System and method for tracking real-time position for scanning overlay measurements

Abstract

The method may include the step of receiving time-varying interference signals from two or more photodetectors associated with a grating structure and a reference grating structure. The grating structure may include one or more diffraction gratings, the reference grating structure may include a reference grating positioned next to one or more diffraction gratings of the grating structure, and one or more illumination beams may interact simultaneously with the grating structure and the reference grating structure as the sample is scanned with respect to the illumination beams. The method may include the step of determining at least one of the real-time position or scanning speed of the grating structure during scanning based on the reference grating signal. The method may also include the step of determining one or more overlay errors based on the grating signal from the grating structure during scanning and the real-time position of the grating structure, which are determined based on the reference grating signal.

Description

Technical Field

[0001] Cross - reference to Related Applications The present applicant claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63 / 457,137, filed on April 4, 2023, the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure generally relates to overlay measurement, and more particularly to scatterometry overlay measurement.

Background Art

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

[0004] The requirements to reduce feature size and increase feature density correspondingly increase the requirements for an accurate and efficient overlay measurement system. The measurement system typically generates measurement data related to a sample by measuring or inspecting overlay measurement targets distributed throughout the sample.

[0005] Overlay measurement targets are typically designed to provide diagnostic information regarding the alignment of multiple layers of a sample by characterizing overlay targets having target features located on the sample layers of interest. Further, the overlay alignment of multiple layers is typically determined by aggregating the overlay measurement values of multiple overlay targets at various positions throughout the sample. For example, an overlay measurement target can be scanned to provide overlay measurement values at various positions throughout the sample.

[0006] During scanning, errors can be due to the instability of the scanning speed. Position can be used to improve the accuracy and stability of scanning measurements. Currently, position is monitored using an encoder on the moving device (e.g., a translation stage or mirror). The main drawback of using an encoder on the moving device is that it does not provide 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 the chuck and mount (which hold the wafer). Therefore, errors caused by chuck vibrations, for example, are not recorded by the stage encoder. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Patent Application Publication No. 2022 / 0214285 [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, it is desirable to provide a system and method for curing the above-mentioned defects. [Means for solving the problem]

[0009] An overlay measurement system is disclosed according to one or more embodiments of the present disclosure. In the embodiment, the overlay measurement system includes an illumination subsystem. In the embodiment, the illumination subsystem includes an illumination source configured to generate one or more illumination beams. In the embodiment, the illumination subsystem includes one or more illumination optics configured to direct one or more illumination beams to an overlay target on a sample when the sample is scanned to one or more illumination beams along the scanning direction when a measurement recipe is implemented. In the embodiment, the overlay target according to the measurement recipe includes one or more cells having a grating structure and a reference grating structure. In the embodiment, the grating structure includes one or more diffraction gratings, the reference grating structure includes a reference grating positioned next to one or more diffraction gratings of the grating structure, one or more illumination beams interact simultaneously with the grating structure and the reference grating structure when the sample is scanned to one or more illumination beams, one or more diffraction gratings and reference gratings are periodic along the scanning direction, and the reference grating has one or more known parameters. In the embodiment, the overlay measurement system includes an acquisition subsystem. In an embodiment, the acquisition subsystem includes two or more photodetectors positioned in the pupil plane to capture time-varying interference signals related to the diffraction order of a grid structure in one or more cells and time-varying interference signals related to the diffraction order of a reference grid structure when performing a measurement recipe. In an embodiment, the overlay measurement 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 one or more processors to receive time-varying interference signals from the two or more photodetectors, the time-varying interference signals including grid signals related to the grid structure in one or more cells as the overlay target is scanned according to the measurement recipe and reference grid signals related to a reference grid structure in one or more cells as the overlay target is scanned according to the measurement recipe.In one embodiment, the program instructions are configured to cause one or more processors to determine at least one of the real-time position or scanning speed of the grid structure being scanned, based on a reference grid signal from a reference grid. In another embodiment, the program instructions are configured to cause one or more processors to determine one or more overlay errors, based on a grid signal from the grid structure and at least one of the real-time position or scanning speed of the grid structure being scanned, determined based on the reference grid signal from the reference grid structure.

[0010] Methods according to one or more embodiments of the present disclosure are disclosed. In embodiments, the method includes receiving time-varying interference signals from two or more photodetectors associated with a grid structure and a reference grid structure in one or more cells as an overlay target is scanned according to a measurement recipe. In embodiments, the overlay target according to the measurement recipe includes one or more cells having a grid structure and a reference grid structure, the grid structure includes one or more diffraction gratings, the reference grid structure includes a reference grating positioned next to one or more diffraction gratings of the grid structure, one or more illumination beams interact simultaneously with the grid structure and the reference grid structure as the sample is scanned with respect to the illumination beams, the one or more diffraction gratings and the reference grating are periodic along the scanning direction, and the reference grating has one or more known parameters. In embodiments, the time-varying interference signals include a grid signal associated with the grid structure in one or more cells as the overlay target is scanned according to the measurement recipe, and a reference grid signal associated with the reference grid structure in one or more cells as the overlay target is scanned according to the measurement recipe. In embodiments, the method includes determining at least one of the real-time position or scanning speed of the grid structure during scanning based on the reference grid signal from the reference grating. In the embodiment, the method includes the step of determining one or more overlay errors based on a grid signal from a scanning grid structure determined based on a reference grid signal from a reference grid structure and the real-time position of the grid structure.

[0011] One or more embodiments of the present disclosure are disclosed, which are overlay measurement targets. In the embodiments, the overlay measurement target includes one or more cells having a grid structure and a reference grid structure. In the embodiments, the grid structure includes one or more diffraction gratings. In the embodiments, the reference grid structure includes a reference grating positioned adjacent to one or more diffraction gratings of the grid structure. In the embodiments, one or more illumination beams are configured to interact simultaneously with the grid structure and the reference grid structure as the sample is scanned with one or more illumination beams. In the embodiments, one or more diffraction gratings and the reference grating are periodic along the scanning direction. In the embodiments, the reference grating has one or more known parameters.

[0012] It should be understood that both the general description above and the detailed description below are illustrative and descriptive only and do not necessarily limit the claimed invention. The accompanying drawings incorporated herein and constituting part of this specification illustrate embodiments of the invention and, together with the general description, help to illustrate the principles of the invention.

[0013] Many of the advantages of this disclosure can be better understood by those skilled in the art by referring to the accompanying drawings. [Brief explanation of the drawing]

[0014] [Figure 1A] This is a conceptual diagram of a system for performing scattering measurement overlay measurement on an overlay target using pupil manipulation, according to one or more embodiments of the present disclosure. [Figure 1B] This is a schematic diagram of an overlay measurement tool according to one or more embodiments of the present disclosure. [Figure 2A] This is a schematic diagram of a cell of an overlay target on a sample, including a lattice structure and a reference lattice structure, according to one or more embodiments of the present disclosure. [Figure 2B]Schematic diagram of a cell 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. [Figure 3A] Top view of an illumination pupil in an illumination pupil plane of an overlay measurement tool according to one or more embodiments of the present disclosure. [Figure 3B] Top view of a collection pupil in a collection pupil plane of an overlay measurement tool including a grating diffraction lobe related to the illumination profile of FIG. 3A according to one or more embodiments of the present disclosure. [Figure 4A] Schematic diagram of an illumination beam spot on an overlay target according to one or more embodiments of the present disclosure. [Figure 4B] Plot showing an illumination beam spot on an overlay target of FIG. 4A according to one or more embodiments of the present disclosure. [Figure 4C] Plot showing an illumination beam spot on an overlay target according to one or more embodiments of the present disclosure. [Figure 5A] Schematic diagram of a plurality of illumination beam spots on an overlay target according to one or more embodiments of the present disclosure. [Figure 5B] Plot showing a plurality of illumination beam spots on an overlay target of FIG. 5A according to one or more embodiments of the present disclosure. [Figure 5C] Plot showing a plurality of illumination beam spots on an overlay target according to one or more embodiments of the present disclosure. [Figure 6] Flow diagram showing steps executed in a method for scanning an overlay measurement of an overlay target according to one or more embodiments of the present disclosure. [Figure 7A] Plot showing a constant scanning speed according to one or more embodiments of the present disclosure. [Figure 7B] Plot showing a non-constant scanning speed according to one or more embodiments of the present disclosure.

BEST MODE FOR CARRYING OUT THE INVENTION

[0015] Hereinafter, we refer in detail to the disclosed subject matter shown in the attached drawings. This disclosure is shown and described in particular with respect to specific embodiments and their particular features. Embodiments described herein are to be construed as illustrative rather than limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made without departing from the spirit and scope of this disclosure.

[0016] Embodiments of the present disclosure relate to scanning a scattermeter overlay using an overlay target comprising a grating structure and a reference grating structure. For example, the grating structure may comprise one or more diffraction gratings, the constituent gratings having different pitches and not stacked on top of each other. For example, at least one of the diffraction gratings may be printed on an adjacent target (e.g., an AIM target). In another example, the reference target may include a high-frequency grating target placed next to the overlay target. In this regard, the reference target may be used for direct real-time position tracking in which the overlay target and the reference target can be scanned simultaneously.

[0017] For the purposes of this disclosure, the term “scatter measurement” is used to broadly encompass the terms “scatter measurement-based measurement” and “diffraction-based measurement,” in which a sample having periodic features on one or more sample layers is illuminated with an illumination beam having a limited angular range, and one or more distinct diffraction orders are collected for measurement. Furthermore, the term “scanning measurement” is used to describe measurement values ​​produced when the sample is moving relative to the illumination used for measurement. In a general sense, scanning measurement can be performed by moving the sample, the illumination, or both.

[0018] Embodiments of this disclosure relate to systems and methods for scanning overlay measurements based on time-varying interference signals from a grid structure and a reference grid structure (e.g., a clocking grating structure) within the collection pupil plane. Herein, it is considered that measurement conditions, which are linked to the diffraction order of the grid structure and the reference grid structure, may lead to interference. Such interference signals may include, but are not limited to, information relating to asymmetry of the target structure, such as an overlay between an upper and lower grid. Scanning the grid structure against an illumination beam (or vice versa) can provide characterization of the position-dependent overlay of the grid structure, and thus enable the determination of asymmetry, such as, but not limited to, an overlay. Furthermore, herein, it is considered that by simultaneously scanning the grid structure and the reference grid structure (e.g., a clocking grating structure), the reference grid structure can be used as a reference for measuring and / or calibrating instabilities such as scanning speed. For example, time-varying interference signals from a reference grid can be used to generate real-time position and / or scanning speed measurements of a sample during scanning, so that any instabilities in the sample position and / or scanning speed can be compensated when providing an overlay measurement. This specification suggests that time-varying interference signals from a reference grid can enable accurate overlay measurements under a wide range of measurement conditions and improve throughput. For example, the requirement of a constant scanning speed during measurement necessitates relatively long scans to allow the translation stage to achieve a constant scanning speed before reaching the overlay target of interest. In contrast, the use of time-varying interference signals from a reference grid on the sample, acquired simultaneously with the time-varying interference signals from the grid structure, eliminates this requirement and allows measurements when the translation stage is accelerating, decelerating, or otherwise not constant at the location of the overlay target of interest, which can substantially improve measurement throughput.

[0019] Some embodiments of this disclosure relate to scanning scan scatterometry overlay measurements based on overlapping diffraction lobes from the grating of a lattice structure (e.g., an upper or bottom grating) or time-varying interference signals associated with diffraction from the lattice structure. For example, a scan-based scan scatterometry measurement technique may include a fast detector for capturing time-varying interference signals generated as the sample is scanned. The detector may be positioned in the pupil plane at an overlapping position between selected diffraction orders to capture time-varying interference signals as the sample is scanned. Various non-limiting scan scatterometry overlay measurement techniques are described in U.S. Patent No. 11,300,405, issued April 12, 2022; U.S. Patent No. 11,378,394, issued July 5, 2022; U.S. Patent Application No. 17 / 708,958, filed March 30, 2022; U.S. Patent Application No. 17 / 709,200, filed March 30, 2022; and U.S. Patent Application No. 17 / 709,200, issued July 6, 2023. These are described in U.S. Patent Application Publication No. 2023 / 0213875, U.S. Patent Application No. 18 / 099,798 filed on 20 January 2023, U.S. Patent Application No. 18 / 110,746 filed on 16 February 2023, and U.S. Patent Application No. 18 / 372,444 filed on 25 September 2023, all of which are incorporated herein by reference in their entirety. It is intended that the systems and methods of the references incorporated herein may be extended or adapted to provide overlay measurements of grid structures.

[0020] In some embodiments, the overlay measurement system includes two or more photodetectors positioned within the pupil plane at locations corresponding to diffraction lobes from the grating structure. For example, the photodetectors may be positioned at overlapping locations between one of the primary and zeroth order diffraction lobes (e.g., specular reflection), or at a portion of the illumination split from the illumination beam generated before incidence (e.g., split into primary and auxiliary illumination). Herein, it is intended that these combined diffraction orders exhibit a time-varying interference signal (e.g., an AC signal) during scanning measurements, which can be captured using two or more photodetectors. For example, the characteristics of the grating structure (e.g., the pitch of the constituent gratings) and / or measurement conditions (e.g., illumination wavelength, illumination incidence angle, collection angle, etc.) can be selected so that the positive and negative diffraction orders related to the combined diffraction by the grating of the grating structure are collected by the system and captured by two or more photodetectors.

[0021] Some embodiments of this disclosure relate to providing recipes for configuring overlay measurement tools. Overlay measurement tools can be configured according to a recipe that includes a set of parameters for controlling various aspects of an overlay measurement, typically including, but not limited to, illumination of a sample, collection of light from a sample, or position of a sample during measurement. In this way, an overlay measurement tool can be configured to provide a selected type of measurement for one or more overlay target designs of interest. For example, a measurement recipe may include, but is not limited to, illumination parameters such as the number of illumination beams, illumination wavelength, illumination pupil distribution (e.g., distribution of illumination angles and the associated intensity of illumination at those angles), polarization of incident illumination, or spatial distribution of illumination. As another example, a measurement recipe may include, but is not limited to, collection pupil distribution (e.g., a desired distribution of angular light from a sample used for measurement, and the associated filtered intensity at those angles), collection field stop settings for selecting a portion of the sample under consideration, 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 a further example, a measurement recipe may include, but is not limited to, various parameters related to the sample position during measurement, such as the height of the sample, the orientation of the sample, and whether the sample is stationary or moving during measurement (along with related parameters describing speed, scanning pattern, etc.).

[0022] In some embodiments, the characteristics of the grating structure (e.g., pitch of the constituent gratings) and the measurement conditions (e.g., illumination wavelength, illumination incidence angle, collection angle, etc.) are selected in arrangement or otherwise (e.g., using a measurement recipe) such that they provide a selected distribution of diffraction and / or combined diffraction orders, and further provide that two or more photodetectors are positioned appropriately to capture these diffraction orders and generate a time-varying interference signal of interest.

[0023] This specification further intends that the systems and methods disclosed herein can provide high-throughput, high-sensitivity overlay measurements. For example, non-imaging configurations enable the use of high-speed photodetectors suitable for high scanning speeds. As a non-limiting example, a photodetector with a bandwidth of 1 GHz can enable a scanning speed of approximately 10 centimeters per second on a target with a pitch of 1 micrometer.

[0024] The lattice structure can generally be formed as part of an overlay target and can generally be placed anywhere on the sample. Furthermore, the overlay target may include one or more measurement cells, each cell containing printed elements in non-overlapping regions of one or more layers on the sample to form the lattice structure. The overlay measurement can then be based on any combination of measurements from various cells of the overlay target.

[0025] Scatter overlay measurements using a reference grating as disclosed herein are intended to offer many advantages. For example, the systems and methods disclosed herein can utilize overlay targets including non-stacked gratings. As another example, overlay measurements between two or more layers may be determined in a single measurement where one or more layers of the measurement target are not stacked. In one example, pupillary manipulation may enable the measurement of multilayer overlays in a single scan. In another example, pupillary manipulation may enable overlay targets (e.g., moiré, AIM, etc.) where different pitch prints stacked on top of each other are not permitted due to design rules. As yet another example, the systems and methods disclosed herein can overcome the difficulties of measuring each layer in its ideal state because the performance of the laser scanning method does not depend strongly on the wavelength of light used.

[0026] Referring here to Figures 1A to 7B, a system and method for tracking real-time position to scan overlay measurements, according to one or more embodiments of the present disclosure, will be described in more detail.

[0027] Figure 1A is a conceptual diagram of an overlay measurement system 100 for performing scattering measurement overlay measurements on a multi-overlay stacked grating measurement target, according to one or more embodiments of the present disclosure.

[0028] In one embodiment, the overlay measurement system 100 includes an overlay measurement tool 102 for performing a scattering measurement overlay measurement on a sample 104. For example, the overlay measurement tool 102 can perform a scattering measurement overlay measurement on a portion of the sample 104 having a grid structure.

[0029] Figure 1B is a schematic diagram of an overlay measurement tool 102 according to one or more embodiments of the present disclosure.

[0030] In some embodiments, the overlay measurement tool 102 includes an illumination subsystem 106 for generating illumination in the form of one or more illumination beams 108 for illuminating a sample 104, and an acquisition subsystem 110 for collecting light from the illuminated sample 104. For example, one or more illumination beams 108 may be angularly restricted on the sample 104 so that the lattice structure can generate discrete diffraction orders (e.g., in one or more cells of the overlay target). Furthermore, one or more illumination beams 108 may be spatially restricted so that they can illuminate selected portions of the sample 104. For example, each of the one or more illumination beams 108 may be spatially restricted to illuminate a particular cell of the overlay target. In some embodiments, one or more illumination beams 108 underfill a particular cell of the overlay target.

[0031] Next, the collection subsystem 110 can collect at least several diffraction orders related to the diffraction of the illumination beam 108 from the grating structure. Furthermore, the collection subsystem 110 may include at least two photodetectors 112 positioned on the collection pupil plane 114 at locations related to time-varying interference signals indicating overlays. 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 related to positive and negative diffraction orders, or locations related to overlaps between diffraction orders of the constituent gratings of the grating structure (e.g., overlapping regions between +1 diffraction orders of the grating, or overlapping regions between -1 diffraction order and 0th order diffraction of the grating).

[0032] In this embodiment, the overlay measurement tool 102 includes a translation stage 116 for scanning the sample 104 through the measurement field of the overlay measurement tool 102 during measurement to perform scanning measurement.

[0033] In one embodiment, the overlay measurement tool 102 includes a beam scanning subsystem 118 configured to modify or control the position of at least one illumination beam 108 on the sample 104. For example, the beam scanning subsystem 118 can scan the illumination beam 108 in a direction along the scanning direction (e.g., the direction in which the translation stage 116 scans the sample 104) during measurement.

[0034] Referring here to Figures 2A to 3B, the arrangement of two or more photodetectors 112 for collecting diffraction order from a lattice structure and for scatrometry overlay measurements, according to one or more embodiments of the present disclosure, will be described in more detail.

[0035] Figures 2A and 2B are schematic diagrams of one or more cells 202 according to one or more embodiments of the present disclosure.

[0036] In the embodiment, the overlay target 204 includes one or more cells 202, and any particular cell 202 of the one or more cells 202 may include a lattice structure 206 having periodicity along any direction and a reference lattice structure 208 having periodicity along a similar direction. For example, as shown in Figure 2A, the overlay target 204 may include a single cell 202 having a lattice structure 206 and a reference lattice structure 208 having periodicity along a common direction. As another example, as shown in Figure 2B, the overlay target 204 may include a plurality of cells 202a, b, where different cells 202a, b have different configurations of periodicity of the associated lattices. For example, as shown in Figure 2B, the overlay target 204 may include a plurality of cells 202a, b, where each cell 202a, b includes a lattice structure 206 having periodicity along a common direction and a reference lattice 208 having periodicity along a common direction, and different cells 202a, b have different configurations of periodicity of the associated lattices.

[0037] In the embodiment, as shown in Figure 2A, 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 a first layer 212 of the sample 104 and a second exposure structure 214 located on a second layer 216 of the sample 104. For example, the grating structure 206 may include a grating-over-grating structure, where the first exposure structure 210 and the second exposure structure 214 overlap.

[0038] In the embodiment, as shown in Figure 2B, 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 a first layer 212 of the sample 104 and a second exposure structure 214 located on a second layer 216 of the sample 104, wherein 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. The first exposure structure 210 may be associated with a first lithography exposure, and the second exposure structure 214 may be associated with a second lithography exposure, and the first and second lithography exposures may be on the same layer or different layers (as shown in Figures 2A to 2B).

[0039] In the embodiment, the first exposure structure 210 and the second exposure structure 214 may have different pitches. For example, in Figure 2A, the pitches of the first exposure structure 210 and the second exposure structure 214 are shown as P and Q, respectively. It should be noted that the configuration shown in Figure 2A is provided for illustrative purposes only and should not be construed as limiting the scope of this disclosure. Therefore, the lattice structure 206 may be formed from any number of layers having any variety of pitches. For example, the lattice structure 206 may be formed from two or more layers.

[0040] In the embodiment, the first exposure structure 210 and the second exposure structure 214 may have the same pitch. For example, as shown in Figure 2B, the first exposure structure 210 and the second exposure structure 214 may have the same pitch. When the grid structure 206 has the same pitch, it is thought that tool-induced shift (TIS) error can be reduced (for example, as shown in Figure 2B).

[0041] In this embodiment, the reference grid structure 208 includes a reference grid 218. For example, the reference grid 218 may be located on a third layer 220 of the sample. Figures 2A and 2B show the reference grid 218 on the third layer 220, but the reference grid 218 may be located on either the first or second layer, and rather, Figures 2A and 2B are provided for illustrative purposes only.

[0042] In this specification, the reference grid structure 208 may be located in the same cell as the grid structure 206 or in a different cell.

[0043] The frequency (or pitch) of the reference grid 218 may differ from the frequencies (or pitches) of the grids 210 and 214 of the grid structure 206. For example, the frequency of the reference grid 218 may be greater than the frequencies of the grids 210 and 214 of the grid structure 206. In other words, the pitch of the reference grid 218 may be smaller than the pitch of the grids 210 and 214 of the grid structure 206. For example, as described above in Figure 2A, the pitches of the first exposure structure 210 and the second exposure structure 214 may be P and Q, respectively, and the pitch of the reference grid 218 may be R.

[0044] The reference grid 218 may have one or more known parameters. For example, the frequency of the reference grid 218 may be known. In this regard, the frequency of the reference grid 218 may be monitored to determine either the real-time position or the scanning speed, so that variations in the scanning speed can be compensated for.

[0045] In the embodiment, the reference grid structure 206 is positioned next to the grid structure 206 (for example, in a non-overlapping arrangement). For example, the reference grid 218 may be positioned adjacent to the first exposure structure 210 and the second exposure structure 214 of the grid structure 206. In one example, as shown in Figure 2A, the reference grid 218 may be positioned between the overlapping first exposure structure 210 and the second exposure structure 214 of the grid structure 206. In another example, as shown in Figure 2B, the reference grid 218 may be positioned below the first exposure structure 210 of the grid structure 208 and the second exposure structure 214 of the grid structure 206. In this regard, as will be further described herein, when the overlay target 204 is scanned by the illumination beam, the illumination beam can interact with the grid structure 206 and the reference structure 206 simultaneously.

[0046] However, it should be understood that the overlay target 204 and related descriptions in Figures 2A and 2B are provided for illustrative purposes only and should not be construed as limiting. Rather, the overlay target 204 can include any suitable grating overlay target design. For example, the overlay target 204 can include any number of cells 202 suitable for measurement. Furthermore, the cells 202 may be distributed in any pattern or arrangement. In embodiments, the overlay target 204 includes one or more cell groups distributed along the scanning direction (e.g., the direction of movement of the sample 104), and the cells 202 within each particular cell group are oriented to periodically have a lattice structure 206 along a common direction.

[0047] Referring here to Figures 3A and 3B, various non-limiting configurations for generating and measuring time-varying interference signals from the grid structure 206 and reference grid structure 208 within the cell 202 of the overlay target 204 are described according to one or more embodiments of the present disclosure.

[0048] Figure 3A is a top view of the illumination pupil 302 in the illumination pupil surface 120 of an overlay measurement tool 102 according to one or more embodiments of the present disclosure. For example, the illumination pupil surface 120 may correspond to a pupil surface in the illumination subsystem 106, as shown in Figure 1B. In the embodiment, the illumination subsystem 106 illuminates the overlay target 204 with one or more illumination beams 108 with perpendicular incidence (or nearly perpendicular incidence), as shown in Figure 3A. In this regard, the overlay target 204 can diffract one or more illumination beams 108 to discrete diffraction orders.

[0049] Figure 3B shows a non-limiting configuration of the relevant positions of two or more photodetectors 112 in the collection pupil plane 114, suitable for capturing time-varying interference signals that can extract the diffraction order of the illumination beam 108 related to the overlay measurement target 204 shown in Figure 2A, and the overlay measurement. Herein, it is assumed that two or more photodetectors 112 positioned within the collection pupil plane 114 in relation to diffraction lobes can capture time-varying interference signals indicating the overlay. Herein, it is further intended that when each of the relevant diffraction lobes is incident on the photodetector 112 (e.g., within the measurement area of ​​the photodetector 112), time-varying interference signals associated with combined diffraction lobes can be captured by the photodetector 112. Thus, the relevant diffraction lobes do not necessarily need to overlap within the collection pupil plane 114, but may rather overlap on the photodetector 112.

[0050] It is recognized herein that the distribution of diffraction orders of the illumination beam 108 by a periodic structure such as the grid structure 206 or the reference grid structure 208 may be influenced by various parameters, but are not limited to, the wavelength of the illumination beam 108, the angle of incidence of the illumination beam 108 in both the altitude and azimuthal directions, the grid pitch of the grid structure 206, or the numerical aperture (NA) of the collecting lens. Accordingly, in embodiments of the present disclosure, the illumination subsystem 106, the collection subsystem 110, and the overlay target 204 may be configured to provide a desired distribution of diffraction orders within the collecting pupil surface 114 suitable for generating a time-varying interference pattern exhibiting an overlay (e.g., according to a measurement recipe that defines a selected set of relevant parameters). For example, the illumination subsystem 106 and / or the collection subsystem 110 may be configured to generate measurements relating to a grid structure having a selected range of periodicity in order to provide a desired distribution in the collecting pupil surface 114. Furthermore, various components of the illumination subsystem 106 and / or the collection subsystem 110 (e.g., stops, pupils, etc.) may be adjustable to provide a desired distribution in the collecting pupil surface 114.

[0051] In the embodiment, the collection pupil plane 114 can correspond to the pupil plane in the collection subsystem 110, as shown in Figure 1B. For example, Figure 3B shows the zero-order diffraction 306, -1st-order lattice diffraction 308, and +1st-order lattice diffraction 310 distributed along the periodic direction of the lattice structure 206 (e.g., in this case, the X direction) within the collection pupil plane 114 for each grit of the overlay target 204 shown in Figure 2A. For example, the -1st-order lattice diffraction 308a and +1st-order lattice diffraction 310a may be associated with lattice diffraction from a first exposure structure 210, the -1st-order lattice diffraction 308b and +1st-order lattice diffraction 310b may be associated with lattice diffraction from a second exposure structure 214, and the -1st-order lattice diffraction 308c and +1st-order lattice diffraction 310c may be associated with lattice diffraction from a reference grit 218, with the diffraction angles based on the grit pitch and illumination wavelength. In this regard, the diffraction lobes of the +1st order lattice diffraction 308a~c from each layer 210, 214, and 218 may overlap, and the -1st order lattice diffraction 310a~c from each layer 210, 214, and 218 may overlap.

[0052] In this specification, it is considered that the phases 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 time-varying interference signals, and that the overlay can be determined based on these oscillating phases. As a result, overlay measurements can be performed by capturing and comparing these time-varying interference patterns. For example, the phase difference between the -1st and +1st order grating diffraction gratings 308, 310 from each individual grating can be used to measure the position of the grating relative to the optical system.

[0053] However, please understand that the specific configurations shown in Figure 3B and related explanations are not limited to those shown. In particular, this specification suggests that time-varying interference signals can be captured using various measurement overlay techniques, which are described in U.S. Patent No. 11,300,405 issued on 12 April 2022, U.S. Patent No. 11,378,394 issued on 5 July 2022, U.S. Patent Application No. 17 / 708,958 filed on 30 March 2022, U.S. Patent Application No. 17 / 709,200 filed on 30 March 2022, U.S. Patent Application Publication No. 2023 / 0213875 published on 6 July 2023, U.S. Patent Application No. 18 / 099,798 filed on 20 January 2023, and U.S. Patent Application No. 18 / 110,746 filed on 16 February 2023, each of which is incorporated in its entirety by reference.

[0054] For example, the moiré diffraction lobes may overlap with the zero-order diffraction at the collection pupil plane (as provided, for example, by the measurement recipe). In this example, the first photodetector may be positioned in the overlapping region between the -1st-order moiré diffraction and the zero-order diffraction, and the second photodetector may be positioned in the overlapping region between the +1st-order moiré diffraction and the zero-order diffraction, and each of the photodetectors 112 can then capture a time-varying interference signal as the sample 104 is scanned. Furthermore, the overlay measurement may be determined based on a time-varying signal related only to the primary moiré diffraction lobes (without referring, for example, the zero-order diffraction). In another example, the primary diffractions from the first exposure structure 210 and the second exposure structure 214 overlap within the collection pupil 304. For example, the first photodetector captures the -1st-order diffraction (-1) from the first exposure structure 210. TOP ) and the -1 order diffraction (-1 BOTTOM The second photodetector may be located in the first overlapping region between the first exposure structure 210 and the first exposure structure 210, and the first photodetector may be located in the first overlapping region between the first exposure structure 210 and the TOP ) and the +1 order diffraction (+1 BOTTOM) may be located in a second overlapping region between them. As another example, the overlay measurement may be determined based on time-varying signals related to the primary and secondary diffraction lobes (without reference to, for example, the zeroth-order diffraction 306). Furthermore, the primary diffraction lobes do not necessarily have to overlap within the collection pupil plane and may overlap on the respective photodetectors 112a,b in some embodiments. Furthermore, in some embodiments, the overlay measurement may be determined based on time-varying signals related only to the primary grid diffraction lobes (without reference to, for example, the zeroth-order diffraction 306). For example, the overlay measurement may be determined based on time-varying signals related to the overlap between auxiliary illumination (e.g., illumination split from the generated illumination beam) and the primary diffraction lobes, as is generally discussed in U.S. Patent Application No. 18 / 110,746 filed February 16, 2023, which is incorporated herein in its entirety by reference.

[0055] It is further conceivable that the zero-order diffraction 306 does not necessarily have to overlap with the -1st-order lattice diffraction 308 and the +1st-order lattice diffraction 310 in the collecting pupil 304, as shown in Figure 3B. Rather, in some embodiments, these diffraction lobes are close enough to each other that the zero-order diffraction 306 overlaps with the -1st-order lattice diffraction 308 on the first photodetector 112a, and the zero-order diffraction 306 overlaps with the +1st-order lattice diffraction 310 on the second photodetector 112b.

[0056] Referring to Figures 4A to 5C in general, in the embodiment, one or more illumination beams 108 of the illumination subsystem 106 interact simultaneously with both the grid structure 206 and the reference grid structure 208. For example, when the overlay measurement target 204 is scanned by one or more illumination beams 108, one or more illumination beams 108 interact with the grid of the grid structure 206 (e.g., the first exposure structure 210 and the second exposure structure 214) and the reference grid 218 of the reference grid structure 208. In this regard, the reference grid structure 208 can be used as a reference for directly calibrating the time-varying interference signal from the grid structure 208 based on observed values ​​(e.g., the position or velocity of the reference beam) derived from the time-varying interference signal from the reference grid structure 206.

[0057] The simultaneous interaction of illumination beams is generally discussed in U.S. Patent Application No. 18 / 372,444, filed on 25 September 2023, which is incorporated herein by reference in its entirety.

[0058] Figure 4A is a schematic diagram of a cell 202 of an overlay measurement target 204 being scanned by an illumination beam 108, according to one or more embodiments of the present disclosure. Figure 4B is a graph 400 showing the apodizer function 402 used to generate the illumination beam 108 of Figure 4A, according to one or more embodiments of the present disclosure. Figure 4C is a graph 404 showing a simulated illumination spot 401 generated using the apodizer function 402 of Figure 4B, according to one or more embodiments of the present disclosure.

[0059] Referring to Figures 4A to 4C in general, in the embodiment, one or more illumination beams 108 are elongated perpendicular to the scanning direction. For example, one or more illumination beams 108 may be elongated perpendicular to the scanning direction so that the grid structure 206 and the reference grid structure 208 are scanned simultaneously.

[0060] Referring to Figures 4B to 4C, in the embodiment, one or more illumination beams 108 can be modified using one or more optical elements 134 of the illumination subsystem 106. For example, an elongated illumination beam 401 can be generated using an apodizer function 402 in the illumination pupil field. For example, an elongated illumination beam 401 can be generated using the apodization function 402 in the pupil field shown in Figure 4B. In this regard, as shown in Figure 4A, the elongated illumination beam 401 can interact with the first exposure structure 210 and the second exposure structure 214 of the grid structure 208 and the reference grid 218 of the reference grid structure 208 as the overlay target 204 is scanned.

[0061] Figure 5A is a schematic diagram of a cell 202 of an overlay measurement target 204 being scanned by two illumination beams 108, according to one or more embodiments of the present disclosure. Figure 5B is a graph 500 showing an apodizer function 502 used to generate the separated illumination beams 108 of Figure 5A, according to one or more embodiments of the present disclosure. Figure 5C is a graph 504 showing separated simulated illumination spots 501a,b generated using the apodizer function 502 of Figure 5B, according to one or more embodiments of the present disclosure.

[0062] Referring to Figures 5A to 5C in general, in the embodiment, one or more illumination beams 108 are separated to generate two separate illumination beams 501a, 501b within 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 grid structure 206, and the second illumination beam 501b may interact with the reference grid structure 208.

[0063] In the embodiment, separated illumination beams 501a, 501b can be generated by separating one or more illumination beams 108 using one or more optical elements 134 of the illumination subsystem 106 (e.g., an apodizer). For example, separated illumination beams 501a, 501b can be generated using an apodizer function 502 in the pupil field. For example, the apodization spot 502 in the pupil field shown in Figure 5B may be used to generate separated illumination beams 501a, 501b such that the separated illumination beams 501a, 501b are coherent with each other (e.g., the phases of the associated time-varying interference signals are synchronized). In this regard, as shown in Figure 5A, the separated illumination beams 501a, 501b can interact simultaneously with the first exposure structure 210 and the second exposure structure 214 of the grating structure 208 and the reference grating 216 of the reference grating structure 208 as the overlay target 204 is scanned.

[0064] While Figures 5A–5C show two spots, it should be noted that Figures 5A–5C are provided for illustrative purposes only and should not be construed as limiting the scope of this disclosure. For example, the systems and methods of this disclosure may be used to measure three or more side-by-side grids.

[0065] Furthermore, it is conceivable that any optical element and / or illumination source can be used to generate either an elongated beam or a separated illumination beam; therefore, Figures 4A–5C are provided for illustrative purposes only and should not be construed as limiting the scope of this disclosure.

[0066] Referring again to Figure 1A, additional components of the overlay measurement tool 102 according to one or more embodiments of the present disclosure are described in more detail.

[0067] In one embodiment, the overlay measurement system 100 includes a controller 122 that is communicatively coupled to the overlay measurement tool 102. The controller 122 may include one or more processors 124 and a memory device 126 or memory. For example, one or more processors 124 may be configured to execute a set of program instructions held in the memory device 126.

[0068] In embodiments, the controller 122 can perform any of the various processing steps related to overlay measurement. For example, the controller 122 may be configured to generate control signals for instructing or controlling the overlay measurement tool 102 or any component thereof. For example, the controller 122 may be configured to instruct the translation stage 116 to translate the sample 104 along one or more measurement paths or swaths to scan one or more overlay targets through the measurement field of the overlay measurement tool 102, and / or to instruct the beam scanning subsystem 118 to position or scan one or more corrective illumination beams on the sample 104. As another example, the controller 122 may be configured to receive signals from the photodetector 112 corresponding to time-varying interference signals. As yet another example, the controller 122 may generate a correction table for one or more additional manufacturing tools as feedback and / or feedforward control of one or more additional manufacturing tools based on the overlay measurements from the overlay measurement tool 102.

[0069] In the embodiment, the controller 122 acquires the interference signal detected by the photodetector 112. For example, the controller 122 may acquire data such as the magnitude or phase of the time-varying interference signal, but is not limited to, using any technique known in the art, such as frequency domain analysis (e.g., FFT) or one or more phase-locked loops. Furthermore, the controller 122 may acquire the interference signal, or any data related to the interference signal, using any combination of hardware (e.g., circuitry) or software techniques.

[0070] In the embodiment, the controller 122 separates the interference signals detected by the photodetector 112. For example, interference signals associated with the reference grid structure 208 may be separated from interference signals associated with the grid 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.

[0071] In some embodiments, interference signals associated with the reference grid structure 208 are spatially separated from interference signals associated with the grid structure 206. For example, the spatially separated signals may be read using a dedicated diode in the field. In this regard, the controller 122 may receive the spatially separated signals so that the controller 122 can determine the position or scanning speed in real time.

[0072] In the embodiment, the controller 122 determines either the real-time position or the scanning speed of the sample or grid structure during scanning, based on a reference grid signal from a reference grid. For example, in a non-limiting example, the controller 122 may be configured to determine a reference time-varying interference signal based on a separated time-varying interference signal. In 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.

[0073] In some embodiments, the reference time-varying interference signal can be used as a real-time position or scan speed. For example, the reference grid time-varying interference signal can be used to analyze the grid time-varying interference signal from the grid structure 206. In this regard, the reference grid time-varying interference signal may be used as a feedback or feedforward loop to adjust one or more parameters of the grid structure 206 or one or more components of the system (e.g., the scan speed of the system).

[0074] In non-limiting examples, the frequency of a reference grid time-varying interference signal during scanning can be measured. If the frequency of the reference grid time-varying interference signal shifts (e.g., does not correspond to the known frequency of the reference grid before scanning), the grid time-varying interference signal can be adjusted based on the frequency shift of the reference grid time-varying interference signal.

[0075] In the embodiment, the controller 122 determines the interlayer overlay measurement of the overlay target along the measurement direction based on a comparison of interference signals. For example, the interlayer overlay error related to the lattice structure in one or more cells 202 of the overlay target 204 is determined based on a multilayer time-varying interference signal and a real-time position determined based on a reference lattice time-varying interference signal. For example, the controller 122 can determine the overlay measurement based on the magnitude and / or phase of the interference signal. U.S. Patent No. 10,824,079, referenced above and incorporated herein in whole by reference, generally describes the electric field of diffraction order at the collection pupil and further provides a specific relationship between the overlay at the pupil plane and the measured intensity. It is considered herein that the systems and methods disclosed herein can be extended to time-varying interference signals captured by a photodetector positioned in the overlapping region between diffraction order 0 and + / -1. In particular herein it is intended that the overlay on the sample may be proportional to the relative phase shift between two time-varying interference signals.

[0076] Furthermore, the controller 122 can calibrate or modify the overlay measurements based on known, assumed, or measured characteristics of the sample, which may also affect time-varying interference signals, such as sidewall angles or other sample asymmetries.

[0077] The photodetector 112 can generally include any type of photodetector known in the art that is 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.

[0078] In a general sense, the bandwidth or response time of the photodetector 112 should be sufficient to resolve the time frequency of interference fringes related to the grid pitch of the grid structure 206 and the reference grid structure 208, and the scanning speed along the measurement direction (the direction of periodicity of the grid structure 206 and the reference grid structure 208). For example, with a scanning speed of 10 centimeters per second in the measurement direction and a target pitch of 1 micrometer, the interference signal will oscillate at a speed of about 100 kHz. In some embodiments, the photodetector 112 includes a photodetector having a bandwidth of at least 200 kHz (the Nyquist frequency limit). However, it should be understood that this value is not a requirement. Rather, the bandwidth of the photodetector 112, the translational speed along the measurement direction, and the pitch of the grid structure and the reference grid structure can be selected together to provide a desired sampling rate of the interference signal.

[0079] One or more processors 124 of the controller 122 may generally include any processor or processing element known in the art. For the purposes of this disclosure, the terms “processor” or “processing element” may be broadly defined to include any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application-specific integrated circuit (ASIC) devices, one or more field-programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, one or more processors 124 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). In some embodiments, as described throughout this disclosure, one or more processors 124 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute a program configured to work in conjunction with the overlay measurement system 100. Furthermore, different subsystems of the overlay measurement system 100 may include processors or logic elements suitable for performing at least some of the steps described in this disclosure. Therefore, the above description should not be construed as an limitation to embodiments of the present disclosure, but rather as an example. Furthermore, the steps described throughout the present disclosure may be performed by a single controller or, alternatively, by multiple controllers. In addition, controller 122 may include one or more controllers housed in a common housing or multiple housings. In this way, any controller or combination of controllers can be separately packaged as modules suitable for integration into the overlay measurement system 100.Furthermore, the controller 122 can analyze or process the data received from the photodetector 112 and supply the data to additional components within or outside the overlay measurement system 100.

[0080] Furthermore, the memory device 126 may include any storage medium known in the art that is suitable for storing program instructions executable by one or more associated processors 124. For example, the memory device 126 may include a non-temporary memory medium. Additional examples include, but are not limited to, read-only memory, random-access memory, magnetic or optical memory devices (e.g., disks), magnetic tapes, solid-state drives, etc. It should be further noted that the memory device 126 may be housed in a controller housing common to one or more processors 124.

[0081] Referring again to Figure 1B, various components of the overlay measurement tool 102 according to one or more embodiments of the present disclosure are described in more detail.

[0082] In the embodiment, the illumination subsystem 106 includes an illumination source 128 configured to produce at least one illumination beam 108. Illumination from the illumination source 128 may include one or more selected wavelengths of light, including but not limited to ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0083] The illumination source 128 may 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, a coherent light source may be a laser light source. For example, the illumination source 128 may include, but is not limited to, one or more narrowband laser sources, broadband laser sources, ultracontinuous laser sources, white light laser sources, etc. In this regard, the illumination source 128 may 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 may include, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for including one or more elements that can emit broadband illumination when excited to a plasma state by a laser source.

[0084] In some embodiments, the illumination subsystem 106 includes one or more optical components suitable for modifying and / or adjusting the illumination beam 108 and guiding the illumination beam 108 to the sample 104. For example, the illumination subsystem 106 may include one or more illumination lenses 130 (for example, to collimate the illumination beam 108 and relay the illumination pupil plane 120 and / or illumination field plane 132, etc.). In some embodiments, the illumination subsystem 106 includes one or more illumination control optics 134 for shaping or 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, translationable mirrors, scanning mirrors, etc.).

[0085] In the embodiment, the overlay measurement tool 102 includes an objective lens 136 for focusing the illumination beam 108 onto the sample 104 (for example, an overlay target having overlay target elements arranged on two or more layers of the sample 104).

[0086] In some embodiments, the illumination subsystem 106 illuminates the sample 104 with two or more illumination beams 108. Furthermore, the two or more illumination beams 108 may, but do not necessarily, be incident on different parts of the sample 104 within the measurement field (e.g., the field of view of the objective lens 136) (e.g., different cells of the overlay target). It is considered herein that the two or more illumination beams 108 can be generated using various techniques. In some embodiments, the illumination subsystem 106 includes two or more apertures in the illumination field plane 132. In some embodiments, the illumination subsystem 106 includes one or more beam splitters for splitting illumination from the illumination source 128 into 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 can be considered part of a different illumination channel, regardless of the technique used to generate the various illumination beams 108.

[0087] In some embodiments, the collection subsystem 110 includes at least two photodetectors 112 (e.g., photodetectors 112a, b) positioned on a collection pupil plane 114 configured to capture light from a sample 104 (e.g., collected light 138), the collected light 138 including at least a 0th-order diffraction 306, a -1st-order diffraction 308, and a +1st-order diffraction 310, as shown in Figure 3B. The collection subsystem 110 may include one or more optical elements suitable for modifying and / or adjusting the light 138 collected from the sample 104. In some embodiments, the collection subsystem 110 includes one or more collection lenses 140 (for example, to collimate the illumination beam 108 and relay the pupil and / or field plane), which may include, but do not have to include, an objective lens 136. In some embodiments, the collection subsystem 110 includes one or more collection control optics 142 for shaping or controlling the collected light 138. For example, the acquisition control optical system 142 may include, but is not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translationable mirrors, scanning mirrors, etc.).

[0088] In the embodiment, the acquisition subsystem 110 includes two or more acquisition channels 144, each having a separate pair of photodetectors 112. For example, as shown in Figure 1B, the overlay measurement tool 102 may include one or more beam splitters 146 arranged to split the acquired light 138 into the acquisition channels 144. Furthermore, the beam splitters 146 may be polarizing beam splitters, unpolarizing beam splitters, or a combination thereof. However, it should be understood that the diagram of two acquisition channels 144 in Figure 1B is provided for illustrative purposes only and should not be interpreted as limiting. For example, the acquisition subsystem 110 may include a single acquisition channel 144 or multiple acquisition channels 144.

[0089] In some embodiments, multiple collection channels 144 are configured to collect light from multiple illumination beams 108 on the sample 104. For example, if the overlay target 204 has one or more cells 202 distributed in a direction different from the scanning direction, the overlay measurement tool 102 can simultaneously illuminate different cells 202 with different illumination beams 108 and simultaneously capture interference signals associated with each illumination beam 108. Furthermore, in some embodiments, the multiple illumination beams 108 directed at the sample 104 may have different polarizations. In this way, the diffraction order associated with each illumination beam 108 can be separated. For example, a polarizing beam splitter 146 can efficiently separate the diffraction orders associated with different illumination beams 108. As another example, a polarizer may be used in one or more collection channels 144 to separate a desired diffraction order for measurement.

[0090] In the embodiment, the overlay measurement 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.

[0091] The beam scanning subsystem 118 may include any type or combination of elements suitable for scanning the position of one or more illumination beams 108. In some embodiments, the beam scanning subsystem 118 includes one or more deflectors suitable for changing the direction of the illumination beams 108. For example, the deflector may include, but is not limited to, a rotatable mirror (e.g., a mirror with an adjustable tip and / or tilt). Furthermore, the rotatable mirror may be actuated using any technique known in the art. For example, the deflector may include, but is not limited to, a galvanometer, a piezoelectric mirror, or a micro-electromechanical system (MEMS) device. As another example, the beam scanning subsystem 118 may include an electro-optic modulator, an acousto-optic modulator, and the like.

[0092] Deflectors can be further positioned at any suitable location within the overlay measurement tool 102. In some embodiments, one or more deflectors are positioned on one or more pupil planes common to both the illumination subsystem 106 and the acquisition subsystem 110. In this regard, the beam scanning subsystem 118 may be a pupil plane beam scanner, and the associated deflectors can modify the position of one or more illumination beams 108 on the sample 104 without affecting the position of diffraction orders within the acquisition pupil plane 114. Furthermore, the distribution of one or more illumination beams 108 within the illumination field plane 132 can be further stabilized because the beam scanning subsystem 118 modifies the position of one or more illumination beams 108 on the sample 104. Pupil plane beam scanning is generally described in U.S. Patent No. 11,300,524, issued April 12, 2022, which is incorporated in its entirety by reference.

[0093] Figure 6 is a flowchart illustrating the steps performed in Method 600 for scanning an overlay measurement of an overlay target, according to one or more embodiments of the present disclosure. The applicant notes that the embodiments and enabling techniques described herein in the context of the overlay measurement system 100 should be interpreted as extending to Method 600. However, it should be further noted that Method 600 is not limited to the architecture of the overlay measurement system 100.

[0094] In step 602, one or more cells of the overlay target are illuminated. For example, one or more cells 202 of the overlay target 204 on the sample 104 are illuminated as the sample 104 is scanned for illumination, and one or more cells include a lattice structure 206 formed from non-overlapping grids of different pitches.

[0095] In step 604, time-varying interference signals from one or more photodetectors 112a,b can be collected. For example, time-varying interference signals from two photodetectors 112a,b positioned in a region of the collection pupil related to overlapping diffraction from the grating in the grating structure 206. For example, non-limiting configurations include, but are not limited to, that the photodetectors may be positioned to include exclusively grating diffraction order, both grating diffraction order and zero-order diffraction, or only first-order diffraction from the grating of the grating structure 206.

[0096] In an optional step 606, time-varying interference signals from one or more photodetectors 112a,b can be separated. For example, a time-varying interference signal associated with the reference grid structure 208 may be separated from a time-varying interference signal associated with the grid structure 206. In one example, the controller 122 may be configured to separate the respective interference signals using Fourier transform techniques. In another example, the controller 122 may be configured to separate the respective interference signals using model fitting.

[0097] In some embodiments, interference signals associated with the reference grid structure 208 are spatially separated from interference signals associated with the grid structure 206. For example, the spatially separated signals may be read using a dedicated diode in the field. In this regard, the controller 122 can receive the spatially separated signals, as will be further described herein.

[0098] In step 608, either the real-time position or the scanning speed is determined based on a reference grid time-varying interference signal from the reference grid. For example, in a non-limiting example, the controller 122 may be configured to determine the reference time-varying interference signal based on the isolated time-varying interference signal. In another example, in a non-limiting example, the controller 122 may be configured to receive the reference time-varying interference signal from a dedicated diode.

[0099] As previously stated herein, errors may be due to the stability of the scanning speed, and position may be used to improve the accuracy and stability of the scanning measurement. A reference signal can be used to improve the accuracy and stability of the system. For example, in a non-limiting example, the frequency of a reference grid time-varying interference signal can be monitored during scanning. In this non-limiting example, if the frequency of the reference grid time-varying interference signal changes during scanning, the scanning speed may have changed during scanning. Therefore, the grid time-varying interference signal can be adjusted using any shift in the frequency of the reference grid time-varying interference signal so as to improve the accuracy and stability of the scanning measurement.

[0100] As another non-limiting example, the position of a reference grid time-varying interference signal can be monitored during scanning. In this non-limiting example, if the position of the reference grid time-varying interference signal changes during scanning, its position may have changed during scanning. Therefore, the grid time-varying interference signal can be adjusted using any shift in the position of the reference grid time-varying interference signal to improve the accuracy and stability of the scanning measurement.

[0101] Figure 7A is a plot 700 showing a measurement signal under a constant scanning speed according to one or more embodiments of the present disclosure. Figure 7B is a plot 710 showing a measurement signal under a non-constant scanning speed according to one or more embodiments of the present disclosure.

[0102] When the scanning speed is constant (e.g., the speed is stable), each time-varying interference signal of the reference grid 208 can have a constant periodicity, as shown in plot 700 in Figure 7A. However, when the scanning speed is not constant (e.g., the speed is unstable), the frequency and / or phase of each time-varying interference signal of the reference grid 208 may not have a constant periodicity, as shown in plot 710 in Figure 7B. In a non-limiting example, when the scanning speed is increased (or ramped up), as shown in Figure 7B, each time-varying interference signal of the reference grid 208 can reflect such an increase in speed. Thus, the time-varying interference signals of the reference grid 208 can be used to calibrate (or adjust) the time-varying signals of the grid structure 208 when the time-varying interference signals of the reference grid structure 206 are unstable (e.g., when the scanning speed is unstable). In other words, time-varying interference signals from a reference grid can be used to generate real-time position and / or scan rate measurements of the sample during scanning, so that any instability in the sample position and / or scan rate can be compensated for when providing overlay measurements. Hereinafter, it is considered that time-varying interference signals from the reference grid 208 can enable accurate overlay measurements under a wide range of measurement conditions and improve throughput. For example, if a constant scan rate is required during measurement (e.g., as shown in Figure 7A), a relatively long sample scan pattern is required to allow the translation stage to achieve a constant scan rate before reaching the overlay target of interest. In contrast, the use of time-varying interference signals from the reference grid 208 on the sample, acquired simultaneously with time-varying interference signals from the grid structure 206, eliminates this requirement and allows measurement when the translation stage is accelerating (e.g., as shown in Figure 7B), decelerating, or otherwise inconsistent at the position of the overlay target of interest, which can substantially improve measurement throughput.

[0103] In the embodiment, the phase information of the time-varying interference signal from the grid structure is calibrated (or adjusted) based on the phase information of the time-varying interference signal from a reference grid structure. For example, the phase information of the time-varying inference signal may be extracted from the reference grid structure and used to adjust the phase information of the time-varying interference signal extracted from the grid structure, and the time-varying interference signal from the grid structure is corrected based on the reference grid structure. In this regard, the real-time position and / or scanning speed can be determined, and then each time-varying interference signal from the grid structure 206 can be calibrated accordingly.

[0104] In step 610, the overlay error between one or more sample layers associated with the lattice structure can be determined. For example, the overlay error between sample layers associated with the lattice structure in one or more cells 202 of the overlay target 204 is determined based on a multilayer time-varying interference signal and a real-time position determined based on a reference lattice time-varying interference signal. For example, the overlay error along the direction of periodicity of the lattice structure 206 may be proportional to the phase difference between the time-varying interference signals from two photodetectors. The phase difference can be determined using 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). Furthermore, in some embodiments, overlay measurements of the sample along a specific measurement direction can be generated based on data from multiple cells of an overlay target having a lattice structure with periodicity along a specific measurement direction.

[0105] In the embodiment, the overlay error between one or more sample layers related to the lattice structure 206 can be determined based on Equation 1, as shown and explained below. OVL P-Q =X P -X Q (1)

[0106] Here, the position X of the grid with pitches P and Q is shown and explained by the following equations 2.1 to 2.2.

number

number

[0107] In this specification, Method 600 is considered applicable to a wide variety of overlay target designs suitable for 1D or 2D measurement.

[0108] In some embodiments, a reference time-varying interference signal can be used as the real-time position of the sample. For example, a reference grid time-varying interference signal can be used to analyze a grid time-varying interference signal from the grid structure 206. In this regard, the reference grid time-varying interference signal may be used as a feedback or feedforward loop to adjust one or more parameters of the grid structure 206 or one or more components of the system (e.g., the scanning speed of the system).

[0109] In the embodiment, method 600 includes scanning multiple illumination beams simultaneously and collecting the relevant overlapping diffraction orders for parallel measurements.

[0110] In embodiments, method 600 includes scanning one or more illumination beams along a beam scanning direction different from the stepped scanning direction to provide diagonal or triangular wave paths across the sample. In this regard, cells having a grid structure with different periodic directions can be efficiently investigated by a common illumination beam within the measurement swath.

[0111] The subject matter described herein may include different components that are contained within or connected to other components. It should be understood that the architectures shown in this manner are merely illustrative, and in practice, many other architectures can be implemented to achieve the same function. Conceptually, any arrangement of components to achieve the same function is effectively “associated” in such a way that the desired function is achieved. Thus, any two components described herein combined to achieve a particular function, regardless of architecture or intermediate components, can be considered “associated” with one another in such a way that the desired function is achieved. Similarly, any two components thus associated can be considered “connected” or “joined” with one another in such a way that the desired function is achieved, and any two components that can be associated in such a way can be considered “joinable” with one another in such a way that the desired function is achieved. Specific examples of joinable components include, but are not limited to, components that are physically interactable and / or interact physically, as well as components that are wirelessly interactable and / or interact wirelessly, as well as components that are logically interactable and / or interact logically.

[0112] Many of the present disclosure and its associated advantages are to be understood from the foregoing description, and it will be clear that various modifications can be made to the form, structure, and arrangement of the components without departing from the disclosed subject matter or sacrificing all of the advantages of the material. The described forms are for illustrative purposes only, and it is the intent of the following claims to encompass and include such modifications. Furthermore, it should be understood that the present invention is defined by the appended claims.

Claims

1. It is an overlay measurement system, A lighting subsystem, A lighting source configured to generate one or more illumination beams, The measurement recipe includes one or more illumination optical systems configured to direct one or more illumination beams toward an overlay target on the sample when the sample is scanned along the scanning direction with respect to one or more illumination beams, The overlay target according to the measurement recipe includes one or more cells having a grid structure and a reference grid structure, The lattice structure includes one or more diffraction gratings, the reference lattice structure includes a reference grating positioned adjacent to the one or more diffraction gratings of the lattice structure, the one or more illumination beams interact simultaneously with the lattice structure and the reference lattice structure when the sample is scanned with respect to the one or more illumination beams, and the one or more diffraction gratings and the reference grating are periodic along the scanning direction. The reference grid has one or more known parameters, and the illumination subsystem A collection subsystem, An acquisition subsystem, which includes two or more photodetectors positioned in the pupil plane to capture time-varying interference signals related to the diffraction order of the lattice structure in one or more cells and time-varying interference signals related to the diffraction order of the reference lattice structure when implementing the measurement recipe, A controller communicatively coupled to the two or more photodetectors, wherein the controller includes one or more processors configured to execute program instructions, and the program instructions are executed by the one or more processors, The time-varying interference signal is received from the two or more photodetectors, and the time-varying interference signal includes a grid signal related to the grid structure in one or more cells when the overlay target is scanned according to the measurement recipe, and a reference grid signal related to the reference grid structure in one or more cells when the overlay target is scanned according to the measurement recipe, Based on the reference grid signal from the reference grid, the real-time position or scanning speed of the grid structure during scanning is determined. An overlay measurement system including a controller that causes a controller to determine one or more overlay errors based on the grid signal from the grid structure and at least one of the real-time position of the grid structure during scanning or the scanning speed determined based on the reference grid signal from the reference grid structure.

2. The one or more processors, The phase information related to the aforementioned grid signal and the aforementioned reference grid signal is extracted. The overlay measurement system according to claim 1, configured to execute a program instruction that adjusts the phase information of the grid signal based on the phase information of the reference grid signal.

3. The one or more processors, The overlay measurement system according to claim 1, configured to execute a program instruction that adjusts the scanning speed based on the reference grid time-varying interference signal related to the reference grid structure.

4. The one or more processors, The overlay measurement system according to claim 1, configured to execute a program instruction that separates the reference signal related to the reference grid structure from the grid signal related to the grid structure.

5. The one or more illumination beams The overlay measurement system according to claim 1, comprising a spatially coherent illumination beam.

6. The overlay measurement system according to claim 1, wherein the one or more illumination beams include one or more elongated beams, the one or more elongated beams are elongated perpendicular to the scanning direction, and the one or more elongated beams interact simultaneously with the grid structure and the one or more diffraction gratings of the reference grid when the overlay target is scanned.

7. The overlay measurement system according to claim 6, wherein the one or more illumination optical systems are configured to modify the one or more illumination beams to generate the one or more elongated beams.

8. The overlay measurement system according to claim 7, wherein the one or more illumination optical systems include one or more apodizers.

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

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

11. The overlay measurement system according to claim 10, wherein the one or more illumination optical systems are configured to separate the one or more illumination beams and generate the one or more separated illumination beams.

12. The overlay measurement system according to claim 11, wherein the one or more illumination optical systems include one or more apodizers.

13. The one or more diffraction gratings of the aforementioned grating structure The first exposure structure on the first layer of the sample, The overlay measurement system according to claim 1, comprising a second exposure structure on a second layer of the sample.

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

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

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

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

18. The overlay measurement system according to claim 1, wherein the two or more photodetectors are arranged in the pupil plane at two or more positions, and a first position including a first photodetector includes positions of +1 order lattice diffraction and 0 order diffraction related to lattice diffraction from the lattice structure and the reference lattice structure, and a second position including a second photodetector includes positions of -1 order lattice diffraction and 0 order diffraction related to lattice diffraction from the lattice structure and the reference lattice structure.

19. The overlay measurement system according to claim 1, wherein the two or more photodetectors are arranged at two or more positions within the pupil plane, and a first position including a first photodetector includes a position for +1 lattice order diffraction related to lattice diffraction from the lattice structure and the reference lattice structure, and a portion of illumination separated from the one or more generated illumination beams before incidence onto the sample, and a second position including a second photodetector includes a position for -1 lattice order diffraction related to lattice diffraction from the lattice structure and the reference lattice structure, and a portion of illumination separated from the one or more generated illumination beams before incidence onto the sample.

20. The overlay measurement system according to claim 1, wherein the one or more illumination optical systems direct the one or more illumination beams toward the overlay target at a perpendicular incidence angle.

21. A translation stage for translating the sample along the scanning direction, further comprising one or more illumination optical systems that direct the illumination beam onto the overlay target on the sample as the sample is scanned by the translation stage, The overlay measurement system according to claim 1.

22. The system further includes one or more beam scanning optical systems for scanning the illumination beam along the scanning direction. The overlay measurement system according to claim 1.

23. It is a method, The step of receiving time-varying interference signals from two or more photodetectors associated with a grid structure and a reference grid structure in one or more cells as an overlay target is scanned according to a measurement recipe, The overlay target according to the measurement recipe comprises one or more cells having the grid structure and the reference grid structure, the grid structure comprises one or more diffraction gratings, the reference grid structure comprises a reference grating positioned adjacent to one or more diffraction gratings of the grid structure, the one or more illumination beams interact simultaneously with the grid structure and the reference grid structure when the sample is scanned with respect to the illumination beams, the one or more diffraction gratings and the reference grating are periodic along the scanning direction, and the reference grating has one or more known parameters. The time-varying interference signal includes a grid signal relating to the grid structure in one or more cells when the overlay target is scanned according to the measurement recipe, and a reference grid signal relating to the reference grid structure in one or more cells when the overlay target is scanned according to the measurement recipe, a step, A step of determining at least one of the real-time position or scanning speed of the grid structure during scanning based on the reference grid signal from the reference grid, A method comprising the step of determining one or more overlay errors based on the grid signal from the grid structure and the real-time position of the grid structure during scanning, determined based on the reference grid signal from the reference grid structure.

24. A step of extracting phase information related to the grid signal and the reference grid signal, A step of adjusting the phase information of the grid signal based on the phase information of the reference grid signal, The method according to claim 23, further comprising:

25. The step further includes adjusting the scanning speed based on the reference grid signal related to the reference grid structure, The method according to claim 23.

26. The step further includes separating the reference signal related to the reference grid structure from the grid signal related to the grid structure, The method according to claim 23.

27. The method according to claim 23, wherein the one or more illumination beams include one or more elongated beams, the one or more elongated beams are elongated perpendicular to the scanning direction, and the one or more elongated beams interact simultaneously with the grid structure and the one or more diffraction gratings of the reference grid when the overlay target is scanned.

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

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. It is an overlay measurement target, It includes one or more cells having a lattice structure and a reference lattice structure, The lattice structure includes one or more diffraction gratings, The reference grating structure includes a reference grating arranged adjacent to one or more diffraction gratings of the grating structure, One or more illumination beams are configured to interact simultaneously with the grid structure and the reference grid structure when the sample is scanned with respect to the one or more illumination beams. The one or more diffraction gratings and the reference grating are periodic along the scanning direction. The reference grid is an overlay measurement target having one or more known parameters.

31. The one or more diffraction gratings of the aforementioned grating structure The first exposure structure on the first layer of the sample, The overlay measurement target according to claim 30, comprising a second exposure structure on a second layer of the sample.

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

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

34. The overlay measurement target according to claim 30, wherein one or more known parameters of the reference grid include a known pitch.

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

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