Parallel scatterometry and overlay metrology

Abstract

The overlay metrology tool may include an illumination source generating a first illumination beam distribution having a first linear polarization and a second illumination beam distribution having a second linear polarization orthogonal to the first linear polarization, and an illumination subsystem for sequentially illuminating two or more cell pairs of an overlay target on a sample having orthogonally oriented grating-over-grating structures. A collection subsystem having two collection channels for capturing light collected from the illuminated cell pairs and filtering optics for directing light from different cells in the illuminated cell pairs to different collection channels for detection. The tool may further include a controller for generating separate overlay measurements for the orthogonally oriented grating-over-grating structures in the two or more cell pairs.

Description

[Technical field]

[0001] The present disclosure relates generally to overlay metrology, and more particularly to scatterometry-based overlay metrology. [Background technology]

[0002] Overlay metrology generally refers to the measurement of the relative alignment of layers on a sample, such as, but not limited to, a semiconductor device. Overlay metrology or overlay error measurement typically refers to the measurement of misalignment of fabricated features on one or more sample layers. In a general sense, proper alignment of fabricated features on multiple sample layers is necessary for proper functioning of the device. The demand for decreasing feature size and increasing feature density has resulted in a corresponding increased demand for accurate and efficient overlay metrology. Many existing overlay metrology techniques require separate metrology steps of multiple cells of an overlay target to generate overlay data in a particular direction, and additional sets of metrology steps to generate overlay data in additional directions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2018 / 0335346 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0116819 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the time required to perform such measurement steps may limit the throughput of the overlay metrology system. Therefore, there is a need to develop systems and methods to overcome these drawbacks. [Means for solving the problem]

[0005] An overlay metrology tool is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the tool includes an illumination source that generates a first illumination beam distribution having a first linear polarization and a second illumination beam distribution having a second linear polarization orthogonal to the first linear polarization. In another exemplary embodiment, the tool includes an illumination subsystem that sequentially illuminates two or more cell pairs of an overlay target on a specimen. A particular one of the two or more cell pairs can include a first directional cell having a lattice-over-lattice structure having periodicity along a first direction and a second directional cell having a lattice-over-lattice structure having periodicity along a second direction orthogonal to the first direction. In another exemplary embodiment, the illumination subsystem simultaneously illuminates the first directional cell with the first illumination beam distribution and the second directional cell with the second illumination beam distribution. In another exemplary embodiment, the tool includes a collection subsystem having a first collection channel including one or more first channel detectors at a first channel detection plane, a second collection channel including one or more second channel detectors at a second channel detection plane, and an objective lens for collecting light from the sample as collected light. And, the one or more filtering optics direct a portion of the collected light associated with a first direction cell of the two or more cell pairs to the first collection channel and direct a portion of the collected light associated with a second direction cell of the two or more cell pairs to the second collection channel. In another exemplary embodiment, the tool includes a controller that generates a first overlay measurement along the first direction based on data associated with the first direction cells of the two or more cell pairs from the one or more first channel detectors. And, generates a second overlay measurement along the second direction based on data associated with the second direction cells of the two or more cell pairs from the one or more second channel detectors.

[0006] An overlay metrology tool is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the tool includes an illumination source that generates a first illumination beam distribution having a first linear polarization and a second illumination beam distribution having a second linear polarization orthogonal to the first linear polarization. In another exemplary embodiment, the tool includes an illumination subsystem that sequentially illuminates two or more cell pairs of an overlay target on a specimen. A particular one of the two or more cell pairs can include a first directional cell having a lattice-over-lattice structure with periodicity along a first direction and a second directional cell having a lattice-over-lattice structure with periodicity along a second direction orthogonal to the first direction. In another exemplary embodiment, the illumination system includes a first illumination channel that directs a first illumination beam distribution to a first directional cell of one of the two or more cell pairs, the first illumination beam distribution including one or more first illumination beams having a first linear polarization. In another exemplary embodiment, the illumination subsystem further includes a second illumination channel for directing a second illumination beam distribution simultaneously with the first illumination beam distribution to a second direction cell of one of the two or more cell pairs, the second illumination beam distribution including one or more second illumination beams having a second linear polarization. In another exemplary embodiment, the tool includes a collection subsystem having a first collection channel including one or more first channel detectors at a first channel detection plane, a second collection channel including one or more second channel detectors at a second channel detection plane, and an objective lens for collecting light from the sample as collected light. And, the polarizing beam splitter directs a portion of the collected light associated with the first direction cell having the first linear polarization to the first collection channel and directs a portion of the collected light associated with the second direction cell of the two or more cell pairs having the second linear polarization to the second collection channel. In another exemplary embodiment, the tool includes a controller for generating a first overlay measurement along the first direction based on data associated with the first direction cell of the two or more cell pairs from the one or more first channel detectors. A second overlay measurement along the second direction is then generated based on data associated with the second direction cells of the two or more cell pairs from the one or more second channel detectors.

[0007] An overlay metrology method is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the method includes generating a first illumination beam distribution having a first linear polarization and a second illumination beam distribution having a second linear polarization orthogonal to the first linear polarization. In another exemplary embodiment, the method includes sequentially illuminating two or more cell pairs of an overlay target on a sample, each of the two or more cell pairs including a first directional cell having a lattice-over-lattice structure having periodicity along a first direction and a second directional cell having a lattice-over-lattice structure having periodicity along a second direction orthogonal to the first direction. Here, the illumination subsystem simultaneously illuminates the first directional cell with the first illumination beam distribution and the second directional cell with the second illumination beam distribution. In another exemplary embodiment, the method includes collecting light from the sample as collected light. In another exemplary embodiment, the method includes directing a portion of the collected light associated with the first directional cell of the two or more cell pairs to a first collection channel. In another exemplary embodiment, the method includes directing a portion of the collected light associated with a second direction cell of the two or more cell pairs to a second collection channel. In another exemplary embodiment, the method includes generating a first overlay measurement along the first direction based on data associated with the first direction cell of the two or more cell pairs. In another exemplary embodiment, the method includes generating a second overlay measurement along the second direction based on data associated with the second direction cell of the two or more cell pairs.

[0008] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention. [Brief description of the drawings]

[0009] Many advantages of the present disclosure may be better understood by those skilled in the art by reference to the following drawings. [Figure 1A] FIG. 1 is a block diagram of an overlay metrology system in accordance with one or more embodiments of the present disclosure. [Figure 1B] FIG. 1 is a schematic diagram of an overlay metrology tool showing two illumination channels and two collection channels in accordance with one or more embodiments of the present disclosure. [Figure 1C] FIG. 1 is a schematic diagram of a portion of an overlay metrology tool showing two illumination channels with separately configurable lighting conditions based on linearly varying filters in accordance with one or more embodiments of the present disclosure. [Figure 2A] FIG. 13 is a side view of a lattice-over-lattice structure in a single cell of an overlay target in accordance with one or more embodiments of the present disclosure. [Figure 2B] FIG. 2 is a top view of an overlay target in accordance with one or more embodiments of the present disclosure. [Figure 3A] FIG. 2C is a top view of the pupil plane illustrating the distribution of diffraction orders from the X-direction cells of the overlay target of FIG. 2B in accordance with one or more embodiments of the present disclosure. [Figure 3B] FIG. 2C is a top view of the pupil plane illustrating the distribution of diffraction orders from the Y direction cells of the overlay target 108 of FIG. 2B in accordance with one or more embodiments of the present disclosure. [Figure 4] 1 is a flow diagram illustrating steps performed in a method for overlay metrology in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings. The present disclosure has been specifically shown and described with respect to certain embodiments and certain features thereof. The embodiments described herein are to be construed as illustrative and not restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail may be made therein without departing from the spirit and scope of the present disclosure.

[0011] Embodiments of the present disclosure relate to systems and methods for generating parallel measurements of cells of an overlay target using scatterometry techniques. In some embodiments, two cells of an overlay target associated with an overlay measurement along two different (e.g., orthogonal) directions are illuminated simultaneously, light from the two illuminated cells is collected simultaneously, and the collected light associated with the illuminated cells is directed to separate detection paths. In this manner, measurements of multiple cells of an overlay target can be performed in parallel, which may advantageously increase measurement throughput relative to sequential measurements of each cell on the target. Further embodiments are directed to a multi-channel scatterometry overlay tool suitable for simultaneously illuminating multiple cells of an overlay target and separating light from the multiple cells into separate detection channels.

[0012] For purposes of this disclosure, the term overlay is generally used to describe the relative position of features on a sample fabricated by two or more lithographic patterning steps, and the term overlay error describes the deviation of features from a nominal arrangement. For example, a multi-layer device may include features patterned on multiple sample layers using different lithographic steps for each layer, and the alignment of features between layers must typically be tightly controlled to ensure proper performance of the resulting device. Thus, overlay measurements can characterize the relative positions of features on two or more sample layers. As another example, features can be fabricated on a single sample layer using multiple lithographic steps. Such techniques are commonly referred to as double patterning or multi-patterning techniques and can facilitate the fabrication of high density features approaching the resolution of the lithography system. Overlay measurements in this context can characterize the relative positions of features from different lithographic steps on this single layer. It should be understood that examples and illustrations throughout this disclosure of specific applications of overlay metrology are provided for illustrative purposes only and should not be construed as limiting the present disclosure.

[0013] Although in some applications overlay measurements may be performed directly on the features of the fabricated device (e.g., device features), overlay measurements are typically performed on dedicated overlay targets printed with the same lithography step as the device features. In this manner, the features of the overlay target (e.g., target features) may be specially designed to facilitate overlay measurements. Furthermore, overlay measured in one fabrication step (e.g., after fabrication of one or more sample layers) may be used to generate correctives for precisely aligning process tools (e.g., lithography tools, etc.) for fabrication of additional sample layers in subsequent fabrication steps.

[0014] In some embodiments, an overlay target suitable for scatterometry measurements as disclosed herein may include one or more cells having a grating-over-grating structure that includes periodic features (e.g., grating features) on overlapping regions of two or more layers of interest. In this manner, various grating features on the layers of interest can contribute to the diffraction of the incident illumination, and overlay measurements can be generated based on an analysis of the diffracted light. For example, the overlay measurements may be generated based on pupil plane data (e.g., related to the relative intensity differences between selected diffraction orders in the pupil plane). As another example, the overlay measurements may be generated based on field plane data (e.g., related to the relative intensities of images of the target's cells generated using selected diffraction orders).

[0015] As used throughout this disclosure, the term "specimen" generally refers to a substrate formed from a semiconductor or non-semiconductor material (e.g., a wafer, etc.). For example, the semiconductor or non-semiconductor material may include, but is not limited to, monocrystalline silicon, gallium arsenide, and indium phosphide. The specimen may include one or more layers. For example, such layers may include, but are not limited to, resist, dielectric material, conductive material, and semiconductor material. Many different types of such layers are known in the art, and the term specimen as used herein is intended to encompass specimens on which all types of such layers may be formed. The one or more layers formed on the specimen may be patterned or unpatterned. For example, the specimen may include multiple dies, each die having repeatable patterned features. The formation and processing of such layers of material may ultimately result in a completed device. Many different types of devices may be formed on the specimen, and the term specimen as used herein is intended to encompass specimens on which any type of device known in the art is fabricated. Furthermore, for purposes of this disclosure, the terms specimen and wafer should be construed as interchangeable. Additionally, for the purposes of this disclosure, the terms patterning device, mask, and reticle should be considered interchangeable.

[0016] In some embodiments, the overlay metrology tool simultaneously illuminates two cells of the overlay target with two illumination beams, the two cells including a grating-over-grating structure where the orientation of the grating in one cell is orthogonal to the orientation of the grating in the other cell. For example, the overlay metrology tool can simultaneously illuminate an X-direction cell including a grating-over-grating structure with periodicity along the X-direction with a first illumination beam, and simultaneously illuminate a Y-direction cell including a grating-over-grating structure with periodicity along the Y-direction with a second illumination beam. It should be understood that the description of X and Y directions is used herein for illustrative purposes only to refer to any orthogonal directions on the sample. Furthermore, the two cells can be illuminated with light having orthogonal linear polarizations (e.g., one cell is illuminated with light linearly polarized along the X-direction and one cell is illuminated with light linearly polarized along the Y-direction). In particular, the overlay metrology tool can illuminate each of the two cells with one or more illumination beam distributions (e.g., illumination beam distributions), the illumination beam distributions on each cell being smaller than the cell such that the cell is underfilled. Additionally, various aspects of the illumination light on each cell may be individually controlled or adjusted, such as, but not limited to, spectrum (e.g., spectral bandwidth and / or central wavelength), intensity, illumination angle, angular distribution of illumination, or focal position.

[0017] In some embodiments, the overlay metrology tool simultaneously separates the light collected from the illuminated cells into separate detection channels for each cell. In this way, measurement data related to the illuminated cells can be isolated from each other despite simultaneous collection. Various techniques for separating the collected light into separate detection channels may be used within the spirit and scope of the present disclosure. For example, the light collected from the illuminated cells may be separated based on parameters such as, but not limited to, polarization, a pupil stop filter (e.g., a spatial filter in the pupil plane that passes selected diffraction orders), or a field stop filter (e.g., a spatial filter in the field plane that passes light from selected cells).

[0018] In some embodiments, the overlay metrology tool includes beam control optics in the illumination and / or collection paths to various aspects of the illumination or collection light. For example, the overlay metrology tool may include one or more scanning mirrors that scan the illumination beam across each cell during measurement, which may reduce noise associated with target defects. As another example, the overlay metrology tool may include beam control optics that control or adjust the separation between two illumination beams, which may be used to match the illumination beam separation to the layout of cells in a particular overlay target. Additionally, the overlay metrology tool may adjust the illumination and / or collection field apertures based on the selected illumination beam separation.

[0019] Further embodiments of the present disclosure relate to overlay targets suitable for parallel measurement by an overlay metrology tool. In some embodiments, the overlay target includes X-direction cells distributed along a first row and Y-direction cells distributed along a second row. In this way, cells associated with a particular direction can be sequentially illuminated with the same or similar illumination conditions (e.g., polarization, spectrum, intensity, angular distribution of illumination, focal position of the sample during illumination, etc.) by simply scanning the overlay target along the row. For example, some overlay measurement techniques may require data capture from multiple cells with different intended offsets of the grating-over-grating structure. Thus, arranging cells with a common direction of periodicity along the row may reduce the burden on the overlay metrology tool, as the illumination conditions can be the same or substantially the same as the target is scanned along the row direction.

[0020] 1A-4, systems and methods for generating parallel measurements of cells of an overlay target using scatterometry techniques are shown.

[0021] FIG. 1A is a block diagram of an overlay metrology system 100 in accordance with one or more embodiments of the present disclosure.

[0022] In some embodiments, the overlay metrology system 100 has a dual channel illumination subsystem 104 that separately illuminates two cells 106 of an overlay target 108 on a sample 110 with a spatially separated distribution (e.g., an illumination beam distribution) of one or more illumination beams 112 having orthogonal linear polarizations, and a dual channel collection subsystem 114 that separately detects light or other radiation emanating from the sample 110 (e.g., collected light 116) associated with the two cells 106.

[0023] In some embodiments, the sample 110 is disposed on a sample stage 118 suitable for fixing the sample 110 and further configured to position the sample 110 relative to the overlay metrology tool 102. For example, the sample stage 118 may include any combination of linear, rotational, or angular (e.g., tip / tilt) actuators suitable for positioning the sample 110 at any selected orientation.

[0024] The overlay metrology tool 102 can be any type of overlay metrology tool known in the art suitable for generating an overlay signal suitable for determining an overlay associated with an overlay target on the sample 110. For example, the overlay metrology tool 102 may collect pupil plane data (e.g., one or more pupil plane images or portions thereof) in which the collected light 116 is analyzed at a pupil plane to characterize an angular distribution of radiation from the cell 106 (e.g., related to scattering and / or diffraction of radiation by the cell 106). As another example, the overlay metrology tool 102 can collect field plane data (e.g., one or more field plane images or portions thereof) based on selected diffraction orders from the cell 106. Additionally, the overlay metrology tool 102 can characterize the cell 106 while the sample 110 is stationary (e.g., in a static or moving measurement (MAM) mode) or while the sample 110 is moving (e.g., in a scanning mode).

[0025] 2A-2B, various configurations of overlay targets 108 suitable for parallel characterization of constituent cells 106 are described in greater detail in accordance with one or more embodiments of the present disclosure.

[0026] 2A is a side view of a lattice-over-lattice structure in a single cell 106 of an overlay target 108 according to one or more embodiments of the present disclosure. In some embodiments, the lattice-over-lattice structure in each cell 106 includes a first layer lattice feature 202 located on a first layer 204 of the sample 110 and a second layer lattice feature 206 located on a second layer 208 of the sample 110 that are oriented such that the regions including the first layer lattice feature 202 and the second layer lattice feature 206 overlap. In this manner, the first layer lattice feature 202 and the second layer lattice feature 206 may each diffract the incident illumination beam 112 into discrete diffraction orders. In general, any number of additional layers (not shown) may be located above, below, or between the first layer 204, the second layer 208, and the substrate 210.

[0027] In a general sense, the first layer grating features 202 and the second layer grating features 206 may have the same or different distributions and may be intentionally offset from one another by any selected intended offset 212. In some embodiments, the first layer grating features 202 and the second layer grating features 206 have the same pitch along the same direction such that associated diffraction orders overlap in the pupil plane. In some embodiments, the first layer grating features 202 and the second layer grating features 206 have different pitches along a particular direction, which may result in moiré fringes associated with a moiré pitch that is greater than the pitch of the first layer grating features 202 and the second layer grating features 206. Overlay metrology techniques utilizing the Moire effect are generally described in U.S. Patent No. 9,182,219 (November 10, 2015), published March 11, 2011, U.S. Patent No. 7,440,105 (October 21, 2008), U.S. Patent No. 7,349,105 (March 25, 2008), U.S. Patent No. 10,551,749 (February 4, 2020), U.S. Patent Application Publication No. 2021 / 0072650, U.S. Patent Application No. 16 / 935,117 (July 21, 2020), and U.S. Patent Application No. 16 / 931,078 (July 16, 2020), all of which are incorporated by reference in their entireties herein.

[0028] 2B is a top view of an overlay target 108 in accordance with one or more embodiments of the present disclosure. In some embodiments, the overlay target includes two or more cells 106 associated with each measurement direction of interest. For example, different cells 106 associated with a particular measurement direction may include grating-over-grating structures having different intended offsets 212.

[0029] FIG. 2B illustrates an overlay target 108 having two cells 106 with periodicity along the X direction (e.g., X-direction cells 106) for overlay measurements along the X direction, and two cells 106 with periodicity along the Y direction (e.g., Y-direction cells 106) for overlay measurements along the Y direction. The various cells 106 may generally be arranged in any suitable distribution. In some embodiments, as shown in FIG. 2B, cells 106 with the same periodic direction are distributed in rows. For example, FIG. 2B illustrates X-direction cells 106 along a first row 214 and Y-direction cells along a second row 216. As described in more detail below, this configuration can facilitate efficient sequential illumination of cells with the same periodic direction under the same or similar illumination conditions.

[0030] However, it should be understood that the overlay target 108 of Figures 2A-2B and the associated description are provided for illustrative purposes only and should not be construed as limiting. Rather, the overlay target 108 may include any suitable grating-over-grating-over-grating overlay target design. For example, the overlay target 108 may generally include any number of cells 106 suitable for measurements along two directions. Furthermore, the cells 106 may be distributed in any pattern or arrangement. For example, metrology target designs suitable for scanning metrology are generally described in U.S. Patent Application Serial No. 16 / 598,146 (October 10, 2019), which is incorporated herein by reference in its entirety.

[0031] 1A-3B generally, parallel characterization of multiple cells 106 of an overlay target 108 in accordance with one or more embodiments of the present disclosure will be described in more detail.

[0032] 1B is a schematic diagram of an overlay metrology tool 102 illustrating two illumination channels 120 and two collection channels 122, in accordance with one or more embodiments of the present disclosure. In this manner, the overlay metrology tool 102 can simultaneously characterize two cells 106 of an overlay target 108, such as, but not limited to, the overlay target 108 shown in FIGS. 2A-2B. In some embodiments, the overlay metrology tool 102 simultaneously characterizes two cells 106 having orthogonal directions of periodicity (e.g., one X-direction cell 106 and one Y-direction cell 106).

[0033] In some embodiments, the overlay metrology tool 102 includes at least one illumination source 124 configured to generate illumination 126 suitable for forming an illumination beam distribution that is directed at the cells 106 .

[0034] The illumination 126 from the illumination source 124 may include light of one or more selected wavelengths, including, but not limited to, ultraviolet (UV) radiation, visible light, or infrared (IR) radiation.

[0035] The illumination source 124 may include any type of illumination source known in the art. In some embodiments, the illumination source 124 is a laser source. For example, the illumination source 124 may include, but is not limited to, one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, and the like. In this regard, the illumination source 124 may provide illumination with high coherence (e.g., high spatial coherence and / or temporal coherence). In some embodiments, the illumination source 124 includes a laser-sustained plasma (LSP) source. For example, the illumination source 124 may include, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for housing one or more elements capable of emitting broadband illumination when excited into a plasma state by a laser source. In some embodiments, the illumination source 124 includes a lamp source. For example, the illumination source 124 may include, but is not limited to, an arc lamp, a discharge lamp, an electrodeless lamp, and the like. In this regard, the illumination source 124 may provide illumination having low coherence (eg, low spatial coherence and / or temporal coherence).

[0036] Each illumination channel 120 can direct a distribution of one or more illumination beams 112 (e.g., an illumination beam distribution) to a particular location on the sample 110. An illumination beam distribution can generally include one or more illumination beams 112 or illumination lobes directed to a particular cell 106 having a selected distribution of illumination parameters, such as, but not limited to, angles of incidence (e.g., azimuthal and polar angles of incidence), spectrum, or polarization. For example, an illumination beam distribution can include, but is not limited to, a single illumination beam 112 at a selected angle of incidence, a dipole distribution of illumination beams 112, or a quadrupole distribution of illumination beams 112. In this manner, the illumination channel 120 can simultaneously provide different illumination conditions for different cells 106 on the overlay target 108. Furthermore, when an illumination beam distribution includes multiple illumination beams 112, these illumination beams 112 can be provided simultaneously or sequentially in a given measurement of a cell 106.

[0037] In some embodiments, the illumination channels 120 provide illumination beams 112 with orthogonal linear polarizations. For example, one illumination channel 120 can provide a distribution of one or more illumination beams 112 with linear polarizations along a first direction (e.g., X-direction), and another illumination channel 120 can provide a distribution of one or more illumination beams 112 with linear polarizations along a second direction (e.g., Y-direction) that is orthogonal to the first direction. It is contemplated herein that providing orthogonal linear polarizations in the illumination channels 120 can have various benefits, including, but not limited to, efficiently utilizing available power from the illumination source 124, providing well-controlled diffraction by the grating-over-grating structure in each cell 106, and / or facilitating separation of the collected light 146 of the illuminated cells 106 into different collection channels 122 with high extinction ratios to prevent cross-contamination of signals.

[0038] Additionally, the various cells 106 of the overlay target 108 may be illuminated with any selected polarization direction. For example, the overlay metrology tool 102 may illuminate the X-direction cells 106 with light linearly polarized along the X direction and the Y-direction cells 106 with light linearly polarized along the Y direction, or vice versa.

[0039] The overlay metrology tool 102 may generally include any combination of optical components for simultaneously generating multiple illumination beam distributions.

[0040] In some embodiments, the overlay metrology tool 102 may include a single illumination source 124 that generates the illumination 126 for each illumination channel 120. For example, the overlay metrology tool 102 may include a polarizing beam splitter that splits the illumination 126 into orthogonal linearly polarized light directed to the different illumination channels 120. In some embodiments, the overlay metrology tool 102 includes separate illumination sources 124 for one or more of the illumination channels 120.

[0041] The overlay metrology tool 102 may further include various optical components for generating a selected illumination beam distribution for each illumination channel 120. In some embodiments, as illustrated in FIG. 1B, each illumination channel 120 may include one or more illumination lenses 128 or one or more illumination control optics 130 to control various illumination parameters. For example, the illumination control optics 130 may include, but are not limited to, one or more field stops or filters, one or more pupil stops or filters, one or more polarizers, one or more spectral filters, one or more spatial filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, etc.). As an example, each illumination channel 120 may include an aperture stop for generating one or more illumination beam 112 distributions, and / or a field stop for limiting the spatial extent of the illumination beam 112 in that channel to an area below the cell 106 such that the cell is underfilled with illumination.

[0042] In a general sense, each illumination channel 120 can provide independent control of illumination parameters of one or more illumination beams 112. In some embodiments, although not explicitly shown in FIG. 1B , the overlay metrology tool 102 can include illumination lenses 128 and / or illumination control optics 130 for manipulating the illumination 126 before entering the illumination channel 120. In this manner, selected aspects of the illumination beam distribution can be aligned between the illumination channels 120.

[0043] Further, the lighting parameters within each lighting channel 120 may be static or adjustable. The tunable lighting parameters may be provided using any technique known in the art. The generation of tunable lighting parameters is generally described in U.S. Patent No. 10,371,626 (August 6, 2019) and U.S. Patent Application No. 17,076,312 (October 21, 2020), both of which are incorporated herein by reference in their entireties.

[0044] In some embodiments, the adjustable illumination parameters are provided by selectively directing the illumination 126 onto one of a plurality of available light paths with one or more static filters (e.g., spectral filters, neutral density filters, etc.). In some embodiments, the tunable illumination parameters are provided by adjusting the position of one or more tunable filters (e.g., spectral filters, neutral density filters, etc.) within the illumination channel 120. In some embodiments, the adjustable illumination parameters are provided by selectively controlling the position of the illumination 126 from the illumination source 124 onto one or more spatially varying filters (e.g., spectral filters, neutral density filters, etc.).

[0045] FIG. 1C is a schematic diagram of a portion of an overlay metrology tool 102 illustrating two illumination channels 120 with separately configurable illumination conditions based on linearly varying filters, in accordance with one or more embodiments of the present disclosure. A linearly varying filter may include a filter having filtering characteristics that vary along a linear filtering direction. For example, a linearly varying neutral density filter may provide various amounts of broadband intensity reduction based on the spatial position of the input beam along the linear axis. As another example, a linearly varying low-pass (or high-pass) filter may provide low-pass filtering with a cutoff wavelength that varies based on the spatial position of the input beam along the linear filtering direction. As another example, a linearly varying filter may be formed as a polarizer, and the direction of polarized light passed by the linearly varying filter may be different in different directions along the linear filtering direction. It is contemplated herein that the systems and methods disclosed herein may utilize linearly varying filters that modify any selected characteristic of the input beam.

[0046] In some embodiments, the overlay metrology tool 102 includes an illumination source 124 having a spectral bandwidth covering a range of wavelengths of interest, and a polarizer 132 that splits the illumination 126 from the illumination source 124 along two paths associated with the two illumination channels 120. For example, the polarizer 132 may be a polarizing beam splitter that provides orthogonal linearly polarized light into the two illumination channels 120.

[0047] Each illumination channel 120 may include at least one tunable filter 134 that provides adjustable control of one or more illumination parameters. In some embodiments, the tunable filter 134 includes a pair of focusing optics 136 in a 4-f configuration, a linearly varying filter 138 located at a pupil plane (e.g., a focal plane common to the focusing optics 136), and an angle scanner 140 located at the other focal plane of the focusing optics 136 as an input and / or output coupler to the tunable filter 134. In this manner, the position of the illumination 126 on the linearly varying filter 138, and thus the resulting filtering effect on the illumination 126, may be controlled by adjusting the angle of the input angle scanner 140 that receives the illumination 126. Furthermore, regardless of the angle of the input angle scanner 140 and the associated position on the linearly varying filter 138, the illumination 126 is redirected to a common position on the output tunable filter 134, which may direct the filtered illumination 126 along any desired optical path. For example, the input and output angle scanners 140 may be adjusted simultaneously to provide adjustable filtering without modifying the output beam path and therefore without affecting the alignment of additional optics in the overlay metrology system 100.

[0048] Additionally, multiple tunable filters 134 may be arranged in series to provide tuning of multiple illumination parameters. For example, FIG. 1C shows three tunable filters 134 in each illumination channel 120. Such a configuration may be suitable for adjusting the intensity and spectrum of the illumination 126 in each illumination channel 120, but is not limited thereto. For example, one linearly varying filter 138 may be a linearly varying intensity filter, one linearly varying filter 138 may be a linearly varying low-pass spectral filter, and one linearly varying filter 138 may be a linearly varying high-pass spectral filter.

[0049] In some embodiments, the overlay metrology tool 102 includes one or more focus control optics 142 for adjusting or controlling a focus position of one or more illumination beams 112 in one or more illumination channels 120. It is contemplated herein that focus position adjustment may be particularly useful for, but not limited to, measurements having different wavelengths or measuring features at different depths. For example, the illumination beams 112 in different illumination channels 120 may have different spectral ranges. As another example, measurement robustness may be improved by capturing data from each cell 106 at multiple different wavelengths. In either case, chromatic aberrations in the sample 110 and / or the overlay metrology system 100 may result in different focusing or imaging conditions at different wavelengths such that focus correction in one or more illumination channels 120 may be required.

[0050] 1B includes focus control optics 142 in each of the illumination channels 120 to provide independent focus control for the associated illumination beams 112. The focus control optics 142 may include any type or combination of optical elements suitable for modifying the focus position of at least one illumination beam 112, such as, but not limited to, one or more deformable mirrors, one or more acousto-optic lenses, one or more voice coils, or one or more translatable lenses (e.g., any of the illumination lenses 128). In some embodiments, the focus control optics 142 can be designed to provide focus switching within the time required to adjust one or more additional illumination parameters (e.g., illumination spectrum, intensity, angular distribution, etc.) to facilitate high measurement throughput. In this manner, the focus control optics 142 can operate as a high-speed focus controller.

[0051] 1A-1C, the overlay metrology tool 102 may generate or control the illumination beam distribution (e.g., the number and incidence angle of the constituent illumination beams 112) using any technique known in the art.

[0052] In some embodiments, the overlay metrology system 100 includes one or more apertures (e.g., illumination control optics 130) at an illumination pupil plane to define one or more illumination beams 112. In some embodiments, the overlay metrology system 100 generates the illumination beams 112 by providing light to two or more optical fibers, where the light output from each optical fiber is provided to or directed to the illumination pupil to provide the illumination beam 112. In some embodiments, the overlay metrology system 100 generates the one or more illumination beams 112 by diffracting illumination 126 from an illumination source 124 into two or more diffraction orders, where at least one of the diffraction orders forms at least one illumination beam 112. Efficient generation of multiple illumination beams by controlled diffraction is generally described in U.S. Patent Application Publication US2020 / 0124408, published April 23, 2020, which is incorporated by reference herein in its entirety.

[0053] In some embodiments, the overlay metrology tool 102 includes an objective lens 144 for capturing light or other radiation (e.g., collected light 146) emanating from both illuminated cells 106. Additionally, the illumination beam 112 from any illumination channel 120 may generally be directed to the sample 110 through the objective lens 144 (e.g., in a through-the-lens (TTL) configuration) or outside the numerical aperture of the objective lens 144 (e.g., in an out-of-lens (OTL) configuration). For example, FIG. 1B shows a TTL configuration.

[0054] In some embodiments, the overlay metrology tool 102 includes one or more filtering optics to separate the collected light 146 from the two illuminated cells 106 into different collection channels 122. For example, the filtering optics can selectively direct a portion of the collected light 116 associated with the X-direction cell 106 into one collection channel 122 and the collected light 116 associated with the Y-direction cell 106 into another collection channel 122.

[0055] The one or more filtering optics may use any technique or combination of techniques to separate the collected light 116 associated with the two illuminated cells 106, including, but not limited to, polarization filtering, pupil plane filtering, or field plane filtering.

[0056] In some embodiments, the filtering optics includes one or more polarizing filters, such as, but not limited to, one or more linear polarizers or one or more polarizing beam splitters, to implement polarization filtering. It is contemplated herein that polarization filtering may be particularly effective when the illumination channels 120 provide illumination beam distributions having orthogonal linear polarizations, as the collected light 116 may generally retain the polarization direction of the illumination.

[0057] 1B, the overlay metrology tool 102 includes a polarizing beam splitter 148 at a location common to the illumination 126 and the collected light 116. In this configuration, the polarizing beam splitter 148 can receive orthogonal linearly polarized illumination 126 from each of the illumination channels 120 and send this light to the objective lens 144. This polarizing beam splitter 148 can then receive the collected light 116 from both illuminated cells 106 and split this collected light 116 into the two collection channels 122 based on polarization. FIG. 1B further shows two non-polarizing beam splitters 150, one associated with each polarization direction to separate the illumination 126 and collected light 116 for that polarization direction.

[0058] As another example, although not explicitly shown, the overlay metrology tool 102 can include one or more linear polarizers in either or both of the collection channels 122. For example, one collection channel 122 can include a linear polarizer aligned along the X direction and one collection channel 122 can include a linear polarizer aligned along the Y direction. In this configuration, the linear polarizers can perform polarization filtering, which can be achieved even when the illumination beam distribution does not have orthogonal linear polarizations. Additionally, the polarizers in the collection channels 122 can provide a higher extinction ratio than that provided by the polarizing beam splitter 148, thus further reducing crosstalk between collected light 116 associated with different cells 106.

[0059] In some embodiments, the filtering optics includes one or more spatial filters (e.g., pupil plane filters) in one or more pupil planes. It is contemplated herein that the grating-over-grating structure generates diffraction orders that are distributed in the direction of the periodicity. Thus, the diffraction orders from cells 106 having orthogonal directions of periodicity are distributed in orthogonal directions in the pupil plane and can therefore be filtered using pupil plane filters.

[0060] 3A-3B show spatial distributions of diffraction orders from illuminated cells 106 of the overlay target 108 of FIG. 2B, in accordance with one or more embodiments of the present disclosure. FIG. 3A is a top view of a pupil plane showing a distribution of diffraction orders from an X-direction cell 106 of the overlay target 108 of FIG. 2B, in accordance with one or more embodiments of the present disclosure. In particular, FIG. 3A shows a zeroth diffraction order 302 (e.g., specular reflection), an X-direction -1st diffraction order 304, and an X-direction +1st diffraction order 306 within a pupil boundary 308 in response to a single illumination beam 112 at a normal incidence angle. FIG. 3B is a top view of a pupil plane showing a distribution of diffraction orders from a Y-direction cell 106 of the overlay target 108 of FIG. 2B, in accordance with one or more embodiments of the present disclosure. In particular, FIG. 3B shows a zeroth diffraction order 302, a Y-direction -1st diffraction order 310, and a Y-direction +1st diffraction order 312 within a pupil boundary 308 in response to a single illumination beam 112 at a normal incidence angle. As shown in Figures 3A and 3B, the non-zero diffraction orders from the X-direction cell 106 and the Y-direction cell 106 do not overlap in the pupil plane and can be separated using a pupil plane filter. For example, one collection channel 122 may include a pupil plane filter with an aperture oriented to pass at least the X-direction -1st diffraction order 304 and the X-direction +1st diffraction order 306 to separate the collected light 116 from the illuminated X-direction cell 106. And one collection channel 122 may include a pupil plane filter with an aperture oriented to pass at least the Y-direction -1st diffraction order 310 and the Y-direction +1st diffraction order 312 to separate the collected light 116 from the illuminated Y-direction cell 106.

[0061] In some embodiments, the filtering optics includes one or more spatial filters (e.g., field plane filters) in one or more field planes. For example, FIG. 1B shows a field stop 152 in each of the collection channels 122. In particular, the field stop 152 in a collection channel 122 can limit the collection area in that channel to a particular cell 106.

[0062] In some embodiments, each collection channel 122 includes one or more detectors 154 configured to capture light 116 collected within the channel. Each collection channel 122 may further include one or more optical elements suitable for modifying and / or conditioning light 146 collected from the sample 110. In some embodiments, collection channel 122 includes one or more collection path lenses 156 (e.g., for collimating illumination, relaying pupil and / or field planes, etc.), which may, but need not, include objective lens 144. In some embodiments, collection channel 122 includes one or more collection path optics 158 that shape or otherwise control collected light 146. For example, the collection path optics 158 may include, but are not limited to, one or more field stops, one or more aperture stops, one or more polarizers, one or more spectral filters, one or more intensity filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, etc.).

[0063] The detector 154 can be positioned at any selected location within the collection channel 122. In some embodiments, the overlay metrology tool 102 includes a detector 154 at a pupil plane (e.g., a diffraction plane) to generate a pupil image. In this regard, the pupil image may correspond to an angular distribution of light from the sample 110 on the detector 154. For example, diffraction orders associated with diffraction from a grating-over-grating structure in the cell 106 may be imaged or otherwise observed in the pupil plane. In a general sense, the detector 154 may capture any combination of reflected (or transmitted), scattered, or diffracted light from the sample 110. In some embodiments, the overlay metrology tool 102 includes a detector 154 at a field plane (e.g., a plane conjugate to the sample 110) to generate an image of the sample 110 based on selected diffraction orders from the cell 106.

[0064] The overlay metrology tool 102 may generally include any number or type of detectors 154 suitable for capturing light from the sample 110 indicative of overlay. In some embodiments, the detectors 154 include one or more detectors 154 suitable for characterizing a static sample. In this regard, the overlay metrology tool 102 may operate in a static mode in which the sample 110 is static during measurement. For example, the detectors 154 may include a two-dimensional pixel array, such as, but not limited to, a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) device. In this regard, the detectors 154 may generate a two-dimensional image (e.g., a field plane image or a pupil plane image) in a single measurement.

[0065] In some embodiments, the detector 154 includes one or more detectors 154 suitable for characterizing a moving sample (e.g., a scanned sample). In this regard, the overlay metrology tool 102 may operate in a scanning mode in which the sample 110 is scanned relative to a measurement field of view during measurement. For example, the detector 154 may include a 2D pixel array having a capture time and / or refresh rate sufficient to capture one or more images during a scan within a selected image tolerance (e.g., image blur, contrast, sharpness, etc.). As another example, the detector 154 may include a line scan detector that sequentially generates images of one line of pixels at a time. As another example, the detector 154 may include a time delay integration (TDI) detector. The TDI detector may generate continuous images of the sample 110 when the motion of the sample 110 is synchronized to a charge transfer clock signal in the TDI detector.

[0066] In some embodiments, the overlay metrology system 100 includes one or more beam scanning optics 160 that control the position of the one or more illumination beams 112 (or illumination beam distributions) on the specimen 110. By way of example, FIG. 1B includes beam scanning optics 160 in each illumination channel 120.

[0067] It is contemplated herein that the beam scanning optics 160 may be utilized in a variety of ways in accordance with one or more embodiments of the present disclosure.

[0068] In some embodiments, the beam scanning optics 160 disposed in both illumination channels 120 can scan in a synchronous pattern to scan the respective illumination distributions across the cells 106. This synchronous scanning may advantageously reduce noise associated with imperfections in the grating-over-grating structure and / or reduce the effects of speckle associated with the coherent illumination 126. However, it is contemplated herein that such speckle may additionally or alternatively be reduced using other techniques. For example, the coherent illumination 126 can be scanned on an input face of a multimode fiber, the output of which is imaged onto the sample 110. Such a multimode fiber may be located in front of or within either of the illumination channels 120.

[0069] In some embodiments, beam scanning optics 160 in one or more illumination channels 120 are used to adjust or otherwise control the separation of the associated illumination beam distributions. In this manner, the illumination beam distributions from each illumination channel 120 can be centered on different cells 106. Furthermore, this configuration can provide flexibility for measuring targets having any selected cell separation. For example, in FIG. 1B, the beam scanning optics 160 can be tilted in the plane of the figure to deviate the associated illumination beam distributions on the sample 110 in the plane of the figure.

[0070] It is further contemplated herein that it may be desirable to ensure that the illumination 126 and / or collected light 116 are centered in any field stop to avoid asymmetric diffraction during either illumination or collection. In some embodiments, the overlay metrology system 100 includes one or more adjustable field stops (e.g., actuator-mounted field stops, etc.), which may, but need not, be synchronized to other components. For example, FIG. 1B shows adjustable field stops 152 in both the illumination channel 120 and the collection channel 122, which can optionally be synchronized to the beam scanning optics 160. In this way, the illumination 126 and collected light 116 can remain centered in their respective stops even as the position of the illumination beam distribution on the sample 110 is adjusted.

[0071] Referring again to FIG. 1A, various additional components of overlay metrology system 100 will now be described in greater detail in accordance with one or more embodiments of the present disclosure.

[0072] In some embodiments, the overlay metrology system 100 includes a controller 162 communicatively coupled to the overlay metrology tool 102 and / or any components therein. In some embodiments, the controller 162 includes one or more processors 164. For example, the one or more processors 164 may be configured to execute a set of program instructions maintained in a memory device 166 or memory. The one or more processors 164 of the controller 162 may include any processing element known in the art. In this sense, the one or more processors 164 may include any microprocessor-type device configured to execute algorithms and / or instructions.

[0073] The one or more processors 164 of the controller 162 may include any processor or processing element known in the art. For purposes of this disclosure, the term "processor" or "processing element" may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application specific integrated circuits (ASIC) devices, one or more field programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, the one or more processors 164 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in a memory). In some embodiments, the one or more processors 164 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute programs that operate or are configured to operate with the overlay metrology system 100 as described throughout this disclosure. Additionally, different subsystems of the overlay metrology system 100 may include processors or logic elements suitable for performing at least some of the steps described in this disclosure. Thus, the above description should not be construed as a limitation on the embodiments of the present disclosure, but merely as an example. Additionally, the steps described throughout the present disclosure may be performed by a single controller, or alternatively, by multiple controllers. Additionally, the controller 162 may include one or more controllers housed within a common housing or multiple housings. In this manner, any controller or combination of controllers may be separately packaged as a module suitable for integration into the overlay metrology system 100.

[0074] The memory device 166 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 164. For example, the memory device 166 may include a non-transitory memory medium, and as another example, the memory device 166 may include, but is not limited to, a read-only memory (ROM), a random access memory (RAM), a magnetic or optical memory device (e.g., disk), a magnetic tape, a solid-state drive, and the like. Additionally, it should be noted that the memory device 166 may be housed within a common controller housing along with one or more processors 164. In some embodiments, the memory device 166 may be located remotely relative to the physical location of the one or more processors 164 and the controller 162. For example, one or more processors 164 of the controller 162 may access a remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, etc.).

[0075] The controller 162 may direct or receive data (e.g., via control signals) from the overlay metrology tool 102 or any components therein. The controller 162 may be further configured to perform any of the various process steps described throughout this disclosure.

[0076] In some embodiments, the overlay metrology system 100 includes a user interface 168 communicatively coupled to the controller 162. In some embodiments, the user interface 168 may include, but is not limited to, one or more desktops, laptops, tablets, and the like. In some embodiments, the user interface 168 includes a display used to display data of the overlay metrology system 100 to a user. The display of the user interface 168 may include any display known in the art. For example, the display may include, but is not limited to, a liquid crystal display (LCD), an organic light emitting diode (OLED) based display, or a CRT display. Those skilled in the art should recognize that any display device capable of integration with the user interface 168 is suitable for implementation in the present disclosure. In some embodiments, a user may input selections and / or commands in response to data displayed to the user via a user input device of the user interface 168.

[0077] Reference is now made to Figure 4, which is a flow diagram illustrating steps performed in a method 400 for overlay metrology in accordance with one or more embodiments of the present disclosure. Applicant notes that the embodiments and enabling techniques previously described herein in the context of overlay metrology system 100 should be construed as extending to method 400. However, it is further noted that method 400 is not limited to the architecture of overlay metrology system 100.

[0078] In some embodiments, the method 400 includes step 402 of simultaneously illuminating a first directional cell of a cell pair on the overlay target with a first illumination beam distribution having a first linear polarization and simultaneously illuminating a second directional cell of the cell pair with a second illumination beam distribution having a second linear polarization that is orthogonal to the first linear polarization. For example, the overlay target may include two or more cell pairs having orthogonally oriented grating-over-grating structures as shown in FIGS. 2A-2B.

[0079] Step 402 may include illuminating the first and second directional cells with any number or configuration of illumination beams, and the first and second illumination beam distributions may be controlled separately. In some embodiments, step 404 may include underfilling both the first and second directional cells with the first and second illumination beam distributions. Additionally, step 402 may include synchronously scanning the first and second illumination beam distributions over the first and second directional cells, which may reduce target noise and / or speckle.

[0080] In some embodiments, the method 400 includes collecting 404 light from the sample (e.g., a first direction cell and a second direction cell) as collected light. In some embodiments, the method 400 includes directing 406 a portion of the collected light associated with a first direction cell of the two or more cell pairs to a first collection channel. In some embodiments, the method 400 includes directing 408 a portion of the collected light associated with a second direction cell of the two or more cell pairs to a second collection channel. In this manner, collected light indicative of an overlay of the first direction cell and the second direction cell can be collected in parallel. For example, step 406 and / or step 408 may be implemented using any combination of polarizing filters, pupil plane filters, or field plane filters, such as, but not limited to, those shown in the context of the overlay metrology system 100.

[0081] In some embodiments, method 400 includes generating 410 a first overlay measurement along a first direction based on data associated with a first directional cell of two or more cell pairs (e.g., based on repeating steps 402-408 for two or more cell pairs). In some embodiments, method 400 includes generating 412 a second overlay measurement along a second direction based on data associated with a second directional cell of the two or more cell pairs.

[0082] It is contemplated herein that method 400 may advantageously provide parallel measurements of target cells with minimal or negligible crosstalk of collected light. In this manner, method 400 may reduce the required number of sequential measurements of a given overlay target by a factor of two relative to techniques in which all cells are measured sequentially. Moreover, this increase in throughput may not come at the expense of measurement accuracy or sensitivity.

[0083] The subject matter described herein illustrates different components that are sometimes included within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and that in fact many other architectures that achieve the same functionality may be implemented. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Thus, any two components herein that are combined to achieve a particular functionality can be considered to be "associated" with each other such that the desired functionality is achieved, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" with each other to achieve the desired functionality, and any two components capable of being so associated can also be considered to be "couplable" with each other to achieve the desired functionality. Specific examples of components that can be coupled include, but are not limited to, 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.

[0084] It is believed that the present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes can be made in the form, construction and arrangement of the elements without departing from the disclosed subject matter or sacrificing all of its material advantages. The forms described are merely illustrative, and it is the intent of the following claims to embrace and include such modifications. It is to be understood, further, that the invention is defined by the appended claims.

Claims

1. An overlay measurement tool, comprising: An illumination source configured to generate a first illumination beam distribution having a first linearly polarized light and a second illumination beam distribution having a second linearly polarized light orthogonal to the first linearly polarized light; An illumination subsystem configured to sequentially illuminate two or more cell pairs of an overlay target on a sample, wherein a specific one of the two or more cell pairs has a first direction cell having a grating-over-grating structure with periodicity along a first direction and a second direction cell having a grating-over-grating structure with periodicity along a second direction orthogonal to the first direction, and simultaneously illuminates the first direction cell with the first illumination beam distribution and the second direction cell with the second illumination beam distribution; A collection subsystem, comprising: A first collection channel including one or more first channel detectors on a first channel detection plane; A second collection channel including one or more second channel detectors on a second channel detection plane; An objective lens for condensing the light from the sample as collected light; One or more filtering optical systems for directing a portion of the collected light related to the first direction cell of two or more cell pairs to the first collection channel and a portion of the collected light related to the second direction cell of two or more cell pairs to the second collection channel; A collection subsystem comprising; A controller communicatively coupled to the first and second collection channels, comprising: Generating a first overlay measurement value along the first direction based on data related to the first direction cell of two or more cell pairs from the one or more first channel detectors; Generating a second overlay measurement value along the second direction based on data related to the second direction cell of two or more cell pairs from the one or more second channel detectors; One or more processors configured to execute program instructions for performing the above steps; An overlay measurement tool comprising the above components.

2. One or more beam scanning optical systems configured to adjust the separation between the first and second illumination beam distributions. The overlay measurement tool according to claim 1, further comprising the above components.

3. The one or more beam scanning optical systems adjust a separation between the first illumination beam distribution and the second illumination beam distribution to center the first illumination beam distribution and the second illumination beam distribution on the first direction cells and the second direction cells of the illuminated cells among two or more cell pairs. The overlay measurement tool according to claim 2, characterized in that.

4. A first illumination field stop that defines a spatial range of the first illumination beam distribution, A second illumination field stop that defines a spatial range of the second illumination beam distribution, And at least one of the first illumination field stop or the second illumination field stop is adjustable such that the first illumination beam distribution and the second illumination beam distribution are centered on the first illumination field stop and the second illumination field stop when the separation between the first illumination beam distribution and the second illumination beam distribution is adjusted, and is synchronized with the one or more beam scanning optical systems. The overlay measurement tool according to claim 2.

5. A first collection field stop for defining a collection field for the first collection channel, A second collection field stop for defining a collection field for the second collection channel, And at least one of the first collection field stop or the second collection field stop is adjustable such that the first collection field and the second collection field are aligned with the first illumination beam distribution and the second illumination beam distribution when the separation between the first illumination beam distribution and the second illumination beam distribution is adjusted, and is synchronized with the one or more beam scanning optical systems. The overlay measurement tool according to claim 2.

6. One or more beam scanning optical systems configured to modulate the first and second illumination beam distributions across the first direction cells and the second direction cells of the illuminated cells among two or more cell pairs during measurement. The overlay measurement tool according to claim 1, further comprising.

7. The lattice-over-lattice structure in the first direction cells of the two or more cell pairs is arranged along the first row of the overlay target, and the lattice-over-lattice structure in the second direction cells of the two or more cell pairs is arranged along the second row of the overlay target. The overlay measurement tool according to claim 1, characterized in that.

8. The lattice over-lattice structure in the first-direction cells of the two or more cell pairs has different intended overlay offsets along the first direction, and the lattice over-lattice structure in the second-direction cells of the two or more cell pairs has different intended overlay offsets along the second direction. The overlay measurement tool according to claim 1, characterized in that.

9. The two or more cell pairs further include a first cell pair and a second cell pair, and the first-direction cells of the first cell pair and the first-direction cells of the second cell pair have equal and opposite intended offsets along the first direction, and the second-direction cells of the first cell pair and the second-direction cells of the second cell pair have equal and opposite intended offsets along the second direction. The overlay measurement tool according to claim 1, characterized in that.

10. The overlay measurement tool according to claim 1, characterized in that the second illumination beam distribution is equal to the first illumination beam distribution.

11. The overlay measurement tool according to claim 1, characterized in that the second illumination beam distribution is different from the first illumination beam distribution.

12. The overlay measurement tool according to claim 1, characterized in that the second illumination beam distribution is different from the first illumination beam distribution based on at least one of a plurality of illumination beams, the wavelength of one or more illumination beams, or the incident angle of one or more illumination beams.

13. At least one of the first or the second illumination beam distributions comprises a single illumination beam The overlay measurement tool according to claim 1, characterized in that.

14. The first illumination beam distribution comprises two illumination beams of a dipole distribution aligned along the first direction, and the second illumination beam distribution comprises two illumination beams of a dipole distribution aligned along the second direction. The overlay measurement tool according to claim 1, characterized in that.

15. The one or more filtering optical systems include at least one of one or more polarization filtering optical systems, one or more pupil plane filters, or one or more field plane filters. The overlay measurement tool according to claim 1, characterized in that.

16. The one or more polarization filtering optical systems ​ One or more polarization beam splitters that direct the portion of the collected light having the first linearly polarized light toward the first collection channel and the portion of the collected light having the second linearly polarized light toward the second collection channel. The overlay measurement tool according to claim 15, characterized by comprising the same. **Claim 17** The one or more polarization filtering optical systems At least one of a first polarizer in the first collection channel oriented to pass the first linearly polarized light or a second polarizer in the second collection channel oriented to pass the second linearly polarized light. The overlay measurement tool according to claim 15, characterized by comprising the same. **Claim 18** The one or more pupil plane filters At least one of a first aperture in the pupil plane of the first collection channel that passes the portion of the collected light related to diffraction along the first direction, a second aperture in the pupil plane of the second collection channel that passes the portion of the collected light related to diffraction along the second direction, or a beam splitter in the common pupil plane of the first and second collection channels that directs the portion of the collected light related to diffraction toward the first collection channel along the first direction and the portion of the collected light related to diffraction toward the second collection channel along the second direction. The overlay measurement tool according to claim 15, characterized by comprising the same. **Claim 19** The one or more field plane filters At least one of an aperture in the field plane of the first collection channel for passing the portion of the collected light related to the first direction cell or an aperture in the field plane of the second collection channel for passing the portion of the collected light related to the second direction cell. The overlay measurement tool according to claim 15, characterized by comprising the same. **Claim 20** A translation stage that sequentially arranges two or more cell pairs for illumination by an illumination subsystem. The overlay measurement tool according to claim 1, further comprising the same. **Claim 21** One or more focus control optical systems for adjusting at least one focal position of the first or second illumination beam distribution. The overlay measurement tool according to claim 1, further comprising the same. **Claim 22** At least one of the first or second detection planes Is a pupil plane The overlay measurement tool according to claim 1, characterized by comprising the same. **Claim 23** At least one of the first or second detection planes is a field plane The overlay measurement tool according to claim 1, characterized in that it comprises

24. An overlay measurement tool, An illumination source configured to generate a first illumination beam distribution having a first linearly polarized light and a second illumination beam distribution having a second linearly polarized light orthogonal to the first linearly polarized light, An illumination subsystem for sequentially illuminating two or more cell pairs of an overlay target on a sample, wherein a specific one of the two or more cell pairs has a lattice-over-lattice structure having periodicity along a first direction A first-direction cell, and a second-direction cell having a lattice-over-lattice structure having periodicity along a second direction orthogonal to the first direction, an illumination subsystem; comprising The illumination subsystem A first illumination channel that directs the first illumination beam distribution to a first-direction cell of one of the two or more cell pairs, wherein the first illumination beam distribution includes one or more first illumination beams having the first linearly polarized light, the first illumination channel; A second illumination channel that directs a second illumination beam distribution to a second-direction cell of one of the two or more cell pairs simultaneously with the first illumination beam distribution, wherein the second illumination beam distribution includes one or more second illumination beams having the second linearly polarized light, the second illumination channel; comprising A collection subsystem, A first collection channel including one or more first channel detectors on a first channel detection plane, A second collection channel including one or more second channel detectors on a second channel detection plane, An objective lens that condenses the light from the sample as collected light, A polarization beam splitter that directs a portion of the collected light related to the first-direction cell having the first linearly polarized light to the first collection channel and a portion of the collected light related to the second-direction cell of two or more cell pairs having the second linearly polarized light to the second collection channel, A collection subsystem comprising A controller communicatively coupled to the first and second collection channels, Generating a first overlay measurement value along the first direction based on data related to the first-direction cell of the two or more cell pairs from the one or more first channel detectors, Generating a second overlay measurement value along the second direction based on data related to the second direction cells of the two or more cell pairs from the one or more second channel detectors; A controller including one or more processors configured to execute program instructions to cause the above to be performed; An overlay measurement tool comprising the above. **Claim 25** The overlay measurement tool according to claim 24, further comprising at least one of: a first aperture within the pupil plane of the first collection channel that passes a portion of the collected light related to diffraction along the first direction; a second aperture within the pupil plane of the second collection channel that passes a portion of the collected light related to diffraction along the second direction; or a beam splitter within a common pupil plane of the first and second collection channels that directs a portion of the collected light related to diffraction along the first direction to the first collection channel and a portion of the collected light related to diffraction along the second direction to the second collection channel. **Claim 26** The overlay measurement tool according to claim 24, further comprising at least one of: an aperture within the field plane of the first collection channel for passing a portion of the collected light related to the first direction cell; or an aperture within the field plane of the second collection channel for passing a portion of the collected light related to the second direction cell. **Claim 27** One or more beam scanning optical systems configured to adjust the separation between the first and second illumination beam distributions; The overlay measurement tool according to claim 24, further comprising the above. **Claim 28** The overlay measurement tool according to claim 27, wherein the one or more beam scanning optical systems adjust the separation between the first and second illumination beam distributions to center the first and second illumination beam distributions on the first direction cell and the second direction cell of the illuminated cells of two or more cell pairs. **Claim 29** A first illumination field stop that defines the spatial extent of the first illumination beam distribution; A second illumination field stop that defines the spatial extent of the second illumination beam distribution; further comprising, at least one of the first illumination field stop or the second illumination field stop being adjustable such that the first illumination beam distribution and the second illumination beam distribution are centered on the first illumination field stop and the second illumination field stop when the separation between the first illumination beam distribution and the second illumination beam distribution is adjusted, and being synchronized with the one or more beam scanning optical systems, The overlay measurement tool according to claim 27.

30. a first collection field stop defining a collection field for the first collection channel, a second collection field stop defining a collection field for the second collection channel, further comprising, at least one of the first collection field stop or the second collection field stop being adjustable such that the first collection field and the second collection field are aligned with the first illumination beam distribution and the second illumination beam distribution when the separation between the first illumination beam distribution and the second illumination beam distribution is adjusted, and being synchronized with the one or more beam scanning optical systems, The overlay measurement tool according to claim 27.

31. An overlay measurement method, comprising: generating a first illumination beam distribution having a first linearly polarized light and a second illumination beam distribution having a second linearly polarized light orthogonal to the first linearly polarized light; sequentially illuminating two or more cell pairs of an overlay target on a sample using an illumination system, each of the two or more cell pairs including a first-direction cell having a grating-over-grating structure having periodicity along a first direction and a second-direction cell having a grating-over-grating structure having periodicity along a second direction orthogonal to the first direction, the illumination system simultaneously illuminating the first-direction cell with the first illumination beam distribution and the second-direction cell with the second illumination beam distribution; collecting light from the sample as collected light; directing a portion of the collected light related to the first-direction cells of the two or more cell pairs to a first collection channel; directing a portion of the collected light related to the second-direction cells of the two or more cell pairs to a second collection channel; generating a first overlay measurement value along the first direction based on data related to the first-direction cells of the two or more cell pairs; Generating a second overlay measurement value along the second direction based on data related to the second-direction cells of the two or more cell pairs; An overlay measurement method comprising the above.

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