System and method for determining overlay measurements of a scanning target

Abstract

In this method, when an overlay target is scanned according to a weighing recipe, time-varying interference signals from two or more photodetectors can be received relating to a first exposed structure and a second exposed structure within one or more cells, provided that the first and second exposed structures form a side-by-side grid, and that this grid has one or more diffraction gratings, at least one of which is a non-overlapping side-by-side grid, the first exposed structure is located in close proximity to the second exposed structure, and the side-by-side grid is periodic along the scanning direction. Furthermore, in this method, with the time-varying interference signals corresponding to the non-overlapping first and second exposed structures synchronized, the overlay error between one of the first and second exposed structures of the sample can be determined based on the time-varying interference signals.

Description

[Technical Field]

[0001] Cross-references to related applications This application asserts a benefit under Section 119(e) of the United States Patent Act based on U.S. Provisional Patent Application No. 63 / 457137, filed on 4 April 2023, which is incorporated into this application in its entirety by reference.

[0002] This disclosure relates in general to overlay metricing, and more specifically to scanning scatterometry overlay metricing. [Background technology]

[0003] Overlay metricing generally refers to the measurement of the relative alignment of various layers on a sample, such as a semiconductor device, although this is not the only example. Overlay measurement, or measurement of overlay error, typically involves measuring the misalignment of fabricated features on two or more sample layers. Generally, proper alignment of fabricated features on multiple sample layers is necessary for the device to function correctly.

[0004] The demand for larger feature sizes and higher feature density has consequently led to a corresponding increase in the demand for accurate and efficient overlay metrology systems. In a metrology system, metrology data for a sample is typically generated by inspecting, for example, measuring, overlay metrology targets that are distributed across the sample.

[0005] Overlay metric targets are typically designed so that diagnostic information regarding the alignment of multiple layers of a sample is obtained by characterizing the overlay targets where the target features are located on the sample layer of interest. Furthermore, the degree of overlay alignment of these multiple layers is usually determined by aggregating overlay measurements for multiple overlay targets located at various points on the sample.

[0006] In some types of overlay metric targets (e.g., imaging AIM metric targets), features within multiple layers are spatially separated within the sample plane and arranged to exhibit a common center of symmetry. Therefore, the overlay represents the measurement based on the difference in symmetry centers between the pairs of layers of interest. Such metric targets (e.g., imaging AIM metric targets) require a relatively large space on the sample. Consequently, depending on the case, it may not be possible to print two or more targets stacked vertically, particularly within the cut mask process layer. Furthermore, measurements of such metric targets (e.g., imaging AIM metric targets) are often performed using area imaging, a measurement mode that is not very accurate and suffers from tool-induced inaccuracies.

[0007] Further overlay metric targets include those with multiple individual overlay targets that are measured sequentially (e.g., scatterometry overlay (SCOL) metric targets and moiré fringe metric targets). Such metric targets (e.g., SCOL metric targets and moiré fringe metric targets) have periodic structures configured to produce diffraction patterns, and it is possible to determine the metric measurement value by analyzing these diffraction patterns. Among such metric targets (e.g., SCOL metric targets and moiré fringe metric targets), those containing multiple cells that occupy a wide area of ​​the sample surface decrease as the measurement time increases with the measurement of each additional overlay metric target. Such metric targets (e.g., SCOL metric targets and moiré fringe metric targets) are often measured using scanning coherent spots and tend to be plagued by tool-induced inaccuracies. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent No. 11300405 [Patent Document 2] U.S. Patent No. 11378394 [Patent Document 3] U.S. Patent Application Publication No. 2023 / 0213875 [Patent Document 4] U.S. Patent No. 10824079 [Overview of the project] [Problems that the invention aims to solve]

[0009] Therefore, it is desirable to provide a system and method that mitigates the aforementioned shortcomings. [Means for solving the problem]

[0010] An overlay weighing system is disclosed according to one or more embodiments of the present disclosure. The overlay weighing system of the embodiments has an illumination subsystem. In the embodiments, the illumination subsystem has an illumination source configured to generate one or more illumination beams. In the embodiments, the illumination subsystem has one or more illumination optics configured to direct one or more illumination beams onto an overlay target on a specimen when the specimen is scanned along the scanning direction with respect to one or more illumination beams during the execution of a weighing recipe. In the embodiments, the overlay target for the weighing recipe has a side-by-side grid, the side-by-side grid has one or more diffraction gratings in one or more cells, at least one diffraction grating is a non-overlapping side-by-side grid, the side-by-side grid has at least a first exposed structure and a second exposed structure, the first exposed structure is located near the second exposed structure, and the side-by-side grid is periodic along the scanning direction. The overlay weighing system of the embodiments has a focusing subsystem. In some embodiments, the focusing subsystem has two or more photodetectors positioned in the pupil plane at two or more locations capable of capturing multiple-order diffractions from a side-by-side grid in one or more cells when a metric recipe is executed. In some embodiments, the focusing subsystem has a controller that is communicatively coupled to these two or more photodetectors. In some embodiments, the controller has one or more processors configured to execute program instructions. In some embodiments, the one or more processors are configured to execute program instructions that cause them to receive time-variable interference signals from two or more photodetectors relating to a side-by-side grid in one or more cells when an overlay target is scanned according to a metric recipe. In various embodiments, one or more processors are configured to execute program instructions that determine the overlay error between one of the first and second exposed structures of a sample based on the time-varying interference signals, while the time-varying interference signals corresponding to the non-overlapping first and second exposed structures are synchronized to one of the processors.

[0011] According to one or more embodiments of the present disclosure, a method is disclosed. In the method of the embodiments, when an overlay target is scanned according to a metrology recipe, a time-varying interference signal resulting from two or more photodetectors related to a first exposed structure and a second exposed structure in one or more cells is received; provided that the first exposed structure and the second exposed structure form a side-by-side grid, the side-by-side grid has one or more diffraction gratings, at least one diffraction grating is a non-overlapping side-by-side grid, the first exposed structure is disposed adjacent to the second exposed structure, and the side-by-side grid is periodic along the scanning direction. In the method of the embodiments, while the time-varying interference signals corresponding to the non-overlapping first exposed structure and second exposed structure are synchronized, an overlay error between one of the first exposed structure and the second exposed structure of the specimen is determined based on the time-varying interference signal.

[0012] According to one or more embodiments of the present disclosure, an overlay metrology target is disclosed. The overlay metrology target of the embodiments has one or more cells having a side-by-side grid. In the embodiments, the side-by-side grid has one or more diffraction gratings disposed on two or more layers of a specimen. In the embodiments, the two or more layers of the specimen include at least a first layer and a second layer. In the embodiments, the first layer has a first exposed structure, and the second layer has a second exposed structure. In the embodiments, the first exposed structure and the second exposed structure form a non-overlapping side-by-side grid, the first exposed structure is disposed adjacent to the second exposed structure, and the side-by-side grid is periodic along the scanning direction.

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

[0014] Those skilled in the art of the present disclosure (so-called persons skilled in the art) can better understand many advantages of the present disclosure by referring to the following attached drawings.

Brief Description of the Drawings

[0015] [Figure 1A] It is a conceptual diagram of a system that performs scatterometry overlay metrology on an overlay target using pupil operation according to one or more embodiments of the present disclosure. [Figure 1B] It is a schematic diagram of an overlay metrology tool according to one or more embodiments of the present disclosure. [Figure 2A] It is a schematic diagram of a cell of an overlay target on a specimen according to one or more embodiments of the present disclosure. [Figure 2B] It is a schematic diagram of a cell of an overlay target on a specimen according to one or more embodiments of the present disclosure. [Figure 2C] It is a schematic diagram of a cell of an overlay target on a specimen according to one or more embodiments of the present disclosure. [Figure 3A] It is a top view of the illumination pupil in the illumination pupil plane of an overlay metrology tool according to one or more embodiments of the present disclosure. [Figure 3B] It is a top view of the condenser pupil in the condenser pupil plane of an overlay metrology tool according to one or more embodiments of the present disclosure, and the grating diffraction lobes related to the overlay target shown in FIG. 2A are inherent. [Figure 3C] It is a top view of the condenser pupil in the condenser pupil plane of an overlay metrology tool according to one or more embodiments of the present disclosure, and the grating diffraction lobes related to the overlay target shown in FIG. 2B are inherent. [Figure 3D] It is a top view of the condenser pupil in the condenser pupil plane of an overlay metrology tool according to one or more embodiments of the present disclosure, and the grating diffraction lobes related to the overlay target shown in FIG. 2C are inherent. [Figure 4A]This is a schematic diagram of an illumination beam spot on an overlay target shown in Figure 2A, relating to one or more embodiments of the present disclosure. [Figure 4B] Figure 2A shows a top view of the lattice diffraction lobes related to the overlay target shown in Figure 2A, relating to one or more embodiments of the present disclosure, with associated phase extraction information from the overlay target also indicated. [Figure 5A] Figure 2B is a schematic diagram of an illumination beam spot on an overlay target shown in Figure 2B, relating to one or more embodiments of the present disclosure. [Figure 5B] Figure 4A is a plot diagram showing the apodizer intensity of one or more illumination beam spots according to the embodiments of the present disclosure, in relation to the illumination beam spots shown. [Figure 5C] The plot diagram shows a simulated derived spot according to one or more embodiments of the disclosure, plotted in relation to the apodizer intensity plot shown in Figure 5B. [Figure 6A] This is a schematic diagram of multiple illumination beam spots on an overlay target shown in Figure 2C, relating to one or more embodiments of the present disclosure. [Figure 6B] This plot shows the apodizer intensities of multiple illumination beam spots according to one or more embodiments of the present disclosure, in relation to the illumination beam spots shown in Figure 6A. [Figure 6C] Figure 6B is a plot diagram in which multiple simulated derived spots according to one or more embodiments of the present disclosure are plotted in relation to the apodizer intensity plot shown. [Figure 7] This flowchart illustrates the steps performed in a scanning overlay metering method for an overlay target according to one or more embodiments of the present disclosure. [Modes for carrying out the invention]

[0016] The following is a detailed reference to the disclosed subject matter depicted in the attached drawings. The disclosure is illustrated and described in detail in relation to certain embodiments and their specific features. The embodiments described herein should be understood as illustrative examples, not limitations. As will be immediately apparent to those skilled in the art, various modifications and alterations can be made to the form and details without deviating from the essence and technical scope of the disclosure.

[0017] The embodiments of this disclosure are scanning scatterometry overlays using an overlay target with a horizontal grid, where two or more diffraction gratings are arranged horizontally within the horizontal grid. In certain embodiments, these compositional gratings are arranged orthogonal to the scanning direction. In certain embodiments, these compositional gratings are arranged along the scanning direction.

[0018] In light of the purpose of this disclosure, the term "scatterometry metric" is used to broadly encompass the terms "scatterometry-based metric" and "diffraction-based metric," in which a sample with periodic features on one or more sample layers is illuminated with an angularly spread-constrained illumination beam, and one or more discrete-order diffractions are collected for measurement. Furthermore, the term "scanning metric" is used to describe metric measurements that occur when the sample is in relative motion to the measurement illumination. Generally, scanning metric can be performed by moving the sample, the illumination, or both.

[0019] The embodiments disclosed herein are intended for systems and methods for scanning overlay metricing based on time-varying interference signals derived from a horizontal grid within the focusing pupil plane. As considered in this application, depending on the measurement conditions, different order diffractions from a horizontal grid may overlap, causing interference. Such interference signals may contain information related to the asymmetry of the target feature, including, but not limited to, inter-grid overlays. As further considered in this application, scanning motion of a horizontal grid with respect to the illumination beam (or vice versa) can provide results for clarifying the position-dependent overlay of the horizontal grid, and thus enable the determination of asymmetries such as, but not limited to, overlays.

[0020] Certain embodiments of the present disclosure aim at scanning scatterometry overlay metricing based on time-varying interference signals related to diffraction lobes that overlap and are emitted from the grids constituting a horizontal grid. For example, a high-speed detector can be incorporated into scanning-based scatterometry measurement technology to capture time-varying interference signals generated during sample scanning. These detectors should be positioned within the pupil plane at overlapping locations between diffractions of a specified order in order to capture time-varying interference signals during sample scanning. Various non-limiting scanning scatterometry overlay metricing techniques are described in Patent Document 1, published April 12, 2022; Patent Document 2, published July 5, 2022; U.S. Patent Application No. 17 / 708958, filed March 30, 2022; U.S. Patent Application No. 17 / 709200, filed March 30, 2022; Patent Document 3, published July 6, 2023; U.S. Patent Application No. 18 / 099798, filed January 20, 2023; and U.S. Patent Application No. 18 / 110746, filed February 16, 2023; all of these are incorporated into this application by reference. As considered in this application, the systems and methods of the above incorporated references can be adapted, for example, extended, to yield overlay measurements of a side-by-side grid.

[0021] In certain embodiments, the overlay metricing system includes a photodetector positioned within the pupil plane at locations corresponding to diffraction lobes from a horizontal grid. For example, the photodetector may be positioned at the overlapping location between the primary diffraction lobe and one of the following: the zeroth-order diffraction (e.g., specular reflection) and the illumination components branched from the generated beam prior to incidence (e.g., branched into primary and auxiliary illumination). As considered in this application, these combined diffractions will exhibit time-varying interference signals (e.g., AC signals) during scanning measurement, which can be detected using the photodetector. For example, by appropriately selecting the characteristics of the horizontal grid (e.g., the pitch of the compositional grid) and / or measurement conditions (e.g., illumination wavelength, illumination incidence angle, focusing angle, etc.), the positive and negative diffractions related to the combined diffraction of the grid present in the horizontal grid can be focused by the system and detected by the photodetector.

[0022] Certain embodiments of the present disclosure aim to provide recipes for configuring overlay metrology tools. Overlay metrology tools can be configured according to recipes that incorporate a set of parameters for controlling various aspects of overlay measurement, such as, but not limited to, the illumination of a sample, the collection of light from that sample, or the position of the sample during measurement. In this way, the overlay metrology tool can be configured to produce specified types of measurements for one or more overlay target designs of interest. For example, the metrology recipe may incorporate illumination parameters such as, but not limited to, the number of illumination beams, illumination wavelength, illumination pupil distribution (e.g., distribution of illumination angles and corresponding illumination intensity at those angles), polarization of incident illumination, or spatial distribution of illumination. In another example, the metrology recipe may incorporate focusing parameters, including, but not limited to, the focusing pupil distribution (e.g., the desired distribution of angular light emitted from the specimen and used for measurement, and the corresponding filtered intensity at those angles), the focusing aperture setting for selecting a portion of the specimen of interest, the polarization of the collected light, wavelength filters, the position of one or more detectors (e.g., photodetectors), or parameters for controlling one or more detectors. In yet another example, the metrology recipe may incorporate various parameters related to the specimen position during measurement, including, but not limited to, the specimen height, specimen orientation, whether the specimen is stationary or moving during measurement (and related parameters describing velocity, scanning pattern, etc.).

[0023] In certain embodiments, the characteristics of the side-by-side grid (e.g., the pitch of the compositional grid) and the measurement conditions (e.g., illumination wavelength, illumination incidence angle, focusing angle, etc.) are selected, for example, using a metric recipe, so that diffraction and / or coupled diffraction of a specified distribution are produced, and furthermore, the photodetector is positioned at a location suitable for capturing diffraction of those orders and generating a time-variable interference signal of interest.

[0024] The systems and methods disclosed herein enable high-throughput, high-sensitivity overlay metricing. For example, in non-imaging configurations, it is possible to use 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.

[0025] A horizontally aligned grating can generally be formed as a component of an overlay target and can generally be located anywhere on the specimen. Furthermore, one or more measurement cells can be provided within the overlay target, with at least one non-stacked (i.e., non-overlapping) diffraction grating in each cell. In this case, the overlay measurement would be based on some combination of measurements on various cells of the overlay target. For example, the accuracy and / or sensitivity of the measurement can be improved by designing multiple cells of the overlay target with different intentional offsets (e.g., intentionally misaligning the gratings in various layers of the specimen with known offset values).

[0026] The scatterometry overlay metricing disclosed herein offers significant advantages. For example, the system and method disclosed herein can utilize a multilayer overlay target with non-stacked grids. In another example, if one or more layers of the metric target are not stacked, the overlay measurement can be determined in a single metric measurement. Furthermore, the grids of the multilayer overlay target can be made to interact simultaneously with one or more illumination beams as the target is scanned. In this case, the simultaneous scanning makes it possible to measure the multilayer overlay in a single scan. Alternatively, the grids of the multilayer overlay target can be made to interact sequentially with one or more illumination beams as the target is scanned. In this case, by using a region of interest, the grids can be made to start at exactly the same location during phase extraction. In another example, the system and method disclosed herein can operate side-by-side overlay targets (e.g., moiré, AIM, etc.) when design rules do not allow them to be printed on top of each other at different pitches. Furthermore, the system and method disclosed herein overcome the difficulties in measuring each layer under ideal conditions because the performance of its laser scanning method does not strongly depend on the wavelength of the light used. In this case, a wide wavelength range can be used. In addition, if the horizontally aligned grids within the overlay target have the same pitch, the target can reduce tool-induced shift errors. Moreover, the system and method disclosed herein enables the measurement of extremely small printed targets close to the size of actual devices, thereby improving the target accuracy. Furthermore, the system and method disclosed herein are not strongly affected by amplitude asymmetry induced by asymmetric process fluctuations or by symmetric process fluctuations.

[0027] The systems and methods for determining the overlay measurement values ​​of a scanning target will be described in detail below with reference to Figures 1A to 7, according to one or more embodiments of the present disclosure.

[0028] Figure 1A is a conceptual diagram of an overlay weighing system 100 that performs scatterometry overlay weighing on a side-by-side grid weighing target according to one or more embodiments of the present disclosure.

[0029] In some embodiments, the overlay weighing system 100 includes an overlay weighing tool 102 that performs scatterometry overlay measurements of a sample 104. For example, the overlay weighing tool 102 can perform scatterometry overlay measurements on parts of the sample 104 that have a horizontal grid.

[0030] Figure 1B is a schematic diagram of an overlay weighing tool 102 according to one or more embodiments of the present disclosure.

[0031] In some embodiments, the overlay weighing tool 102 includes an illumination subsystem 106 that generates illumination in the form of one or more illumination beams 108 to illuminate a sample 104, and a focusing subsystem 110 that collects light from the illuminated sample 104. For example, one or more illumination beams 108 can be angle-limited relative to the sample 104 so that discrete diffraction occurs in a horizontal grid (e.g., within one or more cells of the overlay target). Furthermore, one or more illumination beams 108 can be spatially limited so that designated parts of the sample 104 are illuminated by them. For example, each of the one or more illumination beams 108 can be spatially limited to illuminate a specific cell of the overlay target. In certain embodiments, a specific cell of the overlay target is partially underfilled by one or more illumination beams 108.

[0032] The focusing subsystem 110 can focus at least some of the various order diffractions related to the diffraction of the illumination beam 108 from the horizontally arranged grating. In some embodiments, the focusing subsystem 110 may have at least two photodetectors 112 positioned within the focusing pupil surface 114 at locations related to time-varying interference signals that exhibit overlays. For example, as will be described in detail later, suitable locations for the photodetectors 112 include, but are not limited to, locations related to positive and negative diffractions, and locations related to the overlap between the various order diffractions of the compositional gratings of the horizontally arranged grating (e.g., the overlapping region between the first-order diffraction and the zero-order diffraction of each grating). In some embodiments, the focusing subsystem 110 may have an area sensor positioned within the focusing pupil surface 114 at locations related to time-varying interference signals that exhibit overlays.

[0033] In various embodiments, the overlay weighing tool 102 has a translational stage 116 that scans the sample 104 within the measurement field of the overlay weighing tool 102 during measurement in order to perform scanning weighing.

[0034] In some embodiments, the overlay weighing tool 102 has a beam scanning subsystem 118 configured to control, for example, correct the position of at least one illumination beam 108 on the sample 104. For example, the beam scanning subsystem 118 can cause the illumination beam 108 to scan along a direction perpendicular to the scanning direction (e.g., the direction in which the translation stage 116 scans the sample 104) during measurement.

[0035] The arrangement of the photodetector 112 for collecting multiple-order diffractions from a side-by-side grating and for scanning scatterometry overlay metricing will be described in detail below with reference to Figures 2A to 3D, according to one or more embodiments of the present disclosure.

[0036] Figures 2A to 2C are schematic diagrams of one or more cells 202 according to one or more embodiments of the present disclosure.

[0037] In general, according to Figures 2A to 2C, in various embodiments, the overlay target 204 may have one or more cells 202, and all individual cells 202 of that one or more cells 202 may have a horizontal grid 206 that exhibits periodicity along some direction. For example, as shown in Figure 2A, multiple cells 202 can be provided within the overlay target 204 in such a way that different cells 202 have different configurations of the periodicity of the corresponding grid. For example, if the overlay target 204 contains a first cell 202a with a first exposure structure 208 and a second cell 202b with a second exposure structure 212, and their periodicity follows a common direction, then the combination of these first and second grids can be called a horizontal grid 206. In another example, as shown in Figures 2B and 2C, a single cell 202 can be provided within the overlay target 204, having a horizontally aligned grid 206 that exhibits periodicity along a common direction.

[0038] In various embodiments, the horizontally arranged grid 206 has one or more diffraction gratings, and at least one of the diffraction gratings within the horizontally arranged grid 206 is not stacked.

[0039] According to Figure 2A, for example, the horizontal grid 206 can have a first exposure structure 208 located on the first layer 210 of the sample and a second exposure structure 212 located on the second layer 214 of the sample 104, with the first exposure structure 208 and the second exposure structure 212 arranged along the scanning direction. For example, the second exposure structure 212 can be placed near the first exposure structure 208 so that the first exposure structure 208 does not overlap with the second exposure structure 212. When the first exposure structure 208 relates to the first lithography exposure and the second exposure structure 212 relates to the second lithography exposure, the targets of the first and second lithography exposures may be the same layer (as shown in Figure 2A) or different layers.

[0040] As shown in Figure 2B, for example, the horizontal grid 206 can have a first exposed structure 208 located on the first layer 210 of the sample 104 and a second exposed structure 212 located on the second layer 214 of the sample 104, with the first exposed structure 208 and the second exposed structure 212 arranged orthogonally with respect to the scanning direction. As an example, the second exposed structure 212 can be placed below the first exposed structure 208, while ensuring that the first exposed structure 208 is not stacked above the second exposed structure 212.

[0041] A horizontal grid 206 may have a stacked grid as long as there is at least one non-overlapping (i.e., non-stacked) grid. As shown in Figure 2C, for example, the horizontal grid 206 may have a first exposed structure 208 located on the first layer 210 of the sample 104, a second exposed structure 212 located on the second layer 214 of the sample 104, and a third exposed structure 216 located on the third layer 218 of the sample, with the first exposed structure 208, the second exposed structure 212, and the third exposed structure 216 arranged orthogonally with respect to the scanning direction. As an example, the first exposed structure 208 and the second exposed structure 212 may be stacked (i.e., overlapped) while ensuring that at least the first exposed structure 208 and the second exposed structure 212 are not stacked above the third exposed structure 216.

[0042] In some embodiments, the grids of the horizontal grid 206 can have the same pitch. For example, the first exposed structure 208 and the second exposed structure 212 can have the same pitch. Upon consideration, it has been found that if the horizontal grid 206 has the same pitch, tool-induced shift (TIS) error can be reduced (as shown in Figure 2A, for example).

[0043] In some embodiments, the grids of the horizontally arranged grid 206 can have different pitches. For example, the first exposed structure 208 and the second exposed structure 212 can have different pitches. As an example, Figure 2B shows the pitches of the first exposed structure 208 and the second exposed structure 212 as P and Q, respectively. In another example, the first exposed structure 208, the second exposed structure 212, and the third layer grid 216 can have different pitches. As an example, Figure 2C shows the pitches of the first exposed structure 208, the second exposed structure 212, and the third layer grid 216 as P, Q, and R, respectively.

[0044] The configurations depicted in Figures 2A to 2C are presented solely for illustrative purposes and are not intended to limit the technical scope of this disclosure. Therefore, the horizontal grid 206 may be formed in any number of layers and at any variety of pitches. Furthermore, the overlay target 204 may have any number of cells 202 suitable for measurement. In addition, the cells 202 may be distributed according to any pattern or arrangement. In some embodiments, one or more cell groups are distributed within the overlay target 204 along the scanning direction (e.g., the direction of motion of the sample 104), and the cells 202 within each specific cell group are oriented such that the horizontal grid 206 exhibits periodicity along a common direction. In this way, all cells 202 within a specific cell group can be simultaneously imaged while the sample 104 is scanning within the measurement field of view of the focusing subsystem 110.

[0045] With reference to Figures 3A to 3D, various non-limiting configurations for generating and measuring time-variable interference signals from the horizontal grid 206 within one or more cells 202 of the overlay target 204 will be described below in accordance with one or more embodiments of the present disclosure.

[0046] Figure 3A is a top view of the illumination pupil 302 on the illumination pupil surface 120 of an overlay weighing tool 102 according to one or more embodiments of the present disclosure. For example, this illumination pupil surface 120 can be associated with the pupil surface in the illumination subsystem 106 depicted in Figure 1B. In some embodiments, the illumination subsystem 106 illuminates the overlay target 204 with one or more illumination beams 108 at a right angle (or near-right angle) incidence, as depicted in Figure 3A. Furthermore, the illumination of the overlay target 204 by the one or more illumination beams 108 can be limited to a limited range of incidence angles, as depicted within a finite size in the focusing pupil surface 114. In this case, the one or more illumination beams 108 can be diffracted at the overlay target 204 to produce discrete order diffraction.

[0047] Figures 3B to 3D illustrate various non-limiting configurations for capturing time-variable interference signals from an overlay target 204 with a horizontal grid 206 in a scanning configuration.

[0048] Figure 3B depicts the non-restrictive configuration of the various order diffractions of the illumination beam 108 related to the overlay metric target shown in Figure 2A at the focusing pupil 114, and the position of the photodetector 112 related thereto, which is suitable for capturing time-varying interference signals from which overlay measurements can be extracted. In particular, Figure 3B depicts the 0th order diffraction 306, -1st order lattice diffraction 308, and +1st order lattice diffraction 310 distributed along the periodic direction (e.g., the X direction in this case) of the overlay target 204 within the focusing pupil 114. For example, the -1st order lattice diffraction 308 and +1st order lattice diffraction 310 can be related to lattice diffraction from the first exposed structure 208 or the second exposed structure 212, and their diffraction angles are based on the pitch of those gratings and the illumination wavelength. In this case, the primary diffraction lobes 308 and 310 of the first exposed structure 208 and the second exposed structure 21 can be made to overlap with the zeroth-order diffraction lobe, as shown in Figure 4B.

[0049] Figure 3C depicts the non-restrictive configuration of the various order diffractions of the illumination beam 108 related to the overlay metric target shown in Figure 2B at the focusing pupil 114, and the position of the photodetector 112 related thereto, which is suitable for capturing time-varying interference signals from which overlay measurements can be extracted. In particular, Figure 3C depicts the 0th order diffraction 306, -1st order lattice diffraction 308, and +1st order lattice diffraction 310 distributed along the periodic direction (e.g., the X direction in this case) of the horizontally arranged gratings 206 within the focusing pupil 114. For example, the -1st order lattice diffraction 308a and +1st order lattice diffraction 310a can be associated with lattice diffraction from the first exposed structure 208, and the -1st order lattice diffraction 308b and +1st order lattice diffraction 310b can be associated with lattice diffraction from the second exposed structure 212, and their diffraction angles are based on the pitch of those gratings and the illumination wavelength. In this case, the individual diffraction lobes of the +1st order lattice diffraction 308a and 310b from each layer 210 and 214 can be superimposed, and the -1st order lattice diffraction 310a and 310b from each layer 210 and 214 can also be superimposed, so that the 1st order lattice diffraction from each overlaps with the 0th order lattice diffraction.

[0050] Figure 3D depicts the non-limiting configuration of the various order diffractions of the illumination beam 108 related to the overlay metric target shown in Figure 2C at the focusing pupil plane 114, and the position of the photodetector 112 related thereto, which is a position suitable for capturing time-variable interference signals from which overlay measurements can be extracted. In particular, Figure 3D depicts the 0th order diffraction 306, -1st order lattice diffraction 308, and +1st order lattice diffraction 310 distributed along the periodic direction (e.g., the X direction in this case) of the horizontally arranged grid 206 within the focusing pupil plane 114. For example, the -1st order lattice diffraction 308a and +1st order lattice diffraction 310a can be associated with lattice diffraction from the first exposed structure 208, the -1st order lattice diffraction 308b and +1st order lattice diffraction 310b can be associated with lattice diffraction from the second exposed structure 212, and the -1st order lattice diffraction 308b and +1st order lattice diffraction 310b can be associated with lattice diffraction from the third exposed structure 216, and their diffraction angles are based on the pitch of their gratings and the illumination wavelength. In this case, the individual diffraction lobes of the +1st order lattice diffractions 308a to c from the individual layers 210, 214, and 216 can be superimposed, and the -1st order lattice diffractions 310a to c from the individual layers 210, 214, and 216 can be superimposed, and the 1st order lattice diffraction from each will overlap with the 0th order lattice diffraction.

[0051] Among the photodetectors 112, those positioned within the focusing pupil surface 114 related to diffraction lobes (e.g., areas where the primary diffraction lobe may overlap with the zeroth-order diffraction lobe) can capture time-variable interference signals exhibiting overlay. Further consideration in this application has shown that time-variable interference signals related to various diffraction lobes can be captured by the photodetector 112 when each of the related diffraction lobes (e.g., areas where the primary diffraction lobe may overlap with the zeroth-order diffraction lobe) is incident on the photodetector 112 (e.g., within the measurement area of ​​the photodetector 112). In this case, the related diffraction lobes do not necessarily need to overlap within the focusing pupil surface 114; rather, it is sufficient if they overlap on the photodetector 112.

[0052] As recognized in this application, the distribution of the order diffraction of the illumination beam 108 by a periodic structure, such as a grating 206, can be influenced by various parameters, including, but are not limited to, the wavelength of the illumination beam 108, the incident angles of the illumination beam 108 along the altitude and azimuthal directions, the pitch of the gratings in the horizontal grating 206, and the numerical aperture (NA) of the focusing lens. Therefore, in the embodiments of this disclosure, the illumination subsystem 106, the focusing subsystem 110, and the overlay target 204 may be configured to produce a desired in-pull pupil 114 order diffraction distribution suitable for generating a time-varying interference pattern exhibiting an overlay (e.g., according to a metric recipe defining a specified set of relevant parameters). For example, the illumination subsystem 106 and / or the focusing subsystem 110 may be configured to generate measured values ​​for a horizontal grating having a specified range of periodicity to produce a desired in-pull pupil 114 distribution. Furthermore, various components of the lighting subsystem 106 and / or the focusing subsystem 110 (e.g., aperture, pupil, etc.) can be made adjustable to achieve a desired distribution of light within the focusing pupil surface 114.

[0053] However, the specific configurations and related descriptions shown in Figure 3B are not limiting. In particular, time-varied interference signals can be captured using various metric overlay techniques, as outlined in Patent Document 1 issued on April 12, 2022; Patent Document 2 issued on July 5, 2022; U.S. Patent Application No. 17 / 708958 filed on March 30, 2022; U.S. Patent Application No. 17 / 709200 filed on March 30, 2022; U.S. Patent Application No. 17 / 709104 filed on March 30, 2022; U.S. Patent Application No. 18 / 099798 filed on January 20, 2023; and U.S. Patent Application No. 18 / 110746 filed on February 16, 2023.

[0054] For example, the moiré diffraction lobes can be overlapped with the zero-order diffraction within the focusing pupil plane (as specified by, e.g., the metric recipe). In this example, the first photodetector can be positioned in the overlapping region between the -1st-order moiré diffraction and the zero-order diffraction, and the second photodetector can be positioned in the overlapping region between the +1st-order moiré diffraction and the zero-order diffraction, so that time-varying interference signals can be captured by each photodetector 112 as the sample 104 is scanned. In addition, the overlay measurement can be determined based on the time-varying signal relating only to the first-order moiré diffraction lobes (e.g., without referring to the zero-order diffraction). In another example, the first-order diffractions from the first exposure structure 208 and the second exposure structure 212 overlap within the focusing pupil 304. As an example, the first photodetector can be positioned in the overlapping region between the -1st-order diffraction (-1) from the first exposure structure 208. TOP ) and -1 order diffraction (-1 BOTTOM The second photodetector can be located in the first overlapping region between the first exposure structure 208 and the first exposure structure 208 (+1 TOP ) and the +1 order diffraction (+1 BOTTOM ) can be located in the second overlap region between them. In another example, the overlay measurement can be determined based on time-varying signals relating to the first-order lattice diffraction lobe and the second-order diffraction lobe (without referring to e.g., zero-order diffraction 306). Furthermore, depending on the embodiment, the first-order diffraction lobes do not necessarily need to overlap in the focusing pupil plane, but rather may overlap on the individual photodetectors 112a,b. In addition, in certain embodiments, the overlay measurement can be determined based on time-varying signals relating only to the first-order lattice diffraction lobe (without referring to e.g., zero-order diffraction 306). For example, the overlay measurement can be determined based on time-varying signals relating to the overlap between auxiliary illumination (e.g., illumination branched from the generated illumination beam) and the first-order diffraction lobe, which is outlined in U.S. Patent Application No. 18 / 110746 filed on February 16, 2023, and its full details are incorporated into this application by reference.

[0055] As previously described in this application, it is not necessarily required to make the zero-order diffraction 306 overlap with the -1st-order lattice diffraction 308 and the +1st-order lattice diffraction 310 within the focusing pupil 304 shown in Figures 3B to 3D. Rather, in certain embodiments, the diffraction lobes are sufficiently densely packed so 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] Based on careful consideration in this application, with general reference to Figures 3B to 3D, it is possible to form a time-varying interference signal by causing the phases of each order of lattice diffraction (e.g., first-order diffractions 308, 310) to vibrate during scanning, and to determine the overlay value based on these vibrations. As a result, overlay measurement can be performed by capturing and comparing these time-varying interference patterns. For example, the position of the lattice relative to the optical system can be measured using the phase difference of the -1st and +1st order lattice diffractions 308, 310 from each individual lattice of one or more exposed areas, as further discussed in this application.

[0057] In general, as shown in Figures 4A to 6C, in various embodiments, the overlay metering target 204 is scanned by one or more illumination beams 108 of the illumination subsystem 106. As shown in Figure 4A, the overlay metering target 204 is scanned by one or more illumination beams 108 arranged along the scanning direction, and one or more illumination beams 108 can be sequentially interacted with the grids of the horizontal grid 206 when the overlay metering target 204 is scanned (e.g., when the first exposed structure 208 is scanned first and then the second exposed structure 212 is scanned second). As shown in Figures 5A to 6C, the overlay metering target 204 is scanned by one or more illumination beams 108 arranged orthogonally to the scanning direction, and one or more illumination beams 108 can be made to interact simultaneously with all the grids of the horizontal grid 206 (e.g., the first exposed structure 208, the second exposed structure 212, and possibly the third exposed structure 216) when scanning the overlay metering target 204.

[0058] In some embodiments, while the illumination beam 108 is scanning over the multi-layer overlay target 204, the primary signal may be mixed with the zero-order signal and collected in a time-separated manner.

[0059] For example, the overlapping area between the primary signal and the zero-order signal may be vibrated as a function of the location of the illumination spot as presented and described by Equation 1 below: I ±1 =|E0 + E + / -1 | 2 =|E0| 2 +|E + / -1 | 2 +2|E0E + / -1 | =2A + / -1 A0cos[(2π / P1)(X - X0) ± φ] + constant Equation 1 Where, I + / -1 is the intensity of the interference signal in the overlapping area of the zero-order and primary signals respectively, E0 is the electric field amplitude in the zero-order diffraction lobe, E + / -1 is the electric field amplitude in the primary diffraction lobe, A + / -1 is the amplitude of the primary signal, A0 is the amplitude of the zero-order signal, X is the position of the grating, φ is the constant phase term, and P1 is the pitch.

[0060] In some embodiments, the phase difference of the primary signal from each individual grating may be used to measure the position of that grating with respect to the system. For example, the position of the grating with respect to the system can be determined based on the first-order phase shift as presented and described by Equations 2.1 to 2.3 below: φ 1,+ / -1 = -(2π / P1)X0 ± φ Equation 2.1 X0 = (1 / 4π)(P(φ 1,1 + φ 1,-1 )) Equation 2.2 X0 = (1 / 4π)(P(φ 2,1 + φ 2,-1 )) Equation 2.3 Where, φ 1,+ / -1 is the phase shift of the primary signal (+ / -1) in the first cell (1), φ 2,+ / -1is the phase shift of the primary signal (+ / -1) in the second cell (2), P is the pitch, X0 is its grid position relative to the system, equation 2.2 can be used to determine the position of the first exposed structure 208 relative to the system, and equation 2.3 can be used to determine the position of the second exposed structure 212 relative to the system.

[0061] As previously discussed in this application, the overlay target 204 may have at least one non-overlapping (e.g., non-stacked) diffraction grating. In this case, in order to determine the overlay, it is necessary to synchronize the phase information relating to the non-overlapping regions on the overlay target 204. In some embodiments, the synchronization of the phase information relating to the non-overlapping regions on the overlay target 204 is achieved by having one or more illumination beams 108 interact simultaneously with the entire grating of the side-by-side grating 206 when the overlay metric target 204 is scanned. For example, as further discussed in this application, one or more illumination beams 108 can be extended or split so that they interact simultaneously with the entire grating of the side-by-side grating 206. In this case, since the phase information is collected simultaneously, the phase information relating to the non-overlapping regions on the overlay target 204 is inherently synchronized by the simultaneous interaction with the entire grating of the side-by-side grating 206.

[0062] In some embodiments, phase information relating to non-overlapping regions on the overlay target 204 is synchronized after the overlay metering target 204 has been scanned. For example, when the overlay metering target 204 is scanned by one or more illumination beams 108, the illumination beams 108 sequentially interact with the grids of the horizontal grid 206 as the overlay metering target 204 is scanned, and phase information is sequentially collected. That is, by determining one or more regions of interest, the phase information can be synchronized after scanning, and the reference point for the phase of the second exposed structure can be set to the same starting point as that of the phase of the first exposed structure, thus enabling relative position extraction as further discussed in this application.

[0063] In various embodiments, the overlay error between one or more sample layers relating to the horizontally arranged grid 206 can be determined based on Equation 3, which is presented and described below: OVL = (P1 / 4π)(φ 1,1 +φ 1,-1 -φ 2,1 -φ 2,-1 ) Equation 3

[0064] Figure 4A is a schematic diagram of an illumination beam spot on an overlay target shown in Figure 2A, relating to one or more embodiments of the present disclosure. Figure 4B is a top view of a lattice diffraction lobe relating to the overlay target shown in Figure 2A, with associated phase extraction information from the overlay target, according to one or more embodiments of the present disclosure.

[0065] As shown in Figure 4A, in various embodiments, the overlay metering target 204 is scanned by one or more illumination beams 108 of the illumination subsystem 106, and as the overlay metering target 204 is scanned, the first exposed structure 208 and the second exposed structure 212 of the horizontal grid 206 are scanned sequentially. For example, as previously discussed in this application, the first exposed structure 208 and the second exposed structure 212 may be arranged along the scanning direction. In this case, the first exposed structure 208 of the first layer 210 will be scanned first, and the second exposed structure 212 of the second layer 214 will be scanned second.

[0066] As previously discussed in this application, phase information relating to non-overlapping regions on the overlay target 204 can be synchronized after the overlay metric target 204 has been scanned. This can be done by determining one or more regions of interest so that the phase information can be synchronized after scanning. Relative position extraction can be made possible by setting the phase reference of the second exposure structure to the same starting point as that of the phase of the first exposure structure.

[0067] Depending on the embodiment, one or more corrections will be performed while the overlay metering target 204 is being scanned by one or more illumination beams 108 aligned along the scanning direction.

[0068] Depending on the embodiment, one or more regions of interest (ROIs) may be determined. For example, these one or more ROIs can enable relative position extraction during phase extraction.

[0069] In some embodiments, as shown in Figure 4A, when the scanning speed is stable, one or more ROIs 400, 402 can be defined by a shift of n times the period of their grid, where n is an integer greater than 1. In this case, the separation interval between the first ROI 400 related to the first exposure structure 208 and the second ROI 402 related to the second exposure structure 212 can be defined by a shift of n times the period of their grid, and relative position extraction can be made possible by setting the starting points of the first exposure structure 208 and the second exposure structure 212 to the same point. According to Figure 4B, for example, one or more ROIs 400, 402 can be defined by a shift of n times the pitch of the time-varying interference signal, where n is an integer greater than 1. In this case, the separation interval between the first ROI 400 related to the time-varying interference signal of the first exposure structure 208 and the second ROI 402 related to the time-varying interference signal of the second exposure structure 212 can be determined by a shift that is n times the pitch of the time-varying interference signal, and relative position extraction can be made possible by setting the starting points of the first exposure structure 208 and the second exposure structure 212 to the same point.

[0070] However, errors can sometimes be due to the instability of the scanning speed. Therefore, in certain embodiments, the time-variable interference signal is calibrated (or corrected) when the scanning speed is unstable, thereby compensating for scanning speed instability and other sampling instability. For example, one or more sample reference signals can be used to perform one or more corrections. These one or more sample reference signals can be received from the stage itself (e.g., through the function of a stage encoder) or from an external monitoring system. In this case, the phase information of individual time-variable interference signals can be adjusted by monitoring the speed of the stage (or sample) and using it as an anchor to perform one or more corrections.

[0071] Figure 5A is a schematic diagram of a cell 202 of an overlay metering target 204 being scanned by an illumination beam 108, relating to one or more embodiments of the present disclosure. Figure 5B is a graph 500 showing the apodizer function 502 used to generate the illumination beam 108 in Figure 5A, relating to one or more embodiments of the present disclosure. Figure 5C is a graph 504 showing a simulated derived illumination spot 501 generated using the apodizer function 502 in Figure 5B, relating to one or more embodiments of the present disclosure.

[0072] As shown in Figures 5A to 5C, depending on the embodiment, one or more illumination beams 108 are extended orthogonally with respect to the scanning direction. For example, one or more illumination beams 108 can be extended orthogonally with respect to the scanning direction such that the one or more illumination beams 108 interact with the first exposure structure 208 and the second exposure structure 212.

[0073] Depending on 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 extended illumination beam 501 can be generated using an in-pupil apodizer function 502. As an example, an extended illumination beam 501 can be generated using the in-pupil apodization function 502 shown in Figure 5B. In this case, as shown in Figure 5A, the extended illumination beam 501 can be made to interact with the first exposed structure 208 and the second exposed structure 212 of the horizontal grid 206 when the overlay target 204 is scanned.

[0074] Figure 6A is a schematic diagram of a cell 202 of an overlay metering target 204 being scanned by two mutually coherent illumination beams 108, relating to one or more embodiments of the present disclosure. Figure 6B is a graph 600 showing the apodizer function 602 used to generate the separated illumination beams 108 in Figure 6A, relating to one or more embodiments of the present disclosure. Figure 6C is a graph 604 showing the separated simulated derived illumination spots 601a,b generated using the apodizer function 602 in Figure 6B, relating to one or more embodiments of the present disclosure.

[0075] As shown in Figures 6A to 6C, depending on the embodiment, by separating one or more illumination beams 108, two mutually coherent, separated illumination beams 108 are generated within the pupil field. For example, by separating one or more illumination beams 108, two separate illumination beams 108a and 108b can be generated. As an example, the first illumination beam 108a can be made to interact with the first exposed structure 208, and the second illumination beam 108b can be made to interact with the second exposed structure 212.

[0076] In various embodiments, one or more optical elements 134 (e.g., apodizers) of the illumination subsystem 134 may be used to separate one or more illumination beams 108, thereby generating separated illumination beams 601a and 601b. For example, the separated illumination beams 601a and 601b can be generated using the in-pupil apodizer function 602, such that they are coherent with each other. As an example, the separated illumination beams 601a and 601b can be generated using the in-pupil apodization spot 602 shown in Figure 6B. In this case, as shown in Figure 6A, the separated illumination beams 601a and 601b can interact simultaneously with the first exposure structure 208 and the second exposure structure 212 of the horizontal grid 206 when the overlay target 204 is scanned.

[0077] Although Figures 6A to 6C depict two spots, it should be noted that Figures 6A to 6C are presented solely for illustrative purposes and are not intended to limit the technical scope of the disclosure. For example, the system and method of the disclosure may be used to measure three or more side-by-side grids.

[0078] Referring again to Figure 1A, additional components of the overlay weighing tool 102 will be described in detail according to one or more embodiments of the present disclosure.

[0079] In various embodiments, the overlay weighing system 100 has a controller 122 that is communicatively coupled to the overlay weighing tool 102. The controller 122 may have one or more processors 124 and a storage device 126 or memory. For example, the one or more processors 124 may be configured to execute a set of program instructions held in the storage device 126.

[0080] According to various embodiments, the controller 122 can perform any of the various processing steps related to overlay weighing. For example, the controller 122 can be configured to generate control signals to control the overlay weighing tool 102 or any of its components, for example, by instructing it. For example, the controller 122 can be configured to instruct the translation stage 116 to translate the sample 104 along one or more measurement paths i.e., swaths, to scan one or more overlay targets within the measurement field of the overlay weighing tool 102, and / or to instruct the beam scanning subsystem 118 to position one or more corrective illumination beams on the sample 104 or to scan the sample 104 with them. In another example, the controller 122 can be configured to receive signals corresponding to time-variable interference signals from the photodetector 112. In another example, the controller 122 can generate correction variables for one or more additional manufacturing tools as feedback and / or feedforward control of those tools, based on the overlay measurements from the overlay weighing tool 102.

[0081] In various embodiments, the controller 122 captures the interference signal detected by the photodetector 112. For example, the controller 122 can generally capture data such as the phase of the time-varying interference signal, and can use any known technology in the art, such as frequency domain analysis (e.g., FFT) or one or more phase-locked loops, but is not limited to this. Furthermore, the controller 122 can capture the interference signal or any data related to such interference signals, and can use any combination of hardware (e.g., circuits) and software technology.

[0082] In various embodiments, the controller 122 can determine the overlay measurement values ​​between layers of the overlay target along the measurement direction based on the comparison results of the interference signals. For example, the controller 122 can determine the overlay measurement values ​​based on the phase of the interference signals. As an example, the aforementioned Patent Document 4, whose entirety is incorporated into this application by reference, outlines the electric fields of various order diffractions in the focusing pupil, and further presents the specific relationship between the overlay and the measured intensity in the pupil plane. As considered in this application, the teachings in Patent Document 4 can be extended to time-variable interference signals captured by a photodetector placed in the overlapping region between 0th and + / -1st order diffractions using the systems and methods disclosed in this application. In particular, as considered in this application, the overlay on the sample may be proportional to the relative phase shift between two time-variable interference signals.

[0083] Furthermore, the controller 122 can modify, for example, the overlay measurement based on known, expected, or measured characteristics of the sample, such as sidewall angles and other sample asymmetries, which may also affect the time-varying interference signal.

[0084] In various embodiments, the illumination subsystem 106 includes an illumination source 128 configured to generate at least one illumination beam 108. Illumination from the illumination source 128 may include, but is not limited to, one or more specified wavelengths of light, including ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0085] The illumination source 128 may include any type of illumination source suitable for supplying at least one illumination beam 108. In certain embodiments, the illumination source 128 is a laser light source. For example, the illumination source 128 may include, but is not limited to, one or more narrowband laser light sources, broadband laser light sources, ultracontinuum (ultrabroadband) laser light sources, white laser light sources, etc. In this case, the illumination source 128 can supply an illumination beam 108 having high coherence (e.g., high spatial coherence and / or temporal coherence). In certain embodiments, the illumination source 128 has a laser-sustained plasma (LSP) light source. For example, the illumination source 128 may include, but is not limited to, an LSP lamp, LSP bulb, or LSP chamber suitable for containing one or more elements that can be excited into a plasma state by a laser light source and emit broadband illumination.

[0086] In some embodiments, the illumination subsystem 106 has one or more optical components suitable for modifying and / or dimming the illumination beam 108 and directing the illumination beam 108 toward the specimen 104. For example, the illumination subsystem 106 may have one or more illumination lenses 130 (e.g., for collimating the illumination beam 108, or for relaying the illumination surface 120 and / or illumination field of view 132). In certain embodiments, the illumination subsystem 106 has one or more illumination control optics 134 for controlling, for example, shaping the illumination beam 108. For example, the illumination control optical system 134 may have, but is not limited to, one or more apodizers, one or more field diaphragms, one or more pupil diaphragms, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more beam shapers, or one or more mirrors (e.g., stationary mirrors, translational mirrors, scanning mirrors, etc.).

[0087] In various embodiments, the overlay weighing tool 102 has an objective lens 136 that focuses an illumination beam 108 onto a specimen 104 (e.g., onto an overlay target having overlay target elements located on two or more layers of the specimen 104).

[0088] In some embodiments, the specimen 104 is illuminated by two or more illumination beams 108 from the illumination subsystem 106. Furthermore, these two or more illumination beams 108 may be incident on different parts of the specimen 104 within the measurement field of view (e.g., the field of view of the objective lens 136) (e.g., different cells of the overlay target), although this is not required. Various techniques can be used to generate these two or more illumination beams 108. In some embodiments, the illumination subsystem 106 has two or more apertures on the illumination field of view 132. In some embodiments, the illumination subsystem 106 has one or more beam splitters that split the illumination from the illumination source 128 into two or more illumination beams 108. In some embodiments, two or more illumination beams 108 are directly generated by at least one illumination source 128. In general, regardless of the technique used to generate the various illumination beams 108, each illumination beam 108 can be considered part of a separate illumination channel.

[0089] In some embodiments, the focusing subsystem 110 has at least two photodetectors 112 (e.g., photodetectors 112a,b) configured to capture light from the specimen 104 (e.g., collected light 138) and positioned on the focusing pupil plane 114, wherein the collected light 138 includes at least a zero-order diffraction 306, a -1st-order diffraction 308, and a +1st-order diffraction 310, as shown in Figure 3B. The focusing subsystem 110 may also have one or more optical elements suitable for modifying and / or dimming the collected light 138 from the specimen 104. In certain embodiments, the focusing subsystem 110 has one or more focusing lenses 140 (e.g., for collimating the illumination beam 108, for relaying the pupil and / or field plane, etc.), which may include an objective lens 136, although this is not required. In certain embodiments, the focusing subsystem 110 has one or more focusing control optics 142 that control, for example, shape the collected light 138. For example, the focusing control optics 142 may have, but are not limited to, one or more field diaphragms, one or more pupil diaphragms, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., stationary mirrors, translational mirrors, scanning mirrors, etc.).

[0090] In various embodiments, the focusing subsystem 110 has two or more focusing channels 144, each having a separate pair of photodetectors 112. For example, as shown in Figure 1B, the overlay metering tool 102 may have one or more beam splitters 146 arranged to branch and supply the collected light 138 into the focusing channels 144. Furthermore, the beam splitters 146 may be polarizing beam splitters, unpolarizing beam splitters, or a combination thereof. However, the depiction of two focusing channels 144 in Figure 1B is presented for illustrative purposes only and should not be taken as limiting. For example, the focusing subsystem 110 may have one focusing channel 144 or multiple focusing channels 144.

[0091] In some embodiments, multiple focusing 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 along directions other than the scanning direction, the overlay metering tool 102 can simultaneously illuminate different cells 202 with different illumination beams 108 and simultaneously capture interference signals related to each illumination beam 108. In addition, in some embodiments, the multiple illumination beams 108 directed towards the sample 104 can have different polarizations. Doing so allows for the separation of various order diffractions related to each illumination beam 108. For example, a polarizing beam splitter 146 can efficiently separate the various order diffractions related to different illumination beams 108. In another example, polarizers can be used within one or more focusing channels 144 to separate diffractions of a desired order for measurement.

[0092] In some embodiments, the overlay weighing tool 102 has a beam scanning subsystem 118 that, during measurement, positions, scans, or modulates one or more illumination beams 108 on the sample 104.

[0093] The beam scanning subsystem 118 may have any type and combination of elements suitable for scanning the position of one or more illumination beams 108. In certain embodiments, the beam scanning subsystem 118 may have one or more deflectors suitable for correcting the direction of the illumination beams 108. For example, a deflector may include, but is not limited to, a rotatable mirror (e.g., a mirror with adjustable tip and / or tilt). Furthermore, the rotatable mirror may be operated 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. In another example, the beam scanning subsystem 118 may include an electro-optic modulator, an acousto-optic modulator, and the like.

[0094] Furthermore, the deflector may be located at any preferred location within the overlay weighing tool 102. In certain embodiments, one or more deflectors are arranged on one or more pupil planes common to both the illumination subsystem 106 and the focusing subsystem 110. In this case, the beam scanning subsystem 118 can be a pupil plane beam scanner, and its associated deflector can correct the position of one or more illumination beams 108 on the specimen 104 without affecting the position of the order diffractions on the focusing pupil plane 114. Furthermore, since the position of one or more illumination beams 108 on the specimen 104 is corrected by the beam scanning subsystem 118, the distribution of one or more illumination beams 108 on the illumination field of view 132 can be made even more stable. Pupil plane beam scanning is outlined in U.S. Patent Application No. 17 / 142783, filed on January 6, 2021, and its full details are referenced below.

[0095] Figure 7 is a flowchart illustrating the steps performed in the scanning overlay metering method 700 of an overlay target according to one or more embodiments of the present disclosure. In the applicant's view, the embodiments and enabling technologies described herein should be understood to be extended to Method 700 in the context of the overlay metering system 100. However, it should be further noted that Method 700 is not limited to the architecture of the overlay metering system 100.

[0096] In step 702, one or more cells of the overlay target are illuminated. For example, as sample 104 is scanning with respect to the illumination, one or more cells 202 of the overlay target 204 on sample 104 are illuminated.

[0097] As an example, the overlay metering target 204 can be scanned by one or more illumination beams 108 arranged orthogonally to the scanning direction, in which case, while the overlay metering target 204 is being scanned, one or more illumination beams 108 will simultaneously interact with all the grids of the horizontal grid 206 (e.g., the first exposed structure 208, the second exposed structure 212, and possibly the third exposed structure 216). As an alternative example, the overlay metering target 204 can be scanned by one or more illumination beams 108 arranged along the scanning direction, in which case, while the overlay metering target 204 is being scanned (e.g., the first exposed structure 208 is scanned first, followed by the second exposed structure 212), one or more illumination beams 108 will sequentially interact with the grids of the horizontal grid 206.

[0098] In step 704, time-varying interference signals can be collected from one or more photodetectors 112a,b. For example, time-varying interference signals from two photodetectors 112a,b positioned within the region of the focusing pupil related to overlapping diffraction from the grids in the horizontal grid 206. For example, although not limited to this, the photodetectors can be positioned in locations where only first-order grid diffractions from the grids of the horizontal grid 206 are present, where both first-order and zero-order grid diffractions are present, or where first-order diffraction is present. In this case, while the illumination beam 108 is scanning the multilayer overlay target 204, the first-order signal and the zero-order signal (or branched illumination / auxiliary illumination) can form the time-varying interference signal described in this application, and the overlapping area between the zero-order signal (or auxiliary illumination) and the first-order signal can be made to oscillate as a function of the illumination spot location according to Equation 1 previously discussed in this application.

[0099] In step 706, the overlay error between one or more sample layers relating to the horizontal grid can be determined according to equations 2-1 to 2-3 presented and described earlier. For example, the overlay error between sample layers relating to the horizontal grid within one or more cells 202 of the overlay target 204 is determined based on signals from two photodetectors 112a and 112b. For example, the overlay error along the periodicity direction of the horizontal grid 206 may be proportional to the phase difference between the time-varying interference signals from the two photodetectors. The determination of this phase difference can be performed using any technique known in the present art, including, but is not limited to, the application of frequency domain analysis techniques (e.g., Fast Fourier Transform, etc.) to these two time-varying interference signals. Furthermore, in certain embodiments, the overlay measurement value of a sample along a specific measurement direction can be generated based on data from multiple cells of an overlay target having periodicity along that specific measurement direction.

[0100] Method 700 can be applied to a wide range of overlay target designs suitable for 1D or 2D metrology.

[0101] In certain embodiments, overlay measurements are generated based on signals from an overlay target having multiple cells with varying differences (e.g., pitch differences) in a horizontal grid. For example, in an optional step 708, the measurements can be averaged to reduce or eliminate tool-induced shift (TIS) errors. For instance, the TIS error of the overlay target 204 can be determined based on the difference between the overlay errors of one or more cells among the multiple cells 202.

[0102] In various embodiments, the TIS error can be determined based on the overlay error between multiple cells 202. For example, TIS correction using two layers is generally performed by averaging measurements from two cells with inverse pitch distributions for those layers (e.g., PQ / QP, PR / RP, QR / RP). The determination of the TIS error is outlined in U.S. Patent Application No. 18 / 099798, filed December 20, 2023, and its full details are incorporated into this application by reference.

[0103] Depending on the embodiment, parallel measurement is performed in method 700 by simultaneously scanning with multiple illumination beams and collecting related overlapping diffractions.

[0104] In some embodiments, method 700 provides a diagonal or triangular wave path across the sample by scanning with one or more illumination beams along a beam scanning direction different from the stage scanning direction. In this case, cells having horizontally aligned grids with different periodic directions can be efficiently examined along the measurement swath with a common illumination beam.

[0105] The subject matter described in this application is sometimes depicted as various components incorporated into or connected to other components. As you can see, such illustrated architectures are merely examples, and in fact, many other architectures can be implemented to achieve the same function. Conceptually, any arrangement of components that achieves the same function is effectively "coordinated" to achieve that desired function. Therefore, any two components in this application that are combined to achieve a particular function can be considered to be "coordinated" with each other to achieve that desired function, regardless of the architecture or intervening components. Similarly, any two components that are coordinated in this way can be considered to be "connected, linked" or "joined" with each other to achieve that desired function, and any two components that can be coordinated in this way can be understood as "joinable" with each other to achieve that desired function. Specific examples of connectable components, though not limited to these, include physically interactable and / or physically interacting components, and / or wirelessly interactable and / or wirelessly interacting components, and / or logically interactable and / or logically interacting components.

[0106] Many of the advantages of this disclosure and its associated benefits can be understood from the above description, and it will also be clear that various modifications can be made to the form, configuration, and arrangement of the components without deviating from the disclosed subject matter or compromising all of its main advantages. The forms described are purely descriptive, and the intent of the claims below is to encompass and include such modifications. Furthermore, the claims in another section define the present invention.

Claims

1. An overlay weighing system, It has a lighting subsystem, and that lighting subsystem is A lighting source configured to generate one or more illumination beams, and One or more illumination optics configured to direct one or more illumination beams toward an overlay target on the specimen when scanning the specimen along the scanning direction with reference to one or more illumination beams during the execution of a weighing recipe, The overlay target relating to the weighing recipe has a horizontal grid, the horizontal grid has one or more diffraction gratings in one or more cells, at least one diffraction grating is a non-overlapping horizontal grid, the horizontal grid has at least a first exposed structure and a second exposed structure, the first exposed structure is located in close proximity to the second exposed structure, and the horizontal grid is periodic along the scanning direction. It is equipped with a light-gathering subsystem, and that light-gathering subsystem, The system includes two or more photodetectors positioned within the pupil plane to capture the multiple diffractions from the horizontally arranged grid within one or more cells when the aforementioned weighing recipe is performed, The device comprises a controller that is communicatively coupled to two or more photodetectors, and the controller has one or more processors configured to execute program instructions, and the program instructions to be executed are configured on one or more of these processors. When the overlay target is scanned according to the aforementioned weighing recipe, it receives time-variable interference signals from two or more photodetectors relating to the horizontal grid within one or more cells, and With the time-varying interference signals corresponding to the non-overlapping first and second exposure structures synchronized, the overlay error between one of the first and second exposure structures of the sample is determined based on the time-varying interference signals. An overlay weighing system.

2. An overlay weighing system according to claim 1, wherein when scanning the sample with respect to one or more illumination beams, the one or more illumination beams simultaneously interact with the first exposed structure of the first layer of the horizontal grid and the second exposed structure of the second layer of the horizontal grid.

3. An overlay weighing system according to claim 1, wherein the one or more illumination beams include one or more extension beams, the one or more extension beams are extended orthogonal to the scanning direction, and the one or more extension beams interact simultaneously with at least the first exposed structure and the second exposed structure when the overlay target is scanned.

4. An overlay metering system according to claim 3, wherein the one or more illumination optical systems are configured to modify the one or more illumination beams to generate the one or more extended beams.

5. An overlay weighing system according to claim 4, wherein the one or more illumination optical systems are comprised of one or more apodizers.

6. An overlay metering system according to claim 3, wherein the illumination source is configured to generate the one or more extended beams.

7. An overlay weighing system according to claim 1, wherein the one or more illumination beams include one or more separate illumination beams, and when the overlay target is scanned, a first illumination beam among the one or more separate illumination beams interacts with the first exposed structure and a second illumination beam among the one or more separate illumination beams interacts with the second exposed structure.

8. An overlay weighing system according to claim 7, wherein the one or more illumination optical systems are configured to separate the one or more illumination beams to generate the one or more separated illumination beams.

9. An overlay weighing system according to claim 8, wherein the one or more illumination optical systems comprises one or more apodizers.

10. An overlay weighing system according to claim 1, wherein when the specimen is scanned with respect to one or more illumination beams, the one or more illumination beams sequentially interact with the first exposure structure and the second exposure structure of the horizontally arranged grid.

11. An overlay weighing system according to claim 1, wherein the two or more photodetectors are positioned at two or more locations within the pupil plane, and the first location containing the first photodetector includes locations for +1st-order lattice diffraction and 0th-order diffraction related to lattice diffraction from the first exposed structure, and the second location containing the second photodetector includes locations for -1st-order lattice diffraction and 0th-order diffraction related to lattice diffraction from the second exposed structure.

12. An overlay weighing system according to claim 1, wherein one or more processors are configured to execute program instructions, and the program instructions to be executed are configured on one or more processors Extract the phase information related to the aforementioned time-varying interference signal, and The overlay error between the first exposed structure and the second exposed structure of the specimen is determined based on the phase information. An overlay weighing system.

13. An overlay metering system according to claim 12, wherein the phase information relating to the time-variable interference signal is extracted using fast Fourier transform technology.

14. An overlay weighing system according to claim 12, wherein one or more processors are configured to execute program instructions, and the program instructions to be executed are configured on one or more processors One or more sample reference signals are received, and The extracted phase information relating to the aforementioned time-varying interference signal is adjusted based on the received one or more sample reference signals. An overlay weighing system.

15. An overlay weighing system according to claim 12, wherein one or more processors are configured to execute program instructions, and the program instructions to be executed are configured on one or more processors To determine one or more regions of interest (ROI) with respect to the first exposure structure and the second exposure structure of the horizontally arranged grid, An overlay weighing system.

16. An overlay metering system according to claim 15, wherein the ROI of the second exposed structure is defined by a shift of n times the period of the second exposed structure relative to the ROI of the first exposed structure.

17. An overlay weighing system according to claim 1, wherein the first exposed structure has a first pitch and the second exposed structure has a second pitch, and the first pitch is different from the second pitch.

18. An overlay weighing system according to claim 17, wherein one or more processors are configured to execute program instructions, and the program instructions to be executed are configured on one or more processors Based on the aforementioned time-varying interference signal, the tool-induced shift error is determined. An overlay weighing system.

19. An overlay weighing system according to claim 10, wherein the first exposed structure and the second exposed structure have the same pitch.

20. An overlay metering 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 right-angle incidence angle.

21. The overlay metering system according to claim 1, wherein the one or more illumination beams are An overlay weighing system that includes a time-coherent illumination beam.

22. The overlay weighing system according to claim 1, further, An overlay weighing system comprising a translation stage that translates the sample along the scanning direction, wherein when the sample is scanned by the translation stage, one or more illumination optical systems direct the illumination beams toward the overlay target on the sample.

23. The overlay weighing system according to claim 1, further, An overlay metering system comprising one or more beam scanning optical systems that scan the illumination beam along the aforementioned scanning direction.

24. It is a method, As the overlay target is scanned according to the weighing recipe, time-varying interference signals are received from two or more photodetectors relating to a first exposed structure and a second exposed structure within one or more cells, wherein the first exposed structure and the second exposed structure form a side-by-side grid, the side-by-side grid has one or more diffraction gratings, at least one diffraction grating is a non-overlapping side-by-side grid, the first exposed structure is located in close proximity to the second exposed structure, and the side-by-side grid is periodic along the scanning direction. With the time-varying interference signals corresponding to the non-overlapping first and second exposure structures synchronized, the overlay error between one of the first and second exposure structures of the sample is determined based on the time-varying interference signals. method.

25. The method according to claim 24, further, The phase information related to the aforementioned time-varying interference signal is extracted, and The overlay error between the first exposed structure and the second exposed structure of the sample is determined based on the phase information. method.

26. The method according to claim 24, further, One or more sample reference signals are received, and The extracted phase information relating to the time-varying interference signal is adjusted based on the received one or more sample reference signals. method.

27. The method according to claim 24, further, A method for determining one or more regions of interest (ROI) with respect to the first exposure structure and the second exposure structure of the horizontally arranged grid.

28. The method according to claim 27, wherein the ROI of the second exposure structure is defined by a shift of n times the period of the second exposure structure relative to the ROI of the first exposure structure.

29. An overlay metric target, The specimen comprises one or more cells having a horizontally arranged grid, the horizontally arranged grid having one or more diffraction gratings arranged on two or more layers of the specimen, and the two or more layers of the specimen include at least a first layer and a second layer. The first layer has a first exposed structure and the second layer has a second exposed structure, The first exposed structure and the second exposed structure form a non-overlapping horizontal grid, and the first exposed structure is located adjacent to the second exposed structure. The aforementioned horizontally aligned grid forms a periodic overlay metric target along the scanning direction.

30. An overlay weighing target according to claim 29, wherein the two or more layers further have a third layer, and the third layer has a third exposed structure.

31. An overlay weighing target according to claim 30, wherein the third exposed structure overlaps with the non-overlapping structure formed by the first exposed structure and the second exposed structure.

32. An overlay weighing target according to claim 30, wherein the first exposed structure has a first pitch, the second exposed structure has a second pitch, and the third exposed structure has a third pitch, the first pitch is different from the second pitch and the third pitch, and the second pitch is different from the first pitch and the third pitch.

33. An overlay weighing target according to claim 29, wherein the first exposed structure has a first pitch and the second exposed structure has a second pitch, and the first pitch is different from the second pitch.

34. An overlay metric target, It comprises one or more cells having a horizontally arranged grid, and the horizontally arranged grid has one or more diffraction gratings arranged on one or more of the specimens, The one or more layers have a first exposed structure and a second exposed structure, The first exposed structure and the second exposed structure form a non-overlapping horizontal grid, and the first exposed structure is located adjacent to the second exposed structure. The aforementioned horizontally aligned grid forms a periodic overlay metric target along the scanning direction.

35. An overlay weighing target according to claim 34, wherein the first exposed structure has a first pitch and the second exposed structure has a second pitch, and the first pitch is different from the second pitch.

36. An overlay weighing target according to claim 34, wherein the first exposed structure and the second exposed structure have the same pitch.

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