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 generally refers to 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, typically refers to 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. Patent No. 10,824,079 [Patent Document 3] U.S. Patent No. 10,197,389 [Patent Document 4] U.S. Patent No. 7,440,105 [Patent Document 5] U.S. Patent No. 1,164,307 [Patent Document 6] U.S. Patent Application Publication No. 2021 / 0072650 [Patent Document 7] US Patent Application Publication No. 2022 / 0034652 [Patent Document 8] U.S. Patent No. 1,107,3768 [Patent Document 9] U.S. 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. Metrology systems typically generate metrology data for a specimen 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 so that the metrology targets are sequentially moved 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 for the translation stage to stabilize prior to measurement, which can adversely affect throughput. Therefore, it would be desirable to provide a system and method that can address 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 including 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 having 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, the system includes a collection subsystem including a first photodetector located at a first location in the pupil plane and configured to capture at least one of multiple Moiré diffraction orders and multiple overlapping diffraction orders from the Moiré structure in the one or more cells during execution of a metrology recipe, and a second photodetector located at a second location in the pupil plane and configured to capture at least one of multiple Moiré diffraction orders and multiple overlapping diffraction orders from the Moiré structure in the one or more cells during execution of a metrology recipe. In another example embodiment, the system includes a controller configured to receive time-varying interference signals associated with the Moiré structure in the one or more cells from the first and second photodetectors during scanning of the overlay target in accordance with the metrology recipe, and to determine 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 that illuminate an overlay target on a specimen when the specimen is scanned along a stage scan direction by a translation stage during execution of a metrology recipe. In another 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 another 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, each associated with a first illumination channel and a second illumination channel, respectively. In another 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 Moiré diffraction orders and multiple overlapping diffraction orders from the Moiré structure within 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 Moiré diffraction orders and multiple overlapping diffraction orders from the Moiré structure within the one or more cells during execution of the metrology recipe. In another 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 according to 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 one exemplary embodiment, the system includes an illumination subsystem including an illumination source that generates an illumination beam. In another 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 orthogonal to the beam scan direction when the specimen is translated along the stage scan direction by a translation stage during metrology recipe execution. In another exemplary embodiment, the overlay target associated with the metrology recipe includes 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, the overlapping grating structure being periodic along at least one of the scan direction and a direction orthogonal to the stage scan direction, the one or more cells being distributed along a diagonal direction angled with respect to the stage scan direction. In one example embodiment, the system includes a collection subsystem including a first photodetector located at a first location in the pupil plane and configured to capture at least one of multiple Moiré diffraction orders and multiple overlapping diffraction orders from the Moiré 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 Moiré diffraction orders and multiple overlapping diffraction orders from the Moiré structure in the one or more cells during execution of the metrology recipe. In another example embodiment, the system includes a controller configured to receive time-varying interference signals from the first and second photodetectors during scanning of the overlay target during execution of the metrology recipe, and to determine 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 in accordance with 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 that scan 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 the stage scan direction during metrology recipe execution. 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 the stage scan direction, and a second set of cells having a Moiré structure formed as an overlapping grating structure with unequal pitches along the beam scan direction. In another 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, each of which is associated with a first illumination channel and a second illumination channel. In another 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 Moiré diffraction orders and multiple overlapping diffraction orders from the Moiré structure within 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 Moiré diffraction orders and multiple overlapping diffraction orders from the Moiré structure within the one or more cells during execution of the metrology recipe. In another 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 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 explanation 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 moiré structure, in accordance with one or more embodiments of the present disclosure. [Figure 1B] FIG. 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] 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] 1 is a side view of an overlay target having two cells with different moiré structure configurations suitable for overlay measurement along a particular measurement direction, according to one or more embodiments of the present disclosure. FIG. [Figure 3A] FIG. 1 illustrates a top view of an illumination pupil at an illumination pupil plane of an overlay metrology tool according to one or more embodiments of the present disclosure. [Figure 3B] 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. FIG. [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 the separated first order Moire diffraction of the illumination profile of FIG. 3A and the underlying Moire structure. [Figure 3D] 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 the underlying moiré structure. [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, according to one or more embodiments of the present disclosure. [Figure 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 moiré 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 oriented diagonally relative to the stage scan direction, in accordance with one or more embodiments of the present disclosure. [Figure 6B] FIG. 10 is a top view of a second 2D overlay target having cells with periodicity oriented diagonally 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. 10 is a top view of a second overlay target suitable for overlay measurement along the X direction with a scanning motion of the 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 using 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. 10 is a top view of a second overlay target suitable for overlay measurement along the X direction with a scanning motion of the 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. 10 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 INVENTION

[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 particularly shown and described with reference to certain embodiments and their particular features. The embodiments described herein are to 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 therein 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 moiré structures, for example, the moiré 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 to broadly encompass scatterometry-based metrology and diffraction-based metrology, i.e., illuminating a specimen having periodic features on one or more specimen 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 specimen is in motion relative to the illumination used for the measurement. In general, scanning metrology can be performed by moving the specimen, 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 two specimen layers within an overlap region. Various techniques for determining overlay metrology with such scatterometry overlay targets are outlined in U.S. Patent No. 6,233,999, published November 25, 2021, U.S. Patent No. 6,233,999, published November 3, 2020, and U.S. Patent No. 6,233,999, published February 9, 2019, all of which are incorporated herein by reference in their entireties.

[0016] Further contemplation herein 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 moiré diffraction patterns. The moiré diffraction patterns can be related to the overlay through a gain factor related to the difference between the pitches of the constituent gratings. As a result, such overlay targets can achieve highly sensitive overlay metrology. Overlay metrology using overlay targets with moiré grating structures is generally described in U.S. Patent No. 6,239,999, issued October 21, 2008; U.S. Patent No. 6,239,999, issued November 2, 2021; U.S. Patent No. 6,239,999, issued March 21, 2021; and U.S. Patent No. 6,239,999, issued February 9, 2019, all of which are incorporated herein by reference in their entireties.

[0017] However, overlay targets with moiré structures 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 these position-dependent offsets and fully characterize the moiré structure. While static image-based systems can capture such position-dependent differences in apparent overlay within a single image (e.g., as position-dependent phase), 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 entire moiré structure.

[0018] Embodiments of the present disclosure are directed to scanning overlay metrology systems and methods based on time-varying interference signals from Moiré structures at a collection pupil plane. It is contemplated herein that metrology conditions leading to multiple overlapping or multiple Moiré diffraction orders (e.g., compound diffraction, double diffraction, etc.) from the constituent gratings of the Moiré structure can lead to interference. Such interference signals can contain information about asymmetries within the target structure, such as, but not limited to, overlay between upper and lower gratings. It is further contemplated herein that scanning the Moiré structure relative to an illumination beam (or vice versa) can characterize the position-dependent overlay of the Moiré structure, thereby enabling 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 the upper and lower gratings of a moiré structure or associated with moiré diffraction from the moiré structure. Overlay metrology of common-pitch grating-over-grating structures based on time-varying interference signals in the collection pupil is outlined in U.S. Patent No. 6,299,234, published February 3, 2022, and incorporated herein by reference in its entirety. In U.S. Patent No. 6,999,234, overlay measurements of common-pitch grating-over-grating structures are generated based on a comparison of time-varying interference patterns within overlap regions between the zeroth and ±1st diffraction orders generated during scanning and captured within those regions by a photodetector. Contemplated herein, the systems and methods of U.S. Patent No. 6,999,234 can be adapted, e.g., extended, to perform overlay metrology of moiré structures. In doing so, certain embodiments of the present disclosure extend or adapt the systems and methods of U.S. Patent No. 6,999,234 to incorporate differences between common-pitch grating-over-grating structures and moiré structures. However, the present disclosure is not limited to such extensions or adaptations of the systems and methods of US Pat. No. 6,279,999.

[0020] In certain embodiments of the overlay metrology system, a photodetector is positioned in the pupil plane at a location 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 positioned at a location where a Moiré diffraction lobe overlaps with a zero-order diffraction (e.g., specular reflection). Alternatively, the photodetector can be positioned at a location where only a Moiré diffraction lobe exists. As contemplated herein, time-varying interference signals (e.g., AC signals) resulting from these multiple-order complex diffractions appear during scanning measurements and can be captured using a photodetector. For example, by appropriately selecting the characteristics of the Moiré structure (e.g., the pitch of the composite grating) and / or the measurement conditions (e.g., illumination wavelength, illumination angle of incidence, collection angle, etc.), the positive and negative Moiré diffraction orders (e.g., double diffraction orders) associated with the complex diffraction from the Moiré structure grating can be collected by the system and captured by the photodetector. As contemplated herein, the pitch of the compositional grating of the Moiré structure does not need to be resolved by the overlay system. Furthermore, this configuration allows the pitch of the Moiré structure to be similar to that of 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 measurement. In this manner, 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., illumination angles and the associated illumination intensity distribution at those angles), polarization of incident illumination, or spatial distribution of illumination. According to another example, a metrology recipe can include light collection parameters, such as, but not limited to, collection pupil distribution (e.g., desired distribution of angular measurement light from the specimen 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, a metrology recipe can include various parameters related to 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 velocity, 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., designed (e.g., using a metrology recipe), to produce a specified distribution of Moiré diffraction orders and / or composite diffraction, and further, to position the photodetector in a location appropriate for capturing those diffraction orders and generating a time-varying interference signal of interest.

[0023] The disclosed systems and methods may be suitable for a wide range of specimen layouts, including specimens with relatively thin specimen layers and specimens with relatively thick specimen layers. For example, the disclosed systems and methods may be well suited to specimens with relatively thin specimen 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 specimens with relatively thick layers. In such cases, the photodetectors may be precisely positioned within the symmetric regions of the positive and negative diffraction orders. Furthermore, the system and / or measurements may be calibrated to improve measurement accuracy.

[0024] Further contemplated herein, the disclosed systems and methods are capable of high-sensitivity overlay metrology at high throughput. For example, non-imaging configurations allow the use of high-speed photodetectors suitable for high scanning speeds. By way of a non-limiting example, a photodetector with a bandwidth of 1 GHz can achieve a scanning speed of approximately 10 centimeters per second on a 1-micrometer pitch moiré target.

[0025] Additionally, the disclosed systems and methods can be relatively insensitive to target edge effects, enabling the use of small targets and more efficient use of the space on the specimen required for overlay metrology. For example, target edge effects typically manifest 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 at the pupil plane) and capture time-varying data at those angles. Furthermore, according to certain embodiments, extending the illumination beam along the grating structure direction (e.g., perpendicular to the periodicity direction) can smooth out target noise related to small fluctuations in Moiré-structured features.

[0026] These Moiré structures may generally be formed as part of overlay targets and may generally be located anywhere on the specimen. According to certain embodiments, overlay metrology can be performed directly on device features having suitable geometries. According to other examples, overlay metrology can be performed on dedicated overlay targets, which can be located in any suitable location, including, but not limited to, within a die or at an inter-die scribe line. Thus, overlay measurements on the overlay target can serve as a proxy for the overlay of the device features. Dedicated overlay targets generally have features designed to enable accurate overlay metrology based on a specific overlay metrology technique. Furthermore, the overlay target may have one or more metrology cells, and printed elements within each cell that are within overlapping regions of one or more layers on the specimen may form Moiré structures. Overlay metrology can then be based on any combination of measurements from 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 the grating 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 measurements in at least two directions. In certain embodiments, an overlay target includes two sets of cells, one set of cells having Moiré 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 Moiré 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 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 the first set of cells are periodic along the stage scan direction and the Moiré structures in the 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 can 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, cells within two or more rows can be simultaneously illuminated by two or more illumination beams for parallel measurement while the sample is scanned along the stage scan direction. Furthermore, each of these spatially separated illumination beams can have different optical parameters, such as, but not limited to, polarization or wavelength. This type of optical parameter multiplexing can provide various benefits, including, but not limited to, improving measurement accuracy and / or sensitivity by generating metrology data with multiple optical configurations or providing an efficient mechanism for separating measurement light from the sample associated with different illuminated cells. It should be 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 scanning a specimen can eliminate the stage acceleration / deceleration time required to capture a stationary target image, thereby providing a relatively high measurement throughput. This can significantly increase the number of overlay measurements within a given time period. According to another example, the disclosed systems and methods enable the use of a relatively large portion of the pupil, thereby achieving high light budget and corresponding signal-to-noise ratio benefits. According to 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. Alternatively, as previously mentioned, the relative insensitivity to target edge effects and the provision of noise smoothing through spot shape control may allow the use of relatively small targets, thereby facilitating both high speed measurements and efficient use of space above the specimen. Note that these considerations may also apply to metrology systems designed for stationary targets.

[0031] Further contemplation herein reveals that the scatterometry overlay metrology of 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 / 140,999, filed January 4, 2021, the entire contents of which are incorporated herein by reference.

[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] FIG. 1A is a conceptual diagram of an overlay metrology system 100 that performs scatterometry overlay metrology on an overlay target having at least one moiré structure, according to one or more embodiments of the present disclosure. The overlay metrology system 100 of certain embodiments includes an overlay metrology tool 102 that performs 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. FIG. 1B is a schematic diagram of the overlay metrology tool 102, according to 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 one or more illumination beams 108 can be angularly confined on the specimen 104, thereby producing discrete diffraction orders due to Moiré structures (e.g., within one or more cells of the overlay target). Additionally, the one or more illumination beams 108 can be spatially confined, thereby illuminating a specified portion of the specimen 104. For example, each of the one or more illumination beams 108 can be spatially confined to illuminate a specific cell of the overlay target. In certain embodiments, the one or more illumination beams 108 can underfill a specific cell of the overlay target.

[0035] At least some diffraction orders associated with the diffraction of the illumination beam 108 from the Moiré structure can then be collected by a collection subsystem 110. The collection subsystem 110 can further include at least two photodetectors 112 positioned within a collection pupil plane 114 at locations associated with the time-varying interference signal indicative of overlay. For example, as described in more detail below, suitable locations for the photodetectors 112 can include, but are not limited to, locations associated with positive and negative Moiré diffraction orders (e.g., multiple diffraction orders, double diffraction orders, etc.) and locations associated with overlap between diffraction orders of the constituent gratings of the Moiré structure (e.g., overlap regions between the +1 diffraction order of the upper and lower gratings and overlap regions between the −1 diffraction order of the 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, the 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 orthogonal to the scan direction being measured (e.g., the direction in which the translation stage 116 scans the specimen 104).

[0038] 2A-3B, the collection of diffraction orders from the moiré structure 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] Figure 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. Figure 2B is a side view of a single cell 202 of the overlay target 204 of Figure 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) located on a first layer 212 of the specimen 104 and a second layer grating 214 (e.g., a lower grating) located 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. Furthermore, the first layer grating 210 and the second layer grating 214 have different pitches. For example, in FIG. 2B, the pitches of the first layer grating 210 and the 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. Furthermore, in certain embodiments, an overlay target 204 may have multiple cells 202 with moiré structures 206 that are periodic along a common direction, with different cells 202 having different configurations of the periodicity of the associated grating.

[0041] 2C illustrates a side view of an overlay target 204 suitable for overlay measurement along a particular measurement direction (e.g., the X direction here) according to one or more embodiments of the present disclosure, the overlay target 204 having two cells 202a,b with different configurations of Moiré structures 206. Specifically, FIG. 2C illustrates an inverted Moiré structure pair, where 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 the first pitch (P). This inverted Moiré structure pair facilitates overlay determination based on time-varying interference signals generated when both cells 202 are scanned 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, thereby enabling known and accountable phase transitions associated with the degenerated interference signal. Such an arrangement of the inverted moiré structure pair can be referred to as a vertical overlay target, although this is not required. Notably, 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 provides a reference point for the phase transition (e.g., φ) at the center of the composite inverted moiré structure pair, as will be described in more detail below.

[0043] It should be understood, however, that the overlay target 204 and related description in Figures 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 include any number of cells 202 suitable for measurement 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. 2021 / 012999, issued July 27, 2021, which is incorporated herein by reference in its entirety. In certain embodiments, the overlay target 204 includes one or more cell groups distributed along a scanning direction (e.g., the direction of movement 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. This allows all cells 202 in a particular cell group to be simultaneously imaged as the sample 104 is scanned through the field of view of the collection subsystem 110. By way of 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. 2021 / 012999, published November 25, 2021, the entire contents of which are incorporated herein by reference.

[0044] 2A also illustrates an illumination spot on the cell 202 associated with 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, thereby minimizing or substantially eliminating target edge effects. 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 illumination beam 108 along the measurement direction (here, the X direction) is set to approximately half the pitch of the grating in moiré structure 206. By way of a non-limiting example, dimensions of 1.5 micrometers in the Y direction and 0.5 micrometers in the X direction, which may be suitable for illumination beam 108 dimensions for 10-micrometer square cells 202, can be achieved with an oval pupil in illumination pupil plane 120 with a NA of 0.9 x 0.3. However, it should be understood that the depiction of illumination beam 108 in FIG. 2A is provided solely for illustrative purposes and should not be construed as limiting. Illumination beam 108 may generally be 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 mitigate 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 Moiré structures 206 within cells 202 of overlay target 204 will be described in accordance with one or more embodiments of the present disclosure.

[0048] 3A illustrates 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 may correspond to a pupil plane within 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 may illuminate the overlay target 204 over a limited range of angles of incidence, as depicted by the limited size within the collection pupil plane 114. In this case, the overlay target 204 may 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 an overlay target 204 with a moiré structure 206 in a scanning configuration. In particular, FIGS. 3B-3D depict various non-limiting configurations that the diffraction orders of the illumination beam 108 depicted in FIG. 3A may assume at the collection pupil plane 114, and the associated locations of the photodetector 112 suitable for capturing time-varying interference signals from which an overlay measurement can 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., compound 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 the 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 associated diffraction lobe is incident on (e.g., within the measurement area of) that photodetector 112. This allows associated diffraction lobes to overlap on photodetector 112, while eliminating the need for overlap 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, such as the moiré structures 206, can be affected by various parameters, including, but not limited to, the wavelength of the illumination beam 108, the angle of incidence of the illumination beam 108 in both the 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 can 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 can be configured to generate measurements of moiré structures having a specified range of periodicity, resulting in a desired distribution within the collection pupil plane 114. Additionally, various components (eg, diaphragms, 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] 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, showing the moiré diffraction lobes due to the moiré structures 206 associated with the illumination profile of FIG. 3A. For example, the collection pupil plane 114 can be mapped to the pupil plane within the collection subsystem 110 as depicted in FIG. 1B. In particular, the depiction in FIG. 3B shows that the 0th diffraction order 306, the −1st moiré diffraction order 308 (e.g., −M diffraction), and the +1st moiré diffraction order 310 (e.g., +M diffraction) are distributed along the periodicity direction (e.g., the X direction here) of the moiré structures 206 at the collection pupil plane 114. For example, the -1st order moiré diffraction 308 and the +1st order moiré diffraction 310 can be associated with moiré 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 moiré interference related to the pitch difference between the first layer grating 210 and the second layer grating 214.

[0053] As contemplated herein, by oscillating the phase of each of the Moiré diffraction orders (e.g., −1 Moiré diffraction order 308 and +1 Moiré diffraction order 310) during scanning, a time-varying interference signal can be formed, and overlay can be determined based on the asymmetry of these oscillations. 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 positioned to capture overlapping zeroth-order and moiré diffractions. For example, the configuration depicted in FIG. 3B overlaps the moiré diffraction lobe with the zeroth-order diffraction lobe in the collection pupil plane 114 (e.g., as suggested by a metrology recipe). FIG. 3B also depicts a first photodetector 112a positioned at the overlap with the −1st-order moiré diffraction 308 and a second photodetector 112b positioned at the overlap with the +1st-order moiré diffraction 310. Each photodetector 112 can then capture a time-varying interference signal as the specimen 104 undergoes scanning motion, and the difference between the time-varying interference signals captured by the photodetectors 112 indicates overlay.

[0055] As contemplated herein, the pitch difference between the upper and lower 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, scanning the overlay target 204 along the periodic direction of the moiré structure 206 (e.g., the X direction in FIGS. 2A and 2B ) shifts the phases of the moiré diffraction orders in opposite directions. However, by capturing the phase shifts throughout the entire length of the moiré structure 206 along the measurement direction during scanning, 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 using an image-based system, while 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 inverse Moiré 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] It should be understood, however, that the specific configuration depicted in Figure 3B and the associated description are not limiting. For example, as described herein, it is not necessary for the zeroth diffraction order 306 to overlap with the -1st Moiré diffraction order 308 and the +1st Moiré diffraction order 310 within the collection pupil 304 as depicted in Figure 3B. Rather, according to certain embodiments, the diffraction lobes can be positioned close enough so that the zeroth diffraction order 306 overlaps with the -1st Moiré diffraction order 308 on the first photodetector 112a and the zeroth diffraction order 306 overlaps with the +1st Moiré diffraction order 310 on the second photodetector 112b. Additionally, in certain embodiments, overlay measurements are determined based on the time-varying signal associated with only the first Moiré diffraction order lobe (e.g., without reference to the zeroth diffraction order 306). FIG. 3C is a top view of the collection pupil 304 of the overlay metrology tool 102 according to one or more embodiments of the present disclosure, showing the isolated first order Moiré diffraction of the illumination profile of FIG. 3A due to the Moiré 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, showing the overlapping first diffraction orders of the illumination profile of Figure 3A due to the moiré 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 moiré diffraction order 308, and +1st moiré 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 +1 order diffraction 320 (+1 TOP ) and +1st order diffraction 322 (+1 BOTTOM ) in a second overlap region 318 between the first and second diffraction orders 314, 316, 320, and 322. Furthermore, the first diffraction order lobes 314, 316, 320, and 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] It is contemplated herein that by vibrating the intensity and phase in each of the overlap regions (e.g., first overlap region 312 and second overlap region 318) in Figure 3D, time-varying interference patterns similar to those in Figure 3B can be formed that also indicate overlay between first layer 212 and second layer 216. In this way, a measurement of the physical overlay-to-physical overlay overlay (or overlay error) between first layer 212 and second layer 216 can similarly be 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 inverse Moiré structure pair is:

[0066]

number

[0067] Based on equations (6) and (7), the phase information for the negative diffraction order 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 written 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 cases depicted in FIGS. 3A-3D are for the diffraction of illumination beam 108 incident on a specimen at normal incidence. However, as contemplated herein, illumination beam 108 may generally have any profile suitable for achieving collection of multiple complex or overlapping diffraction orders (e.g., multiple Moiré diffraction orders associated with complex diffraction from overlapping gratings of moiré structure 206, overlapping Moiré diffraction and zeroth order diffraction, overlapping first order diffraction from overlapping gratings of moiré structure 206, etc.) as disclosed herein. In certain embodiments, illumination beam 108 has an annular profile. As contemplated herein, an annular profile of illumination beam 108 facilitates separation of multiple overlapping diffraction orders in collection pupil plane 114. The use of an annular aperture to separate overlapping diffraction orders is generally described in U.S. Patent Application Publication No. 2019 / 023999, issued February 9, 2019, which is incorporated herein by reference in its entirety. It is noted that while U.S. Patent Application Publication No. 2019 / 023999 describes stationary metrology, the use of annular illumination beam 108 can be utilized in scanning metrology as well, as disclosed herein. Notably, in certain embodiments, photodetector 112 is positioned at the location of overlapping diffraction orders generated by annular illumination beam 108 (e.g., overlapping Moiré and zeroth diffraction orders, overlapping first diffraction orders from the composite grating of Moiré structure 206, etc.).

[0070] Referring again to FIG. 1A, additional components of the overlay metrology tool 102 will now be 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 of one or more illumination beams 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 temporal 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 value 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 terms "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 configured to operate or operate in conjunction with the overlay metrology system 100 as described elsewhere in this disclosure. Additionally, various subsystems of the overlay metrology system 100 may include processors or logic elements suitable for performing at least a portion of the steps described herein. Therefore, the above description should be construed as merely illustrative and not limiting 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 include one or more controllers housed within a common housing or in multiple housings. In this manner, any controller or combination of controllers may be individually packaged 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, storage device 126 may include any storage medium known in the art suitable for storing program instructions executable by one or more associated processors 124. For example, storage device 126 may include a non-transitory storage medium. As additional examples, 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 storage device 126 may be housed within a common controller housing along with one or more processors 124.

[0076] In this regard, the controller 122 can perform any of a variety of process steps associated with overlay metrology. For example, the controller 122 can 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 can be configured to command the translation stage 116 to translate the specimen 104 along one or more measurement paths or swaths, thereby scanning 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 can be configured to receive a signal corresponding to the time-varying interference signal from the photodetector 112. According to another example, based on the overlay measurements from the overlay metrology tool 102, the controller 122 may generate collectables (correction variables) for one or more additive manufacturing tools as feedback and / or feedforward control of the one or more additive manufacturing tools.

[0077] In another embodiment, controller 122 captures the interference signal detected by photodetector 112. 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. Furthermore, 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 a 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) through (15). For example, U.S. Patent No. 6,275,999, previously referenced and incorporated herein by reference in its entirety, outlines the electric fields of diffraction orders at the collection pupil and further describes a specific relationship between measured intensity at the pupil plane and overlay. Contemplated herein, the systems and methods disclosed herein enable the teachings of U.S. Patent No. 6,275,999 to be extended to time-varying interference signals captured by photodetectors positioned within the overlap region between the zeroth 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 specimen, such as, but not limited to, sidewall angle and other specimen asymmetries, which may also affect the time-varying interference signal.

[0080] Referring again to FIG. 1B, various components of the overlay metrology tool 102 will now be 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 light of one or more specified wavelengths, including, but not limited to, ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

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

[0083] In certain embodiments, the illumination subsystem 106 includes one or more optical elements suitable for modifying and / or modulating the illumination beam 108 and directing the illumination beam 108 toward the specimen 104. For example, the illumination subsystem 106 can include one or more illumination lenses 130 (e.g., for collimating the illumination beam 108, 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 can, but need not, be incident on different portions of the specimen 104 (e.g., different cells of an overlay target) within the measurement field of view (e.g., the field of view of the objective lens 136). As contemplated herein, various techniques can be used to generate the two or more illumination beams 108. In certain embodiments, the illumination subsystem 106 includes two or more apertures in 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 can 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) at a collection pupil plane 114 configured to capture light from the specimen 104 (e.g., collected light 138), the collected light 138 including at least a zeroth diffraction order 306, a −1st Moiré diffraction order 308, and a +1st Moiré diffraction order 310, as depicted in FIG. 3B . The collection subsystem 110 can include one or more optical elements suitable for modifying and / or adjusting the collected light from the specimen 104. In certain embodiments, the collection subsystem 110 includes one or more collection lenses 140 (e.g., for collimating the illumination beam 108, relaying pupil and / or field planes, 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 can 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 can include one or more beam splitters 146 arranged to split the collected light 138 into the collection channels 144. Furthermore, the beam splitters 146 can 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 considered limiting. For example, the collection subsystem 110 can 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 toward the specimen 104 can be of different polarizations, thereby separating the diffraction orders associated with each illumination beam 108. For example, a polarizing beam splitter 146 can efficiently separate the diffraction orders associated with the different illumination beams 108. Alternatively, 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 one or more illumination 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 deflectors may include, but are not limited to, rotatable mirrors (e.g., mirrors with adjustable ends and / or tilts). Furthermore, any technique known in the art may be used to drive the rotatable mirrors. For example, the deflectors may include, but are not limited to, galvanometers, piezoelectric mirrors, or microelectromechanical systems (MEMS) devices. Alternatively, the beam scanning subsystem 118 may include electro-optic modulators, acousto-optic modulators, etc.

[0091] The deflectors 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 capable of modifying the position of 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, because the beam scanning subsystem 118 modifies the position of one or more illumination beams 108 on the specimen 104, the distribution of the one or more illumination beams 108 at the illumination field plane 132 may be more stable. 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 overlay targets 204 and corresponding configurations of overlay metrology tools 102 are described in detail 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 using 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 example, different cells 202 in an overlay target 204 may have different moiré structures 206. In one example, 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, the systems and methods disclosed herein may be used to implement any overlay technique 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 according to one or more embodiments of the present disclosure, illustrating the placement of overlay targets 204 and their corresponding measurement paths 402 (e.g., swaths) for measuring the overlay targets 204.

[0094] In certain embodiments, multiple 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 various overlay targets 204.

[0095] The overlay target 204 may have any number of cells 202, and the moiré structure within each cell 202 may have any periodicity along any specified direction. In this regard, various designs of overlay targets 204 may be utilized within the spirit and scope of the present disclosure. For example, the overlay target 204 in FIG. 4 is depicted as 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 moiré structure that is periodic along a first direction, and a second set of one or more cells 202, each with a moiré structure that is periodic along a second direction. Furthermore, although this is not required, the second direction may be orthogonal to the first direction. In this manner, the first set of one or more cells 202 may be suitable for overlay measurement along the first direction, and the second set of one or more cells 202 may be suitable for overlay measurement along the second direction, thereby enabling full 2D overlay measurement results to be obtained.

[0097] In general, providing multiple cells 202 within the overlay target 204 suitable for measurement along a particular direction can facilitate measurement over a larger area than that provided by a single cell 202, thereby improving the accuracy and / or sensitivity of the measurement. Furthermore, the various cells 202 suitable for measurement 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 measurement 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 the 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., the 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., the Y direction), thereby enabling 2D overlay measurement of the specimen 104. It is contemplated herein that 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 periodic moiré structure 206 along a direction diagonal to the scanning 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 FIGS. 6A and 6B depict the distribution of diffraction orders 602 of interest at the collection pupil plane 114 and the locations of the corresponding photodetector pairs 112 for the corresponding cells 202. For example, the diffraction order distribution depicted in the shear images in FIGS. 6A and 6B can be similar to that in FIG. 3C , except that the Moiré diffraction orders (e.g., −1st and +1st orders 308 and 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 moiré structure 206, as depicted in Figure 3D. In another example, the overlay target 204 in Figures 6A and 6B may be suitable for measuring moiré diffractions (e.g., -1st order moiré diffraction 308 and +1st order moiré 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 and 108b while the specimen 104 is being scanned.

[0104] Furthermore, the various non-limiting configurations of cells 202 depicted in FIGS. 6A and 6B are periodic along two orthogonal directions suitable for 2D overlay metrology. In FIG. 6A, cells 202 oriented to exhibit periodicity 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 across each row, as depicted in the shear image in FIG. 6A. In FIG. 6B, each illumination beam 108 scans across cells 202 that are periodic along both diagonals. This reduces systematic errors associated with a particular illumination beam 108. However, as depicted in the shear image in FIG. 6B, different cells 202 along the stage scan direction 502 can have different orientations of the photodetectors 112. In certain embodiments, the light collection subsystem 110 is configured with a single collection channel 144 with photodetectors 112 suitably positioned within the overlapping areas of both diagonals, and the controller 122 can selectively analyze the pair of photodetectors 112 associated with each cell 202 when generating overlay measurements. In certain embodiments, the light collection subsystem 110 is configured with two collection channels 144 with each pair of photodetectors 112 positioned within the overlapping areas of a single diagonal, and the controller 122 can selectively analyze the pair of photodetectors 112 associated with each cell 202 when generating overlay measurements.

[0105] It is recognized herein that in certain applications it may be desirable or common 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 a beam scanning subsystem 118 scans one or more illumination beams 108 during measurement will be described in detail, according to 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 specimen 104 is scanning along the stage scan direction 502. In this manner, each illumination beam 108 can scan 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 speeds along the stage scan direction 502 and the beam scan direction 702, the destination of the illumination beam 108 can be moved between 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 using a scanning motion of the illumination beam 108 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 using a scanning motion of the illumination beam 108 along the -Y direction, according to one or more embodiments of the present disclosure. Similar to FIGS. 7A and 7B, by appropriately selecting the scanning speeds along the stage scan direction 502 and the beam scan direction 702, the destination of the illumination beam 108 can be moved between opposing corners of the 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 illustrate 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 distributions depicted in the shear images in Figures 7A-7D 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) 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 Moiré diffraction (e.g., -1st order Moiré diffraction 308 and +1st order Moiré diffraction 310) and the overlapping 0th order light, as depicted in Figure 3B.

[0110] Additionally, Figures 7A-7D illustrate the use of an elongated 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 micrometer, which can be achieved with an ovoid pupil with a NA of 0.9 x 0.45. Accordingly, the associated effect on the diffraction order distribution in the collection pupil plane 114 is depicted in the shear image.

[0111] In certain embodiments, the illumination beam 108 is oscillated along the beam scan direction 702 (e.g., by a vibrating deflector in the beam scanning subsystem 118). In this case, the illumination beam 108 can be caused to trace a triangular wave-like path across the sample 104. Thus, multiple overlay targets 204 (or multiple combinations of their 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 selecting 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, overlay targets 204 suitable for 2D overlay metrology using beam scanning are 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 FIGS. 8A and 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 FIGS. 8A and 8B depict the photodetector 112 arrangement in the collection pupil plane 114 and the corresponding diffraction order distributions for measuring various cells 202. For example, the diffraction order distributions depicted in the shear images in FIGS. 8A and 8B may be similar to those in FIG. 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 rather than being limited to the specific arrangement of FIG. 3C. However, it should be understood that FIGS. 8A and 8B are not limited by the specific arrangement of FIG. 3C. For example, the overlay target 204 in FIGS. 8A and 8B may be suitable for measuring overlapping first diffraction orders from the upper and lower gratings of the Moiré structure 206 depicted in FIG. 3D. 8A and 8B may be suitable for measuring Moiré diffraction (e.g., −1st and +1st order Moiré diffraction 308 and 310) and the overlapping zeroth order, as depicted in FIG. 3B. It should be further noted that while the illumination beam 108 is depicted as circular in FIGS. 8A and 8B, it should be understood that elongating the illumination beam 108 can reduce noise associated with target roughness, as described herein.

[0114] In Figure 8A, cells 202 with a common periodicity direction are diagonally distributed within the overlay target 204. However, as contemplated herein, the signal strength of diffraction orders may depend on the periodicity direction and the polarization of the illumination beam 108. As discussed above, in certain embodiments, simultaneous measurement of multiple cells 202 with multiple illumination beams 108 (e.g., those depicted in Figures 8A and 8B and previously described Figures 6A and 6B) is achieved by separating the diffraction orders associated with 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 appropriate elements (e.g., polarizing filters, polarizing beam splitters, spectral filters, spectral beam splitters, etc.) within the collection subsystem 110. 8A , each illumination beam 108 interrogates one X-direction cell 202 and one Y-direction cell 202, which can 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 can 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, thereby 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. Applicant notes 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 or cells have a Moiré structure formed by 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 positioned near the collection pupil that are associated with at least one of the Moiré diffractions (e.g., compound diffractions, double diffractions, etc.) or overlapping diffractions from the gratings in the Moiré structures, step 904. For example, non-limiting configurations may include, but are not limited to, locating photodetectors at only Moiré diffraction orders, at both multiple Moiré diffraction orders and the zeroth diffraction order, or at the first diffraction order from the top and bottom gratings of the Moiré structures.

[0119] In certain embodiments, method 900 determines, at step 906, an overlay error between specimen layers associated with Moiré structures within one or more cells of the overlay target based on signals from the two photodetectors. For example, the overlay error along the periodic direction of the Moiré structures may be proportional to the 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-locking technique to the two time-varying interference signals. Furthermore, 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 that are periodic along the particular measurement direction.

[0120] As contemplated herein, method 900 can be applied to a wide variety of overlay target designs suitable for 1D or 2D metrology. In certain embodiments, method 900 involves simultaneous scanning with multiple illumination beams, and associated overlapping diffraction orders are collected for parallel measurement. In certain embodiments, method 900 involves scanning 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. This configuration allows cells with Moiré structures with different periodicity directions to be efficiently interrogated with a common illumination beam along the measurement swath.

[0121] In some places, the subject matter described herein is depicted as including various elements within or connected to other elements. 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 elements that achieves the same function effectively "cooperates" with one another to achieve the desired function. Thus, any two elements herein that are combined to achieve a particular function can be viewed as "cooperating" with one another to achieve the desired function, regardless of the configuration or intervening elements. Similarly, any two elements so coordinated can be viewed as "connected" or "coupled" with one another to achieve the desired function, and any two elements that can be coordinated can be viewed as "combinable" with one another to achieve the desired function. Examples of connectable include, but are not limited to, members being able to and / or physically interacting with each other, and / or members being able to and / or wirelessly interacting with each other, and / or members being able to 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 can be made in the form, construction and arrangement of the parts without departing from the disclosed subject matter or diminishing all of its essential advantages. The described form is merely illustrative, and it is the intent of the following claims to encompass and embrace all such modifications. It will further be 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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