Scanning Scatterometry Overlay Metrology

Abstract

The overlay metrology system may include an illumination source generating an illumination beam and one or more illumination optics directing the illumination beam to an overlay target on the specimen during scanning motion of the specimen relative to the illumination beam along a scan direction, the target comprising one or more cells having Moire structures. The system may further include two photodetectors at a pupil plane for multiple Moire orders or overlapping diffractions from the Moire structures. The system may then generate an overlay measurement based on time-varying interference signals captured by the detectors as the specimen is scanned.

Description

[Technical field]

[0001] The present disclosure relates generally to overlay metrology, and more specifically to scanning scatterometry overlay metrology. [Background technology]

[0002] Overlay metrology is generally the measurement of the relative alignment of layers on a specimen, such as, but not limited to, a semiconductor device. Overlay metrology, or overlay error metrology, is generally the measurement of the misalignment of fabricated features on two or more specimen layers. Proper alignment of fabricated features on multiple specimen layers is typically required for the device to function properly. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2021 / 0364279 [Patent Document 2] U.S. Pat. No. 10,824,079 [Patent Document 3] U.S. Pat. No. 10,197,389 [Patent Document 4] U.S. Patent No. 7,440,105 [Patent Document 5] U.S. Pat. No. 1,164,307 [Patent Document 6] US Patent Application Publication No. 2021 / 0072650 [Patent Document 7] US Patent Application Publication No. 2022 / 0034652 [Patent Document 8] U.S. Pat. No. 1,107,3768 [Patent Document 9] US Patent Application Publication No. 2021 / 0364935 Summary of the Invention [Problem to be solved by the invention]

[0004] The demand for smaller feature sizes and higher feature densities has led to a corresponding increase in the demand for accurate and efficient overlay metrology. In metrology systems, metrology data for a specimen is typically generated by inspecting, e.g., measuring, dedicated metrology targets distributed across the specimen. To this end, the specimen is typically mounted on a translation stage and translated such that the metrology targets are moved sequentially into the measurement field of view. In typical metrology systems employing the move-and-measure (MAM) method, the specimen remains stationary during each measurement. However, time is required to stabilize the translation stage prior to measurement, which can adversely affect throughput. It is therefore desirable to provide a system and method that can remedy the above-mentioned shortcomings. [Means for solving the problem]

[0005] An overlay metrology system is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system includes an illumination subsystem that includes an illumination source that generates an illumination beam and one or more illumination optics that direct the illumination beam to an overlay target on the specimen as the specimen is scanned relative to the illumination beam along a scan direction during execution of a metrology recipe. In one exemplary embodiment, the overlay target associated with the metrology recipe includes one or more cells that include a moiré structure formed as an overlapping grating structure in which gratings with different pitches overlap, and the overlapping grating structures are periodic along at least one of the scan direction and the cross-scan direction. In one example embodiment of the system, the collection subsystem includes a first photodetector located at a first location in the pupil plane and configured to capture at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the one or more cells when a metrology recipe is performed, and a second photodetector located at a second location in the pupil plane and configured to capture at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the one or more cells when a metrology recipe is performed. In one example embodiment of the system, the controller receives time-varying interference signals associated with the Moire structure in the one or more cells from the first and second photodetectors when the overlay target is scanned in accordance with the metrology recipe, and determines an overlay error between the first and second layers of the specimen based on the time-varying interference signals.

[0006] An overlay metrology system is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system includes an illumination subsystem having a first illumination channel and a second illumination channel for illuminating an overlay target on a specimen when the translation stage scans the specimen along a stage scan direction during execution of a metrology recipe. In one exemplary embodiment, the overlay target associated with the metrology recipe includes a first set of cells having a moiré structure formed as an overlapping grating structure with unequal pitches along a first direction and a second set of cells having a moiré structure formed as an overlapping grating structure with unequal pitches along a second direction orthogonal to the first direction, and the stage scan direction is angled with respect to the first and second directions. In one exemplary embodiment, the first and second illumination channels illuminate separate cells on the overlay target that are separated along a direction orthogonal to the stage scan direction. In one exemplary embodiment, the system includes a collection subsystem having a first detection channel and a second detection channel, which are associated with the first illumination channel and the second illumination channel, respectively. In one exemplary embodiment, a particular detection channel includes a first photodetector located at a first location in the pupil plane and configured to capture at least one of multiple Moire diffractions and multiple overlapping diffractions from the Moire structure in the one or more cells when the metrology recipe is performed, and a second photodetector located at a second location in the pupil plane and configured to capture at least one of multiple Moire diffractions and multiple overlapping diffractions from the Moire structure in the one or more cells when the metrology recipe is performed. In one exemplary embodiment, the system includes a controller that receives time-varying interference signals from the first and second photodetectors of the first and second detection channels, respectively, when the overlay target is scanned in accordance with the metrology recipe, and determines an overlay error between the first and second layers of the specimen based on the time-varying interference signals.

[0007] An overlay metrology system is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment of the system, an illumination subsystem includes an illumination source that generates an illumination beam. In an exemplary embodiment, the illumination subsystem also includes a scanning mirror that scans the illumination beam across an overlay target on the specimen along a stage scan direction perpendicular to the beam scan direction when the translation stage translates the specimen along a stage scan direction perpendicular to the beam scan direction during execution of a metrology recipe. In an exemplary embodiment, the overlay target associated with the metrology recipe includes one or more cells, the or each cell having a moiré structure formed as an overlapping grating structure in which gratings with different pitches overlap each other and a periodic overlapping grating structure along at least one of the scan direction and the direction perpendicular to the stage scan direction, the one or each cell being distributed along a diagonal direction angled with respect to the stage scan direction. In one illustrative embodiment of the system, the collection subsystem includes a first photodetector located at a first location in the pupil plane and configured to capture at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the one or more cells during execution of the metrology recipe, and a second photodetector located at a second location in the pupil plane and configured to capture at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the one or more cells during execution of the metrology recipe. In one illustrative embodiment of the system, a controller receives time-varying interference signals from the first and second photodetectors during scanning motion of the overlay target during execution of the metrology recipe, and determines an overlay error between the first and second layers of the specimen based on the time-varying interference signals.

[0008] An overlay metrology system is disclosed according to one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system includes an illumination subsystem including a first illumination channel providing a first illumination beam, a second illumination channel providing a second illumination beam, and one or more beam scanners for scanning the first and second illumination beams across portions of an overlay target on the specimen along a beam scan direction when a translation stage is used to scan the specimen along a stage scan direction during execution of a metrology recipe. In one exemplary embodiment, the overlay target associated with the metrology recipe includes a first set of cells having a moiré structure formed as an overlapping grating structure with different pitches along the stage scan direction, and a second set of cells having a moiré structure formed as an overlapping grating structure with different pitches along the beam scan direction. In one exemplary embodiment, the first and second illumination channels illuminate separate cells of the overlay target that are separated along the beam scan direction. In one exemplary embodiment, the system includes a collection subsystem having a first detection channel and a second detection channel associated with the first illumination channel and the second illumination channel, respectively. In one exemplary embodiment, a particular detection channel includes a first photodetector located at a first location in the pupil plane and configured to capture at least one of multiple Moire diffractions and multiple overlapping diffractions from the Moire structure in the one or more cells during execution of the metrology recipe, and a second photodetector located at a second location in the pupil plane and configured to capture at least one of multiple Moire diffractions and multiple overlapping diffractions from the Moire structure in the one or more cells during execution of the metrology recipe. In one exemplary embodiment, the system includes a controller that receives time-varying interference signals from the first and second photodetectors of the first and second detection channels, respectively, during scanning of the overlay target during execution of the metrology recipe, and determines an overlay error between the first and second layers of the specimen based on the time-varying interference signals.

[0009] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention.

[0010] The numerous advantages of the present disclosure may be better appreciated by those skilled in the art by reference to the accompanying drawings, in which: [Brief description of the drawings]

[0011] [Figure 1A] FIG. 1 is a conceptual diagram of a system for performing scatterometry overlay metrology on an overlay target having at least one moire structure in accordance with one or more embodiments of the present disclosure. [Figure 1B] 1 is a schematic diagram of an overlay metrology tool according to one or more embodiments of the present disclosure. [Figure 2A] FIG. 2 is a top view of a cell of an overlay target having a moire structure in accordance with one or more embodiments of the present disclosure. [Figure 2B] FIG. 2B is a side view of a single cell of the overlay target of FIG. 2A on a substrate in accordance with one or more embodiments of the present disclosure. [Figure 2C] FIG. 2 is a side view of an overlay target having two cells with different moire structure configurations suitable for overlay measurement along a specific measurement direction in accordance with one or more embodiments of the present disclosure. [Figure 3A] FIG. 2 illustrates a top view of an illumination pupil at an illumination pupil plane of an overlay metrology tool in accordance with one or more embodiments of the present disclosure. [Figure 3B] FIG. 3B is a top view of a collection pupil at a collection pupil plane of an overlay metrology tool according to one or more embodiments of the present disclosure, showing the moire diffraction lobes due to the moire structure associated with the illumination profile of FIG. 3A. [Figure 3C]FIG. 3B is a top view of a collection pupil of an overlay metrology tool according to one or more embodiments of the present disclosure, showing a separated first order Moire diffraction of the illumination profile of FIG. 3A and the intrinsic Moire structure. [Figure 3D] FIG. 3B is a top view of a collection pupil at a collection pupil plane of an overlay metrology tool according to one or more embodiments of the present disclosure, showing overlapping first order diffractions of the illumination profile of FIG. 3A and intrinsic moire structures. [Figure 4] FIG. 1 is a conceptual diagram of a specimen illustrating the placement of overlay targets and corresponding measurement paths for measuring the overlay targets in accordance with one or more embodiments of the present disclosure. [Diagram 5] FIG. 1 is a top view of a 1D overlay target having two cells aligned along the stage scan direction, each of which has a moire structure that exhibits periodicity along the stage scan direction, in accordance with one or more embodiments of the present disclosure. [Figure 6A] FIG. 2 is a top view of a first 2D overlay target having cells with periodicity in a diagonal direction relative to the stage scan direction, in accordance with one or more embodiments of the present disclosure. [Figure 6B] FIG. 13 is a top view of a second 2D overlay target having cells with periodicity in a diagonal direction relative to the stage scan direction, in accordance with one or more embodiments of the present disclosure. [Figure 7A] FIG. 2 is a top view of a first overlay target suitable for overlay measurement along the Y direction with a scanning motion of an illumination beam along the +Y direction in accordance with one or more embodiments of the present disclosure. [Figure 7B] FIG. 2 is a top view of a second overlay target suitable for overlay measurement along the X direction with a scanning motion of an illumination beam along the +Y direction in accordance with one or more embodiments of the present disclosure. [Figure 7C] FIG. 2 is a top view of a first overlay target suitable for overlay measurement along the Y direction with a scanning motion of an illumination beam along the −Y direction in accordance with one or more embodiments of the present disclosure. [Figure 7D]FIG. 2 is a top view of a second overlay target suitable for overlay measurement along the X direction with a scanning motion of an illumination beam along the −Y direction in accordance with one or more embodiments of the present disclosure. [Figure 8A] FIG. 2 is a top view of a first overlay target suitable for 2D overlay metrology with two parallel illumination beams in accordance with one or more embodiments of the present disclosure. [Figure 8B] FIG. 2 is a top view of a second overlay target suitable for 2D overlay metrology with two parallel illumination beams in accordance with one or more embodiments of the present disclosure. [Figure 9] FIG. 1 is a flow diagram illustrating steps performed in a method for scanning overlay metrology of an overlay target having at least one moire structure, in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings. The present disclosure will be specifically shown and described with reference to certain embodiments and their individual features. The embodiments described herein should be understood as illustrative and not limiting. As will be understood by those skilled in the art, various changes and modifications in form and detail can be made without departing from the spirit and scope of the present disclosure.

[0013] Embodiments of the present disclosure are directed to scanning scatterometry overlay using overlay targets having moire structures, for example, the moire structures can comprise grating-over-grating structures whose constituent gratings have distinct periods.

[0014] For purposes of this disclosure, the term scatterometry metrology is used broadly to encompass scatterometry-based metrology and diffraction-based metrology, i.e., illuminating a sample having periodic features on one or more sample layers with an illumination beam having a limited angular range and collecting one or more individual diffraction orders for measurement. Additionally, the term scanning metrology is used to describe metrology measurements that occur when the sample is in motion relative to the illumination used for the measurement. In general, scanning metrology can be performed by moving the sample, the illumination, or both.

[0015] As contemplated herein, scatterometry overlay metrology is typically performed using a scatterometry overlay target having one or more grating-over-grating structures formed as diffraction gratings exhibiting a common pitch (e.g., period) and periodicity direction on the two sample layers in the overlap region. Various techniques for determining overlay metrology with such scatterometry overlay targets are outlined in U.S. Pat. No. 6,399,433, published on November 25, 2021, U.S. Pat. No. 6,399,433, published on November 3, 2020, and U.S. Pat. No. 6,399,433, published on February 9, 2019, all of which are incorporated herein by reference in their entireties.

[0016] Further contemplation of the present application has revealed that overlay targets with grating-over-grating structures (referred to herein as moiré structures), in which gratings with different pitches overlap, can exploit the moiré effect to generate a moiré diffraction pattern. The moiré diffraction pattern can be related to the overlay by a gain factor related to the difference between the pitches of the constituent gratings. As a result, such overlay targets can provide highly sensitive overlay metrology. Overlay metrology using overlay targets with moiré grating structures is outlined in U.S. Pat. No. 6,399,433, issued Oct. 21, 2008, U.S. Pat. No. 6,399,433, issued Nov. 2, 2021, U.S. Pat. No. 6,399,433, issued Mar. 21, 2021, and U.S. Pat. No. 6,399,433, issued Feb. 9, 2019, all of which are incorporated herein by reference in their entireties.

[0017] However, overlay targets with moiré structure targets present additional metrology challenges related to the common pitch grating-over-grating structure. Because the moiré structure's constituent gratings have different pitches, the physical offset between the individual lines of the constituent gratings varies across the cell. That is, the apparent overlay (or apparent overlay error) observable using conventional techniques varies depending on the specific location of the illumination beam used to characterize the target. As a result, data over an extended portion of the cell is generally required to capture the position-dependent offsets and fully characterize the moiré structure. While static image-based systems can capture such position-dependent differences in apparent overlay (e.g., as position-dependent phase) within a single image, they suffer from the typical throughput challenges discussed above. Furthermore, static scatterometry-based systems that utilize illumination beams smaller than the cell (e.g., underfill illumination) may fail to capture position-dependent differences in apparent overlay across the moiré structure.

[0018] The presently disclosed embodiments are directed to a scanning overlay metrology system and method based on time-varying interference signals from a Moiré structure at a collection pupil plane. As contemplated herein, metrology conditions that lead to multiple overlapping or multiple Moiré diffraction orders (e.g., complex, double, etc.) from the constituent gratings of the Moiré structure may lead to interference. Such interference signals may contain information about asymmetries in the target structure, such as, but not limited to, overlay between top and bottom gratings. As further contemplated herein, scanning motion of the Moiré structure relative to an illumination beam (or vice versa) may characterize the position-dependent overlay of the Moiré structure, which may then allow for discriminatory determination of asymmetries, such as, but not limited to, overlay.

[0019] Certain embodiments of the present disclosure are directed to scanning scatterometry overlay metrology based on time-varying interference signals associated with overlapping diffraction lobes from above and below gratings of a moiré structure or associated with moiré diffraction from the moiré structure. Overlay metrology of a common pitch grating-over-grating structure based on time-varying interference signals at a collection pupil is outlined in U.S. Patent No. 6,399,233, published Feb. 3, 2022, and is incorporated herein by reference in its entirety. In U.S. Patent No. 6,399,233, overlay metrology of a common pitch grating-over-grating structure is generated based on a comparison of time-varying interference patterns in overlap regions between 0th and ±1st diffraction orders generated during a scan and captured by a photodetector in those regions. In accordance with the present contemplation, the system and method of U.S. Patent No. 6,399,233 can be adapted, e.g., extended, to perform overlay metrology of a moiré structure. In doing so, certain embodiments of the present disclosure extend or adapt the system and method of U.S. Patent No. 6,399,233 to incorporate differences between the common pitch grating-over-grating structure and the moiré structure. However, the present disclosure is not limited to such extensions or adaptations of the systems and methods of US Pat. No. 6,399,633.

[0020] In certain embodiments of the overlay metrology system, the photodetector is located in the pupil plane at a position corresponding to a moiré diffraction lobe from the moiré structure (e.g., double diffraction from the upper and lower gratings of the moiré structure). For example, the photodetector can be located at a position where the moiré diffraction lobe overlaps with the zeroth diffraction order (e.g., specular reflection). In another embodiment, the photodetector can be located at a position where only the moiré diffraction lobe exists. As contemplated herein, time-varying interference signals (e.g., AC signals) due to the multiple order complex diffractions appear during the scanning measurement and can be captured using the photodetector. For example, by appropriately selecting the characteristics of the moiré structures (e.g., the pitch of the composite gratings) and / or the measurement conditions (e.g., the illumination wavelength, the illumination incidence angle, the collection angle, etc.), the positive and negative order moiré diffractions (e.g., double order diffractions) due to the complex diffractions due to the gratings of the moiré structure can be collected by the system and captured by the photodetector. As contemplated herein, the pitch of the compositional grating of the Moiré structures does not need to be resolved by the overlay system, and furthermore, this configuration allows the pitch of the Moiré structures to be similar to those present in the device features on the specimen, thereby enabling highly accurate overlay measurements and / or relatively small target sizes.

[0021] Certain embodiments of the present disclosure are directed to providing recipes for configuring an overlay metrology tool. An overlay metrology tool can be configured according to a recipe that typically includes a set of parameters for controlling various aspects of overlay metrology, such as, but not limited to, illumination of the specimen, collection of light from the specimen, or position of the specimen during the measurement. In this way, the overlay metrology tool can be configured to perform a specified type of measurement on one or more overlay target designs of interest. For example, a metrology recipe can include illumination parameters, such as, but not limited to, the number of illumination beams, illumination wavelength, illumination pupil distribution (e.g., the distribution of illumination angles and associated illumination intensities at those angles), polarization of incident illumination, or spatial distribution of illumination. According to another example, the metrology recipe can include collection parameters such as, but not limited to, collection pupil distribution (e.g., desired distribution of angular light from the specimen for measurement and associated filtered intensity at those angles), collection field stop settings for selecting specimen portions of interest, polarization of collected light, wavelength filters, position of one or more detectors (e.g., photodetectors), or parameters for controlling the one or more detectors, etc. According to a further example, the metrology recipe can include various parameters related to the specimen position during measurement, such as, but not limited to, specimen height, specimen orientation, whether the specimen is stationary during measurement or whether the specimen is moving during measurement (and associated parameters describing the speed, scan pattern, etc.).

[0022] In certain embodiments, the characteristics of the Moiré structures (e.g., pitch of the composite grating, etc.) and measurement conditions (e.g., illumination wavelength, illumination incidence angle, collection angle, etc.) can be appropriately selected, e.g., engineered (e.g., using a metrology recipe) to produce a specified distribution of Moiré diffraction orders and / or complex diffraction, and further, to position the photodetector in a suitable location to capture those diffraction orders and generate a time-varying interference signal of interest.

[0023] The disclosed systems and methods may be suitable for a wide range of sample layouts, including samples with relatively thin samples and samples with relatively thick sample layers. For example, the disclosed systems and methods may be well suited for samples with relatively thin sample layers, such as, but not limited to, dynamic random access memory (DRAM) structures. In such cases, the intensity distribution of the diffraction orders at the collection pupil may be relatively uniform as described herein, providing a relatively low tolerance for the placement of the photodetectors in the overlap region. However, the disclosed systems and methods may also be suitable for samples with relatively thick layers, where the placement of the photodetectors may be precisely located within the symmetrical regions of the positive and negative diffraction orders. Additionally, the system and / or measurements may be calibrated to improve measurement accuracy.

[0024] As further contemplated herein, the disclosed systems and methods provide high sensitivity overlay metrology at high throughput. For example, in non-imaging configurations, high speed photodetectors can be used that are suitable for high scanning speeds. In one non-limiting example, a photodetector bandwidth of 1 GHz can achieve a scanning speed of approximately 10 centimeters per second on a moire target with a pitch of 1 micron.

[0025] In addition, the disclosed systems and methods can be relatively insensitive to target edge effects, allowing the use of small size targets and a more efficient use of the space on the specimen required for overlay metrology. For example, target edge effects can generally appear as diffracted light in the pupil plane at angles related to the target dimensions. However, the disclosed systems and methods limit the collection of light to a narrow static collection angle range (e.g., related to the size and location of the photodetector in the pupil plane) and capture time-varying data at those angles. Furthermore, according to certain embodiments, the illumination beam can be extended along the grating structure direction (e.g., perpendicular to the periodicity direction) to smooth out target noise related to small fluctuations in the moiré structured features.

[0026] The moiré structures may generally be formed as parts of overlay targets and may generally be located anywhere on the specimen. In certain embodiments, overlay metrology may be performed directly on device features having suitable geometries. In other embodiments, overlay metrology may be performed on dedicated overlay targets and the dedicated overlay targets may be located in any suitable location, including but not limited to within a die or at a scribe line between the dies. In this way, overlay measurements on the overlay targets may be a proxy for overlay of the device features. The dedicated overlay targets may generally have features designed to perform accurate overlay measurements based on a particular overlay metrology technique. Additionally, the overlay target may have one or more metrology cells, and the printed elements in each cell may form moiré structures on the specimen in overlapping areas of one or more layers. The overlay metrology may then be based on any combination of measurements on the various cells of the overlay target. For example, by designing multiple cells of an overlay target with different intentional offsets (e.g., by intentionally misaligning lattice structures in various layers of the specimen with known offset values), the accuracy and / or sensitivity of the measurement can be improved.

[0027] Additional embodiments of the present disclosure are directed to overlay metrology in at least two directions. In some embodiments, an overlay target includes two sets of cells, a first set of cells having moire structures oriented along a first diagonal direction that is different from, but not orthogonal to, the scan direction, and a second set of cells having moire structures oriented along a second diagonal direction that is orthogonal to the first diagonal direction. In this manner, overlay measurements along the first and second diagonal directions can be generated during a scan. Furthermore, the scan can be performed by translating the sample and / or translating one or more illumination beams through a measurement field of view.

[0028] In certain embodiments, the sample is scanned by a translation stage along a stage scan direction, and one or more illumination beams are scanned along a beam scan direction, e.g., a direction perpendicular to the stage scan direction. The overlay target in this configuration can have two sets of cells, where the moiré structures in a first set of cells are periodic along the stage scan direction and the moiré structures in a second set of cells are periodic along the beam scan direction. Furthermore, the illumination beam can follow a diagonal path along each cell during measurement.

[0029] Additional embodiments of the present disclosure are directed to simultaneous illumination of an overlay target with two or more spatially separated illumination beams. For example, an overlay target may have two or more parallel rows of cells, with one or more cells within each row distributed along the stage scan direction. In this manner, two or more illumination beams may simultaneously illuminate two or more rows of cells for parallel metrology while the specimen is scanned along the stage scan direction. Furthermore, each of the spatially separated illumination beams may have different optical parameters, such as, but not limited to, polarization or wavelength. This type of optical parameter multiplexing may provide various benefits, including, but not limited to, improved measurement accuracy and / or sensitivity by generating metrology data with multiple optical configurations, or providing an efficient mechanism for separating measurement light coming from the specimen associated with different illuminated cells. It is noted that the use of simultaneous illumination of multiple cells may also be beneficial in the context of metrology systems designed for stationary targets.

[0030] As contemplated herein, the moiré-structured scatterometry overlay metrology disclosed herein can provide numerous benefits. For example, the ability to capture metrology signals indicative of overlay while the specimen is in scanning motion can eliminate stage acceleration / deceleration times required to capture stationary target images, thus providing a relatively high measurement throughput. This can significantly increase the number of overlay measurements within a given time period. In another example, the disclosed systems and methods can utilize a relatively large portion of the pupil, providing a high light budget and corresponding signal-to-noise ratio benefits. In another example, the disclosed systems and methods can provide a straightforward extension of current scatterometry overlay metrology architectures and targets to scanning mode metrology. For example, systems designed for pupil plane imaging can be modified or supplemented to incorporate photodetectors that generate time-varying interference signals as disclosed herein. As another example, as previously discussed, the relative insensitivity to target edge effects and the provision of noise smoothing through spot shape control allows the use of relatively small targets, thereby facilitating both high speed measurements and efficient use of space above the specimen. Of note, these considerations may also apply to metrology systems designed for stationary targets.

[0031] Further contemplation herein reveals that the scatterometry overlay metrology of the moiré structures disclosed herein can be performed in combination with additional scanning scatterometry overlay metrology techniques. According to certain embodiments, the generation of a time-varying interference signal using two pupil plane photodetectors can be combined with image plane scatterometry overlay metrology techniques. For example, image plane scatterometry overlay metrology is generally described in U.S. Patent Application No. 17 / 140999, filed January 4, 2021, which is incorporated herein by reference in its entirety.

[0032] 1-9, a scatterometry overlay metrology system and method will now be described in detail in accordance with one or more embodiments of the present disclosure.

[0033] FIGURE 1A is a conceptual diagram of an overlay metrology system 100 for performing scatterometry overlay metrology on an overlay target having at least one moiré structure, in accordance with one or more embodiments of the present disclosure. The overlay metrology system 100 of certain embodiments includes an overlay metrology tool 102 for performing scatterometry overlay metrology on a specimen 104. For example, the overlay metrology tool 102 may perform scatterometry overlay metrology on portions of the specimen 104 that have moiré structures, such as, but not limited to, a dedicated overlay target. FIGURE 1B is a schematic diagram of the overlay metrology tool 102, in accordance with one or more embodiments of the present disclosure.

[0034] In certain embodiments, the overlay metrology tool 102 includes an illumination subsystem 106 that generates illumination in the form of one or more illumination beams 108 to illuminate the specimen 104, and a collection subsystem 110 that collects light from the illuminated specimen 104. For example, the illumination beams 108 can be angularly limited on the specimen 104, thereby causing discrete diffraction orders due to Moiré structures (e.g., within one or more cells of an overlay target). Additionally, the illumination beams 108 can be spatially limited, thereby causing a designated portion of the specimen 104 to be illuminated. For example, each of the illumination beams 108 can be spatially limited to illuminate a particular cell of the overlay target. In certain embodiments, the illumination beams 108 can underfill a particular cell of the overlay target.

[0035] At least some of the diffraction orders of the illumination beam 108 from the Moiré structure may then be collected by a collection subsystem 110. The collection subsystem 110 may further include at least two photodetectors 112 located in a collection pupil plane 114 at locations of the time-varying interference signal indicative of overlay. For example, as described in more detail below, suitable locations for the photodetectors 112 may include, but are not limited to, locations of positive and negative Moiré diffraction orders (e.g., multiple diffraction orders, double diffraction orders, etc.) and locations of overlap between diffraction orders of the constituent gratings of the Moiré structure (e.g., overlap regions between +1 diffraction orders of upper and lower gratings and overlap regions between -1 diffraction orders of upper and lower gratings).

[0036] In certain embodiments, the overlay metrology tool 102 includes a translation stage 116 that scans the specimen 104 through a field of view of the overlay metrology tool 102 during measurement to perform scanning metrology.

[0037] In certain embodiments, the overlay metrology tool 102 includes a beam scanning subsystem 118 configured to control, e.g., modify, a position of the at least one illumination beam 108 on the specimen 104. For example, the beam scanning subsystem 118 can cause the illumination beam 108 to scan in a direction that is orthogonal to a scanning direction (e.g., a direction in which the translation stage 116 scans the specimen 104) during measurement.

[0038] 2A-3B, the collection of diffraction orders from the moire structures and the placement of photodetector 112 for scanning scatterometry overlay metrology will now be described in detail in accordance with one or more embodiments of the present disclosure.

[0039] FIG 2A is a top view of a cell 202 of an overlay target 204 having a moiré structure 206 in accordance with one or more embodiments of the present disclosure. FIG 2B is a side view of a single cell 202 of the overlay target 204 of FIG 2A on a substrate 208 in accordance with one or more embodiments of the present disclosure. In certain embodiments, the moiré structure 206 includes a first layer grating 210 (e.g., an upper grating) on ​​a first layer 212 of the specimen 104 and a second layer grating 214 (e.g., a lower grating) on ​​a second layer 216 of the specimen 104, oriented such that the regions within the first layer grating 210 and the regions within the second layer grating 214 overlap to form a grating-over-grating structure. Additionally, the first layer grating 210 and the second layer grating 214 have distinct pitches. For example, in FIG. 2B, the pitches of first layer grating 210 and second layer grating 214 are depicted as P and Q, respectively.

[0040] In general, an overlay target 204 may be formed with any number of cells 202, and any particular cell 202 may have a moiré structure 206 with periodicity along any direction. Moreover, in certain embodiments, an overlay target 204 may include a plurality of cells 202 with moiré structures 206 having periodicity along a common direction, where different cells 202 have different configurations of periodicity of their associated gratings.

[0041] 2C is a side view of an overlay target 204 having two cells 202a,b with different configurations of moiré structures 206 suitable for overlay measurement along a particular measurement direction (e.g., here, X-direction) according to one or more embodiments of the present disclosure. Specifically, FIG. 2C illustrates an inverted moiré structure pair, in which a first cell 202a includes a first layer grating 210 with a first pitch (P) and a second layer grating 214 with a second pitch (Q), while a second cell 202b includes a first layer grating 210 with a second pitch (Q) and a second layer grating 214 with a first pitch (P). As contemplated herein, such an inverted moiré structure pair can facilitate overlay determination based on time-varying interference signals generated when both cells 202 are subjected to a scanning motion relative to the illumination beam 108 during measurement.

[0042] As contemplated herein, the distinct cells 202a,b of the inverted moiré structure pair can be oriented in various configurations within the overlay target 204. In certain embodiments, the cells 202a,b are oriented side-by-side along the periodicity direction (e.g., the X direction in FIG. 2C). Furthermore, as depicted in FIG. 2C, the cells 202 can be appropriately arranged to provide a continuous structure, and thus the phase transitions associated with the degenerated interference signal can be known and taken into account. The inverted moiré structure pair in such an arrangement can be referred to as a vertical overlay target, although this is not required. In particular, in the specific non-limiting configuration depicted in FIG. 2C, the central target feature 218 on the first layer 212 overlaps with that on the second layer 216. This can provide a reference point for the phase transition (e.g., φ0) at the center of the composite inverted moiré structure pair, as will be described in more detail below.

[0043] However, it should be understood that the overlay target 204 and the related description in FIGS. 2A-2C are presented for illustrative purposes only and should not be construed as limiting. Rather, the overlay target 204 may include any suitable moiré overlay target design. For example, the overlay target 204 may have any number of cells 202 suitable for metrology along two directions. Furthermore, the cells 202 may be distributed according to any pattern or arrangement. For example, metrology target designs suitable for scanning metrology are outlined in U.S. Patent Application Publication No. 2010 / 0139999, issued July 27, 2021, which is incorporated herein by reference in its entirety. In certain embodiments, the overlay target 204 may have one or more cell groups distributed along a scanning direction (e.g., a direction of motion of the specimen 104), and the cells 202 within each particular cell group are oriented to have a periodic moiré structure along a common direction. For example, one or more cells 202 in a first cell group may be periodic along the X direction, and one or more cells 202 in a second cell group may be periodic along the Y direction. In this way, all cells 202 in a particular cell group may be imaged simultaneously as the sample 104 is scanned through the measurement field of view of the collection subsystem 110. In another example, a diagonal target suitable for metrology measurements along orthogonal directions in a single scan is outlined in U.S. Patent Application Publication No. 2020 / 0139994, published Nov. 25, 2021, the entire contents of which are incorporated herein by reference.

[0044] FIG. 2A also illustrates an illumination spot on the cell 202 for the illumination beam 108. According to certain embodiments, the illumination subsystem 106 can underfill the cell 202 such that the size of the illumination beam 108 is smaller than the cell 202. As a result, the light distribution in the collection pupil plane 114 can be substantially limited to light diffracted by the grating-over-grating features in the cell 202, thus minimizing or substantially eliminating the target edge effect. Furthermore, the illumination beam 108 can be sized based on the size and / or pitch of the moiré structures in the cell 202. In general, sizing the illumination beam 108 to be approximately less than the height of the cell 202 and having a width at least one pitch smaller than the width of the cell 202 can result in sharp interference fringes.

[0045] As an example, in the depiction in FIG. 2A, the width of the illumination beam 108 along the measurement direction (here, the X direction) is set to about half the pitch of the grating in the moiré structure 206. According to one non-limiting example, dimensions of 1.5 micrometers in the Y direction and 0.5 micrometers in the X direction, which may be suitable dimensions of the illumination beam 108 for a 10 micrometer square cell 202, can be achieved with an oval pupil in the illumination pupil plane 120 with a NA of 0.9×0.3. However, it should be understood that the description of the illumination beam 108 in FIG. 2A is provided for illustrative purposes only and should not be taken as limiting. The illumination beam 108 may generally be of any size suitable for generating overlapping zeroth and first diffraction orders as described herein.

[0046] According to certain embodiments, elongating the illumination beam 108 along a direction perpendicular to the measurement direction can further reduce target-induced noise caused by imperfections within the cell 202, such as, but not limited to, roughness of the first layer grating 210 or the second layer grating 214. For example, the illumination beam 108 depicted in FIG. 2A is elongated along the Y direction.

[0047] 3A-3C, various non-limiting configurations for generating and measuring time-varying interference signals from Moire structures 206 within cells 202 of overlay target 204 will now be described in accordance with one or more embodiments of the present disclosure.

[0048] 3A is a top view of an illumination pupil 302 at an illumination pupil plane 120 of an overlay metrology tool 102 according to one or more embodiments of the present disclosure. For example, the illumination pupil plane 120 can correspond to a pupil plane in the illumination subsystem 106 as depicted in FIG. 1B. In certain embodiments, the illumination subsystem 106 illuminates the overlay target 204 with one or more illumination beams 108 at normal incidence (or near normal incidence) as depicted in FIG. 3A. Furthermore, the illumination beam(s) 108 can illuminate the overlay target 204 with a limited range of incidence angles as depicted by the limited size in the collection pupil plane 114. In that case, the overlay target 204 can diffract the illumination beam(s) 108 into discrete diffraction orders.

[0049] 3B-3D depict various non-limiting configurations for capturing time-varying interference signals from the overlay target 204 with the moiré structure 206 in a scanning configuration. In particular, FIGs. 3B-3D depict various non-limiting configurations in which the diffraction orders of the illumination beam 108 depicted in FIG. 3A may appear at the collection pupil plane 114, and associated positions of the photodetector 112 suitable for capturing time-varying interference signals from which an overlay metric may be extracted. It is contemplated that the photodetector 112 may be positioned at the collection pupil plane 114 at locations associated with moiré diffraction lobes (e.g., composite diffraction lobes, double diffraction lobes, etc.) and / or overlapping diffraction lobes (e.g., areas with first order diffraction lobes from the first layer grating 210 and second layer grating 214 of the moiré structure 206) to capture time-varying interference signals indicative of overlay. In accordance with further contemplation herein, a time-varying interference signal associated with a composite diffraction lobe can be captured by photodetector 112 when each of the associated diffraction lobes is incident on (e.g., within a measurement area of) that photodetector 112. In this way, associated diffraction lobes can be overlapped on photodetector 112 while not necessarily overlapping in collection pupil plane 114.

[0050] It is recognized herein that the distribution of diffraction orders of the illumination beam 108 due to periodic structures, e.g., moiré structures 206, may be influenced by various parameters, such as, but not limited to, the wavelength of the illumination beam 108, the angle of incidence of the illumination beam 108 in both elevation and azimuth directions, the pitch of the grating of the moiré structures 206, or the numerical aperture (NA) of the collection lens. In this regard, in embodiments of the present disclosure, the illumination subsystem 106, the collection subsystem 110, and the overlay target 204 may be appropriately configured (e.g., according to a metrology recipe defining a selected set of relevant parameters) to produce a desired distribution of diffraction orders within the collection pupil plane 114, i.e., a time-varying interference pattern indicative of overlay. For example, the illumination subsystem 106 and / or the collection subsystem 110 may be configured to generate measurements of moiré structures having a specified range of periodicity to produce a desired distribution within the collection pupil plane 114. Additionally, various components (eg, apertures, pupils, etc.) of the illumination subsystem 106 and / or collection subsystem 110 may be adjustable to provide a desired distribution within collection pupil plane 114 .

[0051] Furthermore, the size and shape of the diffraction orders at the collection pupil plane 114 can generally be related to the size and shape of the illumination beam 108 on the specimen 104. For example, although not shown, if the illumination beam 108 is elongated (e.g., as depicted in FIG. 2A ), the associated diffraction orders can be similarly elongated (e.g., along an orthogonal direction).

[0052] FIG 3B is a top view of a collection pupil 304 at a collection pupil plane 114 of an overlay metrology tool 102 in accordance with one or more embodiments of the present disclosure, with moire diffraction lobes due to the moire structures 206 according to the illumination profile of FIG 3A. For example, the collection pupil plane 114 can be mapped to a pupil plane in the collection subsystem 110 as depicted in FIG 1B. Notably, in the depiction in FIG 3B, a 0th diffraction order 306, a -1st moire diffraction order 308 (e.g., -M diffraction), and a +1st moire diffraction order 310 (e.g., +M diffraction) are distributed along the periodicity direction (e.g., here, the X direction) of the moire structures 206 at the collection pupil plane 114. For example, the -1st order moire diffraction 308 and the +1st order moire diffraction 310 can be associated with moire diffraction (e.g., double order diffraction) from the first layer grating 210 and the second layer grating 214, and the diffraction angle is determined based on the pitch of the moire interference related to the pitch difference between the first layer grating 210 and the second layer grating 214.

[0053] As contemplated herein, the phase of each of the Moire diffraction orders (e.g., −1 Moire diffraction order 308 and +1 Moire diffraction order 310) can be oscillated during scanning to form a time-varying interference signal, and the asymmetry of these oscillations can be used to determine overlay. As a result, overlay metrology can be performed by capturing and comparing these time-varying interference patterns.

[0054] In certain embodiments, the overlay metrology tool 102 includes photodetectors 112 in suitable positions to capture overlapping zeroth and moiré diffraction orders. For example, the configuration depicted in FIG. 3B has a moiré diffraction lobe overlapping with the zeroth diffraction order in the collection pupil plane 114 (e.g., as suggested by a metrology recipe). FIG. 3B further depicts a first photodetector 112a at the overlap with the −1st moiré diffraction order 308 and a second photodetector 112b at the overlap with the +1st moiré diffraction order 310. Each photodetector 112 can then capture a time-varying interference signal as the specimen 104 undergoes a scanning motion, and the difference between the time-varying interference signals captured by the photodetectors 112 is indicative of overlay.

[0055] As contemplated herein, the pitch difference between the top and bottom gratings of the moiré structure 206 (e.g., between the first layer grating 210 and the second layer grating 214) causes a phase shift in the moiré diffraction orders (e.g., −1st and +1st order moiré diffractions 308 and 310). Specifically, when the overlay target 204 is scanned along the periodic direction of the moiré structure 206 (e.g., the X-direction in FIGS. 2A and 2B), the phases of the moiré diffraction orders shift in opposite directions. However, by capturing the phase shifts along the measurement direction during scanning and over the entire length of the moiré structure 206, the actual physical overlay of the first layer 212 and the second layer 216 can be determined. In this way, the data collected during scanning metrology can be functionally equivalent or comparable to that of static metrology by an image-based system, while still maintaining the benefits of scanning overlay, such as increased throughput.

[0056] For example, as depicted in FIG. 2C, the time-varying signal associated with cells 202a,b of overlay target 204 forming an inverted Moire structure pair is

[0057]

number

[0058] Based on equations (1) and (2),

number

[0059] Equations (1) to (4) are combined to give the overlay OVL=(P m / 8π)·(φ 1,1 +φ 1,-1 -φ 2,1 -φ 2,-1 ) (5) This can be solved as follows.

[0060] However, it should be understood that the specific configuration depicted in Figure 3B and the associated description are not limiting. For example, as described herein, it is not necessary that the zeroth diffraction order 306 overlap with the -1st and +1st Moire diffraction orders 308 and 310 in the collection pupil 304 as depicted in Figure 3B. Rather, according to certain embodiments, the diffraction lobes can be close enough together so that the zeroth diffraction order 306 overlaps with the -1st Moire diffraction order 308 on the first photodetector 112a, and the zeroth diffraction order 306 overlaps with the +1st Moire diffraction order 310 on the second photodetector 112b. Additionally, in certain embodiments, an overlay measurement is determined based on a time-varying signal associated with only the first Moire diffraction order lobe (e.g., without reference to the zeroth diffraction order 306). FIG. 3C is a top view of collection pupil 304 of overlay metrology tool 102 according to one or more embodiments of the present disclosure, showing a separate first order Moire diffraction of the illumination profile of FIG. 3A, due to Moire structure 206.

[0061] Referring now to FIG. 3D, overlay determination based on time-varying interference signals of overlapping first order diffractions from gratings on the first layer 212 and the second layer 216 will be described in accordance with one or more embodiments of the present disclosure.

[0062] Figure 3D is a top view of a collection pupil 304 at the collection pupil plane 114 of an overlay metrology tool 102 in accordance with one or more embodiments of the present disclosure, with overlapping first diffraction orders of the illumination profile of Figure 3A due to the moire structure 206. In Figure 3D, various diffraction orders that may be present have been omitted for clarity, including but not limited to the 0th diffraction order 306, -1st moire diffraction order 308, and +1st moire diffraction order 310.

[0063] In certain embodiments, the illumination subsystem 106, collection subsystem 110, and overlay target 204 are configured such that the first diffraction order from the first layer grating 210 and the second layer grating 214 overlap within the collection pupil 304. In FIG. 3D, the first photodetector 112a detects the −1 order diffraction 314 (−1 TOP ) and the −1st order diffraction 316(−1 BOTTOM ) and the second photodetector 112b detects the +1st order diffraction 320 (+1 TOP ) and +1 order diffraction 322(+1 BOTTOM ) in a second overlap region 318 between the first and second photodetectors 112a,b. Furthermore, the first diffraction order lobes 314, 316, 320, 322 do not necessarily overlap in the collection pupil plane 114, but may overlap on the respective photodetectors 112a,b according to certain embodiments.

[0064] In accordance with the present contemplation, by vibrating the intensity and phase in each of the overlap regions in Figure 3D (e.g., first overlap region 312 and second overlap region 318), time-varying interference patterns can be formed in a manner similar to Figure 3B, which also indicate overlay between first layer 212 and second layer 216. In this way, a measurement of physical overlay-to-physical overlay overlay (or overlay error) between first layer 212 and second layer 216 can be similarly generated based on a comparison of the time-varying interference patterns captured by photodetector 112 in Figure 3D.

[0065] For example, as depicted in FIG. 2C, the time-varying signal associated with cells 202a,b of overlay target 204 forming an inverted Moire structure pair is

[0066]

number

[0067] Based on equations (6) and (7), the phase information for the negative diffraction orders is given by φ1=2π(-X0 / Q+(X0+OVL) / P-ΔΨ1 / (2π)) (8) φ2=2π(-X0 / P+(X0+OVL) / Q-ΔΨ2 / (2π)) (9) The phase information related to the positive order diffraction can be expressed as φ3=2π(-X0 / Q+(X0+OVL) / P+ΔΨ1 / (2π)) (10) φ4=2π(-X0 / P+(X0+OVL) / Q+ΔΨ2 / (2π)) (11) It can be written as:

[0068] Then, the overlay (OVL) is calculated based on equations (8) to (11). φ1-φ2=2π((1 / P+1 / Q)·OVL-ΔΨ1 / (2π)+ΔΨ2 / (2π)) (12) φ3-φ4=2π((1 / P+1 / Q)·OVL+ΔΨ1 / (2π)-ΔΨ2 / (2π)) (12) 2π((P+Q) / PQ)·OVL=(φ1-φ2+φ3-φ4) / 2 (13) OVL=((φ1-φ2+φ3-φ4) / (4π))·PQ / (P+Q) (15) It can be determined as follows.

[0069] With general reference to FIGS. 3A-3D, it should be understood that FIGS. 3A-3D are presented for illustrative purposes only and should not be construed as limiting. For example, the non-limiting case depicted in FIGS. 3A-3D is for the diffraction of the illumination beam 108 incident on the specimen at normal incidence. However, as contemplated herein, the illumination beam 108 may generally have any profile suitable for achieving collection of multiple complex or overlapping diffraction orders (e.g., multiple Moire diffraction orders for complex diffraction from overlapping gratings of the Moire structure 206, overlapping Moire diffraction and zeroth order diffraction, overlapping first order diffraction from the overlapping gratings of the Moire structure 206, etc.) as disclosed herein. In certain embodiments, the illumination beam 108 has an annular profile. As contemplated herein, the annular profile of the illumination beam 108 can facilitate separation of multiple overlapping diffraction orders in the collection pupil plane 114. The use of annular apertures to separate overlapping diffraction orders is generally described in U.S. Patent Application Publication No. 2019 / 0133633, issued Feb. 9, 2019, which is incorporated herein by reference in its entirety. It is noted that while stationary metrology is described in U.S. Patent Application Publication No. 2019 / 0133633, the use of annular illumination beam 108 may be used in scanning metrology as well, as disclosed herein. Notably, in certain embodiments, photodetector 112 is positioned at the location of overlapping diffraction orders (e.g., overlapping Moiré and 0th order diffractions, overlapping 1st order diffractions from the composite grating of Moiré structure 206, etc.) generated from annular illumination beam 108.

[0070] Referring again to FIG. 1A, additional components of the overlay metrology tool 102 are detailed in accordance with one or more embodiments of the present disclosure.

[0071] Photodetector 112 may generally include any type of optical detector known in the art suitable for capturing interference signals generated during translation of specimen 104 by translation stage 116 and / or scanning motion of illumination beam(s) 108 by beam scanning subsystem 118. For example, photodetector 112 may include, but is not limited to, high speed photodiodes, photomultiplier tubes, and avalanche photodiodes.

[0072] In general, the bandwidth and response time of the photodetector 112 should be sufficient to resolve the time frequency of the interference fringes associated with the pitch of the upper and lower gratings of the moiré structure 206 and the scanning speed along the measurement direction (the direction of periodicity of the moiré structure 206). For example, a scanning speed along the measurement direction of 10 centimeters per second and a target pitch of 1 micrometer will result in an interference signal oscillating at a rate on the order of 100 kHz. In certain embodiments, the photodetectors 112 include photodetectors with a bandwidth of at least 1 GHz, although it should be understood that this is not required. Rather, the bandwidth of the photodetector 112, the translation speed along the measurement direction, and the pitch of the moiré structure can be jointly selected to provide a desired interference signal sampling rate.

[0073] The overlay metrology system 100 of certain embodiments includes a controller 122 communicatively coupled to the overlay metrology tool 102. The controller 122 may include 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 that are maintained in the storage device 126.

[0074] The one or more processors 124 of the controller 122 may generally include any processor or processing element known in the art. For purposes of this disclosure, the term "processor" or "processing element" may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application specific integrated circuit (ASIC) devices, one or more field programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, the one or more processors 124 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). According to certain embodiments, the one or more processors 124 may be implemented as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute a program, the program being configured to operate or operate in conjunction with the overlay metrology system 100 as described elsewhere in this disclosure. Additionally, the various subsystems of the overlay metrology system 100 may have processors or logic elements suitable for performing at least a portion of the steps described herein. Thus, the above description should be taken as merely illustrative and not as a limitation on the embodiments of the present disclosure. Furthermore, the steps described elsewhere in this disclosure may be performed by a single controller or, alternatively, by multiple controllers. Additionally, the controller 122 may have one or more controllers housed within a common housing or in multiple housings. In this way, any controller or combination of controllers may be packaged separately as a module suitable for integration into the metrology overlay metrology system 100.Additionally, data received from photodetector 112 may be processed, eg, analyzed, by controller 122 and sent to additional components within or external to overlay metrology system 100 .

[0075] Additionally, the storage device 126 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 124. For example, the storage device 126 may include a non-transitory storage medium. As additional examples, the storage device 126 may include, but is not limited to, read-only memory, random access memory, magnetic or optical storage devices (e.g., disks), magnetic tape, solid state drives, etc. It is further noted that the storage device 126 may be housed within a common controller housing along with the one or more processors 124.

[0076] In this regard, the controller 122 may be configured to perform any of a variety of process steps associated with overlay metrology. For example, the controller 122 may be configured to generate control signals to control, e.g., command, the overlay metrology tool 102 or any of its components. For example, the controller 122 may be configured to command the translation stage 116 to translate the specimen 104 along one or more measurement paths or swaths, and thus scan one or more overlay targets through a measurement field of view of the overlay metrology tool 102, and / or to command the beam scanning subsystem 118 to position or scan one or more illumination beams 108 over the specimen 104. In another example, the controller 122 may be configured to receive a signal corresponding to a time-varying interference signal from the photodetector 112. According to another example, based on the overlay measurements from the overlay metrology tool 102, collectables (correction variables) for one or more additive manufacturing tools can be generated by the controller 122 as feedback and / or feedforward control of the one or more additive manufacturing tools.

[0077] In another embodiment, the controller 122 captures the interference signal detected by the photodetector 112. The controller 122 may generally use any technique known in the art, such as, but not limited to, one or more phase-locked loops, to capture data, such as, but not limited to, the magnitude or phase of the time-varying interference signal. Additionally, the controller 122 may use any combination of hardware (e.g., circuitry) or software techniques to capture the interference signal or any data related to the interference signal.

[0078] In certain embodiments, the controller 122 determines an overlay measurement between layers of the overlay target 204 (e.g., between the first layer 212 and the second layer 216) along the measurement direction based on the comparison of the interference signals. For example, the controller 122 can determine the overlay measurement based on the magnitude and / or phase of the interference signals, such as, but not limited to, as described in Equations (1)-(15). For example, U.S. Patent No. 6,399,633, which was previously referenced and is incorporated herein by reference in its entirety, provides an overview of the electric fields of the diffraction orders at the collection pupil, and further provides a specific relationship between the measured intensity at the pupil plane and overlay. As contemplated herein, the systems and methods disclosed herein can extend the teachings of U.S. Patent No. 6,399,633 to a time-varying interference signal captured by a photodetector located in the overlap region between the 0th and ±1st diffraction orders. In particular, as contemplated herein, the overlay on the specimen can be proportional to an asymmetry, such as, but not limited to, the relative phase shift between two time-varying interference signals.

[0079] Additionally, the controller 122 may modify, e.g., calibrate, the overlay measurements based on known, assumed, or measured characteristics of the sample that may also affect the time-varying interference signal, such as, but not limited to, sidewall angle and other sample asymmetries.

[0080] Referring again to FIG. 1B, various components of overlay metrology tool 102 are detailed in accordance with one or more embodiments of the present disclosure.

[0081] In certain embodiments, the illumination subsystem 106 includes an illumination source 128 configured to generate at least one illumination beam 108. The illumination from the illumination source 128 may include one or more specified wavelengths of light, including, but not limited to, ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0082] The illumination source 128 may include any type of illumination source suitable for providing 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 sources, broadband laser sources, supercontinuum (ultra-broadband) laser sources, white laser sources, etc. In such cases, the illumination source 128 may provide the illumination beam 108 with high coherence (e.g., high spatial and / or temporal coherence). In certain embodiments, the illumination source 128 may include a laser-sustained plasma (LSP) light source. For example, the illumination source 128 may include, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for containing one or more elements that may emit broadband illumination when excited into a plasma state by a laser light source.

[0083] In certain embodiments, the illumination subsystem 106 includes one or more optical elements suitable for modifying and / or dimming the illumination beam 108 and directing the illumination beam 108 to the specimen 104. For example, the illumination subsystem 106 may include one or more illumination lenses 130 (e.g., for collimating the illumination beam 108, for relaying the illumination pupil plane 120 and / or the illumination field plane 132, etc.). In certain embodiments, the illumination subsystem 106 includes one or more illumination control optics 134 for controlling, e.g., shaping, the illumination beam 108. For example, the illumination control optics 134 may include, but is not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., stationary mirrors, translating mirrors, scanning mirrors, etc.).

[0084] In certain embodiments, the overlay metrology tool 102 has an objective lens 136 that focuses the illumination beam 108 onto the specimen 104 (e.g., onto an overlay target having overlay target components located on two or more layers of the specimen 104).

[0085] In certain embodiments, the illumination subsystem 106 illuminates the specimen 104 with two or more illumination beams 108. Furthermore, the two or more illumination beams 108 may, but need not, be incident on different portions of the specimen 104 (e.g., different cells of an overlay target) within a measurement field of view (e.g., a field of view of the objective lens 136). As contemplated herein, various techniques may be used to generate the two or more illumination beams 108. In certain embodiments, the illumination subsystem 106 includes two or more apertures at the illumination field plane 132. In certain embodiments, the illumination subsystem 106 includes one or more beam splitters that split illumination from the illumination source 128 into the two or more illumination beams 108. In certain embodiments, at least one illumination source 128 directly generates the two or more illumination beams 108. In general, each illumination beam 108 may be considered part of a separate illumination channel, regardless of the technique by which the various illumination beams 108 are generated.

[0086] In certain embodiments, the collection subsystem 110 includes at least two photodetectors 112 (e.g., photodetectors 112a,b) configured to capture light (e.g., collected light 138) from the sample 104 and located at a collection pupil plane 114, the collected light 138 including at least a 0th diffraction order 306, a -1st Moire diffraction order 308, and a +1st Moire diffraction order 310 as depicted in FIG. 3B. The collection subsystem 110 may include one or more optical elements suitable for modifying and / or adjusting the collected light from the sample 104. In certain embodiments, the collection subsystem 110 includes one or more collection lenses 140 (e.g., for collimating the illumination beam 108, relaying a pupil and / or field plane, etc.), such as, but not limited to, an objective lens 136. In certain embodiments, the collection subsystem 110 includes one or more collection control optics 142 that control, e.g., shape, the collected light 138. For example, the collection control optics 142 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., stationary mirrors, translating mirrors, scanning mirrors, etc.).

[0087] In certain embodiments, the collection subsystem 110 has two or more collection channels 144, each with a separate pair of photodetectors 112. For example, as depicted in FIG. 1B, the overlay metrology tool 102 may include one or more beam splitters 146 arranged to split the collected light 138 into the collection channels 144. Further, the beam splitters 146 may be polarizing beam splitters, non-polarizing beam splitters, or a combination thereof. However, it should be understood that the depiction of two collection channels 144 in FIG. 1B is provided for illustrative purposes only and should not be taken as limiting. For example, the collection subsystem 110 may include a single collection channel 144 or multiple collection channels 144.

[0088] In certain embodiments, multiple collection channels 144 are configured to collect light from multiple illumination beams 108 on the specimen 104. For example, if the overlay target 204 has two or more cells 202 distributed along a direction other than the scan direction, the overlay metrology tool 102 can simultaneously illuminate the different cells 202 with different illumination beams 108 and simultaneously capture interference signals associated with each illumination beam 108. Additionally, in certain embodiments, the multiple illumination beams 108 directed to the specimen 104 can be of different polarizations. In this way, the diffraction orders associated with each illumination beam 108 can be separated. For example, a polarizing beam splitter 146 can efficiently separate the diffraction orders associated with the different illumination beams 108. In another embodiment, a polarizer can be used in one or more collection channels to separate desired diffraction orders for measurement.

[0089] In certain embodiments, the overlay metrology tool 102 includes a beam scanning subsystem 118 that positions, scans, or modulates the position of one or more illumination beams 108 on the specimen 104 during measurement.

[0090] The beam scanning subsystem 118 may include any type or combination of elements suitable for scanning the position of the illumination beam 108 or beams 108. In certain embodiments, the beam scanning subsystem 118 includes one or more deflectors suitable for modifying the direction of the illumination beam 108. For example, the deflector may include, but is not limited to, a rotatable mirror (e.g., a mirror with an adjustable end and / or tilt). Furthermore, the rotatable mirror may be actuated using any technique known in the art. For example, the deflector may include, but is not limited to, a galvanometer, a piezoelectric mirror, or a microelectromechanical system (MEMS) device. In another example, the beam scanning subsystem 118 may include an electro-optic modulator, an acousto-optic modulator, or the like.

[0091] The deflector may also be located at any suitable location within the overlay metrology tool 102. In certain embodiments, one or more deflectors are located at one or more pupil planes common to both the illumination subsystem 106 and the collection subsystem 110. In this case, the beam scanning subsystem 118 may be a pupil plane beam scanner with associated deflectors to modify the position of the one or more illumination beams 108 on the specimen 104 without affecting the positions of the diffraction orders at the collection pupil plane 114. Furthermore, the distribution of the one or more illumination beams 108 at the illumination field plane 132 may be more stable since the position of the one or more illumination beams 108 on the specimen 104 is modified by the beam scanning subsystem 118. Pupil plane beam scanning is generally described in U.S. Patent Application No. 17 / 142,783, filed January 6, 2021, which is incorporated herein by reference in its entirety.

[0092] 4-8B, various exemplary configurations of the overlay target 204 and corresponding configurations of the overlay metrology tool 102 are detailed in accordance with one or more embodiments of the present disclosure. In FIGS. 4-8B, only the first layer grating 210 is shown for clarity. However, it should be understood that the overlay target 204 includes a moiré structure 206 as described herein. Additionally, overlay data for the first layer 212 and second layer 216 of the specimen 104 may be based on measurements of any number of cells 202 with moiré structures 206 based on any overlay technique known in the art. For example, different cells 202 of the overlay target 204 may include moiré structures 206 with different intentional offsets. In another embodiment, different cells 202 in an overlay target 204 may have different configurations of moiré structures 206. In one embodiment, at least one pair of cells 202 in an overlay target 204 may have moiré structures 206 with inverted pitches, forming an inverted moiré structure pair (e.g., as depicted in FIG. 2C). In general, any overlay technique may be implemented using the systems and methods disclosed herein with any arrangement of overlay targets 204 having at least one moiré structure 206.

[0093] FIG. 4 is a conceptual diagram of a specimen 104 in accordance with one or more embodiments of the present disclosure illustrating an arrangement of overlay targets 204 and corresponding measurement paths 402 (e.g., swaths) for measuring the overlay targets 204.

[0094] In certain embodiments, a number of overlay targets 204 are distributed across the specimen 104 at locations suitable for overlay measurement, including but not limited to, along the scribe lines. Additionally, various measurement paths 402 defining scan paths are defined to measure specific overlay targets 204 across the specimen 104. For example, multiple measurement paths 402 along the Y direction as depicted in FIG. 4 may be used to measure the various overlay targets 204.

[0095] The overlay target 204 may have any number of cells 202 and the moire structure within each cell 202 may have any periodicity along any specified direction. In this regard, various designs of overlay target 204 may be utilized within the spirit and scope of the present disclosure. For example, the overlay target 204 in FIG. 4 is depicted having two cells 202 distributed along the X direction.

[0096] In certain embodiments, the overlay target 204 includes a first set of one or more cells 202, each with a moire structure having periodicity along a first direction, and a second set of one or more cells 202, each with a moire structure having periodicity along a second direction. Additionally, the second direction may be orthogonal to the first direction, although this is not required. In this manner, the first set of one or more cells 202 may be suitable for overlay metrology along the first direction, and the second set of one or more cells 202 may be suitable for overlay metrology along the second direction, thereby enabling full 2D overlay metrology results to be obtained.

[0097] In general, providing multiple cells 202 suitable for measurements along a particular direction within an overlay target 204 can facilitate measurements over a larger area than that provided by a single cell 202, thereby improving the accuracy and / or sensitivity of the measurements. Additionally, the various cells 202 suitable for measurements along a particular direction can be distributed along the measurement direction and / or along a direction perpendicular to the measurement direction.

[0098] 5-6B, a design of an overlay target 204 suitable for overlay metrology along one or two directions using a stationary illumination beam 108 (e.g., without a beam scanning subsystem 118) will be described in detail in accordance with one or more embodiments of the present disclosure.

[0099] 5 illustrates a top view of a 1D overlay target 204 having two cells 202 aligned along a stage scan direction 502, with each cell 202 having a moiré structure 206 that is periodic along the stage scan direction 502, in accordance with one or more embodiments of the present disclosure. In this manner, the stage scan direction 502 and a measurement direction associated with the periodicity of the moiré structures 206 are fully aligned. With this configuration, a first set of measurement paths 402 can be generated to measure the overlay target 204 configured for measurement in one direction (e.g., X direction) and a second set of measurement paths 402 can be generated to measure the overlay target 204 configured for measurement in a second direction (e.g., Y direction), thereby allowing 2D overlay measurement of the specimen 104. As contemplated herein, such an orientation may be suitable for, but is not limited to, a vertical target structure, such as that depicted in FIG. 2C, with controlled spacing between individual cells 202 along the stage scan direction 502.

[0100] 6A and 6B depict a 2D overlay target 204 having a moire structure 206 that is periodic along a direction diagonal to the scan direction.

[0101] FIG. 6A is a top view of a first 2D overlay target 204 having cells 202 with periodicity oriented diagonally relative to the stage scan direction 502, according to one or more embodiments of the present disclosure. FIG. 6B is a top view of a second 2D overlay target 204 having cells 202 with periodicity oriented diagonally relative to the stage scan direction 502, according to one or more embodiments of the present disclosure. The shear images in FIG. 6A and FIG. 6B depict the distribution of the diffraction orders of interest 602 at the collection pupil plane 114 and the corresponding locations of the photodetector 112 pairs for the corresponding cells 202. For example, the diffraction order distribution depicted in the shear images in FIG. 6A and FIG. 6B may be similar to FIG. 3C, except that the Moire diffraction orders (e.g., −1st Moire diffraction order 308 and +1st Moire diffraction order 310) are rotated based on the periodicity direction of each cell 202. However, it should be understood that Figures 6A and 6B are not limited to the specific arrangement of Figure 3C, but can also include other arrangements, such as, but not limited to, those depicted in Figures 3B and 3D.

[0102] For example, the overlay target 204 in Figures 6A and 6B may be suitable for measuring overlapping first order diffractions from the top and bottom gratings of the moire structure 206, as depicted in Figure 3D. According to another example, the overlay target 204 in Figures 6A and 6B may be suitable for measuring moire diffractions (e.g., -1st order moire diffraction 308 and +1st order moire diffraction 310) and the overlapping zeroth order light.

[0103] 6A and 6B includes a first set of cells 202 that are distributed along the stage scan direction 502 and can be illuminated with a first illumination beam 108a, and a second set of cells 202 that are distributed along the stage scan direction 502 and can be illuminated with a second illumination beam 108b. Furthermore, the first and second sets of cells 202 are aligned in a direction perpendicular to the stage scan direction 502. This allows different cells 202 to be simultaneously probed with both illumination beams 108a,b while the sample 104 is moving in a scanning motion.

[0104] Moreover, the various non-limiting configurations of cells 202 depicted in Figures 6A and 6B are periodic along two mutually orthogonal directions suitable for 2D overlay metrology. In Figure 6A, cells 202 oriented to be periodic along a common diagonal direction are grouped into rows. In this case, the orientations of the diffraction orders, and therefore the orientations of the photodetectors 112 required to obtain measurements for the cells 202, are constant for each row, as depicted in the shear image in Figure 6A. In Figure 6B, each illumination beam 108 scans across the cells 202 that are periodic along both diagonals. This reduces systematic errors associated with a particular illumination beam 108. However, the orientations of the photodetectors 112 can be different for different cells 202 along the stage scan direction 502, as depicted in the shear image in Figure 6B. In certain embodiments, the collection subsystem 110 includes a single collection channel 144 with photodetectors 112 suitably positioned within both diagonal overlap areas, and the controller 122 can selectively analyze the corresponding pair of photodetectors 112 associated with each cell 202 when generating overlay measurements. In certain embodiments, the collection subsystem 110 includes two collection channels 144 with a pair of photodetectors 112 each positioned within a single diagonal overlap area, and the controller 122 can selectively analyze the corresponding collection channel 144 associated with each cell 202 when generating overlay measurements.

[0105] It is recognized herein that in certain applications it may be desirable or customary to provide overlay measurements along the stage scan direction 502. Accordingly, a linear transformation may be used to transform the overlay measurements along the first and second diagonal directions to provide overlay measurements along any desired direction on the specimen 104.

[0106] 7A-8B, an overlay target 204 designed for overlay metrology in which the beam scanning subsystem 118 scans one or more illumination beams 108 during measurement will be described in detail in accordance with one or more embodiments of the present disclosure. In FIGs. 7A-8B, the beam scanning subsystem 118 scans one or more illumination beams 108 along a beam scan direction 702 that is different from (e.g., perpendicular to) the stage scan direction 502 while the sample 104 is being scanned along the stage scan direction 502. In this manner, each illumination beam 108 can be scanned across the overlay target 204 (or its cells 202) along a diagonal path.

[0107] 7A-7D depict 1D overlay targets 204 suitable for overlay measurement along the X and Y directions, according to one or more embodiments of the present disclosure. FIG. 7A illustrates a top view of a first overlay target 204 suitable for overlay measurement along the Y direction with a scanning motion of the illumination beam 108 along the +Y direction, according to one or more embodiments of the present disclosure. FIG. 7B illustrates a top view of a second overlay target 204 suitable for overlay measurement along the X direction with a scanning motion of the illumination beam 108 along the +Y direction, according to one or more embodiments of the present disclosure. In FIGS. 7A and 7B, by appropriately selecting the scanning speed along the stage scanning direction 502 and along the beam scanning direction 702, the destination of the illumination beam 108 can be moved between the opposing corners of the cell 202 along a first diagonal direction 704. In this way, multiple cells 202 can be distributed along the first diagonal direction 704 to increase the effective measurement area of ​​the overlay target 204, thereby improving overlay measurements.

[0108] 7C and 7D depict similar overlay targets 204 suitable for beam scanning along the -Y direction. FIG. 7C illustrates a top view of a first overlay target 204 suitable for Y-direction overlay measurement with illumination beam 108 scanning along the -Y direction, according to one or more embodiments of the present disclosure. FIG. 7D illustrates a top view of a second overlay target 204 suitable for X-direction overlay measurement with illumination beam 108 scanning along the -Y direction, according to one or more embodiments of the present disclosure. As with FIGS. 7A and 7B, by appropriately selecting the scanning speed along the stage scanning direction 502 and the beam scanning direction 702, the destination of illumination beam 108 can be moved between opposite corners of cells 202 along a second diagonal direction 706, and multiple cells 202 can be distributed along the second diagonal direction 706.

[0109] The shear images in Figures 7A-7D depict the arrangement of photodetectors 112 at the collection pupil plane 114 and the distribution of diffraction orders for measurements with individual overlay targets 204. For example, the diffraction order distribution depicted in the shear images in Figures 7A-7D may be similar to that of Figure 3C, except that the Moiré diffraction orders (e.g., -1st Moiré diffraction order 308 and +1st Moiré diffraction order 310) are rotated based on the periodicity direction of each cell 202. However, it should be understood that Figures 7A-7D are not limited by the specific arrangement of Figure 3C. For example, the overlay targets 204 in Figures 7A-7D may be suitable for measuring overlapping first diffraction orders from the top and bottom gratings of the Moiré structure 206 depicted in Figure 3D. In another example, the overlay target 204 in Figures 7A-7D may be suitable for measuring Moire diffraction (e.g., -1st order Moire diffraction 308 and +1st order Moire diffraction 310) and the overlapping 0th order light, as depicted in Figure 3B.

[0110] Additionally, Figures 7A-7D illustrate the use of a long illumination beam 108 to mitigate the effects of target roughness as described herein. In the non-limiting example, the illumination beam 108 in Figures 7A-7D is sized to 0.5 x 1 micrometers, which can be achieved with an oval pupil with a NA of 0.9 x 0.45. Thus, the associated effect on the distribution of diffraction orders in the collection pupil plane 114 is illustrated in the shear image.

[0111] In certain embodiments, the illumination beam 108 is oscillated (e.g., by a vibration deflector in the beam scanning subsystem 118) along the beam scan direction 702. In this case, the illumination beam 108 can be made to follow a triangular wave-like path on the sample 104. Thus, multiple overlay targets 204 (or multiple combinations of the cells 202) can be distributed along the triangular wave pattern of the illumination beam 108 to achieve sequential measurements. For example, the overlay targets 204 depicted in FIGS. 7A and 7B can be interleaved with the overlay targets 204 depicted in FIGS. 7C and 7D. Continuing with the non-limiting example of a 10 micrometer square cell 202, this can be achieved by choosing a stage speed along the scan direction 502 of 10 cm / sec and a resonant frequency along the beam scan direction 702 of 10 kHz.

[0112] 8A and 8B, an overlay target 204 suitable for 2D overlay metrology using beam scanning will be described in accordance with one or more embodiments of the present disclosure. FIG. 8A is a top view of a first overlay target 204 suitable for 2D overlay metrology with two parallel illumination beams 108 in accordance with one or more embodiments of the present disclosure. FIG. 8B is a top view of a second overlay target 204 suitable for 2D overlay metrology with two parallel illumination beams 108 in accordance with one or more embodiments of the present disclosure. In both FIG. 8A and FIG. 8B, a first illumination beam 108a follows a triangular wave path across a first intra-row cell 202, and a second illumination beam 108b follows a triangular wave path across a second intra-row cell 202. Continuing with the non-limiting example of a 10 micrometer square cell 202, this can be achieved by choosing a velocity along the stage scan direction 502 of 10 cm / sec and a resonant frequency along the beam scan direction 702 of 20 kHz.

[0113] Additionally, the shear images in Figures 8A and 8B depict the photodetector 112 arrangement in the collection pupil plane 114 and the corresponding diffraction order distributions for measuring the various cells 202. For example, the diffraction order distributions depicted in the shear images in Figures 8A and 8B may be similar to those in Figure 3C, except that the Moiré diffraction orders (e.g., -1st Moiré diffraction order 308 and +1st Moiré diffraction order 310) may be rotated based on 8A and 8B and not limited to the specific arrangement of Figure 3C. However, it should be understood that Figures 8A and 8B are not limited to the specific arrangement of Figure 3C. For example, the overlay target 204 in Figures 8A and 8B may be suitable for measuring overlapping first diffraction orders from the top and bottom gratings of the Moiré structure 206 depicted in Figure 3D. As another example, the overlay target 204 in Figures 8A and 8B may be suitable for measuring Moire diffraction (e.g., -1 and +1 orders 308 and 310) and the overlapping zeroth order, as depicted in Figure 3B. As a further note, although the illumination beam 108 is depicted as circular in Figures 8A and 8B, it should be understood that, as described herein, the illumination beam 108 may be elongated to reduce noise associated with target roughness.

[0114] In FIG. 8A, cells 202 with a common periodicity direction are distributed diagonally in the overlay target 204. However, as contemplated herein, the signal strength of the diffraction orders may depend on the periodicity direction and the polarization of the illumination beam 108. As discussed herein, in certain embodiments, simultaneous measurement of multiple cells 202 with multiple illumination beams 108 (e.g., those depicted in FIGS. 8A and 8B and those depicted in FIGS. 6A and 6B above) is performed by separating the diffraction orders of the multiple illumination beams 108 into separate collection channels 144. This separation can be efficiently achieved by differentiating the illumination beams 108 by polarization, color, or some other parameter and separating the resulting diffraction orders with suitable elements (e.g., polarizing filters, polarizing beam splitters, spectral filters, spectral beam splitters, etc.) in the collection subsystem 110. 8A, interrogating one X-direction cell 202 and one Y-direction cell 202 with each illumination beam 108 may introduce disparities in the associated signals of the two illumination beams 108. In certain embodiments, such disparities are algorithmically mitigated. In certain embodiments, the optical configuration of each illumination beam 108 may be switched, e.g., alternated, to provide common measurement conditions for cells having a common periodicity direction.

[0115] 8B is positioned such that cells 202 having a common periodicity direction are interrogated by a common illumination beam 108. In this way, measurements of various cells 202 having a common periodicity direction can be performed using common measurement conditions, thus improving the accuracy of the overlay measurements.

[0116] 9 is a flow diagram illustrating steps performed in a method 900 for scanning overlay metrology of an overlay target having at least one moiré structure, according to one or more embodiments of the present disclosure. Applicants note that the embodiments and enabling technologies described herein in the context of overlay metrology system 100 should be understood to extend to method 900. However, it is further noted that method 900 is not limited by the architecture of overlay metrology system 100.

[0117] In certain embodiments of method 900, in step 902, one or more cells of an overlay target on the specimen, where the cell has a moiré structure formed of overlapping gratings with different pitches, are illuminated while scanning the specimen relative to the illumination.

[0118] In certain embodiments of method 900, time-varying interference signals are collected from two photodetectors located near the collection pupil for at least one of the moire diffractions (e.g., multiple diffractions, double diffractions, etc.) or overlapping diffractions from the gratings in the moire structures, step 904. For example, non-limiting configurations may include, but are not limited to, placement of photodetectors at only moire diffraction orders, at both multiple moire diffraction orders and the zeroth diffraction order, or at the first diffraction order from the top and bottom gratings of the moire structure.

[0119] In certain embodiments, the method 900 determines, at step 906, an overlay error between the specimen layers associated with the moiré structures in one or more cells of the overlay target based on the signals from the two photodetectors. For example, the overlay error along the periodicity direction of the moiré structures may be proportional to a phase difference between the time-varying interference signals from the two photodetectors. The phase difference may be determined using any technique known in the art, including, but not limited to, applying a phase lock technique to the two time-varying interference signals. Additionally, an overlay measurement of the specimen along a particular measurement direction may be generated based on data from multiple cells of the overlay target with moiré structures having periodicity along the particular measurement direction.

[0120] As contemplated herein, the method 900 can be applied to a wide variety of overlay target designs suitable for 1D or 2D metrology. In certain embodiments, the method 900 performs simultaneous scanning with multiple illumination beams and collects associated overlapping diffraction orders for parallel measurement. In certain embodiments, the method 900 scans one or more illumination beams along a beam scan direction different from the stage scan direction, resulting in a diagonal or triangular wave path across the sample. With this configuration, cells with moiré structures with different periodicity directions can be efficiently interrogated by a common illumination beam along the measurement swath.

[0121] The subject matter described herein is depicted in places with various components included or connected to other components. It should be understood that the illustrated configurations are merely exemplary, and that in fact many other configurations can be implemented to achieve the same function. Conceptually, any arrangement of components that achieves the same function achieves the desired function through an effective "cooperation." Thus, any two components in this application that are combined to achieve a particular function can be viewed as "cooperating" with each other to achieve the desired function, regardless of the configuration or intervening components. Similarly, any two components that are so coordinated can be viewed as "connected" or "coupled" to each other to achieve the desired function, and any two components that can be so coordinated can be viewed as "combinable" with each other to achieve the desired function. Examples of coupleable include, but are not limited to, components being capable of and / or physically interacting with each other, and / or components being capable of and / or wirelessly interacting with each other, and / or components being capable of and / or logically interacting with each other.

[0122] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will also be apparent that various changes in the form, construction and arrangement of the parts may be made without departing from the disclosed subject matter or diminishing all of its essential advantages. The form described is merely illustrative, and it is the intent of the following claims to encompass and embrace all such modifications. It will be further understood that it is the appended claims which define the invention.

Claims

1. 1. An overlay metrology system, comprising: a lighting subsystem configured to implement a metering recipe; an illumination source configured to generate an illumination beam; and one or more illumination optics configured to direct the illumination beam to an overlay target on the specimen during scanning motion of the specimen relative to the illumination beam along a scan direction during execution of the metrology recipe; the overlay target associated with the metrology recipe has one or more cells, the or each cell having a Moiré structure formed as an overlapping grating structure having a different pitch on a first layer than on a second layer of the specimen, the overlapping grating structure being periodic along at least one of the scanning direction and a direction orthogonal to the scanning direction; a lighting subsystem; a collection subsystem configured to implement the metrology recipe; a first photodetector located at a first location in a pupil plane, the first photodetector capturing at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the one or more cells during execution of the metrology recipe; and a second photodetector located at a second location in the pupil plane and configured to capture at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the one or more cells during execution of the metrology recipe; a light collection subsystem comprising: a controller communicatively coupled to the first photodetector and the second photodetector and having one or more processors, the one or more processors configured to execute program instructions; receiving a time-varying interference signal associated with the Moire structure in the one or more cells from the first and second photodetectors during scanning movement of the overlay target in accordance with the metrology recipe; and determining an overlay error between the first layer and the second layer of the specimen based on the time-varying interference signal; a configured controller; An overlay metrology system comprising:

2. 2. The overlay metrology system of claim 1, wherein the first location of the first photodetector includes locations of +1st and 0th order Moire diffractions from the overlapping grating structures of the Moire structure, and the second location of the second photodetector includes locations of −1st and 0th order Moire diffractions from the overlapping grating structures of the Moire structure.

3. 3. The overlay metrology system of claim 2, wherein at least one of the first pitch and the second pitch of the overlapping grid structure is not resolved by the overlay metrology system.

4. 2. The overlay metrology system of claim 1, wherein the first location of the first photodetector includes a location of +1 order moire diffraction associated with the overlapping grating structures of the moire structure, and the second location of the second photodetector includes a location of −1 order moire diffraction associated with the overlapping grating structures of the moire structure.

5. 2. The overlay metrology system of claim 1, wherein the first location of the first photodetector includes an overlap between +1 order diffractions from the overlapping grating structures of the moiré structure, and the second location of the second photodetector includes an overlap between −1 order diffractions from the overlapping grating structures of the moiré structure.

6. 10. The overlay metrology system of claim 1, the first photodetector and the second photodetector include phase-locked photodetectors locked to the frequency of the time-varying interference signal; The one or more processors further execute program instructions to: extracting at least one of intensity and phase information of the time-varying interference signal using a phase-locking technique; and determining the overlay error between the first and second layers of the specimen based on the at least one of intensity and phase information; The configured overlay metrology system.

7. 10. The overlay metrology system of claim 1, wherein a spot size of an illumination lobe on the overlay target is elongated along a direction perpendicular to a stage scan direction, thereby providing target noise averaging.

8. 2. The overlay metrology system of claim 1, wherein the one or more illumination optics direct the illumination beams to the overlay target at an orthogonal angle of incidence.

9. 2. The overlay metrology system of claim 1, wherein the illumination beam: An overlay metrology system that includes a spatially coherent illumination beam.

10. 10. The overlay metrology system of claim 1, the one or more cells of the overlay target include two cells having a moiré structure that exhibits periodicity along the scanning direction; determining the overlay error between the first and second layers of the specimen based on the time-varying interference signals, determining the overlay error between the first and second layers of the specimen along the scanning direction based on the time-varying interference signals; Overlay metrology system.

11. 11. The overlay metrology system of claim 10, wherein the two cells include: a first cell having a first moiré structure formed by a first layer grating having a first pitch and on the first layer, and a second layer grating having a second pitch and on the second layer; a second cell having a second moiré structure formed by a first layer grating having the second pitch and on the first layer, and a second layer grating having the first pitch and on the second layer; Includes overlay metering system.

12. 10. The overlay metrology system of claim 1, the one or more cells of the overlay target include two cells having a moiré structure that exhibits periodicity along a direction orthogonal to the scanning direction; determining the overlay error between the first layer and the second layer of the specimen based on the time-varying interference signal; determining the overlay error between the first layer and the second layer of the specimen along a direction perpendicular to the scanning direction based on the time-varying interference signal; Overlay metrology system.

13. 13. The overlay metrology system of claim 12, wherein the two cells include: a first cell having a first moiré structure formed by a first layer grating having a first pitch and on the first layer, and a second layer grating having a second pitch and on the second layer; a second cell having a second moiré structure formed by a first layer grating having the second pitch and on the first layer, and a second layer grating having the first pitch and on the second layer; Includes overlay metering system.

14. 10. The overlay metrology system of claim 1, further comprising: an overlay metrology system comprising a translation stage that translates the specimen along the scan direction, wherein the one or more illumination optics direct the illumination beam to the overlay target on the specimen during scanning motion of the specimen by the translation stage.

15. 2. The overlay metrology system of claim 1, further comprising one or more beam scanning optics for causing scanning motion of said illumination beam along said scan direction.

16. 1. An overlay metrology system, comprising: a lighting subsystem configured to implement a metering recipe; a first illumination channel and a second illumination channel configured to execute the metrology recipe by illuminating an overlay target on the specimen with a first illumination beam and a second illumination beam during scanning of the specimen along a stage scan direction by a translation stage, the overlay target associated with the metrology recipe comprising: a first set of cells on the first and second layers of the specimen, the cells having a moiré structure formed as an overlapping grating structure with overlapping gratings having different pitches along a first direction; and a second set of cells on the first and second layers of the specimen, each having a moiré structure formed as an overlapping grating structure in which gratings having different pitches overlap each other along a second direction perpendicular to the first direction; wherein the stage scanning direction is angled with respect to the first direction and the second direction; the first illumination channel and the second illumination channel are separated along a direction perpendicular to the stage scan direction and illuminate separate cells of the overlay target; a lighting subsystem; a collection subsystem configured to implement the metrology recipe; a first detection channel and a second detection channel associated with the first illumination channel and the second illumination channel, respectively, wherein a particular detection channel comprises: a first photodetector located at a first location in a pupil plane to capture at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the overlay target during execution of the metrology recipe; and a second photodetector located at a second location in the pupil plane and configured to capture at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the overlay target during execution of the metrology recipe; a light collection subsystem comprising: a controller communicatively coupled to the first and second photodetectors and having one or more processors, the one or more processors configured to execute program instructions; receiving a time-varying interference signal from the first photodetector and the second photodetector of the first detection channel and the second detection channel, respectively, during scanning motion of the overlay target during execution of the metrology recipe; and determining an overlay error between the first layer and the second layer of the specimen based on the time-varying interference signal; a configured controller; An overlay metrology system comprising:

17. 17. The overlay metrology system of claim 16, wherein the first set of cells of the overlay target are distributed along the stage scan direction and aligned with the first illumination channel, and the second set of cells of the overlay target are distributed along the stage scan direction and aligned with the second illumination channel.

18. 17. The overlay metrology system of claim 16, wherein the first set of cells of the overlay target are distributed along a first diagonal direction relative to the stage scan direction, with one cell of the first set aligned with the first illumination channel and one cell of the first set aligned with the second illumination channel; and the second set of cells of the overlay target are distributed along a second diagonal direction perpendicular to the first diagonal direction, with one cell of the second set aligned with the first illumination channel and one cell of the second set aligned with the second illumination channel.

19. 17. The overlay metrology system of claim 16, wherein the first set of cells comprises: a first cell having a first moiré structure formed by a first layer grating having a first pitch and on the first layer, and a second layer grating having a second pitch and on the second layer; a second cell having a second moiré structure formed by a first layer grating having the second pitch and on the first layer, and a second layer grating having the first pitch and on the second layer; and the second set of cells includes: a third cell having a third moiré structure formed by a first layer grating having the first pitch and on the first layer, and a second layer grating having the second pitch and on the second layer; a fourth cell having a fourth moiré structure formed by a first layer grating having the second pitch and on the first layer, and a second layer grating having the first pitch and on the second layer; Includes overlay metering system.

20. 17. The overlay metrology system of claim 16, wherein the first location of the first photodetector includes a location of +1 order moire diffraction from the overlapping grating structures of the moire structure, and the second location of the second photodetector includes a location of −1 order moire diffraction from the overlapping grating structures of the moire structure.

21. 17. The overlay metrology system of claim 16, wherein the first location of the first photodetector includes an overlap between +1 order moire diffraction and 0 order light associated with moire diffraction from the overlapping grating structures of the moire structure, and the second location of the second photodetector includes an overlap between −1 order moire diffraction and 0 order light associated with moire diffraction from the overlapping grating structures of the moire structure.

22. 22. The overlay metrology system of claim 21, wherein at least one of the first pitch and the second pitch of the overlapping grid structure is not resolved by the overlay metrology system.

23. 17. The overlay metrology system of claim 16, wherein the first location of the first photodetector includes an overlap between +1 order diffractions from the overlapping grating structures of the moiré structure, and the second location of the second photodetector includes an overlap between −1 order diffractions from the overlapping grating structures of the moiré structure.

24. 17. The overlay metrology system of claim 16, the first photodetector and the second photodetector of the first detection channel and the second detection channel, respectively, include a phase-locked photodetector that is locked to the frequency of the time-varying interference signal; The one or more processors further execute program instructions to: extracting at least one of intensity and phase information of the time-varying interference signal using a phase-locking technique; and determining the overlay error between the first and second layers of the specimen based on the at least one of intensity and phase information; The configured overlay metrology system.

25. 17. The overlay metrology system of claim 16, wherein the first illumination beam has a polarization that is orthogonal to a polarization of the second illumination beam.

26. 17. The overlay metrology system of claim 16, wherein the first illumination beam has a different wavelength than the second illumination beam.

27. 17. The overlay metrology system of claim 16, wherein the first illumination beam and the second illumination beam comprise spatially coherent illumination beams.

28. 1. An overlay metrology system, comprising: a lighting subsystem configured to implement a metering recipe; an illumination source configured to generate an illumination beam; and a deflector configured to cause a scanning motion of the illumination beam along a beam scan direction across an overlay target on the specimen when the specimen is translated along a stage scan direction orthogonal to the beam scan direction by a translation stage during execution of the metrology recipe; the overlay target associated with the metrology recipe has one or more cells, the one or more cells having a moiré structure formed as an overlapping grating structure in which gratings with different pitches overlap on a first layer and a second layer, the overlapping grating structure being periodic along at least one of the stage scanning direction and a direction orthogonal to the stage scanning direction, and the one or more cells being distributed along a diagonal direction angled with respect to the stage scanning direction; a lighting subsystem; a collection subsystem configured to implement the metrology recipe; a first photodetector located at a first location in a pupil plane, the first photodetector capturing at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the one or more cells during execution of the metrology recipe; and a second photodetector located at a second location in the pupil plane and configured to capture at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the one or more cells during execution of the metrology recipe; a light collection subsystem comprising: a controller communicatively coupled to the first photodetector and the second photodetector and having one or more processors, the one or more processors configured to execute program instructions; receiving time-varying interference signals from the first photodetector and the second photodetector during scanning movement of the overlay target according to the metrology recipe; and determining an overlay error between the first layer and the second layer of the specimen based on the time-varying interference signal; a configured controller; An overlay metrology system comprising:

29. 30. The overlay metrology system of claim 28, wherein the first location of the first photodetector includes a location of +1 order moire diffraction from the overlapping grating structures of the moire structure, and the second location of the second photodetector includes a location of −1 order moire diffraction from the overlapping grating structures of the moire structure.

30. 30. The overlay metrology system of claim 28, wherein the first location of the first photodetector includes an overlap between +1 order moire diffraction and 0 order light associated with moire diffraction from the overlapping grating structures of the moire structure, and the second location of the second photodetector includes an overlap between −1 order moire diffraction and 0 order light associated with moire diffraction from the overlapping grating structures of the moire structure.

31. 31. The overlay metrology system of claim 30, wherein at least one of the first pitch and the second pitch of the overlapping grid structure is not resolved by the overlay metrology system.

32. 30. The overlay metrology system of claim 28, wherein the first location of the first photodetector includes an overlap between +1 order diffractions from the overlapping grating structures of the moiré structure, and the second location of the second photodetector includes an overlap between −1 order diffractions from the overlapping grating structures of the moiré structure.

33. 30. The overlay metrology system of claim 28, the first photodetector and the second photodetector include phase-locked photodetectors locked to the frequency of the time-varying interference signal; The one or more processors further execute program instructions to: extracting at least one of intensity and phase information of the time-varying interference signal using a phase-locking technique; and determining the overlay error between the first and second layers of the specimen based on the at least one of intensity and phase information; The configured overlay metrology system.

34. 30. The overlay metrology system of claim 28, wherein a spot size of the illumination beam on the overlay target is elongated, thereby providing target noise averaging.

35. 30. The overlay metrology system of claim 28, wherein the illumination beam: An overlay metrology system that includes a spatially coherent illumination beam.

36. 30. The overlay metrology system of claim 28, the one or more cells of the overlay target include two cells having a moiré structure that exhibits periodicity along the stage scanning direction; determining the overlay error between the first and second layers of the specimen based on the time-varying interference signals, determining the overlay error between the first and second layers of the specimen along the stage scan direction based on the time-varying interference signals; Overlay metrology system.

37. 37. The overlay metrology system of claim 36, wherein the two cells include: a first cell having a first moiré structure formed by a first layer grating having a first pitch and on the first layer, and a second layer grating having a second pitch and on the second layer; a second cell having a second moiré structure formed by a first layer grating having the second pitch and on the first layer, and a second layer grating having the first pitch and on the second layer; Includes overlay metering system.

38. 30. The overlay metrology system of claim 28, the one or more cells of the overlay target include two cells having a moiré structure that exhibits periodicity along the beam scanning direction; determining the overlay error between the first and second layers of the specimen based on the time-varying interference signals, determining the overlay error between the first and second layers of the specimen along the beam scanning direction based on the time-varying interference signals; Overlay metrology system.

39. 39. The overlay metrology system of claim 38, wherein the two cells include: a first cell having a first moiré structure formed by a first layer grating having a first pitch and on the first layer, and a second layer grating having a second pitch and on the second layer; a second cell having a second moiré structure formed by a first layer grating having the second pitch and on the first layer, and a second layer grating having the first pitch and on the second layer; Includes overlay metering system.

40. 1. An overlay metrology system, comprising: a lighting subsystem configured to implement a metering recipe; a first illumination channel providing a first illumination beam; a second illumination channel providing a second illumination beam; and one or more deflectors for scanning the first illumination beam and the second illumination beam across portions of an overlay target on the specimen along a beam scan direction when the specimen is scanned along a stage scan direction using a translation stage during execution of the metrology recipe; wherein the overlay target associated with the metrology recipe is a first set of cells having a moiré structure formed as an overlapping grating structure in which gratings having different pitches on a first layer and a second layer along the stage scanning direction overlap; and a second set of cells having a moiré structure formed as an overlapping grating structure in which gratings having different pitches on the first layer and the second layer along the beam scanning direction overlap each other; wherein the first illumination channel and the second illumination channel illuminate separate cells of the overlay target that are separated along the beam scanning direction. a lighting subsystem; a collection subsystem configured to implement the metrology recipe; a first detection channel and a second detection channel associated with the first illumination channel and the second illumination channel, respectively, wherein a particular detection channel comprises: a first photodetector located at a first location in a pupil plane to capture at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the overlay target during execution of the metrology recipe; and a second photodetector located at a second location in the pupil plane and configured to capture at least one of multiple Moire diffraction orders and multiple overlapping diffraction orders from the Moire structure in the overlay target during execution of the metrology recipe; a light collection subsystem comprising: a controller communicatively coupled to the first photodetector and the second photodetector and having one or more processors, the one or more processors configured to execute program instructions; receiving a time-varying interference signal from the first photodetector and the second photodetector of the first detection channel and the second detection channel, respectively, during scanning movement of the overlay target according to the metrology recipe; and determining an overlay error between the first layer and the second layer of the specimen based on the time-varying interference signal; a configured controller; An overlay metrology system comprising:

41. 41. The overlay metrology system of claim 40, wherein the first set of cells of the overlay target are distributed along the stage scan direction and aligned with the first illumination channel, and the second set of cells of the overlay target are distributed along the stage scan direction and aligned with the second illumination channel.

42. 41. The overlay metrology system of claim 40, wherein the first set of cells of the overlay target are distributed along a first diagonal direction relative to the stage scan direction, with one cell of the first set aligned with the first illumination channel and one cell of the first set aligned with the second illumination channel; and the second set of cells of the overlay target are distributed along a second diagonal direction perpendicular to the first diagonal direction, with one cell of the second set aligned with the first illumination channel and one cell of the second set aligned with the second illumination channel.

43. 41. The overlay metrology system of claim 40, wherein the first set of cells comprises: a first cell having a first moiré structure formed by a first layer grating having a first pitch and on the first layer, and a second layer grating having a second pitch and on the second layer; a second cell having a second moiré structure formed by a first layer grating having the second pitch and on the first layer, and a second layer grating having the first pitch and on the second layer; and the second set of cells includes: a third cell having a third moiré structure formed by a first layer grating having the first pitch and on the first layer, and a second layer grating having the second pitch and on the second layer; a fourth cell having a fourth moiré structure formed by a first layer grating having the second pitch and on the first layer, and a second layer grating having the first pitch and on the second layer; Includes overlay metering system.

44. 41. The overlay metrology system of claim 40, wherein the first location of the first photodetector includes a location of +1 order moire diffraction from the overlapping grating structures of the moire structure, and the second location of the second photodetector includes a location of -1 order moire diffraction from the overlapping grating structures of the moire structure.

45. 45. The overlay metrology system of claim 44, wherein at least one of the first pitch and the second pitch of the overlapping grid structure is not resolved by the overlay metrology system.

46. 41. The overlay metrology system of claim 40, wherein the first location of the first photodetector includes an overlap between +1 order moire diffraction and 0 order light associated with moire diffraction from the overlapping grating structures of the moire structure, and the second location of the second photodetector includes an overlap between −1 order moire diffraction and 0 order light associated with moire diffraction from the overlapping grating structures of the moire structure.

47. 41. The overlay metrology system of claim 40, wherein the first location of the first photodetector includes an overlap between +1 order diffractions from the overlapping grating structures of the moiré structure, and the second location of the second photodetector includes an overlap between −1 order diffractions from the overlapping grating structures of the moiré structure.

48. 41. The overlay metrology system of claim 40, the first photodetector and the second photodetector of the first detection channel and the second detection channel, respectively, include a phase-locked photodetector that is locked to the frequency of the time-varying interference signal; The one or more processors further execute program instructions to: extracting at least one of intensity and phase information of the time-varying interference signal using a phase-locking technique; and determining the overlay error between the first and second layers of the specimen based on the at least one of intensity and phase information; The configured overlay metrology system.

49. 41. The overlay metrology system of claim 40, wherein the first illumination beam has a polarization that is orthogonal to a polarization of the second illumination beam.

50. 41. The overlay metrology system of claim 40, wherein the first illumination beam has a different wavelength than the second illumination beam.

51. 41. The overlay metrology system of claim 40, wherein the first illumination beam and the second illumination beam are: An overlay metrology system that includes a spatially coherent illumination beam.

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