-varying interference signal of the reference grating 208 may not have a constant periodicity. In a non-limiting example, as shown in Figure 7B in the case of an accelerating (or ramping) scan speed, the corresponding time-varying interference signal of the reference grating 208 can reflect this acceleration. Thus, when the time-varying interference signal of the reference grating structure 208 is unstable (e.g., when the scan speed is unstable), the time-varying interference signal of the reference grating 208 can be used to calibrate (or adjust) the time-varying signal of the grating structure 206. In other words, the time-varying interference signal from the reference grating can be used to generate real-time position and / or scan speed measurements of a sample during a scan such that any instability in the sample position and / or scan speed can be compensated for when providing an overlay measurement. Contemplated herein, the time-varying interference signal from the reference grating 208 can enable accurate overlay measurements under a wide range of measurement conditions, which can increase throughput. As an illustration, requiring a constant scan speed during a measurement (e.g., as depicted in Figure 7A ) would require a relatively long sample scan pattern to allow the translation stage to achieve a constant scan speed before reaching the overlay target of interest. In contrast, using simultaneous capture of the time-varying interference signal from the reference grating 208 on the sample and the time-varying interference signal from the grating structure 206 obviates this requirement and enables measurements when the translation stage is accelerating (e.g., as depicted in Figure 7B ), decelerating, or otherwise non-constant at the position of the overlay target of interest, which can substantially improve measurement throughput.

[0117] In an embodiment, the phase information of the time-varying interference signal from the grating structure is calibrated (or adjusted) based on the phase information of the time-varying interference signal from the reference grating structure. For example, the phase information of the time-varying interference signal can be extracted from the reference grating structure and used to adjust the phase information of the time-varying interference signal extracted from the grating structure, such that the time-varying interference signal from the grating structure is corrected based on the reference grating structure. In this regard, the real-time position and / or the scanning speed can be determined and then the corresponding time-varying interference signal from grating structure 206 can be calibrated accordingly.

[0118] In step 610, the overlay error between one or more sample layers associated with the grating structure can be determined. For example, the overlay error between the sample layers associated with the grating structure in one or more cells 202 of the overlay target 204 is determined based on the multi-layer time-varying interference signal and the real-time position is determined based on the reference grating time-varying interference signal. For example, the overlay error along the periodic direction of the grating structure 206 can be proportional to the phase difference between the time-varying interference signals from two photodetectors. Any technique known in the art (including but not limited to frequency domain analysis techniques applied to the two time-varying interference signals (e.g., fast Fourier transform or the like)) can be used to determine the phase difference. Additionally, in some embodiments, the overlay measurement of the sample along a particular measurement direction can be generated based on data from multiple cells of an overlay target having a grating structure that is periodic along the particular measurement direction.

[0119] In an embodiment, the overlay error between one or more sample layers associated with the grating structure 206 can be determined based on Equation 1, as shown and described below:

[0120] OVL P-Q =X P -X Q (1)

[0121] where the position X of the gratings with pitches P and Q is shown and described by Equations 2.1 to 2.2 below:

[0122]

[0123] Contemplated herein, method 600 can be applied to a wide variety of overlay target designs suitable for 1D or 2D metrology measurements.

[0124] In an embodiment, the reference time-varying interference signal can be used as the real-time position of the sample. For example, the reference grating time-varying interference signal can be used to analyze the grating time-varying interference signal from the grating structure 206. In this regard, the reference grating time-varying interference signal can be used as a feedback or feed-forward loop to adjust one or more parameters of the grating structure 206 or one or more components of the system (e.g., the scanning speed of the system or the like).

[0125] In an embodiment, method 600 includes simultaneously scanning a plurality of illumination beams and collecting associated overlapping diffraction orders for parallel measurement.

[0126] In an embodiment, method 600 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 grating structures with different periodicity directions can be effectively interrogated by measuring the common illumination beam in the scan band.

[0127] The subject matter described herein sometimes illustrates different components contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and in fact, many other architectures can be implemented that achieve the same functionality. In a conceptual sense, any arrangement of components that achieves the same functionality is effectively "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 intermediate 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. Particular instances of couplable 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.

[0128] It is believed that the present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction, and arrangement of the components without departing from the disclosed subject matter or sacrificing all of its significant advantages. The described form is merely illustrative, and the appended claims are intended to cover and include such changes. Additionally, it should be understood that the invention is defined by the appended claims.

Claims

1. A superposition metrology system, comprising: An illumination subsystem, comprising: An illumination source configured to generate one or more illumination beams; and One or more illumination optics configured to direct the one or more illumination beams onto a superposition target on a sample along a scan direction relative to the one or more illumination beams when implementing a metrology recipe, Wherein the superposition target according to the metrology recipe comprises one or more cells having a grating structure and a reference grating structure, Wherein the grating structure comprises one or more diffraction gratings, wherein the reference grating structure comprises a reference grating arranged close to the one or more diffraction gratings of the grating structure, and wherein when scanning the sample relative to the one or more illumination beams, the one or more illumination beams interact with the grating structure and the reference grating structure simultaneously, and wherein the one or more diffraction gratings and the reference grating are periodic along the scan direction, Wherein the reference grating has one or more known parameters; A photon collection subsystem, comprising: Two or more photodetectors positioned in a pupil plane to capture time-varying interference signals associated with diffraction orders of the grating structure in the one or more cells and time-varying interference signals associated with diffraction orders of the reference grating structure when implementing the metrology recipe; and A controller communicatively coupled to the two or more photodetectors, the controller comprising one or more processors configured to execute program instructions to cause the one or more processors to: Receive the time-varying interference signals from the two or more photodetectors, the time-varying interference signals comprising a grating signal associated with the grating structure in the one or more cells and a reference grating signal associated with the reference grating structure in the one or more cells when scanning the superposition target according to the metrology recipe; Determine at least one of a real-time position or a scan speed of the grating structure during the scan based on the reference grating signal from the reference grating; and Determine one or more superposition errors based on the grating signal from the grating structure and determine at least one of the real-time position or the scan speed of the grating structure during the scan based on the reference grating signal from the reference grating structure.

2. The superposition metrology system according to claim 1, wherein the one or more processors are configured to execute program instructions to cause the one or more processors to: Extract phase information associated with the grating signal and the reference grating signal; and Adjust the phase information of the grating signal based on the phase information of the reference grating signal.

3. The superposition metrology system according to claim 1, wherein the one or more processors are configured to execute program instructions to cause the one or more processors to: Adjust the scan speed based on the reference grating time-varying interference signal associated with the reference grating structure.

4. The overlay metrology system according to claim 1, wherein the one or more processors are configured to execute program instructions that cause the one or more processors to: Separate the reference signal associated with the reference grating structure from the grating signal associated with the grating structure.

5. The overlay metrology system according to claim 1, wherein the one or more illumination beams include: Spatially coherent illumination beams.

6. The overlay metrology system according to claim 1, wherein the one or more illumination beams include one or more elongated beams, wherein the one or more elongated beams extend orthogonally in the scan direction, and wherein, when scanning the overlay target, the one or more elongated beams interact with the one or more diffraction gratings of the grating structure and the reference grating simultaneously.

7. The overlay metrology system according to claim 6, wherein the one or more illumination optics are configured to modify the one or more illumination beams to produce the one or more elongated beams.

8. The overlay metrology system according to claim 7, wherein the one or more illumination optics include one or more apodizers.

9. The overlay metrology system according to claim 6, wherein the illumination source is configured to produce the one or more elongated beams.

10. The overlay metrology system according to claim 1, wherein the one or more illumination beams include one or more separated illumination beams, wherein, when scanning the overlay target, a first illumination beam of the one or more separated illumination beams interacts with the one or more diffraction gratings of the grating structure and a second illumination beam of the one or more separated illumination beams interacts with the reference grating of the reference grating structure.

11. The overlay metrology system according to claim 10, wherein the one or more illumination optics are configured to separate the one or more illumination beams to produce the one or more separated illumination beams.

12. The overlay metrology system according to claim 11, wherein the one or more illumination optics include one or more apodizers.

13. The overlay metrology system according to claim 1, wherein the one or more diffraction gratings of the grating structure include: A first exposure structure on a first layer of the sample; And A second exposure structure on a second layer of the sample.

14. The overlay metrology system according to claim 13, wherein the first exposure structure and the second exposure structure form a grating-on-grating structure, wherein the first exposure structure overlaps the second exposure structure.

15. The overlay metrology system according to claim 13, wherein the first exposure structure and the second exposure structure form a non-overlapping side-by-side grating structure, wherein the first exposure structure is arranged adjacent to the second exposure structure.

16. The overlay metrology system according to claim 1, wherein the one or more known parameters of the reference grating include a known pitch.

17. The overlay metrology system according to claim 16, wherein the known pitch of the reference grating is different from the pitch of the one or more diffraction gratings of the grating structure.

18. The superposition metrology system according to claim 1, wherein the two or more photodetectors are positioned at two or more positions in the pupil plane, wherein the first position including the first photodetector includes positions of the +1 order grating diffraction and the 0 order diffraction associated with the grating diffraction from the grating structure and the reference grating structure, and wherein the second position including the second photodetector includes positions of the -1 order grating diffraction and the 0 order diffraction associated with the grating diffraction from the grating structure and the reference grating structure.

19. The superposition metrology system according to claim 1, wherein the two or more photodetectors are positioned at two or more positions in the pupil plane, wherein the first position including the first photodetector includes positions of the +1 order grating diffraction associated with the grating diffraction from the grating structure and the reference grating structure and a portion of the illumination separated from the one or more generated illumination beams before being incident on the sample, and wherein the second position including the second photodetector includes positions of the -1 order grating diffraction associated with the grating diffraction from the grating structure and the reference grating structure and a portion of the illumination separated from the one or more generated illumination beams before being incident on the sample.

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

21. The superposition metrology system according to claim 1, further comprising: a translation stage configured to translate the sample along the scan direction, wherein when the sample is scanned by the translation stage, the one or more illumination optics direct the illumination beams to the superposition target on the sample.

22. The superposition metrology system according to claim 1, further comprising: one or more beam scanning optics configured to scan the illumination beams along the scan direction.

23. A method, comprising: receiving time-varying interference signals from two or more photodetectors associated with a grating structure and a reference grating structure in one or more cells when scanning a superposition target according to a metrology recipe; wherein the superposition target according to the metrology recipe includes the one or more cells having the grating structure and the reference grating structure, wherein the grating structure includes one or more diffraction gratings, wherein the reference grating structure includes reference gratings arranged close to the one or more diffraction gratings of the grating structure, wherein when the sample is scanned relative to the one or more illumination beams, the illumination beams interact with the grating structure and the reference grating structure simultaneously, wherein the one or more diffraction gratings and the reference gratings are periodic along the scan direction, and wherein the reference grating has one or more known parameters. The time-varying interference signal includes a grating signal associated with the grating structure in the one or more units and a reference grating signal associated with the reference grating structure in the one or more units when scanning the superposition target according to the metrology recipe; Determine at least one of the real-time position or the scanning speed of the grating structure during the scanning based on the reference grating signal from the reference grating; and Determine one or more superposition errors based on the grating signal from the grating structure and determine the real-time position of the grating structure during the scanning based on the reference grating signal from the reference grating structure.

24. The method according to claim 23, further comprising: Extracting phase information associated with the grating signal and the reference grating signal; and Adjusting the phase information of the grating signal based on the phase information of the reference grating signal.

25. The method according to claim 23, further comprising: Adjusting the scanning speed based on the reference grating signal associated with the reference grating structure.

26. The method according to claim 23, further comprising: Separating the reference signal associated with the reference grating structure from the grating signal associated with the grating structure.

27. The method according to claim 23, wherein the one or more illumination beams include one or more elongated beams, wherein the one or more elongated beams are orthogonally elongated in the scanning direction, and wherein, when scanning the superposition target, the one or more elongated beams simultaneously interact with the one or more diffraction gratings of the grating structure and the reference grating.

28. The method according to claim 27, wherein the one or more illumination beams include one or more separated illumination beams, wherein, when scanning the superposition target, a first illumination beam of the one or more separated illumination beams interacts with the one or more diffraction gratings of the grating structure and a second illumination beam of the one or more separated illumination beams interacts with the reference grating of the reference grating structure.

29. The method according to claim 23, wherein the one or more known parameters of the reference grating include a known pitch, and the known pitch of the reference grating is different from the pitch of the one or more diffraction gratings of the grating structure.

30. A superposition metrology target, comprising: One or more units having a grating structure and a reference grating structure, wherein the grating structure includes one or more diffraction gratings, wherein the reference grating structure includes a reference grating arranged adjacent to the one or more diffraction gratings of the grating structure, wherein one or more illumination beams are configured to simultaneously interact with the grating structure and the reference grating structure when scanning a sample relative to the one or more illumination beams, wherein the one or more diffraction gratings and the reference grating are periodic along the scanning direction, wherein the reference grating has one or more known parameters.

31. The overlay metrology target according to claim 30, wherein the one or more diffraction gratings of the grating structure comprise: a first exposure structure on a first layer of the sample; and a second exposure structure on a second layer of the sample.

32. The overlay metrology target according to claim 31, wherein the first exposure structure and the second exposure structure form a grating-on-grating structure, wherein the first exposure structure overlaps the second exposure structure.

33. The overlay metrology target according to claim 31, wherein the first exposure structure and the second exposure structure form a non-overlapping side-by-side grating structure, wherein the first exposure structure is arranged adjacent to the second exposure structure.

34. The overlay metrology target according to claim 30, wherein the one or more known parameters of the reference grating comprise a known pitch.

35. The overlay metrology target according to claim 34, wherein the known pitch of the reference grating is different from the pitch of the one or more diffraction gratings of the grating structure.

Images