Systems, methods, and targets for wafer alignment - Patents.com

Abstract

The wafer alignment system includes an imaging subsystem, a controller, and a stage. The controller receives image data for the fiducial point targets and determines a center position for each of the fiducial point targets. The center position determination includes identifying subpatterns within each fiducial point target and identifying a plurality of center position candidates for each fiducial point target. The step of identifying a plurality of center position candidates for each fiducial point target includes applying a model to each identified subpattern of each fiducial point target, where the model generates a hot spot for each subpattern that identifies the center position candidate for each fiducial point target. The controller is further configured to determine a center position of each fiducial point target based on the plurality of center position candidates and to determine an orientation of the wafer based on the center position determination of the fiducial point target.

Description

[Technical field]

[0001] The present disclosure relates generally to wafer alignment, and more particularly to targets and processes that improve wafer alignment and reduce the time required to perform the wafer alignment process. [Background technology]

[0002] REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 63 / 024,616 (filed May 14, 2020) to the present inventor, Arkady Simkin, which is incorporated herein by reference in its entirety.

[0003] Wafer alignment using high-resolution cameras involves the acquisition of fiducials (i.e., patterns printed on the wafer that are unique in the field of view). For this purpose, simple patterns such as "cross in square" are currently used. In the currently implemented approach, the target acquisition process is very sensitive to the accuracy of the camera positioning on the fiducial pattern (RPP). If the pattern is partially seen in the field of view, the acquisition score of the pattern is low, which may lead to a failure to acquire the pattern. If the shift in the wafer position is large enough that the fiducial pattern is not seen in the field of view, an overlay tool can be used to scan around the expected location to find the fiducial. The scan requires acquiring overlapping images to ensure that one of the images completely contains the fiducial. This process is time-consuming and impacts throughput. To ensure accurate positioning, current approaches include performing a pre-alignment step before the high-resolution camera alignment step. This pre-alignment step is performed with a low-resolution camera with a larger field of view than the high-resolution camera. Such an approach requires additional optics and components for a given tool and impact. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 8,339,605 Summary of the Invention [Problem to be solved by the invention]

[0005] It would therefore be desirable to provide a system and method that addresses the shortcomings of the currently used approaches discussed above. [Means for solving the problem]

[0006] In accordance with one or more exemplary embodiments of the present disclosure, a wafer alignment system is disclosed. In one exemplary embodiment, the system includes an imaging subsystem. In another exemplary embodiment, the system includes a stage configured to clamp and actuate a wafer, and two or more fiducial targets are formed on the wafer, each fiducial target including a plurality of sub-patterns arranged in an array, each sub-pattern being different from the other sub-patterns of the plurality of sub-patterns. In another exemplary embodiment, the system includes a controller coupled to the imaging subsystem and the stage, the controller including one or more processors configured to execute program instructions that cause the one or more processors to: receive image data of two or more fiducial targets from the imaging subsystem; determine a center position of each of the two or more fiducial targets, the determining a center position of each of the two or more fiducial targets comprising identifying each sub-pattern within each fiducial target via a pattern recognition process; identify a plurality of center position candidates for each fiducial target, the identifying a plurality of center position candidates for each fiducial target comprising applying a model to each identified sub-pattern of each fiducial target, the model generating hot spots for each sub-pattern that identify the center position candidates for each fiducial target; and determine a center position of each fiducial target based on the plurality of center position candidates. The controller is further configured to: determine an orientation of the wafer relative to a coordinate system of the stage based on the determined center positions of each of the two or more fiducial targets; and direct the stage to adjust the position of the wafer to align the wafer to the stage coordinate system based on the determined orientation of the wafer.

[0007] According to one or more exemplary embodiments of the present disclosure, a method of wafer alignment is disclosed. In one exemplary embodiment, the method includes acquiring image data of a fiducial target including a set of sub-patterns. In another exemplary embodiment, the method includes determining a center position of each of the fiducial targets, where determining the center position of each of the two or more fiducial targets includes: identifying each sub-pattern within each fiducial target via a pattern recognition process; identifying a plurality of center point candidates for each of the fiducial targets, where the identifying a plurality of center point candidates for each of the fiducial targets includes applying a model to each identified sub-pattern of each of the respective fiducial targets to identify center position candidates for each of the respective fiducial targets, where the model generates a hot spot for each sub-pattern identifying the center position candidates associated with each of the respective fiducial targets; and determining a center position of each of the respective fiducial targets based on the plurality of center candidates. In another exemplary embodiment, the method includes determining an orientation of the wafer relative to a stage coordinate system based on the determined center positions for each of the two or more fiducial targets. In another exemplary embodiment, the method includes directing the stage to adjust the position of the wafer to align the wafer with the stage coordinate system based on the determined orientation of the wafer.

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

[0009] Many advantages of the present disclosure may be better understood by those skilled in the art by reference to the following drawings. [Figure 1A]FIG. 1 is a conceptual diagram of a wafer alignment system in accordance with one or more embodiments of the present disclosure. [Figure 1B] FIG. 1 is a conceptual diagram of a wafer orientation measurement process in accordance with one or more embodiments of the present disclosure. [Figure 2A] FIG. 2 illustrates a top view of a fiducial target suitable for use with a wafer alignment system in accordance with one or more embodiments of the present disclosure. [Figure 2B] 1 illustrates a top view of a fiducial target suitable for use with a wafer alignment system in accordance with one or more alternative embodiments of the present disclosure. [Figure 2C] 1 illustrates a top view of a fiducial target suitable for use with a wafer alignment system in accordance with one or more alternative embodiments of the present disclosure. [Figure 2D] 1 illustrates a top view of a fiducial target suitable for use with a wafer alignment system in accordance with one or more alternative embodiments of the present disclosure. [Diagram 3] 1 illustrates a top view of a fiducial target showing the locations of potential center locations identified by a sub-pattern of the fiducial target, in accordance with one or more embodiments of the present disclosure. [Figure 4] 1 illustrates a top view of a reference point target when the reference point target is only partially located within the field of view (FOV), in accordance with one or more embodiments of the present disclosure. [Diagram 5] 1 illustrates a top view of a reference point target when a foreign object / pattern that is not part of the reference point target is located within the FOV, in accordance with one or more embodiments of the present disclosure. [Figure 6] 1 illustrates a top view of a series of reference point targets configured to reduce search time and number of image grabs, in accordance with one or more embodiments of the present disclosure. [Figure 7] FIG. 1 is a simplified schematic diagram of a wafer alignment system in accordance with one or more embodiments of the present disclosure. [Figure 8] 1 is a flow chart illustrating a method of wafer alignment in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0011] The embodiments of the present disclosure are directed to a fiducial target suitable for implementation within a wafer alignment system and process. The fiducial target includes multiple unique sub-patterns (i.e., different orientations and / or shapes). The embodiments of the present disclosure utilize a model that identifies these sub-patterns and, for each sub-pattern, identifies a hot spot that corresponds to a center location candidate. A center location of the fiducial target is then determined based on the multiple center location candidates associated with the sub-patterns. The embodiments of the present disclosure determine the orientation of the wafer by obtaining center locations for the multiple fiducial target. The embodiments of the present disclosure can be implemented to provide automatic wafer alignment and can increase the robustness of the wafer alignment process to various overlay tools (e.g., the same design fiducial pattern target design can be used for both high-resolution metrology cameras and medium-resolution cameras). The embodiments of the present disclosure can enable robust trainless wafer alignment. During recipe setup, a user only needs to specify the type and location of the pattern to implement the wafer alignment system and process of the present disclosure.

[0012] FIG. 1A is a conceptual diagram of a wafer alignment system 100 according to one or more embodiments of the present disclosure. The system 100 may include, but is not limited to, an imaging subsystem 102. The system 100 may further include, but is not limited to, a controller 104. The controller 104 may include one or more processors 106 and a memory medium 108. In an embodiment, the imaging subsystem 102 may be configured to acquire an image of a fiducial target 110. For example, the imaging subsystem 102 may direct illumination 103 to a wafer 112 disposed on a stage 114. The imaging subsystem 102 may collect (e.g., via a camera) radiation emanating (e.g., reflected, scattered, or diffracted) from the wafer 112 (e.g., a semiconductor wafer) and the fiducial target 110 to generate an image of the fiducial target 110. The fiducial target 110 disposed on the wafer 112 may be used to make rotational adjustments to the wafer 112 (via the stage 114) to align the wafer 112 with a coordinate system of the stage 114. It should be noted that while the focus of this disclosure is wafer alignment, the scope of this disclosure is not limited to alignment of wafers only, in this sense, embodiments of the present disclosure may be extended to any sample known in the art, such as, but not limited to, a reticle, a photomask, or a sensor array.

[0013] In an embodiment, a controller 104 is communicatively coupled to the imaging subsystem 102. The one or more processors 106 of the controller 104 may perform any of the various process steps described throughout this disclosure. In an embodiment, the controller 104 is configured to generate and provide one or more control signals configured to perform one or more adjustments of the stage 114 to adjust the position / orientation of the wafer 112.

[0014] The imaging subsystem 102 may include any optical subsystem 102 known in the art. In this sense, the imaging subsystem 102 and the controller 104 may form a wafer alignment system 100 (or a wafer alignment tool). It should be noted that the wafer alignment system 100 may be integrated with any characterization system / tool ​​known in the art. For example, the functionality of the wafer alignment system 100 may be integrated with an imaging overlay metrology system or an optical inspection system. In this sense, the controller 104 of the wafer alignment system 100 may be integrated with the cameras and optics of such a characterization system / tool.

[0015] FIG. 1B illustrates a conceptual diagram of the use of a fiducial target 110 to align a wafer 112, according to one or more embodiments of the present disclosure. In an embodiment, two or more fiducial targets 110a, 110b are disposed on the wafer 112. As shown in FIG. 1B, the fiducial targets 110a, 110b may be disposed in different fields of the wafer along a straight line. The fiducial targets 110a, 110b may be formed on the wafer 112 by any method known in the art. For example, the fiducial targets 110a, 110b may be formed by lithographic printing.

[0016] In an embodiment, wafer alignment system 100 measures the angular orientation (i.e., the angle) of wafer 112 relative to the coordinate system of stage 114. Controller 104 of wafer alignment system 100 can then direct stage 114 to rotate wafer 112 by a selected angle to align wafer 112 with the coordinate system of stage 114.

[0017] In an embodiment, the wafer alignment system 100 acquires the positions of two or more fiducial targets 110a, 110b located on the wafer 112. In an embodiment, the controller 104 calculates a wafer angle 122, which may be defined by a vector 118 between the fiducial targets 110a, 110b and a vector 120 related to the direction of the stage movement angle. In an embodiment, the controller 104 of the wafer alignment system 100 instructs the stage 114 to rotate the wafer 112 by the calculated angle. It should be noted that when the precision of the wafer rotation does not allow for precise alignment, the measured angle of the wafer 112 can be mathematically applied to further movement to compensate for the remaining wafer angle between the vectors 120 and 118.

[0018] In an embodiment, the controller 104 can execute process steps to determine the positions of the fiducial targets 110a, 110b. For purposes of this disclosure, the controller 104 determines the center positions of the fiducial targets and utilizes the center positions as the positions of the respective fiducial targets. In this sense, the "center positions" and "positions" of the fiducial targets should be construed as interchangeable.

[0019] The controller 104 can determine the center location of each of the fiducial point targets 110a, 110b using the target designs of the targets described in this disclosure. Examples of fiducial point target designs are described throughout this disclosure.

[0020] FIG. 2A illustrates a top view of a fiducial target 110 suitable for use with a wafer alignment system 100, according to one or more embodiments of the present disclosure. In an embodiment, each fiducial target 110 is formed with a set of sub-patterns. For example, as shown in FIG. 2A, the fiducial target 110 may include, but is not limited to, sub-patterns 202a-202i. In an embodiment, the sub-patterns 202a-202i may be arranged in an array (e.g., a 3×3 array of cells). In an embodiment, the size of the fiducial target 110 may be selected to match the size of the field of view (FOV) of the camera system of the imaging subsystem 102. For example, the size and spacing of the sub-patterns 202a-202i may be selected to match the size of the FOV (e.g., 60 μm) of the camera system of the imaging subsystem 102. Note that while the examples of the present disclosure focus on a fiducial target including nine sub-patterns, this should not be construed as a limitation on the scope of the present disclosure. Rather, it should be noted that the fiducial target of the present disclosure may include any number of sub-patterns in an array of any size (e.g., 2x2, 3x3, 4x4, etc.).

[0021] In an embodiment, each subpattern is different from the other subpatterns in the array of subpatterns. For example, subpattern 202a is different from 202b-202i, subpattern 202b is different from 202a and 202c-202i, and so on. In this sense, for a 3×3 array, a given fiducial target 110 may include nine unique subpatterns evenly distributed throughout the fiducial target 110. It should be noted that the differences between the subpatterns help reduce the possibility of ambiguity in the subpattern acquisition / measurement process.

[0022] Differences between sub-patterns within a given fiducial target 110 may be achieved by varying the orientation and / or shape of each sub-pattern.

[0023] In an embodiment, the subpatterns 202a-202i of a given fiducial pattern 110 have the same shape and different orientations. For example, as shown in FIG. 2A, each of the subpatterns 202a-202i has a trilinear shape. In this example, each trilinear pattern is rotated 12° relative to its nearest neighboring subpattern. For example, subpattern 202b is rotated 12° (clockwise) relative to subpattern 202a, subpattern 202c is rotated 12° (clockwise) relative to subpattern 202b, subpattern 202d is rotated 12° (clockwise) relative to subpattern 202c, and so on. As another example, as shown in FIG. 2B, each of the subpatterns 202a-202i has a cross-sectional shape. In this example, each cross-sectional shape is rotated 9° relative to its nearest neighboring subpattern. As another example, as shown in FIG. 2C, each of the subpatterns 202a-202i has a triangle (e.g., an open-angle triangle). In this example, each triangular shape is rotated 12° relative to its nearest neighboring subpattern. It should be noted that the subpatterns of the fiducial target 110 of the present disclosure are not limited to the trilinear, cross-sectional, or triangular shapes shown in Figures 2A-2C. Rather, it should be noted that the scope of the present disclosure may be extended to any shape known in the art and capable of reducing ambiguity between subpatterns in the image capture process.

[0024] In an embodiment, the sub-patterns 202a-202i of a given fiducial pattern 110 have different shapes. For example, as shown in FIG. 2D, each of the sub-patterns 202a-202i has a different shape. In this example, the various shapes of the sub-patterns 202a-202i may include, but are not limited to, crosses, circles, stars, triangles, lines, or arrows. It is noted that the sub-patterns of the fiducial target 110 of the present disclosure are not limited to the shapes shown in FIG. 2D. Rather, it is noted that the scope of the present disclosure may be extended to any set of shapes known in the art and capable of reducing sub-pattern-to-sub-pattern ambiguity in the image capture process.

[0025] Referring again to FIG. 1A, in an embodiment, the controller 104 receives image data of the two or more fiducial point targets 110a, 110b from the imaging subsystem 102. The controller 104 can then determine a center position of each of the two or more fiducial point targets. In an embodiment, the controller 104 determines a center position of each of the two or more fiducial point targets using the following procedure. In an embodiment, the controller 104 can identify each sub-pattern within each fiducial point target via a pattern recognition process. For example, any pattern recognition algorithm / software can be used by the controller 104 to identify the sub-patterns 202a-202i within each of the fiducial point targets 110a, 110b. For example, the controller 104 can apply any correlation or geometric model finder (GMF) known in the art.

[0026] In an embodiment, once the sub-patterns 202a-202i of each fiducial target 110 are identified, the controller 104 may identify a center location candidate for each fiducial target 110. The step of identifying a center location candidate for each fiducial target 110 may include applying a model to image data acquired for each sub-pattern 202a-202i of each fiducial target 110. The model generates hot spots for each sub-pattern that identify center location candidates for each fiducial target 110. In this regard, the model / models executed by the controller 104 are digital representations of the sub-patterns 202a-202i of the fiducial target 110. The model includes hot spot information that correlates with the modeled sub-pattern information. Thus, once the controller 104 identifies a given sub-pattern (one of 202a-202i), the model identifies a hot spot location associated with the particular sub-pattern (one of 202a-202i). The hot spot location corresponds to a center location candidate for the particular sub-pattern.

[0027] In an embodiment, once the controller 104 identifies each of the center location candidates (through hotspot location identification for each sub-pattern), the controller 104 determines a center location of the respective fiducial target 110 based on the identified center location candidates. In an embodiment, the controller 104 may perform a voting scheme. In this case, the controller 104 may identify the center location of the respective fiducial target 110 as the center location candidate identified by the majority of the identified sub-patterns 202a-202i. For example, as shown in FIG. 3, the hotspot information for each of the sub-patterns 202a-202i may point to a center location candidate. The center location candidate is represented by the intersection 301 in FIG. 3. The controller 104 may designate the center location candidate most identified by the hotspots of the sub-patterns 202a-202i as the center location of the entire complex pattern of the fiducial target 110.

[0028] Note that slight variations in the location of intersections 301 in FIG. 3 represent variations in the pattern recognition process from sub-pattern to sub-pattern. Due to these variations, the analysis applied by controller 104 may apply a selected tolerance that provides an acceptable spread of center location candidates. In this example, center location candidates that fall within the same selected tolerance area should be treated as the "same" center location candidate. In this case, controller 104 may calculate the final location as the average of the found locations.

[0029] In an embodiment, after the center position of each of the fiducial targets 110a, 110b is obtained, the controller 104 can determine an orientation of the wafer 112 relative to the coordinate system of the stage 114 based on the determined center position for each of the two or more fiducial targets, as described above (see FIG. 1B). In an embodiment, once the wafer orientation is determined, the controller 104 instructs the stage 114 to adjust the position (e.g., rotational position) of the wafer 112 to align the wafer 112 with the stage coordinate system based on the determined orientation of the wafer 112.

[0030] 4 illustrates a top view of the fiducial target 110 in which the fiducial target is only partially located within the FOV, according to one or more embodiments of the present disclosure. When the fiducial target 110 is only partially observed within the FOV 404, but some sub-patterns such as 202c, 202f, and 202i are still completely contained within the FOV 404, embodiments of the present disclosure lead to successful acquisition. For example, shifting in the x-direction by 2 / 3 of the FOV 404 results in only 1 / 3 of the fiducial target 110 being present within the FOV 404. In this example, only three sub-patterns 202c, 202f, and 202i are completely within the FOV 404. In an embodiment, these three sub-patterns 202c, 202f, and 202i are acquired by the controller 104, and the hotspot information associated with the three sub-patterns 202c, 202f, and 202i will point to the correct center position 401 for the reference point target 110, even though the center of the reference point target 110 is outside the FOV.

[0031] FIG. 5 illustrates a top view of the fiducial target 110 where a foreign object / pattern that is not part of the fiducial target 110 is located within the FOV, according to one or more embodiments of the present disclosure. In this case, the foreign object / pattern 504a, 504b may be acquired by the imaging subsystem 102 and analyzed by the controller 104. However, during the acquisition process, the hotspot information acquired for each of the foreign objects / patterns 504a, 504b will point to different center point positions 505a, 505b. At the same time, the acquisitions of the actual sub-patterns 202a-202i all point to the same position 501 (within a selected tolerance range), which is selected as the correct center position of the center position of the fiducial target 110. In the example shown in FIG. 5, the fiducial target 110 is only partially seen within the FOV 502, with four of the nine cells being contained within the FOV 502. In addition, two foreign objects / patterns 504a, 504b are present near the fiducial target 110, which introduces noise. Intersection 501 represents a correct detection, and intersections 505a, 505b represent locations pointed to by incorrectly detected patterns. In this case, the fiducial center is found correctly because the four discovered patterns point to the same location (within a selected tolerance level) compared to the two foreign patterns, each pointing to a different location.

[0032] It should be noted that the complexity and nature of the reference pattern targets of the present disclosure are highly unique, significantly reducing the risk of mis-acquisition of other patterns. The primary factors that increase uniqueness are the inclusion of non-orthogonal lines and the fact that the fiducial target is constructed from multiple independent and unique sub-patterns organized in a specified order.

[0033] In an embodiment, the fiducial point target 110 may not be observed at all within the FOV. In this case, a scan may be performed without overlap to find the fiducial point target 110. Since no overlap is required, the number of image grabs required is reduced and the search time is shorter. For example, if the FOV size is X μm and the fiducial point target is X×X μm, the scan step may be X μm. That is, the scan step size may be as large as the size of the FOV.

[0034] 6 illustrates a plan view 600 of a series of fiducial point targets 110a-110c configured to reduce search time and number of image grabs in accordance with one or more embodiments of the present disclosure. For example, if a large navigation distance is required before reaching a fiducial point location, a series of fiducial point targets 110a-110c may be printed on the scribe lines of a wafer to eliminate the need to search along one of the axes. This approach reduces the number of image grabs during the search process as the square root of the grabs required to search along both axes.

[0035] In an embodiment, each fiducial target 110a-110c includes a modified pattern, and the central sub-pattern 602a-602c is replaced with a different pattern. For example, as shown in FIG. 6, the central three-line sub-pattern as used throughout this disclosure is replaced by a cross 602a-602c. In an embodiment, the central sub-patterns 602a-602c are oriented at different angles. In an embodiment, a two-phase acquisition can be applied to identify a block center position 604 representing the center position of a block of three fiducial targets 110a-110c. The two-phase acquisition can include acquiring the center position of a given fiducial target (one of 110a-110c) using eight non-center sub-patterns that are within the FOV. The FOV can then be centered on the center location of the given fiducial target, and an acquisition process can be applied to the central sub-patterns 602a-c, whereby the controller 104 is programmed to direct the hotspots from the applied model to direct the central sub-patterns 602a-c to the center location 604 of the block of three fiducial targets 110a-c. Note that this second acquisition phase operates in the same manner as the acquisition processes described throughout this disclosure, with the hotspot information pointing to block center locations rather than individual fiducial target center locations.

[0036] In the example of Fig. 6, the series of fiducial pattern targets 110a-110c covers a distance equal to three times the FOV width (along the X direction), making it possible to eliminate searching along the X direction for navigation errors within this range. Therefore, only searching along the Y direction is required. Once any of the fiducial point targets 110a-110c is acquired during such a scan along the Y direction, the X position is found as described above.

[0037] 7 is a simplified schematic diagram of a wafer alignment system 100 in accordance with one or more embodiments of the present disclosure. The system 100 can generate one or more images of the wafer 112 on at least one camera 704 using any method known in the art. In an embodiment, the system 100 includes an imaging subsystem 102 and a controller 104.

[0038] The imaging subsystem 102 includes an illumination source 702 for generating an illumination beam 711. The illumination source 702 can include any illumination source known in the art. For example, the illumination source 702 can include broadband (e.g., a plasma broadband source) or narrowband (e.g., one or more lasers). The illumination beam 711 can include one or more selected wavelengths of light, including, but not limited to, vacuum ultraviolet (VUV) light, deep ultraviolet (DUV) light, ultraviolet (UV) light, visible light, or infrared (IR) light. The illumination source 702 can further generate an illumination beam 711 having any temporal profile. For example, the illumination source 702 can generate a continuous illumination beam 711, a pulsed illumination beam 711, or a modulated illumination beam 711. Additionally, the illumination beam 711 can be delivered from the illumination source 702 via free space propagation or guided light (e.g., optical fiber, light pipe, etc.).

[0039] In an embodiment, the imaging subsystem 102 includes a set of optical systems 703. The illumination source 702 directs an illumination beam 711 to the wafer 112 via an illumination path 707. The illumination path 710 may include one or more optical components 715 suitable for modifying and / or conditioning the illumination beam 711. For example, the one or more illumination optical components 715 may include, but are not limited to, one or more lenses, one or more mirrors, 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, or one or more beam shapers. In an embodiment, the imaging subsystem 102 includes an objective lens 705 for focusing the illumination beam 711 onto the wafer 112.

[0040] In an embodiment, the wafer 112 is positioned on a wafer stage 114. The wafer stage 114 may include any device suitable for positioning / rotating the wafer 112 within the system 100. For example, the wafer stage 114 may include any combination of linear translation stages, rotational stages, tip / tilt stages, etc.

[0041] In an embodiment, the camera 704 (or detector / sensor) is configured to capture illumination emanating from the wafer 112 and the fiducial target 110 through a collection path 709. The collection path 709 may include any number of collection optical components 713 for directing and / or modifying the illumination collected by the objective lens 705, including, but not limited to, one or more lenses, one or more mirrors, 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, or one or more beam shapers.

[0042] The camera 704 may include any camera or detector system known in the art suitable for measuring and / or imaging illumination received from the wafer 112 and the fiducial target 110. For example, the camera 704 may include one or more sensors suitable for generating one or more images of the wafer 112 and the fiducial target 110, such as, but not limited to, a charge-coupled device (CCD), a complementary metal-oxide semiconductor (CMOS) sensor, a photomultiplier tube (PMT) array, or an avalanche photodiode (APD) array. As another example, the detector 704 may include a sensor suitable for moving one or more images of the wafer 112 and the fiducial target 110 (e.g., a scanning mode of operation). For example, the camera 704 may include a line sensor including rows of pixels. In this regard, the system 100 may generate successive images one row at a time (e.g., a strip image) by translating the wafer 112 through a measurement field of view in a scan direction perpendicular to the pixel rows and successively timing the line sensor during successive exposure windows. In another example, the camera 704 may include a TDI sensor that includes multiple pixel rows and readout rows. The TDI sensor may operate similarly to a line sensor, except that a clocking signal may continuously move charge from one pixel row to the next until the charge reaches a readout row where a row of an image is generated. By synchronizing the charge transfer (e.g., based on a clock signal) with the movement of the sample along the scan direction, charge may continue to accumulate across the pixel rows, providing a relatively high signal-to-noise ratio compared to a line sensor.

[0043] In another embodiment, the system 100 includes a controller 130. In another embodiment, the controller 130 includes one or more processors 132 configured to execute program instructions maintained on a memory medium 134. In this regard, the one or more processors 132 of the controller 130 may perform any of the various process steps described throughout this disclosure. Additionally, the controller 130 may be configured to receive data, including but not limited to images of the wafer 112, from the detector 704.

[0044] The one or more processors 106 of the controller 104 may include any processor or processing element known in the art. For purposes of this disclosure, the term "processor" or "processing element" may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application specific integrated circuits (ASIC) devices, one or more field programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, the one or more processors 106 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in a memory). In an embodiment, the one or more processors 106 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a network computer, or any other computer system configured to execute programs that operate or are configured to operate with the system 100 as described throughout this disclosure. Furthermore, different subsystems of the system 100 may include processors or logic elements suitable for performing at least some of the steps described in this disclosure. Thus, the above description should not be construed as a limitation on the embodiments of the present disclosure, but merely as an example. Additionally, the steps described throughout this disclosure may be performed by a single controller or, alternatively, by multiple controllers. Additionally, controller 104 may include one or more controllers housed within a common housing or multiple housings. In this manner, any controller or combination of controllers may be separately packaged as a module suitable for integration into system 100. Additionally, controller 104 may analyze data received from detector 704 and provide data to additional components within or external to system 100.

[0045] The memory medium 108 may include any storage medium known in the art suitable for storing program instructions executable by the associated processor(s) 106. For example, the storage medium 108 may include a non-transitory storage medium. As another example, the storage medium 108 may include, but is not limited to, a read-only memory (ROM), a random access memory (RAM), a magnetic or optical memory device (e.g., disk), a magnetic tape, a solid-state drive, and the like. Additionally, it is noted that the storage medium 108 may be housed within a common controller housing along with the one or more processors 106. In an embodiment, the memory medium 108 may be located remotely relative to the physical location of the one or more processors 106 and the controller 104. For example, the one or more processors 106 of the controller 104 may access a remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, etc.).

[0046] FIG. 8 shows a flow diagram 800 illustrating a method of wafer alignment according to one or more embodiments of the present disclosure. Applicant notes that the embodiments and techniques described herein above in the context of the wafer alignment system 100 should be construed to extend to the method 200. However, it is further noted that the method 800 is not limited to the architecture of the wafer alignment system 100. In step 802, image data of a plurality of fiducial point targets is acquired. For example, as shown in FIGS. 1A-7, the imaging subsystem 102 may capture image data for two or more fiducial point targets 110a, 110b and transmit the image data to the controller 104. In step 804, a sub-pattern within the Nth fiducial point target is identified. For example, as shown in FIGS. 1A-7, the controller 104 may perform a pattern recognition process to identify a sub-pattern having the Nth fiducial point target 110. In step 806, a center position candidate of the Nth fiducial point target 110 is identified based on the hot spot acquisition of each sub-pattern. For example, as shown in FIG. 1A-FIG. 7, the controller 104 can apply the model to each sub-pattern (e.g., 202a-202i) of the Nth fiducial target 110, whereby the model identifies hot spots corresponding to potential center locations of each sub-pattern (e.g., 202a-202i). In step 808, the center location of the Nth fiducial target 110 is determined based on the center location targets found in step 806. For example, as shown in FIG. 1A-FIG. 7, the controller 104 can apply a voting scheme to identify the center location of the Nth reflective target 110 based on the center location candidates identified by the majority of the sub-patterns (via the hot spots of the model). In step 810, the controller 104 determines whether there are additional fiducial targets to analyze. If there are additional fiducial targets to analyze, the method 800 repeats steps 802-810 until all fiducial targets are analyzed. If there are no additional fiducial targets to analyze, the method 800 moves to step 812.In step 812, the controller 104 determines an orientation of the wafer based on the central positions (identified in steps 802-810) of the 1-N fiducial point targets 110. In step 814, the controller 104 instructs the stage to adjust the angular position of the wafer based on the orientation determined in step 812.

[0047] All of the methods described herein may include storing results of one or more steps of the method embodiments in a 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 memory described herein, or any other suitable storage medium known in the art. After the results are stored, they can be accessed in the 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 a random access memory (RAM), and the results may not necessarily persist indefinitely in the memory.

[0048] It is further contemplated that each of the method embodiments described above may include any other step(s) of any other method described herein. In addition, each of the method embodiments described above may be performed by any of the systems described herein.

[0049] Those skilled in the art will recognize that the component operations, devices, objects, and their accompanying discussion described herein are used as examples for conceptual clarity, and that various configuration modifications are contemplated. Thus, as used herein, the specific examples described and the accompanying discussion are intended to be representative of their more general classes. In general, the use of any specific example is intended to represent its class, and non-inclusion of specific components, operations, devices, and objects should not be construed as limiting.

[0050] As used herein, directional terms such as "top", "bottom", "up", "down", "up", "upper", "lower", "lower" and the like are intended to provide relative positions for purposes of description and are not intended to indicate an absolute frame of reference. 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.

[0051] With respect to the use of virtually any plural and / or singular term herein, those of skill in the art can convert from plural to singular and / or from singular to plural as appropriate to the context and / or application. The various singular / plural permutations are not expressly set forth herein for ease of understanding.

[0052] The subject matter described herein illustrates different components that are sometimes included within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and that in fact many other architectures that achieve the same functionality may be implemented. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Thus, any two components herein that are combined to achieve a particular functionality can be considered to be "associated" with each other such that the desired functionality is achieved, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" with each other to achieve the desired functionality, and any two components capable of being so associated can also be considered to be "couplable" with each other to achieve the desired functionality. Specific examples of what can be coupled include, but are not limited to, physically coupleable and / or physically interacting components and / or wirelessly interactable and / or wirelessly interacting components and / or logically interacting and / or logically interacting components.

[0053] It should further be understood that the present invention is defined by the appended claims. In general, those skilled in the art will understand that the terms used in this specification and in particular 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 "includes but not limited to", etc.). Those skilled in the art will further understand that if a specific number of claim recitations introduced are intended, such intention will be explicitly stated in the claim, and in the absence of such recitation, no such intention exists. For example, as an aid to understanding, the following appended claims can include the use of the introductory phrases "at least one" and "one or more" to introduce the claim recitation. However, the use of such phrases should not be interpreted as meaning that the introduction of a claim recitation with the indefinite article "a" or "an" limits any particular claim that includes such an introduced claim recitation to an invention that includes only one such recitation. The same applies to the use of clear articles used to introduce claim recitations, even when the same claim includes the introductory phrase "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should typically be interpreted to mean "at least one" or "one or more"). Also, those skilled in the art will recognize that even when a specific number of introduced claim recitations is explicitly recited, such recitation should typically be interpreted to mean at least the recited number (e.g., a bare recitation of "two recitations" without other modifiers typically means at least two recitations, or two or more recitations).Furthermore, in instances where a conventional expression similar to "such as at least one of A, B, and C" is used, such a configuration is generally intended in the sense that one of ordinary skill in the art would understand the conventional expression (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together). In instances where a conventional expression similar to "such as at least one of A, B, or C" is used, such a configuration is generally intended in the sense that one of ordinary skill in the art would understand the conventional expression (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together). Those skilled in the art will further appreciate that virtually any disjunctive word and / or phrase presenting two or more alternative terms, wherever 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" will be understood to include the possibilities of "A" or "B" or "A and B."

[0054] It is believed that the present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes can be made in the form, construction and arrangement of the elements without departing from the disclosed subject matter or sacrificing all of its material advantages. The forms described are merely illustrative, and it is the intent of the following claims to embrace and include such modifications. It is to be understood, further, that the invention is defined by the appended claims.

Claims

1. 1. A wafer alignment system, comprising: an imaging subsystem; a stage configured to hold and move a wafer, the stage comprising two or more fiducial targets formed on the wafer, each fiducial target including a plurality of sub-patterns arranged in an array, each sub-pattern being different from the other sub-patterns of the plurality of sub-patterns; A controller coupled to the imaging subsystem and the stage, the controller including one or more processors configured to execute program instructions, the one or more processors comprising: receiving image data for two or more of the fiducial targets from the imaging subsystem; determining a center position of each of two or more of the reference point targets, identifying each sub-pattern within each of said fiducial targets via a pattern recognition process; identifying a plurality of center location candidates for each fiducial point target, wherein identifying a plurality of center location candidates for each of the fiducial point targets comprises applying a model to each identified sub-pattern of each of the fiducial point targets, the model generating hot spots for each sub-pattern that identify the center location candidates for each of the fiducial point targets; and determining the center location of each of the fiducial point targets based on the plurality of center location candidates; determining an orientation of the wafer relative to a coordinate system of the stage based on the determined center position for each of two or more of the fiducial targets; commanding the stage to adjust a rotational position of the wafer to align the wafer with a stage coordinate system based on the determined orientation of the wafer; Wafer alignment system.

2. 2. The system of claim 1, wherein the step of determining a center location of each of the reference point targets based on a plurality of the center location candidates comprises determining a center location of each of the reference point targets based on a plurality of the center location candidates via a voting scheme, the voting scheme identifying a center location as the center location candidate identified by a majority of the identified sub-patterns.

3. 3. The system of claim 2, wherein the controller is further configured to apply a selected tolerance when executing the voting scheme, the selected tolerance comprising an acceptable variance of the plurality of center location candidates.

4. The system of claim 1 , wherein an area of ​​each fiducial target is substantially equal to a field of view of the imaging subsystem.

5. 2. The system of claim 1, wherein the first fiducial target is in a first field and the second fiducial target is in a second field.

6. The system of claim 1 , wherein each sub-pattern of the two or more fiducial targets has a same shape and a different orientation than the other sub-patterns.

7. 7. The system of claim 6, wherein each subpattern includes a tri-line pattern and is rotated 12 degrees relative to adjacent subpatterns.

8. The system of claim 6 , wherein each subpattern includes a cross pattern and is rotated nine degrees relative to an adjacent subpattern.

9. The system of claim 6 , wherein each subpattern comprises a triangular pattern and is rotated 12 degrees relative to an adjacent subpattern.

10. The system of claim 1 , wherein each sub-pattern of the two or more fiducial targets has a different shape.

11. The system of claim 1 , wherein at least one of the sub-patterns includes at least one of a cross, a circle, a star, a triangle, a line, or an arrow.

12. The system of claim 1 , wherein the fiducial target is lithographically formed on the wafer.

13. The system of claim 1 , wherein the stage comprises at least one of a rotational stage or a translation stage.

14. The imaging subsystem includes: An illumination source; An optical system set; Camera and The system of claim 1 , comprising:

15. The system of claim 1 , wherein the imaging subsystem comprises at least one of an imaging overlay metrology subsystem or an inspection subsystem.

16. 2. The system of claim 1, wherein the controller is further configured to implement a two-phase acquisition process utilizing at least three of the fiducial point targets, a central sub-pattern of each fiducial point target being different from an outer sub-pattern of each fiducial point target.

17. 1. A wafer alignment method, comprising: acquiring image data of a fiducial target including a set of sub-patterns; determining a center position of each of the fiducial point targets, the determining a center position of each of the two or more fiducial point targets comprising: identifying each sub-pattern within each said fiducial target via a pattern recognition process; identifying a plurality of center candidates for each fiducial point target, wherein identifying a plurality of center point candidates for each fiducial point target comprises applying a model to each identified sub-pattern of each of the fiducial point targets to identify center location candidates for each of the fiducial point targets, the model generating hot spots for each sub-pattern identifying center location candidates associated with each of the fiducial point targets; and determining a center location of each of the fiducial point targets based on the plurality of center location candidates; determining an orientation of the wafer relative to a coordinate system of a stage based on the determined center positions of each of the two or more fiducial targets; directing the stage to adjust a rotational position of the wafer to align the wafer with a stage coordinate system based on the determined orientation of the wafer; The method includes:

18. 20. The method of claim 17, wherein determining a center location of each of the fiducial point targets based on a plurality of the center location candidates comprises determining a center location of each of the fiducial point targets based on a plurality of the center location candidates via a voting scheme, the voting scheme identifying a center location as the center location candidate identified by a majority of the identified sub-patterns.

19. 20. The method of claim 18, further comprising applying a selected tolerance when performing the voting scheme, the selected tolerance comprising an acceptable variance of the center location candidates.

20. The method of claim 17 , wherein an area of ​​each fiducial point target is substantially equal to a field of view of the imaging subsystem.

21. 20. The method of claim 17, wherein a first fiducial target is in a first field of the wafer and a second fiducial target is in a second field of the wafer.

22. The method of claim 17 , wherein each sub-pattern of two or more of the fiducial targets has the same shape and a different orientation than the other sub-patterns.

23. 23. The method of claim 22, wherein each subpattern comprises a tri-line pattern and is rotated 12 degrees relative to adjacent subpatterns.

24. 23. The method of claim 22, wherein each subpattern comprises a cross pattern and is rotated 9 degrees relative to an adjacent subpattern.

25. 23. The method of claim 22, wherein each subpattern comprises a triangular pattern and is rotated 12 degrees relative to adjacent subpatterns.

26. The method of claim 17 , wherein each sub-pattern of the two or more fiducial targets has a different shape.

27. The method of claim 17 , wherein at least one of the sub-patterns includes at least one of a cross, a circle, a star, a triangle, a line, or an arrow.

28. The method of claim 17 , wherein the fiducial target is lithographically formed on the wafer.

29. 20. The method of claim 17, further comprising implementing a two-phase acquisition process utilizing at least three fiducial point targets, a central sub-pattern of each of the fiducial point targets being different from an outer sub-pattern of each of the fiducial point targets.

30. 1. A fiducial target for use in a wafer alignment system, comprising: A reference point target comprising a plurality of sub-patterns arranged in an array, each sub-pattern being different from other sub-patterns of the plurality of sub-patterns, each sub-pattern having a size approximately the same as a field of view (FOV) of a wafer alignment system, and each sub-pattern configured to identify a potential center location of the reference point target.

31. 31. The target of claim 30, wherein the array comprises an m x n array, where m and n are 1 or greater.

32. 32. The target of claim 31 , wherein the array comprises at least one of a 2×2 array, a 3×3 array, or a 4×4 array.

33. 31. The target of claim 30, wherein each sub-pattern has the same shape and a different orientation as the other sub-patterns.

34. 34. The target of claim 33, wherein each subpattern comprises a three-line pattern and is rotated 12 degrees relative to adjacent subpatterns.

35. 34. The target of claim 33, wherein each subpattern comprises a cross pattern and is rotated 9 degrees relative to an adjacent subpattern.

36. 34. The target of claim 33, wherein each subpattern comprises a triangular pattern and is rotated 12 degrees relative to an adjacent subpattern.

37. 31. The target of claim 30, wherein each sub-pattern has a different shape.

38. 38. The target of claim 37, wherein at least one of the sub-patterns includes at least one of a cross, a circle, a star, a triangle, a line, or an arrow.

39. The target of claim 30 , wherein a plurality of the sub-patterns are lithographically formed on the wafer.

Images