Multi-pitch grating overlay target for scanning overlay metrology

Abstract

An overlay metrology system having pitch in multiple directions within a single cell is disclosed. The overlay target can include a multilayer structure in two or more layers of a sample cell according to a metrology recipe. The multilayer structure can include structures in each layer having one or more pitches in one or more periodic directions. The multilayer structure can include structures having a first pitch in a first direction, a second pitch in a second direction, a third pitch in the first direction, and a fourth pitch in the second direction. At least one of the first pitch or the third pitch can be different from at least one of the second pitch or the fourth pitch.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. Section 119(e) of U.S. Provisional Application No. 63 / 400,131, entitled "New OVL Metrology Target Design for Two-Dimensional Scanning Measurement," filed August 23, 2022, and listing Yuval Lubashevsky, Itay Gdor, Daria Negri, and Eitan Hajaj as inventors, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates generally to overlay metrology, and more particularly to a system and method for overlay metrology that enables compact pitch design of overlay targets. [Background technology]

[0003] The demand for smaller feature sizes and increased feature densities is driving the need for accurate and efficient overlay metrology, which refers to the measurement of the relative alignment of layers on a sample, such as, but not limited to, a semiconductor device.

[0004] Overlay targets are typically formed on the surface of a wafer sample and may contain cells with grating structures with varying pitches in overlapping layers. The wafer sample is typically mounted on a translation stage and translated to sequentially move the overlay targets into the measurement field. In typical metrology systems employing a move-and-measure (MAM) approach, the sample remains stationary between measurements. However, the time required to position the translation stage before measurements can negatively impact throughput.

[0005] Additionally, various sources can introduce errors into the overlay metrology data, and footprint space on the wafer is at a premium. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0191279 [Patent Document 2] U.S. Patent Application Publication No. 2022 / 0034652 Summary of the Invention [Problem to be solved by the invention]

[0007] It would therefore be desirable to provide a system and method for obviating the above-mentioned deficiencies. [Means for solving the problem]

[0008] An overlay metrology system is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the overlay metrology system may include a controller including one or more processors, the one or more processors configured to execute program instructions that direct the one or more processors to execute a metrology recipe. In another exemplary embodiment, the metrology recipe may include receiving detection signals from one or more detectors from an overlay target of a sample (e.g., a wafer) and determining one or more overlay measurements of the overlay target based on the detection signals. In another exemplary embodiment, the overlay target may include a multi-layer structure on two or more layers of a cell of the sample. In another exemplary embodiment, the multi-layer structure may include structures in each layer having one or more pitches in one or more periodic directions. In another exemplary embodiment, the multi-layer structure may include structures having a first pitch in a first direction, a second pitch in a second direction, a third pitch in the first direction, and a fourth pitch in the second direction. In another exemplary embodiment, at least one of the first pitch or the third pitch may be different from at least one of the second pitch or the fourth pitch.

[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 summary serve to explain the principles of the invention. [Brief explanation of the drawings]

[0010] The numerous advantages of the present disclosure may be better understood by those skilled in the art by reference to the accompanying drawings. [Figure 1A] FIG. 1 is a conceptual diagram of an overlay metrology system in accordance with one or more embodiments of the present disclosure. [Figure 1B] FIG. 1 is a schematic diagram of an optical subsystem in accordance with one or more embodiments of the present disclosure. [Figure 2A] FIG. 1 is a conceptual diagram of an illumination pupil plane distribution of a circular illumination beam, in accordance with one or more embodiments of the present disclosure. [Figure 2B] FIG. 2B is a conceptual diagram of a collection pupil plane distribution of diffraction orders of the circular illumination beam of FIG. 2A in accordance with one or more embodiments of the present disclosure. [Figure 3] FIG. 1 is a top view of an overlay target formed as an overlapping structure including two structures in two grid-like arrays, in accordance with one or more embodiments of the present disclosure. [Figure 4] 1 is a top view of a grid-like array structure and an overlay target formed as an overlapping structure including two grids, in accordance with one or more embodiments of the present disclosure. FIG. [Figure 5] FIG. 10 is a top view of an overlay target that is narrow along the scan direction to reduce footprint, in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present disclosure has been particularly shown and described with reference to certain embodiments and particular features thereof. The embodiments described herein are to be construed as illustrative and not limiting. Those skilled in the art will readily appreciate that various changes and modifications in form and detail may be made therein without departing from the spirit and scope of the present disclosure. Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings.

[0012] Overlay metrology can be performed using a variety of overlay metrology techniques. For example, techniques include a static moving measurement mode, in which the sample remains stationary during measurement, and a scanning mode, in which an illumination beam is scanned across the sample during measurement. In static scatterometry overlay (SCOL), the use of a charge-coupled device (CCD) camera can require time to read and transfer data to a storage buffer, which may require two separate measurements per direction. Therefore, measuring the target can be relatively time-consuming. On the other hand, scanning-based scatterometry techniques can be faster and include a high-speed detector to capture the time-varying interference signal generated as the sample is scanned. The detector can be positioned in the pupil plane at the overlap between selected diffraction orders to capture the time-varying interference signal as the sample is scanned. Various scanning scatterometry overlay measurement techniques are described in U.S. Patent Publication No. 2022 / 0034652, filed February 17, 2021, U.S. Patent Application No. 17 / 119,536, filed December 11, 2020, U.S. Patent Application No. 17 / 708,958, filed March 30, 2022, U.S. Patent Application No. 17 / 709,104, filed March 30, 2022, and U.S. Patent Application No. 17 / 709,200, filed March 30, 2022, all of which are incorporated by reference herein in their entireties. It should be noted that such scanning examples are not limiting, and embodiments herein may include one or more detectors in the field of view, and may include various types of detectors, such as one or more diode array sensors.

[0013] The embodiments herein may work well with scanning SCOL technology, but are not necessarily limited to such technology.

[0014] In some scanning methods, the scanning target may include separate targets and / or separate cells for each direction (e.g., X and Y directions) that are measured separately. For example, two cells may be arranged back-to-back, as shown in Figure 6B of U.S. Patent Application No. 18 / 099,798, filed January 20, 2023, the entirety of which is incorporated herein by reference. While U.S. Patent Application No. 18 / 099,798 discloses reducing overlay errors by reversing the order of pitches of multilayer gratings within two or more cells, the present disclosure may enable more compact (e.g., single-cell) overlay targets.

[0015] Embodiments of the present disclosure relate to an overlay metrology system configured to determine overlay measurements of an overlay target having a single cell with a different pitch along each of two orthogonal directions (e.g., X and Y directions). Having a different pitch in each direction allows for avoidance of crosstalk between overlay measurements in each direction, and allows for clear separation of data capture of corresponding time-varying X and Y signals.

[0016] Avoiding crosstalk may mean that X-pitch and Y-pitch signals can be clearly distinguished from one another. For example, without the present disclosure, a single-cell overlay target measured diagonally may exhibit crosstalk if the structures are not spaced differently in the X direction compared to their spacing in the Y direction. However, embodiments herein may enable reduced crosstalk compared to such a scenario by using at least one different spacing (i.e., pitch) of structures in each direction. For example, a grid of structures (e.g., unconnected rectangles and / or squares of rows and columns) in a single layer may be used, with a spacing between rows (i.e., a first pitch) and a second spacing between columns (i.e., a second pitch). Two additional pitches may be implemented in another layer with a grid of structures, or in two additional layers with a grid on each layer, providing at least four pitches. Furthermore, at least one pitch in each direction may differ from one another. For example, a first pitch in the X direction may differ from one of the pitches in the Y direction, a second grid pitch in the Y direction, etc.

[0017] It is contemplated herein that structures characterized by different pitches in each direction can potentially offer distinct advantages. In particular, these structures can effectively mitigate crosstalk, particularly within measurements. For example, scanning measurements of overlay targets can be performed in both the X and Y directions, and further, scanning can be performed diagonally in both the X and Y directions. Measurements in each scenario can benefit from reduced crosstalk by being based on targets with different pitches in each direction. As wafer footprints become increasingly dense and valuable, minimizing the footprint size of overlay targets can free up valuable space, thereby improving wafer chip throughput.

[0018] FIG. 1A shows a conceptual diagram of an overlay metrology system 100 in accordance with one or more embodiments of the present disclosure.

[0019] In an embodiment, overlay metrology system 100 includes an optical subsystem 102 configured to acquire one or more images from a sample 104 (e.g., a wafer) for use in determining overlay measurements.

[0020] In an embodiment, overlay metrology system 100 includes a controller 122. Controller 122 may include one or more processors 124 and memory 126. For example, controller 122 may be configured to determine overlay measurements based on signals received from detectors of optical subsystem 102.

[0021] FIG. 1B shows a simplified schematic diagram of optical subsystem 102 in accordance with one or more embodiments of the present disclosure.

[0022] In an embodiment, the optical subsystem 102 includes an illumination subsystem 106 and a collection subsystem 110 .

[0023] The illumination subsystem 106 is configured to generate illumination in the form of one or more illumination beams 108 to illuminate the sample 104. The collection subsystem 110 is configured to collect light from the illuminated sample 104 (e.g., according to a metrology recipe). Additionally, the one or more illumination beams 108 may be spatially restricted to illuminate selected portions of the sample 104. For example, each of the one or more illumination beams 108 may be spatially restricted to illuminate a specific cell of an overlay target.

[0024] In an embodiment, the illumination beam 108 is split (e.g., via an additional beam splitter) before the sample 104 to generate an external beam (e.g., an auxiliary beam) for purposes of a phase reference (e.g., holography). For example, U.S. Patent Application No. 18 / 110,746, filed February 16, 2023, which is incorporated herein by reference in its entirety, discloses that an auxiliary beam is split and combined with diffraction orders from the sample. For example, an external beam (e.g., a portion of the illumination beam 108) may be superimposed with selected diffraction orders from the sample 104 to generate a time-varying interference signal suitable for overlay measurements, as disclosed herein. This configuration may reduce constraints on the design of the overlay target and may enable relatively small-pitch features with little or no overlap between diffraction lobes in the pupil plane.

[0025] For example, overlay metrology system 100 may be configured to image a particular type of sample according to a metrology recipe. For example, overlay metrology system 100 may be designed (configured) and / or programmed (e.g., programmed via program instructions) to calculate overlay measurements of a particular type of feature (e.g., a grating-over-grating target) of sample 104 according to the metrology recipe.

[0026] In an embodiment, the optical subsystem 102 may include a translation stage 116 to scan the sample 104 through a measurement field of view of the optical subsystem 102 during overlay measurement.

[0027] As previously described herein, overlay metrology system 100 may include one or more detectors 112 for scanning overlay metrology. In an embodiment, one or more detectors 112 may include any type of optical detector known in the art suitable for capturing interference signals generated when sample 104 is translated by translation stage 116 and / or when one or more illumination beams 108 are scanned by optical subsystem 102. For example, one or more detectors 112 may be diode array sensors and / or charge-coupled device (CCD) sensors.

[0028] In an embodiment, one or more detectors 112 may be positioned in the collection pupil plane 114 to measure diffraction orders emanating from the sample 104 .

[0029] For example, performing scanning-based overlay metrology can include receiving detection signals from one or more detectors 112 while the sample 104 is moving, such that the detection signals are time-varying interference signals.

[0030] In an embodiment, the optical subsystem 102 may perform scatterometry overlay measurements on a portion of the sample 104 having an overlay target, for example, but not limited to, a grating-over-grating target.

[0031] It is recognized herein that the distribution of diffraction orders of the illumination beam 108 produced by a periodic structure (e.g., a grating-over-grating structure) may be affected by various parameters, such as, but not limited to, the wavelength of the illumination beam 108, the angle of incidence of the illumination beam 108 in both the elevation and azimuth directions, the period (i.e., pitch) of the periodic structure, or the numerical aperture (NA) of the collection lens. For example, the illumination subsystem 106, the collection subsystem 110, and / or the overlay target may be configured to provide an overlapping distribution of zeroth and first diffraction orders at the collection pupil plane 114 of the collection subsystem 110. The illumination subsystem 106 and / or the collection subsystem 110 may be configured to determine or facilitate measurement of a grating-over-grating structure having a selected range of periodicity that provides an overlapping distribution. As another example, the illumination subsystem, the collection subsystem 110, and / or the overlay target may be configured to overlap the first diffraction order from the overlay target with a portion of the illumination beam 108 (such as an external beam, an auxiliary beam, etc.). Additionally, various components of the illumination subsystem 106 and / or collection subsystem 110 (e.g., aperture, pupil, etc.) may be adjustable to provide overlapping distributions of given structures suitable for generating time-varying signals from which overlay measurements may be determined.

[0032] The collection subsystem 110 may be configured to collect at least one of a zeroth diffraction order (eg, specular reflection) and + / −1st diffraction orders from the sample 104 associated with the diffraction of the illumination beam 108 .

[0033] In an embodiment, the optical subsystem 102 includes an objective lens 136 that focuses the illumination beam 108 onto the sample 104 (e.g., an overlay target having structures disposed on two or more layers of the sample 104). The objective lens 136 may be configured to collect measurement light emitted from the sample 104 in response to the illumination beam 108 as the sample 104 is scanned along a scan direction.

[0034] The optical subsystem 102 may implement a variety of illumination beam distributions. For example, the illumination beam 108 may be circular, annular, and / or similarly shaped.

[0035] FIG. 2A shows a conceptual diagram of an illumination pupil plane distribution 200 of a circular illumination beam 204, in accordance with one or more embodiments of the present disclosure.

[0036] 2B shows a conceptual diagram of a collection pupil plane distribution 202 of diffraction orders of the circular illumination beam 204 of FIG. 2A in accordance with one or more embodiments of the present disclosure. For example, after the circular illumination beam 204 emanates from the sample 104, it becomes a measurement beam of collectible light 138 and forms circular diffraction orders at the collection pupil plane 114. For a target with pitch and edges in both the X and Y directions, diffraction orders are generated in the horizontal and vertical directions of the pupil plane, as shown by the five horizontal and five vertical circles in FIG. 2B. The circular diffraction orders in the X direction can include a zeroth (0) circular diffraction order 206a, a first (+1) X circular diffraction order 206c, a first (-1) X circular diffraction order 206b, a second (+1) X circular diffraction order 212c, and a second (-1) X circular diffraction order 212b. In the Y direction, the circular diffraction orders may include a zeroth (0) circular diffraction order 206a, a first (+1) Y circular diffraction order 206e, a first (-1) Y circular diffraction order 206d, a second (+1) Y circular diffraction order 212e, and a second (-1) Y circular diffraction order 212d. One or more detectors 112 may be positioned to capture overlapping regions 208a, 208b of such diffraction orders. For example, a detector 112 (such as a diode array sensor) may be positioned at the pupil plane 114, and the one or more detectors 112 capture light from detection regions 210c, 210b corresponding to the diffraction orders in the X direction. For clarity and brevity, only the detection regions 210c, 210b in the X direction are labeled; however, it should be noted that the corresponding overlapping regions in the Y direction may be captured by similar detection regions in the Y direction (not shown). It is noted that the detection regions 210c, 210b may be any size, for example, smaller than, equal to, or larger than the overlapping regions 208a, 208b.

[0037] When scanning diagonally, the signal may include diffraction orders emanating from structures with pitch in both the X and Y directions, and thus overlay can be determined in both the X and Y directions using a single diagonal scan. FIG. 2B illustrates diffraction orders in both the X and Y directions from pitch in the X and Y directions. For example, the detected signal (of the diagonal scan) may include a first detected signal corresponding to a diffraction order in a first direction (e.g., the X direction) and a second detected signal corresponding to a diffraction order in a second direction (e.g., the Y direction). In an embodiment, determining the overlay measurement may include determining an overlay measurement in the first direction based on the first detected signal and determining an overlay measurement in the second direction based on the second detected signal. For example, the overlay measurement in the first direction may indicate overlay between the first structure 310 and the second structure 308 in the X direction, which may be used to adjust the manufacturing process to reduce unwanted overlay.

[0038] For example, the first detected signal may be based on (e.g., corresponds to) an overlap of diffraction orders 206a, 210b, 212b, 210c, and / or 212c. For example, the first detected signal may be received from X-direction detection regions 210c, 210b using detectors 112 (e.g., photodiode detectors) positioned in each of X-direction detection regions 210c, 210b. The second detected signal may be based on an overlap of diffraction orders 206a, 210d, 212d, 210e, and / or 212e.

[0039] Further, in this manner, determining the overlay measurement may include determining an overlay measurement in a first direction (e.g., X-direction overlay in the X direction) based on the first detection signal and determining an overlay measurement in a second direction (e.g., Y-direction overlay) based on the second detection signal. Such determination may be made based on differences between various overlapping regions, e.g., differences in time-varying light intensity between overlapping region 208a and overlapping region 208b, to determine X-direction overlay. In this manner, a single diagonal scan may be used to simultaneously determine overlay in two directions.

[0040] Figures 3-5 show examples of overlay targets where the pitch in the X direction is different from the pitch in the Y direction, avoiding crosstalk and enabling simultaneous data capture of corresponding time-varying signals, allowing for clear differentiation between X and Y signals. Figure 3 shows a moiré target with grating structures in two layers. Figure 4 shows a three-layer overlay target with grating structures in one layer and line / space features in the other two layers. This allows measurements between the grating layer in each direction and each line / space layer. Both Figures 3 and 4 allow for diagonal scanning between the X and Y directions to determine X and Y overlay measurements simultaneously, or for scanning the X and Y directions separately. Figure 5 shows how the overlay target of Figure 4 can be made smaller and narrower when scanned diagonally.

[0041] FIG. 3 shows a top view 300 of an overlay target 304 formed as an overlapping structure including two sets of structures 308, 310 in two grid-like arrangements in accordance with one or more embodiments of the present disclosure.

[0042] In embodiments, the overlay target 304 includes a multilayer structure on two or more layers of the cell of the sample 104. For example, the multilayer structure may include a structure in each layer having one or more pitches in one or more periodic directions within a single cell. In embodiments, the overlay target herein may have (at least) four pitches, where at least one pitch in a first direction is different from another pitch in a second direction. For example, the overlay target may include first and third pitches in a first direction and second and fourth pitches in a second direction. For example, at least one of the first and third pitches may be different from at least one of the second and fourth pitches. In this way, different pitches are achieved in each direction, reducing crosstalk. Such pitches may be present in the same layer (e.g., a grating pattern with two pitches, one in each direction) and / or in different layers (e.g., a more general diffraction grating with a single pitch in a single direction).

[0043] In embodiments, the overlay target 304 includes a multilayer structure 304 formed as overlapping structures with different pitches on two or more layers of the sample 104. For example, the two or more layers of the sample 104 may include at least a first layer and a second layer (as shown). For example, the multilayer structure 304 may include at least two different pitches 320, 330 in a first direction (e.g., the X direction) and at least two different pitches 322, 332 in a second direction (e.g., the Y direction orthogonal to the X direction). The multilayer structure may include at least a first layer arrangement of first structures 310 with periodicity in a first direction and a second direction. Such periodicity may be a first pitch 320 and a second pitch 322, where the first structures 310 may include the first pitch 320 in the first direction and the second pitch 322 in the second direction.

[0044] To achieve two pitches in each direction, various additional layers with various structures can be used in addition to the layer with the grating structure. For example, as shown in FIG. 3, a second layer structure 308 within a second grating can be used. By using one (first) grating and one second grating in each layer, a total of four pitches can be achieved with only two layers within a single cell. As another example, two more layers with a grating in each layer (i.e., a second layer and a third layer) can be used, as shown in gratings 312 and 314 in FIGS. 4 and 5. In this way, only three layers within a single cell are required to achieve four pitches (i.e., a grating with two pitches in one layer and two more layers with gratings in each layer).

[0045] In an embodiment, the multilayer structure 304 can include a second layer arrangement of second structures 308 with periodicity in a first direction and a second direction. The second structures 308 can include a third pitch 340 in the first direction and a fourth pitch 350 in the second direction. The first pitch 320 and the third pitch 340 in the first direction can be different, and the second pitch 322 and the fourth pitch 350 in the second direction can be different.

[0046] FIG. 4 shows a top view 400 formed as an overlapping structure 402 including a grid-like arrangement of structure 310 and two grids 312, 314 in accordance with one or more embodiments of the present disclosure.

[0047] In an embodiment, the multi-layer structure 304 further includes a second layer grating 312 on the second layer with a third pitch 340 in the first direction.

[0048] In an embodiment, the multi-layer structure 304 further includes a third layer grating 314 on the third layer with a fourth pitch 350 in the second direction. The fourth pitch 350 may be different from the first pitch 320 and / or the third pitch 340. In this manner, a different pitch is achieved in each direction. Alternatively and / or additionally, the second pitch 322 may be different from the first pitch 320 and / or the third pitch 340. In this manner, a different pitch is achieved in each direction.

[0049] 5 shows a top view 500 of an overlay target 502 that is narrow along the scan direction 306 to reduce footprint, in accordance with one or more embodiments of the present disclosure. The illumination beam 108 is scanned along the scan direction 306. Scanning the overlay target 304 a length equal to the pitch of the grating-over-grating structure may result in a phase shift of 2π in each of the + / -1 diffraction orders (in opposite directions), and the intensity captured by each of the one or more detectors 112 may oscillate through the interference fringes.

[0050] In an embodiment, the multi-layer structure is configured to be scanned separately along both the first and second directions (e.g., along the pitch periodicity) and / or along a third direction 306 (i.e., diagonal direction). In an embodiment, the third direction 306 is different from the first and second directions.

[0051] In embodiments, such scanning may be used in a photodiode-based scanning scatterometry overlay (e.g., SCOLAR) system and / or method. For example, the illumination beam 108 may scan each target in the X direction and then in the Y direction, or vice versa. In another example, the illumination beam 108 may be scanned diagonally along a narrow diagonally periodic target, such as the overlay target 502 shown in FIG. 5. For example, the third direction 306 may be within 45° to 10° of the first and second directions of periodicity.

[0052] In an embodiment, a relatively narrow overlay target 502 is used, as shown in FIG. 5 . For example, the multilayer structure 502 may have a scan length along the third direction 306 (i.e., the total length of the overlay target 502) that is greater than the width (i.e., the total width) of the multilayer structure 502, where the width is measured orthogonally (i.e., 90°) to the third direction 306. This may define a narrow overlay target 502 that includes edges parallel to the scan direction and is configured to be scanned in a third direction (e.g., a diagonal direction) that is different from the first and second directions. For example, rather than scanning diagonally from corner to corner in a diamond shape (such as a rotated square overlay target) with the distal corners of each side jutting outward, the design may be truncated so that the edges of the outer corners are trimmed inward to narrow. Using a narrower overlay target 502 leaves space on the sample 104 for other features.

[0053] As shown, the illumination beam 108 may occupy a spot size that is smaller than the overlay target 304 itself. However, it should be understood that the overlay targets of Figures 3-5 and the associated description are provided for illustrative purposes only and should not be construed as limiting.

[0054] 1A-1B, additional components of the optical subsystem 102 are described in accordance with one or more embodiments of the present disclosure. For example, the controller 122, the processor 124, and various optical components are described in detail below for overlay metrology.

[0055] In an embodiment, the controller 122 determines an overlay measurement between layers (e.g., a first layer and a second layer) of the overlay target 304 along the measurement direction based on a comparison of the detected signals. For example, the controller 122 may compare the magnitude and / or phase of the detected signals to determine the overlay measurement. For example, U.S. Pat. No. 10,824,079, issued November 3, 2020, and incorporated herein by reference in its entirety, describes diffraction orders in a collection pupil and further provides a specific relationship between overlay at the pupil plane and measured intensity. It is herein contemplated that the systems and methods disclosed herein may extend the teachings of U.S. Pat. No. 10,824,079 to detected signals captured by one or more detectors positioned in the overlap region between 0 and + / -1 diffraction orders. In particular, it is herein contemplated that overlay on a sample may be proportional to the relative phase shift between two detected signals. In another example, the relative intensities of the diffraction orders in the pupil plane may be extracted from the detected signals. In this manner, any overlay algorithm based on relative intensity differences of diffraction orders known in the art may be applied to determine the overlay measurement.

[0056] In an embodiment, overlay metrology system 100 includes a controller 122 communicatively coupled to optical subsystem 102. Controller 122 may include one or more processors 124 and a memory device 126, or memory. For example, one or more processors 124 may be configured to execute a series of program instructions stored in memory device 126.

[0057] The one or more processors 124 of the controller 122 may include any processor or processing element known in the art. For purposes of this disclosure, the term “processor” or “processing element” may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application-specific integrated 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 a memory). In one embodiment, the one or more processors 124 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute programs configured to operate as described throughout this disclosure or to operate with the overlay metrology system 100. Furthermore, different subsystems of the overlay metrology system 100 may include processors or logic elements suitable for performing at least a portion of the steps described in this disclosure. Therefore, the above description should not be construed as a limitation on embodiments of the present disclosure, but merely as illustrative. Furthermore, steps described throughout this disclosure may be performed by a single controller or, alternatively, by multiple controllers. Additionally, controller 122 may include one or more controllers housed within a common housing or multiple housings. In this manner, any controller or combination of controllers may be packaged separately as a module suitable for integration into system 100. Furthermore, controller 122 may analyze or process data received from one or more detectors 112 and communicate the data to additional components within or external to overlay metrology system 100.

[0058] Furthermore, memory device 126 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 124. For example, memory device 126 may include a non-transitory memory medium. As additional examples, memory device 126 may include, but is not limited to, read-only memory, random access memory, magnetic or optical memory devices (e.g., disks), magnetic tape, solid-state drives, etc. It should be further noted that memory device 126 may be housed in a common controller housing with one or more processors 124.

[0059] In this regard, the controller 122 may perform any of a variety of processing steps associated with overlay metrology. For example, the controller 122 may be configured to determine control signals to direct or control the optical subsystem 102 or any component thereof. For example, the controller 122 may be configured to direct the translation stage 116 to translate the sample 104 along one or more measurement paths or swaths to scan one or more overlay targets through a measurement field of view of the optical subsystem 102. As another example, the controller 122 may be configured to receive signals corresponding to detection signals from one or more detectors 112. As another example, the controller 122 may determine correctables for one or more additional manufacturing tools based on the overlay measurements from the optical subsystem 102 as feedback and / or feedforward control of the one or more additional manufacturing tools.

[0060] In an embodiment, the controller 122 captures the detected signals detected by the one or more detectors 112. The controller 122 may typically capture data such as the magnitude or phase of the detected signals using any technique known in the art, such as, but not limited to, one or more phase-locked loops. Additionally, the controller 122 may capture the detected signal(s) or any data related to the detected signals using any combination of hardware (e.g., circuitry) or software techniques.

[0061] Referring again to FIG. 1B, various components of the optical subsystem 102 will be described in more detail, in accordance with one or more embodiments of the present disclosure.

[0062] In an embodiment, 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 selected wavelengths, including, but not limited to, ultraviolet (UV) radiation, visible light, or infrared (IR) radiation.

[0063] In an embodiment, the illumination subsystem 106 includes one or more optical components suitable for modifying and / or conditioning the illumination beam 108 and directing the illumination beam 108 toward the sample 104. For example, the illumination subsystem 106 may include one or more illumination lenses 130 (e.g., to collimate the illumination beam 108, to relay the illumination pupil plane 120 and / or the illumination field plane 132, etc.). In another embodiment, the illumination subsystem 106 includes one or more illumination control optics 134 to shape or control the illumination beam 108. For example, the illumination control optics 134 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, movable mirrors, scanning mirrors, etc.).

[0064] The collection subsystem 110 may include one or more optical elements suitable for modifying and / or conditioning the light 138 collected from the sample 104. In one embodiment, the collection subsystem 110 includes one or more collection lenses 140 (e.g., to collimate the illumination beam 108, relay a pupil plane and / or a field plane, etc.), which may, but need not, include the objective lens 136. In another embodiment, the collection subsystem 110 includes one or more collection control optics 142 to shape or control the collected light 138. For example, the collection control optics 142 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, movable mirrors, scanning mirrors, etc.). In another example, the collection subsystem 110 may include one or more collection field surfaces 150.

[0065] In an embodiment, the collection subsystem 110 includes two or more collection channels 144, each with a separate detector 112 (or multiple detectors 112). For example, the optical subsystem 102 may include one or more beam splitters 146 positioned to split the collected light 138 among the collection channels 144. Furthermore, the beam splitters 146 may be polarizing beam splitters, non-polarizing beam splitters, or a combination thereof.

[0066] 1A , it is noted herein that one or more components of overlay metrology system 100 may be communicatively coupled to various other components of system 100 in any manner known in the art. For example, one or more processors 124 may be communicatively coupled to each other and to the other components via a wired (copper wire, fiber optic cable, etc.) or wireless connection (RF coupling, IR coupling, WiMax, Bluetooth, 3G, 4G, 4G LTE, 5G, etc.). As another example, controller 122 may be communicatively coupled to one or more components of optical subsystem 102 via any wired or wireless connection known in the art.

[0067] In one embodiment, the one or more processors 124 may include any one or more processing elements known in the art. In this sense, the one or more processors 124 may include any microprocessor-type device configured to execute software algorithms and / or instructions. In one embodiment, the one or more processors 124 may comprise a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or other computer system (e.g., a networked computer) configured to execute programs configured to operate the overlay metrology system 100 as described throughout this disclosure. It should be appreciated that the steps described throughout this disclosure may be performed by a single computer system or, alternatively, by multiple computer systems. Furthermore, it should be appreciated that the steps described throughout this disclosure may be performed by any one or more of the one or more processors 124. In general, the term “processor” may be broadly defined to encompass any device having one or more processing elements that execute program instructions from memory 126. Furthermore, the 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 throughout this disclosure. Therefore, the above description should not be construed as a limitation on the present disclosure, but merely as illustrative.

[0068] Those skilled in the art will recognize that the components (e.g., operations), devices, objects, and accompanying descriptions described herein are used as examples for conceptual clarity, and that various configurational variations are contemplated. Thus, as used herein, the specific examples described and the accompanying descriptions are intended to represent their more general classification. In general, the use of a specific example is intended to represent that classification and should not be considered a limitation that excludes the inclusion of the specific components (e.g., operations), devices, and objects.

[0069] Those skilled in the art will understand that there are a variety of vehicles (e.g., hardware, software, and / or firmware) in which the processes and / or systems and / or other techniques described herein may be implemented, and that the preferred vehicle will vary depending on the context in which the processes and / or systems and / or other techniques are deployed. For example, if speed and accuracy are determined by the implementer to be paramount, the implementer may select a primarily hardware and / or firmware vehicle; alternatively, if flexibility is paramount, the implementer may select a primarily software implementation, or again alternatively, the implementer may select some combination of hardware, software, and / or firmware. Thus, there are several possible vehicles that may affect the processes and / or devices and / or other techniques described herein, and any vehicle utilized is a choice that depends on the context in which the vehicle is deployed and the particular interests of the implementer (e.g., speed, flexibility, or predictability), all of which may vary. No vehicle is inherently superior to another.

[0070] The foregoing description is presented to enable any person skilled in the art to make and use the invention as provided in the context of a particular application and its requirements. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0071] With respect to the use of substantially any plural and / or singular term herein, those of ordinary skill in the art may translate from the plural to the singular and / or from the singular to the plural as appropriate to the context and / or application. The various singular / plural permutations are not expressly set forth herein for the sake of clarity.

[0072] All methods described herein may include storing results of one or more steps of a method embodiment in memory. The results may include any of the results described herein and may be stored in any manner known in the art. The memory may include any of the memories described herein or any other suitable storage medium known in the art. After storing the results, the results may be accessed in memory, used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, etc. Furthermore, the results may be stored "permanently," "semi-permanently," "temporarily," or for a period of time. For example, the memory may be random access memory (RAM), and the results may not necessarily persist in memory indefinitely.

[0073] It is further contemplated that each of the method embodiments described above may include any other step(s) of any other method(s) described herein. In addition, each of the method embodiments described above may be performed by any of the systems described herein.

[0074] The subject matter described herein may depict different components contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and that in fact many other architectures that achieve the same functionality may be implemented. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Thus, any two components herein that combine to achieve a particular function may be considered to be “associated” with each other, such that the desired functionality is achieved without regard to the architecture or intermediate components. Similarly, any two components so associated may also be considered to be “connected” or “coupled” to each other to achieve the desired functionality, and any two components that may be so associated may also be considered to be “couplable” with each other to achieve the desired functionality. Specific examples of what may be coupled include, but are not limited to, physically interactable and / or physically interacting components, wirelessly interactable and / or wirelessly interacting components, and / or logically interacting and / or logically interacting components.

[0075] It should further be understood that the present invention is defined by the appended claims. In general, it will be understood by those skilled in the art that the terms used herein, particularly in the appended claims (e.g., the body of the appended claims), are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "including but not limited to," etc.). Where a specific number of introduced claim recitations is intended, such intention will be explicitly set forth in the claim, and it will be further understood by those skilled in the art that, in the absence of such a recitation, no such intention exists. For example, to aid in understanding, the following appended claims may include the use of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to mean that the introduction of a claim recitation with the indefinite article "a" or "an" limits the scope of any particular claim containing the claim recitation so introduced to inventions containing only one such recitation, even if the same claim includes the introductory phrase "one or more" or "at least one" with the indefinite article "a" or "an," etc. (e.g., "a" and / or "an" should generally be interpreted to mean "at least one" or "one or more"). The same applies to the use of definite articles used to introduce claim recitations. In addition, even when a specific number of introduced claim recitations is explicitly recited, those skilled in the art will recognize that such a recitation should generally be interpreted to mean at least the recited number (e.g., a recitation of "two recitations" alone, without any other modifier, generally means at least two recitations, or more than two recitations).Furthermore, in instances where phrases similar to "at least one of A, B, and C, etc." are used, such configurations are generally intended to mean what one of ordinary skill in the art would understand the phrase (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, systems having A only, B only, C only, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). In instances where phrases similar to "at least one of A, B, or C, etc." are used, such configurations are generally intended to mean what one of ordinary skill in the art would understand the phrase (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, systems having A only, B only, C only, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). It will further be understood by those skilled in the art that virtually any disjunctive word and / or phrase expressing two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibility of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" would be understood to include the possibilities of "A" or "B" or "A and B."

[0076] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes in form, construction, and arrangement of elements may be made without departing from the disclosed subject matter or sacrificing all of its important advantages. The described embodiments are merely illustrative, and it is the intent of the following claims to embrace and include all such modifications. It is to be further understood that the invention is defined by the appended claims.

Claims

1. an illumination subsystem including an illumination source configured to generate an illumination beam; a light collection subsystem comprising: one or more detectors; and a collection subsystem including an objective configured to collect measurement light emanating from the sample in response to the illumination beam as the sample is scanned, the sample including an overlay target according to a metrology recipe; a controller communicatively coupled to the collection subsystem, the controller including one or more processors configured to execute program instructions, the program instructions directing the one or more processors to: receiving a detection signal from the one or more detectors from the overlay target; a controller configured to perform one or more overlay measurements of the overlay target by determining the overlay measurements based on the detection signals; wherein the overlay target, according to the metrology recipe, includes a multi-layer structure on two or more layers of a cell of the sample, the multi-layer structure comprising a structure having one or more pitches in each layer in one or more periodic directions; wherein the multilayer structure comprises a structure having a first pitch in a first direction, a second pitch in a second direction, a third pitch in the first direction, and a fourth pitch in the second direction, and at least one of the first pitch or the third pitch is different from at least one of the second pitch or the fourth pitch; Overlay measurement system.

2. The overlay metrology system of claim 1 , wherein the scanning of the sample comprises one or more scans in one or more scan directions, the one or more scan directions comprising the first direction and the second direction.

3. 2. The overlay metrology system of claim 1, wherein the scanning of the sample comprises one or more scans in one or more scan directions, the one or more scan directions comprising a third direction different from both the first direction and the second direction.

4. The overlay metrology system of claim 3 , wherein the detection signals include a first detection signal corresponding to a diffraction order in the first direction and a second detection signal corresponding to a diffraction order in the second direction.

5. The determining of the one or more overlay measurements includes: determining an overlay measurement in a first direction based on the first detection signal; determining an overlay measurement in a second direction based on the second detection signal; and The overlay metrology system of claim 4 , comprising:

6. The overlay metrology system of claim 1 , wherein the one or more detectors include at least one detector located at a pupil plane.

7. The overlay metrology system of claim 1 , wherein the one or more detectors include at least one diode array sensor.

8. The overlay metrology system of claim 1 , wherein the illumination beam has a circular illumination pupil plane distribution.

9. The overlay metrology system of claim 1 , wherein the illumination beam has an annular illumination pupil plane distribution.

10. The overlay metrology system of claim 1 , wherein the detected signal comprises a time-varying interference signal associated with an overlap of first and zeroth diffraction orders from the multi-layer structure.

11. 10. The overlay metrology system of claim 1, wherein the illumination subsystem further comprises a beam splitter configured to generate an external beam as a portion of the illumination beam, and wherein the detected signal comprises a time-varying interference signal associated with an overlap of a first order diffraction from the multilayer structure and the external beam.

12. a controller including one or more processors configured to execute program instructions, the program instructions directing the one or more processors to: by receiving a detection signal from one or more detectors from a target overlaying the sample; a controller configured to perform one or more overlay measurements of the overlay target by determining the overlay measurements based on the detection signals; wherein the overlay target, according to the metrology recipe, includes a multi-layer structure on two or more layers of a cell of the sample, the multi-layer structure comprising a structure having one or more pitches in each layer in one or more periodic directions; wherein the multilayer structure comprises a structure having a first pitch in a first direction, a second pitch in a second direction, a third pitch in the first direction, and a fourth pitch in the second direction, and at least one of the first pitch or the third pitch is different from at least one of the second pitch or the fourth pitch; Overlay measurement system.

13. 13. The overlay metrology system of claim 12, wherein the controller is further configured to execute the metrology recipe by scanning the sample along one or more scan directions, the one or more scan directions comprising the first direction and the second direction.

14. 13. The overlay metrology system of claim 12, wherein the controller is further configured to execute the metrology recipe by scanning the sample along one or more scan directions, the one or more scan directions including a third direction different from both the first direction and the second direction.

15. The overlay metrology system of claim 12 , wherein the one or more detectors include at least one detector located at a pupil plane.

16. The overlay metrology system of claim 12 , wherein the one or more detectors include at least one diode array sensor.

17. a multilayer structure on two or more layers of the sample cell, the multilayer structure including a structure having one or more pitches in one or more periodic directions in each layer; wherein the multilayer structure comprises a structure having a first pitch in a first direction, a second pitch in a second direction, a third pitch in the first direction, and a fourth pitch in the second direction, and at least one of the first pitch or the third pitch is different from at least one of the second pitch or the fourth pitch; Overlay measurement targets.

18. The multilayer structure comprises: a first layer arrangement on a first layer having the first pitch in the first direction and the second pitch in the second direction; 20. The overlay metrology target of claim 17, comprising:

19. The multilayer structure comprises: a second layer grating on a second layer having the third pitch in the first direction; 20. The overlay metrology target of claim 17, comprising:

20. The multilayer structure comprises: a third layer grating on the third layer having the fourth pitch in the second direction; 20. The overlay metrology target of claim 19, comprising:

21. 21. The overlay metrology target of claim 20, wherein the multi-layer structure is configured to be scanned along a third direction, the third direction being different from the first direction and the second direction.

22. 22. The overlay metrology target of claim 21, wherein the multilayer structure has a scan length along the third direction that is greater than a width of the multilayer structure, the width being measured orthogonal to the third direction.

23. 20. The overlay metrology target of claim 17, wherein the multi-layer structure is configured to be scanned along a third direction, the third direction being different from the first direction and the second direction, and the third direction being within 45° to 10° of the first direction and the second direction.

24. The multilayer structure comprises: a second layer arrangement on a second layer having the third pitch in the first direction and the fourth pitch in the second direction; The overlay metrology target of claim 17 further comprising:

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